WorldWideScience

Sample records for simulated interstellar ices

  1. Organic Synthesis in Simulated Interstellar Ice Analogs

    Science.gov (United States)

    Dworkin, Jason P.; Bernstein, Max P.; Sandford, Scott A.; Allamandola, Louis J.; Deamer, David W.; Elsila, Jamie; Zare, Richard N.

    2001-01-01

    Comets and carbonaceous micrometeorites may have been significant sources of organic compounds on the early Earth. Ices on grains in interstellar dense molecular clouds contain a variety of simple molecules as well as aromatic molecules of various sizes. While in these clouds the icy grains are processed by ultraviolet light and cosmic radiation which produces more complex organic molecules. We have run laboratory simulations to identify the types of molecules which could have been generated photolytically in pre-cometary ices. Experiments were conducted by forming various realistic interstellar mixed-molecular ices with and without polycyclic aromatic hydrocarbons (PAHs) at approx. 10 K under high vacuum irradiated with UV light from a hydrogen plasma lamp. The residue that remained after warming to room temperature was analyzed by HPLC, and by laser desorption mass spectrometry. The residue contains several classes of compounds which may be of prebiotic significance.

  2. Monte Carlo kinetics simulations of ice-mantle formation on interstellar grains

    Science.gov (United States)

    Garrod, Robin

    2015-08-01

    The majority of interstellar dust-grain chemical kinetics models use rate equations, or alternative population-based simulation methods, to trace the time-dependent formation of grain-surface molecules and ice mantles. Such methods are efficient, but are incapable of considering explicitly the morphologies of the dust grains, the structure of the ices formed thereon, or the influence of local surface composition on the chemistry.A new Monte Carlo chemical kinetics model, MIMICK, is presented here, whose prototype results were published recently (Garrod 2013, ApJ, 778, 158). The model calculates the strengths and positions of the potential mimima on the surface, on the fly, according to the individual pair-wise (van der Waals) bonds between surface species, allowing the structure of the ice to build up naturally as surface diffusion and chemistry occur. The prototype model considered contributions to a surface particle's potential only from contiguous (or "bonded") neighbors; the full model considers contributions from surface constituents from short to long range. Simulations are conducted on a fully 3-D user-generated dust-grain with amorphous surface characteristics. The chemical network has also been extended from the simple water system previously published, and now includes 33 chemical species and 55 reactions. This allows the major interstellar ice components to be simulated, such as water, methane, ammonia and methanol, as well as a small selection of more complex molecules, including methyl formate (HCOOCH3).The new model results indicate that the porosity of interstellar ices are dependent on multiple variables, including gas density, the dust temperature, and the relative accretion rates of key gas-phase species. The results presented also have implications for the formation of complex organic molecules on dust-grain surfaces at very low temperatures.

  3. Organic Chemistry in Interstellar Ices: Connection to the Comet Halley Results

    Science.gov (United States)

    Schutte, W. A.; Agarwal, V. K.; deGroot, M. S.; Greenberg, J. M.; McCain, P.; Ferris, J. P.; Briggs, R.

    1997-01-01

    Mass spectroscopic measurements on the gas and dust in the coma of Comet Halley revealed the presence of considerable amounts of organic species. Greenberg (1973) proposed that prior to the formation of the comet UV processing of the ice mantles on grains in dense clouds could lead to the formation of complex organic molecules. Theoretical predictions of the internal UV field in dense clouds as well as the discovery in interstellar ices of species like OCS and OCN- which have been formed in simulation experiments by photoprocessing of interstellar ice analogues point to the importance of such processing. We undertook a laboratory simulation study of the formation of organic molecules in interstellar ices and their possible relevance to the Comet Halley results.

  4. CO{sub 2} INFRARED PHONON MODES IN INTERSTELLAR ICE MIXTURES

    Energy Technology Data Exchange (ETDEWEB)

    Cooke, Ilsa R. [Department of Chemistry, University of Virginia, McCormick Road, Charlottesville, VA 22904 (United States); Fayolle, Edith C.; Öberg, Karin I., E-mail: irc5zb@virginia.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

    2016-11-20

    CO{sub 2} ice is an important reservoir of carbon and oxygen in star- and planet-forming regions. Together with water and CO, CO{sub 2} sets the physical and chemical characteristics of interstellar icy grain mantles, including desorption and diffusion energies for other ice constituents. A detailed understanding of CO{sub 2} ice spectroscopy is a prerequisite to characterize CO{sub 2} interactions with other volatiles both in interstellar ices and in laboratory experiments of interstellar ice analogs. We report laboratory spectra of the CO{sub 2} longitudinal optical (LO) phonon mode in pure CO{sub 2} ice and in CO{sub 2} ice mixtures with H{sub 2}O, CO, and O{sub 2} components. We show that the LO phonon mode position is sensitive to the mixing ratio of various ice components of astronomical interest. In the era of the James Webb Space Telescope , this characteristic could be used to constrain interstellar ice compositions and morphologies. More immediately, LO phonon mode spectroscopy provides a sensitive probe of ice mixing in the laboratory and should thus enable diffusion measurements with higher precision than has been previously possible.

  5. Interstellar Ices and Radiation-induced Oxidations of Alcohols

    Science.gov (United States)

    Hudson, R. L.; Moore, M. H.

    2018-04-01

    Infrared spectra of ices containing alcohols that are known or potential interstellar molecules are examined before and after irradiation with 1 MeV protons at ∼20 K. The low-temperature oxidation (hydrogen loss) of six alcohols is followed, and conclusions are drawn based on the results. The formation of reaction products is discussed in terms of the literature on the radiation chemistry of alcohols and a systematic variation in their structures. The results from these new laboratory measurements are then applied to a recent study of propargyl alcohol. Connections are drawn between known interstellar molecules, and several new reaction products in interstellar ices are predicted.

  6. UV IRRADIATION OF AROMATIC NITROGEN HETEROCYCLES IN INTERSTELLAR ICE ANALOGS

    Science.gov (United States)

    Elsila, J. E.; Bernstein, M. P.; Sanford, S. A.

    2005-01-01

    Here, we present information on the properties of the ANH quinoline frozen in interstellar water-ice analogs. Quinoline is a two-ring compound structurally analogous to the PAH naphthalene. In this work, binary mixtures of water and quinoline were frozen to create interstellar ice analogs, which were then subjected to ultraviolet photolysis. We will present the infrared spectra of the resulting ices at various temperatures, as well as chromatographic analysis of the residues remaining upon warm-up of these ices to room temperature.

  7. Interstellar matrices: the chemical composition and evolution of interstellar ices as observed by ISO.

    Science.gov (United States)

    d'Hendecourt, L; Dartois, E

    2001-03-15

    Matrix isolation techniques have been developed in the early sixties as a tool for studying the spectroscopic properties of out of equilibrium species (atoms, radicals, ions, reactive molecules), embedded in rare gas inert matrices at low temperatures. Cold interstellar grains surfaces are able to condense out gas phase molecules, routinely observed by radioastronomy. These grain 'mantles' can be considered as 'interstellar matrices'. However, these matrices are not clean and unreactive. They are made principally of dirty ices whose composition must be determined carefully to assess the importance of the solid state chemistry that takes place in the Interstellar Medium. Infrared spectroscopy, both in astronomy and in the laboratory, is the unique tool to determine the chemical composition of these ices. Astronomical spectra can directly be compared with laboratory ones obtained using classical matrix isolation techniques. Furthermore, dedicated experiments may be undertaken to further improve the understanding of the basic physico-chemical processes that take place in cosmic ices.

  8. ON THE FORMATION OF CO2 AND OTHER INTERSTELLAR ICES

    International Nuclear Information System (INIS)

    Garrod, R. T.; Pauly, T.

    2011-01-01

    We investigate the formation and evolution of interstellar dust-grain ices under dark-cloud conditions, with a particular emphasis on CO 2 . We use a three-phase model (gas/surface/mantle) to simulate the coupled gas-grain chemistry, allowing the distinction of the chemically active surface from the ice layers preserved in the mantle beneath. The model includes a treatment of the competition between barrier-mediated surface reactions and thermal-hopping processes. The results show excellent agreement with the observed behavior of CO 2 , CO, and water ice in the interstellar medium. The reaction of the OH radical with CO is found to be efficient enough to account for CO 2 ice production in dark clouds. At low visual extinctions, with dust temperatures ∼>12 K, CO 2 is formed by direct diffusion and reaction of CO with OH; we associate the resultant CO 2 -rich ice with the observational polar CO 2 signature. CH 4 ice is well correlated with this component. At higher extinctions, with lower dust temperatures, CO is relatively immobile and thus abundant; however, the reaction of H and O atop a CO molecule allows OH and CO to meet rapidly enough to produce a CO:CO 2 ratio in the range ∼2-4, which we associate with apolar signatures. We suggest that the observational apolar CO 2 /CO ice signatures in dark clouds result from a strongly segregated CO:H 2 O ice, in which CO 2 resides almost exclusively within the CO component. Observed visual-extinction thresholds for CO 2 , CO, and H 2 O are well reproduced by depth-dependent models. Methanol formation is found to be strongly sensitive to dynamical timescales and dust temperatures.

  9. Analysis of proton irradiation products in simulated interstellar dusts by mass spectrometry

    International Nuclear Information System (INIS)

    Kasamatsu, Takashi; Kaneko, Takeo; Tsuchiya, Masahiko; Kobayashi, Kensei

    1996-01-01

    It is known that various kinds of organic compounds exist in space. In order to study the possibility of the formation of organic compounds in comets or their precursory bodies (interstellar dust grains), ice mixtures of carbon monoxide (or methane), ammonia and water made in a cryostat at 10 K ('simulated cometary ices') were irradiated with high energy protons. Irradiated ice products were warmed up to room temperature, while sublimed gases were analyzed with a quadrupole mass spectrometer. Some hydrocarbons and alcohols were detected. 'Amino acid precursors' (compounds yielding amino acids after hydrolysis) were detected in non-volatile products remaining on the substrate at room temperature. These results suggest the possible formation of organic compounds in interstellar dust grains by cosmic radiation. (author)

  10. THz Time-Domain Spectroscopy of Interstellar Ice Analogs

    Science.gov (United States)

    Ioppolo, Sergio; McGuire, Brett A.; de Vries, Xander; Carroll, Brandon; Allodi, Marco; Blake, Geoffrey

    2015-08-01

    The unambiguous identification of nearly 200 molecular species in different astronomical environments proves that our cosmos is a ‘Molecular Universe’. The cumulative outcome of recent observations, laboratory studies, and astrochemical models indicates that there is a strong interplay between the gas and the solid phase throughout the process of forming molecules in space. Observations of interstellar ices are generally limited to lines-of-sight along which infrared absorption spectroscopy is possible. Therefore, the identification of more complex prebiotic molecules in the mid-IR is difficult because of their low expected interstellar abundances and the overlap of their absorption features with those from the more abundant species. In the THz region, telescopes can detect Interstellar ices in emission or absorption against dust continuum. Thus, THz searches do not require a background point source. Moreover, since THz spectra are the fingerprint of inter- and intramolecular forces, complex species can present unique modes that do not overlap with those from simpler, more abundant molecules. THz modes are also sensitive to temperature and phase changes in the ice. Therefore, spectroscopy at THz frequencies has the potential to better characterize the physics and chemistry of the ISM. Currently, the Herschel Space Telescope, SOFIA, and ALMA databases contain a vast amount of new THz spectral data that require THz laboratory spectra for interpretation. The latter, however, are largely lacking. We have recently constructed a new THz time-domain spectroscopy system operating in the range between 0.3 - 7.5 THz. This work focuses on the laboratory investigation of the composition and structure of the most abundant interstellar ice analogs compared to some more complex species. Different temperatures, mixing ratios, and matrix isolation experiments will be shown. The ultimate goal of this research is to provide the scientific community with an extensive THz ice

  11. Skating on thin ice: surface chemistry under interstellar conditions

    Science.gov (United States)

    Fraser, H.; van Dishoeck, E.; Tielens, X.

    Solid CO2 has been observed towards both active star forming regions and quiescent clouds (Gerakines et. al. (1999)). The high abundance of CO2 in the solid phase, and its low abundance in the gas phase, support the idea that CO2 is almost exclusively formed in the solid state. Several possible formation mechanisms have been postulated (Ruffle &Herbst (2001): Charnley &Kaufman (2000)), and the detection of CO2 towards quiescent sources such as Elias 16 (Whittet et. al. (1998)) clearly suggests that CO2 can be produced in the absence of UV or electron mediated processes. The most likely route is via the surface reactions between O atoms, or OH radicals, and CO. The tools of modern surface- science offer us the potential to determine many of the physical and chemical attributes of icy interstellar grain mantles under highly controlled conditions, that closely mimic interstellar environments. The Leiden Surface Reaction Simulation Device ( urfreside) combines UHV (UltraS High Vacuum) surface science techniques with an atomic beam to study chemical reactions occurring on the SURFACE and in the BULK of interstellar ice grain mimics. By simultaneously combining two or more surface analysis techniques, the chemical kinetics, reaction mechanisms and activation energies can be determined directly. The experiment is aimed at identifying the key barrierless reactions and desorption pathways on and in H2 O and CO ices under interstellar conditions. The results from traditional HV (high vacuum) and UHV studies of the CO + O and CO + OH reactions will be presented in this paper. Charnley, S.B., & Kaufman, M.J., 2000, ApJ, 529, L111 Gerakines, P.A., 1999, ApJ, 522, 357 Ruffle, D.P., & Herbst, E., 2001, MNRAS, 324, 1054 Whittet, D.C.B., et.al., 1998, ApJ, 498, L159

  12. SOFT X-RAY IRRADIATION OF PURE CARBON MONOXIDE INTERSTELLAR ICE ANALOGUES

    Energy Technology Data Exchange (ETDEWEB)

    Ciaravella, A.; Candia, R.; Collura, A. [INAF-Osservatorio Astronomico di Palermo, P.za Parlamento 1, 90134 Palermo (Italy); Jimenez-Escobar, A.; Munoz Caro, G. M. [Centro de Astrobiologia (CSIC-INTA), Carretera de Ajalvir, km 4, Torrejon de Ardoz, 28850 Madrid (Spain); Cecchi-Pestellini, C. [INAF-Osservatorio Astronomico di Cagliari, Strada n.54, Loc. Poggio dei Pini, I-09012 Capoterra (Italy); Giarrusso, S. [INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica, Via U. La Malfa 153, I-90146 Palermo (Italy); Barbera, M., E-mail: aciaravella@astropa.unipa.it [Dipartimento di Scienze Fisiche and Astronomiche, Universita di Palermo, Sezione di Astronomia, Piazza del Parlamento 1, I-90134 Palermo (Italy)

    2012-02-10

    There is an increasing evidence for the existence of large organic molecules in the interstellar and circumstellar medium. Very few among such species are readily formed in conventional gas-phase chemistry under typical conditions of interstellar clouds. Attention has therefore focused on interstellar ices as a potential source of these relatively complex species. Laboratory experiments show that irradiation of interstellar ice analogues by fast particles or ultraviolet radiation can induce significant chemical complexity. However, stars are sources of intense X-rays at almost every stage of their formation and evolution. Such radiation may thus provide chemical changes in regions where ultraviolet radiation is severely inhibited. After H{sub 2}O, CO is often the most abundant component of icy grain mantles in dense interstellar clouds and circumstellar disks. In this work we present irradiation of a pure carbon monoxide ice using a soft X-ray spectrum peaked at 0.3 keV. Analysis of irradiated samples shows formation of CO{sub 2}, C{sub 2}O, C{sub 3}O{sub 2}, C{sub 3}, C{sub 4}O, and CO{sub 3}/C{sub 5}. Comparison of X-rays and ultraviolet irradiation experiments, of the same energy dose, shows that X-rays are more efficient than ultraviolet radiation in producing new species. With the exception of CO{sub 2}, X-ray photolysis induces formation of a larger number of products with higher abundances, e.g., C{sub 3}O{sub 2} column density is about one order of magnitude higher in the X-ray experiment. To our knowledge this is the first report on X-ray photolysis of CO ices. The present results show that X-ray irradiation represents an efficient photo-chemical way to convert simple ices to more complex species.

  13. CARBON DIOXIDE INFLUENCE ON THE THERMAL FORMATION OF COMPLEX ORGANIC MOLECULES IN INTERSTELLAR ICE ANALOGS

    Energy Technology Data Exchange (ETDEWEB)

    Vinogradoff, V.; Fray, N.; Bouilloud, M.; Cottin, H. [LISA Laboratoire Interuniversitaire des Systèmes Atmosphériques, UMR CNRS 7583, Université Paris Est Créteil (UPEC), Université Paris Diderot (UPD), Institut Pierre Simon Laplace, Labex ESEP, Paris (France); Duvernay, F.; Chiavassa, T., E-mail: vvinogradoff@mnhn.fr [PIIM, Laboratoire de Physique des Interactions Ioniques et Moléculaires, Université Aix-Marseille, UMR CNRS 7345, Marseille (France)

    2015-08-20

    Interstellar ices are submitted to energetic processes (thermal, UV, and cosmic-ray radiations) producing complex organic molecules. Laboratory experiments aim to reproduce the evolution of interstellar ices to better understand the chemical changes leading to the reaction, formation, and desorption of molecules. In this context, the thermal evolution of an interstellar ice analogue composed of water, carbon dioxide, ammonia, and formaldehyde is investigated. The ice evolution during the warming has been monitored by IR spectroscopy. The formation of hexamethylenetetramine (HMT) and polymethylenimine (PMI) are observed in the organic refractory residue left after ice sublimation. A better understanding of this result is realized with the study of another ice mixture containing methylenimine (a precursor of HMT) with carbon dioxide and ammonia. It appears that carbamic acid, a reaction product of carbon dioxide and ammonia, plays the role of catalyst, allowing the reactions toward HMT and PMI formation. This is the first time that such complex organic molecules (HMT, PMI) are produced from the warming (without VUV photolysis or irradiation with energetic particles) of abundant molecules observed in interstellar ices (H{sub 2}O, NH{sub 3}, CO{sub 2}, H{sub 2}CO). This result strengthens the importance of thermal reactions in the ices’ evolution. HMT and PMI, likely components of interstellar ices, should be searched for in the pristine objects of our solar system, such as comets and carbonaceous chondrites.

  14. CARBON DIOXIDE INFLUENCE ON THE THERMAL FORMATION OF COMPLEX ORGANIC MOLECULES IN INTERSTELLAR ICE ANALOGS

    International Nuclear Information System (INIS)

    Vinogradoff, V.; Fray, N.; Bouilloud, M.; Cottin, H.; Duvernay, F.; Chiavassa, T.

    2015-01-01

    Interstellar ices are submitted to energetic processes (thermal, UV, and cosmic-ray radiations) producing complex organic molecules. Laboratory experiments aim to reproduce the evolution of interstellar ices to better understand the chemical changes leading to the reaction, formation, and desorption of molecules. In this context, the thermal evolution of an interstellar ice analogue composed of water, carbon dioxide, ammonia, and formaldehyde is investigated. The ice evolution during the warming has been monitored by IR spectroscopy. The formation of hexamethylenetetramine (HMT) and polymethylenimine (PMI) are observed in the organic refractory residue left after ice sublimation. A better understanding of this result is realized with the study of another ice mixture containing methylenimine (a precursor of HMT) with carbon dioxide and ammonia. It appears that carbamic acid, a reaction product of carbon dioxide and ammonia, plays the role of catalyst, allowing the reactions toward HMT and PMI formation. This is the first time that such complex organic molecules (HMT, PMI) are produced from the warming (without VUV photolysis or irradiation with energetic particles) of abundant molecules observed in interstellar ices (H 2 O, NH 3 , CO 2 , H 2 CO). This result strengthens the importance of thermal reactions in the ices’ evolution. HMT and PMI, likely components of interstellar ices, should be searched for in the pristine objects of our solar system, such as comets and carbonaceous chondrites

  15. Kinetic Monte Carlo simulations of water ice porosity: extrapolations of deposition parameters from the laboratory to interstellar space

    Science.gov (United States)

    Clements, Aspen R.; Berk, Brandon; Cooke, Ilsa R.; Garrod, Robin T.

    2018-02-01

    Using an off-lattice kinetic Monte Carlo model we reproduce experimental laboratory trends in the density of amorphous solid water (ASW) for varied deposition angle, rate and surface temperature. Extrapolation of the model to conditions appropriate to protoplanetary disks and interstellar dark clouds indicate that these ices may be less porous than laboratory ices.

  16. From ice to gas : constraining the desorption processes of interstellar ices

    NARCIS (Netherlands)

    Fayolle, Edith Carine

    2013-01-01

    The presence of icy mantles on interstellar dust grains play a key role in the formation of molecules observed at all stages of star formation. This thesis addresses thermal and UV-induced ice sublimation. Using state of the art laboratory experiments and synchrotron-based UV radiation, the

  17. Interstellar hydrogen bonding

    Science.gov (United States)

    Etim, Emmanuel E.; Gorai, Prasanta; Das, Ankan; Chakrabarti, Sandip K.; Arunan, Elangannan

    2018-06-01

    This paper reports the first extensive study of the existence and effects of interstellar hydrogen bonding. The reactions that occur on the surface of the interstellar dust grains are the dominant processes by which interstellar molecules are formed. Water molecules constitute about 70% of the interstellar ice. These water molecules serve as the platform for hydrogen bonding. High level quantum chemical simulations for the hydrogen bond interaction between 20 interstellar molecules (known and possible) and water are carried out using different ab-intio methods. It is evident that if the formation of these species is mainly governed by the ice phase reactions, there is a direct correlation between the binding energies of these complexes and the gas phase abundances of these interstellar molecules. Interstellar hydrogen bonding may cause lower gas abundance of the complex organic molecules (COMs) at the low temperature. From these results, ketenes whose less stable isomers that are more strongly bonded to the surface of the interstellar dust grains have been observed are proposed as suitable candidates for astronomical observations.

  18. OBSERVATIONAL CONSTRAINTS ON METHANOL PRODUCTION IN INTERSTELLAR AND PREPLANETARY ICES

    International Nuclear Information System (INIS)

    Whittet, D. C. B.; Cook, A. M.; Herbst, Eric; Chiar, J. E.; Shenoy, S. S.

    2011-01-01

    Methanol (CH 3 OH) is thought to be an important link in the chain of chemical evolution that leads from simple diatomic interstellar molecules to complex organic species in protoplanetary disks that may be delivered to the surfaces of Earthlike planets. Previous research has shown that CH 3 OH forms in the interstellar medium predominantly on the surfaces of dust grains. To enhance our understanding of the conditions that lead to its efficient production, we assemble a homogenized catalog of published detections and limiting values in interstellar and preplanetary ices for both CH 3 OH and the other commonly observed C- and O-bearing species, H 2 O, CO, and CO 2 . We use this catalog to investigate the abundance of ice-phase CH 3 OH in environments ranging from dense molecular clouds to circumstellar envelopes around newly born stars of low and high mass. Results show that CH 3 OH production arises during the CO freezeout phase of ice-mantle growth in the clouds, after an ice layer rich in H 2 O and CO 2 is already in place on the dust, in agreement with current astrochemical models. The abundance of solid-phase CH 3 OH in this environment is sufficient to account for observed gas-phase abundances when the ices are subsequently desorbed in the vicinity of embedded stars. CH 3 OH concentrations in the ices toward embedded stars show order-of-magnitude object-to-object variations, even in a sample restricted to stars of low mass associated with ices lacking evidence of thermal processing. We hypothesize that the efficiency of CH 3 OH production in dense cores and protostellar envelopes is mediated by the degree of prior CO depletion.

  19. Surface science studies of ethene containing model interstellar ices

    Science.gov (United States)

    Puletti, F.; Whelan, M.; Brown, W. A.

    2011-05-01

    The formation of saturated hydrocarbons in the interstellar medium (ISM) is difficult to explain only by taking into account gas phase reactions. This is mostly due to the fact that carbonium ions only react with H_2 to make unsaturated hydrocarbons, and hence no viable route to saturated hydrocarbons has been postulated to date. It is therefore likely that saturation processes occur via surface reactions that take place on interstellar dust grains. One of the species of interest in this family of reactions is C_2H_4 (ethene) which is an intermediate in several molecular formation routes (e.g. C_2H_2 → C_2H_6). To help to understand some of the surface processes involving ethene, a study of ethene deposited on a dust grain analogue surface (highly oriented pyrolytic graphite) held under ultra-high vacuum at 20 K has been performed. The adsorption and desorption of ethene has been studied both in water-free and water-dominated model interstellar ices. A combination of temperature programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS) have been used to identify the adsorbed and trapped species and to determine the kinetics of the desorption processes. In all cases, ethene is found to physisorb on the carbonaceous surface. As expected water has a very strong influence on the desorption of ethene, as previously observed for other model interstellar ice systems.

  20. Interstellar ice grains in the Taurus molecular clouds

    International Nuclear Information System (INIS)

    Whittet, D.C.B.; Bode, M.F.; Baines, D.W.T.; Evans, A.

    1983-01-01

    Observations made in November 1981 using the United Kingdom Infrared Telescope (UKIRT) at Mauna Kea of the 3 μm ice absorption feature in the spectra of several obscured stars in the Taurus interstellar clouds are reported. The feature correlated in strength with extinction at visual wavelengths (Asub(v)), and is present in stars with Asub(v) as low as 4-6 mag. Ice may be widespread in the Taurus clouds, vindicating ideas on grain composition and growth first reported nearly 50 yr ago. (author)

  1. Ketene Formation in Interstellar Ices: A Laboratory Study

    Science.gov (United States)

    Hudson, Reggie L.; Loeffler, Mark Josiah

    2013-01-01

    The formation of ketene (H2CCO, ethenone) in polar and apolar ices was studied with in situ 0.8 MeV proton irradiation, far-UVphotolysis, and infrared spectroscopic analyses at 10-20 K. Using isotopically enriched reagents, unequivocal evidencewas obtained for ketene synthesis in H2O-rich and CO2-rich ices, and several reaction products were identified. Results from scavenging experiments suggested that ketene was formed by free-radical pathways, as opposed to acid-base processes or redox reactions. Finally, we use our results to draw conclusions about the formation and stability of ketene in the interstellar medium.

  2. MECHANISTICAL STUDIES ON THE PRODUCTION OF FORMAMIDE (H2NCHO) WITHIN INTERSTELLAR ICE ANALOGS

    International Nuclear Information System (INIS)

    Jones, Brant M.; Bennett, Christopher J.; Kaiser, Ralf I.

    2011-01-01

    Formamide, H 2 NCHO, represents the simplest molecule containing the peptide bond. Consequently, the formamide molecule is of high interest as it is considered an important precursor in the abiotic synthesis of amino acids, and thus significant to further prebiotic chemistry, in more suitable environments. Previous experiments have demonstrated that formamide is formed under extreme conditions similar throughout the interstellar medium via photolysis and the energetic processing of ultracold interstellar and solar system ices with high-energy protons; however, no clear reaction mechanism has been identified. Utilizing a laboratory apparatus capable of simulating the effects of galactic cosmic radiation on ultralow temperature ice mixtures, we have examined the formation of formamide starting from a variety of carbon monoxide (CO) to ammonia (NH 3 ) ices of varying composition. Our results suggest that the primary reaction step leading to the production of formamide in low-temperature ices involves the cleavage of the nitrogen-hydrogen bond of ammonia forming the amino radical (NH 2 ) and atomic hydrogen (H), the latter of which containing excess kinetic energy. These suprathermal hydrogen atoms can then add to the carbon-oxygen triple bond of the carbon monoxide (CO) molecule, overcoming the entrance barrier, and ultimately producing the formyl radical (HCO). From here, the formyl radical may combine without an entrance barrier with the neighboring amino radical if the proper geometry for these two species exists within the matrix cage.

  3. KETENE FORMATION IN INTERSTELLAR ICES: A LABORATORY STUDY

    Energy Technology Data Exchange (ETDEWEB)

    Hudson, Reggie L.; Loeffler, Mark J., E-mail: Reggie.Hudson@NASA.gov [Astrochemistry Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

    2013-08-20

    The formation of ketene (H{sub 2}CCO, ethenone) in polar and apolar ices was studied with in situ 0.8 MeV proton irradiation, far-UV photolysis, and infrared spectroscopic analyses at 10-20 K. Using isotopically enriched reagents, unequivocal evidence was obtained for ketene synthesis in H{sub 2}O-rich and CO{sub 2}-rich ices, and several reaction products were identified. Results from scavenging experiments suggested that ketene was formed by free-radical pathways, as opposed to acid-base processes or redox reactions. Finally, we use our results to draw conclusions about the formation and stability of ketene in the interstellar medium.

  4. Radiation Effects in Hydrogen-Laden Porous Water Ice Films: Implications for Interstellar Ices

    Science.gov (United States)

    Raut, Ujjwal; Baragiola, Raul; Mitchell, Emma; Shi, Jianming

    H _{2} is the dominant gas in the dense clouds of the interstellar medium (ISM). At densities of 10 (5) cm (-3) , an H _{2} molecule arrives at the surface of a 0.1 mum-sized, ice-covered dust grain once every few seconds [1]. At 10 K, H _{2} can diffuse into the pores of the ice mantle and adsorb at high-energy binding sites, loading the ice with hydrogen over the lifetime of the cloud. These icy grains are also impacted by galactic cosmic rays and stellar winds (in clouds with embedded protostar). Based on the available cosmic proton flux spectrum [2], we estimate a small impact rate of nearly 1 hit per year on a 0.1 μm sized grain, or 10 (-7) times the impact frequency of the neutral H _{2}. The energy deposited by such impacts can release the adsorbed H _{2} into the gas phase (impact desorption or sputtering). Recently, we have reported on a new process of ion-induced enhanced adsorption, where molecules from the gas phase are incorporated into the film when irradiation is performed in the presence of ambient gas [3]. The interplay between ion-induced ejection and adsorption can be important in determining the gas-solid balance in the ISM. To understand the effects of cosmic rays/stellar winds impacts on interstellar ice immersed in H _{2} gas, we have performed irradiation of porous amorphous ice films loaded with H _{2} through co-deposition or adsorption following growth. The irradiations were performed with 100 keV H (+) using fluxes of 10 (10) -10 (12) H (+) cm (-2) s (-1) at 7 K, in presence of ambient H _{2} at pressures ranging from 10 (-5) to 10 (-8) Torr. Our initial results show a net loss in adsorbed H _{2} during irradiation, from competing ion-induced ejection and adsorption. The H _{2} loss per ion decreases exponentially with fluence, with a cross-section of 10 (-13) cm (2) . In addition to hydrogen removal, irradiation also leads to trapping of H _{2} in the ice film, from closing of the pores during irradiation [4]. As a result, 2.6 percent

  5. ON THE FORMATION OF DIPEPTIDES IN INTERSTELLAR MODEL ICES

    International Nuclear Information System (INIS)

    Kaiser, R. I.; Kim, Y. S.; Stockton, A. M.; Jensen, E. C.; Mathies, R. A.

    2013-01-01

    The hypothesis of an exogenous origin and delivery of biologically important molecules to early Earth presents an alternative route to their terrestrial in situ formation. Dipeptides like Gly-Gly detected in the Murchison meteorite are considered as key molecules in prebiotic chemistry because biofunctional dipeptides present the vital link in the evolutionary transition from prebiotic amino acids to early proteins. However, the processes that could lead to the exogenous abiotic synthesis of dipeptides are unknown. Here, we report the identification of two proteinogenic dipeptides—Gly-Gly and Leu-Ala—formed via electron-irradiation of interstellar model ices followed by annealing the irradiated samples to 300 K. Our results indicate that the radiation-induced, non-enzymatic formation of proteinogenic dipeptides in interstellar ice analogs is facile. Once synthesized and incorporated into the ''building material'' of solar systems, biomolecules at least as complex as dipeptides could have been delivered to habitable planets such as early Earth by meteorites and comets, thus seeding the beginning of life as we know it.

  6. Formation of Amino Acid Precursors by Bombardment of Interstellar Ice Analogs with High Energy Heavy Ions

    Science.gov (United States)

    Kobayashi, Kensei; Mita, Hajime; Yoshida, Satoshi; Shibata, Hiromi; Enomoto, Shingo; Matsuda, Tomoyuki; Fukuda, Hitoshi; Kondo, Kotaro; Oguri, Yoshiyuki; Kebukawa, Yoko

    2016-07-01

    A wide variety of organic compounds have been detected in extraterrestrial bodies. It has been recognized that carbonaceous chondrites contain pristine amino acids [1]. There are several scenarios of the formation of such extraterrestrial amino acids or their precursors. Greenberg proposed a scenario that complex organic compounds were formed in interstellar ices in dense clouds, which were brought into solar system small bodies when the solar system was formed [2]. The ice mantles of interstellar dust particles (ISDs) in dense clouds are composed of H2O, CO, CH3OH, CH4, CO2, NH3, etc. In order to verify the scenario, a number of laboratory experiments have been conducted where interstellar ice analogs were irradiated with high-energy particles [3,4] or UV [5,6], and formation of complex organic compounds including amino acid precursors were detected in the products. Though ion-molecular reactions in gaseous phase and surface reactions on the ice mantles have been studied intensively, much less works on cosmic rays-induced reaction have been reported. In order to study possible formation of complex molecules in interstellar ices, frozen mixtures of water, methanol and ammonia with various mixing ratios were irradiated with high-energy heavy ions such as carbon ions (290 MeV/u) and neon ions (400 MeV/u) from HIMAC, NIRS, Japan. For comparison, gaseous mixtures of water, ammonia, carbon monoxide, carbon dioxide, and/or methane were irradiated with protons (2.5 MeV) from a Tandem accelerator, Tokyo Tech, Japan. Amino acids in the products were determined by cation exchange HPLC after acid hydrolysis. Products, both before and after acid hydrolysis, were also characterized by FT-IR and other techniques. Amino acids were detected in the hydrolyzed products after mixture of CH3OH, NH3 and H2O with various mixing ratios were irradiated with heavy ions, including when their mixing ratio was set close to the reported value of the interstellar ices (10:1:37). In the HIMAC

  7. Ultraviolet Irradiation of Pyrimidine in Interstellar Ice Analogs: Formation and Photo-Stability of Nucleobases

    Science.gov (United States)

    Nuevo, Michel; Milam, Stefanie N.; Sandford, Scott A.; Elsila, Jamie E.; Dworkin, Jason P.

    2010-01-01

    Astrochemistry laboratory experiments recently showed that molecules of prebiotic interest can potentially form in space, as supported by the detection of amino acids in organic residues formed by the UV photolysis of ices simulating interstellar and cometary environments (H2O, CO, CO2, CH3OH, NH3, etc.). Although the presence of amino acids in the interstellar medium (ISM) is still under debate, experiments and the detection of amino acids in meteorites both support a scenario in which prebiotic molecules could be of extraterrestrial origin, before they are delivered to planets by comets, asteroids, and interplanetary dust particles. Nucleobases, the informational subunits of DNA and RNA, have also been detected in meteorites, although they have not yet been observed in the ISM. Thus, these molecules constitute another family of prebiotic compounds that can possibly form via abiotical processes in astrophysical environments. Nucleobases are nitrogen-bearing cyclic aromatic species with various functional groups attached, which are divided into two classes: pyrimidines (uracil, cytosine, and thymine) and purines (adenine and guanine). In this work, we study how UV irradiation affects pyrimidine mixed in interstellar ice analogs (H2O, NH3, CH3OH). In particular, we show that the UV irradiation of H2O:pyrimidine mixtures leads to the production of oxidized compounds including uracil, and show that both uracil and cytosine are formed upon irradiation of H2O:NH3:pyrimidine mixtures. We also study the photostability of pyrimidine and its photoproducts formed during these experiments.

  8. Hydrocarbons in interstellar ice analogues : UV-vis spectroscopy and VUV photochemistry

    NARCIS (Netherlands)

    Cuylle, Steven Hendrik

    2015-01-01

    This thesis treats the chemical behaviour of carbonaceous molecules in water-dominated interstellar ices. VUV photons are considered as the chemical trigger to induce solid state chemistry as it is omnipresent. Lyman- radiation occurs even in dense molecular clouds as a result of cosmic ray

  9. On the Formation of Interstellar Water Ice: Constraints from a Search for Hydrogen Peroxide Ice in Molecular Clouds

    Science.gov (United States)

    Smith, R. G.; Charnely, S. B.; Pendleton, Y. J.; Wright, C. M.; Maldoni, M. M.; Robinson, G.

    2011-01-01

    Recent surface chemistry experiments have shown that the hydrogenation of molecular oxygen on interstellar dust grains is a plausible formation mechanism, via hydrogen peroxide (H2O2), for the production of water (H2O) ice mantles in the dense interstellar medium. Theoretical chemistry models also predict the formation of a significant abundance of H2O2 ice in grain mantles by this route. At their upper limits, the predicted and experimental abundances are sufficiently high that H2O2 should be detectable in molecular cloud ice spectra. To investigate this further, laboratory spectra have been obtained for H2O2/H2O ice films between 2.5 and 200 micron, from 10 to 180 K, containing 3%, 30%, and 97% H2O2 ice. Integrated absorbances for all the absorption features in low-temperature H2O2 ice have been derived from these spectra. For identifying H2O2 ice, the key results are the presence of unique features near 3.5, 7.0, and 11.3 micron. Comparing the laboratory spectra with the spectra of a group of 24 protostars and field stars, all of which have strong H2O ice absorption bands, no absorption features are found that can definitely be identified with H2O2 ice. In the absence of definite H2O2 features, the H2O2 abundance is constrained by its possible contribution to the weak absorption feature near 3.47 micron found on the long-wavelength wing of the 3 micron H2O ice band. This gives an average upper limit for H2O2, as a percentage of H2O, of 9% +/- 4%. This is a strong constraint on parameters for surface chemistry experiments and dense cloud chemistry models.

  10. Organic Compounds Produced by Photolysis of Realistic Interstellar and Cometary Ice Analogs Containing Methanol

    Science.gov (United States)

    Bernstein, Max P.; Sandford, Scott A.; Allamandola, Louis J.; Chang, Sherwood; Scharberg, Maureen A.

    1995-01-01

    The InfraRed (IR) spectra of UltraViolet (UV) and thermally processed, methanol-containing interstellar / cometary ice analogs at temperatures from 12 to 300 K are presented. Infrared spectroscopy, H-1 and C-13 Nuclear Magnetic Resonance (NMR) spectroscopy, and gas chromatography-mass spectrometry indicate that CO (carbon monoxide), CO2 (carbon dioxide), CH4 (methane), HCO (the formyl radical), H2CO (formaldehyde), CH3CH2OH (ethanol), HC([double bond]O)NH2 (formamide), CH3C([double bond]O)NH2 (acetamide), and R[single bond]C[triple bond]N (nitriles) are formed. In addition, the organic materials remaining after photolyzed ice analogs have been warmed to room temperature contain (in rough order of decreasing abundance), (1) hexamethylenetetramine (HMT, C6H12N4), (2) ethers, alcohols, and compounds related to PolyOxyMethylene (POM, ([single bond]CH2O[single bond](sub n)), and (3) ketones (R[single bond]C([double bond]O)[single bond]R') and amides (H2NC([double bond]O)[single bond]R). Most of the carbon in these residues is thought to come from the methanol in the original ice. Deuterium and C-13 isotopic labeling demonstrates that methanol is definitely the source of carbon in HMT. High concentrations of HMT in interstellar and cometary ices could have important astrophysical consequences. The ultraviolet photolysis of HMT frozen in H2O ice readily produces the 'XCN' band observed in the spectra of protostellar objects and laboratory ices, as well as other nitriles. Thus, HMT may be a precursor of XCN and a source of CN in comets and the interstellar medium. Also, HMT is known to hydrolyze under acidic conditions to yield ammonia, formaldehyde, and amino acids. Thus, HMT may be a significant source of prebiogenic compounds on asteroidal parent bodies. A potential mechanism for the radiative formation of HMT in cosmic ices is outlined.

  11. ON THE FORMATION OF INTERSTELLAR WATER ICE: CONSTRAINTS FROM A SEARCH FOR HYDROGEN PEROXIDE ICE IN MOLECULAR CLOUDS

    Energy Technology Data Exchange (ETDEWEB)

    Smith, R. G.; Wright, C. M.; Robinson, G. [School of Physical, Environmental and Mathematical Sciences, University of New South Wales, Australian Defence Force Academy, Canberra, ACT 2600 (Australia); Charnley, S. B. [Astrochemistry Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Pendleton, Y. J. [NASA Lunar Science Institute, NASA Ames Research Center, Moffett Field, CA 94035 (United States); Maldoni, M. M., E-mail: r.smith@adfa.edu.au, E-mail: c.wright@adfa.edu.au, E-mail: g.robinson@adfa.edu.au, E-mail: Steven.B.Charnley@nasa.gov, E-mail: yvonne.pendleton@nasa.gov [Geoscience Australia, Canberra, ACT 2601 (Australia)

    2011-12-20

    Recent surface chemistry experiments have shown that the hydrogenation of molecular oxygen on interstellar dust grains is a plausible formation mechanism, via hydrogen peroxide (H{sub 2}O{sub 2}), for the production of water (H{sub 2}O) ice mantles in the dense interstellar medium. Theoretical chemistry models also predict the formation of a significant abundance of H{sub 2}O{sub 2} ice in grain mantles by this route. At their upper limits, the predicted and experimental abundances are sufficiently high that H{sub 2}O{sub 2} should be detectable in molecular cloud ice spectra. To investigate this further, laboratory spectra have been obtained for H{sub 2}O{sub 2}/H{sub 2}O ice films between 2.5 and 200 {mu}m, from 10 to 180 K, containing 3%, 30%, and 97% H{sub 2}O{sub 2} ice. Integrated absorbances for all the absorption features in low-temperature H{sub 2}O{sub 2} ice have been derived from these spectra. For identifying H{sub 2}O{sub 2} ice, the key results are the presence of unique features near 3.5, 7.0, and 11.3 {mu}m. Comparing the laboratory spectra with the spectra of a group of 24 protostars and field stars, all of which have strong H{sub 2}O ice absorption bands, no absorption features are found that can definitely be identified with H{sub 2}O{sub 2} ice. In the absence of definite H{sub 2}O{sub 2} features, the H{sub 2}O{sub 2} abundance is constrained by its possible contribution to the weak absorption feature near 3.47 {mu}m found on the long-wavelength wing of the 3 {mu}m H{sub 2}O ice band. This gives an average upper limit for H{sub 2}O{sub 2}, as a percentage of H{sub 2}O, of 9% {+-} 4%. This is a strong constraint on parameters for surface chemistry experiments and dense cloud chemistry models.

  12. Cometary Materials Originating from Interstellar Ices: Clues from Laboratory Experiments

    Energy Technology Data Exchange (ETDEWEB)

    Fresneau, A.; Mrad, N. Abou; LS d’Hendecourt, L.; Duvernay, F.; Chiavassa, T.; Danger, G. [Aix-Marseille Université, PIIM UMR-CNRS 7345, F-13397 Marseille (France); Flandinet, L.; Orthous-Daunay, F.-R.; Vuitton, V.; Thissen, R., E-mail: gregoire.danger@univ-amu.fr [Université Grenoble Alpes, CNRS, IPAG, Grenoble F-38000 (France)

    2017-03-10

    We use laboratory experiments to derive information on the chemistry occurring during the evolution of astrophysical ices from dense molecular clouds to interplanetary objects. Through a new strategy that consists of coupling very high resolution mass spectrometry and infrared spectroscopy (FT-IR), we investigate the molecular content of the organic residues synthesized from different initial ice compositions. We also obtain information on the evolution of the soluble part of the residues after their over-irradiation. The results give insight into the role of water ice as a trapping and diluting agent during the chemical evolution. They also give information about the importance of the amount of ammonia in such ices, particularly regarding its competition with the carbon chemistry. All of these results allow us to build a first mapping of the evolution of soluble organic matter based on its chemical and physical history. Furthermore, our results suggest that interstellar ices should lead to organic materials enriched in heteroatoms that present similarities with cometary materials but strongly differ from meteoritic organic material, especially in their C/N ratios.

  13. Cometary Materials Originating from Interstellar Ices: Clues from Laboratory Experiments

    Science.gov (United States)

    Fresneau, A.; Abou Mrad, N.; d'Hendecourt, L. LS; Duvernay, F.; Flandinet, L.; Orthous-Daunay, F.-R.; Vuitton, V.; Thissen, R.; Chiavassa, T.; Danger, G.

    2017-03-01

    We use laboratory experiments to derive information on the chemistry occurring during the evolution of astrophysical ices from dense molecular clouds to interplanetary objects. Through a new strategy that consists of coupling very high resolution mass spectrometry and infrared spectroscopy (FT-IR), we investigate the molecular content of the organic residues synthesized from different initial ice compositions. We also obtain information on the evolution of the soluble part of the residues after their over-irradiation. The results give insight into the role of water ice as a trapping and diluting agent during the chemical evolution. They also give information about the importance of the amount of ammonia in such ices, particularly regarding its competition with the carbon chemistry. All of these results allow us to build a first mapping of the evolution of soluble organic matter based on its chemical and physical history. Furthermore, our results suggest that interstellar ices should lead to organic materials enriched in heteroatoms that present similarities with cometary materials but strongly differ from meteoritic organic material, especially in their C/N ratios.

  14. Laboratory simulation of interstellar grain chemistry and the production of complex organic molecules

    Science.gov (United States)

    Allamandola, L. J.; Sandford, S. A.; Valero, G. J.

    1990-01-01

    During the past 15 years considerable progress in observational techniques has been achieved in the middle infrared (5000 to 500 cm(-1), 2 to 20 microns m), the spectral region most diagnostic of molecular vibrations. Spectra of many different astronomical infrared sources, some deeply embedded in dark molecular clouds, are now available. These spectra provide a powerful probe, not only for the identification of interstellar molecules in both the gas solid phases, but also of the physical and chemical conditions which prevail in these two very different domains. By comparing these astronomical spectra with the spectra of laboratory ices one can determine the composition and abundance of the icy materials frozen on the cold (10K) dust grains present in the interior of molecular clouds. These grains and their ice mantles may well be the building blocks from which comets are made. As an illustration of the processes which can take place as an ice is irradiated and subsequently warmed, researchers present the infrared spectra of the mixture H2O:CH3OH:CO:NH3:C6H14 (100:50:10:10:10). Apart from the last species, the ratio of these compounds is representative of the simplest ices found in interstellar clouds. The last component was incorporated into this particular experiment as a tracer of the behavior of a non-aromatic hydrocarbon. The change in the composition that results from ultraviolet photolysis of this ice mixture using a UV lamp to simulate the interstellar radiation field is shown. Photolysis produces CO, CO2, CH4, HCO, H2CO, as well as a family of moderately volatile hydrocarbons. Less volatile carbonaceous materials are also produced. The evolution of the infrared spectrum of the ice as the sample is warmed up to room temperature is illustrated. Researchers believe that the changes are similar to those which occur as ice is ejected from a comet and warmed up by solar radiation. The warm-up sequence shows that the nitrile or iso-nitrile bearing compound

  15. Photon- and electron-stimulated desorption from laboratory models of interstellar ice grains

    International Nuclear Information System (INIS)

    Thrower, J. D.; Abdulgalil, A. G. M.; Collings, M. P.; McCoustra, M. R. S.; Burke, D. J.; Brown, W. A.; Dawes, A.; Holtom, P. J.; Kendall, P.; Mason, N. J.; Jamme, F.; Fraser, H. J.; Rutten, F. J. M.

    2010-01-01

    The nonthermal desorption of water from ice films induced by photon and low energy electron irradiation has been studied under conditions mimicking those found in dense interstellar clouds. Water desorption following photon irradiation at 250 nm relies on the presence of an absorbing species within the H 2 O ice, in this case benzene. Desorption cross sections are obtained and used to derive first order rate coefficients for the desorption processes. Kinetic modeling has been used to compare the efficiencies of these desorption mechanisms with others known to be in operation in dense clouds.

  16. Photon-induced Processing of Interstellar Ices in the Laboratory. Focus on Their Non-thermal Desorption.

    Science.gov (United States)

    Martin-Domenech, Rafael; Munoz Caro, Guillermo; Cruz-Diaz, Gustavo A.; Oberg, Karin I.

    2018-06-01

    Some of the processes that take place in the interstellar medium (ISM)can be simulated in laboratories on Earth under astrophysically relevant conditions. For example, the energetic processing of the ice mantles that accrete on top of dust grains in the coldest regions of the ISM, leading to the production of new species and their desorption to the gas phase. In particular, observation of complex organic molecules (COMs) in cold interstellar environments stress the need for not only a solid state formation but also for non-thermal desorption mechanisms that can account for the observed abundances in regions where thermal desorption is inhibited. Laboratory Astrophysics can be used to test different non-thermal desorption processes and extract yields than can be extrapolated to the astrophysical scenario with theoretical models. 0th generation COMs like CH3OH and H2CO can be formed at very low temperatures. In this talk, we present laboratory simulations of the UV photoprocessing of a binary ice mixture composed by water (the main component of astrophysical ices) and methane. Formation of CO, CO2, CH3OH and H2CO was confirmed by IR spectroscopy and subsequent TPD. At the same time, photodesorption of CO and H2CO was detected by means of a Quadrupole Mass Spectrometer, with yields on the order of 10-4 and 10-5 molecules per incident photon, respectively. In general, photodesorption can take place through a direct mechanism, where the absorbing molecule (or its photofragments) are desorbed; or through an indirect mechanism where the absorbed energy is transferred to a surface molecule which is the one finally desorbing. In the case of photoproducts, the evolution of the photodesorption yield gives information on the photodesorption mechanism: a constant photodesorption yield is observed when the photoproducts are desorbed right after their formation; while an increasing yield is measured when the photoproducts are desorbed later after energy transfer from another

  17. On the formation of niacin (vitamin B3) and pyridine carboxylic acids in interstellar model ices

    Energy Technology Data Exchange (ETDEWEB)

    McMurtry, Brandon M.; Turner, Andrew M.; Saito, Sean E.J.; Kaiser, Ralf I. [W. M. Keck Research Laboratory in Astrochemistry, University of Hawaii at Manoa, Honolulu, Hawaii, HI 96822 (United States); Department of Chemistry, University of Hawaii at Manoa, Honolulu, Hawaii, HI 96822 (United States)

    2016-06-15

    The formation of pyridine carboxylic acids in interstellar ice grains was simulated by electron exposures of binary pyridine (C{sub 5}H{sub 5}N)-carbon dioxide (CO{sub 2}) ice mixtures at 10 K under contamination-free ultrahigh vacuum conditions. Chemical processing of the pristine ice and subsequent warm-up phase was monitored on line and in situ via Fourier transform infrared spectroscopy to probe for the formation of new radiation induced species. In the infrared spectra of the irradiated ice, bands assigned to nicotinic acid (niacin; vitamin B3; m-C{sub 5}H{sub 4}NCOOH) along with 2,3-, 2,5-, 3,4-, and 3,5-pyridine dicarboxylic acid (C{sub 5}H{sub 3}N(COOH){sub 2}) were unambiguously identified along with the hydroxycarbonyl (HOCO) radical. Our study suggests that the reactive pathway responsible for pyridine carboxylic acids formation involves a HOCO intermediate, which forms through the reaction of suprathermal hydrogen ejected from pyridine with carbon dioxide. The newly formed pyridinyl radical may then undergo radical–radical recombination with a hydroxycarbonyl radical to form a pyridine carboxylic acid.

  18. Probing the Origin and Evolution of Interstellar and Protoplanetary Biogenic Ices with SPHEREx

    Science.gov (United States)

    Melnick, Gary; SPHEREx Science Team

    2018-01-01

    Many of the most important building blocks of life are locked in interstellar and protoplanetary ices. Examples include H2O, CO, CO2, and CH3OH, among others. There is growing evidence that within the cores of dense molecular clouds and the mid-plane of protoplanetary disks the abundance of these species in ices far exceeds that in the gas phase. As a result, collisions between ice-bearing bodies and newly forming planets are thought to be a major means of delivering these key species to young planets. There currently exist fewer than 250 ice absorption spectra toward Galactic molecular clouds, which is insufficient to reliably trace the ice content of clouds through the various evolutionary stages of collapse to form stars and planets. Likewise, the current number of spectra is inadequate to assess the effects of environment, such as cloud density and temperature, presence or absence of embedded sources, external FUV and X-ray radiation, gas-phase composition, or cosmic-ray ionization rate, on the ice composition of clouds at similar stages of evolution. Ultimately, our goal is to understand how these findings connect to our own Solar System.SPHEREx will be a game changer for the study of interstellar, circumstellar, and protoplanetary disk ices. SPHEREx will obtain spectra over the entire sky in the optical and near-IR, including the 2.5 to 5.0 micron region, which contains the above biogenic ice features. SPHEREx will detect millions of potential background continuum point sources already catalogued by NASA’s Wide-field Infrared Survey Explorer (WISE) at 3.4 and 4.6 microns for which there is evidence for intervening gas and dust based on the 2MASS+WISE colors with sufficient sensitivity to yield ice absorption spectra with SNR ≥ 100 per spectral resolution element. The resulting > 100-fold increase in the number of high-quality ice absorption spectra toward a wide variety of regions distributed throughout the Galaxy will reveal correlations between ice

  19. Laboratory investigations of irradiated acetonitrile-containing ices on an interstellar dust analog

    International Nuclear Information System (INIS)

    Abdulgalil, Ali G. M.; Marchione, Demian; Rosu-Finsen, Alexander; Collings, Mark P.; McCoustra, Martin R. S.

    2012-01-01

    Reflection-absorption infrared spectroscopy is used to study the impact of low-energy electron irradiation of acetonitrile-containing ices, under conditions close to those in the dense star-forming regions in the interstellar medium. Both the incident electron energy and the surface coverage were varied. The experiments reveal that solid acetonitrile is desorbed from its ultrathin solid films with a cross section of the order of 10 −17 cm 2 . Evidence is presented for a significantly larger desorption cross section for acetonitrile molecules at the water–ice interface, similar to that previously observed for the benzene–water system.

  20. THE EFFECTS OF GRAIN SIZE AND TEMPERATURE DISTRIBUTIONS ON THE FORMATION OF INTERSTELLAR ICE MANTLES

    Energy Technology Data Exchange (ETDEWEB)

    Pauly, Tyler; Garrod, Robin T., E-mail: tap74@cornell.edu [Cornell Center for Astrophysics and Planetary Science, Cornell University, Ithaca, NY 14853-6801 (United States)

    2016-02-01

    Computational models of interstellar gas-grain chemistry have historically adopted a single dust-grain size of 0.1 micron, assumed to be representative of the size distribution present in the interstellar medium. Here, we investigate the effects of a broad grain-size distribution on the chemistry of dust-grain surfaces and the subsequent build-up of molecular ices on the grains, using a three-phase gas-grain chemical model of a quiescent dark cloud. We include an explicit treatment of the grain temperatures, governed both by the visual extinction of the cloud and the size of each individual grain-size population. We find that the temperature difference plays a significant role in determining the total bulk ice composition across the grain-size distribution, while the effects of geometrical differences between size populations appear marginal. We also consider collapse from a diffuse to a dark cloud, allowing dust temperatures to fall. Under the initial diffuse conditions, small grains are too warm to promote grain-mantle build-up, with most ices forming on the mid-sized grains. As collapse proceeds, the more abundant, smallest grains cool and become the dominant ice carriers; the large population of small grains means that this ice is distributed across many grains, with perhaps no more than 40 monolayers of ice each (versus several hundred assuming a single grain size). This effect may be important for the subsequent processing and desorption of the ice during the hot-core phase of star formation, exposing a significant proportion of the ice to the gas phase, increasing the importance of ice-surface chemistry and surface–gas interactions.

  1. The Effects of Grain Size and Temperature Distributions on the Formation of Interstellar Ice Mantles

    Science.gov (United States)

    Pauly, Tyler; Garrod, Robin T.

    2016-02-01

    Computational models of interstellar gas-grain chemistry have historically adopted a single dust-grain size of 0.1 micron, assumed to be representative of the size distribution present in the interstellar medium. Here, we investigate the effects of a broad grain-size distribution on the chemistry of dust-grain surfaces and the subsequent build-up of molecular ices on the grains, using a three-phase gas-grain chemical model of a quiescent dark cloud. We include an explicit treatment of the grain temperatures, governed both by the visual extinction of the cloud and the size of each individual grain-size population. We find that the temperature difference plays a significant role in determining the total bulk ice composition across the grain-size distribution, while the effects of geometrical differences between size populations appear marginal. We also consider collapse from a diffuse to a dark cloud, allowing dust temperatures to fall. Under the initial diffuse conditions, small grains are too warm to promote grain-mantle build-up, with most ices forming on the mid-sized grains. As collapse proceeds, the more abundant, smallest grains cool and become the dominant ice carriers; the large population of small grains means that this ice is distributed across many grains, with perhaps no more than 40 monolayers of ice each (versus several hundred assuming a single grain size). This effect may be important for the subsequent processing and desorption of the ice during the hot-core phase of star formation, exposing a significant proportion of the ice to the gas phase, increasing the importance of ice-surface chemistry and surface-gas interactions.

  2. Cosmic ray processing of N2-containing interstellar ice analogues at dark cloud conditions

    Science.gov (United States)

    Fedoseev, G.; Scirè, C.; Baratta, G. A.; Palumbo, M. E.

    2018-04-01

    N2 is believed to lock considerable part of nitrogen elemental budget and, therefore, to be one of the most abundant ice constituent in cold dark clouds. This laboratory-based research utilizes high energetic processing of N2 containing interstellar ice analogues using 200 keV H+ and He+ ions that mimics cosmic ray processing of the interstellar icy grains. It aims to investigate the formation of (iso)cyanates and cyanides in the ice mantles at the conditions typical for cold dark clouds and prestellar cores. Investigation of cosmic ray processing as a chemical trigger mechanism is explained by the high stability of N2 molecules that are chemically inert in most of the atom- and radical-addition reactions and cannot be efficiently dissociated by cosmic ray induced UV-field. Two sets of experiments are performed to closer address solid-state chemistry occurring in two distinct layers of the ice formed at different stages of dark cloud evolution, i.e. `H2O-rich' and `CO-rich' ice layers. Formation of HNCO and OCN- is discussed in all of the performed experiments. Corresponding kinetic curves for HNCO and OCN- are obtained. Furthermore, a feature around 2092 cm-1 assigned to the contributions of 13CO, CN-, and HCN is analysed. The kinetic curves for the combined HCN/CN- abundance are derived. In turn, normalized formation yields are evaluated by interpolation of the obtained results to the low irradiation doses relevant to dark cloud stage. The obtained values can be used to interpret future observations towards cold dark clouds using James Webb Space Telescope.

  3. Enantiomeric separation of complex organic molecules produced from irradiation of interstellar/circumstellar ice analogs

    Science.gov (United States)

    Nuevo, M.; Meierhenrich, U. J.; D'Hendecourt, L.; Muñoz Caro, G. M.; Dartois, E.; Deboffle, D.; Thiemann, W. H.-P.; Bredehöft, J.-H.; Nahon, L.

    Irradiation of interstellar/circumstellar ice analogs by ultraviolet (UV) light followed by warm up in the laboratory leads to the formation of complex organic molecules, stable at room temperature. Hydrolysis of the room temperature residue releases amino acids, the building blocks of proteins. These amino acids exist in two different forms (L and D), but proteins encountered in living beings consist exclusively of L enantiomers. The origin of this property, called homochirality, is still unknown. Amino acids can be detected and quantified by chemical techniques such as chiral gas chromatography coupled with mass spectrometry (GC-MS). Enantiomers of chiral organics are also known to interact selectively with circularly polarized light (CPL), leading to a selective production or destruction of the final compounds. This paper describes how we settled an experiment where amino acids are formed by irradiation of interstellar/circumstellar ice analogs with ultraviolet (UV) CPL, produced by a synchrotron radiation beamline, which allowed us to quantify the effect of such polarized light on the production of amino acids. These results can be compared to the enantiomeric excesses measured in primitive meteorites such as Murchison.

  4. Observations of the interstellar ice grain feature in the Taurus molecular clouds

    International Nuclear Information System (INIS)

    Whittet, D.C.B.; Longmore, A.J.; Baines, D.W.T.; Evans, A.

    1984-01-01

    Although water ice was originally proposed as a major constituent of the interstellar grain population, the advent of infrared astronomy has shown that the expected absorption due to O-H stretching vibrations at 3 μm is illusive. Observations have in fact revealed that the carrier of this feature is apparently restricted to regions deep within dense molecular clouds. However, the exact carrier of this feature is still controversial, and many questions remain as to the conditions required for its appearance. The Taurus molecular clouds were selected for observations, in the form of a preliminary survey in the 2-4 μm window. It is concluded that the carrier of the 3μm absorption feature appears to reside in the general cloud medium and is probably amorphous water ice. (author)

  5. Formation of interstellar methanol ice prior to the heavy CO freeze-out stage

    Science.gov (United States)

    Qasim, D.; Chuang, K.-J.; Fedoseev, G.; Ioppolo, S.; Boogert, A. C. A.; Linnartz, H.

    2018-04-01

    Context. The formation of methanol (CH3OH) on icy grain mantles during the star formation cycle is mainly associated with the CO freeze-out stage. Yet there are reasons to believe that CH3OH also can form at an earlier period of interstellar ice evolution in CO-poor and H2O-rich ices. Aims: This work focuses on CH3OH formation in a H2O-rich interstellar ice environment following the OH-mediated H-abstraction in the reaction, CH4 + OH. Experimental conditions are systematically varied to constrain the CH3OH formation yield at astronomically relevant temperatures. Methods: CH4, O2, and hydrogen atoms are co-deposited in an ultrahigh vacuum chamber at 10-20 K. OH radicals are generated by the H + O2 surface reaction. Temperature programmed desorption - quadrupole mass spectrometry (TPD-QMS) is used to characterize CH3OH formation, and is complemented with reflection absorption infrared spectroscopy (RAIRS) for CH3OH characterization and quantitation. Results: CH3OH formation is shown to be possible by the sequential surface reaction chain, CH4 + OH → CH3 + H2O and CH3 + OH → CH3OH at 10-20 K. This reaction is enhanced by tunneling, as noted in a recent theoretical investigation Lamberts et al. (2017, A&A, 599, A132). The CH3OH formation yield via the CH4 + OH route versus the CO + H route is approximately 20 times smaller for the laboratory settings studied. The astronomical relevance of the new formation channel investigated here is discussed.

  6. High-sensitivity Raman spectrometer to study pristine and irradiated interstellar ice analogs.

    Science.gov (United States)

    Bennett, Chris J; Brotton, Stephen J; Jones, Brant M; Misra, Anupam K; Sharma, Shiv K; Kaiser, Ralf I

    2013-06-18

    We discuss the novel design of a sensitive, normal-Raman spectrometer interfaced to an ultra-high vacuum chamber (5 × 10(-11) Torr) utilized to investigate the interaction of ionizing radiation with low temperature ices relevant to the solar system and interstellar medium. The design is based on a pulsed Nd:YAG laser which takes advantage of gating techniques to isolate the scattered Raman signal from the competing fluorescence signal. The setup incorporates innovations to achieve maximum sensitivity without detectable heating of the sample. Thin films of carbon dioxide (CO2) ices of 10 to 396 nm thickness were prepared and characterized using both Fourier transform infrared (FT-IR) spectroscopy and HeNe interference techniques. The ν+ and ν- Fermi resonance bands of CO2 ices were observed by Raman spectroscopy at 1385 and 1278 cm(-1), respectively, and the band areas showed a linear dependence on ice thickness. Preliminary irradiation experiments are conducted on a 450 nm thick sample of CO2 ice using energetic electrons. Both carbon monoxide (CO) and the infrared inactive molecular oxygen (O2) products are readily detected from their characteristic Raman bands at 2145 and 1545 cm(-1), respectively. Detection limits of 4 ± 3 and 6 ± 4 monolayers of CO and O2 were derived, demonstrating the unique power to detect newly formed molecules in irradiated ices in situ. The setup is universally applicable to the detection of low-abundance species, since no Raman signal enhancement is required, demonstrating Raman spectroscopy as a reliable alternative, or complement, to FT-IR spectroscopy in space science applications.

  7. ON THE FORMATION OF BENZOIC ACID AND HIGHER-ORDER BENZENE CARBOXYLIC ACIDS IN INTERSTELLAR MODEL ICE GRAINS

    Energy Technology Data Exchange (ETDEWEB)

    McMurtry, Brandon M.; Saito, Sean E. J.; Turner, Andrew M.; Chakravarty, Harish K.; Kaiser, Ralf I. [W. M. Keck Research Laboratory in Astrochemistry, University of Hawaii at Manoa, Honolulu, HI 96822 (United States)

    2016-11-10

    With a binary ice mixture of benzene (C{sub 6}H{sub 6}) and carbon dioxide (CO{sub 2}) at 10 K under contamination-free ultrahigh vacuum conditions, the formation of benzene carboxylic acids in interstellar ice grains was studied. Fourier transform infrared spectroscopy was used to probe for the formation of new species during the chemical processing of the ice mixture and during the following temperature-programmed desorption. Newly formed benzene carboxylic acid species, i.e., benzoic acid, as well as meta - and para -benzene dicarboxylic acid, were assigned using newly emerging bands in the infrared spectrum; a reaction mechanism, along with rate constants, was proposed utilizing the kinetic fitting of the coupled differential equations.

  8. Chemical Evolution of Interstellar Methanol Ice Analogs upon Ultraviolet Irradiation: The Role of the Substrate

    Science.gov (United States)

    Ciaravella, A.; Jiménez-Escobar, A.; Cosentino, G.; Cecchi-Pestellini, C.; Peres, G.; Candia, R.; Collura, A.; Barbera, M.; Di Cicca, G.; Varisco, S.; Venezia, A. M.

    2018-05-01

    An important issue in the chemistry of interstellar ices is the role of dust materials. In this work, we study the effect of an amorphous water-rich magnesium silicate deposited onto ZnSe windows on the chemical evolution of ultraviolet-irradiated methanol ices. For comparison, we also irradiate similar ices deposited onto bare ZnSe windows. Silicates are produced at relatively low temperatures exploiting a sol–gel technique. The chemical composition of the synthesized material reflects the forsterite stoichiometry. Si–OH groups and magnesium carbonates are incorporated during the process. The results show that the substrate material does affect the chemical evolution of the ice. In particular, the CO2/CO ratio within the ice is larger for methanol ices deposited onto the silicate substrate as a result of concurrent effects: the photolysis of carbonates present in the adopted substrate as a source of CO2, CO, and carbon and oxygen atoms; reactions of water molecules and hydroxyl radicals released from the substrate with the CO formed in the ice by the photolysis of the methanol ice; and changes in the structure and energy of the silicate surface by ultraviolet irradiation, leading to more favorable conditions for chemical reactions or catalysis at the grain surface. The results of our experiments allow such chemical effects contributed by the various substrate material components to be disentangled.

  9. Parameterizing the interstellar dust temperature

    Science.gov (United States)

    Hocuk, S.; Szűcs, L.; Caselli, P.; Cazaux, S.; Spaans, M.; Esplugues, G. B.

    2017-08-01

    The temperature of interstellar dust particles is of great importance to astronomers. It plays a crucial role in the thermodynamics of interstellar clouds, because of the gas-dust collisional coupling. It is also a key parameter in astrochemical studies that governs the rate at which molecules form on dust. In 3D (magneto)hydrodynamic simulations often a simple expression for the dust temperature is adopted, because of computational constraints, while astrochemical modelers tend to keep the dust temperature constant over a large range of parameter space. Our aim is to provide an easy-to-use parametric expression for the dust temperature as a function of visual extinction (AV) and to shed light on the critical dependencies of the dust temperature on the grain composition. We obtain an expression for the dust temperature by semi-analytically solving the dust thermal balance for different types of grains and compare to a collection of recent observational measurements. We also explore the effect of ices on the dust temperature. Our results show that a mixed carbonaceous-silicate type dust with a high carbon volume fraction matches the observations best. We find that ice formation allows the dust to be warmer by up to 15% at high optical depths (AV> 20 mag) in the interstellar medium. Our parametric expression for the dust temperature is presented as Td = [ 11 + 5.7 × tanh(0.61 - log 10(AV) ]χuv1/5.9, where χuv is in units of the Draine (1978, ApJS, 36, 595) UV field.

  10. FIRST INFRARED BAND STRENGTHS FOR AMORPHOUS CO{sub 2}, AN OVERLOOKED COMPONENT OF INTERSTELLAR ICES

    Energy Technology Data Exchange (ETDEWEB)

    Gerakines, Perry A.; Hudson, Reggie L., E-mail: Reggie.Hudson@NASA.gov [Astrochemistry Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

    2015-08-01

    Solid carbon dioxide (CO{sub 2}) has long been recognized as a component of both interstellar and solar system ices, but a recent literature search has revealed significant qualitative and quantitative discrepancies in the laboratory spectra on which the abundances of extraterrestrial CO{sub 2} are based. Here we report new infrared (IR) spectra of amorphous CO{sub 2}-ice along with band intensities (band strengths) of four mid-IR absorptions, the first such results in the literature. A possible thickness dependence for amorphous-CO{sub 2} IR band shapes and positions also is investigated, and the three discordant reports of amorphous CO{sub 2} spectra in the literature are addressed. Applications of our results are discussed with an emphasis on laboratory investigations and results from astronomical observations. A careful comparison with earlier work shows that the IR spectra calculated from several databases for CO{sub 2} ices, all ices being made near 10 K, are not for amorphous CO{sub 2}, but rather for crystalline CO{sub 2} or crystalline-amorphous mixtures.

  11. Thermoluminescence of Simulated Interstellar Matter after Gamma-ray Irradiation

    OpenAIRE

    Koike, K.; Nakagawa, M.; Koike, C.; Okada, M.; Chihara, H.

    2002-01-01

    Interstellar matter is known to be strongly irradiated by radiation and several types of cosmic ray particles. Simulated interstellar matter, such as forsterite $\\rm Mg_{2}SiO_{4}$, enstatite $\\rm MgSiO_{3}$ and magnesite $\\rm MgCO_{3}$ has been irradiated with the $\\rm ^{60}Co$ gamma-rays in liquid nitrogen, and also irradiated with fast neutrons at 10 K and 70 K by making use of the low-temperature irradiation facility of Kyoto University Reactor (KUR-LTL. Maximum fast neutron dose is $10^{...

  12. DEUTERIUM FRACTIONATION DURING AMINO ACID FORMATION BY PHOTOLYSIS OF INTERSTELLAR ICE ANALOGS CONTAINING DEUTERATED METHANOL

    Energy Technology Data Exchange (ETDEWEB)

    Oba, Yasuhiro; Watanabe, Naoki; Kouchi, Akira [Institute of Low Temperature Science, Hokkaido University, N19W8, Kita-ku, Sapporo, Hokkaido 060-0819 (Japan); Takano, Yoshinori, E-mail: oba@lowtem.hokudai.ac.jp [Department of Biogeochemistry, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima, Yokosuka, Kanagawa 237-0061 (Japan)

    2016-08-10

    Deuterium (D) atoms in interstellar deuterated methanol might be distributed into complex organic molecules through molecular evolution by photochemical reactions in interstellar grains. In this study, we use a state-of-the-art high-resolution mass spectrometer coupled with a high-performance liquid chromatography system to quantitatively analyze amino acids and their deuterated isotopologues formed by the photolysis of interstellar ice analogs containing singly deuterated methanol CH{sub 2}DOH at 10 K. Five amino acids (glycine, α -alanine, β -alanine, sarcosine, and serine) and their deuterated isotopologues whose D atoms are bound to carbon atoms are detected in organic residues formed by photolysis followed by warming up to room temperature. The abundances of singly deuterated amino acids are in the range of 0.3–1.1 relative to each nondeuterated counterpart, and the relative abundances of doubly and triply deuterated species decrease with an increasing number of D atoms in a molecule. The abundances of amino acids increase by a factor of more than five upon the hydrolysis of the organic residues, leading to decreases in the relative abundances of deuterated species for α -alanine and β -alanine. On the other hand, the relative abundances of the deuterated isotopologues of the other three amino acids did not decrease upon hydrolysis, indicating different formation mechanisms of these two groups upon hydrolysis. The present study facilitates both qualitative and quantitative evaluations of D fractionation during molecular evolution in the interstellar medium.

  13. DEUTERIUM FRACTIONATION DURING AMINO ACID FORMATION BY PHOTOLYSIS OF INTERSTELLAR ICE ANALOGS CONTAINING DEUTERATED METHANOL

    International Nuclear Information System (INIS)

    Oba, Yasuhiro; Watanabe, Naoki; Kouchi, Akira; Takano, Yoshinori

    2016-01-01

    Deuterium (D) atoms in interstellar deuterated methanol might be distributed into complex organic molecules through molecular evolution by photochemical reactions in interstellar grains. In this study, we use a state-of-the-art high-resolution mass spectrometer coupled with a high-performance liquid chromatography system to quantitatively analyze amino acids and their deuterated isotopologues formed by the photolysis of interstellar ice analogs containing singly deuterated methanol CH 2 DOH at 10 K. Five amino acids (glycine, α -alanine, β -alanine, sarcosine, and serine) and their deuterated isotopologues whose D atoms are bound to carbon atoms are detected in organic residues formed by photolysis followed by warming up to room temperature. The abundances of singly deuterated amino acids are in the range of 0.3–1.1 relative to each nondeuterated counterpart, and the relative abundances of doubly and triply deuterated species decrease with an increasing number of D atoms in a molecule. The abundances of amino acids increase by a factor of more than five upon the hydrolysis of the organic residues, leading to decreases in the relative abundances of deuterated species for α -alanine and β -alanine. On the other hand, the relative abundances of the deuterated isotopologues of the other three amino acids did not decrease upon hydrolysis, indicating different formation mechanisms of these two groups upon hydrolysis. The present study facilitates both qualitative and quantitative evaluations of D fractionation during molecular evolution in the interstellar medium.

  14. An infrared measurement of chemical desorption from interstellar ice analogues

    Science.gov (United States)

    Oba, Y.; Tomaru, T.; Lamberts, T.; Kouchi, A.; Watanabe, N.

    2018-03-01

    In molecular clouds at temperatures as low as 10 K, all species except hydrogen and helium should be locked in the heterogeneous ice on dust grain surfaces. Nevertheless, astronomical observations have detected over 150 different species in the gas phase in these clouds. The mechanism by which molecules are released from the dust surface below thermal desorption temperatures to be detectable in the gas phase is crucial for understanding the chemical evolution in such cold clouds. Chemical desorption, caused by the excess energy of an exothermic reaction, was first proposed as a key molecular release mechanism almost 50 years ago1. Chemical desorption can, in principle, take place at any temperature, even below the thermal desorption temperature. Therefore, astrochemical network models commonly include this process2,3. Although there have been a few previous experimental efforts4-6, no infrared measurement of the surface (which has a strong advantage to quantify chemical desorption) has been performed. Here, we report the first infrared in situ measurement of chemical desorption during the reactions H + H2S → HS + H2 (reaction 1) and HS + H → H2S (reaction 2), which are key to interstellar sulphur chemistry2,3. The present study clearly demonstrates that chemical desorption is a more efficient process for releasing H2S into the gas phase than was previously believed. The obtained effective cross-section for chemical desorption indicates that the chemical desorption rate exceeds the photodesorption rate in typical interstellar environments.

  15. Simulating Extraterrestrial Ices in the Laboratory

    Science.gov (United States)

    Berisford, D. F.; Carey, E. M.; Hand, K. P.; Choukroun, M.

    2017-12-01

    Several ongoing experiments at JPL attempt to simulate the ice environment for various regimes associated with icy moons. The Europa Penitent Ice Experiment (EPIX) simulates the surface environment of an icy moon, to investigate the physics of ice surface morphology growth. This experiment features half-meter-scale cryogenic ice samples, cryogenic radiative sink environment, vacuum conditions, and diurnal cycling solar simulation. The experiment also includes several smaller fixed-geometry vacuum chambers for ice simulation at Earth-like and intermediate temperature and vacuum conditions for development of surface morphology growth scaling relations. Additionally, an ice cutting facility built on a similar platform provides qualitative data on the mechanical behavior of cryogenic ice with impurities under vacuum, and allows testing of ice cutting/sampling tools relevant for landing spacecraft. A larger cutting facility is under construction at JPL, which will provide more quantitative data and allow full-scale sampling tool tests. Another facility, the JPL Ice Physics Laboratory, features icy analog simulant preparation abilities that range icy solar system objects such as Mars, Ceres and the icy satellites of Saturn and Jupiter. In addition, the Ice Physics Lab has unique facilities for Icy Analog Tidal Simulation and Rheological Studies of Cryogenic Icy Slurries, as well as equipment to perform thermal and mechanical properties testing on icy analog materials and their response to sinusoidal tidal stresses.

  16. The Rosseland mean opacity of interstellar grain

    International Nuclear Information System (INIS)

    Ali, A.; El Shalaby, M.A.; El-Nawawy, M.S.

    1990-10-01

    We have calculated the opacity of interstellar grains in the temperature range 10 deg. K - 1500 deg. K. Two composite grain models have been considered. One of them consists of silicate coated with ice mantle and the second has a graphite core coated also with ice mantle. These models are compared with isolated grain models. An exact analytical and computational development of Guettler's formulae for composite grain models has been used to calculate the extinction coefficient. It has been found that the thickness of the mantle affects the opacity of the interstellar grains. The opacity of composite models differs from that of the isolated models. The effect of the different species (ice, silicate and graphite) is also clear. (author). 22 refs, 4 figs, 1 tab

  17. COMPUTATIONAL STUDY OF INTERSTELLAR GLYCINE FORMATION OCCURRING AT RADICAL SURFACES OF WATER-ICE DUST PARTICLES

    International Nuclear Information System (INIS)

    Rimola, Albert; Sodupe, Mariona; Ugliengo, Piero

    2012-01-01

    Glycine is the simplest amino acid, and due to the significant astrobiological implications that suppose its detection, the search for it in the interstellar medium (ISM), meteorites, and comets is intensively investigated. In the present work, quantum mechanical calculations based on density functional theory have been used to model the glycine formation on water-ice clusters present in the ISM. The removal of either one H atom or one electron from the water-ice cluster has been considered to simulate the effect of photolytic radiation and of ionizing particles, respectively, which lead to the formation of OH . radical and H 3 O + surface defects. The coupling of incoming CO molecules with the surface OH . radicals on the ice clusters yields the formation of the COOH . radicals via ZPE-corrected energy barriers and reaction energies of about 4-5 kcal mol –1 and –22 kcal mol –1 , respectively. The COOH . radicals couple with incoming NH=CH 2 molecules (experimentally detected in the ISM) to form the NHCH 2 COOH . radical glycine through energy barriers of 12 kcal mol –1 , exceedingly high at ISM cryogenic temperatures. Nonetheless, when H 3 O + is present, one proton may be barrierless transferred to NH=CH 2 to give NH 2 =CH 2 + . This latter may react with the COOH . radical to give the NH 2 CH 2 COOH +. glycine radical cation which can then be transformed into the NH 2 CHC(OH) 2 +. species (the most stable form of glycine in its radical cation state) or into the NH 2 CHCOOH . neutral radical glycine. Estimated rate constants of these events suggest that they are kinetically feasible at temperatures of 100-200 K, which indicate that their occurrence may take place in hot molecular cores or in comets exposed to warmer regions of solar systems. Present results provide quantum chemical evidence that defects formed on water ices due to the harsh-physical conditions of the ISM may trigger reactions of cosmochemical interest. The relevance of surface H 3 O

  18. Computational Study of Interstellar Glycine Formation Occurring at Radical Surfaces of Water-ice Dust Particles

    Science.gov (United States)

    Rimola, Albert; Sodupe, Mariona; Ugliengo, Piero

    2012-07-01

    Glycine is the simplest amino acid, and due to the significant astrobiological implications that suppose its detection, the search for it in the interstellar medium (ISM), meteorites, and comets is intensively investigated. In the present work, quantum mechanical calculations based on density functional theory have been used to model the glycine formation on water-ice clusters present in the ISM. The removal of either one H atom or one electron from the water-ice cluster has been considered to simulate the effect of photolytic radiation and of ionizing particles, respectively, which lead to the formation of OH• radical and H3O+ surface defects. The coupling of incoming CO molecules with the surface OH• radicals on the ice clusters yields the formation of the COOH• radicals via ZPE-corrected energy barriers and reaction energies of about 4-5 kcal mol-1 and -22 kcal mol-1, respectively. The COOH• radicals couple with incoming NH=CH2 molecules (experimentally detected in the ISM) to form the NHCH2COOH• radical glycine through energy barriers of 12 kcal mol-1, exceedingly high at ISM cryogenic temperatures. Nonetheless, when H3O+ is present, one proton may be barrierless transferred to NH=CH2 to give NH2=CH2 +. This latter may react with the COOH• radical to give the NH2CH2COOH+• glycine radical cation which can then be transformed into the NH2CHC(OH)2 +• species (the most stable form of glycine in its radical cation state) or into the NH2CHCOOH• neutral radical glycine. Estimated rate constants of these events suggest that they are kinetically feasible at temperatures of 100-200 K, which indicate that their occurrence may take place in hot molecular cores or in comets exposed to warmer regions of solar systems. Present results provide quantum chemical evidence that defects formed on water ices due to the harsh-physical conditions of the ISM may trigger reactions of cosmochemical interest. The relevance of surface H3O+ ions to facilitate chemical

  19. IceCube systematic errors investigation: Simulation of the ice

    Energy Technology Data Exchange (ETDEWEB)

    Resconi, Elisa; Wolf, Martin [Max-Planck-Institute for Nuclear Physics, Heidelberg (Germany); Schukraft, Anne [RWTH, Aachen University (Germany)

    2010-07-01

    IceCube is a neutrino observatory for astroparticle and astronomy research at the South Pole. It uses one cubic kilometer of Antartica's deepest ice (1500 m-2500 m in depth) to detect Cherenkov light, generated by charged particles traveling through the ice, with an array of phototubes encapsulated in glass pressure spheres. The arrival time as well as the charge deposited of the detected photons represent the base measurements that are used for track and energy reconstruction of those charged particles. The optical properties of the deep antarctic ice vary from layer to layer. Measurements of the ice properties and their correct modeling in Monte Carlo simulation is then of primary importance for the correct understanding of the IceCube telescope behavior. After a short summary about the different methods to investigate the ice properties and to calibrate the detector, we show how the simulation obtained by using this information compares to the measured data and how systematic errors due to uncertain ice properties are determined in IceCube.

  20. Untangling the methane chemistry in interstellar and solar system ices toward ionizing radiation: a combined infrared and reflectron time-of-flight analysis.

    Science.gov (United States)

    Abplanalp, Matthew J; Jones, Brant M; Kaiser, Ralf I

    2018-02-21

    Pure methane (CH 4 /CD 4 ) ices were exposed to three ionizing radiation sources at 5.5 K under ultrahigh vacuum conditions to compare the complex hydrocarbon spectrum produced across several interstellar environments. These irradiation sources consisted of energetic electrons to simulate secondary electrons formed in the track of galactic cosmic rays (GCRs), Lyman α (10.2 eV; 121.6 nm) photons simulated the internal VUV field in a dense cloud, and broadband (112.7-169.8 nm; 11.0-7.3 eV) photons which mimic the interstellar ultra-violet field. The in situ chemical evolution of the ices was monitored via Fourier transform infrared spectroscopy (FTIR) and during heating via mass spectrometry utilizing a quadrupole mass spectrometer with an electron impact ionization source (EI-QMS) and a reflectron time-of-flight mass spectrometer with a photoionization source (PI-ReTOF-MS). The FTIR analysis detected six small hydrocarbon products from the three different irradiation sources: propane [C 3 H 8 (C 3 D 8 )], ethane [C 2 H 6 (C 2 D 6 )], the ethyl radical [C 2 H 5 (C 2 D 5 )], ethylene [C 2 H 4 (C 2 D 4 )], acetylene [C 2 H 2 (C 2 D 2 )], and the methyl radical [CH 3 (CD 3 )]. The sensitive PI-ReTOF-MS analysis identified a complex array of products with different products being detected between experiments with general formulae: C n H 2n+2 (n = 4-8), C n H 2n (n = 3-9), C n H 2n-2 (n = 3-9), C n H 2n-4 (n = 4-9), and C n H 2n-6 (n = 6-7) from electron irradiation and C n H 2n+2 (n = 4-8), C n H 2n (n = 3-10), C n H 2n-2 (n = 3-11), C n H 2n-4 (n = 4-11), C n H 2n-6 (n = 5-11), and C n H 2n-8 (n = 6-11) from broadband photolysis and Lyman α photolysis. These experiments show that even the simplest hydrocarbon can produce important complex hydrocarbons such as C 3 H 4 and C 4 H 6 isomers. Distinct isomers from these groups have been shown to be important reactants in the synthesis of polycyclic aromatic hydrocarbons like indene (C 9 H 8 ) and naphthalene (C 10 H 8

  1. Observations of the interstellar ice grain feature in the Taurus molecular clouds

    International Nuclear Information System (INIS)

    Whittet, D.C.B.; Bode, H.F.; Longmore, A.J.; Baines, D.W.T.; Evans, A.

    1983-01-01

    Although water ice was originally proposed as a major constituent of the interstellar grain population (e.g. Oort and van de Hulst, 1946), the advent of infrared astronomy has shown that the expected absorption due to O-H stretching vibrations at 3 μm is illusive. Observations have in fact revealed that the carrier of this feature is apparently restricted to regions deep within dense molecular clouds (Merrill et al., 1976; Willner et al., 1982). However, the exact carrier of this feature is still controversial, and many questions remain as to the conditions required for its appearance. It is also uncertain whether it is restricted to circumstellar shells, rather than the general cloud medium. Detailed discussion of the 3 μm band properties is given elsewhere in this volume. 15 references, 4 figures

  2. Laboratory determination of the infrared band strengths of pyrene frozen in water ice: Implications for the composition of interstellar ices

    Energy Technology Data Exchange (ETDEWEB)

    Hardegree-Ullman, E. E. [New York Center for Astrobiology and Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, 110 8th Street, Troy, NY 12180 (United States); Gudipati, M. S.; Werner, M. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Boogert, A. C. A. [Infrared Processing and Analysis Center, Mail Code 100-22, California Institute of Technology, Pasadena, CA 91125 (United States); Lignell, H. [Department of Chemistry, University of California Irvine, Irvine, CA 92697-2025 (United States); Allamandola, L. J. [Space Science Division, Mail Stop 245-6, NASA Ames Research Center, Moffett Field, CA 94035 (United States); Stapelfeldt, K. R., E-mail: hardee@rpi.edu, E-mail: gudipati@jpl.nasa.gov [NASA Goddard Space Flight Center, Exoplanets and Stellar Astrophysics Laboratory, Code 667, Greenbelt, MD 20771 (United States)

    2014-04-01

    Broad infrared emission features (e.g., at 3.3, 6.2, 7.7, 8.6, and 11.3 μm) from the gas phase interstellar medium have long been attributed to polycyclic aromatic hydrocarbons (PAHs). A significant portion (10%-20%) of the Milky Way's carbon reservoir is locked in PAH molecules, which makes their characterization integral to our understanding of astrochemistry. In molecular clouds and the dense envelopes and disks of young stellar objects (YSOs), PAHs are expected to be frozen in the icy mantles of dust grains where they should reveal themselves through infrared absorption. To facilitate the search for frozen interstellar PAHs, laboratory experiments were conducted to determine the positions and strengths of the bands of pyrene mixed with H{sub 2}O and D{sub 2}O ices. The D{sub 2}O mixtures are used to measure pyrene bands that are masked by the strong bands of H{sub 2}O, leading to the first laboratory determination of the band strength for the CH stretching mode of pyrene in water ice near 3.25 μm. Our infrared band strengths were normalized to experimentally determined ultraviolet band strengths, and we find that they are generally ∼50% larger than those reported by Bouwman et al. based on theoretical strengths. These improved band strengths were used to reexamine YSO spectra published by Boogert et al. to estimate the contribution of frozen PAHs to absorption in the 5-8 μm spectral region, taking into account the strength of the 3.25 μm CH stretching mode. It is found that frozen neutral PAHs contain 5%-9% of the cosmic carbon budget and account for 2%-9% of the unidentified absorption in the 5-8 μm region.

  3. Physics and Chemistry of the Interstellar Medium. General Colloquium, 19-21 November 2012, Paris

    International Nuclear Information System (INIS)

    Aguillon, Francois; Alata, Ivan; Alcaraz, Christian; Alves, Marta; Andre, Philippe; Bachiller, Rafael; Bacmann, Aurore; Baklouti, Donia; Bernard, Jean-Philippe; Berne, Olivier; Beroff, Karine; Bertin, Mathieu; Biennier, Ludovic; Bocchio, Marco; Bonal, Lydie; Bontemps, Sylvain; Bouchez Giret, Aurelia; Boulanger, Francois; Bracco, Andrea; Bron, Emeric; Brunetto, Rosario; Cabrit, Sylvie; Canosa, Andre; Capron, Michael; Ceccarelli, Cecilia; Cernicharo, Jose; Chaabouni, Henda; Chabot, Marin; Chen, Hui-Chen; Chiavassa, Thierry; Cobut, Vincent; Commercon, Benoit; Congiu, Emanuele; Coutens, Audrey; Danger, Gregoire; Daniel, Fabien; Dartois, Emmanuel; Demyk, Karine; Denis, Alpizar; Despois, Didier; D'hendecourt, Louis; Dontot, Leo; Doronin, Mikhail; Dubernet, Marie-Lise; Dulieu, Francois; Dumouchel, Fabien; Duvernay, Fabrice; Ellinger, Yves; Falgarone, Edith; Falvo, Cyril; Faure, Alexandre; Fayolle, Edith; Feautrier, Nicole; Feraud, Geraldine; Fillion, Jean-Hugues; Gamboa, Antonio; Gardez, Aline; Gavilan, Lisseth; Gerin, Maryvonne; Ghesquiere, Pierre; Godard, Benjamin; Godard, Marie; Gounelle, Matthieu; Gratier, Pierre; Grenier, Isabelle; Gruet, Sebastien; Gry, Cecile; Guillemin, Jean-Claude; Guilloteau, Stephane; Gusdorf, Antoine; Guzman, Viviana; Habart, Emilie; Hennebelle, Patrick; Herrera, Cinthya; Hily-Blant, Pierre; Hincelin, Ugo; Hochlaf, Majdi; Huet, Therese; Iftner, Christophe; Jallat, Aurelie; Joblin, Christine; Kahane, Claudine; Kalugina, Yulia; Kleiner, Isabelle; Koehler, Melanie; Kokkin, Damian; Koutroumpa, Dimitra; Krim, Lahouari; Lallement, Rosine; Lanza, Mathieu; Lattelais, Marie; Le Bertre, Thibaut; Le Gal, Romane; Le Petit, Franck; Le Picard, Sebastien; Lefloch, Bertrand; Lemaire, Jean Louis; Lesaffre, Pierre; Lique, Francois; Loison, Jean-Christophe; Lopez Sepulcre, Ana; Maillard, Jean-Pierre; Margules, Laurent; Martin, Celine; Mascetti, Joelle; Michaut, Xavier; Minissale, Marco; Miville-Deschenes, Marc-Antoine; Mokrane, Hakima; Momferratos, Georgios; Montillaud, Julien; Montmerle, Thierry; Moret-Bailly, Jacques; Motiyenko, Roman; Moudens, Audrey; Noble, Jennifer; Padovani, Marco; Pagani, Laurent; Pardanaud, Cedric; Parisel, Olivier; Pauzat, Francoise; Pernet, Amelie; Pety, Jerome; Philippe, Laurent; Piergiorgio, Casavecchia; Pilme, Julien; Pinto, Cecilia; Pirali, Olivier; Pirim, Claire; Puspitarini, Lucky; Rist, Claire; Ristorcelli, Isabelle; Romanzin, Claire; Roueff, Evelyne; Rousseau, Patrick; Sabbah, Hassan; Saury, Eleonore; Schneider, Ioan; Schwell, Martin; Sims, Ian; Spielfiedel, Annie; Stoecklin, Thierry; Talbi, Dahbia; Taquet, Vianney; Teillet-Billy, Dominique; Theule, Patrice; Thi, Wing-Fai; Trolez, Yann; Valdivia, Valeska; Van Dishoeck, Ewine; Verstraete, Laurent; Vinogradoff, Vassilissa; Wiesenfeld, Laurent; Ysard, Nathalie; Yvart, Walter; Zicler Eleonore

    2012-11-01

    ; Ice deuteration: models and observations to interpret the protostar history; Molecular complexity induced by thermal reactions in analogues of interstellar ices; VUV spectroscopy and photochemistry of interstellar and putative pre-biotic molecules; Internal rotation in astrophysical and pre-biotic molecules; Detection and rate of branching of chemical reaction products in gas phase at very low temperatures: new experimental developments; Investigation of ion chemistry and polymerization processes on interstellar grain and meteorite stimulants; Formation of the Sun in a dense collected shell: evidence from meteorites; Dust: from the Milky Way to nearby galaxies; Dust emission in dense areas: separating effects of radiation properties from grain properties; Effect of cosmic rays on hydrocarbon dusts; Stability of isolated and aggregated polycyclic aromatic hydrocarbons probed by collision with slow ions; Recent advances in the simulation of the absorption and emission spectroscopy; Infrared emission of aromatic molecules measured with the FIREFLY spectrometer; From PAHs to carbon clusters in photo-dissociation regions; VO-theory and theoretical services for the interstellar medium

  4. COMPUTATIONAL STUDY OF INTERSTELLAR GLYCINE FORMATION OCCURRING AT RADICAL SURFACES OF WATER-ICE DUST PARTICLES

    Energy Technology Data Exchange (ETDEWEB)

    Rimola, Albert; Sodupe, Mariona [Departament de Quimica, Universitat Autonoma de Barcelona, 08193 Bellaterra (Spain); Ugliengo, Piero, E-mail: albert.rimola@uab.cat [Dipartimento di Chimica, NIS Centre of Excellence and INSTM (Materials and Technology National Consortium), UdR Torino, Universita di Torino, Via P. Giuria 7, 10125 Torino (Italy)

    2012-07-20

    Glycine is the simplest amino acid, and due to the significant astrobiological implications that suppose its detection, the search for it in the interstellar medium (ISM), meteorites, and comets is intensively investigated. In the present work, quantum mechanical calculations based on density functional theory have been used to model the glycine formation on water-ice clusters present in the ISM. The removal of either one H atom or one electron from the water-ice cluster has been considered to simulate the effect of photolytic radiation and of ionizing particles, respectively, which lead to the formation of OH{sup .} radical and H{sub 3}O{sup +} surface defects. The coupling of incoming CO molecules with the surface OH{sup .} radicals on the ice clusters yields the formation of the COOH{sup .} radicals via ZPE-corrected energy barriers and reaction energies of about 4-5 kcal mol{sup -1} and -22 kcal mol{sup -1}, respectively. The COOH{sup .} radicals couple with incoming NH=CH{sub 2} molecules (experimentally detected in the ISM) to form the NHCH{sub 2}COOH{sup .} radical glycine through energy barriers of 12 kcal mol{sup -1}, exceedingly high at ISM cryogenic temperatures. Nonetheless, when H{sub 3}O{sup +} is present, one proton may be barrierless transferred to NH=CH{sub 2} to give NH{sub 2}=CH{sub 2}{sup +}. This latter may react with the COOH{sup .} radical to give the NH{sub 2}CH{sub 2}COOH{sup +.} glycine radical cation which can then be transformed into the NH{sub 2}CHC(OH){sub 2}{sup +.} species (the most stable form of glycine in its radical cation state) or into the NH{sub 2}CHCOOH{sup .} neutral radical glycine. Estimated rate constants of these events suggest that they are kinetically feasible at temperatures of 100-200 K, which indicate that their occurrence may take place in hot molecular cores or in comets exposed to warmer regions of solar systems. Present results provide quantum chemical evidence that defects formed on water ices due to the harsh

  5. Modelling injection rates of PUIs from photoionization using kinetic simulations of interstellar neutrals traversing the heliosphere

    Science.gov (United States)

    Keilbach, D.; Drews, C.; Taut, A.; Wimmer-Schweingruber, R. F.

    2016-12-01

    Recent studies of the inflow direction of the local insterstellar medium from PUI density distributions have shown that the extrema of the longitudinal distribution of PUI velocities (with respect to the solar wind speed) can be attributed to the radial velocity of the interstellar neutral seed population and is symmetric around the inflow direction of the local interstellar medium. This work is aimed to model pickup ion injection rates from photoionization (which is the main process of interstellar PUI production) throughout the heliosphere. To that end a seed population of interstellar neutrals is injected into a model heliosphere at 60 AU distance from the sun, whereas each particle's initial speed is given by a maxwellian distribution at a temperature of 1 eV and an inflow speed of 22 km/s. Then the density of the interstellar neutrals is integrated over the model heliosphere, while the movement of the neutrals is simulated using timestep methods. To model the focusing of the interstellar neutral trajectories from the sun's gravitational potential the model heliosphere contains a central gravitational potential.Each neutral test particle can be ionized via photoionization with a per-timestep probability antiproportional to the neutral's distance to the sun squared. By tracking the ionization rate location-dependently, PUI injection rates have been determined. Therefore using these simulations the density distributions of different species of interstellar neutrals have been calculated. In addition location-dependent injection rates of different species of PUIs have been calculated, which show an increased rate of PUI production in the focusing cone region (e.g. for He+ PUIs), but also in the crescent region (e.g. for O+ PUIs).Furthermore the longitudinal distribution of the neutrals' velocity at 1 AU is calculated from the simulation's results in order to estimate the PUI cut-off as a function of ecliptic longitude. Figure: Simulated He neutral density (left

  6. Hot interstellar tunnels. I. Simulation of interacting supernova remnants

    International Nuclear Information System (INIS)

    Smith, B.W.

    1977-01-01

    Reexamining a suggestion of Cox and Smith, we find that intersecting supernova remnants can indeed generate and maintain hot interstellar regions with napproximately-less-than10 -2 cm -3 and Tapprox.10 6 K. These regions are likely to occupy at least 30% of the volume of a spiral arm near the midplane of the gaseous disk if the local supernova rate there is greater than 1.5 x 10 -7 Myr -1 pc -3 . Their presence in the interstellar medium is supported by observations of the soft X-ray background. The theory required to build a numerical simulation of interacting supernova remnants is developed. The hot cavities within a population of remnants will become connected for a variety of assumed conditions in the outer shells of old remnants. Extensive hot cavity regions or tunnels are built and enlarged by supernovae occurring in relatively dense gas which produce connections, but tunnels are kept hot primarily by supernovae occurring within the tunnels. The latter supernovae initiate fast shock waves which apparently reheat tunnels faster than they are destroyed by thermal conduction in a galactic magnetic field or by radiative cooling. However, the dispersal of these rejuvenating shocks over a wide volume is inhibited by motions of cooler interstellar gas in the interval between shocks. These motions disrupt the contiguity of the component cavities of a tunnel and may cause its death.The Monte Carlo simulations indicate that a quasi-equilibrium is reached within 10 7 years of the first supernova in a spiral arm. This equilibrium is characterized by a constant average filling fraction for cavities in the interstellar volume. Aspects of the equilibrium are discussed for a range of supernova rates. Two predictions of Cox and Smith are not confirmed within this range: critical growth of hot regions to encompass the entire medium, and the efficient quenching of a remnant's expansion by interaction with other cavities

  7. Formation and High-order Carboxylic Acids (RCOOH) in Interstellar Analogous Ices of Carbon Dioxide (CO2) and Methane(CH4)

    Science.gov (United States)

    Zhu, Cheng; Turner, Andrew M.; Abplanalp, Matthew J.; Kaiser, Ralf I.

    2018-01-01

    This laboratory study simulated the abiotic formation of carboxylic acids (RCOOH) in interstellar analogous ices of carbon dioxide (CO2) and methane (CH4) at 10 K upon exposure to energetic electrons. The chemical processing of the ices and the subsequent warm-up phase were monitored online and in situ, exploiting Fourier Transform Infrared Spectrometry and quadrupole mass spectrometry. Characteristic absorptions of functional groups of carboxylic acids (RCOOH) were observed in the infrared spectra of the irradiated ice. Two proposed reaction mechanisms replicated the kinetic profiles of the carboxylic acids along with the decay profile of the precursors during the irradiation via hydrocarbon formation, followed by carboxylation and/or through acetic acid along with mass growth processes of the alkyl chain. Mass spectra recorded during the warm-up phase demonstrated that these acids are distributed from acetic acid (CH3COOH) up to decanoic acid (C9H19COOH). High-dose irradiation studies (91 ± 14 eV) converted low-molecular-weight acids such as acetic acid (CH3COOH) and propionic acid (C2H5COOH) to higher-molecular-weight carboxylic acids, compared to low-dose irradiation studies (18 ± 3 eV). The traces of the {{{H}}}2{{C}}= {{C}}({OH}{)}2+ (m/z = 60) fragment—a link to linear carboxylic acids—implied that higher-order acids (C n H2n+1COOH, n ≥ 5) are likely branched, which correlates with the recent analysis of the structures of the monocarboxylic acids in the Murchison meteorite.

  8. Reactions of nitriles in ices relevant to Titan, comets, and the interstellar medium: formation of cyanate ion, ketenimines, and isonitriles

    Science.gov (United States)

    Hudson, R. L.; Moore, M. H.

    2004-12-01

    Motivated by detections of nitriles in Titan's atmosphere, cometary comae, and the interstellar medium, we report laboratory investigations of the low-temperature chemistry of acetonitrile, propionitrile, acrylonitrile, cyanoacetylene, and cyanogen (CH 3CN, CH 3CH 2CN, CH 2CHCN, HCCCN, and NCCN, respectively). A few experiments were also done on isobutyronitrile and trimethylacetonitrile ((CH 3) 2CHCN and (CH 3) 3CCN, respectively). Trends were sought, and found, in the photo- and radiation chemical products of these molecules at 12-25 K. In the absence of water, all of these molecules isomerized to isonitriles, and CH 3CN, CH 3CH 2CN, and (CH 3) 2CHCN also formed ketenimines. In the presence of H 2O, no isonitriles were detected but rather the cyanate ion (OCN -) was seen in all cases. Although isonitriles, ketenimines, and OCN - were the main focus of our work, we also describe cases of hydrogen loss, to make smaller nitriles, and hydrogen addition (reduction), to make larger nitriles. HCN formation also was seen in most experiments. The results are presented in terms of nitrile ice chemistry on Titan, in cometary ice, and in the interstellar medium. Possible connections to prebiotic chemistry are briefly discussed.

  9. ICE CHEMISTRY IN STARLESS MOLECULAR CORES

    Energy Technology Data Exchange (ETDEWEB)

    Kalvans, J., E-mail: juris.kalvans@venta.lv [Engineering Research Institute “Ventspils International Radio Astronomy Center” of Ventspils University College, Inzenieru 101, Ventspils, LV-3601 (Latvia)

    2015-06-20

    Starless molecular cores are natural laboratories for interstellar molecular chemistry research. The chemistry of ices in such objects was investigated with a three-phase (gas, surface, and mantle) model. We considered the center part of five starless cores, with their physical conditions derived from observations. The ice chemistry of oxygen, nitrogen, sulfur, and complex organic molecules (COMs) was analyzed. We found that an ice-depth dimension, measured, e.g., in monolayers, is essential for modeling of chemistry in interstellar ices. Particularly, the H{sub 2}O:CO:CO{sub 2}:N{sub 2}:NH{sub 3} ice abundance ratio regulates the production and destruction of minor species. It is suggested that photodesorption during the core-collapse period is responsible for the high abundance of interstellar H{sub 2}O{sub 2} and O{sub 2}H and other species synthesized on the surface. The calculated abundances of COMs in ice were compared to observed gas-phase values. Smaller activation barriers for CO and H{sub 2}CO hydrogenation may help explain the production of a number of COMs. The observed abundance of methyl formate HCOOCH{sub 3} could be reproduced with a 1 kyr, 20 K temperature spike. Possible desorption mechanisms, relevant for COMs, are gas turbulence (ice exposure to interstellar photons) or a weak shock within the cloud core (grain collisions). To reproduce the observed COM abundances with the present 0D model, 1%–10% of ice mass needs to be sublimated. We estimate that the lifetime for starless cores likely does not exceed 1 Myr. Taurus cores are likely to be younger than their counterparts in most other clouds.

  10. Evidence of amino acid precursors: C-N bond coupling in simulated interstellar CO2/NH3 ices

    Science.gov (United States)

    Esmaili, Sasan

    2015-08-01

    Low energy secondary electrons are abundantly produced in astrophysical or planetary ices by the numerous ionizing radiation fields typically encountered in space environments and may thus play a role in the radiation processing of such ices [1]. One approach to determine their chemical effect is to irradiate nanometer thick molecular solids of simple molecular constituents, with energy selected electron beams and to monitor changes in film chemistry with the surface analytical techniques [2].Of particular interest is the formation of HCN, which is a signature of dense gases in interstellar clouds, and is ubiquitous in the ISM. Moreover, the chemistry of HCN radiolysis products such as CN- may be essential to understand of the formation of amino acids [3] and purine DNA bases. Here we present new results on the irradiation of multilayer films of CO2 and NH3 with 70 eV electrons, leading to CN bond formations. The electron stimulated desorption (ESD) yields of cations and anions are recorded as a function of electron fluence. The prompt desorption of cationic reaction/scattering products [4], is observed at low fluence (~4x1013 electrons/cm2). Detected ions include C2+, C2O2+, C2O+, CO3+, C2O3+ or CO4+ from pure CO2, and N+, NH+, NH2+, NH3+, NH4+, N2+, N2H+ from pure NH3, and NO+, NOH+ from CO2/NH3 mixtures. Most saliently, increasing signals of negative ion products desorbing during prolonged irradiation of CO2/NH3 films included C2-, C2H-, C2H2-, as well as CN-, HCN- and H2CN-. The identification of particular product ions was accomplished by using 13CO2 and 15NH3 isotopes. The chemistry induced by electrons in pure films of CO2 and NH3 and mixtures with composition ratios (3:1), (1:1), and (1:3), was also studied by X-ray photoelectron spectroscopy (XPS). Irradiation of CO2/NH3 mixed films at 22 K produces species containing the following bonds/functional groups identified by XPS: C=O, O-H, C-C, C-O, C=N and N=O. (This work has been funded by NSERC).

  11. The Identification of Complex Organic Molecules in the Interstellar Medium: Using Lasers and Matrix Isolation Spectroscopy to Simulate the Interstellar Environment

    Science.gov (United States)

    Stone, Bradley M.

    1998-01-01

    The Astrochemistry Group at NASA Ames Research Center is interested in the identification of large organic molecules in the interstellar medium Many smaller organic species (e.g. hydrocarbons, alcohols, etc.) have been previously identified by their radiofrequency signature due to molecular rotations. However, this becomes increasingly difficult to observe as the size of the molecule increases. Our group in interested in the identification of the carriers of the Diffuse Interstellar Bands (absorption features observed throughout the visible and near-infrared in the spectra of stars, due to species in the interstellar medium). Polycyclic Aromatic Hydrocarbons (PAHs) and related molecules are thought to be good candidates for these carriers. Laboratory experiments am performed at Ames to simulate the interstellar environment, and to compare spectra obtained from molecules in the laboratory to those derived astronomically. We are also interested in PAHs with respect to their possible connection to the UIR (Unidentified infrared) and ERE (Extended Red Emission) bands - emission features found to emanate from particular regions of our galaxy (e.g. Orion nebula, Red Rectangle, etc.). An old, "tried and proven spectroscopic technique, matrix isolation spectroscopy creates molecular conditions ideal for performing laboratory astrophysics.

  12. Analyses of volatile organic compounds and refractory organic residues coming from the heating of interstellar ice analogues

    Directory of Open Access Journals (Sweden)

    Danger Grégoire

    2014-02-01

    Full Text Available We use Very High Resolution Mass Spectrometry for analyses of the soluble fraction of yellow stuff produced in laboratory. Their analyses show that they are composed of molecules with high molecular weight (m/z>4000. Fragmentations suggest that grafted molecules constitute a part of them. Hexamethylenetetramine derivatives have also been detected. First results and further analytical developments will be presented to facilitate the understanding of the residue composition and of its chemical evolution. Furthermore, we present for the first time the concept of the VAHIIA project which concerns the analysis of volatiles coming from the heating of interstellar ice analogues.

  13. Three-dimensional simulations of supernovae dominated interstellar media in disk galaxies

    International Nuclear Information System (INIS)

    Cioffi, D.F.

    1985-01-01

    Evolution of the interstellar media of spiral galaxies was studied, assuming that their dynamical and thermal properties are dominated by supernova remnants (SNRs). To do this, a computer simulation was developed that uses standard SNR evolutionary solutions (Sedov-Taylor, pressure-modified snowplow) to redistribute mass and energy throughout a rectangular, three-level grid which models the interstellar medium (ISM). This comprehensive treatment includes bremsstrahlung or metal cooling, the creation and evaporation of clouds, mass injection and return from a galactic halo, multiple SNRs, and internally determined SNR lifetimes. The importance of spatially correlating supernovae sites, which can increase the global evolution rate of the (ISM), is confirmed. The simulations of primeval (zero metal abundance) galaxies revealed that the enhancement ability of bremsstrahlung-cooled SNR to transport mass can continually agitate the ISM, preventing the establishment of long-lived tunnel networks (i.e., hot rarefied volumes). This demonstrated the inadequacy of porosity theory for predicting the topology of the ISM, because it does not account for mass transport

  14. Synthesis of Large Molecules in Cometary Ice Analogs: Physical Properties Related to Self-Assembly Processes

    Science.gov (United States)

    Dworkin, Jason P.; Sandford, Scott A.; Deamer, David W.; Gillette, J. Seb; Zare, Richard N.; Allamandola, Louis J. (Technical Monitor)

    1999-01-01

    The combination of realistic laboratory simulations and infrared observations have revolutionized our understanding of interstellar dust and ice-the main component of comets. Since comets and carbonaceous micrometeorites may have been important sources of volatiles and carbon compounds on the early Earth, their organic composition may be related to the origin of life. Ices on grains in molecular clouds contain a variety of simple molecules. The D/H ratios of the comets Hale-Bopp and Hyakutake are consistent with a primarily interstellar ice mixture. Within the cloud and especially in the presolar nebula through the early solar system, these icy grains would have been photoprocessed by the ultraviolet producing more complex species such as hexamethylenetetramine, polyoxymethylenes, and simple keones. We reported at the 1999 Bioastronomy meeting laboratory simulations studied to identify the types of molecules which could have been generated in pre-cometary ices. Experiments were conducted by forming a realistic interstellar mixed-molecular ice (H2O, CH3OH, NH3 and CO) at approximately 10 K under high vacuum irradiated with UV light from a hydrogen plasma lamp. The gas mixture was typically 100:50:1:1, however when different ratios were used material with similar characteristics was still produced. The residue that remained after warming to room temperature was analyzed by HPLC, and by several mass spectrometric methods. This material contains a rich mixture of complex compounds with mass spectral profiles resembling those found in IDPs and meteorites. Surface tension measurements show that an amphiphilic component is also present. These species do not appear in various controls or in unphotolyzed samples. Residues from the simulations were also dispersed in aqueous media for microscopy. The organic material forms 10-40 gm diameter droplets that fluoresce at 300-450 nm under UV excitation. These droplets have a morphology and internal structure which appear

  15. A spectroscopic study of absorption and emission features of interstellar dust components

    International Nuclear Information System (INIS)

    Zwet, G.P. van der.

    1986-01-01

    The spectroscopic properties of silicate interstellar dust grains are the subject of this thesis. The process of accretion and photolysis is simulated in the laboratory by condensing mixtures of gases onto a cold substrate (T ∼ 12 K) in a vacuum chamber and photolyzing these mixtures with a vacuum ultraviolet source. Alternatively, the gas mixtures may be passed through a microwave discharge first, before deposition. The spectroscopic properties of the ices are investigated using ultraviolet, visible and infrared spectroscopy. (Auth.)

  16. Simulating Arctic clouds during Arctic Radiation- IceBridge Sea and Ice Experiment (ARISE)

    Science.gov (United States)

    Bromwich, D. H.; Hines, K. M.; Wang, S. H.

    2015-12-01

    The representation within global and regional models of the extensive low-level cloud cover over polar oceans remains a critical challenge for quantitative studies and forecasts of polar climate. In response, the polar-optimized version of the Weather Research and Forecasting model (Polar WRF) is used to simulate the meteorology, boundary layer, and Arctic clouds during the September-October 2014 Arctic Radiation- IceBridge Sea and Ice Experiment (ARISE) project. Polar WRF was developed with several adjustments to the sea ice thermodynamics in WRF. ARISE was based out of Eielson Air Force Base near Fairbanks, Alaska and included multiple instrumented C-130 aircraft flights over open water and sea ice of the Beaufort Sea. Arctic boundary layer clouds were frequently observed within cold northeasterly flow over the open ocean and ice. Preliminary results indicate these clouds were primarily liquid water, with characteristics differing between open water and sea ice surfaces. Simulated clouds are compared to ARISE observations. Furthermore, Polar WRF simulations are run for the August-September 2008 Arctic Summer Cloud Ocean Study (ASCOS) for comparison to the ARISE. Preliminary analysis shows that simulated low-level water clouds over the sea ice are too extensive during the the second half of the ASCOS field program. Alternatives and improvements to the Polar WRF cloud schemes are considered. The goal is to use the ARISE and ASCOS observations to achieve an improved polar supplement to the WRF code for open water and sea ice that can be provided to the Polar WRF community.

  17. Chemical Evolution in the Interstellar Medium: From Astrochemistry to Astrobiology

    Science.gov (United States)

    Allamandola, Louis J.

    2009-01-01

    Great strides have been made in our understanding of interstellar material thanks to advances in infrared astronomy and laboratory astrophysics. Ionized polycyclic aromatic hydrocarbons (PAHs), shockingly large molecules by earlier astrochemical standards, are widespread and very abundant throughout much of the Universe. In cold molecular clouds, the birthplace of planets and stars, interstellar molecules freeze onto dust and ice particles forming mixed molecular ices dominated by simple species such as water, methanol, ammonia, and carbon monoxide. Within these clouds, and especially in the vicinity of star and planet forming regions, these ices and PAHs are processed by ultraviolet light and cosmic rays forming hundreds of far more complex species, some of biogenic interest. Eventually, these are delivered to primordial planets by comets and meteorites. Astrochemical evolution, highlights of this field from a chemist's perspective, and the astronomer's infrared toolbox will be reviewed.

  18. Global ice sheet/RSL simulations using the higher-order Ice Sheet System Model.

    Science.gov (United States)

    Larour, E. Y.; Ivins, E. R.; Adhikari, S.; Schlegel, N.; Seroussi, H. L.; Morlighem, M.

    2017-12-01

    Relative sea-level rise is driven by processes that are intimately linked to the evolution ofglacial areas and ice sheets in particular. So far, most Earth System models capable of projecting theevolution of RSL on decadal to centennial time scales have relied on offline interactions between RSL andice sheets. In particular, grounding line and calving front dynamics have not been modeled in a way that istightly coupled with Elasto-Static Adjustment (ESA) and/or Glacial-Isostatic Adjustment (GIA). Here, we presenta new simulation of the entire Earth System in which both Greenland and Antarctica ice sheets are tightly coupledto an RSL model that includes both ESA and GIA at resolutions and time scales compatible with processes suchas grounding line dynamics for Antarctica ice shelves and calving front dynamics for Greenland marine-terminatingglaciers. The simulations rely on the Ice Sheet System Model (ISSM) and show the impact of higher-orderice flow dynamics and coupling feedbacks between ice flow and RSL. We quantify the exact impact of ESA andGIA inclusion on grounding line evolution for large ice shelves such as the Ronne and Ross ice shelves, as well asthe Agasea Embayment ice streams, and demonstate how offline vs online RSL simulations diverge in the long run,and the consequences for predictions of sea-level rise.This work was performed at the California Institute of Technology's Jet Propulsion Laboratory undera contract with the National Aeronautics and Space Administration's Cryosphere Science Program.

  19. Experimental interstellar organic chemistry - Preliminary findings

    Science.gov (United States)

    Khare, B. N.; Sagan, C.

    1973-01-01

    Review of the results of some explicit experimental simulation of interstellar organic chemistry consisting in low-temperature high-vacuum UV irradiation of condensed simple gases known or suspected to be present in the interstellar medium. The results include the finding that acetonitrile may be present in the interstellar medium. The implication of this and other findings are discussed.

  20. Simulation of an extended surface detector IceVeto for IceCube-Gen2

    Energy Technology Data Exchange (ETDEWEB)

    Hansmann, Tim; Auffenberg, Jan; Haack, Christian; Hansmann, Bengt; Kemp, Julian; Konietz, Richard; Leuner, Jakob; Raedel, Leif; Stahlberg, Martin; Schoenen, Sebastian; Wiebusch, Christopher [III. Physikalisches Institut B, RWTH Aachen University (Germany); Collaboration: IceCube-Collaboration

    2016-07-01

    IceCube is a neutrino observatory located at the geographic South Pole. The main backgrounds for IceCube's primary goal, the measurement of astrophysical neutrinos, are muons and neutrinos from cosmic-ray air showers in the Earth's atmosphere. Strong supression of these backgrounds from the Southern hemisphere has been demonstrated by coincident detection of these air showers with the IceTop surface detector. For an extended instrument, IceCube-Gen2, it is considered to build an enlarged surface array, IceVeto, that will improve the detection capabilities of coincident air showers. We will present simulation studies to estimate the IceVeto capabilities to optimize the IceCube-Gen2 design.

  1. High-density amorphous ice: A path-integral simulation

    Science.gov (United States)

    Herrero, Carlos P.; Ramírez, Rafael

    2012-09-01

    Structural and thermodynamic properties of high-density amorphous (HDA) ice have been studied by path-integral molecular dynamics simulations in the isothermal-isobaric ensemble. Interatomic interactions were modeled by using the effective q-TIP4P/F potential for flexible water. Quantum nuclear motion is found to affect several observable properties of the amorphous solid. At low temperature (T = 50 K) the molar volume of HDA ice is found to increase by 6%, and the intramolecular O-H distance rises by 1.4% due to quantum motion. Peaks in the radial distribution function of HDA ice are broadened with respect to their classical expectancy. The bulk modulus, B, is found to rise linearly with the pressure, with a slope ∂B/∂P = 7.1. Our results are compared with those derived earlier from classical and path-integral simulations of HDA ice. We discuss similarities and discrepancies with those earlier simulations.

  2. Software Development Processes Applied to Computational Icing Simulation

    Science.gov (United States)

    Levinson, Laurie H.; Potapezuk, Mark G.; Mellor, Pamela A.

    1999-01-01

    The development of computational icing simulation methods is making the transition form the research to common place use in design and certification efforts. As such, standards of code management, design validation, and documentation must be adjusted to accommodate the increased expectations of the user community with respect to accuracy, reliability, capability, and usability. This paper discusses these concepts with regard to current and future icing simulation code development efforts as implemented by the Icing Branch of the NASA Lewis Research Center in collaboration with the NASA Lewis Engineering Design and Analysis Division. With the application of the techniques outlined in this paper, the LEWICE ice accretion code has become a more stable and reliable software product.

  3. Investigation of HNCO isomer formation in ice mantles by UV and thermal processing: An experimental approach

    Energy Technology Data Exchange (ETDEWEB)

    Jiménez-Escobar, A.; Giuliano, B. M.; Caro, G. M. Muñoz; Cernicharo, J. [Centro de Astrobiología, INTA-CSIC, Carretera de Ajalvir, km 4, Torrejón de Ardoz, E-28850 Madrid (Spain); Marcelino, N., E-mail: bgiuliano@cab.inta-csic.es [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States)

    2014-06-10

    Current gas-phase models do not account for the abundances of HNCO isomers detected in various environments, suggesting their formation in icy grain mantles. We attempted to study a formation channel of HNCO and its possible isomers by vacuum-UV photoprocessing of interstellar ice analogs containing H{sub 2}O, NH{sub 3}, CO, HCN, CH{sub 3}OH, CH{sub 4}, and N{sub 2} followed by warm-up under astrophysically relevant conditions. Only the H{sub 2}O:NH{sub 3}:CO and H{sub 2}O:HCN ice mixtures led to the production of HNCO species. The possible isomerization of HNCO to its higher energy tautomers following irradiation or due to ice warm-up has been scrutinized. The photochemistry and thermal chemistry of H{sub 2}O:NH{sub 3}:CO and H{sub 2}O:HCN ices were simulated using the Interstellar Astrochemistry Chamber, a state-of-the-art ultra-high-vacuum setup. The ice was monitored in situ by Fourier transform mid-infrared spectroscopy in transmittance. A quadrupole mass spectrometer detected the desorption of the molecules in the gas phase. UV photoprocessing of H{sub 2}O:NH{sub 3}:CO and H{sub 2}O:HCN ices lead to the formation of OCN{sup –} as a main product in the solid state and a minor amount of HNCO. The second isomer HOCN has been tentatively identified. Despite its low efficiency, the formation of HNCO and the HOCN isomers by UV photoprocessing of realistic simulated ice mantles might explain the observed abundances of these species in photodissociation regions, hot cores, and dark clouds.

  4. Intercomparison of Antarctic ice-shelf, ocean, and sea-ice interactions simulated by MetROMS-iceshelf and FESOM 1.4

    Science.gov (United States)

    Naughten, Kaitlin A.; Meissner, Katrin J.; Galton-Fenzi, Benjamin K.; England, Matthew H.; Timmermann, Ralph; Hellmer, Hartmut H.; Hattermann, Tore; Debernard, Jens B.

    2018-04-01

    An increasing number of Southern Ocean models now include Antarctic ice-shelf cavities, and simulate thermodynamics at the ice-shelf/ocean interface. This adds another level of complexity to Southern Ocean simulations, as ice shelves interact directly with the ocean and indirectly with sea ice. Here, we present the first model intercomparison and evaluation of present-day ocean/sea-ice/ice-shelf interactions, as simulated by two models: a circumpolar Antarctic configuration of MetROMS (ROMS: Regional Ocean Modelling System coupled to CICE: Community Ice CodE) and the global model FESOM (Finite Element Sea-ice Ocean Model), where the latter is run at two different levels of horizontal resolution. From a circumpolar Antarctic perspective, we compare and evaluate simulated ice-shelf basal melting and sub-ice-shelf circulation, as well as sea-ice properties and Southern Ocean water mass characteristics as they influence the sub-ice-shelf processes. Despite their differing numerical methods, the two models produce broadly similar results and share similar biases in many cases. Both models reproduce many key features of observations but struggle to reproduce others, such as the high melt rates observed in the small warm-cavity ice shelves of the Amundsen and Bellingshausen seas. Several differences in model design show a particular influence on the simulations. For example, FESOM's greater topographic smoothing can alter the geometry of some ice-shelf cavities enough to affect their melt rates; this improves at higher resolution, since less smoothing is required. In the interior Southern Ocean, the vertical coordinate system affects the degree of water mass erosion due to spurious diapycnal mixing, with MetROMS' terrain-following coordinate leading to more erosion than FESOM's z coordinate. Finally, increased horizontal resolution in FESOM leads to higher basal melt rates for small ice shelves, through a combination of stronger circulation and small-scale intrusions of

  5. Validation of 3-D Ice Accretion Measurement Methodology for Experimental Aerodynamic Simulation

    Science.gov (United States)

    Broeren, Andy P.; Addy, Harold E., Jr.; Lee, Sam; Monastero, Marianne C.

    2015-01-01

    Determining the adverse aerodynamic effects due to ice accretion often relies on dry-air wind-tunnel testing of artificial, or simulated, ice shapes. Recent developments in ice-accretion documentation methods have yielded a laser-scanning capability that can measure highly three-dimensional (3-D) features of ice accreted in icing wind tunnels. The objective of this paper was to evaluate the aerodynamic accuracy of ice-accretion simulations generated from laser-scan data. Ice-accretion tests were conducted in the NASA Icing Research Tunnel using an 18-in. chord, two-dimensional (2-D) straight wing with NACA 23012 airfoil section. For six ice-accretion cases, a 3-D laser scan was performed to document the ice geometry prior to the molding process. Aerodynamic performance testing was conducted at the University of Illinois low-speed wind tunnel at a Reynolds number of 1.8 × 10(exp 6) and a Mach number of 0.18 with an 18-in. chord NACA 23012 airfoil model that was designed to accommodate the artificial ice shapes. The ice-accretion molds were used to fabricate one set of artificial ice shapes from polyurethane castings. The laser-scan data were used to fabricate another set of artificial ice shapes using rapid prototype manufacturing such as stereolithography. The iced-airfoil results with both sets of artificial ice shapes were compared to evaluate the aerodynamic simulation accuracy of the laser-scan data. For five of the six ice-accretion cases, there was excellent agreement in the iced-airfoil aerodynamic performance between the casting and laser-scan based simulations. For example, typical differences in iced-airfoil maximum lift coefficient were less than 3 percent with corresponding differences in stall angle of approximately 1 deg or less. The aerodynamic simulation accuracy reported in this paper has demonstrated the combined accuracy of the laser-scan and rapid-prototype manufacturing approach to simulating ice accretion for a NACA 23012 airfoil. For several

  6. A Combined Experimental and Theoretical Study on the Formation of Interstellar Propylene Oxide (CH3CHCH2O)—A Chiral Molecule

    Science.gov (United States)

    Bergantini, Alexandre; Abplanalp, Matthew J.; Pokhilko, Pavel; Krylov, Anna I.; Shingledecker, Christopher N.; Herbst, Eric; Kaiser, Ralf I.

    2018-06-01

    This work reveals via a combined experimental, computational, and astrochemical modeling study that racemic propylene oxide (c-C3H6O)—the first chiral molecule detected outside Earth toward the high-mass star-forming region Sagittarius B2(N)—can be synthesized by non-equilibrium reactions initiated by the effects of secondary electrons generated in the track of cosmic rays interacting with ice-coated interstellar grains through excited-state and spin-forbidden reaction pathways operating within low-temperature interstellar ices at 10 K. Our findings confront traditional hypotheses that thermal chemistries followed by processing of interstellar grains dictate the formation of complex organic molecules (COMs) in molecular clouds. Instead, we reveal a hitherto poorly quantified reaction class involving excited-state and spin-forbidden chemistry leading to racemic mixtures of COMs inside interstellar ices prior to their sublimation in star-forming regions. This fundamental production mechanism is of essential consequence in aiding our understanding of the origin and evolution of chiral molecules in the universe.

  7. Photochemistry of polycyclic aromatic hydrocarbons in cosmic water ice. II. Near UV/VIS spectroscopy and ionization rates

    Science.gov (United States)

    Bouwman, J.; Cuppen, H. M.; Steglich, M.; Allamandola, L. J.; Linnartz, H.

    2011-05-01

    Context. Mid-infrared emission features originating from polycyclic aromatic hydrocarbons (PAHs) are observed towards photon dominated regions in space. Towards dense clouds, however, these emission features are quenched. Observations of dense clouds show that many simple volatile molecules are frozen out on interstellar grains, forming thin layers of ice. Recently, observations have shown that more complex non-volatile species, presumably including PAHs, also freeze out and contribute to the ongoing solid-state chemistry. Aims: The study presented here aims at obtaining reaction rate data that characterize PAH photochemistry upon vacuum ultraviolet (VUV) irradiation in an interstellar H2O ice analogue to explore the potential impact of PAH:H2O ice reactions on overall interstellar ice chemistry. To this end, the experimental results are implemented in a chemical model under simple interstellar cloud conditions. Methods: Time-dependent near-UV/VIS spectroscopy on the VUV photochemistry of anthracene, pyrene, benzo[ghi]perylene and coronene containing interstellar H2O ice analogs is performed at 25 and 125 K, using an optical absorption setup. Results: Near-UV/VIS absorption spectra are presented for these four PAHs and their photoproducts including cationic species trapped in H2O ice. Oscillator strengths of the cation absorption bands are derived relative to the oscillator strength of the neutral parent PAH. The loss of the parent and growth of PAH photoproducts are measured as a function of VUV dose, yielding solid state reaction constants. The rate constants are used in an exploratory astrochemical model, to assess the importance of PAH:H2O ice photoprocessing in UV exposed interstellar environments, compared with the timescales in which PAH molecules are incorporated in interstellar ices. Conclusions: All four PAHs studied here are found to be readily ionized upon VUV photolysis when trapped in H2O ice and exhibit similar rates for ionization at astronomically

  8. Simulating STARDUST: Reproducing Impacts of Interstellar Dust in the Laboratory

    Science.gov (United States)

    Postberg, F.; Srama, R.; Hillier, J. K.; Sestak, S.; Green, S. F.; Trieloff, M.; Grün, E.

    2008-09-01

    Our experiments are carried out to support the analysis of interstellar dust grains, ISDGs, brought to earth by the STARDUST mission. Since the very first investigations, it has turned out that the major problem of STARDUST particle analysis is the modification (partly even the destruction) during capture when particles impact the spacecraft collectors with a velocity of up to 20 km/s. While it is possible to identify, extract, and analyse cometary grains larger than a few microns in aerogel and on metal collector plates, the STARDUST team is not yet ready for the identification, extraction, and analysis of sub-micron sized ISDGs with impact speeds of up to 20 km/s. Reconstructing the original particle properties requires a simulation of this impact capture process. Moreover, due to the lack of laboratory studies of high speed impacts of micron scale dust into interstellar STARDUST flight spares, the selection of criteria for the identification of track candidates is entirely subjective. Simulation of such impact processes is attempted with funds of the FRONTIER program within the framework of the Heidelberg University initiative of excellence. The dust accelerator at the MPI Kernphysik is a facility unique in the world to perform such experiments. A critical point is the production of cometary and interstellar dust analogue material and its acceleration to very high speeds of 20 km/s, which has never before been performed in laboratory experiments. Up to now only conductive material was successfully accelerated by the 2 MV Van de Graaf generator of the dust accelerator facility. Typical projectile materials are Iron, Aluminium, Carbon, Copper, Silver, and the conducting hydrocarbon Latex. Ongoing research now enables the acceleration of any kind of rocky planetary and interstellar dust analogues (Hillier et al. 2008, in prep.). The first batch of dust samples produced with the new method consists of micron and submicron SiO2 grains. Those were successfully

  9. Simulation and Domain Identification of Sea Ice Thermodynamic System

    Directory of Open Access Journals (Sweden)

    Bing Tan

    2012-01-01

    Full Text Available Based on the measured data and characteristics of sea ice temperature distribution in space and time, this study is intended to consider a parabolic partial differential equation of the thermodynamic field of sea ice (coupled by snow, ice, and sea water layers with a time-dependent domain and its parameter identification problem. An optimal model with state constraints is presented with the thicknesses of snow and sea ice as parametric variables and the deviation between the calculated and measured sea ice temperatures as the performance criterion. The unique existence of the weak solution of the thermodynamic system is proved. The properties of the identification problem and the existence of the optimal parameter are discussed, and the one-order necessary condition is derived. Finally, based on the nonoverlapping domain decomposition method and semi-implicit difference scheme, an optimization algorithm is proposed for the numerical simulation. Results show that the simulated temperature of sea ice fit well with the measured data, and the better fit is corresponding to the deeper sea ice.

  10. Glaciations and dense interstellar clouds; and reply

    Energy Technology Data Exchange (ETDEWEB)

    McCrea, W H [Sussex Univ., Brighton (UK); Dennison, B; Mansfield, V N

    1976-09-16

    Reference is made to Dennison and Mansfield (Nature 261:32 (1976)) who offered comments on a previous paper by the author (Nature 255:607 (1975)), in which he suggested that a possible cause of an ice age on the Earth was the passage of the solar system through an interstellar matter compression region bordering a spiral arm of the Galaxy. Dennison and Mansfield criticised this suggestion because it led them to expect to find a dense cloud of interstellar matter still very close to the Earth, whereas no such cloud is known. It is stated here that this criticism ignores the structure of the Galaxy, that provided the basis of the suggestion. A reply by Dennison and Mansfield is appended.

  11. Assimilating the ICE-6G_C Reconstruction of the Latest Quaternary Ice Age Cycle Into Numerical Simulations of the Laurentide and Fennoscandian Ice Sheets

    Science.gov (United States)

    Stuhne, G. R.; Peltier, W. R.

    2017-12-01

    We analyze the effects of nudging 100 kyr numerical simulations of the Laurentide and Fennoscandian ice sheets toward the glacial isostatic adjustment-based (GIA-based) ICE-6G_C reconstruction of the most recent ice age cycle. Starting with the ice physics approximations of the PISM ice sheet model and the SeaRISE simulation protocols, we incorporate nudging at characteristic time scales, τf, through anomalous mass balance terms in the ice mass conservation equation. As should be expected, these mass balances exhibit physically unrealistic details arising from pure GIA-based reconstruction geometry when nudging is very strong (τf=20 years for North America), while weakly nudged (τf=1,000 years) solutions deviate from ICE-6G_C sufficiently to degrade its observational fit quality. For reasonable intermediate time scales (τf=100 years and 200 years), we perturbatively analyze nudged ice dynamics as a superposition of "leading-order smoothing" that diffuses ICE-6G_C in a physically and observationally consistent manner and "higher-order" deviations arising, for instance, from biases in the time dependence of surface climate boundary conditions. Based upon the relative deviations between respective nudged simulations in which these biases follow surface temperature from ice cores and eustatic sea level from marine sediment cores, we compute "ice core climate adjustments" that suggest how local paleoclimate observations may be applied to the systematic refinement of ICE-6G_C. Our results are consistent with a growing body of evidence suggesting that the geographical origins of Meltwater Pulse 1B (MWP1b) may lie primarily in North America as opposed to Antarctica (as reconstructed in ICE-6G_C).

  12. Flight Testing an Iced Business Jet for Flight Simulation Model Validation

    Science.gov (United States)

    Ratvasky, Thomas P.; Barnhart, Billy P.; Lee, Sam; Cooper, Jon

    2007-01-01

    A flight test of a business jet aircraft with various ice accretions was performed to obtain data to validate flight simulation models developed through wind tunnel tests. Three types of ice accretions were tested: pre-activation roughness, runback shapes that form downstream of the thermal wing ice protection system, and a wing ice protection system failure shape. The high fidelity flight simulation models of this business jet aircraft were validated using a software tool called "Overdrive." Through comparisons of flight-extracted aerodynamic forces and moments to simulation-predicted forces and moments, the simulation models were successfully validated. Only minor adjustments in the simulation database were required to obtain adequate match, signifying the process used to develop the simulation models was successful. The simulation models were implemented in the NASA Ice Contamination Effects Flight Training Device (ICEFTD) to enable company pilots to evaluate flight characteristics of the simulation models. By and large, the pilots confirmed good similarities in the flight characteristics when compared to the real airplane. However, pilots noted pitch up tendencies at stall with the flaps extended that were not representative of the airplane and identified some differences in pilot forces. The elevator hinge moment model and implementation of the control forces on the ICEFTD were identified as a driver in the pitch ups and control force issues, and will be an area for future work.

  13. Structural, chemical and isotopic examinations of interstellar organic matter extracted from meteorites and interstellar dust particles

    Science.gov (United States)

    Busemann, Henner; Alexander, Conel M. O'D.; Nittler, Larry R.; Stroud, Rhonda M.; Zega, Tom J.; Cody, George D.; Yabuta, Hikaru; Kilcoyne, A. L. David

    2008-10-01

    Meteorites and Interplanetary Dust Particles (IDPs) are supposed to originate from asteroids and comets, sampling the most primitive bodies in the Solar System. They contain abundant carbonaceous material. Some of this, mostly insoluble organic matter (IOM), likely originated in the protosolar molecular cloud, based on spectral properties and H and N isotope characteristics. Together with cometary material returned with the Stardust mission, these samples provide a benchmark for models aiming to understand organic chemistry in the interstellar medium, as well as for mechanisms that secured the survival of these fragile molecules during Solar System formation. The carrier molecules of the isotope anomalies are largely unknown, although amorphous carbonaceous spheres, so-called nanoglobules, have been identified as carriers. We are using Secondary Ion Mass Spectrometry to identify isotopically anomalous material in meteoritic IOM and IDPs at a ~100-200 nm scale. Organics of most likely interstellar origin are then extracted with the Focused-Ion-Beam technique and prepared for synchrotron X-ray and Transmission Electron Microscopy. These experiments yield information on the character of the H- and N-bearing interstellar molecules: While the association of H and N isotope anomalies with nanoglobules could be confirmed, we have also identified amorphous, micron-sized monolithic grains. D-enrichments in meteoritic IOM appear not to be systematically associated with any specific functional groups, whereas 15N-rich material can be related to imine and nitrile functionality. The large 15N- enrichments observed here (δ15N > 1000 ‰) cannot be reconciled with models using interstellar ammonia ice reactions, and hence, provide new constraints for understanding the chemistry in cold interstellar clouds.

  14. A simulation study of homogeneous ice nucleation in supercooled salty water

    Science.gov (United States)

    Soria, Guiomar D.; Espinosa, Jorge R.; Ramirez, Jorge; Valeriani, Chantal; Vega, Carlos; Sanz, Eduardo

    2018-06-01

    We use computer simulations to investigate the effect of salt on homogeneous ice nucleation. The melting point of the employed solution model was obtained both by direct coexistence simulations and by thermodynamic integration from previous calculations of the water chemical potential. Using a seeding approach, in which we simulate ice seeds embedded in a supercooled aqueous solution, we compute the nucleation rate as a function of temperature for a 1.85 NaCl mol per water kilogram solution at 1 bar. To improve the accuracy and reliability of our calculations, we combine seeding with the direct computation of the ice-solution interfacial free energy at coexistence using the Mold Integration method. We compare the results with previous simulation work on pure water to understand the effect caused by the solute. The model captures the experimental trend that the nucleation rate at a given supercooling decreases when adding salt. Despite the fact that the thermodynamic driving force for ice nucleation is higher for salty water for a given supercooling, the nucleation rate slows down with salt due to a significant increase of the ice-fluid interfacial free energy. The salty water model predicts an ice nucleation rate that is in good agreement with experimental measurements, bringing confidence in the predictive ability of the model. We expect that the combination of state-of-the-art simulation methods here employed to study ice nucleation from solution will be of much use in forthcoming numerical investigations of crystallization in mixtures.

  15. Can spores survive in interstellar space

    Energy Technology Data Exchange (ETDEWEB)

    Weber, P.; Greenberg, J.M.

    1985-08-01

    Inactivation of spores (Bacillus subtilis) has been investigated in the laboratory by vacuum ultraviolet radiation in simulated interstellar conditions. Damage produced at the normal interstellar particle temperature of 10 K is less than at higher temperatures: the major damage being produced by radiation in the 2,000-3,000 A range. The results place constraints on the panspermia hypothesis. (author).

  16. Direct Detection of Complex Organic Products in Ultraviolet (Lyα) and Electron-irradiated Astrophysical and Cometary Ice Analogs Using Two-step Laser Ablation and Ionization Mass Spectrometry

    Science.gov (United States)

    Henderson, Bryana L.; Gudipati, Murthy S.

    2015-02-01

    As discovery of complex molecules and ions in our solar system and the interstellar medium has proliferated, several groups have turned to laboratory experiments in an effort to simulate and understand these chemical processes. So far only infrared (IR) and ultraviolet (UV) spectroscopy has been able to directly probe these reactions in ices in their native, low-temperature states. Here we report for the first time results using a complementary technique that harnesses two-step two-color laser ablation and ionization to measure mass spectra of energetically processed astrophysical and cometary ice analogs directly without warming the ices—a method for hands-off in situ ice analysis. Electron bombardment and UV irradiation of H2O, CH3OH, and NH3 ices at 5 K and 70 K led to complex irradiation products, including HCO, CH3CO, formamide, acetamide, methyl formate, and HCN. Many of these species, whose assignment was also strengthened by isotope labeling studies and correlate with IR-based spectroscopic studies of similar irradiated ices, are important ingredients for the building blocks of life. Some of them have been detected previously via astronomical observations in the interstellar medium and in cometary comae. Other species such as CH3CO (acetyl) are yet to be detected in astrophysical ices or interstellar medium. Our studies suggest that electron and UV photon processing of astrophysical ice analogs leads to extensive chemistry even in the coldest reaches of space, and lend support to the theory of comet-impact-induced delivery of complex organics to the inner solar system.

  17. BENZENE FORMATION ON INTERSTELLAR ICY MANTLES CONTAINING PROPARGYL ALCOHOL

    Energy Technology Data Exchange (ETDEWEB)

    Sivaraman, B.; Mukherjee, R.; Subramanian, K. P.; Banerjee, S. B., E-mail: bhala@prl.res.in [Space and Atmospheric Sciences Division, Physical Research Laboratory, Ahmedabad (India)

    2015-01-10

    Propargyl alcohol (CHCCH{sub 2}OH) is a known stable isomer of the propenal (CH{sub 2}CHCHO) molecule that was reported to be present in the interstellar medium (ISM). At astrochemical conditions in the laboratory, icy layers of propargyl alcohol grown at 85 K were irradiated by 2 keV electrons and probed by a Fourier Transform InfraRed spectrometer in the mid-infrared (IR) region, 4000-500 cm{sup –1}. Propargyl alcohol ice under astrochemical conditions was studied for the first time; therefore, IR spectra of reported amorphous (85 K) and crystalline (180 K) propargyl alcohol ices can be used to detect its presence in the ISM. Moreover, our experiments clearly show benzene (C{sub 6}H{sub 6}) formation to be the major product from propargyl alcohol irradiation, confirming the role of propargyl radicals (C{sub 3}H{sub 3}) formed from propargyl alcohol dissociation that was long expected based on theoretical modeling to effectively synthesize C{sub 6}H{sub 6} in the interstellar icy mantles.

  18. Structural Uncertainty in Antarctic sea ice simulations

    Science.gov (United States)

    Schneider, D. P.

    2016-12-01

    The inability of the vast majority of historical climate model simulations to reproduce the observed increase in Antarctic sea ice has motivated many studies about the quality of the observational record, the role of natural variability versus forced changes, and the possibility of missing or inadequate forcings in the models (such as freshwater discharge from thinning ice shelves or an inadequate magnitude of stratospheric ozone depletion). In this presentation I will highlight another source of uncertainty that has received comparatively little attention: Structural uncertainty, that is, the systematic uncertainty in simulated sea ice trends that arises from model physics and mean-state biases. Using two large ensembles of experiments from the Community Earth System Model (CESM), I will show that the model is predisposed towards producing negative Antarctic sea ice trends during 1979-present, and that this outcome is not simply because the model's decadal variability is out-of-synch with that in nature. In the "Tropical Pacific Pacemaker" ensemble, in which observed tropical Pacific SST anomalies are prescribed, the model produces very realistic atmospheric circulation trends over the Southern Ocean, yet the sea ice trend is negative in every ensemble member. However, if the ensemble-mean trend (commonly interpreted as the forced response) is removed, some ensemble members show a sea ice increase that is very similar to the observed. While this results does confirm the important role of natural variability, it also suggests a strong bias in the forced response. I will discuss the reasons for this systematic bias and explore possible remedies. This an important problem to solve because projections of 21st -Century changes in the Antarctic climate system (including ice sheet surface mass balance changes and related changes in the sea level budget) have a strong dependence on the mean state of and changes in the Antarctic sea ice cover. This problem is not unique to

  19. Numerical flow simulation over clean and iced wind turbine blades

    Energy Technology Data Exchange (ETDEWEB)

    Villalpando, F.; Reggio, M. [Ecole Polytechnique, Montreal, PQ (Canada); Ilinca, A. [Quebec Univ., Rimouski, PQ (Canada). Wind Energy Group

    2009-07-01

    The impact of ice accretion on the drag and lift coefficients of a wind turbine blade was studied. Computerized simulations were conducted for both clean and ice-accreted 2-D airfoils at various angles of attack. The finite volume-based commercial computational fluid dynamics (CFD) program FLUENT was used to simulate the 2-D geometries of turbulent, unsteady and incompressible flow around the airfoils. Pressure coefficients and the contribution of pressure and friction forces to the lift and drag coefficients were analyzed. The study showed that traditional calculations over-predict the lift and drag of ice-accreted airfoil profiles. Ice accreted over the profile's pressure side provoked a bigger lift reduction and drag increase than that caused by ice accreted on the suction side. The poor performance of the aerodynamic coefficients was attributed to the contribution of pressure forces. Further experimentation is required to determine if de-icing systems for turbine blades should be developed to prevent or melt ice over the profile pressure side. 11 refs., 7 tabs., 15 figs.

  20. Global ice volume variations through the last glacial cycle simulated by a 3-D ice-dynamical model

    NARCIS (Netherlands)

    Bintanja, R.; Wal, R.S.W. van de; Oerlemans, J.

    2002-01-01

    A coupled ice sheet—ice shelf—bedrock model was run at 20km resolution to simulate the evolution of global ice cover during the last glacial cycle. The mass balance model uses monthly mean temperature and precipitation as input and incorporates the albedo—mass balance feedback. The model is forced

  1. Simulation of the Greenland Ice Sheet over two glacial–interglacial cycles: investigating a sub-ice-shelf melt parameterization and relative sea level forcing in an ice-sheet–ice-shelf model

    Directory of Open Access Journals (Sweden)

    S. L. Bradley

    2018-05-01

    Full Text Available Observational evidence, including offshore moraines and sediment cores, confirm that at the Last Glacial Maximum (LGM the Greenland ice sheet (GrIS expanded to a significantly larger spatial extent than seen at present, grounding into Baffin Bay and out onto the continental shelf break. Given this larger spatial extent and its close proximity to the neighbouring Laurentide Ice Sheet (LIS and Innuitian Ice Sheet (IIS, it is likely these ice sheets will have had a strong non-local influence on the spatial and temporal behaviour of the GrIS. Most previous paleo ice-sheet modelling simulations recreated an ice sheet that either did not extend out onto the continental shelf or utilized a simplified marine ice parameterization which did not fully include the effect of ice shelves or neglected the sensitivity of the GrIS to this non-local bedrock signal from the surrounding ice sheets. In this paper, we investigated the evolution of the GrIS over the two most recent glacial–interglacial cycles (240 ka BP to the present day using the ice-sheet–ice-shelf model IMAU-ICE. We investigated the solid earth influence of the LIS and IIS via an offline relative sea level (RSL forcing generated by a glacial isostatic adjustment (GIA model. The RSL forcing governed the spatial and temporal pattern of sub-ice-shelf melting via changes in the water depth below the ice shelves. In the ensemble of simulations, at the glacial maximums, the GrIS coalesced with the IIS to the north and expanded to the continental shelf break to the southwest but remained too restricted to the northeast. In terms of the global mean sea level contribution, at the Last Interglacial (LIG and LGM the ice sheet added 1.46 and −2.59 m, respectively. This LGM contribution by the GrIS is considerably higher (∼  1.26 m than most previous studies whereas the contribution to the LIG highstand is lower (∼  0.7 m. The spatial and temporal behaviour of the northern margin was

  2. Ice versus liquid water saturation in simulations of the indian summer monsoon

    Science.gov (United States)

    Glazer, Russell H.; Misra, Vasubandhu

    2018-02-01

    At the same temperature, below 0 °C, the saturation vapor pressure (SVP) over ice is slightly less than the SVP over liquid water. Numerical models use the Clausius-Clapeyron relation to calculate the SVP and relative humidity, but there is not a consistent method for the treatment of saturation above the freezing level where ice and mixed-phase clouds may be present. In the context of current challenges presented by cloud microphysics in climate models, we argue that a better understanding of the impact that this treatment has on saturation-related processes like cloud formation and precipitation, is needed. This study explores the importance of the SVP calculation through model simulations of the Indian summer monsoon (ISM) using the regional spectral model (RSM) at 15 km grid spacing. A combination of seasonal and multiyear simulations is conducted with two saturation parameterizations. In one, the SVP over liquid water is prescribed through the entire atmospheric column (woIce), and in another the SVP over ice is used above the freezing level (wIce). When SVP over ice is prescribed, a thermodynamic drying of the middle and upper troposphere above the freezing level occurs due to increased condensation. In the wIce runs, the model responds to the slight decrease in the saturation condition by increasing, relative to the SVP over liquid water only run, grid-scale condensation of water. Increased grid-scale mean seasonal precipitation is noted across the ISM region in the simulation with SVP over ice prescribed. Modification of the middle and upper troposphere moisture results in a decrease in mean seasonal mid-level cloud amount and an increase in high cloud amount when SVP over ice is prescribed. Multiyear simulations strongly corroborate the qualitative results found in the seasonal simulations regarding the impact of ice versus liquid water SVP on the ISM's mean precipitation and moisture field. The mean seasonal rainfall difference over All India between wIce

  3. Laboratory Investigations into the Spectra and Origin of Propylene Oxide: A Chiral Interstellar Molecule

    Science.gov (United States)

    Hudson, R. L.; Loeffler, M. J.; Yocum, K. M.

    2017-01-01

    Propylene oxide was recently identified in the interstellar medium, but few laboratory results are available for this molecule to guide current and future investigations. To address this situation, here we report infrared spectra, absorption coefficients, and band strengths of solid propylene oxide along with the first measurement of its refractive index and a calculation of its density, all for the amorphous solid form of the compound. We present the first experimental results showing a low-temperature formation pathway for propylene oxide near 10 K in interstellar ice analogs. Connections are drawn between our new results and the interstellar molecules propanal and acetone, and predictions are made about several as yet unobserved vinyl alcohols and methylketene. Comparisons are given to earlier laboratory work and a few applications to interstellar and solar system astrochemistry are described.

  4. Laboratory Investigations into the Spectra and Origin of Propylene Oxide: A Chiral Interstellar Molecule

    Energy Technology Data Exchange (ETDEWEB)

    Hudson, R. L.; Loeffler, M. J. [Astrochemistry Laboratory (Code 691), NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Yocum, K. M., E-mail: Reggie.Hudson@nasa.gov [Department of Chemistry, Kutztown University, Kutztown, PA 19530 (United States)

    2017-02-01

    Propylene oxide was recently identified in the interstellar medium, but few laboratory results are available for this molecule to guide current and future investigations. To address this situation, here we report infrared spectra, absorption coefficients, and band strengths of solid propylene oxide along with the first measurement of its refractive index and a calculation of its density, all for the amorphous solid form of the compound. We present the first experimental results showing a low-temperature formation pathway for propylene oxide near 10 K in interstellar ice analogs. Connections are drawn between our new results and the interstellar molecules propanal and acetone, and predictions are made about several as yet unobserved vinyl alcohols and methylketene. Comparisons are given to earlier laboratory work and a few applications to interstellar and solar system astrochemistry are described.

  5. Experiments on chemical and physical evolution of interstellar grain mantles

    International Nuclear Information System (INIS)

    Greenberg, J.M.

    1984-01-01

    The Astrophysical Laboratory at the University of Leiden is the first to succeed in simulating the essential conditions in interstellar space as they affect the evolution of interstellar grains. (author)

  6. Experimental interstellar organic chemistry: Preliminary findings

    Science.gov (United States)

    Khare, B. N.; Sagan, C.

    1971-01-01

    In a simulation of interstellar organic chemistry in dense interstellar clouds or on grain surfaces, formaldehyde, water vapor, ammonia and ethane are deposited on a quartz cold finger and ultraviolet-irradiated in high vacuum at 77K. The HCHO photolytic pathway which produces an aldehyde radical and a superthermal hydrogen atom initiates solid phase chain reactions leading to a range of new compounds, including methanol, ethanol, acetaldehyde, acetonitrile, acetone, methyl formate, and possibly formic acid. Higher nitriles are anticipated. Genetic relations among these interstellar organic molecules (e.g., the Cannizzaro and Tischenko reactions) must exist. Some of them, rather than being synthesized from smaller molecules, may be degradation products of larger organic molecules, such as hexamethylene tetramine, which are candidate consitituents of the interstellar grains. The experiments reported here may also be relevant to cometary chemistry.

  7. Interaction of Tenebrio Molitor Antifreeze Protein with Ice Crystal: Insights from Molecular Dynamics Simulations.

    Science.gov (United States)

    Ramya, L; Ramakrishnan, Vigneshwar

    2016-07-01

    Antifreeze proteins (AFP) observed in cold-adapting organisms bind to ice crystals and prevent further ice growth. However, the molecular mechanism of AFP-ice binding and AFP-inhibited ice growth remains unclear. Here we report the interaction of the insect antifreeze protein (Tenebrio molitor, TmAFP) with ice crystal by molecular dynamics simulation studies. Two sets of simulations were carried out at 263 K by placing the protein near the primary prism plane (PP) and basal plane (BL) of the ice crystal. To delineate the effect of temperatures, both the PP and BL simulations were carried out at 253 K as well. The analyses revealed that the protein interacts strongly with the ice crystal in BL simulation than in PP simulation both at 263 K and 253 K. Further, it was observed that the interactions are primarily mediated through the interface waters. We also observed that as the temperature decreases, the interaction between the protein and the ice increases which can be attributed to the decreased flexibility and the increased structuring of the protein at low temperature. In essence, our study has shed light on the interaction mechanism between the TmAFP antifreeze protein and the ice crystal. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Improved simulation of Antarctic sea ice due to the radiative effects of falling snow

    Science.gov (United States)

    Li, J.-L. F.; Richardson, Mark; Hong, Yulan; Lee, Wei-Liang; Wang, Yi-Hui; Yu, Jia-Yuh; Fetzer, Eric; Stephens, Graeme; Liu, Yinghui

    2017-08-01

    Southern Ocean sea-ice cover exerts critical control on local albedo and Antarctic precipitation, but simulated Antarctic sea-ice concentration commonly disagrees with observations. Here we show that the radiative effects of precipitating ice (falling snow) contribute substantially to this discrepancy. Many models exclude these radiative effects, so they underestimate both shortwave albedo and downward longwave radiation. Using two simulations with the climate model CESM1, we show that including falling-snow radiative effects improves the simulations relative to cloud properties from CloudSat-CALIPSO, radiation from CERES-EBAF and sea-ice concentration from passive microwave sensors. From 50-70°S, the simulated sea-ice-area bias is reduced by 2.12 × 106 km2 (55%) in winter and by 1.17 × 106 km2 (39%) in summer, mainly because increased wintertime longwave heating restricts sea-ice growth and so reduces summer albedo. Improved Antarctic sea-ice simulations will increase confidence in projected Antarctic sea level contributions and changes in global warming driven by long-term changes in Southern Ocean feedbacks.

  9. CHEMICAL SIMULATIONS OF PREBIOTIC MOLECULES: INTERSTELLAR ETHANIMINE ISOMERS

    Energy Technology Data Exchange (ETDEWEB)

    Quan, Donghui; Durr, Allison [Department of Chemistry, Eastern Kentucky University, Richmond, KY 40475 (United States); Herbst, Eric [Departments of Chemistry and Astronomy, University of Virginia, Charlottesville, VA 22904 (United States); Corby, Joanna F. [Department of Astronomy, University of Virginia, Charlottesville, VA 22904 (United States); Hassel, George [Physics and Astronomy Department, Siena College, Loudonville, NY 12211 (United States)

    2016-06-20

    The E- and Z- isomers of ethanimine (CH{sub 3}CHNH) were recently detected toward the star-forming region Sagittarius (Sgr) B2(N) using the Green Bank Telescope PRIMOS cm-wave spectral data, and imaged by the Australia Telescope Compact Array. Ethanimine is not reported in the hot cores of Sgr B2, but only in gas that absorbs at +64 and +82 km s{sup −1} in the foreground of continuum emission generated by H ii regions. The ethanimine isomers can serve as precursors of the amino acid alanine and may play important roles in forming biological molecules in the interstellar medium. Here we present a study of the chemistry of ethanimine using a gas-grain simulation based on rate equations, with both isothermal and warm-up conditions. In addition, the density, kinetic temperature, and cosmic ray ionization rate have been varied. For a variety of physical conditions in the warm-up models for Sgr B2(N) and environs, the simulations show reasonable agreement with observationally obtained abundances. Isothermal models of translucent clouds along the same line of sight yield much lower abundances, so that ethanimine would be much more difficult to detect in these sources despite the fact that other complex molecules have been detected there.

  10. Chemical Simulations of Prebiotic Molecules: Interstellar Ethanimine Isomers

    Science.gov (United States)

    Quan, Donghui; Herbst, Eric; Corby, Joanna F.; Durr, Allison; Hassel, George

    2016-06-01

    The E- and Z-isomers of ethanimine (CH3CHNH) were recently detected toward the star-forming region Sagittarius (Sgr) B2(N) using the Green Bank Telescope PRIMOS cm-wave spectral data, and imaged by the Australia Telescope Compact Array. Ethanimine is not reported in the hot cores of Sgr B2, but only in gas that absorbs at +64 and +82 km s-1 in the foreground of continuum emission generated by H II regions. The ethanimine isomers can serve as precursors of the amino acid alanine and may play important roles in forming biological molecules in the interstellar medium. Here we present a study of the chemistry of ethanimine using a gas-grain simulation based on rate equations, with both isothermal and warm-up conditions. In addition, the density, kinetic temperature, and cosmic ray ionization rate have been varied. For a variety of physical conditions in the warm-up models for Sgr B2(N) and environs, the simulations show reasonable agreement with observationally obtained abundances. Isothermal models of translucent clouds along the same line of sight yield much lower abundances, so that ethanimine would be much more difficult to detect in these sources despite the fact that other complex molecules have been detected there.

  11. Greenland ice sheet model parameters constrained using simulations of the Eemian Interglacial

    Directory of Open Access Journals (Sweden)

    A. Robinson

    2011-04-01

    Full Text Available Using a new approach to force an ice sheet model, we performed an ensemble of simulations of the Greenland Ice Sheet evolution during the last two glacial cycles, with emphasis on the Eemian Interglacial. This ensemble was generated by perturbing four key parameters in the coupled regional climate-ice sheet model and by introducing additional uncertainty in the prescribed "background" climate change. The sensitivity of the surface melt model to climate change was determined to be the dominant driver of ice sheet instability, as reflected by simulated ice sheet loss during the Eemian Interglacial period. To eliminate unrealistic parameter combinations, constraints from present-day and paleo information were applied. The constraints include (i the diagnosed present-day surface mass balance partition between surface melting and ice discharge at the margin, (ii the modeled present-day elevation at GRIP; and (iii the modeled elevation reduction at GRIP during the Eemian. Using these three constraints, a total of 360 simulations with 90 different model realizations were filtered down to 46 simulations and 20 model realizations considered valid. The paleo constraint eliminated more sensitive melt parameter values, in agreement with the surface mass balance partition assumption. The constrained simulations resulted in a range of Eemian ice loss of 0.4–4.4 m sea level equivalent, with a more likely range of about 3.7–4.4 m sea level if the GRIP δ18O isotope record can be considered an accurate proxy for the precipitation-weighted annual mean temperatures.

  12. The Potsdam Parallel Ice Sheet Model (PISM-PIK) - Part 2: Dynamic equilibrium simulation of the Antarctic ice sheet

    Science.gov (United States)

    Martin, M. A.; Winkelmann, R.; Haseloff, M.; Albrecht, T.; Bueler, E.; Khroulev, C.; Levermann, A.

    2011-09-01

    We present a dynamic equilibrium simulation of the ice sheet-shelf system on Antarctica with the Potsdam Parallel Ice Sheet Model (PISM-PIK). The simulation is initialized with present-day conditions for bed topography and ice thickness and then run to steady state with constant present-day surface mass balance. Surface temperature and sub-shelf basal melt distribution are parameterized. Grounding lines and calving fronts are free to evolve, and their modeled equilibrium state is compared to observational data. A physically-motivated calving law based on horizontal spreading rates allows for realistic calving fronts for various types of shelves. Steady-state dynamics including surface velocity and ice flux are analyzed for whole Antarctica and the Ronne-Filchner and Ross ice shelf areas in particular. The results show that the different flow regimes in sheet and shelves, and the transition zone between them, are captured reasonably well, supporting the approach of superposition of SIA and SSA for the representation of fast motion of grounded ice. This approach also leads to a natural emergence of sliding-dominated flow in stream-like features in this new 3-D marine ice sheet model.

  13. Update on Simulating Ice-Cliff Failure

    Science.gov (United States)

    Parizek, B. R.; Christianson, K. A.; Alley, R. B.; Voytenko, D.; Vankova, I.; Dixon, T. H.; Walker, R. T.; Holland, D.

    2017-12-01

    Using a 2D full-Stokes diagnostic ice-flow model and engineering and glaciological failure criteria, we simulate the limiting physical conditions for rapid structural failure of subaerial ice cliffs. Previously, using a higher-order flowline model, we reported that the threshold height, in crevassed ice and/or under favorable conditions for hydrofracture or crack lubrication, may be only slightly above the 100-m maximum observed today and that under well-drained or low-melt conditions, mechanically-competent ice supports cliff heights up to 220 m (with a likely range of 180-275 m) before ultimately succumbing to tensional and compressive failure along a listric surface. However, proximal to calving fronts, bridging effects lead to variations in vertical normal stress from the background glaciostatic stress state that give rise to the along-flow gradients in vertical shear stress that are included within a full-Stokes momentum balance. When including all flowline stresses within the physics core, diagnostic solutions continue to support our earlier findings that slumping failure ultimately limits the upper bound for cliff heights. Shear failure still requires low cohesive strength, tensile failure leads to deeper dry-crevasse propagation (albeit, less than halfway through the cliff), and compressive failure drops the threshold height for triggering rapid ice-front retreat via slumping to 200 m (145-280 m).

  14. Photochemistry of PAHs in cosmic water ice. The effect of concentration on UV-VIS spectroscopy and ionization efficiency

    Science.gov (United States)

    Cuylle, Steven H.; Allamandola, Louis J.; Linnartz, Harold

    2014-02-01

    Context. Observations and models show that polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the interstellar medium. Like other molecules in dense clouds, PAHs accrete onto interstellar dust grains, where they are embedded in an ice matrix dominated by water. In the laboratory, mixed molecular ices (not containing PAHs) have been extensively studied using Fourier transform infrared absorption spectroscopy. Experiments including PAHs in ices have started, however, the concentrations used are typically much higher than the concentrations expected for interstellar ices. Optical spectroscopy offers a sensitive alternative. Aims: We report an experimental study of the effect PAH concentration has on the electronic spectra and the vacuum UV (VUV) driven processes of PAHs in water-rich ices. The goal is to apply the outcome to cosmic ices. Methods: Optical spectroscopic studies allow us to obtain in-situ and quasi real-time electronic solid state spectra of two prototypical PAHs (pyrene and coronene) embedded in water ice under VUV photoprocessing. The study is carried out on PAH:H2O concentrations in the range of 1:30 000 to pure PAH, covering the temperature range from 12 to 125 K. Results: PAH concentration strongly influences the efficiency of PAH cation formation. At low concentrations, ionization efficiencies are over 60% dropping to about 15% at 1:1000. Increasing the PAH concentration reveals spectral broadening in neutral and cation PAH spectra attributed to PAH clustering inside the ice. At the PAH concentrations expected for interstellar ices, some 10 to 20% may be present as cations. The presence of PAHs in neutral and ion form will add distinctive absorption bands to cosmic ice optical spectra and this may serve as a tool to determine PAH concentrations.

  15. Thermoluminescence of simulated interstellar matter after gamma-ray irradiation. Forsterite, enstatite and carbonates

    Science.gov (United States)

    Koike, K.; Nakagawa, M.; Koike, C.; Okada, M.; Chihara, H.

    2002-08-01

    Interstellar matter is known to be strongly irradiated by cosmic radiation and several types of cosmic ray particles. Simulated interstellar matter, such as synthesized forsterite (Mg2SiO4), enstatite (MgSiO3) and magnesite (MgCO3), has been irradiated with 60Co gamma-rays in liquid nitrogen, and also irradiated with fast neutrons at 10 K and 70 K by making use of the low-temperature irradiation facility of the Kyoto University Reactor (KUR-LTL. Maximum fast neutron dose is 1017nf /cm2). After irradiation, samples are stored in liquid nitrogen for several months to allow the decay of induced radioactivity. We measured the luminescence spectra of the gamma ray irradiated samples during warming to 370 K using a spectrophotometer. For the forsterite and magnesite, the spectra exhibit a rather intense peak at about 645-655 nm and 660 nm respectively, whereas luminescence scarcely appeared in the natural olivine sample. The spectra of forsterite is very similar to the ERE of the Red Rectangle.

  16. An Aerodynamic Simulation Process for Iced Lifting Surfaces and Associated Issues

    Science.gov (United States)

    Choo, Yung K.; Vickerman, Mary B.; Hackenberg, Anthony W.; Rigby, David L.

    2003-01-01

    This paper discusses technologies and software tools that are being implemented in a software toolkit currently under development at NASA Glenn Research Center. Its purpose is to help study the effects of icing on airfoil performance and assist with the aerodynamic simulation process which consists of characterization and modeling of ice geometry, application of block topology and grid generation, and flow simulation. Tools and technologies for each task have been carefully chosen based on their contribution to the overall process. For the geometry characterization and modeling, we have chosen an interactive rather than automatic process in order to handle numerous ice shapes. An Appendix presents features of a software toolkit developed to support the interactive process. Approaches taken for the generation of block topology and grids, and flow simulation, though not yet implemented in the software, are discussed with reasons for why particular methods are chosen. Some of the issues that need to be addressed and discussed by the icing community are also included.

  17. Interstellar space: the astrochemist's laboratory

    International Nuclear Information System (INIS)

    Allen, M.A.

    1976-01-01

    A mechanism for the formation of molecules on small (radius less than or equal to 0.04 μ) interstellar grains is proposed. A simplified H 2 formation model is then presented that utilizes this surface reaction mechanism. This approach is further developed into an ab initio chemical model for dense interstellar clouds that incorporates 598 grain surface reactions, with small grains again providing the key reaction area. Gas-phase molecules are depleted through collisions with grains. The abundances of 372 chemical species are calculated as a function of time and are found to be of sufficient magnitude to explain most observations. The reaction rates for ion-molecule chemistry are approximately the same, therefore indicating that surface and gas-phase chemistry may be coupled in certain regions. The composition of grain mantles is shown to be a function of grain radius. In certain grain size ranges, large molecules containing two or more heavy atoms are more predominant than lighter ''ices''--H 2 O, NH 3 , and CH 4 . It is possible that absorption due to these large molecules in the mantles may contribute to the observed 3μ band in astronomical spectra. The second part of this thesis is an account of a radio astronomy observational program to detect new transitions of both previously observed and yet undetected interstellar molecules. The negative results yield order ofmagnitude upper limits to the column densities of the lower transition states of the various molecules. One special project was the search for the Λ-doublet transitions of the 2 H/sub 3 / 2 /, J = 3 / 2 state of OD. The resulting upper limit for the OD/OH column density ratio towards the galactic center is 1/400 and is discussed with reference to theories about deuterium enrichment in interstellar molecules

  18. On the influence of model physics on simulations of Arctic and Antarctic sea ice

    Directory of Open Access Journals (Sweden)

    F. Massonnet

    2011-09-01

    Full Text Available Two hindcast (1983–2007 simulations are performed with the global, ocean-sea ice models NEMO-LIM2 and NEMO-LIM3 driven by atmospheric reanalyses and climatologies. The two simulations differ only in their sea ice component, while all other elements of experimental design (resolution, initial conditions, atmospheric forcing are kept identical. The main differences in the sea ice models lie in the formulation of the subgrid-scale ice thickness distribution, of the thermodynamic processes, of the sea ice salinity and of the sea ice rheology. To assess the differences in model skill over the period of investigation, we develop a set of metrics for both hemispheres, comparing the main sea ice variables (concentration, thickness and drift to available observations and focusing on both mean state and seasonal to interannual variability. Based upon these metrics, we discuss the physical processes potentially responsible for the differences in model skill. In particular, we suggest that (i a detailed representation of the ice thickness distribution increases the seasonal to interannual variability of ice extent, with spectacular improvement for the simulation of the recent observed summer Arctic sea ice retreats, (ii the elastic-viscous-plastic rheology enhances the response of ice to wind stress, compared to the classical viscous-plastic approach, (iii the grid formulation and the air-sea ice drag coefficient affect the simulated ice export through Fram Strait and the ice accumulation along the Canadian Archipelago, and (iv both models show less skill in the Southern Ocean, probably due to the low quality of the reanalyses in this region and to the absence of important small-scale oceanic processes at the models' resolution (~1°.

  19. Explicit simulation of ice particle habits in a Numerical Weather Prediction Model

    Science.gov (United States)

    Hashino, Tempei

    2007-05-01

    This study developed a scheme for explicit simulation of ice particle habits in Numerical Weather Prediction (NWP) Models. The scheme is called Spectral Ice Habit Prediction System (SHIPS), and the goal is to retain growth history of ice particles in the Eulerian dynamics framework. It diagnoses characteristics of ice particles based on a series of particle property variables (PPVs) that reflect history of microphysieal processes and the transport between mass bins and air parcels in space. Therefore, categorization of ice particles typically used in bulk microphysical parameterization and traditional bin models is not necessary, so that errors that stem from the categorization can be avoided. SHIPS predicts polycrystals as well as hexagonal monocrystals based on empirically derived habit frequency and growth rate, and simulates the habit-dependent aggregation and riming processes by use of the stochastic collection equation with predicted PPVs. Idealized two dimensional simulations were performed with SHIPS in a NWP model. The predicted spatial distribution of ice particle habits and types, and evolution of particle size distributions showed good quantitative agreement with observation This comprehensive model of ice particle properties, distributions, and evolution in clouds can be used to better understand problems facing wide range of research disciplines, including microphysics processes, radiative transfer in a cloudy atmosphere, data assimilation, and weather modification.

  20. Simulating a Dynamic Antarctic Ice Sheet in the Early to Middle Miocene

    Science.gov (United States)

    Gasson, E.; DeConto, R.; Pollard, D.; Levy, R. H.

    2015-12-01

    There are a variety of sources of geological data that suggest major variations in the volume and extent of the Antarctic ice sheet during the early to middle Miocene. Simulating such variability using coupled climate-ice sheet models is problematic due to a strong hysteresis effect caused by height-mass balance feedback and albedo feedback. This results in limited retreat of the ice sheet once it has reached the continental size, as likely occurred prior to the Miocene. Proxy records suggest a relatively narrow range of atmospheric CO2 during the early to middle Miocene, which exacerbates this problem. We use a new climate forcing which accounts for ice sheet-climate feedbacks through an asynchronous GCM-RCM coupling, which is able to better resolve the narrow Antarctic ablation zone in warm climate simulations. When combined with recently suggested mechanisms for retreat into subglacial basins due to ice shelf hydrofracture and ice cliff failure, we are able to simulate large-scale variability of the Antarctic ice sheet in the Miocene. This variability is equivalent to a seawater oxygen isotope signal of ~0.5 ‰, or a sea level equivalent change of ~35 m, for a range of atmospheric CO2 between 280 - 500 ppm.

  1. The influence of atmospheric grid resolution in a climate model-forced ice sheet simulation

    Science.gov (United States)

    Lofverstrom, Marcus; Liakka, Johan

    2018-04-01

    Coupled climate-ice sheet simulations have been growing in popularity in recent years. Experiments of this type are however challenging as ice sheets evolve over multi-millennial timescales, which is beyond the practical integration limit of most Earth system models. A common method to increase model throughput is to trade resolution for computational efficiency (compromise accuracy for speed). Here we analyze how the resolution of an atmospheric general circulation model (AGCM) influences the simulation quality in a stand-alone ice sheet model. Four identical AGCM simulations of the Last Glacial Maximum (LGM) were run at different horizontal resolutions: T85 (1.4°), T42 (2.8°), T31 (3.8°), and T21 (5.6°). These simulations were subsequently used as forcing of an ice sheet model. While the T85 climate forcing reproduces the LGM ice sheets to a high accuracy, the intermediate resolution cases (T42 and T31) fail to build the Eurasian ice sheet. The T21 case fails in both Eurasia and North America. Sensitivity experiments using different surface mass balance parameterizations improve the simulations of the Eurasian ice sheet in the T42 case, but the compromise is a substantial ice buildup in Siberia. The T31 and T21 cases do not improve in the same way in Eurasia, though the latter simulates the continent-wide Laurentide ice sheet in North America. The difficulty to reproduce the LGM ice sheets in the T21 case is in broad agreement with previous studies using low-resolution atmospheric models, and is caused by a substantial deterioration of the model climate between the T31 and T21 resolutions. It is speculated that this deficiency may demonstrate a fundamental problem with using low-resolution atmospheric models in these types of experiments.

  2. Simulation studies of an air Cherenkov telescope, IceACT, for future IceCube surface extensions

    Energy Technology Data Exchange (ETDEWEB)

    Hansmann, Bengt; Auffenberg, Jan; Bekman, Ilja; Kemp, Julian; Roegen, Martin; Schaufel, Merlin; Stahlberg, Martin; Wiebusch, Christopher [III. Physikalisches Institut B, RWTH Aachen, Aachen (Germany); Bretz, Thomas; Hebbeker, Thomas; Middendorf, Lukas; Niggemann, Tim; Schumacher, Johannes [III. Physikalisches Institut A, RWTH Aachen, Aachen (Germany); Collaboration: IceCube-Collaboration

    2015-07-01

    IceACT is a compact air Cherenkov telescope using silicon photomultipliers. The Fresnel lens based design has been adopted from the fluorescence telescope FAMOUS. The goal of IceACT is the efficient detection of cosmic ray induced air showers above the IceCube Neutrino Observatory at the geographic South Pole. This allows to distinguish cosmic ray induced muons and neutrinos in the southern sky from astrophysical neutrinos in the deep ice detector. This leads to an increase in low-background astrophysical neutrinos of several dozen events per year for a detection threshold of several 100 TeV cosmic ray primary energy. To determine the actual telescope performance, dedicated CORSIKA air shower simulations incorporating the full Cherenkov light information are performed.

  3. Simulating mixed-phase Arctic stratus clouds: sensitivity to ice initiation mechanisms

    Directory of Open Access Journals (Sweden)

    G. McFarquhar

    2009-07-01

    Full Text Available The importance of Arctic mixed-phase clouds on radiation and the Arctic climate is well known. However, the development of mixed-phase cloud parameterization for use in large scale models is limited by lack of both related observations and numerical studies using multidimensional models with advanced microphysics that provide the basis for understanding the relative importance of different microphysical processes that take place in mixed-phase clouds. To improve the representation of mixed-phase cloud processes in the GISS GCM we use the GISS single-column model coupled to a bin resolved microphysics (BRM scheme that was specially designed to simulate mixed-phase clouds and aerosol-cloud interactions. Using this model with the microphysical measurements obtained from the DOE ARM Mixed-Phase Arctic Cloud Experiment (MPACE campaign in October 2004 at the North Slope of Alaska, we investigate the effect of ice initiation processes and Bergeron-Findeisen process (BFP on glaciation time and longevity of single-layer stratiform mixed-phase clouds. We focus on observations taken during 9–10 October, which indicated the presence of a single-layer mixed-phase clouds. We performed several sets of 12-h simulations to examine model sensitivity to different ice initiation mechanisms and evaluate model output (hydrometeors' concentrations, contents, effective radii, precipitation fluxes, and radar reflectivity against measurements from the MPACE Intensive Observing Period. Overall, the model qualitatively simulates ice crystal concentration and hydrometeors content, but it fails to predict quantitatively the effective radii of ice particles and their vertical profiles. In particular, the ice effective radii are overestimated by at least 50%. However, using the same definition as used for observations, the effective radii simulated and that observed were more comparable. We find that for the single-layer stratiform mixed-phase clouds simulated, process

  4. Simulating mixed-phase Arctic stratus clouds: sensitivity to ice initiation mechanisms

    Science.gov (United States)

    Sednev, I.; Menon, S.; McFarquhar, G.

    2009-07-01

    The importance of Arctic mixed-phase clouds on radiation and the Arctic climate is well known. However, the development of mixed-phase cloud parameterization for use in large scale models is limited by lack of both related observations and numerical studies using multidimensional models with advanced microphysics that provide the basis for understanding the relative importance of different microphysical processes that take place in mixed-phase clouds. To improve the representation of mixed-phase cloud processes in the GISS GCM we use the GISS single-column model coupled to a bin resolved microphysics (BRM) scheme that was specially designed to simulate mixed-phase clouds and aerosol-cloud interactions. Using this model with the microphysical measurements obtained from the DOE ARM Mixed-Phase Arctic Cloud Experiment (MPACE) campaign in October 2004 at the North Slope of Alaska, we investigate the effect of ice initiation processes and Bergeron-Findeisen process (BFP) on glaciation time and longevity of single-layer stratiform mixed-phase clouds. We focus on observations taken during 9-10 October, which indicated the presence of a single-layer mixed-phase clouds. We performed several sets of 12-h simulations to examine model sensitivity to different ice initiation mechanisms and evaluate model output (hydrometeors' concentrations, contents, effective radii, precipitation fluxes, and radar reflectivity) against measurements from the MPACE Intensive Observing Period. Overall, the model qualitatively simulates ice crystal concentration and hydrometeors content, but it fails to predict quantitatively the effective radii of ice particles and their vertical profiles. In particular, the ice effective radii are overestimated by at least 50%. However, using the same definition as used for observations, the effective radii simulated and that observed were more comparable. We find that for the single-layer stratiform mixed-phase clouds simulated, process of ice phase initiation

  5. The Potsdam Parallel Ice Sheet Model (PISM-PIK – Part 2: Dynamic equilibrium simulation of the Antarctic ice sheet

    Directory of Open Access Journals (Sweden)

    M. A. Martin

    2011-09-01

    Full Text Available We present a dynamic equilibrium simulation of the ice sheet-shelf system on Antarctica with the Potsdam Parallel Ice Sheet Model (PISM-PIK. The simulation is initialized with present-day conditions for bed topography and ice thickness and then run to steady state with constant present-day surface mass balance. Surface temperature and sub-shelf basal melt distribution are parameterized. Grounding lines and calving fronts are free to evolve, and their modeled equilibrium state is compared to observational data. A physically-motivated calving law based on horizontal spreading rates allows for realistic calving fronts for various types of shelves. Steady-state dynamics including surface velocity and ice flux are analyzed for whole Antarctica and the Ronne-Filchner and Ross ice shelf areas in particular. The results show that the different flow regimes in sheet and shelves, and the transition zone between them, are captured reasonably well, supporting the approach of superposition of SIA and SSA for the representation of fast motion of grounded ice. This approach also leads to a natural emergence of sliding-dominated flow in stream-like features in this new 3-D marine ice sheet model.

  6. Synthesis of HCN and HNC in Ion-Irradiated N2-Rich Ices

    Science.gov (United States)

    Moore, M. H.; Hudson, R. L.; Ferrante, R. F.

    2002-11-01

    Near-IR observations reveal that nitrogen-rich ice containing small amounts of methane, CH4, and carbon monoxide, CO, is abundant on the surfaces of Triton, a moon of Neptune, and Pluto (Cruikshank et al.. 1993; Owen et al., 1993). N2-rich apolar ices are also possible in some interstellar environments (Ehrenfreund et al., 1998). To investigate the radiation chemical behavior of N2-dominated ices we performed a systematic IR study of ion-irradiated N2-rich ices containing CH4 and CO. Experiments at 18 K, showed that HCN, HNC, and the reactive molecule diazomethane, CH2N2, formed along with several radicals. NH3 was also identified in irradiated N2 + CH4. Comparing results from similarly photolyzed ices (Bohn et al., 1994) shows that the significant difference between radiolysis and photolysis of these N2-dominated ices is that photolyzed ices do not form detectable HCN and HNC. Our experiments examined different N2/CH4 ratios, the half-life of CH4, possible HCN and HNC formation routes, and competing pathways in the presence of CO. Intrinsic band strengths (A(HCN) and A(HNC)) were measured and used to calculate nearly equal values of HCN and HNC yields in N2+CH4 irradiated ices. Low temperature results apply to interstellar ices. Reaction products that appear at 30-35 K are also expected to form and survive on the surfaces of Triton and Pluto and interstellar grains. We examined the evolution of ice features as species undergo acid-base (acids such as HCN, HNC, HNCO and a base NH3) reactions triggered by warming from 18 K to 30-35 K. We identified anions (OCN-, CN- and N3-) attributed to relatively stable salts in ices where NH4+ is the likely cation. These results also have an astrobiology implication since many of these products (HCN, HNC, HNCO, NH3, NH4OCN, and NH4CN) are reactants used in synthesis studies of bio- molecules such as amino acids and peptides.

  7. Heterogeneous condensation of ice mantle around silicate core grain in molecular cloud

    International Nuclear Information System (INIS)

    Hasegawa, H.

    1984-01-01

    Interstellar water ice grains are observed in the cold and dense regions such as molecular clouds, HII regions and protostellar objects. The water ice is formed from gas phase during the cooling stage of cosmic gas with solid grain surfaces of high temperature silicate minerals. It is a question whether the ice is formed through the homogeneous condensation process (as the ice alone) or the heterogeneous one (as the ice around the pre-existing high temperature mineral grains). (author)

  8. Absorption and emission characteristics of interstellar dust

    International Nuclear Information System (INIS)

    Allamandola, L.J.

    1984-01-01

    Molecular transitions which occur in the middle infrared region of the spectrum correspond with the characteristic frequencies of molecular vibrations. Thus, moderate resolution spectroscopy of the interstellar medium offers unique evidence about the molecules in the condensed and gaseous phases and their distribution. The author discusses the spectral properties of the condensed phase. However, in the astrophysical literature, it is difficult to find a qualitative description of the effects the solid state has on molecular vibrations, and since it is these which largely determine the spectroscopic properties of the interstellar dust, this discussion begins with a general description of these effects and then is directed toward describing the optical characteristics of the molecular ice component of the dust. The properties of this component of the dust are stressed, rather than those expected from more homogeneous components such as silicates, graphite, or amorphous carbon since these have been discussed in considerable detail elsewhere. (Auth.)

  9. Simulating Ice Shelf Response to Potential Triggers of Collapse Using the Material Point Method

    Science.gov (United States)

    Huth, A.; Smith, B. E.

    2017-12-01

    Weakening or collapse of an ice shelf can reduce the buttressing effect of the shelf on its upstream tributaries, resulting in sea level rise as the flux of grounded ice into the ocean increases. Here we aim to improve sea level rise projections by developing a prognostic 2D plan-view model that simulates the response of an ice sheet/ice shelf system to potential triggers of ice shelf weakening or collapse, such as calving events, thinning, and meltwater ponding. We present initial results for Larsen C. Changes in local ice shelf stresses can affect flow throughout the entire domain, so we place emphasis on calibrating our model to high-resolution data and precisely evolving fracture-weakening and ice geometry throughout the simulations. We primarily derive our initial ice geometry from CryoSat-2 data, and initialize the model by conducting a dual inversion for the ice viscosity parameter and basal friction coefficient that minimizes mismatch between modeled velocities and velocities derived from Landsat data. During simulations, we implement damage mechanics to represent fracture-weakening, and track ice thickness evolution, grounding line position, and ice front position. Since these processes are poorly represented by the Finite Element Method (FEM) due to mesh resolution issues and numerical diffusion, we instead implement the Material Point Method (MPM) for our simulations. In MPM, the ice domain is discretized into a finite set of Lagrangian material points that carry all variables and are tracked throughout the simulation. Each time step, information from the material points is projected to a Eulerian grid where the momentum balance equation (shallow shelf approximation) is solved similarly to FEM, but essentially treating the material points as integration points. The grid solution is then used to determine the new positions of the material points and update variables such as thickness and damage in a diffusion-free Lagrangian frame. The grid does not store

  10. Simulations of the Scandinavian ice sheet and its subsurface conditions

    International Nuclear Information System (INIS)

    Boulton, G.S.; Caban, P.; Hulton, N.

    1999-12-01

    An ice sheet model has been applied to an approximate flow line through the area of the Fennoscandian ice sheet. The modelled ice sheet fluctuations have been matched with stratigraphic evidence of Weichselian ice sheet fluctuation in order to simulate ice sheet attributes through time along the flowline. The model predicts extensive melting at the base of the ice sheet. This output has been used as an input to a simplified model of hydrogeology along the southern flank of the ice sheet so as to reconstruct patterns of subglacial groundwater flow. The output from the model is also used to estimate patterns of subglacial stress and strain. Results suggest that large scale subglacial groundwater catchment are formed which were quite different in extent from modern catchment; that fossil subglacial groundwaters should be found at sampling depths; and much fracturing in shallow bedrock in Sweden could be glacially generated

  11. Simulations of the Scandinavian ice sheet and its subsurface conditions

    Energy Technology Data Exchange (ETDEWEB)

    Boulton, G.S.; Caban, P.; Hulton, N. [Edinburgh Univ. (United Kingdom). Dept of Geology and Geophysics

    1999-12-01

    An ice sheet model has been applied to an approximate flow line through the area of the Fennoscandian ice sheet. The modelled ice sheet fluctuations have been matched with stratigraphic evidence of Weichselian ice sheet fluctuation in order to simulate ice sheet attributes through time along the flowline. The model predicts extensive melting at the base of the ice sheet. This output has been used as an input to a simplified model of hydrogeology along the southern flank of the ice sheet so as to reconstruct patterns of subglacial groundwater flow. The output from the model is also used to estimate patterns of subglacial stress and strain. Results suggest that large scale subglacial groundwater catchment are formed which were quite differentin extent from modern catchment; that fossil subglacial groundwaters should be found at sampling depths; and much fracturing in shallow bedrock in Sweden could be glacially generated.

  12. Impact of melt ponds on Arctic sea ice in past and future climates as simulated by MPI-ESM

    Directory of Open Access Journals (Sweden)

    Erich Roeckner

    2012-09-01

    Full Text Available The impact of melt ponds on Arctic sea ice is estimated from model simulations of the historical and future climate. The simulations were performed with and without the effect of melt ponds on sea ice melt, respectively. In the last thirty years of the historical simulations, melt ponds develop predominantly in the continental shelf regions and in the Canadian archipelago. Accordingly, the ice albedo in these regions is systematically smaller than in the no-pond simulations, the sea ice melt is enhanced, and both the ice concentration and ice thickness during the September minimum are reduced. Open ponds decrease the ice albedo, resulting in enhanced ice melt, less sea ice and further pond growth. This positive feedback entails a more realistic representation of the seasonal cycle of Northern Hemisphere sea ice area. Under the premise that the observed decline of Arctic sea ice over the period of modern satellite observations is mainly externally driven and, therefore, potentially predictable, both model versions underestimate the decline in Arctic sea ice. This presupposition, however, is challenged by our model simulations which show a distinct modulation of the downward Arctic sea ice trends by multidecadal variability. At longer time scales, an impact of pond activation on Arctic sea ice trends is more evident: In the Representative Concentration Pathway scenario RCP45, the September sea ice is projected to vanish by the end of the 21st century. In the active-pond simulation, this happens up to two decades earlier than in the no-pond simulations.

  13. Photochirogenesis: Photochemical models on the absolute asymmetric formation of amino acids in interstellar space

    DEFF Research Database (Denmark)

    Meinert, Cornelia; de Marcellus, Pierre; Le Sergeant d'Hendecourt, Louis

    2011-01-01

    Proteins of all living organisms including plants, animals, and humans are made up of amino acid monomers that show identical stereochemical L-configuration. Hypotheses for the origin of this symmetry breaking in biomolecules include the absolute asymmetric photochemistry model by which...... interstellar ultraviolet (UV) circularly polarized light (CPL) induces an enantiomeric excess in chiral organic molecules in the interstellar/circumstellar media. This scenario is supported by a) the detection of amino acids in the organic residues of UV-photo-processed interstellar ice analogues, b......) the occurrence of L-enantiomer-enriched amino acids in carbonaceous meteorites, and c) the observation of CPL of the same helicity over large distance scales in the massive star-forming region of Orion. These topics are of high importance in topical biophysical research and will be discussed in this review...

  14. Formation of complex precursors of amino acids by irradiation of simulated interstellar media with heavy ions

    Science.gov (United States)

    Kobayashi, K.; Suzuki, N.; Taniuchi, T.; Kaneko, T.; Yoshida, S.

    A wide variety of organic compounds have been detected in such extraterrestrial bodies as meteorites and comets Amino acids were identified in the extracts from Murchison meteorite and other carbonaceous chondrites It is hypothesized that these compounds are originally formed in ice mantles of interstellar dusts ISDs in molecular clouds by cosmic rays and ultraviolet light UV Formation of amino acid precursors by high energy protons or UV irradiation of simulated ISDs was reported by several groups The amino acid precursors were however not well-characterized We irradiated a frozen mixture of methanol ammonia and water with heavy ions to study possible organic compounds abiotically formed in molecular clouds by cosmic rays A mixture of methanol ammonia and water was irradiated with carbon beams 290 MeV u from a heavy ion accelerator HIMAC of National Institute of Radiological Sciences Japan Irradiation was performed either at room temperature liquid phase or at 77 K solid phase The products were characterized by gel filtration chromatography GFC FT-IR pyrolysis PY -GC MS etc Amino acids were analyzed by HPLC and GC MS after acid hydrolysis or the products Amino acids such as glycine and alanine were identified in the products in both the cases of liquid phase and solid phase irradiation Energy yields G-values of glycine were 0 014 liquid phase and 0 007 solid phase respectively Average molecular weights of the products were estimated as to 2300 in both the case Aromatic hydrocarbons N-containing heterocyclic

  15. Large and Small Droplet Impingement Data on Airfoils and Two Simulated Ice Shapes

    Science.gov (United States)

    Papadakis, Michael; Wong, See-Cheuk; Rachman, Arief; Hung, Kuohsing E.; Vu, Giao T.; Bidwell, Colin S.

    2007-01-01

    Water droplet impingement data were obtained at the NASA Glenn Icing Research Tunnel (IRT) for four wings and one wing with two simulated ice shapes. The wings tested include three 36-in. chord wings (MS(1)-317, GLC-305, and a NACA 652-415) and a 57-in. chord Twin Otter horizontal tail section. The simulated ice shapes were 22.5- and 45-min glaze ice shapes for the Twin Otter horizontal tail section generated using the LEWICE 2.2 ice accretion program. The impingement experiments were performed with spray clouds having median volumetric diameters of 11, 21, 79, 137, and 168 mm. Comparisons to the experimental data were generated which showed good agreement for the clean wings and ice shapes at lower drop sizes. For larger drop sizes LEWICE 2.2 over predicted the collection efficiencies due to droplet splashing effects which were not modeled in the program. Also for the more complex glaze ice shapes interpolation errors resulted in the over prediction of collection efficiencies in cove and shadow regions of ice shapes.

  16. NUMERICAL SIMULATION OF ICE ACCRETION ON AIRFOIL

    Directory of Open Access Journals (Sweden)

    Nicusor ALEXANDRESCU

    2009-09-01

    Full Text Available This work consists in the simulation of the ice accretion in the leading edge of aerodynamic profiles and our proposed model encompasses: geometry generation, calculation of the potential flow around the body, boundary layer thickness computation, water droplet trajectory computation, heat and mass balances and the consequent modification of the geometry by the ice growth. The flow calculation is realized with panel methods, using only segments defined over the body contour. The viscous effects are considered using the Karman-Pohlhausen method for the laminar boundary layer. The local heat transfer coefficient is obtained by applying the Smith-Spalding method for the thermal boundary layer. The ice accretion limits and the collection efficiency are determined by computing water droplet trajectories impinging the surface. The heat transfer process is analyzed with an energy and a mass balance in each segment defining the body. Finally, the geometry is modified by the addition of the computed ice thickness to the respective panel. The process by repeating all the steps. The model validation is done using a selection of problems with experimental solution, CIRA (the CESAR project. Hereinafter, results are obtained for different aerodynamic profiles, angles of attack and meteorological parameters

  17. Simulating the evolution of the Amundsen Sea Sector with a coupled ice-ocean model

    Science.gov (United States)

    Seroussi, H. L.; Nakayama, Y.; Menemenlis, D.; Larour, E. Y.; Morlighem, M.; Rignot, E. J.

    2017-12-01

    Ice shelves and floating glacier termini play an important role in the stability of ice sheets and interact strongly with the ocean. They account for much of the buttressing against the flow of inland glaciers that drain the Antarctic ice sheet. Changes in their geometry due to ice-front retreat, thinning or even collapse profoundly affect the flow of their tributary glaciers, which in turn affects the volume of grounded ice carried by these tributary glaciers into the ocean, and the extent of resulting sea level rise. Recent simulations of glaciers in Antarctica show that the largest climatic impact on ice dynamics is the rate of ice shelf melting, which rapidly affects glaciers' speed over several hundreds of kilometers upstream of the grounding line. These melting rates, however, as well as their spatial and temporal evolution remain largely unknown. In the absence of direct long-term observations, coupled ice-ocean models are the best available approach to address this question. In a previous study, we simulated the coupled ice-ocean system near Thwaites Glacier using a new two-way coupled system between the Massachusetts Institute of Technology general circulation model (MITgcm) and the Ice Sheet System Model (ISSM). Our results highlighted the impact of ocean conditions on glacier evolution and demonstrated the importance of simulating the coupled ice-ocean system to produce accurate melting rates under the ice shelf and at the grounding line. In this study, we focus on the entire Amundsen Sea sector, a region that experienced glacier acceleration, thinning and grounding line retreat over the past three decades. We investigate the feedbacks between changes in the ice and ocean, and the dynamic response of the glacier to changes in the ocean circulation. The simulations suggest that this region is likely to undergo substantial changes in the coming decades. This work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under a

  18. SURVIVAL OF INTERSTELLAR MOLECULES TO PRESTELLAR DENSE CORE COLLAPSE AND EARLY PHASES OF DISK FORMATION

    International Nuclear Information System (INIS)

    Hincelin, U.; Wakelam, V.; Hersant, F.; Guilloteau, S.; Commerçon, B.

    2013-01-01

    An outstanding question of astrobiology is the link between the chemical composition of planets, comets, and other solar system bodies and the molecules formed in the interstellar medium. Understanding the chemical and physical evolution of the matter leading to the formation of protoplanetary disks is an important step for this. We provide some new clues to this long-standing problem using three-dimensional chemical simulations of the early phases of disk formation: we interfaced the full gas-grain chemical model Nautilus with the radiation-magnetohydrodynamic model RAMSES, for different configurations and intensities of the magnetic field. Our results show that the chemical content (gas and ices) is globally conserved during the collapsing process, from the parent molecular cloud to the young disk surrounding the first Larson core. A qualitative comparison with cometary composition suggests that comets are constituted of different phases, some molecules being direct tracers of interstellar chemistry, while others, including complex molecules, seem to have been formed in disks, where higher densities and temperatures allow for an active grain surface chemistry. The latter phase, and its connection with the formation of the first Larson core, remains to be modeled

  19. A theory-based parameterization for heterogeneous ice nucleation and implications for the simulation of ice processes in atmospheric models

    Science.gov (United States)

    Savre, J.; Ekman, A. M. L.

    2015-05-01

    A new parameterization for heterogeneous ice nucleation constrained by laboratory data and based on classical nucleation theory is introduced. Key features of the parameterization include the following: a consistent and modular modeling framework for treating condensation/immersion and deposition freezing, the possibility to consider various potential ice nucleating particle types (e.g., dust, black carbon, and bacteria), and the possibility to account for an aerosol size distribution. The ice nucleating ability of each aerosol type is described using a contact angle (θ) probability density function (PDF). A new modeling strategy is described to allow the θ PDF to evolve in time so that the most efficient ice nuclei (associated with the lowest θ values) are progressively removed as they nucleate ice. A computationally efficient quasi Monte Carlo method is used to integrate the computed ice nucleation rates over both size and contact angle distributions. The parameterization is employed in a parcel model, forced by an ensemble of Lagrangian trajectories extracted from a three-dimensional simulation of a springtime low-level Arctic mixed-phase cloud, in order to evaluate the accuracy and convergence of the method using different settings. The same model setup is then employed to examine the importance of various parameters for the simulated ice production. Modeling the time evolution of the θ PDF is found to be particularly crucial; assuming a time-independent θ PDF significantly overestimates the ice nucleation rates. It is stressed that the capacity of black carbon (BC) to form ice in the condensation/immersion freezing mode is highly uncertain, in particular at temperatures warmer than -20°C. In its current version, the parameterization most likely overestimates ice initiation by BC.

  20. Destruction of C2H4O2 isomers in ice-phase by X-rays: Implication on the abundance of acetic acid and methyl formate in the interstellar medium

    Science.gov (United States)

    Rachid, Marina G.; Faquine, Karla; Pilling, S.

    2017-12-01

    The C2H4O2 isomers methyl formate (HCOOCH3), acetic acid (CH3COOH) and glycoaldehyde (HOCH2CHO) have been detected in molecular clouds in the interstellar medium, as well as, hot cores, hot corinos and around protostellar objects. However, their abundances are very different, being methyl formate more abundant than the other two isomers. This fact may be related to the different destruction by ionizing radiation of these molecules. The goal of this work is experimentally study the photodissociation processes of methyl formate and acetic acid ices when exposed to broadband soft X-ray from 6 up to 2000 eV. The experiments were performed coupled to the SGM beamline in the Brazilian Synchrotron Light Source (LNLS/CNPEM) at Campinas, Brazil. The simulated astrophysical ices (12 K) were monitored throughout the experiment using infrared vibrational spectroscopy (FTIR). The analysis of processed ices allowed the determination of the effective destruction cross sections of the parent molecules as well as the effective formation cross section of daughter molecular species such as CO, CO2, H2O, CH4 and H2CO (only for methyl formate) and the hydrocarbons C2H6 and C5H10 (only for acetic acid). The half-lives of molecules at ices toward young stellar objects (YSOs) and inside molecular clouds (e.g. Sgr B2 and W51) due to the presence of incoming soft X-rays were estimated. We determined the effective formation rate and the branching ratios for assigned daughter species after the establishment of a chemical equilibrium. The main product from photodissociation of both methyl formate and acetic acid is CO, that can be formed by recombination of ions, formed during the photodissociation, in the ice surface. The relative abundance between methyl formate and acetic acid (NCH3COOH/NHCOOCH3) in different astronomical scenarios and their column density evolution in the presence of X-rays were calculated. Our results suggest that such radiation field can be one of the factors that

  1. Gas-grain chemistry in cold interstellar cloud cores with a microscopic Monte Carlo approach to surface chemistry

    Science.gov (United States)

    Chang, Q.; Cuppen, H. M.; Herbst, E.

    2007-07-01

    Aims:We have recently developed a microscopic Monte Carlo approach to study surface chemistry on interstellar grains and the morphology of ice mantles. The method is designed to eliminate the problems inherent in the rate-equation formalism to surface chemistry. Here we report the first use of this method in a chemical model of cold interstellar cloud cores that includes both gas-phase and surface chemistry. The surface chemical network consists of a small number of diffusive reactions that can produce molecular oxygen, water, carbon dioxide, formaldehyde, methanol and assorted radicals. Methods: The simulation is started by running a gas-phase model including accretion onto grains but no surface chemistry or evaporation. The starting surface consists of either flat or rough olivine. We introduce the surface chemistry of the three species H, O and CO in an iterative manner using our stochastic technique. Under the conditions of the simulation, only atomic hydrogen can evaporate to a significant extent. Although it has little effect on other gas-phase species, the evaporation of atomic hydrogen changes its gas-phase abundance, which in turn changes the flux of atomic hydrogen onto grains. The effect on the surface chemistry is treated until convergence occurs. We neglect all non-thermal desorptive processes. Results: We determine the mantle abundances of assorted molecules as a function of time through 2 × 105 yr. Our method also allows determination of the abundance of each molecule in specific monolayers. The mantle results can be compared with observations of water, carbon dioxide, carbon monoxide, and methanol ices in the sources W33A and Elias 16. Other than a slight underproduction of mantle CO, our results are in very good agreement with observations.

  2. Surface science investigations of photoprocesses in model interstellar ices

    International Nuclear Information System (INIS)

    Thrower, J. D.; Collings, M. P.; McCoustra, M. R. S.; Burke, D. J.; Brown, W. A.; Dawes, A.; Holtom, P. D.; Kendall, P.; Mason, N. J.; Jamme, F.; Fraser, H. J.; Clark, I. P.; Parker, A. W.

    2008-01-01

    The kinetic energy of benzene and water molecules photodesorbed from astrophysically relevant ices on a sapphire substrate under irradiation by a UV laser tuned to the S 1 (leftarrow)S 0 π→π* transition of benzene has been measured using time-of-flight mass spectrometry. Three distinct photodesorption mechanisms have been identified--a direct adsorbate-mediated desorption of benzene, an indirect adsorbate-mediated desorption of water, and a substrate-mediated desorption of both benzene and water. The translational temperature of each desorbing population was well in excess of the ambient temperature of the ice matrix

  3. Three-dimensional simulations of turbulent spectra in the local interstellar medium

    Directory of Open Access Journals (Sweden)

    D. Shaikh

    2007-07-01

    Full Text Available Three-dimensional time dependent numerical simulations of compressible magnetohydrodynamic fluids describing super-Alfvénic, supersonic and strongly magnetized space and laboratory plasmas show a nonlinear relaxation towards a state of near incompressibility. The latter is characterized essentially by a subsonic turbulent Mach number. This transition is mediated dynamically by disparate spectral energy dissipation rates in compressible magnetosonic and shear Alfvénic modes. Nonlinear cascades lead to super-Alfvénic turbulent motions decaying to a sub-Alfvénic regime that couples weakly with (magnetoacoustic cascades. Consequently, the supersonic plasma motion is transformed into highly subsonic motion and density fluctuations experience a passive convection. This model provides a self-consistent explaination of the ubiquitous nature of incompressible magnetoplasma fluctuations in the solar wind and the interstellar medium.

  4. On the potential of computational methods and numerical simulation in ice mechanics

    International Nuclear Information System (INIS)

    Bergan, Paal G; Cammaert, Gus; Skeie, Geir; Tharigopula, Venkatapathi

    2010-01-01

    This paper deals with the challenge of developing better methods and tools for analysing interaction between sea ice and structures and, in particular, to be able to calculate ice loads on these structures. Ice loads have traditionally been estimated using empirical data and 'engineering judgment'. However, it is believed that computational mechanics and advanced computer simulations of ice-structure interaction can play an important role in developing safer and more efficient structures, especially for irregular structural configurations. The paper explains the complexity of ice as a material in computational mechanics terms. Some key words here are large displacements and deformations, multi-body contact mechanics, instabilities, multi-phase materials, inelasticity, time dependency and creep, thermal effects, fracture and crushing, and multi-scale effects. The paper points towards the use of advanced methods like ALE formulations, mesh-less methods, particle methods, XFEM, and multi-domain formulations in order to deal with these challenges. Some examples involving numerical simulation of interaction and loads between level sea ice and offshore structures are presented. It is concluded that computational mechanics may prove to become a very useful tool for analysing structures in ice; however, much research is still needed to achieve satisfactory reliability and versatility of these methods.

  5. THE PRESSURE OF THE STAR-FORMING INTERSTELLAR MEDIUM IN COSMOLOGICAL SIMULATIONS

    International Nuclear Information System (INIS)

    Munshi, Ferah; Quinn, Thomas R.; Governato, Fabio; Christensen, Charlotte; Wadsley, James; Loebman, Sarah; Shen, Sijing

    2014-01-01

    We examine the pressure of the star-forming interstellar medium (ISM) of Milky-Way-sized disk galaxies using fully cosmological SPH+N-body, high-resolution simulations. These simulations include explicit treatment of metal-line cooling in addition to dust and self-shielding, H 2 -based star formation. The four simulated halos have masses ranging from a few times 10 10 to nearly 10 12 solar masses. Using a kinematic decomposition of these galaxies into present-day bulge and disk components, we find that the typical pressure of the star-forming ISM in the present-day bulge is higher than that in the present-day disk by an order of magnitude. We also find that the pressure of the star-forming ISM at high redshift is, on average, higher than ISM pressures at low redshift. This explains why the bulge forms at higher pressures: the disk assembles at lower redshift when the ISM exhibits lower pressure and the bulge forms at high redshift when the ISM has higher pressure. If ISM pressure and IMF variation are tied together, these results could indicate a time-dependent IMF in Milky-Way-like systems as well as a different IMF in the bulge and the disk

  6. PAHs in the Ices of Saturn's Satellites: Connections to the Solar Nebula and the Interstellar Medium

    Science.gov (United States)

    Cruikshank, Dale P.; Pendleton, Yvonne J.

    2015-01-01

    Aliphatic hydrocarbons and PAHs have been observed in the interstellar medium (e.g., Allamandola et al. 1985, Pendleton et al. 1994, Pendleton & Allamandola 2002, Tielens 2013, Kwok 2008, Chiar & Pendleton 2008) The inventory of organic material in the ISM was likely incorporated into the molecular cloud in which the solar nebula condensed, contributing to the feedstock for the formation of the Sun, major planets, and the smaller icy bodies in the region outside Neptune's orbit (transneptunian objects, or TNOs). Additional organic synthesis occurred in the solar nebula (Ciesla & Sandford 2012). Saturn's satellites Phoebe, Iapetus, and Hyperion open a window to the composition of one class of TNO as revealed by the near-infrared mapping spectrometer (VIMS) on the Cassini spacecraft at Saturn. Phoebe (mean diameter 213 km) is a former TNO now orbiting Saturn (Johnson & Lunine 2005). VIMS spectral maps of Phoebe's surface reveal a complex organic spectral signature consisting of prominent aromatic (CH) and aliphatic hydrocarbon (=CH2, -CH3) absorption bands (3.2-3.6 micrometers). Phoebe is the source of a huge debris ring encircling Saturn, and from which particles ((is) approximately 5-20 micrometers size) spiral inward toward Saturn (Verbiscer et al. 2009). They encounter Iapetus and Hyperion where they mix with and blanket the native H2O ice of those two bodies. Quantitative analysis of the hydrocarbon bands on Iapetus demonstrates that aromatic CH is approximately 10 times as abundant as aliphatic CH2+CH3, significantly exceeding the strength of the aromatic signature in interplanetary dust particles, comet particles, and in carbonaceous meteorites (Cruikshank et al. 2014). A similar excess of aromatics over aliphatics is seen in the qualitative analysis of Hyperion and Phoebe itself (Dalle Ore et al. 2012). The Iapetus aliphatic hydrocarbons show CH2/CH3 (is) approximately 4, which is larger than the value found in the diffuse ISM ((is) approximately 2

  7. SOFT X-RAY IRRADIATION OF H{sub 2}S ICE AND THE PRESENCE OF S{sub 2} IN COMETS

    Energy Technology Data Exchange (ETDEWEB)

    Jimenez-Escobar, A.; Munoz Caro, G. M. [Centro de Astrobiologia (CSIC-INTA), Carretera de Ajalvir, km 4, Torrejon de Ardoz, 28850 Madrid (Spain); Ciaravella, A.; Candia, R.; Micela, G. [INAF-Osservatorio Astronomico di Palermo, P.za Parlamento 1, 90134 Palermo (Italy); Cecchi-Pestellini, C., E-mail: munozcg@cab.inta-csic.es [INAF-Osservatorio Astronomico di Cagliari, Strada n.54, Loc. Poggio dei Pini, I-09012 Capoterra (Canada) (Italy)

    2012-06-01

    Little is known about the effects of X-rays in interstellar ices. To understand the sulfur depletion in dense clouds and the presence of S{sub 2} in comets, we simulated experimentally the soft X-ray processing (0.3 keV) of H{sub 2}S ice for the first time. Experiments were performed under ultrahigh vacuum conditions at 8 K using infrared and quadrupole mass spectrometry to monitor the solid and gas phases, respectively. A UV irradiation experiment using a similar dose was made for comparison. After X-ray irradiation, an infrared absorption appears near 4.0 {mu}m which is attributed to H{sub 2}S{sub 2} formation in the ice. This identification is also supported by the desorption at 133 K of m/z 66, 65, 64, corresponding to the mass fragments of H{sub 2}S{sub 2}. The H{sub 2}S{sub 2} species is expected to be present in interstellar and cometary ices that were processed by X-rays. Further irradiation leads to dissociation of this molecule forming S{sub 2} and larger S-molecules up to S{sub 8}, which may explain the depletion of sulfur in dense clouds. CS{sub 2} was so far the parent molecule proposed for S{sub 2} formation in comets. But the abundance of H{sub 2}S{sub 2}, formed by irradiation of pure H{sub 2}S or H{sub 2}S in an H{sub 2}O-ice matrix, should be larger than that of CS{sub 2} in the ice, the latter requiring a carbon source for its formation. Based on our experimental results, we propose that S{sub 2} in comets could be formed by dissociation of H{sub 2}S{sub 2} in the ice.

  8. A transient fully coupled climate-ice-sheet simulation of the last glacial inception

    Science.gov (United States)

    Lofverstrom, M.; Otto-Bliesner, B. L.; Lipscomb, W. H.; Fyke, J. G.; Marshall, S.; Sacks, B.; Brady, E. C.

    2017-12-01

    The last glacial inception occurred around 115 ka, following a relative minimum in the Northern Hemisphere summer insolation. It is believed that small and spatially separated ice caps initially formed in the high elevation regions of northern Canada, Scandinavia, and along the Siberian Arctic coast. These ice caps subsequently migrated down in the valleys where they coalesced and formed the initial seeds of the large coherent ice masses that covered the northern parts of the North American and Eurasian continents over most of the last glacial cycle. Sea level records show that the initial growth period lasted for about 10 kyrs, and the resulting ice sheets may have lowered the global sea level by as much as 30 to 50 meters. Here we examine the transient climate system evolution over the period between 118 and 110 ka, using the fully coupled Community Earth System Model, version 2 (CESM2). This model features a two-way coupled high-resolution (4x4 km) ice-sheet component (Community Ice Sheet model, version 2; CISM2) that simulates ice sheets as an interactive component of the climate system. We impose a transient forcing protocol where the greenhouse gas concentrations and the orbital parameters follow the nominal year in the simulation; the model topography is also dynamically evolving in order to reflect changes in ice elevation throughout the simulation. The analysis focuses on how the climate system evolves over this time interval, with a special focus on glacial inception in the high-latitude continents. Results will highlight how the evolving ice sheets compare to data and previous model based reconstructions.

  9. Stardust Interstellar Preliminary Examination X: Impact Speeds and Directions of Interstellar Grains on the Stardust Dust Collector

    Science.gov (United States)

    Sterken, Veerle J.; Westphal, Andrew J.; Altobelli, Nicolas; Grun, Eberhard; Hillier, Jon K.; Postberg, Frank; Allen, Carlton; Stroud, Rhonda M.; Sandford, S. A.; Zolensky, Michael E.

    2014-01-01

    On the basis of an interstellar dust model compatible with Ulysses and Galileo observations, we calculate and predict the trajectories of interstellar dust (ISD) in the solar system and the distribution of the impact speeds, directions, and flux of ISD particles on the Stardust Interstellar Dust Collector during the two collection periods of the mission. We find that the expected impact velocities are generally low (less than 10 km per second) for particles with the ratio of the solar radiation pressure force to the solar gravitational force beta greater than 1, and that some of the particles will impact on the cometary side of the collector. If we assume astronomical silicates for particle material and a density of 2 grams per cubic centimeter, and use the Ulysses measurements and the ISD trajectory simulations, we conclude that the total number of (detectable) captured ISD particles may be on the order of 50. In companion papers in this volume, we report the discovery of three interstellar dust candidates in the Stardust aerogel tiles. The impact directions and speeds of these candidates are consistent with those calculated from our ISD propagation model, within the uncertainties of the model and of the observations.

  10. The Interstellar Medium

    CERN Document Server

    Lequeux, James

    2005-01-01

    Describing interstellar matter in our galaxy in all of its various forms, this book also considers the physical and chemical processes that are occurring within this matter. The first seven chapters present the various components making up the interstellar matter and detail the ways that we are able to study them. The following seven chapters are devoted to the physical, chemical and dynamical processes that control the behaviour of interstellar matter. These include the instabilities and cloud collapse processes that lead to the formation of stars. The last chapter summarizes the transformations that can occur between the different phases of the interstellar medium. Emphasizing methods over results, "The Interstellar Medium" is written for graduate students, for young astronomers, and also for any researchers who have developed an interest in the interstellar medium.

  11. Stardust Interstellar Preliminary Examination (ISPE)

    Science.gov (United States)

    Westphal, A. J.; Allen, C.; Bajt, S.; Basset, R.; Bastien, R.; Bechtel, H.; Bleuet, P.; Borg, J.; Brenker F.; Bridges, J.

    2009-01-01

    In January 2006 the Stardust sample return capsule returned to Earth bearing the first solid samples from a primitive solar system body, C omet 81P/Wild2, and a collector dedicated to the capture and return o f contemporary interstellar dust. Both collectors were approximately 0.1m(exp 2) in area and were composed of aerogel tiles (85% of the co llecting area) and aluminum foils. The Stardust Interstellar Dust Col lector (SIDC) was exposed to the interstellar dust stream for a total exposure factor of 20 m(exp 2-) day during two periods before the co metary encounter. The Stardust Interstellar Preliminary Examination ( ISPE) is a three-year effort to characterize the collection using no ndestructive techniques. The ISPE consists of six interdependent proj ects: (1) Candidate identification through automated digital microsco py and a massively distributed, calibrated search (2) Candidate extr action and photodocumentation (3) Characterization of candidates thro ugh synchrotronbased FourierTranform Infrared Spectroscopy (FTIR), S canning XRay Fluoresence Microscopy (SXRF), and Scanning Transmission Xray Microscopy (STXM) (4) Search for and analysis of craters in f oils through FESEM scanning, Auger Spectroscopy and synchrotronbased Photoemission Electron Microscopy (PEEM) (5) Modeling of interstell ar dust transport in the solar system (6) Laboratory simulations of h ypervelocity dust impacts into the collecting media

  12. Matrix isolation as a tool for studying interstellar chemical reactions

    Science.gov (United States)

    Ball, David W.; Ortman, Bryan J.; Hauge, Robert H.; Margrave, John L.

    1989-01-01

    Since the identification of the OH radical as an interstellar species, over 50 molecular species were identified as interstellar denizens. While identification of new species appears straightforward, an explanation for their mechanisms of formation is not. Most astronomers concede that large bodies like interstellar dust grains are necessary for adsorption of molecules and their energies of reactions, but many of the mechanistic steps are unknown and speculative. It is proposed that data from matrix isolation experiments involving the reactions of refractory materials (especially C, Si, and Fe atoms and clusters) with small molecules (mainly H2, H2O, CO, CO2) are particularly applicable to explaining mechanistic details of likely interstellar chemical reactions. In many cases, matrix isolation techniques are the sole method of studying such reactions; also in many cases, complexations and bond rearrangements yield molecules never before observed. The study of these reactions thus provides a logical basis for the mechanisms of interstellar reactions. A list of reactions is presented that would simulate interstellar chemical reactions. These reactions were studied using FTIR-matrix isolation techniques.

  13. Chemical reactivities of some interstellar molecules

    Energy Technology Data Exchange (ETDEWEB)

    Chadha, M S

    1980-01-01

    Work in the area of chemical evolution during the last 25 years has revealed the formation of a large number of biologically important molecules produced from simple starting materials under relatively simple experimental conditions. Much of this work has resulted from studies under atmospheres simulating that of the primitive earth or other planets. During the last decade, progress has also been made in the identification of chemical constituents of interstellar medium. A number of these molecules are the same as those identified in laboratory experiments. Even though the conditions of the laboratory experiments are vastly different from those of the cool, low-density interstellar medium, some of the similarities in composition are too obvious to go unnoticed. The present paper highlights some of the similarities in the composition of prebiotic molecules and those discovered in the interstellar medium. Also the chemical reactions which some of the common molecules e.g., NH3, HCN, H2CO, HC(triple bond)-C-CN etc. can undergo are surveyed.

  14. IN-SITU PROBING OF RADIATION-INDUCED PROCESSING OF ORGANICS IN ASTROPHYSICAL ICE ANALOGS—NOVEL LASER DESORPTION LASER IONIZATION TIME-OF-FLIGHT MASS SPECTROSCOPIC STUDIES

    International Nuclear Information System (INIS)

    Gudipati, Murthy S.; Yang Rui

    2012-01-01

    Understanding the evolution of organic molecules in ice grains in the interstellar medium (ISM) under cosmic rays, stellar radiation, and local electrons and ions is critical to our understanding of the connection between ISM and solar systems. Our study is aimed at reaching this goal of looking directly into radiation-induced processing in these ice grains. We developed a two-color laser-desorption laser-ionization time-of-flight mass spectroscopic method (2C-MALDI-TOF), similar to matrix-assisted laser desorption and ionization time-of-flight (MALDI-TOF) mass spectroscopy. Results presented here with polycyclic aromatic hydrocarbon (PAH) probe molecules embedded in water-ice at 5 K show for the first time that hydrogenation and oxygenation are the primary chemical reactions that occur in astrophysical ice analogs when subjected to Lyα radiation. We found that hydrogenation can occur over several unsaturated bonds and the product distribution corresponds to their stabilities. Multiple hydrogenation efficiency is found to be higher at higher temperatures (100 K) compared to 5 K—close to the interstellar ice temperatures. Hydroxylation is shown to have similar efficiencies at 5 K or 100 K, indicating that addition of O atoms or OH radicals to pre-ionized PAHs is a barrierless process. These studies—the first glimpses into interstellar ice chemistry through analog studies—show that once accreted onto ice grains PAHs lose their PAH spectroscopic signatures through radiation chemistry, which could be one of the reason for the lack of PAH detection in interstellar ice grains, particularly the outer regions of cold, dense clouds or the upper molecular layers of protoplanetary disks.

  15. Effect of retreating sea ice on Arctic cloud cover in simulated recent global warming

    Directory of Open Access Journals (Sweden)

    M. Abe

    2016-11-01

    Full Text Available This study investigates the effect of sea ice reduction on Arctic cloud cover in historical simulations with the coupled atmosphere–ocean general circulation model MIROC5. Arctic sea ice has been substantially retreating since the 1980s, particularly in September, under simulated global warming conditions. The simulated sea ice reduction is consistent with satellite observations. On the other hand, Arctic cloud cover has been increasing in October, with about a 1-month lag behind the sea ice reduction. The delayed response leads to extensive sea ice reductions because the heat and moisture fluxes from the underlying open ocean into the atmosphere are enhanced. Sensitivity experiments with the atmospheric part of MIROC5 clearly show that sea ice reduction causes increases in cloud cover. Arctic cloud cover increases primarily in the lower troposphere, but it decreases in the near-surface layers just above the ocean; predominant temperature rises in these near-surface layers cause drying (i.e., decreases in relative humidity, despite increasing moisture flux. Cloud radiative forcing due to increases in cloud cover in autumn brings an increase in the surface downward longwave radiation (DLR by approximately 40–60 % compared to changes in clear-sky surface DLR in fall. These results suggest that an increase in Arctic cloud cover as a result of reduced sea ice coverage may bring further sea ice retreat and enhance the feedback processes of Arctic warming.

  16. Simulation of optimal arctic routes using a numerical sea ice model based on an ice-coupled ocean circulation method

    Directory of Open Access Journals (Sweden)

    Jong-Ho Nam

    2013-06-01

    Full Text Available Ever since the Arctic region has opened its mysterious passage to mankind, continuous attempts to take advantage of its fastest route across the region has been made. The Arctic region is still covered by thick ice and thus finding a feasible navigating route is essential for an economical voyage. To find the optimal route, it is necessary to establish an efficient transit model that enables us to simulate every possible route in advance. In this work, an enhanced algorithm to determine the optimal route in the Arctic region is introduced. A transit model based on the simulated sea ice and environmental data numerically modeled in the Arctic is developed. By integrating the simulated data into a transit model, further applications such as route simulation, cost estimation or hindcast can be easily performed. An interactive simulation system that determines the optimal Arctic route using the transit model is developed. The simulation of optimal routes is carried out and the validity of the results is discussed.

  17. Do Climate Models Simulate the Right Sea Ice Trends for the Wrong Reasons?

    Science.gov (United States)

    Rosenblum, E. J.; Eisenman, I.

    2016-02-01

    Observations indicate that the Arctic sea ice cover is rapidly retreating while the Antarctic sea ice cover is steadily expanding. State-of-the-art climate models, by contrast, predict a moderate decrease in both the Arctic and Antarctic sea ice cover. A number of recent studies have attributed this discrepancy in each hemisphere to natural variability. Here we examine sea ice changes during 1979-2013 in simulations from the most recent Coupled Model Intercomparison Project as well as the Community Earth System Model Large Ensemble. We find that after accounting for biases in the level of global warming in each simulation, the possibility that natural variability alone could explain the difference between models and observations becomes exceedingly small. This suggests instead that there is a systematic bias in the climate models or possibly the observations.

  18. Zonal Detached-Eddy Simulation of Turbulent Unsteady Flow over Iced Airfoils

    KAUST Repository

    Zhang, Yue

    2015-07-23

    This paper presentsamultiscale finite-element formulation for the second modeofzonal detached-eddy simulation. The multiscale formulation corrects the lack of stability of the standard Galerkin formulation by incorporating the effect of unresolved scales to the grid (resolved) scales. The stabilization terms arise naturally and are free of userdefined stability parameters. Validation of the method is accomplished via the turbulent flow over tandem cylinders. The boundary-layer separation, free shear-layer rollup, vortex shedding from the upstream cylinder, and interaction with the downstream cylinder are well reproduced. Good agreement with experimental measurements gives credence to the accuracy of zonal detached-eddy simulation in modeling turbulent separated flows. A comprehensive study is then conducted on the performance degradation of ice-contaminated airfoils. NACA 23012 airfoil with a spanwise ice ridge and Gates Learjet Corporation-305 airfoil with a leading-edge horn-shape glaze ice are selected for investigation. Appropriate spanwise domain size and sufficient grid density are determined to enhance the reliability of the simulations. A comparison of lift coefficient and flowfield variables demonstrates the added advantage that the zonal detached-eddy simulation model brings to the Spalart-Allmaras turbulence model. Spectral analysis and instantaneous visualization of turbulent structures are also highlighted via zonal detached-eddy simulation. Copyright © 2015 by the CFD Lab of McGill University. Published by the American Institute of Aeronautics and Astronautics, Inc.

  19. Photochemistry of Coronene in Cosmic Water Ice Analogs at Different Concentrations

    Science.gov (United States)

    de Barros, A. L. F.; Mattioda, A. L.; Ricca, A.; Cruz-Diaz, G. A.; Allamandola, L. J.

    2017-10-01

    This work presents the photochemistry of ultraviolet (UV) irradiated coronene in water ices at 15 K studied using mid-infrared Fourier transform (FTIR) spectroscopy for C24H12:H2O at concentrations of (1:50), (1:150), (1:200), (1:300), and (1:400). Previous UV irradiation studies of anthracene:H2O, pyrene:H2O, and benzo[ghi]perylene:H2O ices at 15 K have shown that aromatic alcohols and ketones, as well as CO2 and H2CO, are formed at very low temperatures. Likewise, here, in addition to the coronene cation, hydroxy-, keto-, and protonated coronene (coronene H+) are formed. The rate constants for the decay of neutral coronene and for the formation of photoproducts have been derived. It is shown that Polycyclic Aromatic Hydrocarbons (PAHs) and their UV induced PAH:H2O photoproducts have mid-infrared spectroscopic signatures in the 5-8 μm region that can contribute to the interstellar ice components described by Boogert et al. as C1-C5. Our results suggest that oxygenated and hydrogenated PAHs could be in UV-irradiated regions of the interstellar medium where water-rich ices are important.

  20. Spectrally-resolved UV photodesorption of CH4 in pure and layered ices

    Science.gov (United States)

    Dupuy, R.; Bertin, M.; Féraud, G.; Michaut, X.; Jeseck, P.; Doronin, M.; Philippe, L.; Romanzin, C.; Fillion, J.-H.

    2017-07-01

    Context. Methane is among the main components of the ice mantles of interstellar dust grains, where it is at the start of a rich solid-phase chemical network. Quantification of the photon-induced desorption yield of these frozen molecules and understanding of the underlying processes is necessary to accurately model the observations and the chemical evolution of various regions of the interstellar medium. Aims: This study aims at experimentally determining absolute photodesorption yields for the CH4 molecule as a function of photon energy. The influence of the ice composition is also investigated. By studying the methane desorption from layered CH4:CO ice, indirect desorption processes triggered by the excitation of the CO molecules are monitored and quantified. Methods: Tunable monochromatic vacuum ultraviolet light (VUV) light from the DESIRS beamline of the SOLEIL synchrotron is used in the 7-13.6 eV (177-91 nm) range to irradiate pure CH4 or layers of CH4 deposited on top of CO ice samples. The release of species in the gas phase is monitored by quadrupole mass spectrometry, and absolute photodesorption yields of intact CH4 are deduced. Results: CH4 photodesorbs for photon energies higher than 9.1 eV ( 136 nm). The photodesorption spectrum follows the absorption spectrum of CH4, which confirms a desorption mechanism mediated by electronic transitions in the ice. When it is deposited on top of CO, CH4 desorbs between 8 and 9 eV with a pattern characteristic of CO absorption, indicating desorption induced by energy transfer from CO molecules. Conclusions: The photodesorption of CH4 from pure ice in various interstellar environments is around 2.0 ± 1.0 × 10-3 molecules per incident photon. Results on CO-induced indirect desorption of CH4 provide useful insights for the generalization of this process to other molecules co-existing with CO in ice mantles.

  1. Measuring the level of interstellar inheritance in the solar protoplanetary disk

    Science.gov (United States)

    Alexander, Conel M. O'd.; Nittler, Larry R.; Davidson, Jemma; Ciesla, Fred J.

    2017-09-01

    The timing and extent to which the initial interstellar material was thermally processed provide fundamental constraints for models of the formation and early evolution of the solar protoplanetary disk. We argue that the nonsolar (solar Δ17O ≈ -29‰) and near-terrestrial (Δ17O ≈ 0‰) O-isotopic compositions of the Earth and most extraterrestrial materials (Moon, Mars, asteroids, and comet dust) were established very early by heating of regions of the disk that were modestly enriched (dust/gas ≥ 5-10 times solar) in primordial silicates (Δ17O ≈ -29‰) and water-dominated ice (Δ17O ≈ 24‰) relative to the gas. Such modest enrichments could be achieved by grain growth and settling of dust to the midplane in regions where the levels of turbulence were modest. The episodic heating of the disk associated with FU Orionis outbursts were the likely causes of this early thermal processing of dust. We also estimate that at the time of accretion the CI chondrite and interplanetary dust particle parent bodies were composed of 5-10% of pristine interstellar material. The matrices of all chondrites included roughly similar interstellar fractions. Whether this interstellar material avoided the thermal processing experienced by most dust during FU Orionis outbursts or was accreted by the disk after the outbursts ceased to be important remains to be established.

  2. PHOTOCHEMISTRY OF POLYCYCLIC AROMATIC HYDROCARBONS IN COSMIC WATER ICE: THE ROLE OF PAH IONIZATION AND CONCENTRATION

    International Nuclear Information System (INIS)

    Cook, Amanda M.; Mattioda, Andrew L.; Roser, Joseph; Bregman, Jonathan; Ricca, Alessandra; Allamandola, Louis J.; Bouwman, Jordy; Linnartz, Harold

    2015-01-01

    Infrared spectroscopic studies of ultraviolet (UV) irradiated, water-rich, cosmic ice analogs containing small polycyclic aromatic hydrocarbons (PAHs) are described. The irradiation studies of anthracene:H 2 O, pyrene:H 2 O, and benzo[ghi]perylene:H 2 O ices (14 K) at various concentrations reported by Bouwman et al. are extended. While aromatic alcohols and ketones have been reported in residues after irradiated PAH:H 2 O ices were warmed to 270 K, it was not known if they formed during ice irradiation or during warm-up when reactants interact as H 2 O sublimes. Recent work has shown that they form in low temperature ice. Using DFT computed IR spectra to identify photoproducts and PAH cations, we tentatively identify the production of specific alcohols [PAH(OH) n ] and quinones [PAH(O) n ] for all PAH:H 2 O ices considered here. Little evidence is found for hydrogenation at 14 K, consistent with the findings of Gudipati and Yang. Addition of O and OH to the parent PAH is the dominant photochemical reaction, but PAH erosion to smaller PAHs (producing CO 2 and H 2 CO) is also important. DFT spectra are used to assess the contribution of PAH-related species to interstellar absorption features from 5 to 9 μm. The case is made that PAH cations are important contributors to the C2 component and PAH(OH) n and PAH(O) n to the C5 component described by Boogert et al. Thus, interstellar ices should contain neutral and ionized PAHs, alcohols, ketones and quinones at the ∼2%-4% level relative to H 2 O. PAHs, their photoproducts, and ion-mediated processes should therefore be considered when modeling interstellar ice processes

  3. PHOTOCHEMISTRY OF POLYCYCLIC AROMATIC HYDROCARBONS IN COSMIC WATER ICE: THE ROLE OF PAH IONIZATION AND CONCENTRATION

    Energy Technology Data Exchange (ETDEWEB)

    Cook, Amanda M.; Mattioda, Andrew L.; Roser, Joseph; Bregman, Jonathan [NASA Ames Research Center, PO Box 1, M/S 245-6, Moffett Field, CA 94035 (United States); Ricca, Alessandra; Allamandola, Louis J. [SETI Institute, 189 North Bernardo Avenue, Mountain View, CA 94043 (United States); Bouwman, Jordy [Radboud University Nijmegen, Institute for Molecules and Materials, Toernooiveld 5, 6525 ED Nijmegen (Netherlands); Linnartz, Harold [Sackler Laboratory for Astrophysics, Leiden Observatory, University of Leiden, PO Box 9513, NL2300 RA Leiden (Netherlands)

    2015-01-20

    Infrared spectroscopic studies of ultraviolet (UV) irradiated, water-rich, cosmic ice analogs containing small polycyclic aromatic hydrocarbons (PAHs) are described. The irradiation studies of anthracene:H{sub 2}O, pyrene:H{sub 2}O, and benzo[ghi]perylene:H{sub 2}O ices (14 K) at various concentrations reported by Bouwman et al. are extended. While aromatic alcohols and ketones have been reported in residues after irradiated PAH:H{sub 2}O ices were warmed to 270 K, it was not known if they formed during ice irradiation or during warm-up when reactants interact as H{sub 2}O sublimes. Recent work has shown that they form in low temperature ice. Using DFT computed IR spectra to identify photoproducts and PAH cations, we tentatively identify the production of specific alcohols [PAH(OH) {sub n} ] and quinones [PAH(O) {sub n} ] for all PAH:H{sub 2}O ices considered here. Little evidence is found for hydrogenation at 14 K, consistent with the findings of Gudipati and Yang. Addition of O and OH to the parent PAH is the dominant photochemical reaction, but PAH erosion to smaller PAHs (producing CO{sub 2} and H{sub 2}CO) is also important. DFT spectra are used to assess the contribution of PAH-related species to interstellar absorption features from 5 to 9 μm. The case is made that PAH cations are important contributors to the C2 component and PAH(OH) {sub n} and PAH(O) {sub n} to the C5 component described by Boogert et al. Thus, interstellar ices should contain neutral and ionized PAHs, alcohols, ketones and quinones at the ∼2%-4% level relative to H{sub 2}O. PAHs, their photoproducts, and ion-mediated processes should therefore be considered when modeling interstellar ice processes.

  4. Numerical simulation of formation and preservation of Ningwu ice cave, Shanxi, China

    Science.gov (United States)

    Yang, S.; Shi, Y.

    2015-10-01

    Ice caves exist in locations where annual average air temperature is higher than 0 °C. An example is Ningwu ice cave, Shanxi Province, the largest ice cave in China. In order to quantitatively investigate the mechanism of formation and preservation of the ice cave, we use the finite-element method to simulate the heat transfer process at this ice cave. There are two major control factors. First, there is the seasonal asymmetric heat transfer. Heat is transferred into the ice cave from outside very inefficiently by conduction in spring, summer and fall. In winter, thermal convection occurs that transfers heat very efficiently out of the ice cave, thus cooling it down. Secondly, ice-water phase change provides a heat barrier for heat transfer into the cave in summer. The calculation also helps to evaluate effects of global warming, tourists, colored lights, climatic conditions, etc. for sustainable development of the ice cave as a tourism resource. In some other ice caves in China, managers have installed airtight doors at these ice caves' entrances with the intention of "protecting" these caves, but this in fact prevents cooling in winter and these cave ices will entirely melt within tens of years.

  5. Indirect ultraviolet photodesorption from CO:N2 binary ices — an efficient grain-gas process

    International Nuclear Information System (INIS)

    Bertin, Mathieu; Poderoso, Hugo A. M.; Michaut, Xavier; Philippe, Laurent; Jeseck, Pascal; Fillion, Jean-Hugues; Fayolle, Edith C.; Linnartz, Harold; Romanzin, Claire; Öberg, Karin I.

    2013-01-01

    Ultraviolet (UV) ice photodesorption is an important non-thermal desorption pathway in many interstellar environments that has been invoked to explain observations of cold molecules in disks, clouds, and cloud cores. Systematic laboratory studies of the photodesorption rates, between 7 and 14 eV, from CO:N 2 binary ices, have been performed at the DESIRS vacuum UV beamline of the synchrotron facility SOLEIL. The photodesorption spectral analysis demonstrates that the photodesorption process is indirect, i.e., the desorption is induced by a photon absorption in sub-surface molecular layers, while only surface molecules are actually desorbing. The photodesorption spectra of CO and N 2 in binary ices therefore depend on the absorption spectra of the dominant species in the sub-surface ice layer, which implies that the photodesorption efficiency and energy dependence are dramatically different for mixed and layered ices compared with pure ices. In particular, a thin (1-2 ML) N 2 ice layer on top of CO will effectively quench CO photodesorption, while enhancing N 2 photodesorption by a factor of a few (compared with the pure ices) when the ice is exposed to a typical dark cloud UV field, which may help to explain the different distributions of CO and N 2 H + in molecular cloud cores. This indirect photodesorption mechanism may also explain observations of small amounts of complex organics in cold interstellar environments.

  6. The effects of methanol on the trapping of volatile ice components

    Science.gov (United States)

    Burke, Daren J.; Brown, Wendy A.

    2015-04-01

    The evaporation of icy mantles, which have been formed on the surface of dust grains, is acknowledged to give rise to the rich chemistry that has been observed in the vicinity of hot cores and corinos. It has long been established that water ice is the dominant species within many astrophysical ices. However, other molecules found within astrophysical ices, particularly methanol, can influence the desorption of volatile species from the ice. Here we present a detailed investigation of the adsorption and desorption of methanol-containing ices, showing the effect that methanol has on the trapping and release of volatiles from model interstellar ices. OCS and CO2 have been used as probe molecules since they have been suggested to reside in water-rich and methanol-rich environments. Experiments show that methanol fundamentally changes the desorption characteristics of both OCS and CO2, leading to the observation of mainly codesorption of both species with bulk water ice for the tertiary ices and causing a lowering of the temperature of the volcano component of the desorption. In contrast, binary ices are dominated by standard volcano desorption. This observation clearly shows that codepositing astrophysically relevant impurities with water ice, such as methanol, can alter the desorption dynamics of volatiles that become trapped in the pores of the amorphous water ice during the sublimation process. Incorporating experimental data into a simple model to simulate these processes on astrophysical timescales shows that the additional methanol component releases larger amounts of OCS from the ice mantle at lower temperatures and earlier times. These results are of interest to astronomers as they can be used to model the star formation process, hence giving information about the evolution of our Universe.

  7. Interstellar Extinction

    OpenAIRE

    Gontcharov, George

    2017-01-01

    This review describes our current understanding of interstellar extinction. This differ substantially from the ideas of the 20th century. With infrared surveys of hundreds of millions of stars over the entire sky, such as 2MASS, SPITZER-IRAC, and WISE, we have looked at the densest and most rarefied regions of the interstellar medium at distances of a few kpc from the sun. Observations at infrared and microwave wavelengths, where the bulk of the interstellar dust absorbs and radiates, have br...

  8. GPM GROUND VALIDATION SATELLITE SIMULATED ORBITS TWP-ICE V1

    Data.gov (United States)

    National Aeronautics and Space Administration — The GPM Ground Validation Satellite Simulated Orbits TWP-ICE dataset is available in the Orbital database, which takes account for the atmospheric profiles, the...

  9. Anisotropies in TeV Cosmic Rays Related to the Local Interstellar Magnetic Field from the IBEX Ribbon

    International Nuclear Information System (INIS)

    Schwadron, N A; Moebius, E; Adams, F C; Christian, E; Desiati, P; Frisch, P; Funsten, H O; Jokipii, J R; McComas, D J; Zank, G P

    2015-01-01

    The Interstellar Boundary Explorer (IBEX) observes enhanced Energetic Neutral Atoms (ENAs) emission in the keV energy range from a narrow (∼20° wide) ''ribbon'' in the sky that appears to be centered on the direction of the local interstellar (LIS) magnetic field. The Milagro collaboration, the Asγ collaboration and the IceCube observatory have recently made global maps of cosmic ray fluxes in the TeV energy range, revealing anisotropic structures ordered in part by the local interstellar magnetic field and the interstellar flow. This paper following from a recent publication in Science makes the link between these disparate observations by developing a simple model of the magnetic structure surrounding the heliosphere in the Local Interstellar Medium (LISM) that is consistent with both IBEX ENA fluxes and TeV cosmic ray anisotropies. The model also employs the revised velocity direction of the LIC derived from neutral He observations by IBEX. By modeling the propagation of cosmic rays through this magnetic field structure, we specifically show that (1) the large-scale TeV anisotropy provides a roughly consistent orientation for the local interstellar magnetic field at the center of the IBEX Ribbon and corroborates the ∼ 3 μG magnitude of the local interstellar magnetic field derived from IBEX observations of the global heliosphere; (2) and small-scale structures in cosmic rays (over < 30° angular scales) are influenced by the interstellar field interaction with the heliosphere at energies < 10 TeV. Thus, we provide a link between IBEX ENA observations, IBEX neutral observations of interstellar He, and TeV cosmic ray anisotropies, which are strongly influenced by the interactions between the local interstellar magnetic field, the flow of the local interstellar plasma, and the global heliosphere

  10. Simulation of the last glacial cycle with a coupled climate ice-sheet model of intermediate complexity

    Directory of Open Access Journals (Sweden)

    A. Ganopolski

    2010-04-01

    Full Text Available A new version of the Earth system model of intermediate complexity, CLIMBER-2, which includes the three-dimensional polythermal ice-sheet model SICOPOLIS, is used to simulate the last glacial cycle forced by variations of the Earth's orbital parameters and atmospheric concentration of major greenhouse gases. The climate and ice-sheet components of the model are coupled bi-directionally through a physically-based surface energy and mass balance interface. The model accounts for the time-dependent effect of aeolian dust on planetary and snow albedo. The model successfully simulates the temporal and spatial dynamics of the major Northern Hemisphere (NH ice sheets, including rapid glacial inception and strong asymmetry between the ice-sheet growth phase and glacial termination. Spatial extent and elevation of the ice sheets during the last glacial maximum agree reasonably well with palaeoclimate reconstructions. A suite of sensitivity experiments demonstrates that simulated ice-sheet evolution during the last glacial cycle is very sensitive to some parameters of the surface energy and mass-balance interface and dust module. The possibility of a considerable acceleration of the climate ice-sheet model is discussed.

  11. Variable interstellar radiation fields in simulated dwarf galaxies: supernovae versus photoelectric heating

    Science.gov (United States)

    Hu, Chia-Yu; Naab, Thorsten; Glover, Simon C. O.; Walch, Stefanie; Clark, Paul C.

    2017-10-01

    We present high-resolution hydrodynamical simulations of isolated dwarf galaxies including self-gravity, non-equilibrium cooling and chemistry, interstellar radiation fields (ISRF) and shielding, star formation, and stellar feedback. This includes spatially and temporally varying photoelectric (PE) heating, photoionization, resolved supernova (SN) blast waves and metal enrichment. A new flexible method to sample the stellar initial mass function allows us to follow the contribution to the ISRF, the metal output and the SN delay times of individual massive stars. We find that SNe play the dominant role in regulating the global star formation rate, shaping the multiphase interstellar medium (ISM) and driving galactic outflows. Outflow rates (with mass-loading factors of a few) and hot gas fractions of the ISM increase with the number of SNe exploding in low-density environments where radiative energy losses are low. While PE heating alone can suppress star formation as efficiently as SNe alone can do, it is unable to drive outflows and reproduce the multiphase ISM that emerges naturally whenever SNe are included. We discuss the potential origins for the discrepancy between our results and another recent study that claimed that PE heating dominates over SNe. In the absence of SNe and photoionization (mechanisms to disperse dense clouds), the impact of PE heating is highly overestimated owing to the (unrealistic) proximity of dense gas to the radiation sources. This leads to a substantial boost of the infrared continuum emission from the UV-irradiated dust and a far-infrared line-to-continuum ratio too low compared to observations.

  12. Molecular Simulations of Halomethanes at the Air/Ice Interface

    Czech Academy of Sciences Publication Activity Database

    Habartová, Alena; Hormain, L.; Pluhařová, Eva; Briquez, S.; Monnerville, M.; Toubin, C.; Roeselová, Martina

    2015-01-01

    Roč. 119, č. 39 (2015), s. 10052-10059 ISSN 1089-5639 R&D Projects: GA ČR GA13-06181S Institutional support: RVO:61388963 Keywords : molecular dynamics simulations * water models * ice Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.883, year: 2015

  13. Photochemistry of Coronene in Cosmic Water Ice Analogs at Different Concentrations

    Energy Technology Data Exchange (ETDEWEB)

    De Barros, A. L. F. [Departamento de Física, Centro Federal de Educação Tecnológica Celso Suckow da Fonseca, Av. Maracanã 229, 20271-110 Rio de Janeiro, RJ (Brazil); Mattioda, A. L.; Ricca, A.; Cruz-Diaz, G.A.; Allamandola, L. J. [NASA Ames Research Center, Mail Stop 245-6, Moffett Field, CA 94035-1000 (United States)

    2017-10-20

    This work presents the photochemistry of ultraviolet (UV) irradiated coronene in water ices at 15 K studied using mid-infrared Fourier transform (FTIR) spectroscopy for C{sub 24}H{sub 12}:H{sub 2}O at concentrations of (1:50), (1:150), (1:200), (1:300), and (1:400). Previous UV irradiation studies of anthracene:H{sub 2}O, pyrene:H{sub 2}O, and benzo[ghi]perylene:H{sub 2}O ices at 15 K have shown that aromatic alcohols and ketones, as well as CO{sub 2} and H{sub 2}CO, are formed at very low temperatures. Likewise, here, in addition to the coronene cation, hydroxy-, keto-, and protonated coronene (coronene H{sup +}) are formed. The rate constants for the decay of neutral coronene and for the formation of photoproducts have been derived. It is shown that Polycyclic Aromatic Hydrocarbons (PAHs) and their UV induced PAH:H{sub 2}O photoproducts have mid-infrared spectroscopic signatures in the 5–8 μ m region that can contribute to the interstellar ice components described by Boogert et al. as C1–C5. Our results suggest that oxygenated and hydrogenated PAHs could be in UV-irradiated regions of the interstellar medium where water-rich ices are important.

  14. Photochemistry of Coronene in Cosmic Water Ice Analogs at Different Concentrations

    International Nuclear Information System (INIS)

    De Barros, A. L. F.; Mattioda, A. L.; Ricca, A.; Cruz-Diaz, G.A.; Allamandola, L. J.

    2017-01-01

    This work presents the photochemistry of ultraviolet (UV) irradiated coronene in water ices at 15 K studied using mid-infrared Fourier transform (FTIR) spectroscopy for C 24 H 12 :H 2 O at concentrations of (1:50), (1:150), (1:200), (1:300), and (1:400). Previous UV irradiation studies of anthracene:H 2 O, pyrene:H 2 O, and benzo[ghi]perylene:H 2 O ices at 15 K have shown that aromatic alcohols and ketones, as well as CO 2 and H 2 CO, are formed at very low temperatures. Likewise, here, in addition to the coronene cation, hydroxy-, keto-, and protonated coronene (coronene H + ) are formed. The rate constants for the decay of neutral coronene and for the formation of photoproducts have been derived. It is shown that Polycyclic Aromatic Hydrocarbons (PAHs) and their UV induced PAH:H 2 O photoproducts have mid-infrared spectroscopic signatures in the 5–8 μ m region that can contribute to the interstellar ice components described by Boogert et al. as C1–C5. Our results suggest that oxygenated and hydrogenated PAHs could be in UV-irradiated regions of the interstellar medium where water-rich ices are important.

  15. Comparison of surface mass balance of ice sheets simulated by positive-degree-day method and energy balance approach

    Directory of Open Access Journals (Sweden)

    E. Bauer

    2017-07-01

    Full Text Available Glacial cycles of the late Quaternary are controlled by the asymmetrically varying mass balance of continental ice sheets in the Northern Hemisphere. Surface mass balance is governed by processes of ablation and accumulation. Here two ablation schemes, the positive-degree-day (PDD method and the surface energy balance (SEB approach, are compared in transient simulations of the last glacial cycle with the Earth system model of intermediate complexity CLIMBER-2. The standard version of the CLIMBER-2 model incorporates the SEB approach and simulates ice volume variations in reasonable agreement with paleoclimate reconstructions during the entire last glacial cycle. Using results from the standard CLIMBER-2 model version, we simulated ablation with the PDD method in offline mode by applying different combinations of three empirical parameters of the PDD scheme. We found that none of the parameter combinations allow us to simulate a surface mass balance of the American and European ice sheets that is similar to that obtained with the standard SEB method. The use of constant values for the empirical PDD parameters led either to too much ablation during the first phase of the last glacial cycle or too little ablation during the final phase. We then substituted the standard SEB scheme in CLIMBER-2 with the PDD scheme and performed a suite of fully interactive (online simulations of the last glacial cycle with different combinations of PDD parameters. The results of these simulations confirmed the results of the offline simulations: no combination of PDD parameters realistically simulates the evolution of the ice sheets during the entire glacial cycle. The use of constant parameter values in the online simulations leads either to a buildup of too much ice volume at the end of glacial cycle or too little ice volume at the beginning. Even when the model correctly simulates global ice volume at the last glacial maximum (21 ka, it is unable to simulate

  16. Four Interstellar Dust Candidates from the Stardust Interstellar Dust Collector

    Science.gov (United States)

    Westphal, A. J.; Allen, C.; Bajt, S.; Bechtel, H. A.; Borg, J.; Brenker, F.; Bridges, J.; Brownlee, D. E.; Burchell, M.; Burghammer, M.; hide

    2011-01-01

    In January 2006, the Stardust sample return capsule returned to Earth bearing the first solid samples from a primitive solar system body, Comet 81P/Wild2, and a collector dedicated to the capture and return of contemporary interstellar dust. Both collectors were approx. 0.1 sq m in area and were composed of aerogel tiles (85% of the collecting area) and aluminum foils. The Stardust Interstellar Dust Collector (SIDC) was exposed to the interstellar dust stream for a total exposure factor of 20 sq m/day. The Stardust Interstellar Preliminary Examination (ISPE) is a consortium-based project to characterize the collection using nondestructive techniques. The goals and restrictions of the ISPE are described . A summary of analytical techniques is described.

  17. Laboratory Studies of Solid CO2 Ices at Different Temperatures and Annealing Times in Support of Spitzer Space Telescope Observations

    Science.gov (United States)

    White, Douglas; Gerakines, P. A.

    2007-12-01

    The infrared absorption features of solid carbon dioxide have been detected by space observatories in nearly all lines of sight probing the dense interstellar medium (ISM). It has also been shown that the absorption feature of solid CO2 near 658 cm-1 (15.2 μm) should be a sensitive indicator of the physical conditions of the ice (e.g., temperature and composition). However, the profile structure of this feature is not well understood, and previous laboratory studies have concentrated on a limited range of temperatures and compositions for comparisons to observed spectra from both the Infrared Space Observatory and the Spitzer Space Telescope. In the laboratory study described here, the infrared spectra of ices bearing H2O, CH3OH, and CO2 have been measured with systematically varying compositions and temperatures that span the range of the values expected in the interstellar medium. The mid-infrared spectra (λ = 2.5-25 µm) were measured for 47 different ice compositions at temperatures ranging from 5 K to evaporation (at 5 K intervals). Additionally, annealing experiments of some of these ice compositions have been investigated. These data may be used to determine thermal histories of interstellar ices. This research was supported by NASA award NNG05GE44G under the Astronomy and Physics Research & Analysis Program (APRA).

  18. Large-scale Cosmic-Ray Anisotropy as a Probe of Interstellar Turbulence

    Energy Technology Data Exchange (ETDEWEB)

    Giacinti, Gwenael; Kirk, John G. [Max-Planck-Institut für Kernphysik, Postfach 103980, D-69029 Heidelberg (Germany)

    2017-02-01

    We calculate the large-scale cosmic-ray (CR) anisotropies predicted for a range of Goldreich–Sridhar (GS) and isotropic models of interstellar turbulence, and compare them with IceTop data. In general, the predicted CR anisotropy is not a pure dipole; the cold spots reported at 400 TeV and 2 PeV are consistent with a GS model that contains a smooth deficit of parallel-propagating waves and a broad resonance function, though some other possibilities cannot, as yet, be ruled out. In particular, isotropic fast magnetosonic wave turbulence can match the observations at high energy, but cannot accommodate an energy dependence in the shape of the CR anisotropy. Our findings suggest that improved data on the large-scale CR anisotropy could provide a valuable probe of the properties—notably the power-spectrum—of the interstellar turbulence within a few tens of parsecs from Earth.

  19. Amorphous ice. A microporous solid: astrophysical implications

    International Nuclear Information System (INIS)

    Mayer, E.; Pletzer, R.

    1987-01-01

    Vapour deposited amorphous ice, investigated by N 2 -adsorption at 77 K, was found to be a microporous solid. Micropore volumes between 0.21 and 0.12 cm 3 /g were determined by comparison plots and Dubinin-Radushkevich plots. Warming of the adsorbent to 113 K caused sintering and reduction of apparent surface area by about an order of magnitude; in the presence of adsorbed gas, large amounts of gas were enclosed in the solid. The influence of micropores on the H 2 recombination rate on amorphous ice in interstellar dust and on adsorption of volatile gases in comets is discussed briefly

  20. NASA's interstellar probe mission

    International Nuclear Information System (INIS)

    Liewer, P.C.; Ayon, J.A.; Wallace, R.A.; Mewaldt, R.A.

    2000-01-01

    NASA's Interstellar Probe will be the first spacecraft designed to explore the nearby interstellar medium and its interaction with our solar system. As envisioned by NASA's Interstellar Probe Science and Technology Definition Team, the spacecraft will be propelled by a solar sail to reach >200 AU in 15 years. Interstellar Probe will investigate how the Sun interacts with its environment and will directly measure the properties and composition of the dust, neutrals and plasma of the local interstellar material which surrounds the solar system. In the mission concept developed in the spring of 1999, a 400-m diameter solar sail accelerates the spacecraft to ∼15 AU/year, roughly 5 times the speed of Voyager 1 and 2. The sail is used to first bring the spacecraft to ∼0.25 AU to increase the radiation pressure before heading out in the interstellar upwind direction. After jettisoning the sail at ∼5 AU, the spacecraft coasts to 200-400 AU, exploring the Kuiper Belt, the boundaries of the heliosphere, and the nearby interstellar medium

  1. The sea ice mass budget of the Arctic and its future change as simulated by coupled climate models

    Energy Technology Data Exchange (ETDEWEB)

    Holland, Marika M. [National Center for Atmospheric Research, Boulder, CO (United States); Serreze, Mark C.; Stroeve, Julienne [University of Colorado, National Snow and Ice Data Center, Cooperative Institute for Research in Environmental Sciences, Boulder, CO (United States)

    2010-02-15

    Arctic sea ice mass budgets for the twentieth century and projected changes through the twenty-first century are assessed from 14 coupled global climate models. Large inter-model scatter in contemporary mass budgets is strongly related to variations in absorbed solar radiation, due in large part to differences in the surface albedo simulation. Over the twenty-first century, all models simulate a decrease in ice volume resulting from increased annual net melt (melt minus growth), partially compensated by reduced transport to lower latitudes. Despite this general agreement, the models vary considerably regarding the magnitude of ice volume loss and the relative roles of changing melt and growth in driving it. Projected changes in sea ice mass budgets depend in part on the initial (mid twentieth century) ice conditions; models with thicker initial ice generally exhibit larger volume losses. Pointing to the importance of evolving surface albedo and cloud properties, inter-model scatter in changing net ice melt is significantly related to changes in downwelling longwave and absorbed shortwave radiation. These factors, along with the simulated mean and spatial distribution of ice thickness, contribute to a large inter-model scatter in the projected onset of seasonally ice-free conditions. (orig.)

  2. Thermodynamic and dynamic ice thickness contributions in the Canadian Arctic Archipelago in NEMO-LIM2 numerical simulations

    Science.gov (United States)

    Hu, Xianmin; Sun, Jingfan; Chan, Ting On; Myers, Paul G.

    2018-04-01

    Sea ice thickness evolution within the Canadian Arctic Archipelago (CAA) is of great interest to science, as well as local communities and their economy. In this study, based on the NEMO numerical framework including the LIM2 sea ice module, simulations at both 1/4 and 1/12° horizontal resolution were conducted from 2002 to 2016. The model captures well the general spatial distribution of ice thickness in the CAA region, with very thick sea ice (˜ 4 m and thicker) in the northern CAA, thick sea ice (2.5 to 3 m) in the west-central Parry Channel and M'Clintock Channel, and thin ( Program data at first-year landfast ice sites except at the northern sites with high concentration of old ice. At 1/4 to 1/12° scale, model resolution does not play a significant role in the sea ice simulation except to improve local dynamics because of better coastline representation. Sea ice growth is decomposed into thermodynamic and dynamic (including all non-thermodynamic processes in the model) contributions to study the ice thickness evolution. Relatively smaller thermodynamic contribution to ice growth between December and the following April is found in the thick and very thick ice regions, with larger contributions in the thin ice-covered region. No significant trend in winter maximum ice volume is found in the northern CAA and Baffin Bay while a decline (r2 ≈ 0.6, p < 0.01) is simulated in Parry Channel region. The two main contributors (thermodynamic growth and lateral transport) have high interannual variabilities which largely balance each other, so that maximum ice volume can vary interannually by ±12 % in the northern CAA, ±15 % in Parry Channel, and ±9 % in Baffin Bay. Further quantitative evaluation is required.

  3. Optimal control of building storage systems using both ice storage and thermal mass – Part I: Simulation environment

    International Nuclear Information System (INIS)

    Hajiah, Ali; Krarti, Moncef

    2012-01-01

    Highlights: ► A simulation environment is described to account for both passive and active thermal energy storage (TES) systems. ► Laboratory testing results have been used to validate the predictions from the simulation environment. ► Optimal control strategies for TES systems have been developed as part of the simulation environment. - Abstract: This paper presents a simulation environment that can evaluate the benefits of using simultaneously building thermal capacitance and ice storage system to reduce total operating costs including energy and demand charges while maintaining adequate occupant comfort conditions within commercial buildings. The building thermal storage is controlled through pre-cooling strategies by setting space indoor air temperatures. The ice storage system is controlled by charging the ice tank and operating the chiller during low electrical charge periods and melting the ice during on-peak periods. Optimal controls for both building thermal storage and ice storage are developed to minimize energy charges, demand charges, or combined energy and demand charges. The results obtained from the simulation environment are validated using laboratory testing for an optimal controller.

  4. AN ESTIMATE OF THE NEARBY INTERSTELLAR MAGNETIC FIELD USING NEUTRAL ATOMS

    International Nuclear Information System (INIS)

    Heerikhuisen, J.; Pogorelov, N. V.

    2011-01-01

    The strength and orientation of the magnetic field in the nearby interstellar medium have remained elusive, despite continual improvements in observations and models. Data from NASA's Voyager mission and the Solar Wind ANisotropies (SWAN) experiment on board Solar and Heliospheric Observatory (SOHO) have placed observational constraints on the magnetic field, and the more recent Interstellar Boundary Explorer (IBEX) data appear to also bear an imprint of the interstellar magnetic field (ISMF). In this paper, we combine computational models of the heliosphere with data from Voyager, SOHO/SWAN, and IBEX to estimate both the strength and direction of the nearby ISMF. On the basis of our simulations, we find that a field strength of 2-3 μG pointing from ecliptic coordinates (220-224, 39-44), combined with an interstellar hydrogen density of ∼0.15 cm -3 , produces results most consistent with observations.

  5. Physical simulation technique on the behaviour of oil spills in grease ice under wave actions

    International Nuclear Information System (INIS)

    Li, Z.; Hollebone, B.; Fingas, M.; Fieldhouse, B.

    2008-01-01

    Light or medium oil spilled on ice tends to rise and remain the surface in unconsolidated frazil or grease ice. This study looked for a new system for studying the oil emulsion in grease ice under experimental conditions. A physical simulation technique was designed to test the effect of wave energy on the spilled oil grease ice emulsion. The newly developed test system has the ability to perform simulation tests in wave, wave-ice, wave-oil and wave-ice-oil. This paper presented the design concept of the developed test system and introduced the experimental certifications of its capability in terms of temperature control, wave-making and grease ice-making. The key feature of the technique is a mini wave flume which derives its wave making power from an oscillator in a chemical laboratory. Video cameras record the wave action in the flume in order to obtain wave parameters. The wave making capability tests in this study were used to determine the relation of wave height, length and frequency with oscillator power transfer, oscillator frequency and the depth of the water flume. 16 refs., 10 figs

  6. Impact of prescribed Arctic sea ice thickness in simulations of the present and future climate

    Energy Technology Data Exchange (ETDEWEB)

    Krinner, Gerhard [Alfred Wegener Institute for Polar and Marine Research, Potsdam (Germany); INSU-CNRS and UJF Grenoble, Laboratoire de Glaciologie et Geophysique de l' Environnement (LGGE), 54 rue Moliere, BP 96, Saint Martin d' Heres Cedex (France); Rinke, Annette; Dethloff, Klaus [Alfred Wegener Institute for Polar and Marine Research, Potsdam (Germany); Gorodetskaya, Irina V. [INSU-CNRS and UJF Grenoble, Laboratoire de Glaciologie et Geophysique de l' Environnement (LGGE), 54 rue Moliere, BP 96, Saint Martin d' Heres Cedex (France)

    2010-09-15

    This paper describes atmospheric general circulation model climate change experiments in which the Arctic sea-ice thickness is either fixed to 3 m or somewhat more realistically parameterized in order to take into account essentially the spatial variability of Arctic sea-ice thickness, which is, to a first approximation, a function of ice type (perennial or seasonal). It is shown that, both at present and at the end of the twenty-first century (under the SRES-A1B greenhouse gas scenario), the impact of a variable sea-ice thickness compared to a uniform value is essentially limited to the cold seasons and the lower troposphere. However, because first-year ice is scarce in the Central Arctic today, but not under SRES-A1B conditions at the end of the twenty-first century, and because the impact of a sea-ice thickness reduction can be masked by changes of the open water fraction, the spatial and temporal patterns of the effect of sea-ice thinning on the atmosphere differ between the two periods considered. As a consequence, not only the climate simulated at a given period, but also the simulated Arctic climate change over the twenty-first century is affected by the way sea-ice thickness is prescribed. (orig.)

  7. UV/Vis spectroscopy of C60 embedded in water ice

    DEFF Research Database (Denmark)

    Cuylle, Steven; Linnartz, Harold; Thrower, John

    2012-01-01

    Electronic solid state spectra are recorded for C60 embedded in 40 K water ice using broad band direct absorption spectroscopy, and assigned with reference to existing matrix data. The results are interesting in view of the recent gas phase detection of fullerenes in the interstellar medium...

  8. Final Report. Coupled simulations of Antarctic Ice-sheet/ocean interactions using POP and CISM

    Energy Technology Data Exchange (ETDEWEB)

    Asay-Davis, Xylar Storm [Potsdam Institute for Climate Impact Research, Potdam (Germany)

    2015-12-30

    The project performed under this award, referred to from here on as CLARION (CoupLed simulations of Antarctic Ice-sheet/Ocean iNteractions), included important advances in two models of ice sheet and ocean interactions. Despite its short duration (one year), the project made significant progress on its three major foci. First, together with collaborator Daniel Martin at Lawrence Berkeley National Laboratory (LBNL), I developed the POPSICLES coupled ice sheet-ocean model to the point where it could perform a number of pan-Antarctic simulations under various forcing conditions. The results were presented at a number of major conferences and workshops worldwide, and are currently being incorporated into two manuscripts in preparation.

  9. Chemical evolution of interstellar dust, comets and the origins of life

    International Nuclear Information System (INIS)

    Greenberg, J.M.; Zhao, N.; Hage, J.

    1989-01-01

    The chemistry and morphological structure of a comet nucleus as an aggregate of interstellar dust is used to provide comparisons with a variety of comet Halley results: the density of the nucleus and of the dust; the dust cloud model and its consequences on the production of C + and CN in the coma by small organic grains; the surface albedo and the low nucleus heat conductivity and high surface temperature; the appearance of 10 -14 g and 10 -17 g dust particles along with higher masses; the mass spectra of dust and infrared spectroscopy as evidence for complex organic grain mantles and of very small carbonaceous and silicate grains; the appearence of small grains resulting from breakup of larger grains. The cosmic ray dosage of a comet nucleus during its 4.5 billion years in the Oort cloud appears to be many orders of magnitude less than the dosage of the preaggregated interstellar dust by ultraviolet photons except perhaps in the outer few meters of the nucleus of a new comet. The heat conductivity calculated for aggregated dust is certainly less than 10 -4 that of crystalline ice. This, in combination with the interstellar dust microstructure, provide a basis for showing that solar heating of the interior of a nucleus is lower than previously estimated

  10. Comparison of three ice cloud optical schemes in climate simulations with community atmospheric model version 5

    Science.gov (United States)

    Zhao, Wenjie; Peng, Yiran; Wang, Bin; Yi, Bingqi; Lin, Yanluan; Li, Jiangnan

    2018-05-01

    A newly implemented Baum-Yang scheme for simulating ice cloud optical properties is compared with existing schemes (Mitchell and Fu schemes) in a standalone radiative transfer model and in the global climate model (GCM) Community Atmospheric Model Version 5 (CAM5). This study systematically analyzes the effect of different ice cloud optical schemes on global radiation and climate by a series of simulations with a simplified standalone radiative transfer model, atmospheric GCM CAM5, and a comprehensive coupled climate model. Results from the standalone radiative model show that Baum-Yang scheme yields generally weaker effects of ice cloud on temperature profiles both in shortwave and longwave spectrum. CAM5 simulations indicate that Baum-Yang scheme in place of Mitchell/Fu scheme tends to cool the upper atmosphere and strengthen the thermodynamic instability in low- and mid-latitudes, which could intensify the Hadley circulation and dehydrate the subtropics. When CAM5 is coupled with a slab ocean model to include simplified air-sea interaction, reduced downward longwave flux to surface in Baum-Yang scheme mitigates ice-albedo feedback in the Arctic as well as water vapor and cloud feedbacks in low- and mid-latitudes, resulting in an overall temperature decrease by 3.0/1.4 °C globally compared with Mitchell/Fu schemes. Radiative effect and climate feedback of the three ice cloud optical schemes documented in this study can be referred for future improvements on ice cloud simulation in CAM5.

  11. Irradiation of astrophysical ice grains by cosmic-ray ions: a REAX simulation study

    Science.gov (United States)

    Mainitz, Martin; Anders, Christian; Urbassek, Herbert M.

    2016-07-01

    Context. The impact of cosmic rays on ice grains delivers considerable energy, inducing chemical reactions and molecule ejection. Aims: We study the effects of cosmic ray impact on ice grains, including shock wave expansion, grain heating, molecule fragmentation, formation of chemical reaction products, sputtering and evaporation. Methods: Molecular-dynamics simulations using the REAX potential allow us to follow the processes occurring in the irradiated ice grain; the mechanical, thermal and chemical consequences are simulated. The ice grain consists of a mixture of water, carbon dioxide, methanol and ammonia. The case of 1 keV/nm energy deposition is studied as an example. Results: The ion track emits a shock wave into the ambient grain. Due to the strong heating, abundant molecule fragmentation is observed; several of the fragments either recombine or form new product molecules. Prompt sputtering from the ion track is followed by evaporation from the surface of the heated grain. We present mass spectra of the chemically transformed species in the grain and in the ejecta.

  12. The 3 micron ice band

    International Nuclear Information System (INIS)

    Greenberg, J.M.; Bult, C.E.P.M. van de

    1984-01-01

    Ever since it was proposed that H 2 O could be a dominant constituent of interstellar grains, its detection, or lack thereof, has played a large role in theories of grains and their evolution. It now appears possible to provide a basic theoretical structure for the evolution of grains in molecular clouds based on current observational evidence and laboratory experiments on the ice band. Both band strengths and shapes can be reasonably predicted by grain models. (U.K.)

  13. Infrared Spectra and Optical Constants of Astronomical Ices: I. Amorphous and Crystalline Acetylene

    Science.gov (United States)

    Hudson, R. L.; Ferrante, R. F.; Moore, M. H.

    2013-01-01

    Here we report recent measurements on acetylene (C2H2) ices at temperatures applicable to the outer Solar System and the interstellar medium. New near- and mid-infrared data, including optical constants (n, k), absorption coefficients (alpha), and absolute band strengths (A), are presented for both amorphous and crystalline phases of C2H2 that exist below 70 K. Comparisons are made to earlier work. Electronic versions of the data are made available, as is a computer routine to use our reported n and k values to simulate the observed IR spectra. Suggestions are given for the use of the data and a comparison to a spectrum of Makemake is made.

  14. Ice Chemistry in Interstellar Dense Molecular Clouds, Protostellar Disks, and Comets

    Science.gov (United States)

    Sandford, Scott A.

    2015-01-01

    Despite the low temperatures (T less than 20K), low pressures, and low molecular densities found in much of the cosmos, considerable chemistry is expected to occur in many astronomical environments. Much of this chemistry happens in icy grain mantles on dust grains and is driven by ionizing radiation. This ionizing radiation breaks chemical bonds of molecules in the ices and creates a host of ions and radicals that can react at the ambient temperature or when the parent ice is subsequently warmed. Experiments that similar these conditions have demonstrated a rich chemistry associated with these environments that leads to a wide variety of organic products. Many of these products are of considerable interest to astrobiology. For example, the irradiation of simple ices has been shown to abiotically produce amino acids, nucleobases, quinones, and amphiphiles, all compounds that play key roles in modern biochemistry. This suggests extraterrestrial chemistry could have played a role in the origin of life on Earth and, by extension, do so on planets in other stellar systems.

  15. Airframe Icing Research Gaps: NASA Perspective

    Science.gov (United States)

    Potapczuk, Mark

    2009-01-01

    qCurrent Airframe Icing Technology Gaps: Development of a full 3D ice accretion simulation model. Development of an improved simulation model for SLD conditions. CFD modeling of stall behavior for ice-contaminated wings/tails. Computational methods for simulation of stability and control parameters. Analysis of thermal ice protection system performance. Quantification of 3D ice shape geometric characteristics Development of accurate ground-based simulation of SLD conditions. Development of scaling methods for SLD conditions. Development of advanced diagnostic techniques for assessment of tunnel cloud conditions. Identification of critical ice shapes for aerodynamic performance degradation. Aerodynamic scaling issues associated with testing scale model ice shape geometries. Development of altitude scaling methods for thermal ice protections systems. Development of accurate parameter identification methods. Measurement of stability and control parameters for an ice-contaminated swept wing aircraft. Creation of control law modifications to prevent loss of control during icing encounters. 3D ice shape geometries. Collection efficiency data for ice shape geometries. SLD ice shape data, in-flight and ground-based, for simulation verification. Aerodynamic performance data for 3D geometries and various icing conditions. Stability and control parameter data for iced aircraft configurations. Thermal ice protection system data for simulation validation.

  16. Dynamical Conditions of Ice Supersaturation and Ice Nucleation in Convective Systems: A Comparative Analysis Between in Situ Aircraft Observations and WRF Simulations

    Science.gov (United States)

    D’Alessandro, John J.; Diao, Minghui; Wu, Chenglai; Liu, Xiaohong; Chen, Ming; Morrison, Hugh; Eidhammer, Trude; Jensen, Jorgen B.; Bansemer, Aaron; Zondlo, Mark A.; hide

    2017-01-01

    Occurrence frequency and dynamical conditions of ice supersaturation (ISS, where relative humidity with respect to ice (RHi) greater than 100%) are examined in the upper troposphere around convective activity. Comparisons are conducted between in situ airborne observations and the Weather Research and Forecasting model simulations using four double-moment microphysical schemes at temperatures less than or or equal to -40degdegC. All four schemes capture both clear-sky and in-cloud ISS conditions. However, the clear-sky (in-cloud) ISS conditions are completely (significantly) limited to the RHi thresholds of the Cooper parameterization. In all of the simulations, ISS occurrence frequencies are higher by approximately 3-4 orders of magnitude at higher updraft speeds (greater than 1 m s(exp -1) than those at the lower updraft speeds when ice water content (IWC) greater than 0.01 gm(exp -3), while observations show smaller differences up to approximately 1-2 orders of magnitude. The simulated ISS also occurs less frequently at weaker updrafts and downdrafts than observed. These results indicate that the simulations have a greater dependence on stronger updrafts to maintain/generate ISS at higher IWC. At lower IWC (less than or equal or 0.01 gm(exp -3), simulations unexpectedly show lower ISS frequencies at stronger updrafts. Overall, the Thompson aerosol-aware scheme has the closest magnitudes and frequencies of ISS greater than 20% to the observations, and the modified Morrison has the closest correlations between ISS frequencies and vertical velocity at higher IWC and number density. The Cooper parameterization often generates excessive ice crystals and therefore suppresses the frequency and magnitude of ISS, indicating that it should be initiated at higher ISS (e.g.,lees than or equal to 25%).

  17. Carbon Monoxide Hydrogenation on Ice Surfaces.

    Science.gov (United States)

    Kuwahata, Kazuaki; Ohno, Kaoru

    2018-03-14

    We have performed density functional calculations to investigate the carbon monoxide hydrogenation reaction (H+CO→HCO), which is important in interstellar clouds. We found that the activation energy of the reaction on amorphous ice is lower than that on crystalline ice. In the course of this study, we demonstrated that it is roughly possible to use the excitation energy of the reactant molecule (CO) in place of the activation energy. This relationship holds also for small water clusters at the CCSD level of calculation and the two-layer-level ONIOM (CCSD : X3LYP) calculation. Generally, since it is computationally demanding to estimate activation energies of chemical reactions in a circumstance of many water molecules, this relationship enables one to determine the activation energy of this reaction on ice surfaces from the knowledge of the excitation energy of CO only. Incorporating quantum-tunneling effects, we discuss the reaction rate on ice surfaces. Our estimate that the reaction rate on amorphous ice is almost twice as large as that on crystalline ice is qualitatively consistent with the experimental evidence reported by Hidaka et al. [Chem. Phys. Lett., 2008, 456, 36.]. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Interstellar ammonia

    International Nuclear Information System (INIS)

    Ho, P.T.P.; Townes, C.H.

    1983-01-01

    Investigations and results on interstellar NH3 are discussed. The physics of the molecule, its interstellar excitation, and its formation and dissociation mechanisms are reviewed. The observing techniques and instruments, including single-antenna facilities, infrared and submillimeter techniques, and interferometric studies using the Very Large Array are briefly considered. Spectral data analysis is discussed, including the derivation of optical depths, excitation measurements, ortho-para measurements, and cross sections. Progress achieved in understanding the properties and evolution of the interstellar medium through NH3 studies is reviewed, including observations of nearby dark clouds and of clumping effects in molecular clouds, as well as interferometric observations of hot molecular cores in Orion, W51, and Sagittarius A. Research results on extragalactic NH3, far-infrared, submillimeter, and midinfrared NH3 observations are described. 101 references

  19. A Numerical Approach for Hybrid Simulation of Power System Dynamics Considering Extreme Icing Events

    DEFF Research Database (Denmark)

    Chen, Lizheng; Zhang, Hengxu; Wu, Qiuwei

    2017-01-01

    numerical simulation scheme integrating icing weather events with power system dynamics is proposed to extend power system numerical simulation. A technique is developed to efficiently simulate the interaction of slow dynamics of weather events and fast dynamics of power systems. An extended package for PSS...

  20. From Astrochemistry to Astrobiology

    Science.gov (United States)

    Allamandola, L. J.

    2005-01-01

    Tremendous strides have been made in our understanding of interstellar material over the past twenty five years thanks to significant developments in observational astronomy and laboratory astrophysics. Twenty years ago the composition of interstellar dust was largely guessed at, the concept of ices in dense molecular clouds ignored, and the notion of large, abundant, gas phase, carbon-rich molecules widespread throughout the interstellar medium (ISM) considered impossible. Today the composition of interstellar dust is reasonably well understood. In molecular clouds, the birthplace of stars and planets, these cold dust particles are coated with mixed molecular ices whose composition is very well constrained. Lastly, the signature of carbon-rich polycyclic aromatic hydrocarbons (PAHs), shockingly large molecules by early interstellar chemistry standards, is widespread throughout the Universe. The first part of this talk will describe how infrared spectroscopic studies of interstellar space, combined with laboratory simulations of interstellar ice chemistry, have revealed the widespread presence of interstellar PAHs and the composition of interstellar ices, the building blocks of comets. The remainder of the presentation will focus on the photochemical evolution of these materials and astrobiology. Within a molecular cloud, and especially the presolar nebula, materials frozen into the ices are photoprocessed by ultraviolet light and produce more complex molecules. As these materials are the building blocks of comets and related to carbonaceous micrometeorites, they are likely to have been important sources of complex materials delivered to the early Earth and their composition may be related to the origin of life.

  1. From Astrochemistry to Astrobiology ...... and Back Again

    Science.gov (United States)

    Allamandola, L. J.

    2006-01-01

    Tremendous strides have been made in our understanding of interstellar material over the past twenty five years thanks to significant developments in observational infrared astronomy and laboratory astrophysics. Twenty five years ago the composition of interstellar dust was largely guessed at, the concept of ices in dense molecular clouds generally ignored, and the notion of large, abundant, gas phase, carbon-rich molecules widespread throughout the interstellar medium (ISM) considered impossible. Today the composition of interstellar dust is reasonably well understood. In molecular clouds, the birthplace of stars and planets, these cold dust particles are coated with mixed molecular ices whose composition is reasonably well constrained. Lastly, the signature of carbon-rich polycyclic aromatic hydrocarbons (PAHs), shockingly large molecules by early interstellar chemistry standards, is widespread throughout the Universe. The first part of this talk will describe how infrared spectroscopic studies of interstellar space, combined with laboratory simulations and theoretical studies of PAHs and interstellar ices, have revealed the widespread presence of interstellar PAHs and the composition of interstellar precometary ices. The remainder of the presentation will focus on the photochemical evolution of these icy materials. Within a molecular cloud, and especially the presolar nebula, materials frozen into the ices are photoprocessed by ultraviolet light and more complex molecules are produced. As these materials are the building blocks of comets and related to carbonaceous micrometeorites, they are likely to be important sources of complex materials delivered to habitable planets and their composition may be related to the origin of life.

  2. An ice sheet model validation framework for the Greenland ice sheet

    Science.gov (United States)

    Price, Stephen F.; Hoffman, Matthew J.; Bonin, Jennifer A.; Howat, Ian M.; Neumann, Thomas; Saba, Jack; Tezaur, Irina; Guerber, Jeffrey; Chambers, Don P.; Evans, Katherine J.; Kennedy, Joseph H.; Lenaerts, Jan; Lipscomb, William H.; Perego, Mauro; Salinger, Andrew G.; Tuminaro, Raymond S.; van den Broeke, Michiel R.; Nowicki, Sophie M. J.

    2017-01-01

    We propose a new ice sheet model validation framework - the Cryospheric Model Comparison Tool (CmCt) - that takes advantage of ice sheet altimetry and gravimetry observations collected over the past several decades and is applied here to modeling of the Greenland ice sheet. We use realistic simulations performed with the Community Ice Sheet Model (CISM) along with two idealized, non-dynamic models to demonstrate the framework and its use. Dynamic simulations with CISM are forced from 1991 to 2013, using combinations of reanalysis-based surface mass balance and observations of outlet glacier flux change. We propose and demonstrate qualitative and quantitative metrics for use in evaluating the different model simulations against the observations. We find that the altimetry observations used here are largely ambiguous in terms of their ability to distinguish one simulation from another. Based on basin-scale and whole-ice-sheet-scale metrics, we find that simulations using both idealized conceptual models and dynamic, numerical models provide an equally reasonable representation of the ice sheet surface (mean elevation differences of framework demonstrates that our proposed metrics can distinguish relatively better from relatively worse simulations and that dynamic ice sheet models, when appropriately initialized and forced with the right boundary conditions, demonstrate a predictive skill with respect to observed dynamic changes that have occurred on Greenland over the past few decades. An extensible design will allow for continued use of the CmCt as future altimetry, gravimetry, and other remotely sensed data become available for use in ice sheet model validation.

  3. Thresholds in the sliding resistance of simulated basal ice

    Directory of Open Access Journals (Sweden)

    L. F. Emerson

    2007-10-01

    Full Text Available We report laboratory determinations of the shear resistance to sliding melting ice with entrained particles over a hard, impermeable surface. With higher particle concentrations and larger particle sizes, Coulomb friction at particle-bed contacts dominates and the shear stress increases linearly with normal load. We term this the sandy regime. When either particle concentration or particle size is reduced below a threshold, the dependence of shear resistance on normal load is no longer statistically significant. We term this regime slippery. We use force and mass balance considerations to examine the flow of melt water beneath the simulated basal ice. At high particle concentrations, the transition from sandy to slippery behavior occurs when the particle size is comparable to the thickness of the melt film that separates the sliding ice from its bed. For larger particle sizes, a transition from sandy to slippery behavior occurs when the particle concentration drops sufficiently that the normal load is no longer transferred completely to the particle-bed contacts. We estimate that the melt films separating the particles from the ice are approximately 0.1 µm thick at this transition. Our laboratory results suggest the potential for abrupt transitions in the shear resistance beneath hard-bedded glaciers with changes in either the thickness of melt layers or the particle loading.

  4. Path-integral simulation of ice Ih: The effect of pressure

    Science.gov (United States)

    Herrero, Carlos P.; Ramírez, Rafael

    2011-12-01

    The effect of pressure on structural and thermodynamic properties of ice Ih has been studied by means of path-integral molecular dynamics simulations at temperatures between 50 and 300 K. Interatomic interactions were modeled by using the effective q-TIP4P/F potential for flexible water. Positive (compression) and negative (tension) pressures have been considered, which allowed us to approach the limits for the mechanical stability of this solid water phase. We have studied the pressure dependence of the crystal volume, bulk modulus, interatomic distances, atomic delocalization, and kinetic energy. The spinodal point at both negative and positive pressures is derived from the vanishing of the bulk modulus. For P300 K. At positive pressure the spinodal is associated with ice amorphization, and at low temperatures it is found to be between 1.1 and 1.3 GPa. Quantum nuclear effects cause a reduction of the metastability region of ice Ih.

  5. γ Radiolysis of C60 fullerene in water and water/ammonia mixtures: relevance of fullerene fate in ices of interstellar medium

    International Nuclear Information System (INIS)

    Iglesias-Groth, S.; Angelini, G.; Cataldo, F.

    2013-01-01

    The γ radiolysis of fullerene C 60 dispersed in H 2 O, H 2 O/NH 3 , H 2 O/methanol and H 2 O/NH 3 /methanol was studied at 250 and 500 kGy. It was found that C 60 originally insoluble in the above mentioned hosting matrix became soluble as a consequence of multiple hydroxylation and oxidation reaction produced by the free radicals generated by the radiolysis of the hosting matrix. The changes undergone by C 60 were studied by infrared spectroscopy (FT-IR) and by electronic absorption spectroscopy. The astrochemical consequences of the present study are that C 60 ejected in the interstellar medium for instance from protoplanetary and planetary nebulae can condense together with water and other ices in dense molecular clouds. Under the action of high energy radiation C 60 reacts with the free radicals generated from the matrix where it is embedded it is solubilized and consequently its carbon content becomes available for further abiotic processes of synthesis of molecules of astrobiological interest. The behavior of C 60 appears comparable to that of common PAHs which are also hydroxylated and oxidized under similar conditions. (author)

  6. Radiolysis of astrophysical ice analogs by energetic ions: the effect of projectile mass and ice temperature.

    Science.gov (United States)

    Pilling, Sergio; Duarte, Eduardo Seperuelo; Domaracka, Alicja; Rothard, Hermann; Boduch, Philippe; da Silveira, Enio F

    2011-09-21

    An experimental study of the interaction of highly charged, energetic ions (52 MeV (58)Ni(13+) and 15.7 MeV (16)O(5+)) with mixed H(2)O : C(18)O(2) astrophysical ice analogs at two different temperatures is presented. This analysis aims to simulate the chemical and the physicochemical interactions induced by cosmic rays inside dense, cold astrophysical environments, such as molecular clouds or protostellar clouds as well at the surface of outer solar system bodies. The measurements were performed at the heavy ion accelerator GANIL (Grand Accelerateur National d'Ions Lourds) in Caen, France. The gas samples were deposited onto a CsI substrate at 13 K and 80 K. In situ analysis was performed by a Fourier transform infrared (FTIR) spectrometer at different fluences. Radiolysis yields of the produced species were quantified. The dissociation cross section at 13 K of both H(2)O and CO(2) is about 3-4 times smaller when O ions are employed. The ice temperature seems to affect differently each species when the same projectile was employed. The formation cross section at 13 K of molecules such as C(18)O, CO (with oxygen from water), and H(2)O(2) increases when Ni ions are employed. The formation of organic compounds seems to be enhanced by the oxygen projectiles and at lower temperatures. In addition, because the organic production at 13 K is at least 4 times higher than the value at 80 K, we also expect that interstellar ices are more organic-rich than the surfaces of outer solar system bodies.

  7. Multilayer Formation and Evaporation of Deuterated Ices in Prestellar and Protostellar Cores

    Science.gov (United States)

    Taquet, Vianney; Charnley, Steven B.; Sipilä, Olli

    2014-08-01

    Extremely large deuteration of several molecules has been observed toward prestellar cores and low-mass protostars for a decade. New observations performed toward low-mass protostars suggest that water presents a lower deuteration in the warm inner gas than in the cold external envelope. We coupled a gas-grain astrochemical model with a one-dimensional model of a collapsing core to properly follow the formation and the deuteration of interstellar ices as well as their subsequent evaporation in the low-mass protostellar envelopes with the aim of interpreting the spatial and temporal evolutions of their deuteration. The astrochemical model follows the formation and the evaporation of ices with a multilayer approach and also includes a state-of-the-art deuterated chemical network by taking the spin states of H2 and light ions into account. Because of their slow formation, interstellar ices are chemically heterogeneous and show an increase of their deuterium fractionation toward the surface. The differentiation of the deuteration in ices induces an evolution of the deuteration within protostellar envelopes. The warm inner region is poorly deuterated because it includes the whole molecular content of ices, while the deuteration predicted in the cold external envelope scales with the highly deuterated surface of ices. We are able to reproduce the observed evolution of water deuteration within protostellar envelopes, but we are still unable to predict the super-high deuteration observed for formaldehyde and methanol. Finally, the extension of this study to the deuteration of complex organics, important for the prebiotic chemistry, shows good agreement with the observations, suggesting that we can use the deuteration to retrace their mechanisms and their moments of formation.

  8. Multilayer formation and evaporation of deuterated ices in prestellar and protostellar cores

    International Nuclear Information System (INIS)

    Taquet, Vianney; Charnley, Steven B.; Sipilä, Olli

    2014-01-01

    Extremely large deuteration of several molecules has been observed toward prestellar cores and low-mass protostars for a decade. New observations performed toward low-mass protostars suggest that water presents a lower deuteration in the warm inner gas than in the cold external envelope. We coupled a gas-grain astrochemical model with a one-dimensional model of a collapsing core to properly follow the formation and the deuteration of interstellar ices as well as their subsequent evaporation in the low-mass protostellar envelopes with the aim of interpreting the spatial and temporal evolutions of their deuteration. The astrochemical model follows the formation and the evaporation of ices with a multilayer approach and also includes a state-of-the-art deuterated chemical network by taking the spin states of H 2 and light ions into account. Because of their slow formation, interstellar ices are chemically heterogeneous and show an increase of their deuterium fractionation toward the surface. The differentiation of the deuteration in ices induces an evolution of the deuteration within protostellar envelopes. The warm inner region is poorly deuterated because it includes the whole molecular content of ices, while the deuteration predicted in the cold external envelope scales with the highly deuterated surface of ices. We are able to reproduce the observed evolution of water deuteration within protostellar envelopes, but we are still unable to predict the super-high deuteration observed for formaldehyde and methanol. Finally, the extension of this study to the deuteration of complex organics, important for the prebiotic chemistry, shows good agreement with the observations, suggesting that we can use the deuteration to retrace their mechanisms and their moments of formation.

  9. Multilayer formation and evaporation of deuterated ices in prestellar and protostellar cores

    Energy Technology Data Exchange (ETDEWEB)

    Taquet, Vianney; Charnley, Steven B. [Astrochemistry Laboratory and The Goddard Center for Astrobiology, Mailstop 691, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20770 (United States); Sipilä, Olli [Department of Physics, University of Helsinki, P.O. Box 64, FI-00014 Helsinki (Finland)

    2014-08-10

    Extremely large deuteration of several molecules has been observed toward prestellar cores and low-mass protostars for a decade. New observations performed toward low-mass protostars suggest that water presents a lower deuteration in the warm inner gas than in the cold external envelope. We coupled a gas-grain astrochemical model with a one-dimensional model of a collapsing core to properly follow the formation and the deuteration of interstellar ices as well as their subsequent evaporation in the low-mass protostellar envelopes with the aim of interpreting the spatial and temporal evolutions of their deuteration. The astrochemical model follows the formation and the evaporation of ices with a multilayer approach and also includes a state-of-the-art deuterated chemical network by taking the spin states of H{sub 2} and light ions into account. Because of their slow formation, interstellar ices are chemically heterogeneous and show an increase of their deuterium fractionation toward the surface. The differentiation of the deuteration in ices induces an evolution of the deuteration within protostellar envelopes. The warm inner region is poorly deuterated because it includes the whole molecular content of ices, while the deuteration predicted in the cold external envelope scales with the highly deuterated surface of ices. We are able to reproduce the observed evolution of water deuteration within protostellar envelopes, but we are still unable to predict the super-high deuteration observed for formaldehyde and methanol. Finally, the extension of this study to the deuteration of complex organics, important for the prebiotic chemistry, shows good agreement with the observations, suggesting that we can use the deuteration to retrace their mechanisms and their moments of formation.

  10. Physical processes in the interstellar medium

    CERN Document Server

    Spitzer, Lyman

    2008-01-01

    Physical Processes in the Interstellar Medium discusses the nature of interstellar matter, with a strong emphasis on basic physical principles, and summarizes the present state of knowledge about the interstellar medium by providing the latest observational data. Physics and chemistry of the interstellar medium are treated, with frequent references to observational results. The overall equilibrium and dynamical state of the interstellar gas are described, with discussions of explosions produced by star birth and star death and the initial phases of cloud collapse leading to star formation.

  11. Eyes in the sky. Interactions between asymptotic giant branch star winds and the interstellar magnetic field

    Science.gov (United States)

    van Marle, A. J.; Cox, N. L. J.; Decin, L.

    2014-10-01

    Context. The extended circumstellar envelopes (CSEs) of evolved low-mass stars display a large variety of morphologies. Understanding the various mechanisms that give rise to these extended structures is important to trace their mass-loss history. Aims: Here, we aim to examine the role of the interstellar magnetic field in shaping the extended morphologies of slow dusty winds of asymptotic giant branch (AGB) stars in an effort to pin-point the origin of so-called eye shaped CSEs of three carbon-rich AGB stars. In addition, we seek to understand if this pre-planetary nebula (PN) shaping can be responsible for asymmetries observed in PNe. Methods: Hydrodynamical simulations are used to study the effect of typical interstellar magnetic fields on the free-expanding spherical stellar winds as they sweep up the local interstellar medium (ISM). Results: The simulations show that typical Galactic interstellar magnetic fields of 5 to 10 μG are sufficient to alter the spherical expanding shells of AGB stars to appear as the characteristic eye shape revealed by far-infrared observations. The typical sizes of the simulated eyes are in accordance with the observed physical sizes. However, the eye shapes are transient in nature. Depending on the stellar and interstellar conditions, they develop after 20 000 to 200 000 yrs and last for about 50 000 to 500 000 yrs, assuming that the star is at rest relative to the local interstellar medium. Once formed, the eye shape develops lateral outflows parallel to the magnetic field. The explosion of a PN in the centre of the eye-shaped dust shell gives rise to an asymmetrical nebula with prominent inward pointing Rayleigh-Taylor instabilities. Conclusions: Interstellar magnetic fields can clearly affect the shaping of wind-ISM interaction shells. The occurrence of the eyes is most strongly influenced by stellar space motion and ISM density. Observability of this transient phase is favoured for lines-of-sight perpendicular to the

  12. Do detailed simulations with size-resolved microphysics reproduce basic features of observed cirrus ice size distributions?

    Science.gov (United States)

    Fridlind, A. M.; Atlas, R.; van Diedenhoven, B.; Ackerman, A. S.; Rind, D. H.; Harrington, J. Y.; McFarquhar, G. M.; Um, J.; Jackson, R.; Lawson, P.

    2017-12-01

    It has recently been suggested that seeding synoptic cirrus could have desirable characteristics as a geoengineering approach, but surprisingly large uncertainties remain in the fundamental parameters that govern cirrus properties, such as mass accommodation coefficient, ice crystal physical properties, aggregation efficiency, and ice nucleation rate from typical upper tropospheric aerosol. Only one synoptic cirrus model intercomparison study has been published to date, and studies that compare the shapes of observed and simulated ice size distributions remain sparse. Here we amend a recent model intercomparison setup using observations during two 2010 SPARTICUS campaign flights. We take a quasi-Lagrangian column approach and introduce an ensemble of gravity wave scenarios derived from collocated Doppler cloud radar retrievals of vertical wind speed. We use ice crystal properties derived from in situ cloud particle images, for the first time allowing smoothly varying and internally consistent treatments of nonspherical ice capacitance, fall speed, gravitational collection, and optical properties over all particle sizes in our model. We test two new parameterizations for mass accommodation coefficient as a function of size, temperature and water vapor supersaturation, and several ice nucleation scenarios. Comparison of results with in situ ice particle size distribution data, corrected using state-of-the-art algorithms to remove shattering artifacts, indicate that poorly constrained uncertainties in the number concentration of crystals smaller than 100 µm in maximum dimension still prohibit distinguishing which parameter combinations are more realistic. When projected area is concentrated at such sizes, the only parameter combination that reproduces observed size distribution properties uses a fixed mass accommodation coefficient of 0.01, on the low end of recently reported values. No simulations reproduce the observed abundance of such small crystals when the

  13. Magnetic seismology of interstellar gas clouds: Unveiling a hidden dimension.

    Science.gov (United States)

    Tritsis, Aris; Tassis, Konstantinos

    2018-05-11

    Stars and planets are formed inside dense interstellar molecular clouds by processes imprinted on the three-dimensional (3D) morphology of the clouds. Determining the 3D structure of interstellar clouds remains challenging because of projection effects and difficulties measuring the extent of the clouds along the line of sight. We report the detection of normal vibrational modes in the isolated interstellar cloud Musca, allowing determination of the 3D physical dimensions of the cloud. We found that Musca is vibrating globally, with the characteristic modes of a sheet viewed edge on, not the characteristics of a filament as previously supposed. We reconstructed the physical properties of Musca through 3D magnetohydrodynamic simulations, reproducing the observed normal modes and confirming a sheetlike morphology. Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

  14. Simulating ice thickness and velocity evolution of Upernavik Isstrøm 1849-2012 by forcing prescribed terminus positions in ISSM

    Science.gov (United States)

    Haubner, Konstanze; Box, Jason E.; Schlegel, Nicole J.; Larour, Eric Y.; Morlighem, Mathieu; Solgaard, Anne M.; Kjeldsen, Kristian K.; Larsen, Signe H.; Rignot, Eric; Dupont, Todd K.; Kjær, Kurt H.

    2018-04-01

    Tidewater glacier velocity and mass balance are known to be highly responsive to terminus position change. Yet it remains challenging for ice flow models to reproduce observed ice margin changes. Here, using the Ice Sheet System Model (ISSM; Larour et al. 2012), we simulate the ice velocity and thickness changes of Upernavik Isstrøm (north-western Greenland) by prescribing a collection of 27 observed terminus positions spanning 164 years (1849-2012). The simulation shows increased ice velocity during the 1930s, the late 1970s and between 1995 and 2012 when terminus retreat was observed along with negative surface mass balance anomalies. Three distinct mass balance states are evident in the reconstruction: (1849-1932) with near zero mass balance, (1932-1992) with ice mass loss dominated by ice dynamical flow, and (1998-2012), when increased retreat and negative surface mass balance anomalies led to mass loss that was twice that of any earlier period. Over the multi-decadal simulation, mass loss was dominated by thinning and acceleration responsible for 70 % of the total mass loss induced by prescribed change in terminus position. The remaining 30 % of the total ice mass loss resulted directly from prescribed terminus retreat and decreasing surface mass balance. Although the method can not explain the cause of glacier retreat, it enables the reconstruction of ice flow and geometry during 1849-2012. Given annual or seasonal observed terminus front positions, this method could be a useful tool for evaluating simulations investigating the effect of calving laws.

  15. Adaptation of an unstructured-mesh, finite-element ocean model to the simulation of ocean circulation beneath ice shelves

    Science.gov (United States)

    Kimura, Satoshi; Candy, Adam S.; Holland, Paul R.; Piggott, Matthew D.; Jenkins, Adrian

    2013-07-01

    Several different classes of ocean model are capable of representing floating glacial ice shelves. We describe the incorporation of ice shelves into Fluidity-ICOM, a nonhydrostatic finite-element ocean model with the capacity to utilize meshes that are unstructured and adaptive in three dimensions. This geometric flexibility offers several advantages over previous approaches. The model represents melting and freezing on all ice-shelf surfaces including vertical faces, treats the ice shelf topography as continuous rather than stepped, and does not require any smoothing of the ice topography or any of the additional parameterisations of the ocean mixed layer used in isopycnal or z-coordinate models. The model can also represent a water column that decreases to zero thickness at the 'grounding line', where the floating ice shelf is joined to its tributary ice streams. The model is applied to idealised ice-shelf geometries in order to demonstrate these capabilities. In these simple experiments, arbitrarily coarsening the mesh outside the ice-shelf cavity has little effect on the ice-shelf melt rate, while the mesh resolution within the cavity is found to be highly influential. Smoothing the vertical ice front results in faster flow along the smoothed ice front, allowing greater exchange with the ocean than in simulations with a realistic ice front. A vanishing water-column thickness at the grounding line has little effect in the simulations studied. We also investigate the response of ice shelf basal melting to variations in deep water temperature in the presence of salt stratification.

  16. Polarization of submillimetre lines from interstellar medium

    Science.gov (United States)

    Zhang, Heshou; Yan, Huirong

    2018-04-01

    Magnetic fields play important roles in many astrophysical processes. However, there is no universal diagnostic for the magnetic fields in the interstellar medium (ISM) and each magnetic tracer has its limitation. Any new detection method is thus valuable. Theoretical studies have shown that submillimetre fine-structure lines are polarized due to atomic alignment by ultraviolet photon-excitation, which opens up a new avenue to probe interstellar magnetic fields. We will, for the first time, perform synthetic observations on the simulated three-dimensional ISM to demonstrate the measurability of the polarization of submillimetre atomic lines. The maximum polarization for different absorption and emission lines expected from various sources, including star-forming regions are provided. Our results demonstrate that the polarization of submillimetre atomic lines is a powerful magnetic tracer and add great value to the observational studies of the submilimetre astronomy.

  17. One possible origin of ethanol in interstellar medium: Photochemistry of mixed CO2-C2H6 films at 11 K. A FTIR study

    International Nuclear Information System (INIS)

    Schriver, A.; Schriver-Mazzuoli, L.; Ehrenfreund, P.; D'Hendecourt, L.

    2007-01-01

    It has been predicted by theoretical models that ethane and ethanol are present in icy mantles covering dust particles in dense interstellar clouds. Laboratory spectra of ethanol embedded in astrophysically relevant ice matrices were compared to the Infrared Space Observatory and ground-based astronomical spectra of high mass protostars. From this comparison strict upper-limits of ethanol (compared to solid water) on interstellar grains could be derived that are below 1.2%. In dense star forming regions ethanol is observed in gas phase with an abundance which is many orders of magnitude in excess of predictions based on pure gas-phase chemistry. Ethane has not been observed in the interstellar gas or on grains. In contrast, ethane has been detected in several comets with a percentage of 2 + C 2 H 6 , of CH 3 CH 2 OH and CH 3 CHO in addition to photoproducts of CO 2 or C 2 H 6 and their implications for interstellar/cometary chemistry

  18. On the ionization of interstellar magnesium

    International Nuclear Information System (INIS)

    Gurzadyan, G.A.

    1977-01-01

    It has been shown that two concentric ionization zones of interstellar magnesium must exist around each star: internal, with a radius coinciding with that of the zone of hydrogen ionization Ssub(H); and external, with a radius greater than Ssub(H), by one order. Unlike interstellar hydrogen, interstellar magnesium is ionized throughout the Galaxy. It also transpires that the ionizing radiation of ordinary hot stars cannot provide for the observed high degree of ionization of interstellar magnesium. The discrepance can be eliminated by assuming the existence of circumstellar clouds or additional ionization sources of interstellar magnesium (X-ray background radiation, high-energy particles, etc.). Stars of the B5 and BO class play the main role in the formation of ionization zones of interstellar magnesium; the contribution of O class stars is negligible (<1%). (Auth.)

  19. Modelling snow ice and superimposed ice on landfast sea ice in Kongsfjorden, Svalbard

    Directory of Open Access Journals (Sweden)

    Caixin Wang

    2015-08-01

    Full Text Available Snow ice and superimposed ice formation on landfast sea ice in a Svalbard fjord, Kongsfjorden, was investigated with a high-resolution thermodynamic snow and sea-ice model, applying meteorological weather station data as external forcing. The model shows that sea-ice formation occurs both at the ice bottom and at the snow/ice interface. Modelling results indicated that the total snow ice and superimposed ice, which formed at the snow/ice interface, was about 14 cm during the simulation period, accounting for about 15% of the total ice mass and 35% of the total ice growth. Introducing a time-dependent snow density improved the modelled results, and a time-dependent oceanic heat flux parameterization yielded reasonable ice growth at the ice bottom. Model results suggest that weather conditions, in particular air temperature and precipitation, as well as snow thermal properties and surface albedo are the most critical factors for the development of snow ice and superimposed ice in Kongsfjorden. While both warming air and higher precipitation led to increased snow ice and superimposed ice forming in Kongsfjorden in the model runs, the processes were more sensitive to precipitation than to air temperature.

  20. An Arctic source for the Great Salinity Anomaly - A simulation of the Arctic ice-ocean system for 1955-1975

    Science.gov (United States)

    Hakkinen, Sirpa

    1993-01-01

    The paper employs a fully prognostic Arctic ice-ocean model to study the interannual variability of sea ice during the period 1955-1975 and to explain the large variability of the ice extent in the Greenland and Iceland seas during the late 1960s. The model is used to test the contention of Aagaard and Carmack (1989) that the Great Salinity Anomaly (GSA) was a consequence of the anomalously large ice export in 1968. The high-latitude ice-ocean circulation changes due to wind field changes are explored. The ice export event of 1968 was the largest in the simulation, being about twice as large as the average and corresponding to 1600 cu km of excess fresh water. The simulations suggest that, besides the above average ice export to the Greenland Sea, there was also fresh water export to support the larger than average ice cover. The model results show the origin of the GSA to be in the Arctic, and support the view that the Arctic may play an active role in climate change.

  1. Airborne observations and simulations of three-dimensional radiative interactions between Arctic boundary layer clouds and ice floes

    Directory of Open Access Journals (Sweden)

    M. Schäfer

    2015-07-01

    Full Text Available Based on airborne spectral imaging observations, three-dimensional (3-D radiative effects between Arctic boundary layer clouds and highly variable Arctic surfaces were identified and quantified. A method is presented to discriminate between sea ice and open water under cloudy conditions based on airborne nadir reflectivity γλ measurements in the visible spectral range. In cloudy cases the transition of γλ from open water to sea ice is not instantaneous but horizontally smoothed. In general, clouds reduce γλ above bright surfaces in the vicinity of open water, while γλ above open sea is enhanced. With the help of observations and 3-D radiative transfer simulations, this effect was quantified to range between 0 and 2200 m distance to the sea ice edge (for a dark-ocean albedo of αwater = 0.042 and a sea-ice albedo of αice = 0.91 at 645 nm wavelength. The affected distance Δ L was found to depend on both cloud and sea ice properties. For a low-level cloud at 0–200 m altitude, as observed during the Arctic field campaign VERtical Distribution of Ice in Arctic clouds (VERDI in 2012, an increase in the cloud optical thickness τ from 1 to 10 leads to a decrease in Δ L from 600 to 250 m. An increase in the cloud base altitude or cloud geometrical thickness results in an increase in Δ L; for τ = 1/10 Δ L = 2200 m/1250 m in case of a cloud at 500–1000 m altitude. To quantify the effect for different shapes and sizes of ice floes, radiative transfer simulations were performed with various albedo fields (infinitely long straight ice edge, circular ice floes, squares, realistic ice floe field. The simulations show that Δ L increases with increasing radius of the ice floe and reaches maximum values for ice floes with radii larger than 6 km (500–1000 m cloud altitude, which matches the results found for an infinitely long, straight ice edge. Furthermore, the influence of these 3-D radiative effects on the retrieved cloud optical

  2. Airborne observations and simulations of three-dimensional radiative interactions between Arctic boundary layer clouds and ice floes

    Science.gov (United States)

    Schäfer, M.; Bierwirth, E.; Ehrlich, A.; Jäkel, E.; Wendisch, M.

    2015-07-01

    Based on airborne spectral imaging observations, three-dimensional (3-D) radiative effects between Arctic boundary layer clouds and highly variable Arctic surfaces were identified and quantified. A method is presented to discriminate between sea ice and open water under cloudy conditions based on airborne nadir reflectivity γλ measurements in the visible spectral range. In cloudy cases the transition of γλ from open water to sea ice is not instantaneous but horizontally smoothed. In general, clouds reduce γλ above bright surfaces in the vicinity of open water, while γλ above open sea is enhanced. With the help of observations and 3-D radiative transfer simulations, this effect was quantified to range between 0 and 2200 m distance to the sea ice edge (for a dark-ocean albedo of αwater = 0.042 and a sea-ice albedo of αice = 0.91 at 645 nm wavelength). The affected distance Δ L was found to depend on both cloud and sea ice properties. For a low-level cloud at 0-200 m altitude, as observed during the Arctic field campaign VERtical Distribution of Ice in Arctic clouds (VERDI) in 2012, an increase in the cloud optical thickness τ from 1 to 10 leads to a decrease in Δ L from 600 to 250 m. An increase in the cloud base altitude or cloud geometrical thickness results in an increase in Δ L; for τ = 1/10 Δ L = 2200 m/1250 m in case of a cloud at 500-1000 m altitude. To quantify the effect for different shapes and sizes of ice floes, radiative transfer simulations were performed with various albedo fields (infinitely long straight ice edge, circular ice floes, squares, realistic ice floe field). The simulations show that Δ L increases with increasing radius of the ice floe and reaches maximum values for ice floes with radii larger than 6 km (500-1000 m cloud altitude), which matches the results found for an infinitely long, straight ice edge. Furthermore, the influence of these 3-D radiative effects on the retrieved cloud optical properties was investigated

  3. The flow of interstellar dust through the solar system: the role of dust charging

    International Nuclear Information System (INIS)

    Sterken, V. J.; Altobelli, N.; Schwehm, G.; Kempf, S.; Srama, R.; Strub, P.; Gruen, E.

    2011-01-01

    Interstellar dust can enter the solar system through the relative motion of the Sun with respect to the Local Interstellar Cloud. The trajectories of the dust through the solar system are not only influenced by gravitation and solar radiation pressure forces, but also by the Lorentz forces due to the interaction of the interplanetary magnetic field with the charged dust particles. The interplanetary magnetic field changes on two major time scales: 25 days (solar rotation frequency) and 22 years (solar cycle). The short-term variability averages out for regions that are not too close (>∼2 AU) to the Sun. This interplanetary magnetic field variability causes a time-variability in the interstellar dust densities, that is correlated to the solar cycle.In this work we characterize the flow of interstellar dust through the solar system using simulations of the dust trajectories. We start from the simple case without Lorentz forces, and expand to the full simulation. We pay attention to the different ways of modeling the interplanetary magnetic field, and discuss the influence of the dust parameters on the resulting flow patterns. We also discuss the possibilities of using this modeling for prediction of dust fluxes for different space missions or planets, and we pay attention to where simplified models are justified, and where or when a full simulation, including all forces is necessary. One of the aims of this work is to understand measurements of spacecraft like Ulysses, Cassini and Stardust.

  4. Evolution of interstellar organic compounds under asteroidal hydrothermal conditions

    Science.gov (United States)

    Vinogradoff, V.; Bernard, S.; Le Guillou, C.; Remusat, L.

    2018-05-01

    Carbonaceous chondrites (CC) contain a diversity of organic compounds. No definitive evidence for a genetic relationship between these complex organic molecules and the simple organic molecules detected in the interstellar medium (ISM) has yet been reported. One of the many difficulties arises from the transformations of organic compounds during accretion and hydrothermal alteration on asteroids. Here, we report results of hydrothermal alteration experiments conducted on a common constituent of interstellar ice analogs, Hexamethylenetetramine (HMT - C6H12N4). We submitted HMT to asteroidal hydrothermal conditions at 150 °C, for various durations (up to 31 days) and under alkaline pH. Organic products were characterized by gas chromatography mass spectrometry, infrared spectroscopy and synchrotron-based X-ray absorption near edge structure spectroscopy. Results show that, within a few days, HMT has evolved into (1) a very diverse suite of soluble compounds dominated by N-bearing aromatic compounds (> 150 species after 31 days), including for instance formamide, pyridine, pyrrole and their polymers (2) an aromatic and N-rich insoluble material that forms after only 7 days of experiment and then remains stable through time. The reaction pathways leading to the soluble compounds likely include HMT dissociation, formose and Maillard-type reactions, e.g. reactions of sugar derivatives with amines. The present study demonstrates that, if interstellar organic compounds such as HMT had been accreted by chondrite parent bodies, they would have undergone chemical transformations during hydrothermal alteration, potentially leading to the formation of high molecular weight insoluble organic molecules. Some of the diversity of soluble and insoluble organic compounds found in CC may thus result from asteroidal hydrothermal alteration.

  5. Stochastic simulation of climate change impacts on ice road operations, MacKenzie River, Northwest Territories

    International Nuclear Information System (INIS)

    Woo, Mingko; Lonergan, S.

    1990-01-01

    Winter roads constitute an important part of the transportation network in the MacKenzie Delta, the Yellowknife area, and between the MacKenzie Highway and the Canol Road. Climatic changes in the MacKenzie Valley will alter the probabilities of ice cover thickness and duration, impacting on the periods when ice road river crossings are viable. Stochastic models were developed to generate air temperature and precipitation data to analyze climate impacts on when ice road crossing of the MacKenzie River at Norman Wells is feasible. The data were employed to simulate river ice growth and decay. Several general circulation models were employed to determine the impacts of climatic change on the ice regime. For precipitation simulation, the occurrence of wet or dry days was determined from Markov chain transition probabilities. In general, the Goddard Institute of Space Studies (GISS) model predicted the largest increase in monthly precipitation and the Oregon State University (OSU) model predicted the least changes. The various scenarios indicated that the duration for vehicular traffic over ice will be significantly reduced, compared to present day Norman Wells ice crossing operation. For 20 tonne vehicles, the current duration for safe crossing averages 169±14.6 days per year, while for the OSU scenario it will be reduced to 148±14.7 days, is further reduced to 127±24.9 days for the GISS scenario, and drops to 122±21.7 days for the GFDL (General Fluid Dynamics Laboratory) scenario. 5 refs., 1 fig

  6. Ice and water droplets on graphite: A comparison of quantum and classical simulations

    International Nuclear Information System (INIS)

    Ramírez, Rafael; Singh, Jayant K.; Müller-Plathe, Florian; Böhm, Michael C.

    2014-01-01

    Ice and water droplets on graphite have been studied by quantum path integral and classical molecular dynamics simulations. The point-charge q-TIP4P/F potential was used to model the interaction between flexible water molecules, while the water-graphite interaction was described by a Lennard-Jones potential previously used to reproduce the macroscopic contact angle of water droplets on graphite. Several energetic and structural properties of water droplets with sizes between 10 2 and 10 3 molecules were analyzed in a temperature interval of 50–350 K. The vibrational density of states of crystalline and amorphous ice drops was correlated to the one of ice Ih to assess the influence of the droplet interface and molecular disorder on the vibrational properties. The average distance of covalent OH bonds is found 0.01 Å larger in the quantum limit than in the classical one. The OO distances are elongated by 0.03 Å in the quantum simulations at 50 K. Bond distance fluctuations are large as a consequence of the zero-point vibrations. The analysis of the H-bond network shows that the liquid droplet is more structured in the classical limit than in the quantum case. The average kinetic and potential energy of the ice and water droplets on graphite has been compared with the values of ice Ih and liquid water as a function of temperature. The droplet kinetic energy shows a temperature dependence similar to the one of liquid water, without apparent discontinuity at temperatures where the droplet is solid. However, the droplet potential energy becomes significantly larger than the one of ice or water at the same temperature. In the quantum limit, the ice droplet is more expanded than in a classical description. Liquid droplets display identical density profiles and liquid-vapor interfaces in the quantum and classical limits. The value of the contact angle is not influenced by quantum effects. Contact angles of droplets decrease as the size of the water droplet increases

  7. Large Eddy Simulation of Heat Entrainment Under Arctic Sea Ice

    Science.gov (United States)

    Ramudu, Eshwan; Gelderloos, Renske; Yang, Di; Meneveau, Charles; Gnanadesikan, Anand

    2018-01-01

    Arctic sea ice has declined rapidly in recent decades. The faster than projected retreat suggests that free-running large-scale climate models may not be accurately representing some key processes. The small-scale turbulent entrainment of heat from the mixed layer could be one such process. To better understand this mechanism, we model the Arctic Ocean's Canada Basin, which is characterized by a perennial anomalously warm Pacific Summer Water (PSW) layer residing at the base of the mixed layer and a summertime Near-Surface Temperature Maximum (NSTM) within the mixed layer trapping heat from solar radiation. We use large eddy simulation (LES) to investigate heat entrainment for different ice-drift velocities and different initial temperature profiles. The value of LES is that the resolved turbulent fluxes are greater than the subgrid-scale fluxes for most of our parameter space. The results show that the presence of the NSTM enhances heat entrainment from the mixed layer. Additionally there is no PSW heat entrained under the parameter space considered. We propose a scaling law for the ocean-to-ice heat flux which depends on the initial temperature anomaly in the NSTM layer and the ice-drift velocity. A case study of "The Great Arctic Cyclone of 2012" gives a turbulent heat flux from the mixed layer that is approximately 70% of the total ocean-to-ice heat flux estimated from the PIOMAS model often used for short-term predictions. Present results highlight the need for large-scale climate models to account for the NSTM layer.

  8. Sensitivity of Cirrus and Mixed-phase Clouds to the Ice Nuclei Spectra in McRAS-AC: Single Column Model Simulations

    Science.gov (United States)

    Betancourt, R. Morales; Lee, D.; Oreopoulos, L.; Sud, Y. C.; Barahona, D.; Nenes, A.

    2012-01-01

    The salient features of mixed-phase and ice clouds in a GCM cloud scheme are examined using the ice formation parameterizations of Liu and Penner (LP) and Barahona and Nenes (BN). The performance of LP and BN ice nucleation parameterizations were assessed in the GEOS-5 AGCM using the McRAS-AC cloud microphysics framework in single column mode. Four dimensional assimilated data from the intensive observation period of ARM TWP-ICE campaign was used to drive the fluxes and lateral forcing. Simulation experiments where established to test the impact of each parameterization in the resulting cloud fields. Three commonly used IN spectra were utilized in the BN parameterization to described the availability of IN for heterogeneous ice nucleation. The results show large similarities in the cirrus cloud regime between all the schemes tested, in which ice crystal concentrations were within a factor of 10 regardless of the parameterization used. In mixed-phase clouds there are some persistent differences in cloud particle number concentration and size, as well as in cloud fraction, ice water mixing ratio, and ice water path. Contact freezing in the simulated mixed-phase clouds contributed to transfer liquid to ice efficiently, so that on average, the clouds were fully glaciated at T approximately 260K, irrespective of the ice nucleation parameterization used. Comparison of simulated ice water path to available satellite derived observations were also performed, finding that all the schemes tested with the BN parameterization predicted 20 average values of IWP within plus or minus 15% of the observations.

  9. Late Quaternary Variability of Arctic Sea Ice: Insights From Biomarker Proxy Records and Model Simulations

    Science.gov (United States)

    Stein, R. H.; Fahl, K.; Gierz, P.; Niessen, F.; Lohmann, G.

    2017-12-01

    Over the last about four decades, coinciding with global warming and atmospheric CO2increase, the extent and thickness of Arctic sea ice has decreased dramatically, a decrease much more rapid than predicted by climate models. The driving forces of this change are still not fully understood. In this context, detailed paleoclimatic records going back beyond the timescale of direct observations, i.e., high-resolution Holocene records but also records representing more distant warm periods, may help to to distinguish and quantify more precisely the natural and anthropogenic greenhouse gas forcing of global climate change and related sea ice decrease. Here, we concentrate on sea ice biomarker records representing the penultimate glacial/last interglacial (MIS 6/MIS 5e) and the Holocene time intervals. Our proxy records are compared with climate model simulations using a coupled atmosphere-ocean general circulation model (AOGCM). Based on our data, polynya-type sea ice conditions probably occurred off the major ice sheets along the northern Barents and East Siberian continental margins during late MIS 6. Furthermore, we demonstrate that even during MIS 5e, i.e., a time interval when the high latitudes have been significantly warmer than today, sea ice existed in the central Arctic Ocean during summer, whereas sea ice was significantly reduced along the Barents Sea continental margin influenced by Atlantic Water inflow. Assuming a closed Bering Strait (no Pacific Water inflow) during early MIS 5, model simulations point to a significantly reduced sea ice cover in the central Arctic Ocean, a scenario that is however not supported by the proxy record and thus seems to be less realistic. Our Holocene biomarker proxy records from the Chukchi Sea indicate that main factors controlling the millennial Holocene variability in sea ice are probably changes in surface water and heat flow from the Pacific into the Arctic Ocean as well as the long-term decrease in summer insolation

  10. An efficient regional energy-moisture balance model for simulation of the Greenland Ice Sheet response to climate change

    Directory of Open Access Journals (Sweden)

    A. Robinson

    2010-04-01

    Full Text Available In order to explore the response of the Greenland ice sheet (GIS to climate change on long (centennial to multi-millennial time scales, a regional energy-moisture balance model has been developed. This model simulates seasonal variations of temperature and precipitation over Greenland and explicitly accounts for elevation and albedo feedbacks. From these fields, the annual mean surface temperature and surface mass balance can be determined and used to force an ice sheet model. The melt component of the surface mass balance is computed here using both a positive degree day approach and a more physically-based alternative that includes insolation and albedo explicitly. As a validation of the climate model, we first simulated temperature and precipitation over Greenland for the prescribed, present-day topography. Our simulated climatology compares well to observations and does not differ significantly from that of a simple parameterization used in many previous simulations. Furthermore, the calculated surface mass balance using both melt schemes falls within the range of recent regional climate model results. For a prescribed, ice-free state, the differences in simulated climatology between the regional energy-moisture balance model and the simple parameterization become significant, with our model showing much stronger summer warming. When coupled to a three-dimensional ice sheet model and initialized with present-day conditions, the two melt schemes both allow realistic simulations of the present-day GIS.

  11. Interstellar dust within the life cycle of the interstellar medium

    OpenAIRE

    Demyk K.

    2012-01-01

    Cosmic dust is omnipresent in the Universe. Its presence influences the evolution of the astronomical objects which in turn modify its physical and chemical properties. The nature of cosmic dust, its intimate coupling with its environment, constitute a rich field of research based on observations, modelling and experimental work. This review presents the observations of the different components of interstellar dust and discusses their evolution during the life cycle of the interstellar medium.

  12. Development of computer program for simulation of an ice bank system operation, Part I: Mathematical modelling

    Energy Technology Data Exchange (ETDEWEB)

    Halasz, Boris; Grozdek, Marino; Soldo, Vladimir [Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Ivana Lucica 5, 10 000 Zagreb (Croatia)

    2009-09-15

    Since the use of standard engineering methods in the process of an ice bank performance evaluation offers neither adequate flexibility nor accuracy, the aim of this research was to provide a powerful tool for an industrial design of an ice storage system allowing to account for the various design parameters and system arrangements over a wide range of time varying operating conditions. In this paper the development of a computer application for the prediction of an ice bank system operation is presented. Static, indirect, cool thermal storage systems with external ice on coil building/melting were considered. The mathematical model was developed by means of energy and mass balance relations for each component of the system and is basically divided into two parts, the model of an ice storage system and the model of a refrigeration unit. Heat transfer processes in an ice silo were modelled by use of empirical correlations while the performance of refrigeration unit components were based on manufacturers data. Programming and application design were made in Fortran 95 language standard. Input of data is enabled through drop down menus and dialog boxes, while the results are presented via figures, diagrams and data (ASCII) files. In addition, to demonstrate the necessity for development of simulation program a case study was performed. Simulation results clearly indicate that no simple engineering methods or rule of thumb principles could be utilised in order to validate performance of an ice bank system properly. (author)

  13. NON-RACEMIC AMINO ACID PRODUCTION BY ULTRAVIOLET IRRADIATION OF ACHIRAL INTERSTELLAR ICE ANALOGS WITH CIRCULARLY POLARIZED LIGHT

    International Nuclear Information System (INIS)

    De Marcellus, Pierre; Nuevo, Michel; Danger, Gregoire; Deboffle, Dominique; Le Sergeant d'Hendecourt, Louis; Meinert, Cornelia; Filippi, Jean-Jacques; Meierhenrich, Uwe J.; Nahon, Laurent

    2011-01-01

    The delivery of organic matter to the primitive Earth via comets and meteorites has long been hypothesized to be an important source for prebiotic compounds such as amino acids or their chemical precursors that contributed to the development of prebiotic chemistry leading, on Earth, to the emergence of life. Photochemistry of inter/circumstellar ices around protostellar objects is a potential process leading to complex organic species, although difficult to establish from limited infrared observations only. Here we report the first abiotic cosmic ice simulation experiments that produce species with enantiomeric excesses (e.e.'s). Circularly polarized ultraviolet light (UV-CPL) from a synchrotron source induces asymmetric photochemistry on initially achiral inter/circumstellar ice analogs. Enantioselective multidimensional gas chromatography measurements show significant e.e.'s of up to 1.34% for ( 13 C)-alanine, for which the signs and absolute values are related to the helicity and number of CPL photons per deposited molecule. This result, directly comparable with some L excesses measured in meteorites, supports a scenario in which exogenous delivery of organics displaying a slight L excess, produced in an extraterrestrial environment by an asymmetric astrophysical process, is at the origin of biomolecular asymmetry on Earth. As a consequence, a fraction of the meteoritic organic material consisting of non-racemic compounds may well have been formed outside the solar system. Finally, following this hypothesis, we support the idea that the protosolar nebula has indeed been formed in a region of massive star formation, regions where UV-CPL of the same helicity is actually observed over large spatial areas.

  14. Spin-ice behavior of three-dimensional inverse opal-like magnetic structures: Micromagnetic simulations

    Science.gov (United States)

    Dubitskiy, I. S.; Syromyatnikov, A. V.; Grigoryeva, N. A.; Mistonov, A. A.; Sapoletova, N. A.; Grigoriev, S. V.

    2017-11-01

    We perform micromagnetic simulations of the magnetization distribution in inverse opal-like structures (IOLS) made from ferromagnetic materials (nickel and cobalt). It is shown that the unit cell of these complex structures, whose characteristic length is approximately 700 nm, can be divided into a set of structural elements some of which behave like Ising-like objects. A spin-ice behavior of IOLS is observed in a broad range of external magnetic fields. Numerical results describe successfully the experimental hysteresis curves of the magnetization in Ni- and Co-based IOLS. We conclude that ferromagnetic IOLS can be considered as the first realization of three-dimensional artificial spin ice. The problem is discussed of optimal geometrical properties and material characteristics of IOLS for the spin-ice rule fulfillment.

  15. Interstellar organic chemistry.

    Science.gov (United States)

    Sagan, C.

    1972-01-01

    Most of the interstellar organic molecules have been found in the large radio source Sagittarius B2 toward the galactic center, and in such regions as W51 and the IR source in the Orion nebula. Questions of the reliability of molecular identifications are discussed together with aspects of organic synthesis in condensing clouds, degradational origin, synthesis on grains, UV natural selection, interstellar biology, and contributions to planetary biology.

  16. Modeling Commercial Turbofan Engine Icing Risk With Ice Crystal Ingestion

    Science.gov (United States)

    Jorgenson, Philip C. E.; Veres, Joseph P.

    2013-01-01

    The occurrence of ice accretion within commercial high bypass aircraft turbine engines has been reported under certain atmospheric conditions. Engine anomalies have taken place at high altitudes that have been attributed to ice crystal ingestion, partially melting, and ice accretion on the compression system components. The result was degraded engine performance, and one or more of the following: loss of thrust control (roll back), compressor surge or stall, and flameout of the combustor. As ice crystals are ingested into the fan and low pressure compression system, the increase in air temperature causes a portion of the ice crystals to melt. It is hypothesized that this allows the ice-water mixture to cover the metal surfaces of the compressor stationary components which leads to ice accretion through evaporative cooling. Ice accretion causes a blockage which subsequently results in the deterioration in performance of the compressor and engine. The focus of this research is to apply an engine icing computational tool to simulate the flow through a turbofan engine and assess the risk of ice accretion. The tool is comprised of an engine system thermodynamic cycle code, a compressor flow analysis code, and an ice particle melt code that has the capability of determining the rate of sublimation, melting, and evaporation through the compressor flow path, without modeling the actual ice accretion. A commercial turbofan engine which has previously experienced icing events during operation in a high altitude ice crystal environment has been tested in the Propulsion Systems Laboratory (PSL) altitude test facility at NASA Glenn Research Center. The PSL has the capability to produce a continuous ice cloud which are ingested by the engine during operation over a range of altitude conditions. The PSL test results confirmed that there was ice accretion in the engine due to ice crystal ingestion, at the same simulated altitude operating conditions as experienced previously in

  17. A Large Eddy Simulation Study of Heat Entrainment under Sea Ice in the Canadian Arctic Basin

    Science.gov (United States)

    Ramudu, E.; Yang, D.; Gelderloos, R.; Meneveau, C. V.; Gnanadesikan, A.

    2016-12-01

    Sea ice cover in the Arctic has declined rapidly in recent decades. The much faster than projected retreat suggests that climate models may be missing some key processes, or that these processes are not accurately represented. The entrainment of heat from the mixed layer by small-scale turbulence is one such process. In the Canadian Basin of the Arctic Ocean, relatively warm Pacific Summer Water (PSW) resides at the base of the mixed layer. With an increasing influx of PSW, the upper ocean in the Canadian Basin has been getting warmer and fresher since the early 2000s. While studies show a correlation between sea ice reduction and an increase in PSW temperature, others argue that PSW intrusions in the Canadian Basin cannot affect sea ice thickness because the strongly-stratified halocline prevents heat from the PSW layer from being entrained into the mixed layer and up to the basal ice surface. In this study, we try to resolve this conundrum by simulating the turbulent entrainment of heat from the PSW layer to a moving basal ice surface using large eddy simulation (LES). The LES model is based on a high-fidelity spectral approach on horizontal planes, and includes a Lagrangian dynamic subgrid model that reduces the need for empirical inputs for subgrid-scale viscosities and diffusivities. This LES tool allows us to investigate physical processes in the mixed layer at a very fine scale. We focus our study on summer conditions, when ice is melting, and show for a range of ice-drift velocities, halocline temperatures, and halocline salinity gradients characteristic of the Canadian Basin how much heat can be entrained from the PSW layer to the sea ice. Our results can be used to improve parameterizations of vertical heat flux under sea ice in coarse-grid ocean and climate models.

  18. Sticking properties of ice grains

    Science.gov (United States)

    Jongmanns, M.; Kumm, M.; Wurm, G.; Wolf, D. E.; Teiser, J.

    2017-06-01

    We study the size dependence of pull-off forces of water ice in laboratory experiments and numerical simulations. To determine the pull-off force in our laboratory experiments, we use a liquid nitrogen cooled centrifuge. Depending on its rotation frequency, spherical ice grains detach due to the centrifugal force which is related to the adhesive properties. Numerical simulations are conducted by means of molecular dynamics simulations of hexagonal ice using a standard coarse-grained water potential. The pull-off force of a single contact between two spherical ice grains is measured due to strain controlled simulations. Both, the experimental study and the simulations reveal a dependence between the pull-off force and the (reduced) particle radii, which differ significantly from the linear dependence of common contact theories.

  19. Observations and simulations of three-dimensional radiative interactions between Arctic boundary layer clouds and ice floes

    Science.gov (United States)

    Schäfer, M.; Bierwirth, E.; Ehrlich, A.; Jäkel, E.; Wendisch, M.

    2015-01-01

    Based on airborne spectral imaging observations three-dimensional (3-D) radiative effects between Arctic boundary layer clouds and ice floes have been identified and quantified. A method is presented to discriminate sea ice and open water in case of clouds from imaging radiance measurements. This separation simultaneously reveals that in case of clouds the transition of radiance between open water and sea ice is not instantaneously but horizontally smoothed. In general, clouds reduce the nadir radiance above bright surfaces in the vicinity of sea ice - open water boundaries, while the nadir radiance above dark surfaces is enhanced compared to situations with clouds located above horizontal homogeneous surfaces. With help of the observations and 3-D radiative transfer simulations, this effect was quantified to range between 0 and 2200 m distance to the sea ice edge. This affected distance Δ L was found to depend on both, cloud and sea ice properties. For a ground overlaying cloud in 0-200 m altitude, increasing the cloud optical thickness from τ = 1 to τ = 10 decreases Δ L from 600 to 250 m, while increasing cloud base altitude or cloud geometrical thickness can increase Δ L; Δ L(τ = 1/10) = 2200 m/1250 m for 500-1000 m cloud altitude. To quantify the effect for different shapes and sizes of the ice floes, various albedo fields (infinite straight ice edge, circles, squares, realistic ice floe field) were modelled. Simulations show that Δ L increases by the radius of the ice floe and for sizes larger than 6 km (500-1000 m cloud altitude) asymptotically reaches maximum values, which corresponds to an infinite straight ice edge. Furthermore, the impact of these 3-D-radiative effects on retrieval of cloud optical properties was investigated. The enhanced brightness of a dark pixel next to an ice edge results in uncertainties of up to 90 and 30% in retrievals of cloud optical thickness and effective radius reff, respectively. With help of Δ L quantified here, an

  20. SIMULATION OF THE Ku-BAND RADAR ALTIMETER SEA ICE EFFECTIVE SCATTERING SURFACE

    DEFF Research Database (Denmark)

    Tonboe, Rasmus; Andersen, Søren; Pedersen, Leif Toudal

    2006-01-01

    A radiative transfer model is used to simulate the sea ice radar altimeter effective scattering surface variability as a function of snow depth and density. Under dry snow conditions without layering these are the primary snow parameters affecting the scattering surface variability. The model is ...

  1. Sea-ice deformation in a coupled ocean–sea-ice model and in satellite remote sensing data

    Directory of Open Access Journals (Sweden)

    G. Spreen

    2017-07-01

    Full Text Available A realistic representation of sea-ice deformation in models is important for accurate simulation of the sea-ice mass balance. Simulated sea-ice deformation from numerical simulations with 4.5, 9, and 18 km horizontal grid spacing and a viscous–plastic (VP sea-ice rheology are compared with synthetic aperture radar (SAR satellite observations (RGPS, RADARSAT Geophysical Processor System for the time period 1996–2008. All three simulations can reproduce the large-scale ice deformation patterns, but small-scale sea-ice deformations and linear kinematic features (LKFs are not adequately reproduced. The mean sea-ice total deformation rate is about 40 % lower in all model solutions than in the satellite observations, especially in the seasonal sea-ice zone. A decrease in model grid spacing, however, produces a higher density and more localized ice deformation features. The 4.5 km simulation produces some linear kinematic features, but not with the right frequency. The dependence on length scale and probability density functions (PDFs of absolute divergence and shear for all three model solutions show a power-law scaling behavior similar to RGPS observations, contrary to what was found in some previous studies. Overall, the 4.5 km simulation produces the most realistic divergence, vorticity, and shear when compared with RGPS data. This study provides an evaluation of high and coarse-resolution viscous–plastic sea-ice simulations based on spatial distribution, time series, and power-law scaling metrics.

  2. Enhanced ice sheet growth in Eurasia owing to adjacent ice-dammed lakes.

    Science.gov (United States)

    Krinner, G; Mangerud, J; Jakobsson, M; Crucifix, M; Ritz, C; Svendsen, J I

    2004-01-29

    Large proglacial lakes cool regional summer climate because of their large heat capacity, and have been shown to modify precipitation through mesoscale atmospheric feedbacks, as in the case of Lake Agassiz. Several large ice-dammed lakes, with a combined area twice that of the Caspian Sea, were formed in northern Eurasia about 90,000 years ago, during the last glacial period when an ice sheet centred over the Barents and Kara seas blocked the large northbound Russian rivers. Here we present high-resolution simulations with an atmospheric general circulation model that explicitly simulates the surface mass balance of the ice sheet. We show that the main influence of the Eurasian proglacial lakes was a significant reduction of ice sheet melting at the southern margin of the Barents-Kara ice sheet through strong regional summer cooling over large parts of Russia. In our simulations, the summer melt reduction clearly outweighs lake-induced decreases in moisture and hence snowfall, such as has been reported earlier for Lake Agassiz. We conclude that the summer cooling mechanism from proglacial lakes accelerated ice sheet growth and delayed ice sheet decay in Eurasia and probably also in North America.

  3. CO ICE PHOTODESORPTION: A WAVELENGTH-DEPENDENT STUDY

    International Nuclear Information System (INIS)

    Fayolle, Edith C.; Linnartz, Harold; Bertin, Mathieu; Romanzin, Claire; Michaut, Xavier; Fillion, Jean-Hugues; Oeberg, Karin I.

    2011-01-01

    UV-induced photodesorption of ice is a non-thermal evaporation process that can explain the presence of cold molecular gas in a range of interstellar regions. Information on the average UV photodesorption yield of astrophysically important ices exists for broadband UV lamp experiments. UV fields around low-mass pre-main-sequence stars, around shocks and in many other astrophysical environments are however often dominated by discrete atomic and molecular emission lines. It is therefore crucial to consider the wavelength dependence of photodesorption yields and mechanisms. In this work, for the first time, the wavelength-dependent photodesorption of pure CO ice is explored between 90 and 170 nm. The experiments are performed under ultra high vacuum conditions using tunable synchrotron radiation. Ice photodesorption is simultaneously probed by infrared absorption spectroscopy in reflection mode of the ice and by quadrupole mass spectrometry of the gas phase. The experimental results for CO reveal a strong wavelength dependence directly linked to the vibronic transition strengths of CO ice, implying that photodesorption is induced by electronic transition (DIET). The observed dependence on the ice absorption spectra implies relatively low photodesorption yields at 121.6 nm (Lyα), where CO barely absorbs, compared to the high yields found at wavelengths coinciding with transitions into the first electronic state of CO (A 1 Π at 150 nm); the CO photodesorption rates depend strongly on the UV profiles encountered in different star formation environments.

  4. SECONDARY POPULATION OF INTERSTELLAR NEUTRALS seems deflected to the side

    Science.gov (United States)

    Nakagawa, H.; Bzowski, M.; Yamazaki, A.; Fukunishi, H.; Watanabe, S.; Takahashi, Y.; Taguchi, M.

    Recently the neutral hydrogen flow in the inner heliosphere was found to be deflected relative to the helium flow by about 4 degrees Lallement et al 2005 The explanation of this delfection offered was a distortion of the heliosphere under the action of an ambient interstellar magnetic field In a separate study a number of data sets pertaining to interstellar neutral atoms obtained with various techniques were compiled and interpreted as due to an inflow of interstellar gas from an ecliptic longitude shifted by 10 - 40 degrees from the canonical upstream interstellar neutral flow direction at 254 degrees Collier et al 2004 The origin and properties of such a flow is still under debate We have performed a cross-experiment analysis of the heliospheric hydrogen and helium photometric observations performed simltaneously by the Nozomi spacecraft between the Earth and Mars orbit and explored possible deflection of hydrogen and helium flows with respect to the canonical upwind direction For the interpretation we used predictions of a state of the art 3D and fully time-dependent model of the neutral gas in the heliosphere with the boundary conditions ionization rates and radiation pressure taken from literature The model includes two populations of the thermal interstellar hydrogen predicted by the highly-reputed Moscow Monte Carlo model of the heliosphere The agreement between the data and simulations is not satifactory when one assumes that the upwind direction is the same for both populations and identical with the direction derived from inerstellar helium

  5. Improved ice particle optical property simulations in the ultraviolet to far-infrared regime

    International Nuclear Information System (INIS)

    Bi, Lei; Yang, Ping

    2017-01-01

    To derive the bulk radiative properties of ice clouds, aircraft contrails and snow grains, which are fundamental to atmospheric radiative transfer calculations in downstream applications, it is necessary to accurately simulate the scattering of light by individual ice particles. An ice particle optical property database reported in 2013 (hereafter, TAMUice2013) is updated (hereafter, TAMUice2016) to incorporate recent advances in computation of the optical properties of nonspherical particles. Specifically, we employ the invariant imbedding T-matrix (II-TM) method to compute the optical properties of particles with small to moderate size parameters. Both versions use the Improved Geometric Optics Method (IGOM) to compute the optical properties of large ice crystals, but TAMUice2016 improves the treatment of inhomogeneous waves inside the scattering particles in the case where ice is absorptive such as at infrared wavelengths. To bridge the gap between the extinction efficiencies computed from the II-TM and the IGOM, TAMUice2016 includes spectrally dependent higher order terms of the edge effect in addition to the first order counterpart considered in TAMUice2013. Furthermore, the differences between TAMUice2013 and TAMUice2016 are quantified with respect to the computation of the bulk optical properties of ice clouds. - Highlights: • A previous database of the single-scattering properties of ice crystals is improved. • A combination of the invariant imbedding T-matrix and improved geometric optics methods is used. • The treatment of inhomogeneous waves in an absorptive ice crystal is improved. • Higher order terms of the edge effect are considered in the updated database.

  6. Ice Storage Air-Conditioning System Simulation with Dynamic Electricity Pricing: A Demand Response Study

    Directory of Open Access Journals (Sweden)

    Chi-Chun Lo

    2016-02-01

    Full Text Available This paper presents an optimal dispatch model of an ice storage air-conditioning system for participants to quickly and accurately perform energy saving and demand response, and to avoid the over contact with electricity price peak. The schedule planning for an ice storage air-conditioning system of demand response is mainly to transfer energy consumption from the peak load to the partial-peak or off-peak load. Least Squares Regression (LSR is used to obtain the polynomial function for the cooling capacity and the cost of power consumption with a real ice storage air-conditioning system. Based on the dynamic electricity pricing, the requirements of cooling loads, and all technical constraints, the dispatch model of the ice-storage air-conditioning system is formulated to minimize the operation cost. The Improved Ripple Bee Swarm Optimization (IRBSO algorithm is proposed to solve the dispatch model of the ice storage air-conditioning system in a daily schedule on summer. Simulation results indicate that reasonable solutions provide a practical and flexible framework allowing the demand response of ice storage air-conditioning systems to demonstrate the optimization of its energy savings and operational efficiency and offering greater energy efficiency.

  7. The destruction and growth of dust grains in interstellar space

    International Nuclear Information System (INIS)

    Barlow, M.J.

    1978-01-01

    The processes governing the destruction and growth of dust grains in interstellar space are investigated with a view to establishing the conditions required for the existence of ice mantles. In this paper sputtering by particles with energies in the eV to GeV range is considered. Previous sputtering yield estimates which were based on theoretical considerations are shown to be greatly in error for incident particle energies of less than 1 keV. Empirical formulae for the sputtering threshold energy and the sputtering yield are derived from the extensive experimental data available. The sputtering of grains in H II regions, in the inter-cloud medium, and in shock waves produced by cloud-cloud collisions and by supernova remnants, is investigated. Of these, supernova remnants are shown to be the most important, leading to lifetimes of approximately 2 x 10 8 yr for ice grains and between 5 to 20 x 10 8 yr for refractory grains. Destruction rates are estimated for grains bombarded by MeV and GeV cosmic rays. It is shown that collision cascade sputtering dominates evaporative sputtering produced by thermal spikes. It is also shown that even if all electron excitation energy loss in a grain material could be transferred to the lattice particles, the observed cosmic ray flux spectrum could not cause significant destruction of ice grains. (author)

  8. Sticking properties of ice grains

    Directory of Open Access Journals (Sweden)

    Jongmanns M.

    2017-01-01

    Full Text Available We study the size dependence of pull-off forces of water ice in laboratory experiments and numerical simulations. To determine the pull-off force in our laboratory experiments, we use a liquid nitrogen cooled centrifuge. Depending on its rotation frequency, spherical ice grains detach due to the centrifugal force which is related to the adhesive properties. Numerical simulations are conducted by means of molecular dynamics simulations of hexagonal ice using a standard coarse-grained water potential. The pull-off force of a single contact between two spherical ice grains is measured due to strain controlled simulations. Both, the experimental study and the simulations reveal a dependence between the pull-off force and the (reduced particle radii, which differ significantly from the linear dependence of common contact theories.

  9. Eddy-resolving simulations of the Fimbul Ice Shelf cavity circulation: Basal melting and exchange with open ocean

    Science.gov (United States)

    Hattermann, T.; Smedsrud, L. H.; Nøst, O. A.; Lilly, J. M.; Galton-Fenzi, B. K.

    2014-10-01

    Melting at the base of floating ice shelves is a dominant term in the overall Antarctic mass budget. This study applies a high-resolution regional ice shelf/ocean model, constrained by observations, to (i) quantify present basal mass loss at the Fimbul Ice Shelf (FIS); and (ii) investigate the oceanic mechanisms that govern the heat supply to ice shelves in the Eastern Weddell Sea. The simulations confirm the low melt rates suggested by observations and show that melting is primarily determined by the depth of the coastal thermocline, regulating deep ocean heat fluxes towards the ice. Furthermore, the uneven distribution of ice shelf area at different depths modulates the melting response to oceanic forcing, causing the existence of two distinct states of melting at the FIS. In the simulated present-day state, only small amounts of Modified Warm Deep Water enter the continental shelf, and ocean temperatures beneath the ice are close to the surface freezing point. The basal mass loss in this so-called state of "shallow melting" is mainly controlled by the seasonal inflow of solar-heated surface water affecting large areas of shallow ice in the upper part of the cavity. This is in contrast to a state of "deep melting", in which the thermocline rises above the shelf break depth, establishing a continuous inflow of Warm Deep Water towards the deep ice. The transition between the two states is found to be determined by a complex response of the Antarctic Slope Front overturning circulation to varying climate forcings. A proper representation of these frontal dynamics in climate models will therefore be crucial when assessing the evolution of ice shelf basal melting along this sector of Antarctica.

  10. Glycine formation in CO2:CH4:NH3 ices induced by 0-70 eV electrons

    Science.gov (United States)

    Esmaili, Sasan; Bass, Andrew D.; Cloutier, Pierre; Sanche, Léon; Huels, Michael A.

    2018-04-01

    Glycine (Gly), the simplest amino-acid building-block of proteins, has been identified on icy dust grains in the interstellar medium, icy comets, and ice covered meteorites. These astrophysical ices contain simple molecules (e.g., CO2, H2O, CH4, HCN, and NH3) and are exposed to complex radiation fields, e.g., UV, γ, or X-rays, stellar/solar wind particles, or cosmic rays. While much current effort is focused on understanding the radiochemistry induced in these ices by high energy radiation, the effects of the abundant secondary low energy electrons (LEEs) it produces have been mostly assumed rather than studied. Here we present the results for the exposure of multilayer CO2:CH4:NH3 ice mixtures to 0-70 eV electrons under simulated astrophysical conditions. Mass selected temperature programmed desorption (TPD) of our electron irradiated films reveals multiple products, most notably intact glycine, which is supported by control measurements of both irradiated or un-irradiated binary mixture films, and un-irradiated CO2:CH4:NH3 ices spiked with Gly. The threshold of Gly formation by LEEs is near 9 eV, while the TPD analysis of Gly film growth allows us to determine the "quantum" yield for 70 eV electrons to be about 0.004 Gly per incident electron. Our results show that simple amino acids can be formed directly from simple molecular ingredients, none of which possess preformed C—C or C—N bonds, by the copious secondary LEEs that are generated by ionizing radiation in astrophysical ices.

  11. Thermodynamics of high-pressure ice polymorphs : ices III and V

    NARCIS (Netherlands)

    Tchijov, [No Value; Ayala, RB; Leon, GC; Nagornov, O

    Thermodynamic properties of high-pressure ice polymorphs, ices III and V, are studied theoretically. The results of TIP4P molecular dynamics simulations in the NPT ensemble are used to calculate the temperature dependence of the specific volume of ices III and V at pressures 0.25 and 0.5 GPa,

  12. Multiphase Reactive Transport and Platelet Ice Accretion in the Sea Ice of McMurdo Sound, Antarctica

    Science.gov (United States)

    Buffo, J. J.; Schmidt, B. E.; Huber, C.

    2018-01-01

    Sea ice seasonally to interannually forms a thermal, chemical, and physical boundary between the atmosphere and hydrosphere over tens of millions of square kilometers of ocean. Its presence affects both local and global climate and ocean dynamics, ice shelf processes, and biological communities. Accurate incorporation of sea ice growth and decay, and its associated thermal and physiochemical processes, is underrepresented in large-scale models due to the complex physics that dictate oceanic ice formation and evolution. Two phenomena complicate sea ice simulation, particularly in the Antarctic: the multiphase physics of reactive transport brought about by the inhomogeneous solidification of seawater, and the buoyancy driven accretion of platelet ice formed by supercooled ice shelf water onto the basal surface of the overlying ice. Here a one-dimensional finite difference model capable of simulating both processes is developed and tested against ice core data. Temperature, salinity, liquid fraction, fluid velocity, total salt content, and ice structure are computed during model runs. The model results agree well with empirical observations and simulations highlight the effect platelet ice accretion has on overall ice thickness and characteristics. Results from sensitivity studies emphasize the need to further constrain sea ice microstructure and the associated physics, particularly permeability-porosity relationships, if a complete model of sea ice evolution is to be obtained. Additionally, implications for terrestrial ice shelves and icy moons in the solar system are discussed.

  13. The effects of sub-ice-shelf melting on dense shelf water formation and export in idealized simulations of Antarctic margins

    Science.gov (United States)

    Marques, Gustavo; Stern, Alon; Harrison, Matthew; Sergienko, Olga; Hallberg, Robert

    2017-04-01

    Dense shelf water (DSW) is formed in coastal polynyas around Antarctica as a result of intense cooling and brine rejection. A fraction of this water reaches ice shelves cavities and is modified due to interactions with sub-ice-shelf melt water. This modified water mass contributes to the formation of Antarctic Bottom Water, and consequently, influences the large-scale ocean circulation. Here, we investigate the role of sub-ice-shelf melting in the formation and export of DSW using idealized simulations with an isopycnal ocean model (MOM6) coupled with a sea ice model (SIS2) and a thermodynamic active ice shelf. A set of experiments is conducted with variable horizontal grid resolutions (0.5, 1.0 and 2.0 km), ice shelf geometries and atmospheric forcing. In all simulations DSW is spontaneously formed in coastal polynyas due to the combined effect of the imposed atmospheric forcing and the ocean state. Our results show that sub-ice-shelf melting can significantly change the rate of dense shelf water outflows, highlighting the importance of this process to correctly represent bottom water formation.

  14. A multifunctional setup to record FTIR and UV-vis spectra of organic molecules and their photoproducts in astronomical ices.

    Science.gov (United States)

    Kofman, V; Witlox, M J A; Bouwman, J; Ten Kate, I L; Linnartz, H

    2018-05-01

    This article describes a new, multi-functional, high-vacuum ice setup that allows to record the in situ and real-time spectra of vacuum UV (VUV)-irradiated non-volatile molecules embedded in a low-temperature (10 K) amorphous solid water environment. Three complementary diagnostic tools-UV-visible (UV-vis) and Fourier Transform Infrared (FTIR) spectroscopy and temperature-programmed desorption quadrupole mass spectrometry-can be used to simultaneously study the physical and chemical behavior of the organic molecules in the ice upon VUV irradiation. The setup is equipped with a temperature-controlled sublimation oven that enables the controlled homogeneous deposition of solid species such as amino acids, nucleobases, and polycyclic aromatic hydrocarbons (PAHs) in ice mixtures prepared from precursor gases and/or liquids. The resulting ice is photo-processed with a microwave discharge hydrogen lamp, generating VUV radiation with a spectral energy distribution representative for the interstellar medium. The characteristics, performance, and future potential of the system are discussed by describing three different applications. First, a new method is introduced, which uses broadband interference transmission fringes recorded during ice deposition, to determine the wavelength-dependent refractive index, n λ , of amorphous solid water. This approach is also applicable to other solids, pure and mixed. Second, the UV-vis and FTIR spectroscopy of an VUV-irradiated triphenylene:water ice mixture is discussed, monitoring the ionization efficiency of PAHs in interstellar ice environments. The third and final example investigates the stability of solid glycine upon VUV irradiation by monitoring the formation of dissociation products in real time.

  15. A multifunctional setup to record FTIR and UV-vis spectra of organic molecules and their photoproducts in astronomical ices

    Science.gov (United States)

    Kofman, V.; Witlox, M. J. A.; Bouwman, J.; ten Kate, I. L.; Linnartz, H.

    2018-05-01

    This article describes a new, multi-functional, high-vacuum ice setup that allows to record the in situ and real-time spectra of vacuum UV (VUV)-irradiated non-volatile molecules embedded in a low-temperature (10 K) amorphous solid water environment. Three complementary diagnostic tools—UV-visible (UV-vis) and Fourier Transform Infrared (FTIR) spectroscopy and temperature-programmed desorption quadrupole mass spectrometry—can be used to simultaneously study the physical and chemical behavior of the organic molecules in the ice upon VUV irradiation. The setup is equipped with a temperature-controlled sublimation oven that enables the controlled homogeneous deposition of solid species such as amino acids, nucleobases, and polycyclic aromatic hydrocarbons (PAHs) in ice mixtures prepared from precursor gases and/or liquids. The resulting ice is photo-processed with a microwave discharge hydrogen lamp, generating VUV radiation with a spectral energy distribution representative for the interstellar medium. The characteristics, performance, and future potential of the system are discussed by describing three different applications. First, a new method is introduced, which uses broadband interference transmission fringes recorded during ice deposition, to determine the wavelength-dependent refractive index, nλ, of amorphous solid water. This approach is also applicable to other solids, pure and mixed. Second, the UV-vis and FTIR spectroscopy of an VUV-irradiated triphenylene:water ice mixture is discussed, monitoring the ionization efficiency of PAHs in interstellar ice environments. The third and final example investigates the stability of solid glycine upon VUV irradiation by monitoring the formation of dissociation products in real time.

  16. Irradiation effects induced by multiply charged heavy ions on astrophysical materials such as crystals and ices

    International Nuclear Information System (INIS)

    Langlinay, Thomas

    2014-01-01

    The solar system and the interstellar medium are permanently exposed to radiations such as solar wind and cosmic rays. The interaction between energetic particles and astrophysical materials (ices, silicates and carbon-based materials) plays an important role in several astrophysical phenomena. Laboratory experiments correlated to observational data may allow a better understanding of these phenomena. The aim of this thesis was to study the effect of slow and fast heavy ions on lithium fluoride and on astrophysical materials such as ices and silicates. We focused on the sputtering phenomenon. The present study was performed with a time of flight imaging technique (XY-TOF-SIMS) at the CIMAP-GANIL laboratory. The major fraction of secondary ions is found to be emitted in the form of clusters. Several parameters affect sputtering: the stopping power regime, the thickness of the target, the incident angle and, for low highly charged ions, the projectile charge. Our laboratory simulations exhibit the possibility that sputtered particles contribute to the formation of Mercury's and Jupiter's moons exosphere. (author)

  17. Diffusion and infrared properties of molecules in ice mantles

    International Nuclear Information System (INIS)

    Schmitt, B.; Grim, R.; Greenberg, J.M.

    1989-01-01

    Within dense molecular clouds the formation of frozen icy mantles on interstellar dust grains is thought to be the result of various growth conditions. The molecules, which make up the ice mantles are probably completely mixed. To study the physical properties of such ice mixtures the experiments were performed on the evaporation processes and on the spectroscopic properties of CO, CO2, and CH4 in water rich ices. The decrease in concentration of volatile molecules in ice samples deposited at 10 K and subsequently heated is found to occur essentially in two steps. The first one, corresponding to an evaporation of part of the volatile molecules, starts at about 25 K for CO, 32 K for CH4, and 70 K for CO2. During the crystallization of H2O ice at temperatures greater than 120 K a second evaporation occurs leading to the complete disappearance of the volatile molecules in the solid phase. The main astrophysical implications of the diffusion and spectroscopic behaviors are presented. The possible effects of a heating source on the fraction of volatile molecules, such as CO trapped in grain mantles, are discussed

  18. Interstellar turbulence model : A self-consistent coupling of plasma and neutral fluids

    International Nuclear Information System (INIS)

    Shaikh, Dastgeer; Zank, Gary P.; Pogorelov, Nikolai

    2006-01-01

    We present results of a preliminary investigation of interstellar turbulence based on a self-consistent two-dimensional fluid simulation model. Our model describes a partially ionized magnetofluid interstellar medium (ISM) that couples a neutral hydrogen fluid to a plasma through charge exchange interactions and assumes that the ISM turbulent correlation scales are much bigger than the shock characteristic length-scales, but smaller than the charge exchange mean free path length-scales. The shocks have no influence on the ISM turbulent fluctuations. We find that nonlinear interactions in coupled plasma-neutral ISM turbulence are influenced substantially by charge exchange processes

  19. Model simulations with COSMO-SPECS: impact of heterogeneous freezing modes and ice nucleating particle types on ice formation and precipitation in a deep convective cloud

    Directory of Open Access Journals (Sweden)

    K. Diehl

    2018-03-01

    Full Text Available In deep convective clouds, heavy rain is often formed involving the ice phase. Simulations were performed using the 3-D cloud resolving model COSMO-SPECS with detailed spectral microphysics including parameterizations of homogeneous and three heterogeneous freezing modes. The initial conditions were selected to result in a deep convective cloud reaching 14 km of altitude with strong updrafts up to 40 m s−1. At such altitudes with corresponding temperatures below −40 °C the major fraction of liquid drops freezes homogeneously. The goal of the present model simulations was to investigate how additional heterogeneous freezing will affect ice formation and precipitation although its contribution to total ice formation may be rather low. In such a situation small perturbations that do not show significant effects at first sight may trigger cloud microphysical responses. Effects of the following small perturbations were studied: (1 additional ice formation via immersion, contact, and deposition modes in comparison to solely homogeneous freezing, (2 contact and deposition freezing in comparison to immersion freezing, and (3 small fractions of biological ice nucleating particles (INPs in comparison to higher fractions of mineral dust INP. The results indicate that the modification of precipitation proceeds via the formation of larger ice particles, which may be supported by direct freezing of larger drops, the growth of pristine ice particles by riming, and by nucleation of larger drops by collisions with pristine ice particles. In comparison to the reference case with homogeneous freezing only, such small perturbations due to additional heterogeneous freezing rather affect the total precipitation amount. It is more likely that the temporal development and the local distribution of precipitation are affected by such perturbations. This results in a gradual increase in precipitation at early cloud stages instead of a strong increase at

  20. Nature of interstellar turbulence

    International Nuclear Information System (INIS)

    Altunin, V.

    1981-01-01

    A significant role in producing the pattern of interstellar scintillation observed in discrete radio sources may be played by the magnetoacoustic turbulence that will be generated as shock waves are propagated at velocity V/sub sh/roughly-equal 20--100 km/sec through the interstellar medium, as well as by irregularities in stellar wind emanating from type OB stars

  1. A significant reduction of ice adhesion on nanostructured surfaces that consist of an array of single-walled carbon nanotubes: A molecular dynamics simulation study

    Science.gov (United States)

    Bao, Luyao; Huang, Zhaoyuan; Priezjev, Nikolai V.; Chen, Shaoqiang; Luo, Kai; Hu, Haibao

    2018-04-01

    It is well recognized that excessive ice accumulation at low-temperature conditions can cause significant damage to civil infrastructure. The passive anti-icing surfaces provide a promising solution to suppress ice nucleation and enhance ice removal. However, despite extensive efforts, it remains a challenge to design anti-icing surfaces with low ice adhesion. Using all-atom molecular dynamics (MD) simulations, we show that surfaces with single-walled carbon nanotube array (CNTA) significantly reduce ice adhesion due to the extremely low solid areal fraction. It was found that the CNTA surface exhibits up to a 45% decrease in the ice adhesion strength in comparison with the atomically smooth graphene surface. The details of the ice detachment from the CNTA surface were examined for different water-carbon interaction energies and temperatures of the ice cube. Remarkably, the results of MD simulations demonstrate that the ice detaching strength depends linearly on the ratio of the ice-surface interaction energy and the ice temperature. These results open the possibility for designing novel robust surfaces with low ice adhesion for passive anti-icing applications.

  2. Ice flow Modelling of the Greenland Ice Sheet

    DEFF Research Database (Denmark)

    Nielsen, Lisbeth Tangaa

    Models of ice flow have a range of application in glaciology, including investigating the large-scale response of ice sheets to changes in climate, assimilating data to estimate unknown conditions beneath the ice sheet, and in interpreting proxy records obtained from ice cores, among others. In t...... a steady state with respect to the reference climate at the end of the simulation and that the mass balance of the ice sheet at this time was more sensitive to recent climate fluctuations than the temperature forcing in the early or mid-Holocene.......Models of ice flow have a range of application in glaciology, including investigating the large-scale response of ice sheets to changes in climate, assimilating data to estimate unknown conditions beneath the ice sheet, and in interpreting proxy records obtained from ice cores, among others....... In this PhD project, the use of ice flow models for the interpretation of the age-structure of the Greenland ice sheet, i.e. the depth within the ice, at which ice deposited at given times are found at present day. Two different observational data sets of this archive were investigated. Further, paleo...

  3. Spontaneous abrupt climate change due to an atmospheric blocking-sea-ice-ocean feedback in an unforced climate model simulation.

    Science.gov (United States)

    Drijfhout, Sybren; Gleeson, Emily; Dijkstra, Henk A; Livina, Valerie

    2013-12-03

    Abrupt climate change is abundant in geological records, but climate models rarely have been able to simulate such events in response to realistic forcing. Here we report on a spontaneous abrupt cooling event, lasting for more than a century, with a temperature anomaly similar to that of the Little Ice Age. The event was simulated in the preindustrial control run of a high-resolution climate model, without imposing external perturbations. Initial cooling started with a period of enhanced atmospheric blocking over the eastern subpolar gyre. In response, a southward progression of the sea-ice margin occurred, and the sea-level pressure anomaly was locked to the sea-ice margin through thermal forcing. The cold-core high steered more cold air to the area, reinforcing the sea-ice concentration anomaly east of Greenland. The sea-ice surplus was carried southward by ocean currents around the tip of Greenland. South of 70 °N, sea ice already started melting and the associated freshwater anomaly was carried to the Labrador Sea, shutting off deep convection. There, surface waters were exposed longer to atmospheric cooling and sea surface temperature dropped, causing an even larger thermally forced high above the Labrador Sea. In consequence, east of Greenland, anomalous winds changed from north to south, terminating the event with similar abruptness to its onset. Our results imply that only climate models that possess sufficient resolution to correctly represent atmospheric blocking, in combination with a sensitive sea-ice model, are able to simulate this kind of abrupt climate change.

  4. Simulation of how a geo-engineering intervention to restore arctic sea ice might work in practice

    Science.gov (United States)

    Jackson, L. S.; Crook, J. A.; Forster, P.; Jarvis, A.; Leedal, D.; Ridgwell, A. J.; Vaughan, N.

    2013-12-01

    The declining trend in annual minimum Arctic sea ice coverage and years of more pronounced drops like 2007 and 2012 raise the prospect of an Arctic Ocean largely free of sea ice in late summer and the potential for a climate crisis or emergency. In a novel computer simulation, we treated one realisation of a climate model (HadGEM2) as the real world and tried to restore its Arctic sea ice by the rapid deployment of geo-engineering with emission of SO2 into the Arctic stratosphere. The objective was to restore the annual minimum Arctic sea ice coverage to levels seen in the late twentieth century using as little geo-engineering as possible. We took intervention decisions as one might do in the real world: by committee, using a limited set of uncertain 'observations' from our simulated world and using models and control theory to plan the best intervention strategy for the coming year - so learning as we went and being thrown off course by future volcanoes and technological breakdowns. Uncertainties in real world observations were simulated by applying noise to emerging results from the climate model. Volcanic forcing of twenty-first century climate was included with the timing and magnitude of the simulated eruptions unknown by the 'geo-engineers' until after the year of the eruption. Monitoring of Arctic sea ice with the option to intervene with SO2 emissions started from 2018 and continued to 2075. Simulated SO2 emissions were made in January-May each year at a latitude of 79o N and an altitude within the range of contemporary tanker aircraft. The magnitude of emissions was chosen annually using a model predictive control process calibrated using results from CMIP5 models (excluding HadGEM2), using the simplified climate model MAGICC and assimilation of emerging annual results from the HadGEM2 'real world'. We found that doubts in the minds of the 'geo-engineers' of the effectiveness and the side effects of their past intervention, and the veracity of the models

  5. The distribution of interstellar dust

    International Nuclear Information System (INIS)

    Clocchiatti, A.; Marraco, H.G.

    1986-01-01

    We propose the interstellar matter structural function as a tool to derive the features of the interstellar dust distribution. We study that function resolving some ideal dust distribution models. Later we describe the method used to find a reliable computing algorithm for the observational case. Finally, we describe the steps to build a model for the interstellar matter composed by spherically symmetrical clouds. The density distribution for each of these clouds is D(r) = D 0 .esup(-r/r 0 ) 2 . The preliminary results obtained are summarised. (author)

  6. Development of Experimental Icing Simulation Capability for Full-Scale Swept Wings: Hybrid Design Process, Years 1 and 2

    Science.gov (United States)

    Fujiwara, Gustavo; Bragg, Mike; Triphahn, Chris; Wiberg, Brock; Woodard, Brian; Loth, Eric; Malone, Adam; Paul, Bernard; Pitera, David; Wilcox, Pete; hide

    2017-01-01

    This report presents the key results from the first two years of a program to develop experimental icing simulation capabilities for full-scale swept wings. This investigation was undertaken as a part of a larger collaborative research effort on ice accretion and aerodynamics for large-scale swept wings. Ice accretion and the resulting aerodynamic effect on large-scale swept wings presents a significant airplane design and certification challenge to air frame manufacturers, certification authorities, and research organizations alike. While the effect of ice accretion on straight wings has been studied in detail for many years, the available data on swept-wing icing are much more limited, especially for larger scales.

  7. Interstellar depletions and the filling factor of the hot interstellar medium

    International Nuclear Information System (INIS)

    Dwek, E.; Scalo, J.M.

    1979-01-01

    We have examined theoretically the evolution of refractory interstellar grain abundances and corresponding metal deplections in the solar neighborhood. The calculations include a self-consistent treatment of red-giant winds, planetary nebulae, protostellar nebulae, and suprnovae as sources of grains and star formation, and of encounters with supernova blast waves as sinks. We find that in the standard two-phase model for the interstellar medium (ISM), grain destruction is very efficient, and the abundance of refractory grains should be negligible, contrary to observations. In a cloudy three-phase ISM most grains reside in the warm and cold phases of the medium. Supernova blast waves expand predominantly in the hot and tenuous phase of the medium and are showed down as they propagate through a cloud. In order to obtain significant (approx.3) depletions of metals presubably locked up in refractory grain cores, the destruction of grains that reside in the clouds must be minimal. This requires that (a) the density contrast between the cloud and intercloud medium be sufficiently high, and (b) the filling factor of the hot and tenuous gas of the interstellar medium, which presumably gives rise to the O VI absorption and soft X-ray emission, be nearly unity. Much larger depletions (> or approx. =10) must reflect accretion of mantles within interstellar clouds

  8. The IceProd (IceCube Production) Framework

    International Nuclear Information System (INIS)

    Díaz-Vélez, J C

    2014-01-01

    IceProd is a data processing and management framework developed by the IceCube Neutrino Observatory for processing of Monte Carlo simulations and data. IceProd runs as a separate layer on top of middleware or cluster job schedulers and can take advantage of a variety of computing resources including grids such as EGI, OSG, and NorduGrid as well as local clusters running batch systems like HT Condor, PBS, and SGE. This is accomplished by a set of dedicated daemons which process job submission in a coordinated fashion through the use of middleware plug-ins that serve to abstract the details of job submission and job management. IceProd can also manage complex workflow DAGs across distributed computing grids in order to optimize usage of resources. We describe several aspects of IceProd's design and it's applications in collaborative computing environments. We also briefly discuss design aspects of a second generation IceProd, currently being tested in IceCube.

  9. The sensitivity of the Arctic sea ice to orbitally induced insolation changes: a study of the mid-Holocene Paleoclimate Modelling Intercomparison Project 2 and 3 simulations

    Directory of Open Access Journals (Sweden)

    M. Berger

    2013-04-01

    Full Text Available In the present work the Arctic sea ice in the mid-Holocene and the pre-industrial climates are analysed and compared on the basis of climate-model results from the Paleoclimate Modelling Intercomparison Project phase 2 (PMIP2 and phase 3 (PMIP3. The PMIP3 models generally simulate smaller and thinner sea-ice extents than the PMIP2 models both for the pre-industrial and the mid-Holocene climate. Further, the PMIP2 and PMIP3 models all simulate a smaller and thinner Arctic summer sea-ice cover in the mid-Holocene than in the pre-industrial control climate. The PMIP3 models also simulate thinner winter sea ice than the PMIP2 models. The winter sea-ice extent response, i.e. the difference between the mid-Holocene and the pre-industrial climate, varies among both PMIP2 and PMIP3 models. Approximately one half of the models simulate a decrease in winter sea-ice extent and one half simulates an increase. The model-mean summer sea-ice extent is 11 % (21 % smaller in the mid-Holocene than in the pre-industrial climate simulations in the PMIP2 (PMIP3. In accordance with the simple model of Thorndike (1992, the sea-ice thickness response to the insolation change from the pre-industrial to the mid-Holocene is stronger in models with thicker ice in the pre-industrial climate simulation. Further, the analyses show that climate models for which the Arctic sea-ice responses to increasing atmospheric CO2 concentrations are similar may simulate rather different sea-ice responses to the change in solar forcing between the mid-Holocene and the pre-industrial. For two specific models, which are analysed in detail, this difference is found to be associated with differences in the simulated cloud fractions in the summer Arctic; in the model with a larger cloud fraction the effect of insolation change is muted. A sub-set of the mid-Holocene simulations in the PMIP ensemble exhibit open water off the north-eastern coast of Greenland in summer, which can provide a fetch

  10. Diffuse interstellar clouds

    International Nuclear Information System (INIS)

    Black, J.H.

    1987-01-01

    The author defines and discusses the nature of diffuse interstellar clouds. He discusses how they contribute to the general extinction of starlight. The atomic and molecular species that have been identified in the ultraviolet, visible, and near infrared regions of the spectrum of a diffuse cloud are presented. The author illustrates some of the practical considerations that affect absorption line observations of interstellar atoms and molecules. Various aspects of the theoretical description of diffuse clouds required for a full interpretation of the observations are discussed

  11. Organic chemistry and biology of the interstellar medium

    Science.gov (United States)

    Sagan, C.

    1973-01-01

    Interstellar organic chemistry is discussed as the field of study emerging from the discovery of microwave lines of formaldehyde and of hydrogen cyanide in the interstellar medium. The reliability of molecular identifications and comparisons of interstellar and cometary compounds are considered, along with the degradational origin of simple organics. It is pointed out that the contribution of interstellar organic chemistry to problems in biology is not substantive but analogical. The interstellar medium reveals the operation of chemical processes which, on earth and perhaps on vast numbers of planets throughout the universe, led to the origin of life, but the actual molecules of the interstellar medium are unlikely to play any significant biological role.

  12. Formation and Evolution of Interstellar Dust - Bridging Astronomy and Laboratory Astrophysics.

    Science.gov (United States)

    Contreras, Cesar; Ricketts, C. L.; Salama, F.

    2010-05-01

    The study of the formation and the destruction processes of cosmic dust are essential to understand and to quantify the budget of extraterrestrial organic molecules. PAHs are important chemical building blocks of interstellar (IS) dust. They are detected in Interplanetary dust particles (IDPs) and in meteoritic samples. Additionally, observational, laboratory, and theoretical studies have shown that PAHs, in their neutral and ionized forms, are an important, ubiquitous component of the interstellar medium. Carbonaceous materials extracts from mixtures of hydrocarbons (C2H2, C2H4, and benzene) contain a high variety of polycyclic aromatic hydrocarbons (PAHs). (From Jager et al. Carbon 45 (2007) 2981-2994). Studies of large molecular and nano-sized interstellar dust analogs formed from PAH precursors have been performed in our laboratory under conditions that simulate interstellar and circumstellar environments. The species (molecules, molecular fragments, ions, nanoparticles, etc...) formed in the pulsed discharge nozzle (PDN) plasma source are detected and characterized with a high-sensitivity cavity ringdown spectrometer (CRDS) coupled to a Reflectron time-of-flight mass spectrometer (ReTOF-MS), thus providing both spectroscopic and ion mass information in-situ. We will present new experimental results that indicate that nanoparticles are generated in the plasma. From these unique measurements, we derive information on the nature, the size and the structure of interstellar dust particles, the growth and the destruction processes of IS dust and the resulting budget of extraterrestrial organic molecules. Acknowledgments: This research is supported by NASA APRA (Laboratory Astrophysics Program). C. S. C. & C. L. R. acknowledge the support of the NASA Postdoctoral Program.

  13. Ionization of Interstellar Hydrogen

    Science.gov (United States)

    Whang, Y. C.

    1996-09-01

    Interstellar hydrogen can penetrate through the heliopause, enter the heliosphere, and may become ionized by photoionization and by charge exchange with solar wind protons. A fluid model is introduced to study the flow of interstellar hydrogen in the heliosphere. The flow is governed by moment equations obtained from integration of the Boltzmann equation over the velocity space. Under the assumption that the flow is steady axisymmetric and the pressure is isotropic, we develop a method of solution for this fluid model. This model and the method of solution can be used to study the flow of neutral hydrogen with various forms of ionization rate β and boundary conditions for the flow on the upwind side. We study the solution of a special case in which the ionization rate β is inversely proportional to R2 and the interstellar hydrogen flow is uniform at infinity on the upwind side. We solve the moment equations directly for the normalized density NH/NN∞, bulk velocity VH/VN∞, and temperature TH/TN∞ of interstellar hydrogen as functions of r/λ and z/λ, where λ is the ionization scale length. The solution is compared with the kinetic theory solution of Lallement et al. The fluid solution is much less time-consuming than the kinetic theory solutions. Since the ionization rate for production of pickup protons is directly proportional to the local density of neutral hydrogen, the high-resolution solution of interstellar neutral hydrogen obtained here will be used to study the global distribution of pickup protons.

  14. Mechanisms of heating the interstellar matter

    International Nuclear Information System (INIS)

    Lequeux, J.

    1975-01-01

    The knowledge of the interstellar medium has been considerably improved in the recent years, thanks in particular to Radioastronomy and Ultraviolet Space Astronomy. This medium is a natural laboratory where the conditions and various and very different to what can be realised in terrestrial laboratories. To illustrate its interest for physicists here one of the most interesting but controversial points of interstellar astronomy is discussed: the mechanisms for heating and cooling the interstellar medium [fr

  15. Proceedings of the 19. IAHR international symposium on ice : using new technology to understand water-ice interaction

    International Nuclear Information System (INIS)

    Jasek, M.; Andrishak, R.; Siddiqui, A.

    2008-01-01

    This conference provided a venue for scientists, engineers and researchers an opportunity to expand their knowledge of water-ice interactions with reference to water resources, river and coastal hydraulics, risk analysis, energy and the environment. The the theme of new technology falls into 3 basic groups, notably measurement and instrumentation; remote sensing; and numerical simulation. The thermal regime of rivers was discussed along with ice mechanics, ice hydraulics, ice structures and modelling ice phenomena. The titles of the sessions were: river ice, glaciers and climate change; freeze-up processes on rivers and oceans; river ice-structure interactions; numerical simulations in ice engineering; river-ice break-up and ice jam formation; ice measurement; Grasse River ice evaluation; evaluation of structural ice control alternatives; remote sensing; hydropower and dam decommissioning; mechanical behaviour of river ice, ice covered flow and thermal modelling; mathematical and computer model formulations for ice friction and sea ice; ice bergs and ice navigation; ice crushing processes; sea ice and shore/structure interactions; ice properties, testing and physical modelling; ice actions on compliant structures; oil spills in ice; desalination, ice thickness and climate change; and, sea ice ridges. The conference featured 123 presentations, of which 20 have been catalogued separately for inclusion in this database. refs., tabs., figs

  16. Amundsen Sea simulation with optimized ocean, sea ice, and thermodynamic ice shelf model parameters

    Science.gov (United States)

    Nakayama, Y.; Menemenlis, D.; Schodlok, M.; Heimbach, P.; Nguyen, A. T.; Rignot, E. J.

    2016-12-01

    Ice shelves and glaciers of the West Antarctic Ice Sheet are thinning and melting rapidly in the Amundsen Sea (AS). This is thought to be caused by warm Circumpolar Deep Water (CDW) that intrudes via submarine glacial troughs located at the continental shelf break. Recent studies, however, point out that the depth of thermocline, or thickness of Winter Water (WW, potential temperature below -1 °C located above CDW) is critical in determining the melt rate, especially for the Pine Island Glacier (PIG). For example, the basal melt rate of PIG, which decreased by 50% during summer 2012, has been attributed to thickening of WW. Despite the possible importance of WW thickness on ice shelf melting, previous modeling studies in this region have focused primarily on CDW intrusion and have evaluated numerical simulations based on bottom or deep CDW properties. As a result, none of these models have shown a good representation of WW for the AS. In this study, we adjust a small number of model parameters in a regional Amundsen and Bellingshausen Seas configuration of the Massachusetts Institute of Technology general circulation model (MITgcm) to better fit the available observations during the 2007-2010 period. We choose this time period because summer observations during these years show small interannual variability in the eastern AS. As a result of adjustments, our model shows significantly better match with observations than previous modeling studies, especially for WW. Since density of sea water depends largely on salinity at low temperature, this is crucial for assessing the impact of WW on PIG melt rate. In addition, we conduct several sensitivity studies, showing the impact of surface heat loss on the thickness and properties of WW. We also discuss some preliminary results pertaining to further optimization using the adjoint method. Our work is a first step toward improved representation of ice-shelf ocean interactions in the ECCO (Estimating the Circulation and

  17. Icing Simulation Research Supporting the Ice-Accretion Testing of Large-Scale Swept-Wing Models

    Science.gov (United States)

    Yadlin, Yoram; Monnig, Jaime T.; Malone, Adam M.; Paul, Bernard P.

    2018-01-01

    The work summarized in this report is a continuation of NASA's Large-Scale, Swept-Wing Test Articles Fabrication; Research and Test Support for NASA IRT contract (NNC10BA05 -NNC14TA36T) performed by Boeing under the NASA Research and Technology for Aerospace Propulsion Systems (RTAPS) contract. In the study conducted under RTAPS, a series of icing tests in the Icing Research Tunnel (IRT) have been conducted to characterize ice formations on large-scale swept wings representative of modern commercial transport airplanes. The outcome of that campaign was a large database of ice-accretion geometries that can be used for subsequent aerodynamic evaluation in other experimental facilities and for validation of ice-accretion prediction codes.

  18. Interstellar Probe: First Step to the Stars

    Science.gov (United States)

    McNutt, R. L., Jr.

    2017-12-01

    The idea of an "Interstellar Probe," a robotic spacecraft traveling into the nearby interstellar medium for the purpose of scientific investigation, dates to the mid-1960s. The Voyager Interstellar Mission (VIM), an "accidental" 40-year-old by-product of the Grand Tour of the solar system, has provided initial answers to the problem of the global heliospheric configuration and the details of its interface with interstellar space. But the twin Voyager spacecraft have, at most, only another decade of lifetime, and only Voyager 1 has emerged from the heliosheath interaction region. To understand the nature of the interaction, a near-term mission to the "near-by" interstellar medium with modern and focused instrumentation remains a compelling priority. Imaging of energetic neutral atoms (ENAs) by the Ion Neutral CAmera (INCA) on Cassini and from the Interstellar Boundary Explorer (IBEX) in Earth orbit have provided significant new insights into the global interaction region but point to discrepancies with our current understanding. Exploring "as far as possible" into "pristine" interstellar space can resolve these. Hence, reaching large heliocentric distances rapidly is a driver for an Interstellar Probe. Such a mission is timely; understanding the interstellar context of exoplanet systems - and perhaps the context for the emergence of life both here and there - hinges upon what we can discover within our own stellar neighborhood. With current spacecraft technology and high-capability launch vehicles, such as the Space Launch System (SLS), a small, but extremely capable spacecraft, could be dispatched to the near-by interstellar medium with at least twice the speed of the Voyagers. Challenges remain with payload mass and power constraints for optimized science measurements. Mission longevity, as experienced by, but not designed into, the Voyagers, communications capability, and radioisotope power system performance and lifetime are solvable engineering challenges. Such

  19. Computer simulation of dust grain evolution

    Science.gov (United States)

    Liffman, K.

    1989-01-01

    The latest results are reported from a Monte Carlo code that is being developed at NASA Ames. The goal of this program, is to derive from the observed and presumed properties of the interstellar medium (ISM) the following information: (1) the size spectrum of interstellar dust; (2) the chemical structure of interstellar dust; (3) interstellar abundances; and (4) the lifetime of a dust grain in the ISM. Presently this study is restricted to refractory interstellar material, i.e., the formation and destruction of ices are not included in the program. The program is embedded in an analytic solution for the bulk chemical evolution of a two-phase interstellar medium in which stars are born in molecular clouds, but new nucleosynthesis products and stellar return are entered into a complementary intercloud medium. The well-mixed matter of each interstellar phase is repeatedly cycled stochastically through the complementary phase and back. Refractory dust is created by thermal condensation as stellar matter flows away from sites of nucleosynthesis such as novae and supernovae and/or from the matter returned from evolved intermediate stars. The history of each particle is traced by standard Monte Carlo techniques as it is sputtered and fragmented by supernova shock waves in the intercloud medium. It also accretes an amorphous mantle of gaseous refractory atoms when its local medium joins with the molecular cloud medium. Finally it encounters the possibility of astration (destruction by star formation) within the molecular clouds.

  20. Long-term ice sheet-climate interactions under anthropogenic greenhouse forcing simulated with a complex Earth System Model

    Energy Technology Data Exchange (ETDEWEB)

    Vizcaino, Miren [Max-Planck-Institut fuer Meteorologie, Hamburg (Germany); University of California, Department of Geography, Berkeley, CA (United States); Mikolajewicz, Uwe; Maier-Reimer, Ernst [Max-Planck-Institut fuer Meteorologie, Hamburg (Germany); Groeger, Matthias [Max-Planck-Institut fuer Meteorologie, Hamburg (Germany); IFM-GEOMAR, Kiel (Germany); Schurgers, Guy [Max-Planck-Institut fuer Meteorologie, Hamburg (Germany); Lund University, Department of Physical Geography and Ecosystems Analysis, Lund (Sweden); Winguth, Arne M.E. [Center for Climatic Research, Department of Atmospheric and Oceanic Sciences, Madison (United States)

    2008-11-15

    Several multi-century and multi-millennia simulations have been performed with a complex Earth System Model (ESM) for different anthropogenic climate change scenarios in order to study the long-term evolution of sea level and the impact of ice sheet changes on the climate system. The core of the ESM is a coupled coarse-resolution Atmosphere-Ocean General Circulation Model (AOGCM). Ocean biogeochemistry, land vegetation and ice sheets are included as components of the ESM. The Greenland Ice Sheet (GrIS) decays in all simulations, while the Antarctic ice sheet contributes negatively to sea level rise, due to enhanced storage of water caused by larger snowfall rates. Freshwater flux increases from Greenland are one order of magnitude smaller than total freshwater flux increases into the North Atlantic basin (the sum of the contribution from changes in precipitation, evaporation, run-off and Greenland meltwater) and do not play an important role in changes in the strength of the North Atlantic Meridional Overturning Circulation (NAMOC). The regional climate change associated with weakening/collapse of the NAMOC drastically reduces the decay rate of the GrIS. The dynamical changes due to GrIS topography modification driven by mass balance changes act first as a negative feedback for the decay of the ice sheet, but accelerate the decay at a later stage. The increase of surface temperature due to reduced topographic heights causes a strong acceleration of the decay of the ice sheet in the long term. Other feedbacks between ice sheet and atmosphere are not important for the mass balance of the GrIS until it is reduced to 3/4 of the original size. From then, the reduction in the albedo of Greenland strongly accelerates the decay of the ice sheet. (orig.)

  1. A PROTOSOLAR NEBULA ORIGIN FOR THE ICES AGGLOMERATED BY COMET 67P/CHURYUMOV–GERASIMENKO

    Energy Technology Data Exchange (ETDEWEB)

    Mousis, O.; Vernazza, P. [Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, F-13388 Marseille (France); Lunine, J. I. [Center For Radiophysics And Space Research, Space Sciences Building Cornell University, Ithaca, NY 14853 (United States); Luspay-Kuti, A.; Hässig, M.; Waite, J. H. [Department of Space Research, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78228 (United States); Guillot, T. [Laboratoire J.-L. Lagrange, Université de Nice-Sophia Antipolis, CNRS, Observatoire de la Côte d’Azur, BP 4229, F-06304 Nice (France); Marty, B. [CRPG-CNRS, Nancy-Université, 15 rue Notre Dame des Pauvres, F-54501 Vandoeuvre-lès-Nancy (France); Ali-Dib, M. [Université de Franche-Comté, Institut UTINAM, CNRS/INSU, UMR 6213, Besançon Cedex (France); Wurz, P.; Altwegg, K.; Bieler, A.; Rubin, M., E-mail: olivier.mousis@lam.fr [Physikalisches Institut, University of Bern, Sidlerstrasse 5, CH-3012 Bern (Switzerland)

    2016-03-10

    The nature of the icy material accreted by comets during their formation in the outer regions of the protosolar nebula (PSN) is a major open question in planetary science. Some scenarios of comet formation predict that these bodies agglomerated from crystalline ices condensed in the PSN. Concurrently, alternative scenarios suggest that comets accreted amorphous ice originating from the interstellar cloud or from the very distant regions of the PSN. On the basis of existing laboratory and modeling data, we find that the N{sub 2}/CO and Ar/CO ratios measured in the coma of the Jupiter-family comet 67P/Churyumov–Gerasimenko by the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis instrument on board the European Space Agency’s Rosetta spacecraft match those predicted for gases trapped in clathrates. If these measurements are representative of the bulk N{sub 2}/CO and Ar/CO ratios in 67P/Churyumov–Gerasimenko, it implies that the ices accreted by the comet formed in the nebula and do not originate from the interstellar medium, supporting the idea that the building blocks of outer solar system bodies have been formed from clathrates and possibly from pure crystalline ices. Moreover, because 67P/Churyumov–Gerasimenko is impoverished in Ar and N{sub 2}, the volatile enrichments observed in Jupiter’s atmosphere cannot be explained solely via the accretion of building blocks with similar compositions and require an additional delivery source. A potential source may be the accretion of gas from the nebula that has been progressively enriched in heavy elements due to photoevaporation.

  2. Effects of noise on the interstellar polarization law

    International Nuclear Information System (INIS)

    Clarke, D.; Al-Roubaie, A.

    1983-01-01

    A re-appraisal has been made of catalogued four- and seven-colour polarimetric data in terms of the Serkowski law P(lambda)/Psub(max)=exp(-K ln 2 (lambdasub(max)/lambda)) for the wavelength dependence of interstellar polarization. It has been found that the parameter (K) controlling the peakiness of the p(lambda) curve is not a constant at 1.15 but that it is correlated with the value of lambdasub(max), the wavelength corresponding to the maximum value of p(lambda). It has also been found the the form of the correlation depends significantly on the choice of the wavelength values used to measure p(lambda). A numerical exercise involving data simulation shows that the correlations found in the real data could be an artifact of the random noise on the p(lambda) measurements. It is also suggested that a recent proposal to refine the interstellar law reflects, at least partly, the effects of random noise associated with polarimetric measurements. (author)

  3. OXYGEN DEPLETION IN THE INTERSTELLAR MEDIUM: IMPLICATIONS FOR GRAIN MODELS AND THE DISTRIBUTION OF ELEMENTAL OXYGEN

    International Nuclear Information System (INIS)

    Whittet, D. C. B.

    2010-01-01

    This paper assesses the implications of a recent discovery that atomic oxygen is being depleted from diffuse interstellar gas at a rate that cannot be accounted for by its presence in silicate and metallic oxide particles. To place this discovery in context, the uptake of elemental O into dust is considered over a wide range of environments, from the tenuous intercloud gas and diffuse clouds sampled by the depletion observations to dense clouds where ice mantles and gaseous CO become important reservoirs of O. The distribution of O in these contrasting regions is quantified in terms of a common parameter, the mean number density of hydrogen (n H ). At the interface between diffuse and dense phases (just before the onset of ice-mantle growth) as much as ∼160 ppm of the O abundance is unaccounted for. If this reservoir of depleted oxygen persists to higher densities it has implications for the oxygen budget in molecular clouds, where a shortfall of the same order is observed. Of various potential carriers, the most plausible appears to be a form of O-bearing carbonaceous matter similar to the organics found in cometary particles returned by the Stardust mission. The 'organic refractory' model for interstellar dust is re-examined in the light of these findings, and it is concluded that further observations and laboratory work are needed to determine whether this class of material is present in quantities sufficient to account for a significant fraction of the unidentified depleted oxygen.

  4. INTERSTELLAR PICKUP ION PRODUCTION IN THE GLOBAL HELIOSPHERE AND HELIOSHEATH

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Y.; Florinski, V.; Guo, X., E-mail: yw0009@uah.edu [Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, Huntsville, AL 35805 (United States)

    2016-11-20

    Interstellar pickup ions (PUIs) play a significant part in mediating the solar wind (SW) interaction with the interstellar medium. In this paper, we examine the details of spatial variation of the PUI velocity distribution function (VDF) in the SW by solving the PUI transport equation. We assume the PUI distribution is isotropic resulting from strong pitch-angle scattering by wave–particle interaction. A three-dimensional model combining the MHD treatment of the background SW and neutrals with a kinetic treatment of PUIs throughout the heliosphere and the surrounding local interstellar medium has been developed. The model generates PUI power-law tails via second-order Fermi process. We analyze how PUIs transform across the heliospheric termination shock and obtain the PUI phase space distribution in the inner heliosheath including continuing velocity diffusion. Our simulated PUI spectra are compared with observations made by New Horizons , Ulysses , Voyager 1, 2 , and Cassini , and a satisfactory agreement is demonstrated. Some specific features in the observations, for example, a cutoff of PUI VDF at v = V {sub SW} and a f ∝ v {sup -5} tail in the reference frame of the SW, are well represented by the model.

  5. Analysis of "Midnight" Tracks in the Stardust Interstellar Dust Collector: Possible Discovery of a Contemporary Interstellar Dust Grain

    Science.gov (United States)

    Westphal, A. J.; Allen, C.; Bajit, S.; Bastien, R.; Bechtel, H.; Bleuet, P.; Borg, J.; Brenker, F.; Bridges, J.; Brownlee, D. E.; hide

    2010-01-01

    In January 2006, the Stardust sample return capsule returned to Earth bearing the first solid samples from a primitive solar system body, Comet 81P/Wild2, and a collector dedicated to the capture and return of contemporary interstellar dust. Both collectors were approximately 0.1m(exp 2) in area and were composed of aerogel tiles (85% of the collecting area) and aluminum foils. The Stardust Interstellar Dust Collector (SIDC) was exposed to the interstellar dust stream for a total exposure factor of 20 m(exp 2) day. The Stardust Interstellar Preliminary Examination (ISPE) is a three-year effort to characterize the collection using nondestructive techniques.

  6. Recent interstellar molecular line work

    International Nuclear Information System (INIS)

    Winnewisser, G.

    1975-01-01

    A summary of recent interstellar molecular line work is presented. Transitions of the following molecules have been detected in Sgr B2: Vinylcyanide, H 2 C 2 HCN, formic acid, HCOOH, dimethyl ether (CH 3 ) 2 O and isotopically labelled cyanoacetylene- 13 C,HC 13 CCN and HCC 13 CN. The data on cyanoacetylene give an upper limit to the abundance ratio 12 C/ 13 C of 36 +- 5. A short discussion of the interstellar chemistry leads to the conclusion that hydrocarbons such as acetylene, HCCH, ethylen, H 2 CCH 2 and ethane H 3 CCH 3 should be present in interstellar clouds. 13 refs

  7. UV irradiation of polycyclic aromatic hydrocarbons in ices: production of alcohols, quinones, and ethers

    Science.gov (United States)

    Bernstein, M. P.; Sandford, S. A.; Allamandola, L. J.; Gillette, J. S.; Clemett, S. J.; Zare, R. N.

    1999-01-01

    Polycyclic aromatic hydrocarbons (PAHs) in water ice were exposed to ultraviolet (UV) radiation under astrophysical conditions, and the products were analyzed by infrared spectroscopy and mass spectrometry. Peripheral carbon atoms were oxidized, producing aromatic alcohols, ketones, and ethers, and reduced, producing partially hydrogenated aromatic hydrocarbons, molecules that account for the interstellar 3.4-micrometer emission feature. These classes of compounds are all present in carbonaceous meteorites. Hydrogen and deuterium atoms exchange readily between the PAHs and the ice, which may explain the deuterium enrichments found in certain meteoritic molecules. This work has important implications for extraterrestrial organics in biogenesis.

  8. Synbiotic Amazonian palm berry (açai, Euterpe oleracea Mart.) ice cream improved Lactobacillus rhamnosus GG survival to simulated gastrointestinal stress.

    Science.gov (United States)

    Costa, Mayra Garcia Maia; Ooki, Gabriela Namur; Vieira, Antônio Diogo Silva; Bedani, Raquel; Saad, Susana Marta Isay

    2017-02-22

    The effect of açai pulp ice cream and of its supplementation with inulin (I), whey protein concentrate (WC), and/or whey protein isolate (WI) on the viability and resistance to simulated gastrointestinal stress of the probiotic Lactobacillus (Lb.) rhamnosus GG strain throughout storage at -18 °C for up to 112 days was evaluated and morphological changes during stress were monitored. Lb. rhamnosus GG viability was stable in all formulations for up to 112 days of storage, preserving populations around 9 log CFU g -1 . Compared to the fresh culture, Lb. rhamnosus GG showed higher survival under simulated gastrointestinal conditions when incorporated into açai ice cream, indicating that the presence of the food matrix contributed to the microorganism survival. A reduction of at least 5 log cycles of Lb. rhamnosus GG was observed in all formulations after the gastrointestinal simulation in all storage periods assessed. The addition of I, WC, and/or WI did not show any significant effect on the probiotic survival under simulated gastrointestinal stress (p ice cream. Thus, the açai pulp ice cream was shown to be a suitable matrix for Lb. rhamnosus GG, improving its survival under in vitro simulated gastrointestinal conditions.

  9. Climate Impacts of Ice Nucleation

    Science.gov (United States)

    Gettelman, Andrew; Liu, Xiaohong; Barahona, Donifan; Lohmann, Ulrike; Chen, Celia

    2012-01-01

    Several different ice nucleation parameterizations in two different General Circulation Models (GCMs) are used to understand the effects of ice nucleation on the mean climate state, and the Aerosol Indirect Effects (AIE) of cirrus clouds on climate. Simulations have a range of ice microphysical states that are consistent with the spread of observations, but many simulations have higher present-day ice crystal number concentrations than in-situ observations. These different states result from different parameterizations of ice cloud nucleation processes, and feature different balances of homogeneous and heterogeneous nucleation. Black carbon aerosols have a small (0.06 Wm(exp-2) and not statistically significant AIE when included as ice nuclei, for nucleation efficiencies within the range of laboratory measurements. Indirect effects of anthropogenic aerosols on cirrus clouds occur as a consequence of increasing anthropogenic sulfur emissions with different mechanisms important in different models. In one model this is due to increases in homogeneous nucleation fraction, and in the other due to increases in heterogeneous nucleation with coated dust. The magnitude of the effect is the same however. The resulting ice AIE does not seem strongly dependent on the balance between homogeneous and heterogeneous ice nucleation. Regional effects can reach several Wm2. Indirect effects are slightly larger for those states with less homogeneous nucleation and lower ice number concentration in the base state. The total ice AIE is estimated at 0.27 +/- 0.10 Wm(exp-2) (1 sigma uncertainty). This represents a 20% offset of the simulated total shortwave AIE for ice and liquid clouds of 1.6 Wm(sup-2).

  10. THERMODYNAMICS AND CHARGING OF INTERSTELLAR IRON NANOPARTICLES

    Energy Technology Data Exchange (ETDEWEB)

    Hensley, Brandon S. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Draine, B. T., E-mail: brandon.s.hensley@jpl.nasa.gov [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)

    2017-01-10

    Interstellar iron in the form of metallic iron nanoparticles may constitute a component of the interstellar dust. We compute the stability of iron nanoparticles to sublimation in the interstellar radiation field, finding that iron clusters can persist down to a radius of ≃4.5 Å, and perhaps smaller. We employ laboratory data on small iron clusters to compute the photoelectric yields as a function of grain size and the resulting grain charge distribution in various interstellar environments, finding that iron nanoparticles can acquire negative charges, particularly in regions with high gas temperatures and ionization fractions. If ≳10% of the interstellar iron is in the form of ultrasmall iron clusters, the photoelectric heating rate from dust may be increased by up to tens of percent relative to dust models with only carbonaceous and silicate grains.

  11. Prospects for identifying the sources of the Galactic cosmic rays with IceCube

    International Nuclear Information System (INIS)

    Halzen, Francis; Kappes, Alexander; O Murchadha, Aongus

    2008-01-01

    We quantitatively address whether IceCube, a kilometer-scale neutrino detector under construction at the South Pole, can observe neutrinos pointing back at the accelerators of the Galactic cosmic rays. The photon flux from candidate sources identified by the Milagro detector in a survey of the TeV sky is consistent with the flux expected from a typical cosmic-ray generating supernova remnant interacting with the interstellar medium. We show here that IceCube can provide incontrovertible evidence of cosmic-ray acceleration in these sources by detecting neutrinos. We find that the signal is optimally identified by specializing to events with energies above 30 TeV where the atmospheric neutrino background is low. We conclude that evidence for a correlation between the Milagro and IceCube sky maps should be conclusive after several years.

  12. PROPERTIES OF DIFFUSE INTERSTELLAR BANDS AT DIFFERENT PHYSICAL CONDITIONS OF THE INTERSTELLAR MEDIUM

    International Nuclear Information System (INIS)

    Kos, J.; Zwitter, T.

    2013-01-01

    Diffuse interstellar bands (DIBs) can trace different conditions of the interstellar medium (ISM) along the sightline toward the observed stars. A small survey was made in optical wavelengths, producing high-resolution and high signal-to-noise spectra. We present measurements of 19 DIBs' properties in 50 sightlines toward hot stars, distributed at a variety of galactic coordinates and interstellar reddening. Equivalent widths were obtained by fitting asymmetric Gaussian and variable continua to DIBs. Conditions of the ISM were calculated from eight atomic and molecular interstellar lines. Two distinctly different types of DIBs were identified by carefully comparing correlation coefficients between DIBs and reddening and by different behavior in UV-shielded (ζ) and nonshielded (σ) sightlines. A ratio of DIBs at 5780 Å and 5797 Å proved to be reliable enough to distinguish between two different sightline types. Based on the linear relations between DIB equivalent width and reddening for σ and ζ sightlines, we divide DIBs into type I (where both linear relations are similar) and type II (where they are significantly different). The linear relation for ζ type sightlines always shows a higher slope and larger x-intercept parameter than the relation for σ sightlines. Scatter around the linear relation is reduced after the separation, but it does not vanish completely. This means that UV shielding is the dominant factor of the DIB equivalent width versus reddening relation shape for ζ sightlines, but in σ sightlines other physical parameters play a major role. No similar dependency on gas density, electron density, or turbulence was observed. A catalog of all observed interstellar lines is made public

  13. Laurentide Ice-Sheet Meltwater Sources to the Gulf of Mexico During the Last Deglaciation: Assessing Data Reconstructions Using Water Isotope Enabled Simulations

    Science.gov (United States)

    Vetter, L.; LeGrande, A. N.; Ullman, D. J.; Carlson, A. E.

    2017-12-01

    Sediment cores from the Gulf of Mexico show evidence of meltwater derived from the Laurentide Ice Sheet during the last deglaciation. Recent studies using geochemical measurements of individual foraminifera suggest changes in the oxygen isotopic composition of the meltwater as deglaciation proceeded. Here we use the water isotope enabled climate model simulations (NASA GISS ModelE-R) to investigate potential sources of meltwater within the ice sheet. We find that initial melting of the ice sheet from the southern margin contributed an oxygen isotope value reflecting a low-elevation, local precipitation source. As deglacial melting proceeded, meltwater delivered to the Gulf of Mexico had a more negative oxygen isotopic value, which the climate model simulates as being sourced from the high-elevation, high-latitude interior of the ice sheet. This study demonstrates the utility of combining stable isotope analyses with climate model simulations to investigate past changes in the hydrologic cycle.

  14. Autonomous Aerial Ice Observation for Ice Defense

    Directory of Open Access Journals (Sweden)

    Joakim Haugen

    2014-10-01

    Full Text Available One of the tasks in ice defense is to gather information about the surrounding ice environment using various sensor platforms. In this manuscript we identify two monitoring tasks known in literature, namely dynamic coverage and target tracking, and motivate how these tasks are relevant in ice defense using RPAS. An optimization-based path planning concept is outlined for solving these tasks. A path planner for the target tracking problem is elaborated in more detail and a hybrid experiment, which consists of both a real fixed-wing aircraft and simulated objects, is included to show the applicability of the proposed framework.

  15. Magnetohydrodynamic Simulations of the Formation of Molecular Clouds toward the Stellar Cluster Westerlund 2: Interaction of a Jet with a Clumpy Interstellar Medium

    International Nuclear Information System (INIS)

    Asahina, Yuta; Kawashima, Tomohisa; Furukawa, Naoko; Enokiya, Rei; Yamamoto, Hiroaki; Fukui, Yasuo; Matsumoto, Ryoji

    2017-01-01

    The formation mechanism of CO clouds observed with the NANTEN2 and Mopra telescopes toward the stellar cluster Westerlund 2 is studied by 3D magnetohydrodynamic simulations, taking into account the interstellar cooling. These molecular clouds show a peculiar shape composed of an arc-shaped cloud on one side of the TeV γ -ray source HESS J1023-575 and a linear distribution of clouds (jet clouds) on the other side. We propose that these clouds are formed by the interaction of a jet with clumps of interstellar neutral hydrogen (H i). By studying the dependence of the shape of dense cold clouds formed by shock compression and cooling on the filling factor of H i clumps, we found that the density distribution of H i clumps determines the shape of molecular clouds formed by the jet–cloud interaction: arc clouds are formed when the filling factor is large. On the other hand, when the filling factor is small, molecular clouds align with the jet. The jet propagates faster in models with small filling factors.

  16. Magnetohydrodynamic Simulations of the Formation of Molecular Clouds toward the Stellar Cluster Westerlund 2: Interaction of a Jet with a Clumpy Interstellar Medium

    Energy Technology Data Exchange (ETDEWEB)

    Asahina, Yuta; Kawashima, Tomohisa [National Astronomical Observatory of Japan, Osawa, Mitaka, Tokyo 181-8588 (Japan); Furukawa, Naoko; Enokiya, Rei; Yamamoto, Hiroaki; Fukui, Yasuo [Department of Physics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602 (Japan); Matsumoto, Ryoji, E-mail: asahina@cfca.jp [Department of Physics, Graduate School of Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522 (Japan)

    2017-02-20

    The formation mechanism of CO clouds observed with the NANTEN2 and Mopra telescopes toward the stellar cluster Westerlund 2 is studied by 3D magnetohydrodynamic simulations, taking into account the interstellar cooling. These molecular clouds show a peculiar shape composed of an arc-shaped cloud on one side of the TeV γ -ray source HESS J1023-575 and a linear distribution of clouds (jet clouds) on the other side. We propose that these clouds are formed by the interaction of a jet with clumps of interstellar neutral hydrogen (H i). By studying the dependence of the shape of dense cold clouds formed by shock compression and cooling on the filling factor of H i clumps, we found that the density distribution of H i clumps determines the shape of molecular clouds formed by the jet–cloud interaction: arc clouds are formed when the filling factor is large. On the other hand, when the filling factor is small, molecular clouds align with the jet. The jet propagates faster in models with small filling factors.

  17. Interstellar scattering and resolution limitations

    International Nuclear Information System (INIS)

    Dennison, B.

    1987-01-01

    Density irregularities in both the interplanetary medium and the ionized component of the interstellar medium scatter radio waves, resulting in limitations on the achievable resolution. Interplanetary scattering (IPS) is weak for most observational situations, and in principle the resulting phase corruption can be corrected for when observing with sufficiently many array elements. Interstellar scattering (ISS), on the other hand, is usually strong at frequencies below about 8 GHz, in which case intrinsic structure information over a range of angular scales is irretrievably lost. With the earth-space baselines now planned, it will be possible to search directly for interstellar refraction, which is suspected of modulating the fluxes of background sources. 14 references

  18. Comparison in Schemes for Simulating Depositional Growth of Ice Crystal between Theoretical and Laboratory Data

    Science.gov (United States)

    Zhai, Guoqing; Li, Xiaofan

    2015-04-01

    The Bergeron-Findeisen process has been simulated using the parameterization scheme for the depositional growth of ice crystal with the temperature-dependent theoretically predicted parameters in the past decades. Recently, Westbrook and Heymsfield (2011) calculated these parameters using the laboratory data from Takahashi and Fukuta (1988) and Takahashi et al. (1991) and found significant differences between the two parameter sets. There are two schemes that parameterize the depositional growth of ice crystal: Hsie et al. (1980), Krueger et al. (1995) and Zeng et al. (2008). In this study, we conducted three pairs of sensitivity experiments using three parameterization schemes and the two parameter sets. The pre-summer torrential rainfall event is chosen as the simulated rainfall case in this study. The analysis of root-mean-squared difference and correlation coefficient between the simulation and observation of surface rain rate shows that the experiment with the Krueger scheme and the Takahashi laboratory-derived parameters produces the best rain-rate simulation. The mean simulated rain rates are higher than the mean observational rain rate. The calculations of 5-day and model domain mean rain rates reveal that the three schemes with Takahashi laboratory-derived parameters tend to reduce the mean rain rate. The Krueger scheme together with the Takahashi laboratory-derived parameters generate the closest mean rain rate to the mean observational rain rate. The decrease in the mean rain rate caused by the Takahashi laboratory-derived parameters in the experiment with the Krueger scheme is associated with the reductions in the mean net condensation and the mean hydrometeor loss. These reductions correspond to the suppressed mean infrared radiative cooling due to the enhanced cloud ice and snow in the upper troposphere.

  19. Molecular diagnostics of interstellar shocks

    International Nuclear Information System (INIS)

    Hartquist, T.W.; Oppenheimer, M.; Dalgarno, A.

    1980-01-01

    The chemistry of molecules in shocked regions of the interstellar gas is considered and calculations are carried out for a region subjected to a shock at a velocity of 8 km s -1 Substantial enhancements are predicted in the concentrations of the molecules H 2 S, SO, and SiO compared to those anticipated in cold interstellar clouds

  20. Molecular diagnostics of interstellar shocks

    Science.gov (United States)

    Hartquist, T. W.; Dalgarno, A.; Oppenheimer, M.

    1980-02-01

    The chemistry of molecules in shocked regions of the interstellar gas is considered and calculations are carried out for a region subjected to a shock at a velocity of 8 km/sec. Substantial enhancements are predicted in the concentrations of the molecules H2S, SO, and SiO compared to those anticipated in cold interstellar clouds.

  1. Molecular diagnostics of interstellar shocks

    Science.gov (United States)

    Hartquist, T. W.; Dalgarno, A.; Oppenheimer, M.

    1980-01-01

    The chemistry of molecules in shocked regions of the interstellar gas is considered and calculations are carried out for a region subjected to a shock at a velocity of 8 km/sec. Substantial enhancements are predicted in the concentrations of the molecules H2S, SO, and SiO compared to those anticipated in cold interstellar clouds.

  2. Evaluation of RRTMG and Fu-Liou RTM Performance against LBLRTM-DISORT Simulations and CERES Data in terms of Ice Clouds Radiative Effects

    Science.gov (United States)

    Gu, B.; Yang, P.; Kuo, C. P.; Mlawer, E. J.

    2017-12-01

    Evaluation of RRTMG and Fu-Liou RTM Performance against LBLRTM-DISORT Simulations and CERES Data in terms of Ice Clouds Radiative Effects Boyan Gu1, Ping Yang1, Chia-Pang Kuo1, Eli J. Mlawer2 Department of Atmospheric Sciences, Texas A&M University, College Station, TX 77843, USA Atmospheric and Environmental Research (AER), Lexington, MA 02421, USA Ice clouds play an important role in climate system, especially in the Earth's radiation balance and hydrological cycle. However, the representation of ice cloud radiative effects (CRE) remains significant uncertainty, because scattering properties of ice clouds are not well considered in general circulation models (GCM). We analyze the strengths and weakness of the Rapid Radiative Transfer Model for GCM Applications (RRTMG) and Fu-Liou Radiative Transfer Model (RTM) against rigorous LBLRTM-DISORT (a combination of Line-By-Line Radiative Transfer Model and Discrete Ordinate Radiative Transfer Model) calculations and CERES (Clouds and the Earth's Radiant Energy System) flux observations. In total, 6 US standard atmospheric profiles and 42 atmospheric profiles from Atmospheric and Environmental Research (AER) Company are used to evaluate the RRTMG and Fu-Liou RTM by LBLRTM-DISORT calculations from 0 to 3250 cm-1. Ice cloud radiative effect simulations with RRTMG and Fu-Liou RTM are initialized using the ice cloud properties from MODIS collection-6 products. Simulations of single layer ice cloud CRE by RRTMG and LBLRTM-DISORT show that RRTMG, neglecting scattering, overestimates the TOA flux by about 0-15 W/m2 depending on the cloud particle size and optical depth, and the most significant overestimation occurs when the particle effective radius is small (around 10 μm) and the cloud optical depth is intermediate (about 1-10). The overestimation reduces significantly when the similarity rule is applied to RRTMG. We combine ice cloud properties from MODIS Collection-6 and atmospheric profiles from the Modern

  3. Abundances in the diffuse interstellar medium

    International Nuclear Information System (INIS)

    Harris, A.W.

    1988-04-01

    The wealth of interstellar absorption line data obtained with the Copernicus and IUE satellites has opened up a new era in studies of the interstellar gas. It is now well established that certain elements, generally those with high condensation temperatures, are substantially under-abundant in the gas-phase relative to total solar or cosmic abundances. This depletion of elements is due to the existence of solid material in the form of dust grains in the interstellar medium. Surprisingly, however, recent surveys indicate that even volatile elements such as Zn and S are significantly depleted in many sight lines. Developments in this field which have been made possible by the large base of UV interstellar absorption line data built up over recent years are reviewed and the implications of the results for our understanding of the physical processes governing depletion are discussed. (author)

  4. TIME VARIATION OF AV AND RV FOR TYPE Ia SUPERNOVAE BEHIND INTERSTELLAR DUST

    Science.gov (United States)

    Huang, Xiaosheng; Biederman, M.; Herger, B.; Aldering, G. S.

    2014-01-01

    TIME VARIATION OF AV AND RV FOR TYPE Ia SUPERNOVAE BEHIND NON-UNIFORM INTERSTELLAR DUST ABSTRACT We investigate the time variation of the visual extinction, AV, and the total-to-selective extinction ratio, RV, resulting from interstellar dust in front of an expanding photospheric disk of a type Ia supernova (SN Ia). We simulate interstellar dust clouds according to a power law power spectrum and produce extinction maps that either follow a pseudo-Gaussian distribution or a lognormal distribution. The RV maps are produced through a correlation between AV and RV. With maps of AV and RV generated in each case (pseudo-Gaussian and lognormal), we then compute the effective AV and RV for a SN as its photospheric disk expands behind the dust screen. We find for a small percentage of SNe the AV and RV values can vary by a large factor from day to day in the first 40 days after explosion.

  5. Development of a Capacitive Ice Sensor to Measure Ice Growth in Real Time

    Directory of Open Access Journals (Sweden)

    Xiang Zhi

    2015-03-01

    Full Text Available This paper presents the development of the capacitive sensor to measure the growth of ice on a fuel pipe surface in real time. The ice sensor consists of pairs of electrodes to detect the change in capacitance and a thermocouple temperature sensor to examine the ice formation situation. In addition, an environmental chamber was specially designed to control the humidity and temperature to simulate the ice formation conditions. From the humidity, a water film is formed on the ice sensor, which results in an increase in capacitance. Ice nucleation occurs, followed by the rapid formation of frost ice that decreases the capacitance suddenly. The capacitance is saturated. The developed ice sensor explains the ice growth providing information about the icing temperature in real time.

  6. Development of a capacitive ice sensor to measure ice growth in real time.

    Science.gov (United States)

    Zhi, Xiang; Cho, Hyo Chang; Wang, Bo; Ahn, Cheol Hee; Moon, Hyeong Soon; Go, Jeung Sang

    2015-03-19

    This paper presents the development of the capacitive sensor to measure the growth of ice on a fuel pipe surface in real time. The ice sensor consists of pairs of electrodes to detect the change in capacitance and a thermocouple temperature sensor to examine the ice formation situation. In addition, an environmental chamber was specially designed to control the humidity and temperature to simulate the ice formation conditions. From the humidity, a water film is formed on the ice sensor, which results in an increase in capacitance. Ice nucleation occurs, followed by the rapid formation of frost ice that decreases the capacitance suddenly. The capacitance is saturated. The developed ice sensor explains the ice growth providing information about the icing temperature in real time.

  7. Thermal desorption of formamide and methylamine from graphite and amorphous water ice surfaces

    Science.gov (United States)

    Chaabouni, H.; Diana, S.; Nguyen, T.; Dulieu, F.

    2018-04-01

    Context. Formamide (NH2CHO) and methylamine (CH3NH2) are known to be the most abundant amine-containing molecules in many astrophysical environments. The presence of these molecules in the gas phase may result from thermal desorption of interstellar ices. Aims: The aim of this work is to determine the values of the desorption energies of formamide and methylamine from analogues of interstellar dust grain surfaces and to understand their interaction with water ice. Methods: Temperature programmed desorption (TPD) experiments of formamide and methylamine ices were performed in the sub-monolayer and monolayer regimes on graphite (HOPG) and non-porous amorphous solid water (np-ASW) ice surfaces at temperatures 40-240 K. The desorption energy distributions of these two molecules were calculated from TPD measurements using a set of independent Polanyi-Wigner equations. Results: The maximum of the desorption of formamide from both graphite and ASW ice surfaces occurs at 176 K after the desorption of H2O molecules, whereas the desorption profile of methylamine depends strongly on the substrate. Solid methylamine starts to desorb below 100 K from the graphite surface. Its desorption from the water ice surface occurs after 120 K and stops during the water ice sublimation around 150 K. It continues to desorb from the graphite surface at temperatures higher than160 K. Conclusions: More than 95% of solid NH2CHO diffuses through the np-ASW ice surface towards the graphitic substrate and is released into the gas phase with a desorption energy distribution Edes = 7460-9380 K, which is measured with the best-fit pre-exponential factor A = 1018 s-1. However, the desorption energy distribution of methylamine from the np-ASW ice surface (Edes = 3850-8420 K) is measured with the best-fit pre-exponential factor A = 1012 s-1. A fraction of solid methylamine monolayer of roughly 0.15 diffuses through the water ice surface towards the HOPG substrate. This small amount of methylamine

  8. On the feasibility of space-based radar ice sounding of the Antarctic ice sheet at P-band

    DEFF Research Database (Denmark)

    Dall, Jørgen; Kusk, Anders; Corr, Hugh

    . In this study the feasibility of space-based radar ice sounding is assessed. A two-step approach is applied: (1) Key ice sheet parameters are estimated from the airborne POLARIS data acquired in Antarctica. (2) The performance of potential space-based ice sounding radars is simulated based on the estimated ice...... data analysis estimating the scattering patterns via the Doppler spectra of the POLARIS data. The scattering patterns of the ice surfaces are relevant because the geometry of a space-based radar increases the risk that off-nadir surface clutter masks the nadir depth-signal of interest. Currently...... the ice sheet model is being established and validated. At the symposium measured and simulated satellite waveforms will be compared, and the feasibility of space-based ice sounding will be addressed....

  9. The Use of Simulation Training to Accelerate the Rate of Forward Ice Skating Skill Acquisition

    Directory of Open Access Journals (Sweden)

    Nathan J Washington

    2016-04-01

    Full Text Available Background: Australia’s interest and participation in ice hockey is increasing, however a lack of access to facilities means familiarity with this sport is limited, and so too is the facilitation of skill development within an ecologically valid context. Objective: While numerous methods may be employed to address this, one resource which remains relatively unexplored is the StrideDeck Treadmill, therefore the purpose of this study was to investigate the effectiveness of this equipment with specific reference to the biomechanical changes for skating ability. Methods: N = 16 male athletes (Mage = 15.0 ± 0.76 yrs from a junior league competition participated in this intervention based study. n = 9 were assigned to the training intervention (StrideDeck once a week, while the control group (n = 7 continued their normal training routines. Further, monthly sprint tests both on the StrideDeck and an on-ice protocol were conducted to track progress via kinematic analysis. Results: Data analysis revealed no significant overall effects for on-ice sprint skating performance after StrideDeck training; however there were significant kinematic differences between StrideDeck and ice conditions. Conclusions: Therefore while the StrideDeck may have merit in regard to physiological paramters, the results of this study do not support its use as a skill acquisition tool in regard to increasing skating ability. Keywords: Simulation training, skill acquisition, treadmill, ice skating, ice hockey skating, ice skating stride

  10. Observational constraints on interstellar chemistry

    International Nuclear Information System (INIS)

    Winnewisser, G.

    1984-01-01

    The author points out presently existing observational constraints in the detection of interstellar molecular species and the limits they may cast on our knowledge of interstellar chemistry. The constraints which arise from the molecular side are summarised and some technical difficulties encountered in detecting new species are discussed. Some implications for our understanding of molecular formation processes are considered. (Auth.)

  11. ON THE FORMATION AND ISOMER SPECIFIC DETECTION OF PROPENAL (C{sub 2}H{sub 3}CHO) AND CYCLOPROPANONE (c-C{sub 3}H{sub 4}O) IN INTERSTELLAR MODEL ICES—A COMBINED FTIR AND REFLECTRON TIME-OF-FLIGHT MASS SPECTROSCOPIC STUDY

    Energy Technology Data Exchange (ETDEWEB)

    Abplanalp, Matthew J.; Borsuk, Aleca; Jones, Brant M.; Kaiser, Ralf I., E-mail: ralfk@hawaii.edu [W. M. Keck Research Laboratory in Astrochemistry, University of Hawaii at Manoa, Honolulu, Hawaii, HI, 96822 (United States)

    2015-11-20

    The formation routes of two structural isomers—propenal (C{sub 2}H{sub 3}CHO) and cyclopropanone (c-C{sub 3}H{sub 4}O)—were investigated experimentally by exposing ices of astrophysical interest to energetic electrons at 5.5 K thus mimicking the interaction of ionizing radiation with interstellar ices in cold molecular clouds. The radiation-induced processing of these ices was monitored online and in situ via Fourier Transform Infrared spectroscopy and via temperature programmed desorption exploiting highly sensitive reflectron time-of-flight mass spectrometry coupled with single photon ionization in the post irradiation phase. To selectively probe which isomer(s) is/are formed, the photoionization experiments were conducted with 10.49 and 9.60 eV photons. Our studies provided compelling evidence on the formation of both isomers—propenal (C{sub 2}H{sub 3}CHO) and cyclopropanone (c-C{sub 3}H{sub 4}O)—in ethylene (C{sub 2}H{sub 4})—carbon monoxide (CO) ices forming propenal and cyclopropanone at a ratio of (4.5 ± 0.9):1. Based on the extracted reaction pathways, the cyclopropanone molecule can be classified as a tracer of a low temperature non-equilibrium chemistry within interstellar ices involving most likely excited triplet states, whereas propenal can be formed at ultralow temperatures, but also during the annealing phase via non-equilibrium as well as thermal chemistry (radical recombination). Since propenal has been detected in the interstellar medium and our laboratory experiments demonstrate that both isomers originated from identical precursor molecules our study predicts that the hitherto elusive second isomer—cyclopropanone—should also be observable toward those astronomical sources such as Sgr B2(N) in which propenal has been detected.

  12. Bottom Fixed Platform Dynamics Models Assessing Surface Ice Interactions for Transitional Depth Structures in the Great Lakes: FAST8 – IceDyn

    Energy Technology Data Exchange (ETDEWEB)

    Karr, Dale G. [Univ. of Michigan, Ann Arbor, MI (United States); Yu, Bingbin [Principle Power, Inc., Emeryville, CA (United States); Sirnivas, Senu [National Renewable Energy Lab. (NREL), Golden, CO (United States)

    2015-04-01

    To create long-term solutions for offshore wind turbines in a variety of environmental conditions, CAE tools are needed to model the design-driving loads that interact with an offshore wind turbine system during operation. This report describes our efforts in augmenting existing CAE tools used for offshore wind turbine analysis with a new module that can provide simulation capabilities for ice loading on the system. This augmentation was accomplished by creating an ice-loading module coupled to FAST8, the CAE tool maintained by the NREL for simulating land-based and offshore wind turbine dynamics. The new module includes both static and dynamic ice loading that can be applied during a dynamic simulation of the response of an offshore wind turbine. The ice forces can be prescribed, or influenced by the structure’s compliant response, or by the dynamics of both the structure and the ice floe. The new module covers ice failure modes of spalling, buckling, crushing, splitting, and bending. The supporting structure of wind turbines can be modeled as a vertical or sloping form at the waterline. The Inward Battered Guide Structure (IBGS) foundation designed by Keystone Engineering for the Great Lakes was used to study the ice models coupled to FAST8. The IBGS foundation ice loading simulations in FAST8 were compared to the baseline simulation case without ice loading. The ice conditions reflecting those from Lake Huron at Port Huron and Lake Michigan at North Manitou were studied under near rated wind speed of 12 m/s for the NREL 5-MW reference turbine. Simulations were performed on ice loading models 1 through 4 and ice model 6 with their respective sub-models. The purpose of ice model 5 is to investigate ice loading on sloping structures such as ice-cones on a monopile and is not suitable for multi-membered jacketed structures like the IBGS foundation. The key response parameters from the simulations, shear forces and moments from the tower base and IBGS foundation

  13. Ultraviolet Irradiation of Naphthalene in H2O Ice: Implications for Meteorites and Biogenesis

    Science.gov (United States)

    Bernstein, Max P.; Dworkin, Jason; Sandford, Scott A.; Allamandola, Louis J.; DeVincenzi, Donald L. (Technical Monitor)

    2000-01-01

    The polycyclic aromatic hydrocarbon (PAH) naphthalene was exposed to ultraviolet radiation in H2O ice under astrophysical conditions, and the products were analyzed using infrared spectroscopy and high performance liquid chromatography. As we found in our earlier studies on the photoprocessing of coronene in H2O ice, aromatic alcohols and ketones (quinones) were formed. The regiochemistry of the reactions is described and leads to specific predictions of the relative abundances of various oxidized naphthalenes that should exist in meteorites if interstellar ice photochemistry influenced their aromatic inventory. Since oxidized PAHs are present in carbon-rich meteorites and interplanetary dust particles (IDPs), and ubiquitous in and fundamental to biochemistry, the delivery of such extraterrestrial molecules to the early Earth may have played a role in the origin and evolution of life.

  14. A full year of snow on sea ice observations and simulations - Plans for MOSAiC 2019/20

    Science.gov (United States)

    Nicolaus, M.; Geland, S.; Perovich, D. K.

    2017-12-01

    The snow cover on sea on sea ice dominates many exchange processes and properties of the ice covered polar oceans. It is a major interface between the atmosphere and the sea ice with the ocean underneath. Snow on sea ice is known for its extraordinarily large spatial and temporal variability from micro scales and minutes to basin wide scales and decades. At the same time, snow cover properties and even snow depth distributions are among the least known and most difficult to observe climate variables. Starting in October 2019 and ending in October 2020, the international MOSAiC drift experiment will allow to observe the evolution of a snow pack on Arctic sea ice over a full annual cycle. During the drift with one ice floe along the transpolar drift, we will study snow processes and interactions as one of the main topics of the MOSAiC research program. Thus we will, for the first time, be able to perform such studies on seasonal sea ice and relate it to previous expeditions and parallel observations at different locations. Here we will present the current status of our planning of the MOSAiC snow program. We will summarize the latest implementation ideas to combine the field observations with numerical simulations. The field program will include regular manual observations and sampling on the main floe of the central observatory, autonomous recordings in the distributed network, airborne observations in the surrounding of the central observatory, and retrievals of satellite remote sensing products. Along with the field program, numerical simulations of the MOSAiC snow cover will be performed on different scales, including large-scale interaction with the atmosphere and the sea ice. The snow studies will also bridge between the different disciplines, including physical, chemical, biological, and geochemical measurements, samples, and fluxes. The main challenge of all measurements will be to accomplish the description of the full annual cycle.

  15. Ice shelf fracture parameterization in an ice sheet model

    Science.gov (United States)

    Sun, Sainan; Cornford, Stephen L.; Moore, John C.; Gladstone, Rupert; Zhao, Liyun

    2017-11-01

    Floating ice shelves exert a stabilizing force onto the inland ice sheet. However, this buttressing effect is diminished by the fracture process, which on large scales effectively softens the ice, accelerating its flow, increasing calving, and potentially leading to ice shelf breakup. We add a continuum damage model (CDM) to the BISICLES ice sheet model, which is intended to model the localized opening of crevasses under stress, the transport of those crevasses through the ice sheet, and the coupling between crevasse depth and the ice flow field and to carry out idealized numerical experiments examining the broad impact on large-scale ice sheet and shelf dynamics. In each case we see a complex pattern of damage evolve over time, with an eventual loss of buttressing approximately equivalent to halving the thickness of the ice shelf. We find that it is possible to achieve a similar ice flow pattern using a simple rule of thumb: introducing an enhancement factor ˜ 10 everywhere in the model domain. However, spatially varying damage (or equivalently, enhancement factor) fields set at the start of prognostic calculations to match velocity observations, as is widely done in ice sheet simulations, ought to evolve in time, or grounding line retreat can be slowed by an order of magnitude.

  16. Muscle Reaction Time During a Simulated Lateral Ankle Sprain After Wet-Ice Application or Cold-Water Immersion.

    Science.gov (United States)

    Thain, Peter K; Bleakley, Christopher M; Mitchell, Andrew C S

    2015-07-01

    Cryotherapy is used widely in sport and exercise medicine to manage acute injuries and facilitate rehabilitation. The analgesic effects of cryotherapy are well established; however, a potential caveat is that cooling tissue negatively affects neuromuscular control through delayed muscle reaction time. This topic is important to investigate because athletes often return to exercise, rehabilitation, or competitive activity immediately or shortly after cryotherapy. To compare the effects of wet-ice application, cold-water immersion, and an untreated control condition on peroneus longus and tibialis anterior muscle reaction time during a simulated lateral ankle sprain. Randomized controlled clinical trial. University of Hertfordshire human performance laboratory. A total of 54 physically active individuals (age = 20.1 ± 1.5 years, height = 1.7 ± 0.07 m, mass = 66.7 ± 5.4 kg) who had no injury or history of ankle sprain. Wet-ice application, cold-water immersion, or an untreated control condition applied to the ankle for 10 minutes. Muscle reaction time and muscle amplitude of the peroneus longus and tibialis anterior in response to a simulated lateral ankle sprain were calculated. The ankle-sprain simulation incorporated a combined inversion and plantar-flexion movement. We observed no change in muscle reaction time or muscle amplitude after cryotherapy for either the peroneus longus or tibialis anterior (P > .05). Ten minutes of joint cooling did not adversely affect muscle reaction time or muscle amplitude in response to a simulated lateral ankle sprain. These findings suggested that athletes can safely return to sporting activity immediately after icing. Further evidence showed that ice can be applied before ankle rehabilitation without adversely affecting dynamic neuromuscular control. Investigation in patients with acute ankle sprains is warranted to assess the clinical applicability of these interventions.

  17. A chemical model for the interstellar medium in galaxies

    OpenAIRE

    Bovino, S.; Grassi, Tommaso; Capelo, P. R.; Schleicher, D. R. G.; Banerjee, R.

    2016-01-01

    Aims: We present and test chemical models for three-dimensional hydrodynamical simulations of galaxies. We explore the effect of changing key parameters such as metallicity, radiation, and non-equilibrium versus equilibrium metal cooling approximations on the transition between the gas phases in the interstellar medium. Methods: The microphysics was modelled by employing the public chemistry package KROME, and the chemical networks were tested to work in a wide range of densities and temp...

  18. An introduction to the physics of interstellar dust

    CERN Document Server

    Krugel, Endrik

    2007-01-01

    Streamlining the extensive information from the original, highly acclaimed monograph, this new An Introduction to the Physics of Interstellar Dust provides a concise reference and overview of interstellar dust and the interstellar medium. Drawn from a graduate course taught by the author, a highly regarded figure in the field, this all-in-one book emphasizes astronomical formulae and astronomical problems to give a solid foundation for the further study of interstellar medium. Covering all phenomena associated with cosmic dust, this inclusive text eliminates the need to consult special physica

  19. IceProd 2 Usage Experience

    Science.gov (United States)

    Delventhal, D.; Schultz, D.; Diaz Velez, J. C.

    2017-10-01

    IceProd is a data processing and management framework developed by the IceCube Neutrino Observatory for processing of Monte Carlo simulations, detector data, and data driven analysis. It runs as a separate layer on top of grid and batch systems. This is accomplished by a set of daemons which process job workflow, maintaining configuration and status information on the job before, during, and after processing. IceProd can also manage complex workflow DAGs across distributed computing grids in order to optimize usage of resources. IceProd has recently been rewritten to increase its scaling capabilities, handle user analysis workflows together with simulation production, and facilitate the integration with 3rd party scheduling tools. IceProd 2, the second generation of IceProd, has been running in production for several months now. We share our experience setting up the system and things we’ve learned along the way.

  20. The loop I superbubble and the local interstellar magnetic field

    International Nuclear Information System (INIS)

    Frisch, Priscilla Chapman

    2014-01-01

    Recent data on the interstellar magnetic field in the low density nearby interstellar medium suggest a new perspective for understanding interstellar clouds within 40 pc. The directions of the local interstellar magnetic field found from measurements of optically polarized starlight and the very local field found from the Ribbon of energetic neutral atoms discovered by IBEX nearly agree. The geometrical relation between the local magnetic field, the positions and kinematics of local interstellar clouds, and the Loop I S1 superbubble, suggest that the Sun is located in the boundary of this evolved superbubble. The quasiperpendicular angle between the bulk kinematics and magnetic field of the local ISM indicates that a complete picture of low density interstellar clouds needs to include information on the interstellar magnetic field.

  1. The IceProd Framework

    DEFF Research Database (Denmark)

    Aartsen, M.G.; Abbasi, R.; Ackermann, M.

    2015-01-01

    of computational resources. IceProd is a distributed management system based on Python, XML-RPC and GridFTP. It is driven by a central database in order to coordinate and admin- ister production of simulations and processing of data produced by the IceCube detector. IceProd runs as a separate layer on top of other...

  2. Adsorption of naphthalene and ozone on atmospheric air/ice interfaces coated with surfactants: a molecular simulation study.

    Science.gov (United States)

    Liyana-Arachchi, Thilanga P; Valsaraj, Kalliat T; Hung, Francisco R

    2012-03-15

    The adsorption of gas-phase naphthalene and ozone molecules onto air/ice interfaces coated with different surfactant species (1-octanol, 1-hexadecanol, or 1-octanal) was investigated using classical molecular dynamics (MD) simulations. Naphthalene and ozone exhibit a strong preference to be adsorbed at the surfactant-coated air/ice interfaces, as opposed to either being dissolved into the bulk of the quasi-liquid layer (QLL) or being incorporated into the ice crystals. The QLL becomes thinner when the air/ice interface is coated with surfactant molecules. The adsorption of both naphthalene and ozone onto surfactant-coated air/ice interfaces is enhanced when compared to bare air/ice interface. Both naphthalene and ozone tend to stay dissolved in the surfactant layer and close to the QLL, rather than adsorbing on top of the surfactant molecules and close to the air region of our systems. Surfactants prefer to orient at a tilted angle with respect to the air/ice interface; the angular distribution and the most preferred angle vary depending on the hydrophilic end group, the length of the hydrophobic tail, and the surfactant concentration at the air/ice interface. Naphthalene prefers to have a flat orientation on the surfactant coated air/ice interface, except at high concentrations of 1-hexadecanol at the air/ice interface; the angular distribution of naphthalene depends on the specific surfactant and its concentration at the air/ice interface. The dynamics of naphthalene molecules at the surfactant-coated air/ice interface slow down as compared to those observed at bare air/ice interfaces. The presence of surfactants does not seem to affect the self-association of naphthalene molecules at the air/ice interface, at least for the specific surfactants and the range of concentrations considered in this study.

  3. Interstellar grains - the 75th anniversary

    International Nuclear Information System (INIS)

    Li Aigen

    2005-01-01

    The year of 2005 marks the 75th anniversary since Trumpler (1930) provided the first definitive proof of interstellar grains by demonstrating the existence of general absorption and reddening of starlight in the galactic plane. This article reviews our progressive understanding of the nature of interstellar dust

  4. Iced airfoil separation bubble measurements by particle image velocimetry

    Science.gov (United States)

    Jacobs, Jason J.

    Not long after the birth of aviation, pilots began to recognize the dangers posed by aircraft icing. Since that time, research has improved the awareness of this problem and the scientific understanding of the associated aerodynamic impacts, however, few studies have involved detailed, quantitative, flowfield measurements. For this reason, the current investigation was conducted in which high spatial-resolution flowfield measurements were acquired of a NACA 0012 airfoil with two- and three-dimensional, simulated, leading-edge, horn-ice accretions utilizing particle image velocimetry (PIV). These measurements complemented existing iced airfoil performance measurements, revealed previously unknown details regarding the structure and behavior of these flowfields, and could potentially facilitate the development and improvement of computational schemes used to predict largely separated flows, including that of an iced airfoil near stall. Previous iced airfoil investigations have demonstrated somewhat reduced aerodynamic penalties resulting from a three-dimensional ice simulation, compared to those of a two-dimensional ice simulation of a representative cross section. Correspondingly, the current measurements revealed accelerated transition of the separated shear layer emanating from a three-dimensional ice simulation and therefore enhanced pressure recovery and reduced mean separation bubble length, each relative to the flowfield of a representative two-dimensional ice simulation. These effects appeared to result from the quasi-steady distribution of discrete, streamwise vortices which aided the turbulent entrainment of fluid from the recirculation region of the three-dimensional ice simulation separation bubble flowfield. These vortices were generated by a streamwise-vortex instability excited by roughness along the three-dimensional ice simulation and produced spanwise-cell structures throughout this flowfield, as well as significant spanwise variation in peak

  5. SILICATE COMPOSITION OF THE INTERSTELLAR MEDIUM

    International Nuclear Information System (INIS)

    Fogerty, S.; Forrest, W.; Watson, D. M.; Koch, I.; Sargent, B. A.

    2016-01-01

    The composition of silicate dust in the diffuse interstellar medium and in protoplanetary disks around young stars informs our understanding of the processing and evolution of the dust grains leading up to planet formation. An analysis of the well-known 9.7 μ m feature indicates that small amorphous silicate grains represent a significant fraction of interstellar dust and are also major components of protoplanetary disks. However, this feature is typically modeled assuming amorphous silicate dust of olivine and pyroxene stoichiometries. Here, we analyze interstellar dust with models of silicate dust that include non-stoichiometric amorphous silicate grains. Modeling the optical depth along lines of sight toward the extinguished objects Cyg OB2 No. 12 and ζ Ophiuchi, we find evidence for interstellar amorphous silicate dust with stoichiometry intermediate between olivine and pyroxene, which we simply refer to as “polivene.” Finally, we compare these results to models of silicate emission from the Trapezium and protoplanetary disks in Taurus.

  6. SILICATE COMPOSITION OF THE INTERSTELLAR MEDIUM

    Energy Technology Data Exchange (ETDEWEB)

    Fogerty, S.; Forrest, W.; Watson, D. M.; Koch, I. [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States); Sargent, B. A., E-mail: sfogerty@pas.rochester.edu [Center for Imaging Science and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623 (United States)

    2016-10-20

    The composition of silicate dust in the diffuse interstellar medium and in protoplanetary disks around young stars informs our understanding of the processing and evolution of the dust grains leading up to planet formation. An analysis of the well-known 9.7 μ m feature indicates that small amorphous silicate grains represent a significant fraction of interstellar dust and are also major components of protoplanetary disks. However, this feature is typically modeled assuming amorphous silicate dust of olivine and pyroxene stoichiometries. Here, we analyze interstellar dust with models of silicate dust that include non-stoichiometric amorphous silicate grains. Modeling the optical depth along lines of sight toward the extinguished objects Cyg OB2 No. 12 and ζ Ophiuchi, we find evidence for interstellar amorphous silicate dust with stoichiometry intermediate between olivine and pyroxene, which we simply refer to as “polivene.” Finally, we compare these results to models of silicate emission from the Trapezium and protoplanetary disks in Taurus.

  7. Simulation of the European ice sheet through the last glacial cycle and prediction of future glaciation

    International Nuclear Information System (INIS)

    Boulton, G.S.; Payne, A.

    1992-12-01

    Global climates of the recent past appear to correlate with patterns of variation in the earths orbit round the sun. As such orbital changes can be predicted into the future, it is argued that the pattern of natural long-term future change can also be estimated. From this, future trends of glaciation can be inferred. The physical and mathematical basis of a time-dependent, thermo mechanically coupled, three dimensional ice sheet model is described. The model is driven by changes in the equilibrium line altitude (ELA) on its surface. This causes flexure of the underlying lithosphere. The model is tuned to the maximum extension of the last (Weichselian) ice sheet and driven by an ELA fluctuation which reflects the NE Atlantic sea surface temperature fluctuation pattern during the last glacial cycle in such a way that the model reproduces the ice sheet margin at the glacial maximum. The distribution of internal ice sheet velocity, temperature, basal melting rate and sub glacial permafrost penetration are all computed. The model is then tested against its predictions of the areal pattern of ice sheet expansion and decay, the pattern of crustal flexure and relative sea level change, and the distribution of till produced by the last European ice sheet. The tested model is then driven by predictions of future climate change to produce simulations of future ice sheet glaciation in northern Europe

  8. NO ICE HYDROGENATION: A SOLID PATHWAY TO NH2OH FORMATION IN SPACE

    International Nuclear Information System (INIS)

    Congiu, Emanuele; Dulieu, François; Chaabouni, Henda; Baouche, Saoud; Lemaire, Jean Louis; Fedoseev, Gleb; Ioppolo, Sergio; Lamberts, Thanja; Linnartz, Harold; Laffon, Carine; Parent, Philippe; Cuppen, Herma M.

    2012-01-01

    Icy dust grains in space act as catalytic surfaces onto which complex molecules form. These molecules are synthesized through exothermic reactions from precursor radicals and, mostly, hydrogen atom additions. Among the resulting products are species of biological relevance, such as hydroxylamine—NH 2 OH—a precursor molecule in the formation of amino acids. In this Letter, laboratory experiments are described that demonstrate NH 2 OH formation in interstellar ice analogs for astronomically relevant temperatures via successive hydrogenation reactions of solid nitric oxide (NO). Inclusion of the experimental results in an astrochemical gas-grain model proves the importance of a solid-state NO+H reaction channel as a starting point for prebiotic species in dark interstellar clouds and adds a new perspective to the way molecules of biological importance may form in space.

  9. THE COMPOSITION OF INTERSTELLAR GRAINS TOWARD ζ OPHIUCHI: CONSTRAINING THE ELEMENTAL BUDGET NEAR THE DIFFUSE-DENSE CLOUD TRANSITION

    Energy Technology Data Exchange (ETDEWEB)

    Poteet, Charles A.; Whittet, Douglas C. B. [New York Center for Astrobiology, Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110 Eighth Street, Troy, NY 12180 (United States); Draine, Bruce T., E-mail: charles.poteet@gmail.com [Princeton University Observatory, Peyton Hall, Princeton, NJ 08544 (United States)

    2015-03-10

    We investigate the composition of interstellar grains along the line of sight toward ζ Ophiuchi, a well-studied environment near the diffuse-dense cloud transition. A spectral decomposition analysis of the solid-state absorbers is performed using archival spectroscopic observations from the Spitzer Space Telescope and Infrared Space Observatory. We find strong evidence for the presence of sub-micron-sized amorphous silicate grains, principally comprised of olivine-like composition, with no convincing evidence of H{sub 2}O ice mantles. However, tentative evidence for thick H{sub 2}O ice mantles on large (a ≈ 2.8 μm) grains is presented. Solid-state abundances of elemental Mg, Si, Fe, and O are inferred from our analysis and compared to standard reference abundances. We find that nearly all of the Mg and Si atoms along the line of sight reside in amorphous silicate grains, while a substantial fraction of the elemental Fe resides in compounds other than silicates. Moreover, we find that the total abundance of elemental O is largely inconsistent with the adopted reference abundances, indicating that as much as ∼156 ppm of interstellar O is missing along the line of sight. After taking into account additional limits on the abundance of elemental O in other O-bearing solids, we conclude that any missing reservoir of elemental O must reside on large grains that are nearly opaque to infrared radiation.

  10. TEMPERATURE SPECTRA OF INTERSTELLAR DUST GRAINS HEATED BY COSMIC RAYS. I. TRANSLUCENT CLOUDS

    Energy Technology Data Exchange (ETDEWEB)

    Kalvāns, Juris, E-mail: juris.kalvans@venta.lv [Engineering Research Institute “Ventspils International Radio Astronomy Center” of Ventspils University College, Inzenieru 101, Ventspils, LV-3601 (Latvia)

    2016-06-01

    Heating of whole interstellar dust grains by cosmic-ray (CR) particles affects the gas–grain chemistry in molecular clouds by promoting molecule desorption, diffusion, and chemical reactions on grain surfaces. The frequency of such heating, f{sub T}, s{sup −1}, determines how often a certain temperature T{sub CR}, K, is reached for grains hit by CR particles. This study aims to provide astrochemists with a comprehensive and updated data set on CR-induced whole-grain heating. We present calculations of f{sub T} and T{sub CR} spectra for bare olivine grains with radius a of 0.05, 0.1, and 0.2 μ m and such grains covered with ice mantles of thickness 0.1 a and 0.3 a . Grain shape and structure effects are considered, as well as 30 CR elemental constituents with an updated energy spectrum corresponding to a translucent cloud with A{sub V} = 2 mag. Energy deposition by CRs in grain material was calculated with the srim program. We report full T{sub CR} spectra for all nine grain types and consider initial grain temperatures of 10 K and 20 K. We also provide frequencies for a range of minimum T{sub CR} values. The calculated data set can be simply and flexibly implemented in astrochemical models. The results show that, in the case of translucent clouds, the currently adopted rate for heating of whole grains to temperatures in excess of 70 K is underestimated by approximately two orders of magnitude in astrochemical numerical simulations. Additionally, grains are heated by CRs to modest temperatures (20–30 K) with intervals of a few years, which reduces the possibility of ice chemical explosions.

  11. 21st century changes in the surface mass balance of the Greenland ice sheet simulated with the global model CESM

    Science.gov (United States)

    Vizcaíno, M.; Lipscomb, W. H.; Van den Broeke, M.

    2012-04-01

    We present here the first projections of 21st century surface mass balance change of the Greenland ice sheet simulated with the Community Earth System Model (CESM). CESM is a fully-coupled, global climate model developed at many research centers and universities, primarily in the U.S. The model calculates the surface mass balance in the land component (the Community Land Model, CLM), at the same resolution as the atmosphere (1 degree), with an energy-balance scheme. The snow physics included in CLM for non-glaciated surfaces (SNiCAR model, Flanner and Zender, 2005) are used over the ice sheet. The surface mass balance is calculated for 10 elevation classes, and then downscaled to the grid of the ice sheet model (5 km in this case) via vertical linear interpolation between elevation classes combined with horizontal bilinear interpolation. The ice sheet topography is fixed at present-day values for the simulations presented here. The use of elevation classes reduces computational costs while giving results that reproduce well the mass balance gradients at the steep margins of the ice sheet. The simulated present-day surface mass balance agrees well with results from regional models. We focus on the regional model RACMO (Ettema et al. 2009) to compare the results on 20th-century surface mass balance evolution and two-dimensional patterns. The surface mass balance of the ice sheet under RCP8.5. forcing becomes negative in the last decades of the 21st century. The equilibrium line becomes ~500 m higher on average. Accumulation changes are positive in the accumulation zone. We examine changes in refreezing, accumulation, albedo, surface fluxes, and the timing of the melt season.

  12. Ice shelf fracture parameterization in an ice sheet model

    Directory of Open Access Journals (Sweden)

    S. Sun

    2017-11-01

    Full Text Available Floating ice shelves exert a stabilizing force onto the inland ice sheet. However, this buttressing effect is diminished by the fracture process, which on large scales effectively softens the ice, accelerating its flow, increasing calving, and potentially leading to ice shelf breakup. We add a continuum damage model (CDM to the BISICLES ice sheet model, which is intended to model the localized opening of crevasses under stress, the transport of those crevasses through the ice sheet, and the coupling between crevasse depth and the ice flow field and to carry out idealized numerical experiments examining the broad impact on large-scale ice sheet and shelf dynamics. In each case we see a complex pattern of damage evolve over time, with an eventual loss of buttressing approximately equivalent to halving the thickness of the ice shelf. We find that it is possible to achieve a similar ice flow pattern using a simple rule of thumb: introducing an enhancement factor ∼ 10 everywhere in the model domain. However, spatially varying damage (or equivalently, enhancement factor fields set at the start of prognostic calculations to match velocity observations, as is widely done in ice sheet simulations, ought to evolve in time, or grounding line retreat can be slowed by an order of magnitude.

  13. On the nature of interstellar turbulence

    International Nuclear Information System (INIS)

    Altunin, V.I.

    1981-01-01

    Possible reasons of interstellar medium turbulence manifested in pulsar scintillation and radio-frequency emission scattering of extragalactic sources near by the Galaxy plane, are discussed. Sources and conditions of turbulence emergence in HII region shells, supernova, residue and in stellar wind giving observed scattering effects are considered. It is shown that in the formation of the interstellar scintillation pattern of discrete radio-frequency emission sources a certain role can be played by magnetosound turbulence, which arises due to shock-waves propagating in the interstellar medium at a velocity Vsub(sh) approximately 20-100 km/s as well as by stellar-wind inhomogeneity of OB classes stars [ru

  14. Simulation of optimal arctic routes using a numerical sea ice model based on an ice-coupled ocean circulation method

    OpenAIRE

    Jong-Ho Nam; Inha Park; Ho Jin Lee; Mi Ok Kwon; Kyungsik Choi; Young-Kyo Seo

    2013-01-01

    Ever since the Arctic region has opened its mysterious passage to mankind, continuous attempts to take advantage of its fastest route across the region has been made. The Arctic region is still covered by thick ice and thus finding a feasible navigating route is essential for an economical voyage. To find the optimal route, it is necessary to establish an efficient transit model that enables us to simulate every possible route in advance. In this work, an enhanced algorithm to determine the o...

  15. Vortex ice in nanostructured superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Reichhardt, Charles [Los Alamos National Laboratory; Reichhardt, Cynthia J [Los Alamos National Laboratory; Libal, Andras J [Los Alamos National Laboratory

    2008-01-01

    We demonstrate using numerical simulations of nanostructured superconductors that it is possible to realize vortex ice states that are analogous to square and kagome ice. The system can be brought into a state that obeys either global or local ice rules by applying an external current according to an annealing protocol. We explore the breakdown of the ice rules due to disorder in the nanostructure array and show that in square ice, topological defects appear along grain boundaries, while in kagome ice, individual defects appear. We argue that the vortex system offers significant advantages over other artificial ice systems.

  16. From cyclic ice streaming to Heinrich-like events: the grow-and-surge instability in the Parallel Ice Sheet Model

    Directory of Open Access Journals (Sweden)

    J. Feldmann

    2017-08-01

    Full Text Available >Here we report on a cyclic, physical ice-discharge instability in the Parallel Ice Sheet Model, simulating the flow of a three-dimensional, inherently buttressed ice-sheet-shelf system which periodically surges on a millennial timescale. The thermomechanically coupled model on 1 km horizontal resolution includes an enthalpy-based formulation of the thermodynamics, a nonlinear stress-balance-based sliding law and a very simple subglacial hydrology. The simulated unforced surging is characterized by rapid ice streaming through a bed trough, resulting in abrupt discharge of ice across the grounding line which is eventually calved into the ocean. We visualize the central feedbacks that dominate the subsequent phases of ice buildup, surge and stabilization which emerge from the interaction between ice dynamics, thermodynamics and the subglacial till layer. Results from the variation of surface mass balance and basal roughness suggest that ice sheets of medium thickness may be more susceptible to surging than relatively thin or thick ones for which the surge feedback loop is damped. We also investigate the influence of different basal sliding laws (ranging from purely plastic to nonlinear to linear on possible surging. The presented mechanisms underlying our simulations of self-maintained, periodic ice growth and destabilization may play a role in large-scale ice-sheet surging, such as the surging of the Laurentide Ice Sheet, which is associated with Heinrich events, and ice-stream shutdown and reactivation, such as observed in the Siple Coast region of West Antarctica.

  17. Comet Halley and interstellar chemistry

    International Nuclear Information System (INIS)

    Snyder, L.E.

    1989-01-01

    How complex is the chemistry of the interstellar medium? How far does it evolve and how has it interacted with the chemistry of the solar system? Are the galactic chemical processes destroyed, preserved, or even enhanced in comets? Are biogenic molecules formed in space and have the formation mechanisms interacted in any way with prebiotic organic chemical processes on the early earth? Radio molecular studies of comets are important for probing deep into the coma and nuclear region and thus may help answer these questions. Comets are believed to be pristine samples of the debris left from the formation of the solar system and may have been the carrier between interstellar and terrestrial prebiotic chemistries. Recent observations of Comet Halley and subsequent comets have given the author an excellent opportunity to study the relationship between interstellar molecular chemistry and cometary chemistry

  18. Starry messages: Searching for signatures of interstellar archaeology

    Energy Technology Data Exchange (ETDEWEB)

    Carrigan, Richard A., Jr.; /Fermilab

    2009-12-01

    Searching for signatures of cosmic-scale archaeological artifacts such as Dyson spheres or Kardashev civilizations is an interesting alternative to conventional SETI. Uncovering such an artifact does not require the intentional transmission of a signal on the part of the original civilization. This type of search is called interstellar archaeology or sometimes cosmic archaeology. The detection of intelligence elsewhere in the Universe with interstellar archaeology or SETI would have broad implications for science. For example, the constraints of the anthropic principle would have to be loosened if a different type of intelligence was discovered elsewhere. A variety of interstellar archaeology signatures are discussed including non-natural planetary atmospheric constituents, stellar doping with isotopes of nuclear wastes, Dyson spheres, as well as signatures of stellar and galactic-scale engineering. The concept of a Fermi bubble due to interstellar migration is introduced in the discussion of galactic signatures. These potential interstellar archaeological signatures are classified using the Kardashev scale. A modified Drake equation is used to evaluate the relative challenges of finding various sources. With few exceptions interstellar archaeological signatures are clouded and beyond current technological capabilities. However SETI for so-called cultural transmissions and planetary atmosphere signatures are within reach.

  19. Greenland Ice Sheet seasonal and spatial mass variability from model simulations and GRACE (2003-2012)

    Science.gov (United States)

    Alexander, Patrick M.; Tedesco, Marco; Schlegel, Nicole-Jeanne; Luthcke, Scott B.; Fettweis, Xavier; Larour, Eric

    2016-06-01

    Improving the ability of regional climate models (RCMs) and ice sheet models (ISMs) to simulate spatiotemporal variations in the mass of the Greenland Ice Sheet (GrIS) is crucial for prediction of future sea level rise. While several studies have examined recent trends in GrIS mass loss, studies focusing on mass variations at sub-annual and sub-basin-wide scales are still lacking. At these scales, processes responsible for mass change are less well understood and modeled, and could potentially play an important role in future GrIS mass change. Here, we examine spatiotemporal variations in mass over the GrIS derived from the Gravity Recovery and Climate Experiment (GRACE) satellites for the January 2003-December 2012 period using a "mascon" approach, with a nominal spatial resolution of 100 km, and a temporal resolution of 10 days. We compare GRACE-estimated mass variations against those simulated by the Modèle Atmosphérique Régionale (MAR) RCM and the Ice Sheet System Model (ISSM). In order to properly compare spatial and temporal variations in GrIS mass from GRACE with model outputs, we find it necessary to spatially and temporally filter model results to reproduce leakage of mass inherent in the GRACE solution. Both modeled and satellite-derived results point to a decline (of -178.9 ± 4.4 and -239.4 ± 7.7 Gt yr-1 respectively) in GrIS mass over the period examined, but the models appear to underestimate the rate of mass loss, especially in areas below 2000 m in elevation, where the majority of recent GrIS mass loss is occurring. On an ice-sheet-wide scale, the timing of the modeled seasonal cycle of cumulative mass (driven by summer mass loss) agrees with the GRACE-derived seasonal cycle, within limits of uncertainty from the GRACE solution. However, on sub-ice-sheet-wide scales, some areas exhibit significant differences in the timing of peaks in the annual cycle of mass change. At these scales, model biases, or processes not accounted for by models related

  20. Application of GRACE to the Evaluation of an Ice Flow Model of the Greenland Ice Sheet

    Science.gov (United States)

    Schlegel, N.; Wiese, D. N.; Watkins, M. M.; Larour, E. Y.; Box, J. E.; Fettweis, X.; van den Broeke, M. R.; Morlighem, M.; Boening, C.; Seroussi, H. L.

    2014-12-01

    Quantifying Greenland's future contribution to sea level rise is a challenging task and requires accurate estimates of ice flow sensitivity to climate change. Transient ice flow models are promising tools for estimating future ice sheet behavior. However, confidence in these types of future projections is low, especially because evaluation of model historical runs is so challenging due to the scarcity of continental-wide data for validation. For more than a decade, NASA's GRACE has continuously acquired time-variable measurements of the Earth's gravity field and has provided unprecedented surveillance of mass balance of the ice sheets, offering an opportunity for ice sheet model evaluation. Here, we take advantage of a new high-resolution (~300 km) monthly mascon solution for the purpose of mass balance comparison with an independent, historical ice flow model simulation using the Ice Sheet System Model (ISSM). The comparison highlights which regions of the ice sheet differ most from GRACE. Investigation of regional differences in trends and seasonal amplitudes between simulations forced with three different Regional Climate Model (RCM)-based estimates of surface mass balance (SMB) allows us to make conclusions about the relative contributions of various error sources in the model hindcast. This study constitutes the first regional comparison of GRACE data and an ice sheet model. Conclusions will aid in the improvement of RCM SMB estimates as well as ice sheet simulation estimates of present and future rates of sea level rise. This work was performed at the California Institute of Technology's Jet Propulsion Laboratory under a contract with the National Aeronautics and Space Administration's Cryosphere Program and President's and Director's Fund Program.

  1. The ESO Diffuse Interstellar Band Large Exploration Survey (EDIBLES)

    Science.gov (United States)

    Cami, J.; Cox, N. L.; Farhang, A.; Smoker, J.; Elyajouri, M.; Lallement, R.; Bacalla, X.; Bhatt, N. H.; Bron, E.; Cordiner, M. A.; de Koter, A..; Ehrenfreund, P.; Evans, C.; Foing, B. H.; Javadi, A.; Joblin, C.; Kaper, L.; Khosroshahi, H. G.; Laverick, M.; Le Petit, F..; Linnartz, H.; Marshall, C. C.; Monreal-Ibero, A.; Mulas, G.; Roueff, E.; Royer, P.; Salama, F.; Sarre, P. J.; Smith, K. T.; Spaans, M.; van Loon, J. T..; Wade, G.

    2018-03-01

    The ESO Diffuse Interstellar Band Large Exploration Survey (EDIBLES) is a Large Programme that is collecting high-signal-to-noise (S/N) spectra with UVES of a large sample of O and B-type stars covering a large spectral range. The goal of the programme is to extract a unique sample of high-quality interstellar spectra from these data, representing different physical and chemical environments, and to characterise these environments in great detail. An important component of interstellar spectra is the diffuse interstellar bands (DIBs), a set of hundreds of unidentified interstellar absorption lines. With the detailed line-of-sight information and the high-quality spectra, EDIBLES will derive strong constraints on the potential DIB carrier molecules. EDIBLES will thus guide the laboratory experiments necessary to identify these interstellar “mystery molecules”, and turn DIBs into powerful diagnostics of their environments in our Milky Way Galaxy and beyond. We present some preliminary results showing the unique capabilities of the EDIBLES programme.

  2. Ice Load Project Final Technical Report

    Energy Technology Data Exchange (ETDEWEB)

    McCoy, Timothy J. [DNV GL, Seattle, WA (United States); Brown, Thomas [IFC Engineering, Calgary, AB (Canada); Byrne, Alex [DNV GL, Seattle, WA (United States)

    2014-10-30

    As interest and investment in offshore wind projects increase worldwide, some turbines will be installed in locations where ice of significant thickness forms on the water surface. This ice moves under the driving forces of wind, current, and thermal effects and may result in substantial forces on bottom-fixed support structures. The North and Baltic Seas in Europe have begun to see significant wind energy development and the Great Lakes of the United States and Canada may host wind energy development in the near future. Design of the support structures for these projects is best performed through the use of an integrated tool that can calculate the cumulative effects of forces due to turbine operations, wind, waves, and floating ice. The dynamic nature of ice forces requires that these forces be included in the design simulations, rather than added as static forces to simulation results. The International Electrotechnical Commission (IEC) standard[2] for offshore wind turbine design and the International Organization for Standardization (ISO) standard[3] for offshore structures provide requirements and algorithms for the calculation of forces induced by surface ice; however, currently none of the major wind turbine dynamic simulation codes provides the ability to model ice loads. The scope of work of the project described in this report includes the development of a suite of subroutines, collectively named IceFloe, that meet the requirements of the IEC and ISO standards and couples with four of the major wind turbine dynamic simulation codes. The mechanisms by which ice forces impinge on offshore structures generally include the forces required for crushing of the ice against vertical-sided structures and the forces required to fracture the ice as it rides up on conical-sided structures. Within these two broad categories, the dynamic character of the forces with respect to time is also dependent on other factors such as the velocity and thickness of the moving ice

  3. Infrared diffuse interstellar bands

    Science.gov (United States)

    Galazutdinov, G. A.; Lee, Jae-Joon; Han, Inwoo; Lee, Byeong-Cheol; Valyavin, G.; Krełowski, J.

    2017-05-01

    We present high-resolution (R ˜ 45 000) profiles of 14 diffuse interstellar bands in the ˜1.45 to ˜2.45 μm range based on spectra obtained with the Immersion Grating INfrared Spectrograph at the McDonald Observatory. The revised list of diffuse bands with accurately estimated rest wavelengths includes six new features. The diffuse band at 15 268.2 Å demonstrates a very symmetric profile shape and thus can serve as a reference for finding the 'interstellar correction' to the rest wavelength frame in the H range, which suffers from a lack of known atomic/molecular lines.

  4. SIMULATION AND INVESTIGATION OF TIRE TREAD BLOCKS INTERACTION WITH ICE

    Directory of Open Access Journals (Sweden)

    Andrius Ružinskas

    2017-12-01

    Full Text Available The car tire is an essential subject analysing its interaction with the road. From tire’s tread condition, geometry and rubber compound depends grip and vehicle stability. This is especially relevant in winter time, when roads are covered with the layer of snow or ice. Generally, new tires are tested in real traffic conditions using vehicles. However, ensuring these conditions requires many resources and sometimes it could be a big challenge. For this reason, simulation of the tire interaction with the road becomes more important in nowadays tire researches. Since the tire is a complex engineering subject, the tire tread blocks could be separated for individual analysis. The interaction between the dry ice and the tread block with sipes was analysed using finite element analysis. The tread block was described using hyperelastic Mooney­Rivlin material model. The deformations, distribution of the contact pressure and shear stresses were obtained for the soft and hard rubber compounds with different vertical load conditions. Also a solid tread block interaction was analysed and it was found that values of contact pressure and shear stresses are much lower comparing to siped tread block.

  5. Experimental study by infrared spectroscopy of irradiation effects in silicates and ices, applied to astrophysics

    International Nuclear Information System (INIS)

    Rocard, F.

    1986-05-01

    This thesis presents the study of the radiation effects (erosion and synthesis) with ions of low energy (a few KeV/u) in silicates and ices. The erosion of the H 2 O ice is analysed by infrared spectroscopy versus different parameters: ion beam flux, mass and energy of the ions, and the thickness of the samples. The interpretation is that the erosion of the ice comes mainly from the dissociation, along the ion range, of the H 2 O molecules. A study of the synthesis in SiO 2 and H 2 O by carbon, nitrogen and hydrogen implantation leads to the characterization of the synthesized molecules and the determination of the yields. The irradiation of ices mixtures (H 2 O, CO 2 and NH 3 ) leads to the synthesis of a great variety of molecules which are identified. The experimental results are extrapolated to different astrophysical situations in the solar cavity (Moon, satellites of giant planets, comets) and in the interstellar medium (molecular clouds) [fr

  6. The Formation of Nucleobases from the Ultraviolet Photoirradiation of Purine in Simple Astrophysical Ice Analogues.

    Science.gov (United States)

    Materese, Christopher K; Nuevo, Michel; Sandford, Scott A

    2017-08-01

    Nucleobases are the informational subunits of RNA and DNA and are essential to all known forms of life. The nucleobases can be divided into two groups of molecules: the pyrimidine-based compounds that include uracil, cytosine, and thymine, and the purine-based compounds that include adenine and guanine. Previous work in our laboratory has demonstrated that uracil, cytosine, thymine, and other nonbiological, less common nucleobases can form abiotically from the UV photoirradiation of pyrimidine in simple astrophysical ice analogues containing combinations of H 2 O, NH 3 , and CH 4 . In this work, we focused on the UV photoirradiation of purine mixed with combinations of H 2 O and NH 3 ices to determine whether or not the full complement of biological nucleobases can be formed abiotically under astrophysical conditions. Room-temperature analyses of the resulting photoproducts resulted in the detection of adenine, guanine, and numerous other functionalized purine derivatives. Key Words: Pyrimidine-Nucleobases-Interstellar; Ices-Cometary; Ices-Molecular processes-Prebiotic chemistry. Astrobiology 17, 761-770.

  7. Interstellar holography

    NARCIS (Netherlands)

    Walker, M. A.; Koopmans, L. V. E.; Stinebring, D. R.; van Straten, W.

    2008-01-01

    The dynamic spectrum of a radio pulsar is an in-line digital hologram of the ionized interstellar medium. It has previously been demonstrated that such holograms permit image reconstruction, in the sense that one can determine an approximation to the complex electric field values as a function of

  8. NO ICE HYDROGENATION: A SOLID PATHWAY TO NH{sub 2}OH FORMATION IN SPACE

    Energy Technology Data Exchange (ETDEWEB)

    Congiu, Emanuele; Dulieu, Francois; Chaabouni, Henda; Baouche, Saoud; Lemaire, Jean Louis [LERMA-LAMAp, Universite de Cergy-Pontoise, Observatoire de Paris, ENS, UPMC, UMR 8112 du CNRS, 5 Mail Gay Lussac, 95000 Cergy Pontoise Cedex (France); Fedoseev, Gleb; Ioppolo, Sergio; Lamberts, Thanja; Linnartz, Harold [Raymond and Beverly Sackler Laboratory for Astrophysics, Leiden Observatory, University of Leiden, P.O. Box 9513, 2300 RA Leiden (Netherlands); Laffon, Carine; Parent, Philippe [Laboratoire de Chimie-Physique, Matiere et Rayonnement, Universite Pierre-et-Marie Curie (Paris 06) and CNRS (UMR 7614), 11 rue Pierre-et-Marie-Curie, 75231 Paris (France); Cuppen, Herma M., E-mail: emanuele.congiu@u-cergy.fr [Faculty of Science, Radboud University Nijmegen, IMM, P.O. Box 9010, NL 6500 GL Nijmegen (Netherlands)

    2012-05-01

    Icy dust grains in space act as catalytic surfaces onto which complex molecules form. These molecules are synthesized through exothermic reactions from precursor radicals and, mostly, hydrogen atom additions. Among the resulting products are species of biological relevance, such as hydroxylamine-NH{sub 2}OH-a precursor molecule in the formation of amino acids. In this Letter, laboratory experiments are described that demonstrate NH{sub 2}OH formation in interstellar ice analogs for astronomically relevant temperatures via successive hydrogenation reactions of solid nitric oxide (NO). Inclusion of the experimental results in an astrochemical gas-grain model proves the importance of a solid-state NO+H reaction channel as a starting point for prebiotic species in dark interstellar clouds and adds a new perspective to the way molecules of biological importance may form in space.

  9. Synthesis of molecules in interstellar clouds and star formation

    International Nuclear Information System (INIS)

    Ghosh, K.K.; Ghosh, S.N.

    1981-01-01

    Study of the formation and destruction processes of interstellar molecules may throw certain light on interstellar medium. Formation and destruction processes of some interstellar molecules are proposed on the basis of laboratory data. The abundances of these molecules are calculated under steady-state condition. The calculated values are then compared with the observed values, obtained by different investigators. It appears that gas phase ion-neutral reactions are capable of synthesizing most interstellar molecules. The role of ion-neutral reactions to star formation has also been discussed. (author)

  10. Reactions of hot nitrogen in water-ice at 77 K

    International Nuclear Information System (INIS)

    Roessler, K.; Schurwanz, K.

    1985-04-01

    The reactions of hot nitrogen atoms were studied in H 2 O-ice at 77 K. The nitrogen atoms were generated via the nuclear process 16 O(p,α) 13 N with 20 MeV protons from a cyclotron and by implantation of 250 keV 14 N + ions. The formation of chemical compounds of 13 N was studied over a wide dose range of the energy deposited by the protons from Dsup(*)=10 -2 to 26 eV per target molecule. The 13 N-labeled products and their yields as depending on the dose were determined via high performance liquid chromatography (HPLC) and radio-gaschromatography (GC). The reactions of implanted 14 N + ions were studied in H 2 O-ice at 6 K. The analysis of the products was achieved by optical low-temperature spectroscopy in the near UV, visible and infrared spectral regions. Primary (original hot) products of 13 N were: 13 NH 4 + with a radiochemical yield of 51%, 13 NO 2 - (37%), and 13 NO 3 - (9%) as detected after irradiation with the lowest proton dose applied of Dsup(*)=10 -2 eV. With increasing dose the 13 NH 4 + -yield rose to a broad maximum at 95%. Correspondingly the yields of nitrite and nitrate decreased. Applications of the studies are the preparation of 13 N-labeled precursor compounds for the fast synthesis of 13 N-radiopharmaceuticals and the laboratory simulations of chemical processes in the interplanetary and interstellar ice bodies. The ion implantation studies gave first information on the hot formation of nitrogen-oxygen compounds. NH-compounds could not be found in the spectra. This reflects the 13 N-product distribution at high doses in the nuclear recoil experiments. (orig./RB) [de

  11. Streaming of interstellar grains in the solar system

    Science.gov (United States)

    Gustafson, B. A. S.; Misconi, N. Y.

    1979-01-01

    Results of a theoretical study of the interactions between interstellar grains streaming through the solar system and the solar wind are presented. It is shown that although elongated core-mantle interstellar particles of a characteristic radius of about 0.12 microns are subject to a greater force due to radiation pressure than to gravitational attraction, they are still able to penetrate deep inside the solar system. Calculations of particle trajectories within the solar system indicate substantial effects of the solar activity cycle as reflected in the interplanetary magnetic field on the distribution of 0.12- and 0.0005-micron interstellar grains streaming through the solar system, leading to a 50-fold increase in interstellar grain densities 3 to 4 AU ahead of the sun during years 8 to 17 of the solar cycle. It is noted that during the Solar Polar Mission, concentrations are expected which will offer the opportunity of detecting interstellar grains in the solar system.

  12. On Graphene in the Interstellar Medium

    Science.gov (United States)

    Chen, X. H.; Li, Aigen; Zhang, Ke

    2017-11-01

    The possible detection of C24, a planar graphene that was recently reported to be in several planetary nebulae by García-Hernández et al., inspires us to explore whether and how much graphene could exist in the interstellar medium (ISM) and how it would reveal its presence through its ultraviolet (UV) extinction and infrared (IR) emission. In principle, interstellar graphene could arise from the photochemical processing of polycyclic aromatic hydrocarbon (PAH) molecules, which are abundant in the ISM, due to the complete loss of their hydrogen atoms, and/or from graphite, which is thought to be a major dust species in the ISM, via fragmentation caused by grain–grain collisional shattering. Both quantum-chemical computations and laboratory experiments have shown that the exciton-dominated electronic transitions in graphene cause a strong absorption band near 2755 \\mathringA . We calculate the UV absorption of graphene and place an upper limit of ∼5 ppm of C/H (i.e., ∼1.9% of the total interstellar C) on the interstellar graphene abundance. We also model the stochastic heating of graphene C24 in the ISM, excited by single starlight photons of the interstellar radiation field and calculate its IR emission spectra. We also derive the abundance of graphene in the ISM to be <5 ppm of C/H by comparing the model emission spectra with that observed in the ISM.

  13. PAHs in Translucent Interstellar Clouds

    Science.gov (United States)

    Salama, Farid; Galazutdinov, G.; Krelowski, J.; Biennier, L.; Beletsky, Y.; Song, I.

    2011-05-01

    We discuss the proposal of relating the origin of some of the diffuse interstellar bands (DIBs) to neutral polycyclic aromatic hydrocarbons (PAHs) present in translucent interstellar clouds. The spectra of several cold, isolated gas-phase PAHs have been measured in the laboratory under experimental conditions that mimic the interstellar conditions and are compared with an extensive set of astronomical spectra of reddened, early type stars. This comparison provides - for the first time - accurate upper limits for the abundances of specific PAH molecules along specific lines-of-sight. Something that is not attainable from IR observations alone. The comparison of these unique laboratory data with high resolution, high S/N ratio astronomical observations leads to two major findings: (1) a finding specific to the individual molecules that were probed in this study and, which leads to the clear and unambiguous conclusion that the abundance of these specific neutral PAHs must be very low in the individual translucent interstellar clouds that were probed in this survey (PAH features remain below the level of detection) and, (2) a general finding that neutral PAHs exhibit intrinsic band profiles that are similar to the profile of the narrow DIBs indicating that the carriers of the narrow DIBs must have close molecular structure and characteristics. This study is the first quantitative survey of neutral PAHs in the optical range and it opens the way for unambiguous quantitative searches of PAHs in a variety of interstellar and circumstellar environments. // Reference: F. Salama et al. (2011) ApJ. 728 (1), 154 // Acknowledgements: F.S. acknowledges the support of the NASA's Space Mission Directorate APRA Program. J.K. acknowledges the financial support of the Polish State (grant N203 012 32/1550). The authors are deeply grateful to the ESO archive as well as to the ESO staff members for their active support.

  14. Fuzzy Verification of Lower Dimensional Information in a Numerical Simulation of Sea Ice

    Science.gov (United States)

    Sulsky, D.; Levy, G.

    2010-12-01

    Ideally, a verification and validation scheme should be able to evaluate and incorporate lower dimensional features (e.g., discontinuities) contained within a bulk simulation even when not directly observed or represented by model variables. Nonetheless, lower dimensional features are often ignored. Conversely, models that resolve such features and the associated physics well, yet imprecisely are penalized by traditional validation schemes. This can lead to (perceived or real) poor model performance and predictability and can become deleterious in model improvements when observations are sparse, fuzzy, or irregular. We present novel algorithms and a general framework for using information from available satellite data through fuzzy verification that efficiently and effectively remedy the known problems mentioned above. As a proof of concept, we use a sea-ice model with remotely sensed observations of leads in a one-step initialization cycle. Using the new scheme in a sixteen day simulation experiment introduces model skill (against persistence) several days earlier than in the control run, improves the overall model skill and delays its drop off at later stages of the simulation. Although sea-ice models are currently a weak link in climate models, the appropriate choice of data to use, and the fuzzy verification and evaluation of a system’s skill in reproducing lower dimensional features are important beyond the initial application to sea ice. Our strategy and framework for fuzzy verification, selective use of information, and feature extraction could be extended globally and to other disciplines. It can be incorporated in and complement existing verification and validation schemes, increasing their computational efficiency and the information they use. It can be used for model development and improvements, upscaling/downscaling models, and for modeling processes not directly represented by model variables or direct observations. Finally, if successful, it can

  15. Hydrocarbons on Saturns Satellites: Relationship to Interstellar Dust and the Solar Nebula

    Science.gov (United States)

    Cruikshank, D. P.

    2012-01-01

    To understand the origin and evolution of our Solar System, and the basic components that led to life on Earth, we study interstellar and planetary spectroscopic signatures. The possible relationship of organic material detected in carbonaceous meteorites, interplanetary dust particles (IDPs), comets and the interstellar medium have been the source of speculation over the years as the composition and processes that governed the early solar nebula have been explored to understand the extent to which primitive material survived or became processed. The Cassini VIMS has provided new data relevant to this problem. Three of Saturn's satellites, Phoebe, Iapetus, and Hyperion, are found to have aromatic and aliphatic hydrocarbons on their surfaces. The aromatic hydrocarbon signature (C-H stretching mode at 3.28 micrometers) is proportionally significantly stronger (relative to the aliphatic bands) than that seen in other Solar System bodies (e.g., comets) and materials (Stardust samples, IDPs, meteorites) and the distinctive sub-features of the 3.4 micrometer aliphatic band (CH2 and CH3 groups) are reminiscent of those widely detected throughout the diffuse ISM. Phoebe may be a captured object that originated in the region beyond the present orbit of Neptune, where the solar nebula contained a large fraction of original interstellar ice and dust that was less processed than material closer to the Sun. Debris from Phoebe now resident on Iapetus and Hyperion, as well as o Phoebe itself, thus presents a unique blend of hydrocarbons, amenable to comparisons with interstellar hydrocarbons and other Solar System materials. The dust ring surrounding Saturn, in which Phoebe is embedded, probably originated from a collision with Phoebe. Dust ring particles are the likely source of the organic-bearing materials, and perhaps the recently identified small particles of Fe detected on Saturn's satellites. Lab measurements of the absolute band strengths of representative aliphatic and

  16. The Hamburg sea-ice model

    International Nuclear Information System (INIS)

    Stoessel, A.; Owens, W.B.

    1992-10-01

    The general purpose of the model is to simulate sea ice dynamically as well as thermodynamically. Pure sea-ice models are generally highly dependent on the specified atmospheric and oceanic forcing, especially on the winds and the vertical oceanic heat flux. In order to reduce these dependencies, the sea-ice [SI] model was extended to optionally include a prognostic oceanic mixed layer [OML], a diagnostic atmospheric surface layer [ASL] and/or a diagnostic atmospheric boundary layer [ABL], thus shifting the forcing levels further away from the surface (i.e. from the sea ice) and simultaneously providing a modification of the forcing considering boundary-layer adjustments to the instantaneous sea-ice conditions given by the SI model. A further major extension of the model is the (optional) employment of a prognostic snow layer. The special application characterising the present code was sea-ice simulation in the Southern Ocean, employing a spherical, circumpolar grid with a resolution of 2.5 in latitude and 5 in longitude, extending from 50 S to 80 S and using a daily time step. (orig.)

  17. Small-scale structure in the diffuse interstellar medium

    International Nuclear Information System (INIS)

    Meyer, D.M.

    1990-01-01

    The initial results of a study to probe the small-scale structure in the diffuse interstellar medium (ISM) through IUE and optical observations of interstellar absorption lines toward both components of resolvable binary stars is reported. The binaries (Kappa CrA, 57 Aql, 59 And, HR 1609/10, 19 Lyn, and Theta Ser) observed with IUE have projected linear separations ranging from 5700 to 700 Au. Except for Kappa CrA, the strengths of the interstellar absorption lines toward both components of these binaries agree to within 10 percent. In the case of Kappa CrA, the optically thin interstellar Mg I and Mn II lines are about 50 percent stronger toward Kappa-2 CrA than Kappa-1 CrA. Higher resolution observations of interstellar Ca II show that this difference is concentrated in the main interstellar component at V(LSR) = 9 + or - 2 km/s. Interestingly, this velocity corresponds to an intervening cloud that may be associated with the prominent Loop I shell in the local ISM. Given the separation (23 arcsec) and distance (120 pc) of Kappa CrA, the line strength variations indicate that this cloud has structure on scales of 2800 AU or less. 21 refs

  18. Absorption of X-rays in the interstellar medium

    International Nuclear Information System (INIS)

    Ride, S.K.; Stanford Univ., Calif.; Walker, A.B.C. Jr.; Stanford Univ., Calif.

    1977-01-01

    In order to interpret soft X-ray spectra of cosmic X-ray sources, it is necessary to know the photoabsorption cross-section of the intervening interstellar material. Current models suggest that the interstellar medium contains two phases which make a substantial contribution to the X-ray opacity: cool, relatively dense clouds that exist in pressure equilibrium with hot, tenuous intercloud regions. We have computed the soft X-ray photoabsorption cross-section (per hydrogen atom) of each of these two phases. The calculation are based on a model of the interstellar medium which includes chemical evolution of the galaxy, the formation of molecules and grains, and the ionization structure of each of each phase. These cross-sections of clouds and of intercloud regions can be combined to yield the total soft X-ray photoabsorption cross-section of the interstellar medium. By choosing the appropriate linear combination of cloud and intercloud cross-sections, we can tailor the total cross-section to a particular line-of-sight. This approach, coupled with our interstellar model, enables us to better describe a wide range of interstellar features such as H II regions, dense (molecular) clouds, or the ionized clouds which may surround binary X-ray sources. (orig.) [de

  19. Wave-induced stress and breaking of sea ice in a coupled hydrodynamic discrete-element wave-ice model

    Science.gov (United States)

    Herman, Agnieszka

    2017-11-01

    In this paper, a coupled sea ice-wave model is developed and used to analyze wave-induced stress and breaking in sea ice for a range of wave and ice conditions. The sea ice module is a discrete-element bonded-particle model, in which ice is represented as cuboid grains floating on the water surface that can be connected to their neighbors by elastic joints. The joints may break if instantaneous stresses acting on them exceed their strength. The wave module is based on an open-source version of the Non-Hydrostatic WAVE model (NHWAVE). The two modules are coupled with proper boundary conditions for pressure and velocity, exchanged at every wave model time step. In the present version, the model operates in two dimensions (one vertical and one horizontal) and is suitable for simulating compact ice in which heave and pitch motion dominates over surge. In a series of simulations with varying sea ice properties and incoming wavelength it is shown that wave-induced stress reaches maximum values at a certain distance from the ice edge. The value of maximum stress depends on both ice properties and characteristics of incoming waves, but, crucially for ice breaking, the location at which the maximum occurs does not change with the incoming wavelength. Consequently, both regular and random (Jonswap spectrum) waves break the ice into floes with almost identical sizes. The width of the zone of broken ice depends on ice strength and wave attenuation rates in the ice.

  20. Interstellar extinction correlations

    International Nuclear Information System (INIS)

    Jones, A.P.; Williams, D.A.; Duley, W.W.

    1987-01-01

    A recently proposed model for interstellar grains in which the extinction arises from small silicate cores with mantles of hydrogenated amorphous carbon (HAC or α-C:H), and large, but thinly coated, silicate grains can successfully explain many of the observed properties of interstellar dust. The small silicate cores give rise to the 2200 A extinction feature. The extinction in the visual is produced by the large silicates and the HAC mantles on the small cores, whilst the far UV extinction arises in the HAC mantles with a small contribution form the silicate grains. The grain model requires that the silicate material is the more resilient component and that variations in the observed extinction from region to region are due to the nature and depletion of the carbon in the HAC mantles. (author)

  1. Investigating nearby exoplanets via interstellar radar

    Science.gov (United States)

    Scheffer, Louis K.

    2014-01-01

    Interstellar radar is a potential intermediate step between passive observation of exoplanets and interstellar exploratory missions. Compared with passive observation, it has the traditional advantages of radar astronomy. It can measure surface characteristics, determine spin rates and axes, provide extremely accurate ranges, construct maps of planets, distinguish liquid from solid surfaces, find rings and moons, and penetrate clouds. It can do this even for planets close to the parent star. Compared with interstellar travel or probes, it also offers significant advantages. The technology required to build such a radar already exists, radar can return results within a human lifetime, and a single facility can investigate thousands of planetary systems. The cost, although too high for current implementation, is within the reach of Earth's economy.

  2. IceVeto: Extended PeV neutrino astronomy in the Southern Hemisphere with IceCube

    Energy Technology Data Exchange (ETDEWEB)

    Auffenberg, Jan [Physikalisches Institut IIIB RWTH Aachen D-52056, Aachen (Germany); Collaboration: IceCube Collaboration

    2014-11-18

    IceCube, the world's largest high-energy neutrino observatory, built at the South Pole, recently reported evidence of an astrophysical neutrino flux extending to PeV energies in the Southern Hemisphere. This observation raises the question of how the sensitivity in this energy range could be further increased. In the down-going sector, in IceCube's case the Southern Hemisphere, backgrounds from atmospheric muons and neutrinos pose a challenge to the identification of an astrophysical neutrino flux. The IceCube analysis, that led to the evidence for astrophysical neutrinos, is based on an in-ice veto strategy for background rejection. One possibility available to IceCube is the concept of an extended surface detector, IceVeto, which could allow the rejection of a large fraction of atmospheric backgrounds, primarily for muons from cosmic ray (CR) air showers as well as from neutrinos in the same air showers. Building on the experience of IceTop/IceCube, possibly the most cost-effective and sensitive way to build IceVeto is as an extension of the IceTop detector, with simple photomultiplier based detector modules for CR air shower detection. Initial simulations and estimates indicate that such a veto detector will significantly increase the sensitivity to an astrophysical flux of ν{sub μ} induced muon tracks in the Southern Hemisphere compared to current analyses. Here we present the motivation and capabilities based on initial simulations. Conceptual ideas for a simplified surface array will be discussed briefly.

  3. Radio propagation through the turbulent interstellar plasma

    International Nuclear Information System (INIS)

    Rickett, B.J.

    1990-01-01

    The current understanding of interstellar scattering is reviewed, and its impact on radio astronomy is examined. The features of interstellar plasma turbulence are also discussed. It is concluded that methods involving the investigation of the flux variability of pulsars and extragalactic sources and the VLBI visibility curves constitute new techniques for probing the ISM. However, scattering causes a seeing limitation in radio observations. It is now clear that variation due to RISS (refractive interstellar scintillations) is likely to be important for several classes of variable sources, especially low-frequency variables and centimeter-wave flickering. 168 refs

  4. Physics of the galaxy and interstellar matter

    International Nuclear Information System (INIS)

    Scheffler, H.; Elsasser, H.

    1988-01-01

    This book is based on the authors' long standing experience in teaching astronomy courses. It presents in a modern and complete way our present picture of the physics of the Milky Way system. The first part of the book deals with topics of more empirical character, such as the positions and motions of stars, the structure and kinetics of the stellar systems and interstellar phenomena. The more advanced second part is devoted to the interpretation of observational results, i.e. to the physics of interstellar gas and dust, to stellar dynamics, to the theory of spiral structures and the dynamics of interstellar gas

  5. Processes driving sea ice variability in the Bering Sea in an eddying ocean/sea ice model: Mean seasonal cycle

    Science.gov (United States)

    Li, Linghan; McClean, Julie L.; Miller, Arthur J.; Eisenman, Ian; Hendershott, Myrl C.; Papadopoulos, Caroline A.

    2014-12-01

    The seasonal cycle of sea ice variability in the Bering Sea, together with the thermodynamic and dynamic processes that control it, are examined in a fine resolution (1/10°) global coupled ocean/sea-ice model configured in the Community Earth System Model (CESM) framework. The ocean/sea-ice model consists of the Los Alamos National Laboratory Parallel Ocean Program (POP) and the Los Alamos Sea Ice Model (CICE). The model was forced with time-varying reanalysis atmospheric forcing for the time period 1970-1989. This study focuses on the time period 1980-1989. The simulated seasonal-mean fields of sea ice concentration strongly resemble satellite-derived observations, as quantified by root-mean-square errors and pattern correlation coefficients. The sea ice energy budget reveals that the seasonal thermodynamic ice volume changes are dominated by the surface energy flux between the atmosphere and the ice in the northern region and by heat flux from the ocean to the ice along the southern ice edge, especially on the western side. The sea ice force balance analysis shows that sea ice motion is largely associated with wind stress. The force due to divergence of the internal ice stress tensor is large near the land boundaries in the north, and it is small in the central and southern ice-covered region. During winter, which dominates the annual mean, it is found that the simulated sea ice was mainly formed in the northern Bering Sea, with the maximum ice growth rate occurring along the coast due to cold air from northerly winds and ice motion away from the coast. South of St Lawrence Island, winds drive the model sea ice southwestward from the north to the southwestern part of the ice-covered region. Along the ice edge in the western Bering Sea, model sea ice is melted by warm ocean water, which is carried by the simulated Bering Slope Current flowing to the northwest, resulting in the S-shaped asymmetric ice edge. In spring and fall, similar thermodynamic and dynamic

  6. Slow-slip events on the Whillans Ice Plain, Antarctica, described using rate-and-state friction as an ice stream sliding law

    Science.gov (United States)

    Lipovsky, Bradley Paul; Dunham, Eric M.

    2017-04-01

    The Whillans Ice Plain (WIP), Antarctica, experiences twice daily tidally modulated stick-slip cycles. Slip events last about 30 min, have sliding velocities as high as ˜0.5 mm/s (15 km/yr), and have total slip ˜0.5 m. Slip events tend to occur during falling ocean tide: just after high tide and just before low tide. To reproduce these characteristics, we use rate-and-state friction, which is commonly used to simulate tectonic faulting, as an ice stream sliding law. This framework describes the evolving strength of the ice-bed interface throughout stick-slip cycles. We present simulations that resolve the cross-stream dimension using a depth-integrated treatment of an elastic ice layer loaded by tides and steady ice inflow. Steady sliding with rate-weakening friction is conditionally stable with steady sliding occurring for sufficiently narrow ice streams relative to a nucleation length. Stick-slip cycles occur when the ice stream is wider than the nucleation length or, equivalently, when effective pressures exceed a critical value. Ice streams barely wider than the nucleation length experience slow-slip events, and our simulations suggest that the WIP is in this slow-slip regime. Slip events on the WIP show a sense of propagation, and we reproduce this behavior by introducing a rate-strengthening region in the center of the otherwise rate-weakening ice stream. If pore pressures are raised above a critical value, our simulations predict that the WIP would exhibit quasi-steady tidally modulated sliding as observed on other ice streams. This study validates rate-and-state friction as a sliding law to describe ice stream sliding styles.

  7. FORMATION OF S-BEARING SPECIES BY VUV/EUV IRRADIATION OF H2S-CONTAINING ICE MIXTURES: PHOTON ENERGY AND CARBON SOURCE EFFECTS

    International Nuclear Information System (INIS)

    Chen, Y.-J.; Juang, K.-J.; Qiu, J.-M.; Chu, C.-C.; Yih, T.-S.; Nuevo, M.; Jiménez-Escobar, A.; Muñoz Caro, G. M.; Wu, C.-Y. R.; Fung, H.-S.; Ip, W.-H.

    2015-01-01

    Carbonyl sulfide (OCS) is a key molecule in astrobiology that acts as a catalyst in peptide synthesis by coupling amino acids. Experimental studies suggest that hydrogen sulfide (H 2 S), a precursor of OCS, could be present in astrophysical environments. In the present study, we used a microwave-discharge hydrogen-flow lamp, simulating the interstellar UV field, and a monochromatic synchrotron light beam to irradiate CO:H 2 S and CO 2 :H 2 S ice mixtures at 14 K with vacuum ultraviolet (VUV) or extreme ultraviolet (EUV) photons in order to study the effect of the photon energy and carbon source on the formation mechanisms and production yields of S-containing products (CS 2 , OCS, SO 2 , etc.). Results show that (1) the photo-induced OCS production efficiency in CO:H 2 S ice mixtures is higher than that of CO 2 :H 2 S ice mixtures; (2) a lower concentration of H 2 S enhances the production efficiency of OCS in both ice mixtures; and (3) the formation pathways of CS 2 differ significantly upon VUV and EUV irradiations. Furthermore, CS 2 was produced only after VUV photoprocessing of CO:H 2 S ices, while the VUV-induced production of SO 2 occurred only in CO 2 :H 2 S ice mixtures. More generally, the production yields of OCS, H 2 S 2 , and CS 2 were studied as a function of the irradiation photon energy. Heavy S-bearing compounds were also observed using mass spectrometry during the warm-up of VUV/EUV-irradiated CO:H 2 S ice mixtures. The presence of S-polymers in dust grains may account for the missing sulfur in dense clouds and circumstellar environments

  8. The influence of the interstellar medium on climate and life

    International Nuclear Information System (INIS)

    Talbot, R.J. Jr.

    1980-01-01

    Recent studies of the gas and dust between the stars, the interstellar medium, reveal a complex chemistry which indicates that prebiotic organic chemistry is ubiquitous. The relationship between this interstellar chemistry and the organic chemistry of the early solar system and the Earth is explored. The interstellar medium is also considered as likely to have a continuing influence upon the climate of the Earth and other planets. Life forms as known are not only descendants of the organic evolution begun in the interstellar medium, but their continuing evolution is also molded through occasional interactions between the interstellar medium, the Sun and the climate on Earth. (author)

  9. Glacial Cycles and ice-sheet modelling

    NARCIS (Netherlands)

    Oerlemans, J.

    1982-01-01

    An attempt is made to simulate the Pleistocene glacial cycles with a numerical model of the Northern Hemisphere ice sheets. This model treats the vertically-integrated ice flow along a meridian, including computation of bedrock adjustment and temperature distribution in the ice. Basal melt water is

  10. Interaction of D2 with H2O amorphous ice studied by temperature-programmed desorption experiments.

    Science.gov (United States)

    Amiaud, L; Fillion, J H; Baouche, S; Dulieu, F; Momeni, A; Lemaire, J L

    2006-03-07

    The gas-surface interaction of molecular hydrogen D2 with a thin film of porous amorphous solid water (ASW) grown at 10 K by slow vapor deposition has been studied by temperature-programmed-desorption (TPD) experiments. Molecular hydrogen diffuses rapidly into the porous network of the ice. The D2 desorption occurring between 10 and 30 K is considered here as a good probe of the effective surface of ASW interacting with the gas. The desorption kinetics have been systematically measured at various coverages. A careful analysis based on the Arrhenius plot method has provided the D2 binding energies as a function of the coverage. Asymmetric and broad distributions of binding energies were found, with a maximum population peaking at low energy. We propose a model for the desorption kinetics that assumes a complete thermal equilibrium of the molecules with the ice film. The sample is characterized by a distribution of adsorption sites that are filled according to a Fermi-Dirac statistic law. The TPD curves can be simulated and fitted to provide the parameters describing the distribution of the molecules as a function of their binding energy. This approach contributes to a correct description of the interaction of molecular hydrogen with the surface of possibly porous grain mantles in the interstellar medium.

  11. Sea ice roughness: the key for predicting Arctic summer ice albedo

    Science.gov (United States)

    Landy, J.; Ehn, J. K.; Tsamados, M.; Stroeve, J.; Barber, D. G.

    2017-12-01

    Although melt ponds on Arctic sea ice evolve in stages, ice with smoother surface topography typically allows the pond water to spread over a wider area, reducing the ice-albedo and accelerating further melt. Building on this theory, we simulated the distribution of meltwater on a range of statistically-derived topographies to develop a quantitative relationship between premelt sea ice surface roughness and summer ice albedo. Our method, previously applied to ICESat observations of the end-of-winter sea ice roughness, could account for 85% of the variance in AVHRR observations of the summer ice-albedo [Landy et al., 2015]. Consequently, an Arctic-wide reduction in sea ice roughness over the ICESat operational period (from 2003 to 2008) explained a drop in ice-albedo that resulted in a 16% increase in solar heat input to the sea ice cover. Here we will review this work and present new research linking pre-melt sea ice surface roughness observations from Cryosat-2 to summer sea ice albedo over the past six years, examining the potential of winter roughness as a significant new source of sea ice predictability. We will further evaluate the possibility for high-resolution (kilometre-scale) forecasts of summer sea ice albedo from waveform-level Cryosat-2 roughness data in the landfast sea ice zone of the Canadian Arctic. Landy, J. C., J. K. Ehn, and D. G. Barber (2015), Albedo feedback enhanced by smoother Arctic sea ice, Geophys. Res. Lett., 42, 10,714-10,720, doi:10.1002/2015GL066712.

  12. Growing interstellar molecules with ion-molecule reactions

    International Nuclear Information System (INIS)

    Bohme, D.K.

    1989-01-01

    Laboratory measurements of gas-phase ion-molecule reactions continue to provide important insights into the chemistry of molecular growth in interstellar environments. It is also true that the measurements are becoming more demanding as larger molecules capture our interest. While some of these measurements are motivated by current developments in chemical models of interstellar environments or by new molecular observations by astronomers, others explore novel chemistry which can lead to predictions of new interstellar molecules. Here the author views the results of some recent measurements, taken in the Ion Chemistry Laboratory at York University with the SIFT technique, which address some of the current needs of modellers and observers and which also provide some new fundamental insight into molecular growth, particularly when it occurs in the presence of large molecules such as PAH molecules which are now thought to have a major influence on the chemistry of interstellar environments in which they are present

  13. Synthesis of Formamide and Related Organic Species in the Interstellar Medium via Chemical Dynamics Simulations

    Science.gov (United States)

    Spezia, Riccardo; Jeanvoine, Yannick; Hase, William L.; Song, Kihyung; Largo, Antonio

    2016-08-01

    We show, by means of direct dynamics simulations, how it is possible to define possible reactants and mechanisms leading to the formation of formamide in the interstellar medium. In particular, different ion-molecule reactions in the gas phase were considered: NH3OH+, NH2OH{}2+, H2COH+, and NH4 + for the ions and NH2OH, H2CO, and NH3 for the partner neutrals. These calculations were combined with high level ab initio calculations to investigate possible further evolution of the products observed. In particular, for formamide, we propose that the NH2OH{}2+ + H2CO reaction can produce an isomer, NH2OCH{}2+, that, after dissociative recombination, can produce neutral formamide, which was observed in space. The direct dynamics do not pre-impose any reaction pathways and in other reactions, we did not observe the formation of formamide or any possible precursor. On the other hand, we obtained other interesting reactions, like the formation of NH2CH{}2+. Finally, some radiative association processes are proposed. All of the results obtained are discussed in light of the species observed in radioastronomy.

  14. Identifying specific interstellar polycyclic aromatic hydrocarbons

    International Nuclear Information System (INIS)

    Mulas, Giacomo; Malloci, Giuliano; Porceddu, Ignazio

    2005-01-01

    Interstellar Polycyclic Aromatic Hydrocarbons (PAHs) have been thought to be ubiquitous for more than twenty years, yet no single species in this class has been identified in the Interstellar Medium (ISM) to date. The unprecedented sensitivity and resolution of present Infrared Space Observatory (ISO) and forthcoming Herschel observations in the far infrared spectral range will offer a unique way out of this embarrassing impasse

  15. Glacial–interglacial dynamics of Antarctic firn columns: comparison between simulations and ice core air-δ15N measurements

    Directory of Open Access Journals (Sweden)

    E. Capron

    2013-05-01

    Full Text Available Correct estimation of the firn lock-in depth is essential for correctly linking gas and ice chronologies in ice core studies. Here, two approaches to constrain the firn depth evolution in Antarctica are presented over the last deglaciation: outputs of a firn densification model, and measurements of δ15N of N2 in air trapped in ice core, assuming that δ15N is only affected by gravitational fractionation in the firn column. Since the firn densification process is largely governed by surface temperature and accumulation rate, we have investigated four ice cores drilled in coastal (Berkner Island, BI, and James Ross Island, JRI and semi-coastal (TALDICE and EPICA Dronning Maud Land, EDML Antarctic regions. Combined with available ice core air-δ15N measurements from the EPICA Dome C (EDC site, the studied regions encompass a large range of surface accumulation rates and temperature conditions. Our δ15N profiles reveal a heterogeneous response of the firn structure to glacial–interglacial climatic changes. While firn densification simulations correctly predict TALDICE δ15N variations, they systematically fail to capture the large millennial-scale δ15N variations measured at BI and the δ15N glacial levels measured at JRI and EDML – a mismatch previously reported for central East Antarctic ice cores. New constraints of the EDML gas–ice depth offset during the Laschamp event (~41 ka and the last deglaciation do not favour the hypothesis of a large convective zone within the firn as the explanation of the glacial firn model–δ15N data mismatch for this site. While we could not conduct an in-depth study of the influence of impurities in snow for firnification from the existing datasets, our detailed comparison between the δ15N profiles and firn model simulations under different temperature and accumulation rate scenarios suggests that the role of accumulation rate may have been underestimated in the current description of firnification

  16. SPH Modelling of Sea-ice Pack Dynamics

    Science.gov (United States)

    Staroszczyk, Ryszard

    2017-12-01

    The paper is concerned with the problem of sea-ice pack motion and deformation under the action of wind and water currents. Differential equations describing the dynamics of ice, with its very distinct mateFfigrial responses in converging and diverging flows, express the mass and linear momentum balances on the horizontal plane (the free surface of the ocean). These equations are solved by the fully Lagrangian method of smoothed particle hydrodynamics (SPH). Assuming that the ice behaviour can be approximated by a non-linearly viscous rheology, the proposed SPH model has been used to simulate the evolution of a sea-ice pack driven by wind drag stresses. The results of numerical simulations illustrate the evolution of an ice pack, including variations in ice thickness and ice area fraction in space and time. The effects of different initial ice pack configurations and of different conditions assumed at the coast-ice interface are examined. In particular, the SPH model is applied to a pack flow driven by a vortex wind to demonstrate how well the Lagrangian formulation can capture large deformations and displacements of sea ice.

  17. Wave-Ice interaction in the Marginal Ice Zone: Toward a Wave-Ocean-Ice Coupled Modeling System

    Science.gov (United States)

    2015-09-30

    as the ship encountered smaller ice floes. The first spectra is shown in dark blue and later spectra transitioning to aqua. SWAN spectra at this time...with no ice representation, is shown in black for reference. Figure 2 below shows the dissipation rate as a function of frequency by several...shown with the black lines. These estimates are created using large numbers of inexpensive simulations for Beaufort and Chukchi Seas in 2012, to

  18. Transient Conditions at the Ice/bed Interface Under a Palaeo-ice Stream Derived from Numerical Simulation of Groundwater Flow and Sedimentological Observations in a Drumlin Field, NW Poland

    Science.gov (United States)

    Hermanowski, P.; Piotrowski, J. A.

    2017-12-01

    Evacuation of glacial meltwater through the substratum is an important agent modulating the ice/bed interface processes. The amount of meltwater production, subglacial water pressure, flow patterns and fluxes all affect the strength of basal coupling and thus impact the ice-sheet dynamics. Despite much research into the subglacial processes of past ice sheets which controlled sediment transport and the formation of specific landforms, our understanding of the ice/bed interface remains fragmentary. In this study we numerically simulated, using finite difference and finite element codes, groundwater flow pattern and fluxes during an ice advance in the Stargard Drumlin Field, NW Poland to examine the potential influence of groundwater drainage on the landforming processes. The results are combined with sedimentological observations of the internal composition of the drumlins to validate the outcome of the numerical model. Our numerical experiments of groundwater flow suggest a highly time-dependent response of the subglacial hydrogeological system to the advancing ice margin. This is manifested as diversified areas of downward- and upward-oriented groundwater flows whereby the drumlin field area experienced primarily groundwater discharge towards the ice sole. The investigated drumlins are composed of (i) mainly massive till with thin stringers of meltwater sand, and (ii) sorted sediments carrying ductile deformations. The model results and sedimentological observations suggest a high subglacial pore-water pressure in the drumlin field area, which contributed to sediment deformation intervening with areas of basal decoupling and enhanced basal sliding.

  19. Solar wind/local interstellar medium interaction including charge exchange with neural hydrogen

    Science.gov (United States)

    Pauls, H. Louis; Zank, Gary P.

    1995-01-01

    We present results from a hydrodynamic model of the interaction of the solar wind with the local interstellar medium (LISM), self-consistently taking into account the effects of charge exchange between the plasma component and the interstellar neutrals. The simulation is fully time dependent, and is carried out in two or three dimensions, depending on whether the helio-latitudinal dependence of the solar wind speed and number density (both giving rise to three dimensional effects) are included. As a first approximation it is assumed that the neutral component of the flow can be described by a single, isotropic fluid. Clearly, this is not the actual situation, since charge exchange with the supersonic solar wind plasma in the region of the nose results in a 'second' neutral fluid propagating in the opposite direction as that of the LISM neutrals.

  20. Interstellar matter

    International Nuclear Information System (INIS)

    Mezger, P.G.

    1978-01-01

    An overview of the formation of our galaxy is presented followed by a summary of recent work in star formation and related topics. Selected discussions are given on interstellar matter including absorption characteristics of dust, the fully ionised component of the ISM and the energy density of lyc-photons in the solar neighbourhood and the diffuse galactic IR radiation

  1. MEASURING THE FRACTAL STRUCTURE OF INTERSTELLAR CLOUDS

    NARCIS (Netherlands)

    VOGELAAR, MGR; WAKKER, BP

    To study the structure of interstellar matter we have applied the concept of fractal curves to the brightness contours of maps of interstellar clouds and from these estimated the fractal dimension for some of them. We used the so-called perimeter-area relation as the basis for these estimates. We

  2. MEASURING THE FRACTAL STRUCTURE OF INTERSTELLAR CLOUDS

    NARCIS (Netherlands)

    VOGELAAR, MGR; WAKKER, BP

    1994-01-01

    To study the structure of interstellar matter we have applied the concept of fractal curves to the brightness contours of maps of interstellar clouds and from these estimated the fractal dimension for some of them. We used the so-called perimeter-area relation as the basis for these estimates. We

  3. FORMATION OF S-BEARING SPECIES BY VUV/EUV IRRADIATION OF H{sub 2}S-CONTAINING ICE MIXTURES: PHOTON ENERGY AND CARBON SOURCE EFFECTS

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Y.-J.; Juang, K.-J.; Qiu, J.-M.; Chu, C.-C.; Yih, T.-S. [Department of Physics, National Central University, Jhongli City, Taoyuan County 32054, Taiwan (China); Nuevo, M. [NASA Ames Research Center, Moffett Field, CA 94035 (United States); Jiménez-Escobar, A.; Muñoz Caro, G. M. [Centro de Astrobiología, INTA-CSIC, Torrejón de Ardoz, E-28850 Madrid (Spain); Wu, C.-Y. R. [Space Sciences Center and Department of Physics and Astronomy, University of Southern California, Los Angeles, CA 90089-1341 (United States); Fung, H.-S. [National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan (China); Ip, W.-H. [Graduate Institute of Astronomy, National Central University, Jhongli City, Taoyuan County 32049, Taiwan (China)

    2015-01-10

    Carbonyl sulfide (OCS) is a key molecule in astrobiology that acts as a catalyst in peptide synthesis by coupling amino acids. Experimental studies suggest that hydrogen sulfide (H{sub 2}S), a precursor of OCS, could be present in astrophysical environments. In the present study, we used a microwave-discharge hydrogen-flow lamp, simulating the interstellar UV field, and a monochromatic synchrotron light beam to irradiate CO:H{sub 2}S and CO{sub 2}:H{sub 2}S ice mixtures at 14 K with vacuum ultraviolet (VUV) or extreme ultraviolet (EUV) photons in order to study the effect of the photon energy and carbon source on the formation mechanisms and production yields of S-containing products (CS{sub 2}, OCS, SO{sub 2}, etc.). Results show that (1) the photo-induced OCS production efficiency in CO:H{sub 2}S ice mixtures is higher than that of CO{sub 2}:H{sub 2}S ice mixtures; (2) a lower concentration of H{sub 2}S enhances the production efficiency of OCS in both ice mixtures; and (3) the formation pathways of CS{sub 2} differ significantly upon VUV and EUV irradiations. Furthermore, CS{sub 2} was produced only after VUV photoprocessing of CO:H{sub 2}S ices, while the VUV-induced production of SO{sub 2} occurred only in CO{sub 2}:H{sub 2}S ice mixtures. More generally, the production yields of OCS, H{sub 2}S{sub 2}, and CS{sub 2} were studied as a function of the irradiation photon energy. Heavy S-bearing compounds were also observed using mass spectrometry during the warm-up of VUV/EUV-irradiated CO:H{sub 2}S ice mixtures. The presence of S-polymers in dust grains may account for the missing sulfur in dense clouds and circumstellar environments.

  4. Probing the diffuse interstellar medium with diffuse interstellar bands

    Science.gov (United States)

    Theodorus van Loon, Jacco; Bailey, Mandy; Farhang, Amin; Javadi, Atefeh; Khosroshahi, Habib

    2015-08-01

    For a century already, a large number of absorption bands have been known at optical wavelengths, called the diffuse interstellar bands (DIBs). While their carriers remain unidentified, the relative strengths of these bands in various environments make them interesting new probes of the diffuse interstellar medium (ISM). We present the results from two large, dedicated campaigns to map the ISM using DIBs measured in the high signal-to-noise spectra of hundreds of early-type stars: [1] in and around the Local Bubble using ESO's New Technology Telescope and the Isaac Newton Telescope, and [2] across both Magellanic Clouds using the Very Large Telescope and the Anglo-Australian Telescope. We discuss the implications for the structure and dynamics of the ISM, as well as the constraints these maps place on the nature of the carriers of the DIBs. Partial results have appeared in the recent literature (van Loon et al. 2013; Farhang et al. 2015a,b; Bailey, PhD thesis 2014) with the remainder being prepared for publication now.

  5. Interstellar Initiative Web Page Design

    Science.gov (United States)

    Mehta, Alkesh

    1999-01-01

    This summer at NASA/MSFC, I have contributed to two projects: Interstellar Initiative Web Page Design and Lenz's Law Relative Motion Demonstration. In the Web Design Project, I worked on an Outline. The Web Design Outline was developed to provide a foundation for a Hierarchy Tree Structure. The Outline would help design a Website information base for future and near-term missions. The Website would give in-depth information on Propulsion Systems and Interstellar Travel. The Lenz's Law Relative Motion Demonstrator is discussed in this volume by Russell Lee.

  6. Detection of organic matter in interstellar grains.

    Science.gov (United States)

    Pendleton, Y J

    1997-06-01

    Star formation and the subsequent evolution of planetary systems occurs in dense molecular clouds, which are comprised, in part, of interstellar dust grains gathered from the diffuse interstellar medium (DISM). Radio observations of the interstellar medium reveal the presence of organic molecules in the gas phase and infrared observational studies provide details concerning the solid-state features in dust grains. In particular, a series of absorption bands have been observed near 3.4 microns (approximately 2940 cm-1) towards bright infrared objects which are seen through large column densities of interstellar dust. Comparisons of organic residues, produced under a variety of laboratory conditions, to the diffuse interstellar medium observations have shown that aliphatic hydrocarbon grains are responsible for the spectral absorption features observed near 3.4 microns (approximately 2940 cm-1). These hydrocarbons appear to carry the -CH2- and -CH3 functional groups in the abundance ratio CH2/CH3 approximately 2.5, and the amount of carbon tied up in this component is greater than 4% of the cosmic carbon available. On a galactic scale, the strength of the 3.4 microns band does not scale linearly with visual extinction, but instead increases more rapidly for objects near the Galactic Center. A similar trend is noted in the strength of the Si-O absorption band near 9.7 microns. The similar behavior of the C-H and Si-O stretching bands suggests that these two components may be coupled, perhaps in the form of grains with silicate cores and refractory organic mantles. The ubiquity of the hydrocarbon features seen in the near infrared near 3.4 microns throughout out Galaxy and in other galaxies demonstrates the widespread availability of such material for incorporation into the many newly forming planetary systems. The similarity of the 3.4 microns features in any organic material with aliphatic hydrocarbons underscores the need for complete astronomical observational

  7. Constraints on the properties of Pluto's nitrogen-ice rich layer from convection simulations

    Science.gov (United States)

    Wong, T.; McKinnon, W. B.; Schenk, P.

    2016-12-01

    Pluto's Sputnik Planum basin (informally named) displays regular cellular patterns strongly suggesting that solid-state convection is occurring in a several-kilometers-deep nitrogen-ice rich layer (McKinnon et al., Convection in a volatile nitrogen-ice-rich layer drives Pluto's geological vigour, Nature 534, 82-85, 2016). We investigate the behavior of thermal convection in 2-D that covers a range of parameters applicable to the nitrogen ice layer to constrain its properties such that these long-wavelength surface features can be explained. We perform a suite of numerical simulations of convection with basal heating and temperature-dependent viscosity in either exponential form or Arrhenius form. For a plausible range of Rayleigh numbers and viscosity contrasts for solid nitrogen, convection can occur in all possible regimes: sluggish lid, transitional, or stagnant lid, or the layer could be purely conducting. We suggest the range of depth and temperature difference across the layer for convection to occur. We observe that the plume dynamics can be widely different in terms of the aspect ratio of convecting cells, or the width and spacing of plumes, and also in the lateral movement of plumes. These differences depend on the regime of convection determined by the Rayleigh number and the actual viscosity contrast across the layer, but is not sensitive to whether the viscosity is in Arrhenius or exponential form. The variations in plume dynamics result in different types of dynamic topography, which can be compared with the observed horizontal and vertical scales of the cells in Sputnik Planum. Based on these simulations we suggest several different possibilities for the formation and evolution of Sputnik Planum, which may be a consequence of the time-dependent behavior of thermal convection.

  8. Implementing an empirical scalar constitutive relation for ice with flow-induced polycrystalline anisotropy in large-scale ice sheet models

    Science.gov (United States)

    Graham, Felicity S.; Morlighem, Mathieu; Warner, Roland C.; Treverrow, Adam

    2018-03-01

    The microstructure of polycrystalline ice evolves under prolonged deformation, leading to anisotropic patterns of crystal orientations. The response of this material to applied stresses is not adequately described by the ice flow relation most commonly used in large-scale ice sheet models - the Glen flow relation. We present a preliminary assessment of the implementation in the Ice Sheet System Model (ISSM) of a computationally efficient, empirical, scalar, constitutive relation which addresses the influence of the dynamically steady-state flow-compatible induced anisotropic crystal orientation patterns that develop when ice is subjected to the same stress regime for a prolonged period - sometimes termed tertiary flow. We call this the ESTAR flow relation. The effect on ice flow dynamics is investigated by comparing idealised simulations using ESTAR and Glen flow relations, where we include in the latter an overall flow enhancement factor. For an idealised embayed ice shelf, the Glen flow relation overestimates velocities by up to 17 % when using an enhancement factor equivalent to the maximum value prescribed in the ESTAR relation. Importantly, no single Glen enhancement factor can accurately capture the spatial variations in flow across the ice shelf generated by the ESTAR flow relation. For flow line studies of idealised grounded flow over varying topography or variable basal friction - both scenarios dominated at depth by bed-parallel shear - the differences between simulated velocities using ESTAR and Glen flow relations depend on the value of the enhancement factor used to calibrate the Glen flow relation. These results demonstrate the importance of describing the deformation of anisotropic ice in a physically realistic manner, and have implications for simulations of ice sheet evolution used to reconstruct paleo-ice sheet extent and predict future ice sheet contributions to sea level.

  9. TRIANGULATION OF THE INTERSTELLAR MAGNETIC FIELD

    Energy Technology Data Exchange (ETDEWEB)

    Schwadron, N. A.; Moebius, E. [University of New Hampshire, Durham, NH 03824 (United States); Richardson, J. D. [Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Burlaga, L. F. [Goddard Space Flight Center, Greenbelt, MD 20771 (United States); McComas, D. J. [Southwest Research Institute, San Antonio, TX 78228 (United States)

    2015-11-01

    Determining the direction of the local interstellar magnetic field (LISMF) is important for understanding the heliosphere’s global structure, the properties of the interstellar medium, and the propagation of cosmic rays in the local galactic medium. Measurements of interstellar neutral atoms by Ulysses for He and by SOHO/SWAN for H provided some of the first observational insights into the LISMF direction. Because secondary neutral H is partially deflected by the interstellar flow in the outer heliosheath and this deflection is influenced by the LISMF, the relative deflection of H versus He provides a plane—the so-called B–V plane in which the LISMF direction should lie. Interstellar Boundary Explorer (IBEX) subsequently discovered a ribbon, the center of which is conjectured to be the LISMF direction. The most recent He velocity measurements from IBEX and those from Ulysses yield a B–V plane with uncertainty limits that contain the centers of the IBEX ribbon at 0.7–2.7 keV. The possibility that Voyager 1 has moved into the outer heliosheath now suggests that Voyager 1's direct observations provide another independent determination of the LISMF. We show that LISMF direction measured by Voyager 1 is >40° off from the IBEX ribbon center and the B–V plane. Taking into account the temporal gradient of the field direction measured by Voyager 1, we extrapolate to a field direction that passes directly through the IBEX ribbon center (0.7–2.7 keV) and the B–V plane, allowing us to triangulate the LISMF direction and estimate the gradient scale size of the magnetic field.

  10. Peculiarities of Vibration Characteristics of Amorphous Ices

    Science.gov (United States)

    Gets, Kirill V.; Subbotin, Oleg S.; Belosludov, Vladimir R.

    2012-03-01

    Dynamic properties of low (LDA), high (HDA) and very high (VHDA) density amorphous ices were investigated within the approach based on Lattice Dynamics simulations. In this approach, we assume that the short-range molecular order mainly determines the dynamic and thermodynamic properties of amorphous ices. Simulation cell of 512 water molecules with periodical boundary conditions and disordering allows us to study dynamical properties and dispersion curves in the Brillouin zone of pseudo-crystal. Existence of collective phenomena in amorphous ices which is usual for crystals but anomalous for disordered phase was confirmed in our simulations. Molecule amplitudes of delocalized (collective) as well as localized vibrations have been considered.

  11. Optical observations of nearby interstellar gas

    Science.gov (United States)

    Frisch, P. C.; York, D. G.

    1984-11-01

    Observations indicated that a cloud with a heliocentric velocity of approximately -28 km/s and a hydrogen column density that possibly could be on the order of, or greater than, 5 x 10 to the 19 power/square cm is located within the nearest 50 to 80 parsecs in the direction of Ophiuchus. This is a surprisingly large column density of material for this distance range. The patchy nature of the absorption from the cloud indicates that it may not be a feature with uniform properties, but rather one with small scale structure which includes local enhancements in the column density. This cloud is probably associated with the interstellar cloud at about the same velocity in front of the 20 parsec distant star alpha Oph (Frisch 1981, Crutcher 1982), and the weak interstellar polarization found in stars as near as 35 parsecs in this general region (Tinbergen 1982). These data also indicate that some portion of the -14 km/s cloud also must lie within the 100 parsec region. Similar observations of both Na1 and Ca2 interstellar absorption features were performed in other lines of sight. Similar interstellar absorption features were found in a dozen stars between 20 and 100 parsecs of the Sun.

  12. INTERSTELLAR MAGNETIC FIELD SURROUNDING THE HELIOPAUSE

    International Nuclear Information System (INIS)

    Whang, Y. C.

    2010-01-01

    This paper presents a three-dimensional analytical solution, in the limit of very low plasma β-ratio, for the distortion of the interstellar magnetic field surrounding the heliopause. The solution is obtained using a line dipole method that is the integration of point dipole along a semi-infinite line; it represents the magnetic field caused by the presence of the heliopause. The solution allows the variation of the undisturbed magnetic field at any inclination angle. The heliosphere is considered as having blunt-nosed geometry on the upwind side and it asymptotically approaches a cylindrical geometry having an open exit for the continuous outflow of the solar wind on the downwind side. The heliopause is treated as a magnetohydrodynamic tangential discontinuity; the interstellar magnetic field lines at the boundary are tangential to the heliopause. The interstellar magnetic field is substantially distorted due to the presence of the heliopause. The solution shows the draping of the field lines around the heliopause. The magnetic field strength varies substantially near the surface of the heliopause. The effect on the magnetic field due to the presence of the heliopause penetrates very deep into the interstellar space; the depth of penetration is of the same order of magnitude as the scale length of the heliosphere.

  13. Organics and Ices in the Outer Solar System: Connections to the Interstellar Medium

    Science.gov (United States)

    Pendleton, Y. J.; Cruikshank, D. P.

    2017-01-01

    The solar nebula, that aggregate of gas and dust that formed the birthplace of the Sun, planets and plethora of small bodies comprising the Solar System, originated in a molecular cloud that is thought to have spawned numerous additional stars, some with their own planets and attendant small bodies. The question of the chemical and physical reprocessing of the original interstellar materials in the solar nebula has challenged both theory and observations. The acquisition and analysis of samples of comet and asteroid solids, and a growing suite of in-situ and close-up analyses of relatively unaltered small Solar System bodies now adds critical new dimensions to the study of the origin and evolution of the early solar nebula. Better understanding the original composition of the material from which our solar nebula formed, and the processing that material experienced, will aid in formulations of chemistry that might occur in other solar systems. While we seek to understand the compositional history of planetary bodies in our own Solar System, we will inevitably learn more about the materials that comprise exoplanets and their surrounding systems.

  14. The implementation of sea ice model on a regional high-resolution scale

    Science.gov (United States)

    Prasad, Siva; Zakharov, Igor; Bobby, Pradeep; McGuire, Peter

    2015-09-01

    The availability of high-resolution atmospheric/ocean forecast models, satellite data and access to high-performance computing clusters have provided capability to build high-resolution models for regional ice condition simulation. The paper describes the implementation of the Los Alamos sea ice model (CICE) on a regional scale at high resolution. The advantage of the model is its ability to include oceanographic parameters (e.g., currents) to provide accurate results. The sea ice simulation was performed over Baffin Bay and the Labrador Sea to retrieve important parameters such as ice concentration, thickness, ridging, and drift. Two different forcing models, one with low resolution and another with a high resolution, were used for the estimation of sensitivity of model results. Sea ice behavior over 7 years was simulated to analyze ice formation, melting, and conditions in the region. Validation was based on comparing model results with remote sensing data. The simulated ice concentration correlated well with Advanced Microwave Scanning Radiometer for EOS (AMSR-E) and Ocean and Sea Ice Satellite Application Facility (OSI-SAF) data. Visual comparison of ice thickness trends estimated from the Soil Moisture and Ocean Salinity satellite (SMOS) agreed with the simulation for year 2010-2011.

  15. The surface reactivity of acrylonitrile with oxygen atoms on an analogue of interstellar dust grains

    Science.gov (United States)

    Kimber, Helen J.; Toscano, Jutta; Price, Stephen D.

    2018-06-01

    Experiments designed to reveal the low-temperature reactivity on the surfaces of interstellar dust grains are used to probe the heterogeneous reaction between oxygen atoms and acrylonitrile (C2H3CN, H2C=CH-CN). The reaction is studied at a series of fixed surface temperatures between 14 and 100 K. After dosing the reactants on to the surface, temperature-programmed desorption, coupled with time-of-flight mass spectrometry, reveals the formation of a product with the molecular formula C3H3NO. This product results from the addition of a single oxygen atom to the acrylonitrile reactant. The oxygen atom attack appears to occur exclusively at the C=C double bond, rather than involving the cyano(-CN) group. The absence of reactivity at the cyano site hints that full saturation of organic molecules on dust grains may not always occur in the interstellar medium. Modelling the experimental data provides a reaction probability of 0.007 ± 0.003 for a Langmuir-Hinshelwood style (diffusive) reaction mechanism. Desorption energies for acrylonitrile, oxygen atoms, and molecular oxygen, from the multilayer mixed ice their deposition forms, are also extracted from the kinetic model and are 22.7 ± 1.0 kJ mol-1 (2730 ± 120 K), 14.2 ± 1.0 kJ mol-1 (1710 ± 120 K), and 8.5 ± 0.8 kJ mol-1 (1020 ± 100 K), respectively. The kinetic parameters we extract from our experiments indicate that the reaction between atomic oxygen and acrylonitrile could occur on interstellar dust grains on an astrophysical time-scale.

  16. UV photoprocessing of NH3 ice: photon-induced desorption mechanisms

    Science.gov (United States)

    Martín-Doménech, R.; Cruz-Díaz, G. A.; Muñoz Caro, G. M.

    2018-01-01

    Ice mantles detected on the surface of dust grains towards the coldest regions of the interstellar medium can be photoprocessed by the secondary ultraviolet (UV) field present in dense cloud interiors. In this work, we present UV-irradiation experiments under astrophysically relevant conditions of pure NH3 ice samples in an ultra-high vacuum chamber where solid samples were deposited on to a substrate at 8 K. The ice analogues were subsequently photoprocessed with a microwave-discharged hydrogen-flow lamp. The induced radiation and photochemistry led to the production of H2, N2 and N2H4. In addition, photodesorption to the gas phase of the original ice component, NH3, and two of the three detected photoproducts, H2 and N2, was observed thanks to a quadrupole mass spectrometer (QMS). Calibration of the QMS allowed quantification of the photodesorption yields, leading to Ypd (NH3) = 2.1^{+2.1}_{-1.0} × 10-3 molecules/{incident photon}, which remained constant during the whole experiments, while photodesorption of H2 and N2 increased with fluence, pointing towards an indirect photodesorption mechanism involving energy transfer for these species. Photodesorption yield of N2 molecules after a fluence equivalent to that experienced by ice mantles in space was similar to that of the NH3 molecules (Ypd (N2) = 1.7^{+1.7}_{-0.9} × 10-3 molecules/{incident photon}).

  17. Interstellar propulsion using a pellet stream for momentum transfer

    International Nuclear Information System (INIS)

    Singer, C.E.

    1979-10-01

    A pellet-stream concept for interstellar propulsion is described. Small pellets are accelerated in the solar system and accurately guided to an interstellar probe where they are intercepted and transfer momentum. This propulsion system appears to offer orders-of-magnitude improvements in terms of engineering simplicity and power requirements over any other known feasible system for transport over interstellar distance in a time comparable to a human lifespan

  18. Carbon chain molecules in interstellar clouds

    International Nuclear Information System (INIS)

    Winnewisser, G.; Walmsley, C.M.

    1979-01-01

    A survey of the distribution of long carbon chain molecules in interstellar clouds shows that their abundance is correlated. The various formation schemes for these molecules are discussed. It is concluded that the ion-molecule type formation mechanisms are more promising than their competitors. They have also the advantage of allowing predictions which can be tested by observations. Acetylene C 2 H 2 and diacetylene HCCCCH, may be very abundant in interstellar clouds. (Auth.)

  19. Structure and evolution of the interstellar medium

    International Nuclear Information System (INIS)

    Chieze, J.P.

    1985-10-01

    We give a two dimensional hydrodynamical analysis of HI clouds collisions in order to determine the mass spectrum of diffuse interstellar clouds. We have taken into account evaporation and abrasion by supernovae blast waves. The conditions for cloud merging or fragmentation are precised. Applications to the model of the interstellar medium of Mc Kee and Ostriker are also discussed. On the other hand, we show that molecular clouds belong to a one parameter family which can be identified to the sequence of the gravitationally unstable states of clouds bounded by the uniform pressure of the coronal phase of the interstellar medium. Hierarchical fragmentation of molecular clouds is analysed in this context [fr

  20. Spin-Ice Thin Films: Large-N Theory and Monte Carlo Simulations

    Science.gov (United States)

    Lantagne-Hurtubise, Étienne; Rau, Jeffrey G.; Gingras, Michel J. P.

    2018-04-01

    We explore the physics of highly frustrated magnets in confined geometries, focusing on the Coulomb phase of pyrochlore spin ices. As a specific example, we investigate thin films of nearest-neighbor spin ice, using a combination of analytic large-N techniques and Monte Carlo simulations. In the simplest film geometry, with surfaces perpendicular to the [001] crystallographic direction, we observe pinch points in the spin-spin correlations characteristic of a two-dimensional Coulomb phase. We then consider the consequences of crystal symmetry breaking on the surfaces of the film through the inclusion of orphan bonds. We find that when these bonds are ferromagnetic, the Coulomb phase is destroyed by the presence of fluctuating surface magnetic charges, leading to a classical Z2 spin liquid. Building on this understanding, we discuss other film geometries with surfaces perpendicular to the [110] or the [111] direction. We generically predict the appearance of surface magnetic charges and discuss their implications for the physics of such films, including the possibility of an unusual Z3 classical spin liquid. Finally, we comment on open questions and promising avenues for future research.

  1. The Medieval Warm Period, the Little Ice Age and simulated climatic variability

    Energy Technology Data Exchange (ETDEWEB)

    Hunt, B.G. [CSIRO Marine and Atmospheric Research, Aspendale, VIC (Australia)

    2006-12-15

    The CSIRO Mark 2 coupled global climatic model has been used to generate a 10,000-year simulation for 'present' climatic conditions. The model output has been analysed to identify sustained climatic fluctuations, such as those attributed to the Medieval Warm Period (MWP) and the Little Ice Age (LIA). Since no external forcing was permitted during the model run all such fluctuations are attributed to naturally occurring climatic variability associated with the nonlinear processes inherent in the climatic system. Comparison of simulated climatic time series for different geographical locations highlighted the lack of synchronicity between these series. The model was found to be able to simulate climatic extremes for selected observations for century timescales, as well as identifying the associated spatial characteristics. Other examples of time series simulated by the model for the USA and eastern Russia had similar characteristics to those attributed to the MWP and the LIA, but smaller amplitudes, and clearly defined spatial patterns. A search for the frequency of occurrence of specified surface temperature anomalies, defined via duration and mean value, revealed that these were primarily confined to polar regions and northern latitudes of Europe, Asia and North America. Over the majority of the oceans and southern hemisphere such climatic fluctuations could not be sustained, for reasons explained in the paper. Similarly, sustained sea-ice anomalies were mainly confined to the northern hemisphere. An examination of mechanisms associated with the sustained climatic fluctuations failed to identify a role for the North Atlantic Oscillation, the El Nino-Southern Oscillation or the Pacific Decadal Oscillation. It was therefore concluded that these fluctuations were generated by stochastic processes intrinsic to the nonlinear climatic system. While a number of characteristics of the MWP and the LIA could have been partially caused by natural processes within

  2. The turbulent life of dust grains in the supernova-driven, multiphase interstellar medium

    Science.gov (United States)

    Peters, Thomas; Zhukovska, Svitlana; Naab, Thorsten; Girichidis, Philipp; Walch, Stefanie; Glover, Simon C. O.; Klessen, Ralf S.; Clark, Paul C.; Seifried, Daniel

    2017-06-01

    Dust grains are an important component of the interstellar medium (ISM) of galaxies. We present the first direct measurement of the residence times of interstellar dust in the different ISM phases, and of the transition rates between these phases, in realistic hydrodynamical simulations of the multiphase ISM. Our simulations include a time-dependent chemical network that follows the abundances of H+, H, H2, C+ and CO and take into account self-shielding by gas and dust using a tree-based radiation transfer method. Supernova explosions are injected either at random locations, at density peaks, or as a mixture of the two. For each simulation, we investigate how matter circulates between the ISM phases and find more sizeable transitions than considered in simple mass exchange schemes in the literature. The derived residence times in the ISM phases are characterized by broad distributions, in particular for the molecular, warm and hot medium. The most realistic simulations with random and mixed driving have median residence times in the molecular, cold, warm and hot phase around 17, 7, 44 and 1 Myr, respectively. The transition rates measured in the random driving run are in good agreement with observations of Ti gas-phase depletion in the warm and cold phases in a simple depletion model. ISM phase definitions based on chemical abundance rather than temperature cuts are physically more meaningful, but lead to significantly different transition rates and residence times because there is no direct correspondence between the two definitions.

  3. Interstellar Interloper 1I/2017 U1: Observations from the NOT and WIYN Telescopes

    Science.gov (United States)

    Jewitt, David; Luu, Jane; Rajagopal, Jayadev; Kotulla, Ralf; Ridgway, Susan; Liu, Wilson; Augusteijn, Thomas

    2017-12-01

    We present observations of the interstellar interloper 1I/2017 U1 (’Oumuamua) taken during its 2017 October flyby of Earth. The optical colors B - V = 0.70 ± 0.06, V - R = 0.45 ± 0.05, overlap those of the D-type Jovian Trojan asteroids and are incompatible with the ultrared objects that are abundant in the Kuiper Belt. With a mean absolute magnitude H V = 22.95 and assuming a geometric albedo p V = 0.1, we find an average radius of 55 m. No coma is apparent; we deduce a limit to the dust mass production rate of only ˜2 × 10-4 kg s-1, ruling out the existence of exposed ice covering more than a few m2 of the surface. Volatiles in this body, if they exist, must lie beneath an involatile surface mantle ≳0.5 m thick, perhaps a product of prolonged cosmic-ray processing in the interstellar medium. The light curve range is unusually large at ˜2.0 ± 0.2 mag. Interpreted as a rotational light curve the body has axis ratio ≥ {6.3}-1.1+1.3:1 and semi-axes ˜230 m × 35 m. A ≳6:1 axis ratio is extreme relative to most small solar system asteroids and suggests that albedo variations may additionally contribute to the variability. The light curve is consistent with a two-peaked period ˜8.26 hr, but the period is non-unique as a result of aliasing in the data. Except for its unusually elongated shape, 1I/2017 U1 is a physically unremarkable, sub-kilometer, slightly red, rotating object from another planetary system. The steady-state population of similar, ˜100 m scale interstellar objects inside the orbit of Neptune is ˜104, each with a residence time of ˜10 years.

  4. Stochastic evolution of refractory interstellar dust during the chemical evolution of a two-phase interstellar medium

    International Nuclear Information System (INIS)

    Liffman, K.; Clayton, D.D.

    1989-01-01

    The evolution course of refractory interstellar dust during the chemical evolution of a two-phase interstellar medium (ISM) is studied using a simple model of the chemical evolution of ISM. It is assumed that, in this medium, the stars are born in molecular clouds, but new nucleosynthesis products and stellar return are entered into a complementary diffuse medium; the well-mixed matter of each interstellar phase is repeatedly cycled stochastically through the complementary phase and back. The dust is studied on a particle-by-particle bases as it is sputtered by shock waves in the diffuse medium, accretes an amorphous mantle of gaseous refractory atoms while its local medium joins the molecular cloud medium, and encounters the possibility of astration within molecular clouds. Results are presented relevant to the size spectrum of accreted mantles, its age spectrum and the distinction among its several lifetimes, depletion factors of refractory atoms in the diffuse gas, and isotopic anomalies. 26 refs

  5. Ice bridges and ridges in the Maxwell-EB sea ice rheology

    Directory of Open Access Journals (Sweden)

    V. Dansereau

    2017-09-01

    Full Text Available This paper presents a first implementation of a new rheological model for sea ice on geophysical scales. This continuum model, called Maxwell elasto-brittle (Maxwell-EB, is based on a Maxwell constitutive law, a progressive damage mechanism that is coupled to both the elastic modulus and apparent viscosity of the ice cover and a Mohr–Coulomb damage criterion that allows for pure (uniaxial and biaxial tensile strength. The model is tested on the basis of its capability to reproduce the complex mechanical and dynamical behaviour of sea ice drifting through a narrow passage. Idealized as well as realistic simulations of the flow of ice through Nares Strait are presented. These demonstrate that the model reproduces the formation of stable ice bridges as well as the stoppage of the flow, a phenomenon occurring within numerous channels of the Arctic. In agreement with observations, the model captures the propagation of damage along narrow arch-like kinematic features, the discontinuities in the velocity field across these features dividing the ice cover into floes, the strong spatial localization of the thickest, ridged ice, the presence of landfast ice in bays and fjords and the opening of polynyas downstream of the strait. The model represents various dynamical behaviours linked to an overall weakening of the ice cover and to the shorter lifespan of ice bridges, with implications in terms of increased ice export through narrow outflow pathways of the Arctic.

  6. Ice bridges and ridges in the Maxwell-EB sea ice rheology

    Science.gov (United States)

    Dansereau, Véronique; Weiss, Jérôme; Saramito, Pierre; Lattes, Philippe; Coche, Edmond

    2017-09-01

    This paper presents a first implementation of a new rheological model for sea ice on geophysical scales. This continuum model, called Maxwell elasto-brittle (Maxwell-EB), is based on a Maxwell constitutive law, a progressive damage mechanism that is coupled to both the elastic modulus and apparent viscosity of the ice cover and a Mohr-Coulomb damage criterion that allows for pure (uniaxial and biaxial) tensile strength. The model is tested on the basis of its capability to reproduce the complex mechanical and dynamical behaviour of sea ice drifting through a narrow passage. Idealized as well as realistic simulations of the flow of ice through Nares Strait are presented. These demonstrate that the model reproduces the formation of stable ice bridges as well as the stoppage of the flow, a phenomenon occurring within numerous channels of the Arctic. In agreement with observations, the model captures the propagation of damage along narrow arch-like kinematic features, the discontinuities in the velocity field across these features dividing the ice cover into floes, the strong spatial localization of the thickest, ridged ice, the presence of landfast ice in bays and fjords and the opening of polynyas downstream of the strait. The model represents various dynamical behaviours linked to an overall weakening of the ice cover and to the shorter lifespan of ice bridges, with implications in terms of increased ice export through narrow outflow pathways of the Arctic.

  7. Interstellar matter within elliptical galaxies

    Science.gov (United States)

    Jura, Michael

    1988-01-01

    Multiwavelength observations of elliptical galaxies are reviewed, with an emphasis on their implications for theoretical models proposed to explain the origin and evolution of the interstellar matter. Particular attention is given to interstellar matter at T less than 100 K (atomic and molecular gas and dust), gas at T = about 10,000 K, and gas at T = 10 to the 6th K or greater. The data are shown to confirm the occurrence of mass loss from evolved stars, significant accretion from companion galaxies, and cooling inflows; no evidence is found for large mass outflow from elliptical galaxies.

  8. ADVECTIVE TRANSPORT OF INTERSTELLAR PLASMA INTO THE HELIOSPHERE ACROSS THE RECONNECTING HELIOPAUSE

    International Nuclear Information System (INIS)

    Strumik, M.; Grzedzielski, S.; Czechowski, A.; Macek, W. M.; Ratkiewicz, R.

    2014-01-01

    We discuss results of magnetohydrodynamical model simulations of plasma dynamics in the proximity of the heliopause (HP). The model is shown to fit details of the magnetic field variations observed by the Voyager 1 spacecraft during the transition from the heliosphere to the local interstellar medium (LISM). We propose an interpretation of magnetic field structures observed by Voyager 1 in terms of fine-scale physical processes. Our simulations reveal an effective transport mechanism of relatively dense LISM plasma across the reconnecting HP into the heliosphere. The mechanism is associated with annihilation of magnetic sectors in the heliospheric plasma near the HP

  9. Climate Modeling: Ocean Cavities below Ice Shelves

    Energy Technology Data Exchange (ETDEWEB)

    Petersen, Mark Roger [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Computer, Computational, and Statistical Sciences Division

    2016-09-12

    The Accelerated Climate Model for Energy (ACME), a new initiative by the U.S. Department of Energy, includes unstructured-mesh ocean, land-ice, and sea-ice components using the Model for Prediction Across Scales (MPAS) framework. The ability to run coupled high-resolution global simulations efficiently on large, high-performance computers is a priority for ACME. Sub-ice shelf ocean cavities are a significant new capability in ACME, and will be used to better understand how changing ocean temperature and currents influence glacial melting and retreat. These simulations take advantage of the horizontal variable-resolution mesh and adaptive vertical coordinate in MPAS-Ocean, in order to place high resolution below ice shelves and near grounding lines.

  10. Stardust Interstellar Preliminary Examination VII: Synchrotron X-Ray Fluorescence Analysis of Six Stardust Interstellar Candidates Measured with the Advanced Photon Source 2-ID-D Microprobe

    Science.gov (United States)

    Allen, Carlton C.; Anderson, David; Bastien, Ron K.; Brenker, Frank E.; Flynn, George J.; Frank, David; Gainsforth, Zack; Sandford, Scott A.; Simionovici, Alexandre S.; Zolensky, Michael E.

    2014-01-01

    The NASA Stardust spacecraft exposed an aerogel collector to the interstellar dust passing through the solar system. We performed X-ray fluorescence element mapping and abundance measurements, for elements 19 < or = Z < or = 30, on six "interstellar candidates," potential interstellar impacts identified by Stardust@Home and extracted for analyses in picokeystones. One, I1044,3,33, showed no element hot-spots within the designated search area. However, we identified a nearby surface feature, consistent with the impact of a weak, high-speed particle having an approximately chondritic (CI) element abundance pattern, except for factor-of-ten enrichments in K and Zn and an S depletion. This hot-spot, containing approximately 10 fg of Fe, corresponds to an approximately 350 nm chondritic particle, small enough to be missed by Stardust@Home, indicating that other techniques may be necessary to identify all interstellar candidates. Only one interstellar candidate, I1004,1,2, showed a track. The terminal particle has large enrichments in S, Ti, Cr, Mn, Ni, Cu, and Zn relative to Fe-normalized CI values. It has high Al/Fe, but does not match the Ni/Fe range measured for samples of Al-deck material from the Stardust sample return capsule, which was within the field-of-view of the interstellar collector. A third interstellar candidate, I1075,1,25, showed an Al-rich surface feature that has a composition generally consistent with the Al-deck material, suggesting that it is a secondary particle. The other three interstellar candidates, I1001,1,16, I1001,2,17, and I1044,2,32, showed no impact features or tracks, but allowed assessment of submicron contamination in this aerogel, including Fe hot-spots having CI-like Ni/Fe ratios, complicating the search for CI-like interstellar/interplanetary dust.

  11. An object-oriented, coprocessor-accelerated model for ice sheet simulations

    Science.gov (United States)

    Seddik, H.; Greve, R.

    2013-12-01

    Recently, numerous models capable of modeling the thermo-dynamics of ice sheets have been developed within the ice sheet modeling community. Their capabilities have been characterized by a wide range of features with different numerical methods (finite difference or finite element), different implementations of the ice flow mechanics (shallow-ice, higher-order, full Stokes) and different treatments for the basal and coastal areas (basal hydrology, basal sliding, ice shelves). Shallow-ice models (SICOPOLIS, IcIES, PISM, etc) have been widely used for modeling whole ice sheets (Greenland and Antarctica) due to the relatively low computational cost of the shallow-ice approximation but higher order (ISSM, AIF) and full Stokes (Elmer/Ice) models have been recently used to model the Greenland ice sheet. The advance in processor speed and the decrease in cost for accessing large amount of memory and storage have undoubtedly been the driving force in the commoditization of models with higher capabilities, and the popularity of Elmer/Ice (http://elmerice.elmerfem.com) with an active user base is a notable representation of this trend. Elmer/Ice is a full Stokes model built on top of the multi-physics package Elmer (http://www.csc.fi/english/pages/elmer) which provides the full machinery for the complex finite element procedure and is fully parallel (mesh partitioning with OpenMPI communication). Elmer is mainly written in Fortran 90 and targets essentially traditional processors as the code base was not initially written to run on modern coprocessors (yet adding support for the recently introduced x86 based coprocessors is possible). Furthermore, a truly modular and object-oriented implementation is required for quick adaptation to fast evolving capabilities in hardware (Fortran 2003 provides an object-oriented programming model while not being clean and requiring a tricky refactoring of Elmer code). In this work, the object-oriented, coprocessor-accelerated finite element

  12. Dynamics of interstellar matter

    International Nuclear Information System (INIS)

    Kahn, F.D.

    1975-01-01

    A review of the dynamics of interstellar matter is presented, considering the basic equations of fluid flow, plane waves, shock waves, spiral structure, thermal instabilities and early star cocoons. (B.R.H.)

  13. The influence of Cloud Longwave Scattering together with a state-of-the-art Ice Longwave Optical Parameterization in Climate Model Simulations

    Science.gov (United States)

    Chen, Y. H.; Kuo, C. P.; Huang, X.; Yang, P.

    2017-12-01

    Clouds play an important role in the Earth's radiation budget, and thus realistic and comprehensive treatments of cloud optical properties and cloud-sky radiative transfer are crucial for simulating weather and climate. However, most GCMs neglect LW scattering effects by clouds and tend to use inconsistent cloud SW and LW optical parameterizations. Recently, co-authors of this study have developed a new LW optical properties parameterization for ice clouds, which is based on ice cloud particle statistics from MODIS measurements and state-of-the-art scattering calculation. A two-stream multiple-scattering scheme has also been implemented into the RRTMG_LW, a widely used longwave radiation scheme by climate modeling centers. This study is to integrate both the new LW cloud-radiation scheme for ice clouds and the modified RRTMG_LW with scattering capability into the NCAR CESM to improve the cloud longwave radiation treatment. A number of single column model (SCM) simulations using the observation from the ARM SGP site on July 18 to August 4 in 1995 are carried out to assess the impact of new LW optical properties of clouds and scattering-enabled radiation scheme on simulated radiation budget and cloud radiative effect (CRE). The SCM simulation allows interaction between cloud and radiation schemes with other parameterizations, but the large-scale forcing is prescribed or nudged. Comparing to the results from the SCM of the standard CESM, the new ice cloud optical properties alone leads to an increase of LW CRE by 26.85 W m-2 in average, as well as an increase of the downward LW flux at surface by 6.48 W m-2. Enabling LW cloud scattering further increases the LW CRE by another 3.57 W m-2 and the downward LW flux at the surface by 0.2 W m-2. The change of LW CRE is mainly due to an increase of cloud top height, which enhances the LW CRE. A long-term simulation of CESM will be carried out to further understand the impact of such changes on simulated climates.

  14. On the Representation of Ice Nucleation in Global Climate Models, and its Importance for Simulations of Climate Forcings and Feedbacks

    Science.gov (United States)

    Storelvmo, T.

    2015-12-01

    Substantial improvements have been made to the cloud microphysical schemes used in the latest generation of global climate models (GCMs), however, an outstanding weakness of these schemes lies in the arbitrariness of their tuning parameters. Despite the growing effort in improving the cloud microphysical schemes in GCMs, most of this effort has not focused on improving the ability of GCMs to accurately simulate phase partitioning in mixed-phase clouds. Getting the relative proportion of liquid droplets and ice crystals in clouds right in GCMs is critical for the representation of cloud radiative forcings and cloud-climate feedbacks. Here, we first present satellite observations of cloud phase obtained by NASA's CALIOP instrument, and report on robust statistical relationships between cloud phase and several aerosols species that have been demonstrated to act as ice nuclei (IN) in laboratory studies. We then report on results from model intercomparison projects that reveal that GCMs generally underestimate the amount of supercooled liquid in clouds. For a selected GCM (NCAR 's CAM5), we thereafter show that the underestimate can be attributed to two main factors: i) the presence of IN in the mixed-phase temperature range, and ii) the Wegener-Bergeron-Findeisen process, which converts liquid to ice once ice crystals have formed. Finally, we show that adjusting these two processes such that the GCM's cloud phase is in agreement with the observed has a substantial impact on the simulated radiative forcing due to IN perturbations, as well as on the cloud-climate feedbacks and ultimately climate sensitivity simulated by the GCM.

  15. Climate Modeling and Causal Identification for Sea Ice Predictability

    Energy Technology Data Exchange (ETDEWEB)

    Hunke, Elizabeth Clare [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Urrego Blanco, Jorge Rolando [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Urban, Nathan Mark [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2018-02-12

    This project aims to better understand causes of ongoing changes in the Arctic climate system, particularly as decreasing sea ice trends have been observed in recent decades and are expected to continue in the future. As part of the Sea Ice Prediction Network, a multi-agency effort to improve sea ice prediction products on seasonal-to-interannual time scales, our team is studying sensitivity of sea ice to a collection of physical process and feedback mechanism in the coupled climate system. During 2017 we completed a set of climate model simulations using the fully coupled ACME-HiLAT model. The simulations consisted of experiments in which cloud, sea ice, and air-ocean turbulent exchange parameters previously identified as important for driving output uncertainty in climate models were perturbed to account for parameter uncertainty in simulated climate variables. We conducted a sensitivity study to these parameters, which built upon a previous study we made for standalone simulations (Urrego-Blanco et al., 2016, 2017). Using the results from the ensemble of coupled simulations, we are examining robust relationships between climate variables that emerge across the experiments. We are also using causal discovery techniques to identify interaction pathways among climate variables which can help identify physical mechanisms and provide guidance in predictability studies. This work further builds on and leverages the large ensemble of standalone sea ice simulations produced in our previous w14_seaice project.

  16. How ice shelf morphology controls basal melting

    Science.gov (United States)

    Little, Christopher M.; Gnanadesikan, Anand; Oppenheimer, Michael

    2009-12-01

    The response of ice shelf basal melting to climate is a function of ocean temperature, circulation, and mixing in the open ocean and the coupling of this external forcing to the sub-ice shelf circulation. Because slope strongly influences the properties of buoyancy-driven flow near the ice shelf base, ice shelf morphology plays a critical role in linking external, subsurface heat sources to the ice. In this paper, the slope-driven dynamic control of local and area-integrated melting rates is examined under a wide range of ocean temperatures and ice shelf shapes, with an emphasis on smaller, steeper ice shelves. A 3-D numerical ocean model is used to simulate the circulation underneath five idealized ice shelves, forced with subsurface ocean temperatures ranging from -2.0°C to 1.5°C. In the sub-ice shelf mixed layer, three spatially distinct dynamic regimes are present. Entrainment of heat occurs predominately under deeper sections of the ice shelf; local and area-integrated melting rates are most sensitive to changes in slope in this "initiation" region. Some entrained heat is advected upslope and used to melt ice in the "maintenance" region; however, flow convergence in the "outflow" region limits heat loss in flatter portions of the ice shelf. Heat flux to the ice exhibits (1) a spatially nonuniform, superlinear dependence on slope and (2) a shape- and temperature-dependent, internally controlled efficiency. Because the efficiency of heat flux through the mixed layer decreases with increasing ocean temperature, numerical simulations diverge from a simple quadratic scaling law.

  17. SEARCHING FOR NAPHTHALENE CATION ABSORPTION IN THE INTERSTELLAR MEDIUM

    International Nuclear Information System (INIS)

    Searles, Justin M.; Destree, Joshua D.; Snow, Theodore P.; Salama, Farid; York, Donald G.; Dahlstrom, Julie

    2011-01-01

    Interstellar naphthalene cations (C 10 H + 8 ) have been proposed by a study to be the carriers of a small number of diffuse interstellar bands (DIBs). Using an archive of high signal-to-noise spectra obtained at the Apache Point Observatory, we used two methods to test the hypothesis. Both methods failed to detect significant absorption at lab wavelengths of interstellar spectra with laboratory spectra. We thereby conclude that C 10 H + 8 is not a DIB carrier in typical reddened sight lines.

  18. Photodissociation and excitation of interstellar molecules

    International Nuclear Information System (INIS)

    Dishoeck, E.F. van.

    1984-01-01

    Apart from a rather long introduction containing some elementary astrophysics, quantum chemistry and spectroscopy and an incomplete, historical review of molecular observations, this thesis is divided into three sections. In part A, a rigorous quantum chemical and dynamical study is made of the photodissociation processes in the OH and HCl molecules. In part B, the cross sections obtained in part A are used in various astrophysical problems such as the study of the abundances of the OH and HCl molecules in interstellar clouds, the use of the OH abundance as a measure of the cosmic ray ionization rate, the lifetime of the OH radical in comets and the abundance of OH in the solar photosphere. Part C discusses the excitation of the C 2 molecule under interstellar conditions, its use as a diagnostic probe of the temperature, density and strength of the radiation field in interstellar clouds. Quadrupole moments and oscillator strengths are analyzed. (Auth.)

  19. Heavy ion irradiation of crystalline water ice. Cosmic ray amorphisation cross-section and sputtering yield

    Science.gov (United States)

    Dartois, E.; Augé, B.; Boduch, P.; Brunetto, R.; Chabot, M.; Domaracka, A.; Ding, J. J.; Kamalou, O.; Lv, X. Y.; Rothard, H.; da Silveira, E. F.; Thomas, J. C.

    2015-04-01

    Context. Under cosmic irradiation, the interstellar water ice mantles evolve towards a compact amorphous state. Crystalline ice amorphisation was previously monitored mainly in the keV to hundreds of keV ion energies. Aims: We experimentally investigate heavy ion irradiation amorphisation of crystalline ice, at high energies closer to true cosmic rays, and explore the water-ice sputtering yield. Methods: We irradiated thin crystalline ice films with MeV to GeV swift ion beams, produced at the GANIL accelerator. The ice infrared spectral evolution as a function of fluence is monitored with in-situ infrared spectroscopy (induced amorphisation of the initial crystalline state into a compact amorphous phase). Results: The crystalline ice amorphisation cross-section is measured in the high electronic stopping-power range for different temperatures. At large fluence, the ice sputtering is measured on the infrared spectra, and the fitted sputtering-yield dependence, combined with previous measurements, is quadratic over three decades of electronic stopping power. Conclusions: The final state of cosmic ray irradiation for porous amorphous and crystalline ice, as monitored by infrared spectroscopy, is the same, but with a large difference in cross-section, hence in time scale in an astrophysical context. The cosmic ray water-ice sputtering rates compete with the UV photodesorption yields reported in the literature. The prevalence of direct cosmic ray sputtering over cosmic-ray induced photons photodesorption may be particularly true for ices strongly bonded to the ice mantles surfaces, such as hydrogen-bonded ice structures or more generally the so-called polar ices. Experiments performed at the Grand Accélérateur National d'Ions Lourds (GANIL) Caen, France. Part of this work has been financed by the French INSU-CNRS programme "Physique et Chimie du Milieu Interstellaire" (PCMI) and the ANR IGLIAS.

  20. Chemisputtering of interstellar graphite grains

    International Nuclear Information System (INIS)

    Draine, B.T.

    1979-01-01

    The rate of erosion of interstellar graphite grains as a result of chemical reaction with H, N, and O is estimated using the available experiment evidence. It is argued that ''chemical sputtering'' yields for interstellar graphite grains will be much less than unity, contrary to earlier estimates by Barlow and Silk. Chemical sputtering of graphite grains in evolving H II regions is found to be unimportant, except in extremely compact (n/sub H/> or approx. =10 5 cm -3 ) H II regions. Alternative explanations are considered for the apparent weakness of the lambda=2175 A extinction ''bump'' in the direction of several early type stars

  1. Impact of improved Greenland ice sheet surface representation in the NASA GISS ModelE2 GCM on simulated surface mass balance and regional climate

    Science.gov (United States)

    Alexander, P. M.; LeGrande, A. N.; Fischer, E.; Tedesco, M.; Kelley, M.; Schmidt, G. A.; Fettweis, X.

    2017-12-01

    Towards achieving coupled simulations between the NASA Goddard Institute for Space Studies (GISS) ModelE2 general circulation model (GCM) and ice sheet models (ISMs), improvements have been made to the representation of the ice sheet surface in ModelE2. These include a sub-grid-scale elevation class scheme, a multi-layer snow model, a time-variable surface albedo scheme, and adjustments to parameterization of sublimation/evaporation. These changes improve the spatial resolution and physical representation of the ice sheet surface such that the surface is represented at a level of detail closer to that of Regional Climate Models (RCMs). We assess the impact of these changes on simulated Greenland Ice Sheet (GrIS) surface mass balance (SMB). We also compare ModelE2 simulations in which winds have been nudged to match the European Center for Medium-Range Weather Forecasts (ECMWF) ERA-Interim reanalysis with simulations from the Modèle Atmosphérique Régionale (MAR) RCM forced by the same reanalysis. Adding surface elevation classes results in a much higher spatial resolution representation of the surface necessary for coupling with ISMs, but has a negligible impact on overall SMB. Implementing a variable surface albedo scheme increases melt by 100%, bringing it closer to melt simulated by MAR. Adjustments made to the representation of topography-influenced surface roughness length in ModelE2 reduce a positive bias in evaporation relative to MAR. We also examine the impact of changes to the GrIS surface on regional atmospheric and oceanic climate in coupled ocean-atmosphere simulations with ModelE2, finding a general warming of the Arctic due to a warmer GrIS, and a cooler North Atlantic in scenarios with doubled atmospheric CO2 relative to pre-industrial levels. The substantial influence of changes to the GrIS surface on the oceans and atmosphere highlight the importance of including these processes in the GCM, in view of potential feedbacks between the ice sheet

  2. REVISITING ULYSSES OBSERVATIONS OF INTERSTELLAR HELIUM

    International Nuclear Information System (INIS)

    Wood, Brian E.; Müller, Hans-Reinhard; Witte, Manfred

    2015-01-01

    We report the results of a comprehensive reanalysis of Ulysses observations of interstellar He atoms flowing through the solar system, the goal being to reassess the interstellar He flow vector and to search for evidence of variability in this vector. We find no evidence that the He beam seen by Ulysses changes at all from 1994-2007. The direction of flow changes by no more than ∼0.°3 and the speed by no more than ∼0.3 km s –1 . A global fit to all acceptable He beam maps from 1994-2007 yields the following He flow parameters: V ISM = 26.08 ± 0.21 km s –1 , λ = 75.54 ± 0.°19, β = –5.44 ± 0.°24, and T = 7260 ± 270 K; where λ and β are the ecliptic longitude and latitude direction in J2000 coordinates. The flow vector is consistent with the original analysis of the Ulysses team, but our temperature is significantly higher. The higher temperature somewhat mitigates a discrepancy that exists in the He flow parameters measured by Ulysses and the Interstellar Boundary Explorer, but does not resolve it entirely. Using a novel technique to infer photoionization loss rates directly from Ulysses data, we estimate a density of n He = 0.0196 ± 0.0033 cm –3 in the interstellar medium

  3. REVISITING ULYSSES OBSERVATIONS OF INTERSTELLAR HELIUM

    Energy Technology Data Exchange (ETDEWEB)

    Wood, Brian E. [Naval Research Laboratory, Space Science Division, Washington, DC 20375 (United States); Müller, Hans-Reinhard [Department of Physics and Astronomy, Dartmouth College, Hanover, NH 03755 (United States); Witte, Manfred, E-mail: brian.wood@nrl.navy.mil [Max-Planck-Institute for Solar System Research, Katlenburg-Lindau D-37191 (Germany)

    2015-03-01

    We report the results of a comprehensive reanalysis of Ulysses observations of interstellar He atoms flowing through the solar system, the goal being to reassess the interstellar He flow vector and to search for evidence of variability in this vector. We find no evidence that the He beam seen by Ulysses changes at all from 1994-2007. The direction of flow changes by no more than ∼0.°3 and the speed by no more than ∼0.3 km s{sup –1}. A global fit to all acceptable He beam maps from 1994-2007 yields the following He flow parameters: V {sub ISM} = 26.08 ± 0.21 km s{sup –1}, λ = 75.54 ± 0.°19, β = –5.44 ± 0.°24, and T = 7260 ± 270 K; where λ and β are the ecliptic longitude and latitude direction in J2000 coordinates. The flow vector is consistent with the original analysis of the Ulysses team, but our temperature is significantly higher. The higher temperature somewhat mitigates a discrepancy that exists in the He flow parameters measured by Ulysses and the Interstellar Boundary Explorer, but does not resolve it entirely. Using a novel technique to infer photoionization loss rates directly from Ulysses data, we estimate a density of n {sub He} = 0.0196 ± 0.0033 cm{sup –3} in the interstellar medium.

  4. The hydrogen coverage of interstellar PAHs [Polycyclic Aromatic Hydrocarbons

    International Nuclear Information System (INIS)

    Tielens, A.G.G.M.; Allamandola, L.J.; Barker, J.R.; Cohen, M.

    1986-02-01

    The rate at which the CH bond in interstellar Polycyclic Aromatic Hydrocarbons (PAHs) rupture due to the absorption of a uv photon has been calculated. The results show that small PAHs (less than or equal to 25 carbon atoms) are expected to be partially dehydrogenated in regions with intense uv fields, while large PAHs (greater than or equal to 25 atoms) are expected to be completely hydrogenated in those regions. Because estimate of the carbon content of interstellar PAHs lie in the range of 20 to 25 carbon atoms, dehydrogenation is probably not very important. Because of the absence of other emission features besides the 11.3 micrometer feature in ground-based 8 to 13 micrometer spectra, it has been suggested that interstellar PAHs are partially dehydrogenated. However, IRAS 8 to 22 micrometer spectra of most sources that show strong 7.7 and 11.2 micrometer emission features also show a plateau of emission extending from about 11.3 to 14 micrometer. Like the 11.3 micrometer feature, this new feature is attributed to the CH out of plane bending mode in PAHs. This new feature shows that interstellar PAHs are not as dehydrogenated as estimated from ground-based 8 to 13 micrometer spectra. It also constrains the molecular structure of interstellar PAHs. In particular, it seems that very condensed PAHs, such as coronene and circumcoronene, dominate the interstellar PAH mixture as expected from stability arguments

  5. The Use of Satellite Observations in Ice Cover Simulations

    Science.gov (United States)

    1992-01-01

    Io rmotions have been used to map upper-level winds over polar diagnose the origins of a large area of reduced ice ,,ncfl.’c regions (Turner and...was motivated by the availability of coverage in the Arctic. Also shown are November-April s-ver!,_- the multiyear ice concentrations derived from

  6. A modified discrete element model for sea ice dynamics

    Institute of Scientific and Technical Information of China (English)

    LI Baohui; LI Hai; LIU Yu; WANG Anliang; JI Shunying

    2014-01-01

    Considering the discontinuous characteristics of sea ice on various scales, a modified discrete element mod-el (DEM) for sea ice dynamics is developed based on the granular material rheology. In this modified DEM, a soft sea ice particle element is introduced as a self-adjustive particle size function. Each ice particle can be treated as an assembly of ice floes, with its concentration and thickness changing to variable sizes un-der the conservation of mass. In this model, the contact forces among ice particles are calculated using a viscous-elastic-plastic model, while the maximum shear forces are described with the Mohr-Coulomb fric-tion law. With this modified DEM, the ice flow dynamics is simulated under the drags of wind and current in a channel of various widths. The thicknesses, concentrations and velocities of ice particles are obtained, and then reasonable dynamic process is analyzed. The sea ice dynamic process is also simulated in a vortex wind field. Taking the influence of thermodynamics into account, this modified DEM will be improved in the future work.

  7. Indicators of Arctic Sea Ice Bistability in Climate Model Simulations and Observations

    Science.gov (United States)

    2014-09-30

    associated with the ice - albedo feedback and the seasonal melt and growth of sea ice , as well as horizontal climate variations on a global domain. (2...1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Indicators of Arctic Sea Ice Bistability in Climate...possibility that the climate system supports multiple Arctic sea ice states that are relevant for the evolution of sea ice during the next several

  8. Gitting of infrared data to the interstellar polarization law

    Energy Technology Data Exchange (ETDEWEB)

    Clarke, D

    1984-02-15

    The ability of Serkowski's law describing the wavelength dependence of interstellar polarization to encompass new infrared measurements in combination with optical data has been examined. Fitting by least-squares procedures reveals departures from the law in various wavelength zones or at specific wavelength points across the optical and infrared spectrum. These structures may be caused by a combination of effects such as normal experimental noise, complex interstellar clouds or systematic errors in the polarimetry but the possibility remains that some, particularly in the infrared, reflect the scattering properties of interstellar grains. 8 references.

  9. Fitting of infrared data to the interstellar polarization law

    Energy Technology Data Exchange (ETDEWEB)

    Clarke, D [Glasgow Univ., Great Britain

    1984-02-15

    The ability of Serkowski's law describing the wavelength dependence of interstellar polarization to encompass new infrared measurements in combination with optical data has been examined. Fitting by least-squares procedures reveals departures from the law in various wavelength zones or at specific wavelength points across the optical and infrared spectrum. These structures may be caused by a combination of effects such as normal experimental noise, complex interstellar clouds or systematic errors in the polarimetry but the possibility remains that some, particularly in the infrared, reflect the scattering properties of interstellar grains.

  10. Dynamic Antarctic ice sheet during the early to mid-Miocene

    Science.gov (United States)

    Gasson, Edward; DeConto, Robert M.; Pollard, David; Levy, Richard H.

    2016-03-01

    Geological data indicate that there were major variations in Antarctic ice sheet volume and extent during the early to mid-Miocene. Simulating such large-scale changes is problematic because of a strong hysteresis effect, which results in stability once the ice sheets have reached continental size. A relatively narrow range of atmospheric CO2 concentrations indicated by proxy records exacerbates this problem. Here, we are able to simulate large-scale variability of the early to mid-Miocene Antarctic ice sheet because of three developments in our modeling approach. (i) We use a climate-ice sheet coupling method utilizing a high-resolution atmospheric component to account for ice sheet-climate feedbacks. (ii) The ice sheet model includes recently proposed mechanisms for retreat into deep subglacial basins caused by ice-cliff failure and ice-shelf hydrofracture. (iii) We account for changes in the oxygen isotopic composition of the ice sheet by using isotope-enabled climate and ice sheet models. We compare our modeling results with ice-proximal records emerging from a sedimentological drill core from the Ross Sea (Andrill-2A) that is presented in a companion article. The variability in Antarctic ice volume that we simulate is equivalent to a seawater oxygen isotope signal of 0.52-0.66‰, or a sea level equivalent change of 30-36 m, for a range of atmospheric CO2 between 280 and 500 ppm and a changing astronomical configuration. This result represents a substantial advance in resolving the long-standing model data conflict of Miocene Antarctic ice sheet and sea level variability.

  11. Representing culture in interstellar messages

    Science.gov (United States)

    Vakoch, Douglas A.

    2008-09-01

    As scholars involved with the Search for Extraterrestrial Intelligence (SETI) have contemplated how we might portray humankind in any messages sent to civilizations beyond Earth, one of the challenges they face is adequately representing the diversity of human cultures. For example, in a 2003 workshop in Paris sponsored by the SETI Institute, the International Academy of Astronautics (IAA) SETI Permanent Study Group, the International Society for the Arts, Sciences and Technology (ISAST), and the John Templeton Foundation, a varied group of artists, scientists, and scholars from the humanities considered how to encode notions of altruism in interstellar messages . Though the group represented 10 countries, most were from Europe and North America, leading to the group's recommendation that subsequent discussions on the topic should include more globally representative perspectives. As a result, the IAA Study Group on Interstellar Message Construction and the SETI Institute sponsored a follow-up workshop in Santa Fe, New Mexico, USA in February 2005. The Santa Fe workshop brought together scholars from a range of disciplines including anthropology, archaeology, chemistry, communication science, philosophy, and psychology. Participants included scholars familiar with interstellar message design as well as specialists in cross-cultural research who had participated in the Symposium on Altruism in Cross-cultural Perspective, held just prior to the workshop during the annual conference of the Society for Cross-cultural Research . The workshop included discussion of how cultural understandings of altruism can complement and critique the more biologically based models of altruism proposed for interstellar messages at the 2003 Paris workshop. This paper, written by the chair of both the Paris and Santa Fe workshops, will explore the challenges of communicating concepts of altruism that draw on both biological and cultural models.

  12. Interstellar Propulsion Research: Realistic Possibilities and Idealistic Dreams

    Science.gov (United States)

    Johnson, Les

    2009-01-01

    Though physically possible, interstellar travel will be exceedingly difficult. Both the known laws of physics and the limits of our current understanding of engineering place extreme limits on what may actually be possible. Our remote ancestors looked at the night sky and assumed those tiny points of light were campfires around which other tribes were gathered -- and they dreamed of someday making the trip to visit them. In our modern era, we've grown accustomed to humans regularly traveling into space and our robots voyaging ever-deeper into the outer edges of our solar system. Traveling to those distant campfires (stars) has been made to look easy by the likes of Captains Kirk and Picard as well as Han Solo and Commander Adama. Our understanding of physics and engineering has not kept up with our imaginations and many are becoming frustrated with the current pace at which we are exploring the universe. Fortunately, there are ideas that may one day lead to new physical theories about how the universe works and thus potentially make rapid interstellar travel possible -- but many of these are just ideas and are not even close to being considered a scientific theory or hypothesis. Absent any scientific breakthroughs, we should not give up hope. Nature does allow for interstellar travel, albeit slowly and requiring an engineering capability far beyond what we now possess. Antimatter, fusion and photon sail propulsion are all candidates for relatively near-term interstellar missions. The plenary lecture will discuss the dreams and challenges of interstellar travel, our current understanding of what may be possible and some of the "out of the box" ideas that may allow us to become an interstellar species someday in the future.

  13. Ice Accretion on Wind Turbine Blades

    DEFF Research Database (Denmark)

    Hudecz, Adriána; Koss, Holger; Hansen, Martin Otto Laver

    2013-01-01

    In this paper, both experimental and numerical simulations of the effects of ice accretion on a NACA 64-618 airfoil section with 7° angle of attack are presented. The wind tunnel tests were conducted in a closed-circuit climatic wind tunnel at Force Technology in Denmark. The changes of aerodynamic...... forces were monitored as ice was building up on the airfoil for glaze, rime and mixed ice. In the first part of the numerical analysis, the resulted ice profiles of the wind tunnel tests were compared to profiles estimated by using the 2D ice accretion code TURBICE. In the second part, Ansys Fluent...... of the rime iced ice profile follows the streamlines quite well, disturbing the flow the least. The TURBICE analysis agrees fairly with the profiles produced during the wind tunnel testing....

  14. Iron and Silicate Dust Growth in the Galactic Interstellar Medium: Clues from Element Depletions

    Science.gov (United States)

    Zhukovska, Svitlana; Henning, Thomas; Dobbs, Clare

    2018-04-01

    The interstellar abundances of refractory elements indicate a substantial depletion from the gas phase, which increases with gas density. Our recent model of dust evolution, based on hydrodynamic simulations of the life cycle of giant molecular clouds (GMCs), proves that the observed trend for [Sigas/H] is driven by a combination of dust growth by accretion in the cold diffuse interstellar medium (ISM) and efficient destruction by supernova (SN) shocks. With an analytic model of dust evolution, we demonstrate that even with optimistic assumptions for the dust input from stars and without destruction of grains by SNe it is impossible to match the observed [Sigas/H]–n H relation without growth in the ISM. We extend the framework developed in our previous work for silicates to include the evolution of iron grains and address a long-standing conundrum: “Where is the interstellar iron?” Much higher depletion of Fe in the warm neutral medium compared to Si is reproduced by the models, in which a large fraction of interstellar iron (70%) is locked as inclusions in silicate grains, where it is protected from efficient sputtering by SN shocks. The slope of the observed [Fegas/H]–n H relation is reproduced if the remaining depleted iron resides in a population of metallic iron nanoparticles with sizes in the range of 1–10 nm. Enhanced collision rates due to the Coulomb focusing are important for both silicate and iron dust models to match the slopes of the observed depletion–density relations and the magnitudes of depletion at high gas density.

  15. The galactic interstellar medium

    CERN Document Server

    Burton, WB; Genzel, R

    1992-01-01

    This volume contains the papers of three extended lectures addressing advanced topics in astronomy and astrophysics. The topics discussed include the most recent observational data on interstellar matter outside our galaxy and the physics and chemistry of molecular clouds.

  16. Modelling interstellar extinction: Pt. 1

    International Nuclear Information System (INIS)

    Jones, A.P.

    1988-01-01

    Several methods of calculating the extinction of porous silicate grains are discussed, these include effective medium theories and hollow spherical shells. Porous silicate grains are shown to produce enhanced infrared, ultraviolet and far-ultraviolet extinction and this effect can be used to reduce the abundance of carbon required to match the average interstellar extinction, however, matching the visual extinction is rather more problematical. We have shown that the enhanced extinction at long and short wavelengths have different origins, and have explained why the visual extinction is little affected by porosity. The implications of porous grains in the interstellar medium are discussed with particular reference to surface chemistry, the polarization of starlight, and their dynamical evolution. (author)

  17. Interstellar Grains: 50 Years on

    Science.gov (United States)

    Wickramasinghe, N. C.

    Our understanding of the nature of interstellar grains has evolved considerably over the past half century with the present author and Fred Hoyle being intimately involved at several key stages of progress. The currently fashionable graphite-silicate-organic grain model has all its essential aspects unequivocally traceable to original peer-reviewed publications by the author and/or Fred Hoyle. The prevailing reluctance to accept these clear-cut priorities may be linked to our further work that argued for interstellar grains and organics to have a biological provenance -- a position perceived as heretical. The biological model, however, continues to provide a powerful unifying hypothesis for a vast amount of otherwise disconnected and disparate astronomical data.

  18. Greenland ice sheet surface mass balance: evaluating simulations and making projections with regional climate models

    Directory of Open Access Journals (Sweden)

    J. G. L. Rae

    2012-11-01

    Full Text Available Four high-resolution regional climate models (RCMs have been set up for the area of Greenland, with the aim of providing future projections of Greenland ice sheet surface mass balance (SMB, and its contribution to sea level rise, with greater accuracy than is possible from coarser-resolution general circulation models (GCMs. This is the first time an intercomparison has been carried out of RCM results for Greenland climate and SMB. Output from RCM simulations for the recent past with the four RCMs is evaluated against available observations. The evaluation highlights the importance of using a detailed snow physics scheme, especially regarding the representations of albedo and meltwater refreezing. Simulations with three of the RCMs for the 21st century using SRES scenario A1B from two GCMs produce trends of between −5.5 and −1.1 Gt yr−2 in SMB (equivalent to +0.015 and +0.003 mm sea level equivalent yr−2, with trends of smaller magnitude for scenario E1, in which emissions are mitigated. Results from one of the RCMs whose present-day simulation is most realistic indicate that an annual mean near-surface air temperature increase over Greenland of ~ 2°C would be required for the mass loss to increase such that it exceeds accumulation, thereby causing the SMB to become negative, which has been suggested as a threshold beyond which the ice sheet would eventually be eliminated.

  19. Newly detected molecules in dense interstellar clouds

    Science.gov (United States)

    Irvine, William M.; Avery, L. W.; Friberg, P.; Matthews, H. E.; Ziurys, L. M.

    Several new interstellar molecules have been identified including C2S, C3S, C5H, C6H and (probably) HC2CHO in the cold, dark cloud TMC-1; and the discovery of the first interstellar phosphorus-containing molecule, PN, in the Orion "plateau" source. Further results include the observations of 13C3H2 and C3HD, and the first detection of HCOOH (formic acid) in a cold cloud.

  20. Simulating the Holocene climate evolution at northern high latitudes using a coupled atmosphere-sea ice-ocean-vegetation model

    NARCIS (Netherlands)

    Renssen, H.; Goosse, H.; Fichefet, T.; Brovkin, V.; Driesschaert, E.; Wolk, F.

    2005-01-01

    The response of the climate at high northern latitudes to slowly changing external forcings was studied in a 9,000-year long simulation with the coupled atmosphere-sea ice-ocean-vegetation model ECBilt-CLIO-VECODE. Only long-term changes in insolation and atmospheric CO

  1. Detailed Study of the Formation of Sugar Derivatives Produced from the UV Irradiation of Astrophysical Ice Analogs

    Science.gov (United States)

    Nuevo, Michel; Cooper, George; Saunders, John; Buffo, Christina E.; Materese, Christopher K.; Sandford, Scott A.

    2018-01-01

    Carbonaceous meteorites such as Murchison contain a large variety of organic compounds of astrobiological interest such as amino acids, other amphiphilic compounds, functionalized nitrogen heterocycles (including nucleobases), functionalized polycylic aromatic hydro-carbons (including quinones), and sugar derivatives. The presence of such a broad variety of organics in meteorites strongly suggests that molecules essential to life can form abiotically under astrophysical conditions. This hypothesis is strongly supported by laboratory studies in which astrophysical ice analogs (i.e., mixtures of H2O, CO, CO2, CH3OH, CH4, NH3, etc.) are subjected to ultraviolet (UV) irradiation at low temperature (less than 15 K) to simulate cold interstellar environments. These studies have shown that the organic residues recovered at room temperature after irradiation contain organic compounds that are very similar to those found in meteorites. No systematic search for the presence of sugar derivatives in laboratory residues had been carried out until the recent detection of ribose, the sugar of RNA, as well as other sugars, sugar alcohols, and sugar acids in one residue produced from the UV irradiation of an ice mixture containing H2O, CH3OH, and NH3 at 80 K. In this work, we present a detailed study of the formation of sugar derivatives contained in organic residues that are produced from the UV irradiation of ice mixtures of different starting compositions (H2O, CH3OH, CO, CO2, and/or NH3) at less than 15 K. While the presence of sugar alcohols, sugars, and sugar acids-in some cases with up to 6 carbon atoms-could be confirmed in all these residues, their distribution was shown to vary with the composition of the starting ices. In particular, only a few ices result in the formation of sugar derivatives displaying a distribution that resembles that of meteorites, in which sugar alcohols and sugar acids are very abundant while sugars are mostly absent.

  2. Icing modelling in NSMB with chimera overset grids

    Energy Technology Data Exchange (ETDEWEB)

    Pena, D. [Ècole Polytechnique de Montréal (Canada); ICUBE, Strasbourg University (France); Deloze, T.; Laurendeau, E. [Ècole Polytechnique de Montréal (Canada); Hoarau, Y. [ICUBE, Strasbourg University (France)

    2015-03-10

    In aerospace Engineering, the accurate simulation of ice accretion is a key element to increase flight safety and avoid accidents related to icing effects. The icing code developed in the NSMB solver is based on an Eulerian formulation for droplets tracking, an iterative Messinger model using a modified water runback scheme for ice thickness calculation and mesh deformation to track the ice/air interface through time. The whole process is parallelized with MPI and applied with chimera grids.

  3. Ice-sheet mass balance and climate change.

    Science.gov (United States)

    Hanna, Edward; Navarro, Francisco J; Pattyn, Frank; Domingues, Catia M; Fettweis, Xavier; Ivins, Erik R; Nicholls, Robert J; Ritz, Catherine; Smith, Ben; Tulaczyk, Slawek; Whitehouse, Pippa L; Zwally, H Jay

    2013-06-06

    Since the 2007 Intergovernmental Panel on Climate Change Fourth Assessment Report, new observations of ice-sheet mass balance and improved computer simulations of ice-sheet response to continuing climate change have been published. Whereas Greenland is losing ice mass at an increasing pace, current Antarctic ice loss is likely to be less than some recently published estimates. It remains unclear whether East Antarctica has been gaining or losing ice mass over the past 20 years, and uncertainties in ice-mass change for West Antarctica and the Antarctic Peninsula remain large. We discuss the past six years of progress and examine the key problems that remain.

  4. Laboratory Studies of the Formation of Interstellar Dust from Molecular Precursors

    Science.gov (United States)

    Contreras, Cesar S.; Salama, Farid

    2009-06-01

    The study of the formation and the destruction processes of cosmic dust is essential to understand and to quantify the budget of extraterrestrial organic molecules. Interstellar dust presents a continuous size distribution from large molecules, radicals and ions to nanometer-sized particles to micron-sized grains. The lower end of the carbonaceous dust size distribution is thought to be responsible for the ubiquitous spectral features that are seen in emission in the IR (UIBs) and in absorption in the visible (DIBs). The higher end of the dust-size distribution is thought to be responsible for the continuum emission plateau that is seen in the IR and for the strong absorption seen in the interstellar UV extinction curve. All these spectral signatures are characteristic of cosmic organic materials that are ubiquitous and present in various forms from gas-phase molecules to solid-state grains and all are expected to exhibit FIR spectral signatures. Space observations from the UV (HST) to the IR (ISO, Spitzer) help place size constraints on the molecular component of carbonaceous IS dust and its contribution to the IS features in the UV and in the IR. Studies of large molecular and nano-sized IS dust analogs formed from PAH precursors have been performed in our laboratory under conditions that simulate interstellar and circumstellar environments. The species (molecules, molecular fragments, ions, nanoparticles, etc...) formed in the pulsed discharge nozzle (PDN) plasma source are detected and characterized with a high-sensitivity cavity ringdown spectrometer (CRDS) coupled to a Reflectron time-of-flight mass spectrometer (ReTOF-MS). We will present new experimental results that indicate that nanoparticles are generated in the plasma. From these unique measurements, we derive information on the nature, the size and the structure of interstellar dust particles, the growth and the destruction processes of IS dust and the resulting budget of extraterrestrial organic

  5. Sea-ice dynamics strongly promote Snowball Earth initiation and destabilize tropical sea-ice margins

    Directory of Open Access Journals (Sweden)

    A. Voigt

    2012-12-01

    Full Text Available The Snowball Earth bifurcation, or runaway ice-albedo feedback, is defined for particular boundary conditions by a critical CO2 and a critical sea-ice cover (SI, both of which are essential for evaluating hypotheses related to Neoproterozoic glaciations. Previous work has shown that the Snowball Earth bifurcation, denoted as (CO2, SI*, differs greatly among climate models. Here, we study the effect of bare sea-ice albedo, sea-ice dynamics and ocean heat transport on (CO2, SI* in the atmosphere–ocean general circulation model ECHAM5/MPI-OM with Marinoan (~ 635 Ma continents and solar insolation (94% of modern. In its standard setup, ECHAM5/MPI-OM initiates a~Snowball Earth much more easily than other climate models at (CO2, SI* ≈ (500 ppm, 55%. Replacing the model's standard bare sea-ice albedo of 0.75 by a much lower value of 0.45, we find (CO2, SI* ≈ (204 ppm, 70%. This is consistent with previous work and results from net evaporation and local melting near the sea-ice margin. When we additionally disable sea-ice dynamics, we find that the Snowball Earth bifurcation can be pushed even closer to the equator and occurs at a hundred times lower CO2: (CO2, SI* ≈ (2 ppm, 85%. Therefore, the simulation of sea-ice dynamics in ECHAM5/MPI-OM is a dominant determinant of its high critical CO2 for Snowball initiation relative to other models. Ocean heat transport has no effect on the critical sea-ice cover and only slightly decreases the critical CO2. For disabled sea-ice dynamics, the state with 85% sea-ice cover is stabilized by the Jormungand mechanism and shares characteristics with the Jormungand climate states. However, there is no indication of the Jormungand bifurcation and hysteresis in ECHAM5/MPI-OM. The state with 85% sea-ice cover therefore is a soft Snowball state rather than a true

  6. IceVeto. An extension of IceTop to veto air showers for neutrino astronomy with IceCube

    Energy Technology Data Exchange (ETDEWEB)

    Auffenberg, Jan; Kemp, Julian; Raedel, Leif; Rongen, Martin; Schaufel, Merlin; Stahlberg, Martin; Hansmann, Bengt; Wiebusch, Christopher [RWTH Aachen University, Physikalische Institut III b (Germany); Collaboration: IceCube-Collaboration

    2015-07-01

    IceCube is the world's largest high-energy neutrino observatory, built at the geographic South Pole. For neutrino astronomy, a large background-free sample of well-reconstructed astrophysical neutrinos is essential. The main background for this signal are muons and neutrinos which are produced in cosmic-ray air showers in the Earth's atmosphere. The coincident detection of these air showers by the surface detector IceTop has been proven to be a powerful veto for atmospheric neutrinos and muons in the field of view of the southern hemisphere. This motivates a significant extension of IceTop. First estimates indicate that such a veto detector will more than double the discovery potential of current point source analyses. Here, we present the motivation and capabilities of different technologies based on simulations and measurements.

  7. Improvement in simulation of Eurasian winter climate variability with a realistic Arctic sea ice condition in an atmospheric GCM

    International Nuclear Information System (INIS)

    Lim, Young-Kwon; Ham, Yoo-Geun; Jeong, Jee-Hoon; Kug, Jong-Seong

    2012-01-01

    The present study investigates how much a realistic Arctic sea ice condition can contribute to improve simulation of the winter climate variation over the Eurasia region. Model experiments are set up using different sea ice boundary conditions over the past 24 years (i.e., 1988–2011). One is an atmospheric model inter-comparison (AMIP) type of run forced with observed sea-surface temperature (SST), sea ice, and greenhouse gases (referred to as Exp RSI), and the other is the same as Exp RSI except for the sea ice forcing, which is a repeating climatological annual cycle (referred to as Exp CSI). Results show that Exp RSI produces the observed dominant pattern of Eurasian winter temperatures and their interannual variation better than Exp CSI (correlation difference up to ∼0.3). Exp RSI captures the observed strong relationship between the sea ice concentration near the Barents and Kara seas and the temperature anomaly across Eurasia, including northeastern Asia, which is not well captured in Exp CSI. Lagged atmospheric responses to sea ice retreat are examined using observations to understand atmospheric processes for the Eurasian cooling response including the Arctic temperature increase, sea-level pressure increase, upper-level jet weakening and cold air outbreak toward the mid-latitude. The reproducibility of these lagged responses by Exp RSI is also evaluated. (letter)

  8. Improvement in Simulation of Eurasian Winter Climate Variability with a Realistic Arctic Sea Ice Condition in an Atmospheric GCM

    Science.gov (United States)

    Lim, Young-Kwon; Ham, Yoo-Geun; Jeong, Jee-Hoon; Kug, Jong-Seong

    2012-01-01

    The present study investigates how much a realistic Arctic sea ice condition can contribute to improve simulation of the winter climate variation over the Eurasia region. Model experiments are set up using different sea ice boundary conditions over the past 24 years (i.e., 1988-2011). One is an atmospheric model inter-comparison (AMIP) type of run forced with observed sea-surface temperature (SST), sea ice, and greenhouse gases (referred to as Exp RSI), and the other is the same as Exp RSI except for the sea ice forcing, which is a repeating climatological annual cycle (referred to as Exp CSI). Results show that Exp RSI produces the observed dominant pattern of Eurasian winter temperatures and their interannual variation better than Exp CSI (correlation difference up to approx. 0.3). Exp RSI captures the observed strong relationship between the sea ice concentration near the Barents and Kara seas and the temperature anomaly across Eurasia, including northeastern Asia, which is not well captured in Exp CSI. Lagged atmospheric responses to sea ice retreat are examined using observations to understand atmospheric processes for the Eurasian cooling response including the Arctic temperature increase, sea-level pressure increase, upper-level jet weakening and cold air outbreak toward the mid-latitude. The reproducibility of these lagged responses by Exp RSI is also evaluated.

  9. Physics of the interstellar and intergalactic medium

    CERN Document Server

    Draine, Bruce T

    2010-01-01

    This is a comprehensive and richly illustrated textbook on the astrophysics of the interstellar and intergalactic medium--the gas and dust, as well as the electromagnetic radiation, cosmic rays, and magnetic and gravitational fields, present between the stars in a galaxy and also between galaxies themselves. Topics include radiative processes across the electromagnetic spectrum; radiative transfer; ionization; heating and cooling; astrochemistry; interstellar dust; fluid dynamics, including ionization fronts and shock waves; cosmic rays; distribution and evolution of the interstellar medium; and star formation. While it is assumed that the reader has a background in undergraduate-level physics, including some prior exposure to atomic and molecular physics, statistical mechanics, and electromagnetism, the first six chapters of the book include a review of the basic physics that is used in later chapters. This graduate-level textbook includes references for further reading, and serves as an invaluable resourc...

  10. Dust in the Diffuse Neutral Interstellar Medium

    Science.gov (United States)

    Sofia, Ulysses J.

    2008-05-01

    Studies of interstellar dust have always relied heavily upon Laboratory Astrophysics for interpretation. Laboratory values, in the broad sense that includes theory, are needed for the most basic act of measuring interstellar abundances, to the more complex determination of what grains are responsible for particular extinction. The symbiotic relationship between astronomical observations and Laboratory Astrophysics has prompted both fields to move forward, especially in the era of high-resolution ultraviolet spectroscopy when new elemental species could be interpreted and observations were able to show the limits of laboratory determinations. Thanks to this synergy, we currently have a good idea of the quantity of the most abundant elements incorporated into dust in diffuse neutral interstellar clouds: carbon, oxygen, iron, silicon and magnesium. Now the task is to figure out how, chemically and physically, those elements are integrated into interstellar grains. We can do this by comparing extinction curves to grain populations in radiative transfer models. The limitation at the present time is the availability of optical constants in the infrared through ultraviolet for species that are likely to exist in dust, i.e., those that are easy to form in the physical environments around stars and in molecular clouds. Extinction in some lines of sight can be fit within current abundance limits and with the optical constants that are available. However the inability to reproduce other extinction curves suggests that optical constants can be improved, either in quality for compounds that have been measured, or quantity in the sense of providing data for more materials. This talk will address the current state and the future of dust studies in the diffuse neutral interstellar medium. This work is supported by the grant HST-AR-10979.01-A from the Space Telescope Science Institute to Whitman College.

  11. Global ice sheet modeling

    International Nuclear Information System (INIS)

    Hughes, T.J.; Fastook, J.L.

    1994-05-01

    The University of Maine conducted this study for Pacific Northwest Laboratory (PNL) as part of a global climate modeling task for site characterization of the potential nuclear waste respository site at Yucca Mountain, NV. The purpose of the study was to develop a global ice sheet dynamics model that will forecast the three-dimensional configuration of global ice sheets for specific climate change scenarios. The objective of the third (final) year of the work was to produce ice sheet data for glaciation scenarios covering the next 100,000 years. This was accomplished using both the map-plane and flowband solutions of our time-dependent, finite-element gridpoint model. The theory and equations used to develop the ice sheet models are presented. Three future scenarios were simulated by the model and results are discussed

  12. The Sea-Ice Floe Size Distribution

    Science.gov (United States)

    Stern, H. L., III; Schweiger, A. J. B.; Zhang, J.; Steele, M.

    2017-12-01

    The size distribution of ice floes in the polar seas affects the dynamics and thermodynamics of the ice cover and its interaction with the ocean and atmosphere. Ice-ocean models are now beginning to include the floe size distribution (FSD) in their simulations. In order to characterize seasonal changes of the FSD and provide validation data for our ice-ocean model, we calculated the FSD in the Beaufort and Chukchi seas over two spring-summer-fall seasons (2013 and 2014) using more than 250 cloud-free visible-band scenes from the MODIS sensors on NASA's Terra and Aqua satellites, identifying nearly 250,000 ice floes between 2 and 30 km in diameter. We found that the FSD follows a power-law distribution at all locations, with a seasonally varying exponent that reflects floe break-up in spring, loss of smaller floes in summer, and the return of larger floes after fall freeze-up. We extended the results to floe sizes from 10 m to 2 km at selected time/space locations using more than 50 high-resolution radar and visible-band satellite images. Our analysis used more data and applied greater statistical rigor than any previous study of the FSD. The incorporation of the FSD into our ice-ocean model resulted in reduced sea-ice thickness, mainly in the marginal ice zone, which improved the simulation of sea-ice extent and yielded an earlier ice retreat. We also examined results from 17 previous studies of the FSD, most of which report power-law FSDs but with widely varying exponents. It is difficult to reconcile the range of results due to different study areas, seasons, and methods of analysis. We review the power-law representation of the FSD in these studies and discuss some mathematical details that are important to consider in any future analysis.

  13. Riddling bifurcation and interstellar journeys

    International Nuclear Information System (INIS)

    Kapitaniak, Tomasz

    2005-01-01

    We show that riddling bifurcation which is characteristic for low-dimensional attractors embedded in higher-dimensional phase space can give physical mechanism explaining interstellar journeys described in science-fiction literature

  14. Electromagnetic Forces on a Relativistic Spacecraft in the Interstellar Medium

    Energy Technology Data Exchange (ETDEWEB)

    Hoang, Thiem [Korea Astronomy and Space Science Institute, Daejeon 34055 (Korea, Republic of); Loeb, Abraham, E-mail: thiemhoang@kasi.re.kr, E-mail: aloeb@cfa.harvard.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA (United States)

    2017-10-10

    A relativistic spacecraft of the type envisioned by the Breakthrough Starshot initiative will inevitably become charged through collisions with interstellar particles and UV photons. Interstellar magnetic fields would therefore deflect the trajectory of the spacecraft. We calculate the expected deflection for typical interstellar conditions. We also find that the charge distribution of the spacecraft is asymmetric, producing an electric dipole moment. The interaction between the moving electric dipole and the interstellar magnetic field is found to produce a large torque, which can result in fast oscillation of the spacecraft around the axis perpendicular to the direction of motion, with a period of ∼0.5 hr. We then study the spacecraft rotation arising from impulsive torques by dust bombardment. Finally, we discuss the effect of the spacecraft rotation and suggest several methods to mitigate it.

  15. Non-basal dislocations should be accounted for in simulating ice mass flow

    Science.gov (United States)

    Chauve, T.; Montagnat, M.; Piazolo, S.; Journaux, B.; Wheeler, J.; Barou, F.; Mainprice, D.; Tommasi, A.

    2017-09-01

    Prediction of ice mass flow and associated dynamics is pivotal at a time of climate change. Ice flow is dominantly accommodated by the motion of crystal defects - the dislocations. In the specific case of ice, their observation is not always accessible by means of the classical tools such as X-ray diffraction or transmission electron microscopy (TEM). Part of the dislocation population, the geometrically necessary dislocations (GNDs) can nevertheless be constrained using crystal orientation measurements via electron backscattering diffraction (EBSD) associated with appropriate analyses based on the Nye (1950) approach. The present study uses the Weighted Burgers Vectors, a reduced formulation of the Nye theory that enables the characterization of GNDs. Applied to ice, this method documents, for the first time, the presence of dislocations with non-basal [ c ] or Burgers vectors. These [ c ] or dislocations represent up to 35% of the GNDs observed in laboratory-deformed ice samples. Our findings offer a more complex and comprehensive picture of the key plasticity processes responsible for polycrystalline ice creep and provide better constraints on the constitutive mechanical laws implemented in ice sheet flow models used to predict the response of Earth ice masses to climate change.

  16. Methanol Formation via Oxygen Insertion Chemistry in Ices

    Science.gov (United States)

    Bergner, Jennifer B.; Öberg, Karin I.; Rajappan, Mahesh

    2017-08-01

    We present experimental constraints on the insertion of oxygen atoms into methane to form methanol in astrophysical ice analogs. In gas-phase and theoretical studies this process has previously been demonstrated to have a very low or nonexistent energy barrier, but the energetics and mechanisms have not yet been characterized in the solid state. We use a deuterium UV lamp filtered by a sapphire window to selectively dissociate O2 within a mixture of O2:CH4 and observe efficient production of CH3OH via O(1D) insertion. CH3OH growth curves are fit with a kinetic model, and we observe no temperature dependence of the reaction rate constant at temperatures below the oxygen desorption temperature of 25 K. Through an analysis of side products we determine the branching ratio of ice-phase oxygen insertion into CH4: ˜65% of insertions lead to CH3OH, with the remainder leading instead to H2CO formation. There is no evidence for CH3 or OH radical formation, indicating that the fragmentation is not an important channel and that insertions typically lead to increased chemical complexity. CH3OH formation from O2 and CH4 diluted in a CO-dominated ice similarly shows no temperature dependence, consistent with expectations that insertion proceeds with a small or nonexistent barrier. Oxygen insertion chemistry in ices should therefore be efficient under low-temperature ISM-like conditions and could provide an important channel to complex organic molecule formation on grain surfaces in cold interstellar regions such as cloud cores and protoplanetary disk midplanes.

  17. Methanol Formation via Oxygen Insertion Chemistry in Ices

    Energy Technology Data Exchange (ETDEWEB)

    Bergner, Jennifer B. [Harvard University Department of Chemistry and Chemical Biology, 10 Oxford Street, Cambridge, MA 02138 (United States); Öberg, Karin I.; Rajappan, Mahesh [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

    2017-08-10

    We present experimental constraints on the insertion of oxygen atoms into methane to form methanol in astrophysical ice analogs. In gas-phase and theoretical studies this process has previously been demonstrated to have a very low or nonexistent energy barrier, but the energetics and mechanisms have not yet been characterized in the solid state. We use a deuterium UV lamp filtered by a sapphire window to selectively dissociate O{sub 2} within a mixture of O{sub 2}:CH{sub 4} and observe efficient production of CH{sub 3}OH via O({sup 1}D) insertion. CH{sub 3}OH growth curves are fit with a kinetic model, and we observe no temperature dependence of the reaction rate constant at temperatures below the oxygen desorption temperature of 25 K. Through an analysis of side products we determine the branching ratio of ice-phase oxygen insertion into CH{sub 4}: ∼65% of insertions lead to CH{sub 3}OH, with the remainder leading instead to H{sub 2}CO formation. There is no evidence for CH{sub 3} or OH radical formation, indicating that the fragmentation is not an important channel and that insertions typically lead to increased chemical complexity. CH{sub 3}OH formation from O{sub 2} and CH{sub 4} diluted in a CO-dominated ice similarly shows no temperature dependence, consistent with expectations that insertion proceeds with a small or nonexistent barrier. Oxygen insertion chemistry in ices should therefore be efficient under low-temperature ISM-like conditions and could provide an important channel to complex organic molecule formation on grain surfaces in cold interstellar regions such as cloud cores and protoplanetary disk midplanes.

  18. The interstellar medium and star formation in local galaxies: Variations of the star formation law in simulations

    International Nuclear Information System (INIS)

    Becerra, Fernando; Escala, Andrés

    2014-01-01

    We use the adaptive mesh refinement code Enzo to model the interstellar medium (ISM) in isolated local disk galaxies. The simulation includes a treatment for star formation and stellar feedback. We get a highly supersonic turbulent disk, which is fragmented at multiple scales and characterized by a multi-phase ISM. We show that a Kennicutt-Schmidt relation only holds when averaging over large scales. However, values of star formation rates and gas surface densities lie close in the plot for any averaging size. This suggests an intrinsic relation between stars and gas at cell-size scales, which dominates over the global dynamical evolution. To investigate this effect, we develop a method to simulate the creation of stars based on the density field from the snapshots, without running the code again. We also investigate how the star formation law is affected by the characteristic star formation timescale, the density threshold, and the efficiency considered in the recipe. We find that the slope of the law varies from ∼1.4 for a free-fall timescale, to ∼1.0 for a constant depletion timescale. We further demonstrate that a power law is recovered just by assuming that the mass of the new stars is a fraction of the mass of the cell m * = ερ gas Δx 3 , with no other physical criteria required. We show that both efficiency and density threshold do not affect the slope, but the right combination of them can adjust the normalization of the relation, which in turn could explain a possible bi-modality in the law.

  19. Ice accretion modeling for wind turbine rotor blades

    Energy Technology Data Exchange (ETDEWEB)

    Chocron, D.; Brahimi, T.; Paraschivoiu, I.; Bombardier, J.A. [Ecole Polytechnique de Montreal (Canada)

    1997-12-31

    The increasing application of wind energy in northern climates implies operation of wind turbines under severe atmospheric icing conditions. Such conditions are well known in the Scandinavian countries, Canada and most of Eastern European countries. An extensive study to develop a procedure for the prediction of ice accretion on wind turbines rotor blades appears to be essential for the safe and economic operation of wind turbines in these cold regions. The objective of the present paper is to develop a computer code capable of simulating the shape and amount of ice which may accumulate on horizontal axis wind turbine blades when operating in icing conditions. The resulting code is capable to predict and simulate the formation of ice in rime and glaze conditions, calculate the flow field and particle trajectories and to perform thermodynamic analysis. It also gives the possibility of studying the effect of different parameters that influence ice formation such as temperature, liquid water content, droplet diameter and accretion time. The analysis has been conducted on different typical airfoils as well as on NASA/DOE Mod-0 wind turbine. Results showed that ice accretion on wind turbines may reduce the power output by more than 20%.

  20. Chemistry in interstellar space. [environment characteristics influencing reaction dynamics

    Science.gov (United States)

    Donn, B.

    1973-01-01

    The particular characteristics of chemistry in interstellar space are determined by the unique environmental conditions involved. Interstellar matter is present at extremely low densities. Large deviations from thermodynamic equilibrium are, therefore, to be expected. A relatively intense ultraviolet radiation is present in many regions. The temperatures are in the range from 5 to 200 K. Data concerning the inhibiting effect of small activation energies in interstellar clouds are presented in a table. A summary of measured activation energies or barrier heights for exothermic exchange reactions is also provided. Problems of molecule formation are discussed, taking into account gas phase reactions and surface catalyzed processes.

  1. Influence of the interstellar medium on climate and life: the Black Cloud revisited

    Energy Technology Data Exchange (ETDEWEB)

    Talbot, Jr, R J

    1980-06-01

    Recent studies of the gas and dust between the stars, the interstellar medium, reveal a complex chemistry which indicates that prebiotic organic chemistry is ubiquitous. The relationship between this interstellar chemistry and the organic chemistry of the early solar system and the earth is explored. The interstellar medium is also considered as likely to have a continuing influence upon the climate of the earth and other planets. Life forms as we know them are not only descendants of the organic evolution begun in the interstellar medium, but their continuing evolution is also molded through occasional interactions between the interstellar medium, the sun and the climate on earth.

  2. Influence of the interstellar medium on climate and life. The black cloud revisited

    Energy Technology Data Exchange (ETDEWEB)

    Talbot, Jr, R J [Rice Univ., Houston, TX (USA). Dept. of Space Physics and Astronomy

    1980-06-01

    Recent studies of the gas and dust between the stars, the interstellar medium, reveal a complex chemistry which indicates that prebiotic organic chemistry is ubiquitous. The relationship between this interstellar chemistry and the organic chemistry of the early solar system and the Earth is explored. The interstellar medium is also considered as likely to have a continuing influence upon the climate of the Earth and other planets. Life forms as known are not only descendants of the organic evolution begun in the interstellar medium, but their continuing evolution is also molded through occasional interactions between the interstellar medium, the Sun and the climate on Earth.

  3. Lattice Boltzmann Simulation of Water Isotope Fractionation During Growth of Ice Crystals in Clouds

    Science.gov (United States)

    Lu, G.; Depaolo, D.; Kang, Q.; Zhang, D.

    2006-12-01

    The isotopic composition of precipitation, especially that of snow, plays a special role in the global hydrological cycle and in reconstruction of past climates using polar ice cores. The fractionation of the major water isotope species (HHO, HDO, HHO-18) during ice crystal formation is critical to understanding the global distribution of isotopes in precipitation. Ice crystal growth in clouds is traditionally treated with a spherically- symmetric steady state diffusion model, with semi-empirical modifications added to account for ventilation and for complex crystal morphology. Although it is known that crystal growth rate, which depends largely on the degree of vapor over-saturation, determines crystal morphology, there are no existing quantitative models that directly relate morphology to the vapor saturation factor. Since kinetic (vapor phase diffusion-controlled) isotopic fractionation also depends on growth rate, there should be a direct relationship between vapor saturation, crystal morphology, and crystal isotopic composition. We use a 2D Lattice-Boltzmann model to simulate diffusion-controlled ice crystal growth from vapor- oversaturated air. In the model, crystals grow solely according to the diffusive fluxes just above the crystal surfaces, and hence crystal morphology arises from the initial and boundary conditions in the model and does not need to be specified a priori. The input parameters needed are the isotope-dependent vapor deposition rate constant (k) and the water vapor diffusivity in air (D). The values of both k and D can be computed from kinetic theory, and there are also experimentally determined values of D. The deduced values of k are uncertain to the extent that the sticking coefficient (or accommodation coefficient) for ice is uncertain. The ratio D/k is a length that determines the minimum scale of dendritic growth features and allows us to scale the numerical calculations to atmospheric conditions using a dimensionless Damkohler number

  4. The Interstellar Medium in External Galaxies: Summaries of contributed papers

    Science.gov (United States)

    Hollenbach, David J. (Editor); Thronson, Harley A., Jr. (Editor)

    1990-01-01

    The Second Wyoming Conference entitled, The Interstellar Medium in External Galaxies, was held on July 3 to 7, 1989, to discuss the current understanding of the interstellar medium in external galaxies and to analyze the basic physical processes underlying interstellar phenomena. The papers covered a broad range of research on the gas and dust in external galaxies and focused on such topics as the distribution and morphology of the atomic, molecular, and dust components; the dynamics of the gas and the role of the magnetic field in the dynamics; elemental abundances and gas depletions in the atomic and ionized components; cooling flows; star formation; the correlation of the nonthermal radio continuum with the cool component of the interstellar medium; the origin and effect of hot galactic halos; the absorption line systems seen in distant quasars; and the effect of galactic collisions.

  5. Reactions of Ground State Nitrogen Atoms N(4S) with Astrochemically-Relevant Molecules on Interstellar Dusts

    Science.gov (United States)

    Krim, Lahouari; Nourry, Sendres

    2015-06-01

    In the last few years, ambitious programs were launched to probe the interstellar medium always more accurately. One of the major challenges of these missions remains the detection of prebiotic compounds and the understanding of reaction pathways leading to their formation. These complex heterogeneous reactions mainly occur on icy dust grains, and their studies require the coupling of laboratory experiments mimicking the extreme conditions of extreme cold and dilute media. For that purpose, we have developed an original experimental approach that combine the study of heterogeneous reactions (by exposing neutral molecules adsorbed on ice to non-energetic radicals H, OH, N...) and a neon matrix isolation study at very low temperatures, which is of paramount importance to isolate and characterize highly reactive reaction intermediates. Such experimental approach has already provided answers to many questions raised about some astrochemically-relevant reactions occurring in the ground state on the surface of dust grain ices in dense molecular clouds. The aim of this new present work is to show the implication of ground state atomic nitrogen on hydrogen atom abstraction reactions from some astrochemically-relevant species, at very low temperatures (3K-20K), without providing any external energy. Under cryogenic temperatures and with high barrier heights, such reactions involving N(4S) nitrogen atoms should not occur spontaneously and require an initiating energy. However, the detection of some radicals species as byproducts, in our solid samples left in the dark for hours at 10K, proves that hydrogen abstraction reactions involving ground state N(4S) nitrogen atoms may occur in solid phase at cryogenic temperatures. Our results show the efficiency of radical species formation stemming from non-energetic N-atoms and astrochemically-relevant molecules. We will then discuss how such reactions, involving nitrogen atoms in their ground states, might be the first key step

  6. Surface chemistry on interstellar oxide grains

    International Nuclear Information System (INIS)

    Denison, P.; Williams, D.A.

    1981-01-01

    Detailed calculations are made to test the predictions of Duley, Millar and Williams (1978) concerning the chemical reactivity of interstellar oxide grains. A method is established for calculating interaction energies between atoms and the perfect crystal with or without surface vacancy sites. The possibility of reactions between incident atoms and absorbed atoms is investigated. It is concluded that H 2 formation can occur on the perfect crystal surfaces, and that for other diatomic molecules the important formation sites are the Fsub(s)- and V 2- sub(s)-centres. The outline by Duley, Millar and Williams (1979) of interstellar oxide grain growth and destruction is justified by these calculations. (author)

  7. Modeling the imprint of Milankovitch cycles on early Pleistocene ice volume

    Science.gov (United States)

    Roychowdhury, R.; DeConto, R.; Pollard, D.

    2017-12-01

    Global climate during Quaternary and Late Pliocene (present-3.1 Ma) is characterized by alternating glacial and interglacial conditions. Several proposed theories associate these cycles with variations in the Earth's orbital configuration. In this study, we attempt to address the anomalously strong obliquity forcing in the Late Pliocene/Early Pleistocene ice volume records (41 kyr world), which stands in sharp contrast to the primary cyclicity of insolation, which is at precessional periods (23 kyr). Model results from GCM simulations show that at low eccentricities (e0.015), precessional response is important, and the insolation metrics vary out-of-phase between the two hemispheres. Using simulations from a GCM-driven ice sheet model, we simulate time continuous ice volume changes from Northern and Southern Hemispheres. Under eccentricities lower than 0.015, ice sheets in both hemispheres respond only to obliquity cycle, and grow and melt together (in-phase). If the ice sheet is simulated with eccentricity higher than 0.015, both hemispheres become more sensitive to precessional variation, and vary out-of-phase with each other, which is consistent with proxy observations from the late Pleistocene glaciations. We use the simulated ice volumes from 2.0 to 1.0 ma to empirically calculate global benthic δ18O variations based on the assumption that relationships between collapse and growth of ice-sheets and sea level is linear and symmetric and that the isotopic signature of the individual ice-sheets has not changed with time. Our modeled global benthic δ18O values are broadly consistent with the paleoclimate proxy records such as the LR04 stack.

  8. Why do interstellar grains exist

    International Nuclear Information System (INIS)

    Seab, C.G.; Hollenbach, D.J.; Mckee, C.F.; Tielens, A.G.G.M.

    1986-01-01

    There exists a discrepancy between calculated destruction rates of grains in the interstellar medium and postulated sources of new grains. This problem was examined by modelling the global life cycle of grains in the galaxy. The model includes: grain destruction due to supernovae shock waves; grain injection from cool stars, planetary nebulae, star formation, novae, and supernovae; grain growth by accretion in dark clouds; and a mixing scheme between phases of the interstellar medium. Grain growth in molecular clouds is considered as a mechanism or increasing the formation rate. To decrease the shock destruction rate, several new physical processes, such as partial vaporization effects in grain-grain collisions, breakdown of the small Larmor radius approximation for betatron acceleration, and relaxation of the steady-state shock assumption are included

  9. INTERSTELLAR GAS FLOW PARAMETERS DERIVED FROM INTERSTELLAR BOUNDARY EXPLORER-Lo OBSERVATIONS IN 2009 AND 2010: ANALYTICAL ANALYSIS

    International Nuclear Information System (INIS)

    Möbius, E.; Bochsler, P.; Heirtzler, D.; Kucharek, H.; Lee, M. A.; Leonard, T.; Schwadron, N. A.; Wu, X.; Petersen, L.; Valovcin, D.; Wurz, P.; Bzowski, M.; Kubiak, M. A.; Fuselier, S. A.; Crew, G.; Vanderspek, R.; McComas, D. J.; Saul, L.

    2012-01-01

    Neutral atom imaging of the interstellar gas flow in the inner heliosphere provides the most detailed information on physical conditions of the surrounding interstellar medium (ISM) and its interaction with the heliosphere. The Interstellar Boundary Explorer (IBEX) measured neutral H, He, O, and Ne for three years. We compare the He and combined O+Ne flow distributions for two interstellar flow passages in 2009 and 2010 with an analytical calculation, which is simplified because the IBEX orientation provides observations at almost exactly the perihelion of the gas trajectories. This method allows separate determination of the key ISM parameters: inflow speed, longitude, and latitude, as well as temperature. A combined optimization, as in complementary approaches, is thus not necessary. Based on the observed peak position and width in longitude and latitude, inflow speed, latitude, and temperature are found as a function of inflow longitude. The latter is then constrained by the variation of the observed flow latitude as a function of observer longitude and by the ratio of the widths of the distribution in longitude and latitude. Identical results are found for 2009 and 2010: an He flow vector somewhat outside previous determinations (λ ISM∞ = 79. 0 0+3. 0 0(–3. 0 5), β ISM∞ = –4. 0 9 ± 0. 0 2, V ISM∞ 23.5 + 3.0(–2.0) km s –1 , T He = 5000-8200 K), suggesting a larger inflow longitude and lower speed. The O+Ne temperature range, T O+Ne = 5300-9000 K, is found to be close to the upper range for He and consistent with an isothermal medium for all species within current uncertainties.

  10. Impact of surface nanostructure on ice nucleation.

    Science.gov (United States)

    Zhang, Xiang-Xiong; Chen, Min; Fu, Ming

    2014-09-28

    Nucleation of water on solid surface can be promoted noticeably when the lattice parameter of a surface matches well with the ice structure. However, the characteristic length of the surface lattice reported is generally less than 0.5 nm and is hardly tunable. In this paper, we show that a surface with nanoscale roughness can also remarkably promote ice nucleation if the characteristic length of the surface structure matches well with the ice crystal. A series of surfaces composed of periodic grooves with same depth but different widths are constructed in molecular dynamics simulations. Water cylinders are placed on the constructed surfaces and frozen at constant undercooling. The nucleation rates of the water cylinders are calculated in the simulation using the mean first-passage time method and then used to measure the nucleation promotion ability of the surfaces. Results suggest that the nucleation behavior of the supercooled water is significantly sensitive to the width of the groove. When the width of the groove matches well with the specific lengths of the ice crystal structure, the nucleation can be promoted remarkably. If the width does not match with the ice crystal, this kind of promotion disappears and the nucleation rate is even smaller than that on the smooth surface. Simulations also indicate that even when water molecules are adsorbed onto the surface structure in high-humidity environment, the solid surface can provide promising anti-icing ability as long as the characteristic length of the surface structure is carefully designed to avoid geometric match.

  11. Ice condensation on sulfuric acid tetrahydrate: Implications for polar stratospheric ice clouds

    Directory of Open Access Journals (Sweden)

    T. J. Fortin

    2003-01-01

    Full Text Available The mechanism of ice nucleation to form Type 2 PSCs is important for controlling the ice particle size and hence the possible dehydration in the polar winter stratosphere. This paper probes heterogeneous ice nucleation on sulfuric acid tetrahydrate (SAT. Laboratory experiments were performed using a thin-film, high-vacuum apparatus in which the condensed phase is monitored via Fourier transform infrared spectroscopy and water pressure is monitored with the combination of an MKS baratron and an ionization gauge. Results show that SAT is an efficient ice nucleus with a critical ice saturation ratio of S*ice = 1.3 to 1.02 over the temperature range 169.8-194.5 K. This corresponds to a necessary supercooling of 0.1-1.3 K below the ice frost point. The laboratory data is used as input for a microphysical/photochemical model to probe the effect that this heterogeneous nucleation mechanism could have on Type 2 PSC formation and stratospheric dehydration. In the model simulations, even a very small number of SAT particles (e.g., 10-3 cm-3 result in ice nucleation on SAT as the dominant mechanism for Type 2 PSC formation. As a result, Type 2 PSC formation is more widespread, leading to larger-scale dehydration. The characteristics of the clouds are controlled by the assumed number of SAT particles present, demonstrating that a proper treatment of SAT is critical for correctly modeling Type 2 PSC formation and stratospheric dehydration.

  12. The existence and nature of the interstellar bow shock

    Energy Technology Data Exchange (ETDEWEB)

    Ben-Jaffel, Lotfi [UPMC Univ Paris 06, UMR7095, Institut d' Astrophysique de Paris, F-75014, Paris (France); Strumik, M.; Ratkiewicz, R.; Grygorczuk, J., E-mail: bjaffel@iap.fr [Space Research Centre, Polish Academy of Sciences, Bartycka 18A, 00-716 Warsaw (Poland)

    2013-12-20

    We report a new diagnosis of two different states of the local interstellar medium (LISM) near our solar system by using a sensitivity study constrained by several distinct and complementary observations of the LISM, solar wind, and inner heliosphere. Assuming the Interstellar Boundary Explorer (IBEX) He flow parameters for the LISM, we obtain a strength of ∼2.7 ± 0.2 μG and a direction pointing away from galactic coordinates (28, 52) ± 3° for the interstellar magnetic field as a result of fitting Voyager 1 and Voyager 2 in situ plasma measurements and IBEX energetic neutral atoms ribbon. When using Ulysses parameters for the LISM He flow, we recently reported the same direction but with a strength of 2.2 ± 0.1 μG. First, we notice that with Ulysses He flow, our solution is in the expected hydrogen deflection plane (HDP). In contrast, for the IBEX He flow, the solution is ∼20° away from the corresponding HDP plane. Second, the long-term monitoring of the interplanetary H I flow speed shows a value of ∼26 km s{sup –1} measured upwind from the Doppler shift in the strong Lyα sky background emission line. All elements of the diagnosis seem therefore to support Ulysses He flow parameters for the interstellar state. In that frame, we argue that reliable discrimination between superfast, subfast, or superslow states of the interstellar flow should be based on most existing in situ and remote observations used together with global modeling of the heliosphere. For commonly accepted LISM ionization rates, we show that a fast interstellar bow shock should be standing off upstream of the heliopause.

  13. Distribution of Interstellar Reddening Material in the Galactic Plane

    Directory of Open Access Journals (Sweden)

    Chulhee Kim

    1987-12-01

    Full Text Available By using the recently determined color excess and distance data of classical cepheids by Kim(1985, the distribution of interstellar reddening material was studied to see the general picture of the average rate of interstellar absorption out to about 7-8kpc in the Galactic plane in various directions from the sun.

  14. THE AGE OF THE LOCAL INTERSTELLAR BUBBLE

    International Nuclear Information System (INIS)

    Abt, Helmut A.

    2011-01-01

    The Local Interstellar Bubble is an irregular region from 50 to 150 pc from the Sun in which the interstellar gas density is 10 -2 -10 -3 of that outside the bubble and the interstellar temperature is 10 6 K. Evidently most of the gas was swept out by one or more supernovae. I explored the stellar contents and ages of the region from visual double stars, spectroscopic doubles, single stars, open clusters, emission regions, X-ray stars, planetary nebulae, and pulsars. The bubble has three sub-regions. The region toward the galactic center has stars as early as O9.5 V and with ages of 2-4 M yr. It also has a pulsar (PSRJ1856-3754) with a spin-down age of 3.76 Myr. That pulsar is likely to be the remnant of the supernova that drove away most of the gas. The central lobe has stars as early as B7 V and therefore an age of about 160 Myr or less. The Pleiades lobe has stars as early as B3 and therefore an age of about 50 Myr. There are no obvious pulsars that resulted from the supernovae that cleared out those areas. As found previously by Welsh and Lallement, the bubble has five B stars along its perimeter that show high-temperature ions of O VI and C II along their lines of sight, confirming its high interstellar temperature.

  15. Photoionization in Ultraviolet Processing of Astrophysical Ice Analogs at Cryogenic Temperatures

    Science.gov (United States)

    Woon, David E.

    2004-01-01

    Two recent experimental studies have demonstrated that amino acids or amino acid precursors are generated when astrophysical ice analogs are subjected to ultraviolet (UV) irradiation at cryogenic temperatures. Understanding the complete phenomenology of photoprocessing is critical to elucidating chemical reaction mechanisms that can function within an ice matrix under very cold conditions. Pushing beyond the much better characterized study of photolytic dissociation of chemical bonds through electronic excitation, this work explored the ability of UV radiation present in the interstellar medium to ionize small molecules embedded in ices. Quantum chemical calculations, including bulk solvation effects, were used to study the ionization of hydrogen (H2), water, and methanol (CH3OH) bound in small clusters of water. Ionization potentials were found to be much smaller in the condensed phase than in the gas phase; even a small cluster can account for large changes in the ionization potentials in ice, as well as the known formation of an OH--H3O+ pair in the case of H2O photoionization. To gauge the impact of photoionization on subsequent grain chemistry, the reaction between OH and CO in the presence of H3O+ was studied and compared with the potential energy surface without hydronium present, which is relevant to chemistry following photolysis. The differences indicate that the reaction is somewhat more likely to proceed to products (H + CO2) in the case of photoionization.

  16. The Stardust Interstellar Dust Collector and Stardust@home

    Science.gov (United States)

    Westphal, A. J.; Anderson, D.; Bastien, R.; Butterworth, A.; Frank, D.; Gainsforth, Z.; Kelley, N.; Lettieri, R.; Mendez, B.; Prasad, R.; Tsitrin, S.; von Korff, J.; Warren, J.; Wertheimer, D.; Zhang, A.; Zolensky, M.

    2006-12-01

    The Stardust sample return mission is effectively two missions in one. Stardust brought back to earth for analytical study the first solid samples from a known solar system body beyond the moon, comet Wild2. The first results of the analyses of these samples are reported elsewhere in this session. In a separate aerogel collector, Stardust also captured and has returned the first samples of contemporary interstellar dust. Landgraf et al. [1] has estimated that ~ 50 interstellar dust particles in the micron size range have been captured in the Stardust Interstellar Dust Collector. Their state after capture is unknown. Before analysis of these particles can begin, they must be located in the collector. Here we describe the current status of Stardust@home, the massively distributed public search for these tiny interstellar dust particles. So far more than 13,000 volunteers have collectively performed more than 10,000,000 searches in stacks of digital images of ~10% of the collector. We report new estimates of the flux of interplanetary dust at ~2 AU based on the results of this search, and will compare with extant models[2]. References: [1] Landgraf et al., (1999) Planet. Spac. Sci. 47, 1029. [2] Staubach et al. (2001) in Interplanetary Dust, E. Grün, ed., Astron. &Astro. Library, Springer, 2001.

  17. CO-ices in embedded Young Stellar Objects

    Science.gov (United States)

    Teixeira, Teresa Cláeira V. S.

    1998-09-01

    Stars are born in dense cores within molecular clouds, enshrouded in large cocoons of gas and dust which completely obscure the forming star. The large degree of obscuration towards the young stars is due to the presence of solid dust grains in their circumstellar envelopes, which efficiently absorb the radiation from the star at visual and ultraviolet wavelengths, reradiating that energy at far-infrared and submillimeter wavelengths. The composition and structure of the dust grains is not well known, but current studies point to grains having a refractory core and acquiring ice mantles in the cool, shielded conditions of molecular clouds. Such ice mantles are the subject of this thesis. Infrared spectroscopy is an important tool in the study of the complex ice mantles on interstellar grains. A variety of absorption features at these wavelengths, which have been identified as the vibrational transitions of the molecules in the ices, can provide important information on the composition, structure and evolution of the grains. The work reported in this thesis consists of an observational study of the composition of the ice mantles acquired by the dust grains in molecular clouds (with particular emphasis on the CO-ices in the material surrounding embedded Young Stellar Objects in nearby molecular clouds), what can be learned from that about the physical conditions in the regions where the ice mantles exist, and what may affect their survival and evolution. In this work, spectra of the 4.67 micron solid CO absorption feature are presented, mostly towards embedded objects in Taurus. The thesis starts with a brief overview of technical aspects of spectroscopic observations at thermal infrared wavelengths, where the CO stretch absorption feature is located. The observations and data reduction procedures are then reported and discussed in detail. The likely composition of the CO-bearing ices is analysed by fitting the observations with laboratory data. The statistical

  18. Aero-thermal optimization of in-flight electro-thermal ice protection systems in transient de-icing mode

    International Nuclear Information System (INIS)

    Pourbagian, Mahdi; Habashi, Wagdi G.

    2015-01-01

    Highlights: • We introduce an efficient methodology for the optimization of a de-icing system. • We can replace the expensive CHT simulation by ROM without loosing much accuracy. • We propose different criteria affecting the energy usage and aerodynamic performance. • These criteria can significantly improve the performance of the de-icing system. - Abstract: Even if electro-thermal ice protection systems (IPS) consume less energy when operating in de-icing mode than in anti-icing mode, they still need to be optimized for energy usage. The optimization, however, should also take into account the effect of the de-icing system on the aerodynamic performance. The present work offers an optimization framework in which both thermal and aerodynamic viewpoints are taken into account in formulating various objective and constraint functions by considering the energy consumption, the thickness, the volume, the shape and the location of the accreted ice on the surface as the key parameters affecting the energy usage and the aerodynamic performance. The design variables include the power density and the activation time of the electric heating blankets. A derivative-free technique, called the mesh adaptive direct search (MADS) method, is used to carry out the optimization process, which would normally need a large number of unsteady conjugate heat transfer (CHT) calculations for the IPS simulation. To avoid such prohibitive computations, reduced-order modeling (ROM) is used to construct simplified low-dimensional CHT models. The approach is illustrated through several test cases, in which different combinations of objective and constraint functions, design variables and cycling sequence patterns are examined. In these test cases, the energy consumption is significantly reduced compared to the experiments by improving the spatial and temporal distribution of the thermal energy usage. The results show the benefits of the approach in bringing energy, safety and

  19. A COMPREHENSIVE STUDY OF HYDROGEN ADSORBING TO AMORPHOUS WATER ICE: DEFINING ADSORPTION IN CLASSICAL MOLECULAR DYNAMICS

    Energy Technology Data Exchange (ETDEWEB)

    Dupuy, John L.; Lewis, Steven P.; Stancil, P. C. [Department of Physics and Astronomy and the Center for Simulational Physics, University of Georgia, Athens, GA 30602 (United States)

    2016-11-01

    Gas–grain and gas–phase reactions dominate the formation of molecules in the interstellar medium (ISM). Gas–grain reactions require a substrate (e.g., a dust or ice grain) on which the reaction is able to occur. The formation of molecular hydrogen (H{sub 2}) in the ISM is the prototypical example of a gas–grain reaction. In these reactions, an atom of hydrogen will strike a surface, stick to it, and diffuse across it. When it encounters another adsorbed hydrogen atom, the two can react to form molecular hydrogen and then be ejected from the surface by the energy released in the reaction. We perform in-depth classical molecular dynamics simulations of hydrogen atoms interacting with an amorphous water-ice surface. This study focuses on the first step in the formation process; the sticking of the hydrogen atom to the substrate. We find that careful attention must be paid in dealing with the ambiguities in defining a sticking event. The technical definition of a sticking event will affect the computed sticking probabilities and coefficients. Here, using our new definition of a sticking event, we report sticking probabilities and sticking coefficients for nine different incident kinetic energies of hydrogen atoms [5–400 K] across seven different temperatures of dust grains [10–70 K]. We find that probabilities and coefficients vary both as a function of grain temperature and incident kinetic energy over the range of 0.99–0.22.

  20. Wave inhibition by sea ice enables trans-Atlantic ice rafting of debris during Heinrich Events

    Science.gov (United States)

    Wagner, T. J. W.; Dell, R.; Eisenman, I.; Keeling, R. F.; Padman, L.; Severinghaus, J. P.

    2017-12-01

    The thickness of the ice-rafted debris (IRD) layers that signal Heinrich Events declines far more gradually with distance from the iceberg sources than would be expected based on present-day iceberg trajectories. Here we model icebergs as passive Lagrangian tracers driven by ocean currents, winds, and sea surface temperatures. The icebergs are released in a comprehensive climate model simulation of the last glacial maximum (LGM), as well as a simulation of the modern climate. The two simulated climates result in qualitatively similar distributions of iceberg meltwater and hence debris, with the colder temperatures of the LGM having only a relatively small effect on meltwater spread. In both scenarios, meltwater flux falls off rapidly with zonal distance from the source, in contrast with the more uniform spread of IRD in sediment cores. In order to address this discrepancy, we propose a physical mechanism that could have prolonged the lifetime of icebergs during Heinrich events. The mechanism involves a surface layer of cold and fresh meltwater formed from, and retained around, densely packed armadas of icebergs. This leads to wintertime sea ice formation even in relatively low latitudes. The sea ice in turn shields the icebergs from wave erosion, which is the main source of iceberg ablation. We find that allowing sea ice to form around all icebergs during four months each winter causes the model to approximately agree with the distribution of IRD in sediment cores.

  1. Disordered kagomé spin ice

    Science.gov (United States)

    Greenberg, Noah; Kunz, Andrew

    2018-05-01

    Artificial spin ice is made from a large array of patterned magnetic nanoislands designed to mimic naturally occurring spin ice materials. The geometrical arrangement of the kagomé lattice guarantees a frustrated arrangement of the islands' magnetic moments at each vertex where the three magnetic nanoislands meet. This frustration leads to a highly degenerate ground state which gives rise to a finite (residual) entropy at zero temperature. In this work we use the Monte Carlo simulation to explore the effects of disorder in kagomé spin ice. Disorder is introduced to the system by randomly removing a known percentage of magnetic islands from the lattice. The behavior of the spin ice changes as the disorder increases; evident by changes to the shape and locations of the peaks in heat capacity and the residual entropy. The results are consistent with observations made in diluted physical spin ice materials.

  2. The local interstellar medium and gamma-ray astronomy

    International Nuclear Information System (INIS)

    Lebrun, F.; Paul, J.

    1985-08-01

    The recent improvement of the calibration of the galaxy counts used as an interstellar-absorption tracer modifies significantly the picture of the local interstellar medium (ISM). Consequently, previous analyses of the γ-ray emission from the local ISM involving galaxy counts have to be revised. In this paper, we consider the implications regarding the cosmic-ray (CR) density in the local ISM, and in particular within Loop I, a nearby supernova remnant (SNR)

  3. On the Importance of High Frequency Gravity Waves for Ice Nucleation in the Tropical Tropopause Layer

    Science.gov (United States)

    Jensen, Eric J.

    2016-01-01

    Recent investigations of the influence of atmospheric waves on ice nucleation in cirrus have identified a number of key processes and sensitivities: (1) ice concentrations produced by homogeneous freezing are strongly dependent on cooling rates, with gravity waves dominating upper tropospheric cooling rates; (2) rapid cooling driven by high-frequency waves are likely responsible for the rare occurrences of very high ice concentrations in cirrus; (3) sedimentation and entrainment tend to decrease ice concentrations as cirrus age; and (4) in some situations, changes in temperature tendency driven by high-frequency waves can quench ice nucleation events and limit ice concentrations. Here we use parcel-model simulations of ice nucleation driven by long-duration, constant-pressure balloon temperature time series, along with an extensive dataset of cold cirrus microphysical properties from the recent ATTREX high-altitude aircraft campaign, to statistically examine the importance of high-frequency waves as well as the consistency between our theoretical understanding of ice nucleation and observed ice concentrations. The parcel-model simulations indicate common occurrence of peak ice concentrations exceeding several hundred per liter. Sedimentation and entrainment would reduce ice concentrations as clouds age, but 1-D simulations using a wave parameterization (which underestimates rapid cooling events) still produce ice concentrations higher than indicated by observations. We find that quenching of nucleation events by high-frequency waves occurs infrequently and does not prevent occurrences of large ice concentrations in parcel simulations of homogeneous freezing. In fact, the high-frequency variability in the balloon temperature data is entirely responsible for production of these high ice concentrations in the simulations.

  4. Reconstructing the post-LGM decay of the Eurasian Ice Sheets with Ice Sheet Models; data-model comparison and focus on the Storfjorden (Svalbard) ice stream dynamics history

    Science.gov (United States)

    Petrini, Michele; Kirchner, Nina; Colleoni, Florence; Camerlenghi, Angelo; Rebesco, Michele; Lucchi, Renata G.; Forte, Emanuele; Colucci, Renato R.

    2017-04-01

    The challenge of reconstructing palaeo-ice sheets past growth and decay represent a critical task to better understand mechanisms of present and future global climate change. Last Glacial Maximum (LGM), and the subsequent deglaciation until Pre-Industrial time (PI) represent an excellent testing ground for numerical Ice Sheet Models (ISMs), due to the abundant data available that can be used in an ISM as boundary conditions, forcings or constraints to test the ISMs results. In our study, we simulate with ISMs the post-LGM decay of the Eurasian Ice Sheets, with a focus on the marine-based Svalbard-Barents Sea-Kara Sea Ice Sheet. In particular, we aim to reconstruct the Storfjorden ice stream dynamics history by comparing the model results with the marine geological data (MSGLs, GZWs, sediment cores analysis) available from the area, e.g., Pedrosa et al. 2011, Rebesco et al. 2011, 2013, Lucchi et al. 2013. Two hybrid SIA/SSA ISMs are employed, GRISLI, Ritz et al. 2001, and PSU, Pollard&DeConto 2012. These models differ mainly in the complexity with which grounding line migration is treated. Climate forcing is interpolated by means of climate indexes between LGM and PI climate. Regional climate indexes are constructed based on the non-accelerated deglaciation transient experiment carried out with CCSM3, Liu et al. 2009. Indexes representative of the climate evolution over Siberia, Svalbard and Scandinavia are employed. The impact of such refined representation as opposed to the common use of the NGRIP δ18O index for transient experiments is analysed. In this study, the ice-ocean interaction is crucial to reconstruct the Storfjorden ice stream dynamics history. To investigate the sensitivity of the ice shelf/stream retreat to ocean temperature, we allow for a space-time variation of basal melting under the ice shelves by testing two-equations implementations based on Martin et al. 2011 forced with simulated ocean temperature and salinity from the TraCE-21ka coupled

  5. Variations in the Peak Position of the 6.2 micron Interstellar Emission Feature: A Tracer of N in the Interstellar Polycyclic Aromatic Hydrocarbon Population

    Science.gov (United States)

    Hudgins, Douglas M.; Bauschlicher, Charles W.; Allamandola, L. J.

    2005-01-01

    This paper presents the results of an investigation of the molecular characteristics that underlie the observed peak position and profile of the nominal 6.2 micron interstellar emission band generally attributed to the CC stretching vibrations of polycyclic aromatic hydrocarbons (PAHs). It begins with a summary of recent experimental and theoretical studies ofthe spectroscopic properties of large (>30 carbon atoms) PAH cations as they relate to this aspect of the astrophysical problem. It then continues with an examination of the spectroscopic properties of a number of PAH variants within the context of the interstellar 6.2 micron emission, beginning with a class of compounds known as polycyclic aromatic nitrogen heterocycles (PANHs; PAHs with one or more nitrogen atoms substituted into their carbon skeleton). In this regard, we summarize the results of recent relevant experimental studies involving a limited set of small PANHs and their cations and then report the results of a comprehensive computational study that extends that work to larger PANH cations including many nitrogen-substituted variants of coronene(+) (C24H12(+)), ovalene(+) (C32H14(+)), circumcoronene(+) (C54H18(+)), and circum-circumcoronene(+) (C96H24(+)). Finally, we report the results of more focused computational studies of selected representatives from a number of other classes of PAH variants that share one or more of the key attributes of the PANH species studied. These alternative classes of PAH variants include (1) oxygen- and silicon-substituted PAH cations; (2) PAH-metal ion complexes (metallocenes) involving the cosmically abundant elements magnesium and iron; and (3) large, asymmetric PAH cations. Overall, the studies reported here demonstrate that increasing PAH size alone is insuEcient to account for the position of the shortest wavelength interstellar 6.2 micron emission bands, as had been suggested by earlier studies. On the other hand, this work reveals that substitution of one or

  6. Sea-ice evaluation of NEMO-Nordic 1.0: a NEMO-LIM3.6-based ocean-sea-ice model setup for the North Sea and Baltic Sea

    Science.gov (United States)

    Pemberton, Per; Löptien, Ulrike; Hordoir, Robinson; Höglund, Anders; Schimanke, Semjon; Axell, Lars; Haapala, Jari

    2017-08-01

    The Baltic Sea is a seasonally ice-covered marginal sea in northern Europe with intense wintertime ship traffic and a sensitive ecosystem. Understanding and modeling the evolution of the sea-ice pack is important for climate effect studies and forecasting purposes. Here we present and evaluate the sea-ice component of a new NEMO-LIM3.6-based ocean-sea-ice setup for the North Sea and Baltic Sea region (NEMO-Nordic). The setup includes a new depth-based fast-ice parametrization for the Baltic Sea. The evaluation focuses on long-term statistics, from a 45-year long hindcast, although short-term daily performance is also briefly evaluated. We show that NEMO-Nordic is well suited for simulating the mean sea-ice extent, concentration, and thickness as compared to the best available observational data set. The variability of the annual maximum Baltic Sea ice extent is well in line with the observations, but the 1961-2006 trend is underestimated. Capturing the correct ice thickness distribution is more challenging. Based on the simulated ice thickness distribution we estimate the undeformed and deformed ice thickness and concentration in the Baltic Sea, which compares reasonably well with observations.

  7. Diffuse interstellar gas in disk galaxies

    International Nuclear Information System (INIS)

    Vladilo, G.

    1989-01-01

    The physical properties of the diffuse gas in our Galaxy are reviewed and considered as a starting point for interstellar (IS) studies of disk galaxies. Attention is focussed on the atomic and ionic component, detected through radio, optical, ultraviolet (UV) and X-ray observations. The cooling and heating processes in the IS gas are briefly recalled in order to introduce current models of disk and halo gas. Observations of nearby galaxies critical to test IS models are considered, including 21-cm surveys, optical and UV absorptions of bright, extragalactic sources, and X-ray emission from hot halos. Finally, further steps necessary to develop a global model for the structure and evolution of the interstellar medium are indicated. (author)

  8. Observations of Carbon Isotopic Fractionation in Interstellar Formaldehyde

    Science.gov (United States)

    Wirstrom, E. S.; Charnley, S. B.; Geppert, W. D.; Persson, C. M.

    2012-01-01

    Primitive Solar System materials (e.g. chondrites. IDPs, the Stardust sample) show large variations in isotopic composition of the major volatiles (H, C, N, and O ) even within samples, witnessing to various degrees of processing in the protosolar nebula. For ex ample. the very pronounced D enhancements observed in IDPs [I] . are only generated in the cold. dense component of the interstellar medium (ISM), or protoplanetary disks, through ion-molecule reactions in the presence of interstellar dust. If this isotopic anomaly has an interstellar origin, this leaves open the possibility for preservation of other isotopic signatures throughout the form ation of the Solar System. The most common form of carbon in the ISM is CO molecules, and there are two potential sources of C-13 fractionation in this reservoir: low temperature chemistry and selective photodissociation. While gas-phase chemistry in cold interstellar clouds preferentially incorporates C-13 into CO [2], the effect of self-shielding in the presence of UV radiation instead leads to a relative enhancement of the more abundant isotopologue, 12CO. Solar System organic material exhibit rather small fluctuations in delta C-13 as compared to delta N-15 and delta D [3][1], the reason for which is still unclear. However, the fact that both C-13 depleted and enhanced material exists could indicate an interstellar origin where the two fractionation processes have both played a part. Formaldehyde (H2CO) is observed in the gas-phase in a wide range of interstellar environments, as well as in cometary comae. It is proposed as an important reactant in the formation of more complex organic molecules in the heated environments around young stars, and formaldehyde polymers have been suggested as the common origin of chondritic insoluable organic matter (IOM) and cometary refractory organic solids [4]. The relatively high gas-phase abundance of H2CO observed in molecular clouds (10(exp- 9) - 10(exp- 8) relative to H2) makes

  9. Gamma rays from the interstellar medium

    International Nuclear Information System (INIS)

    Bloemen, J.B.G.M.

    1985-01-01

    This thesis describes new gamma-ray views on cosmic rays and the interstellar medium. The author describes the COS-B data base and the pre-launch and in-flight calibration data used for all analyses. Diffuse galactic gamma radiation (> 50 MeV) may be either a result of cosmic-ray-matter interactions, or of the cosmic-ray electrons with the interstellar radiation field (mainly at optical and infrared wavelengths), through the inverse-Compton process. A detailed comparison between the gamma-ray observations of the large complex of interstellar clouds in Orion and Monoceros and the CO and HI surveys of this region is given. It gives insight into the cloud penetration of cosmic rays and in the relation between CO detections and molecular hydrogen column densities. Next, the radial distribution of gamma rays in the Galaxy is studied, as well as the galactic centre (more precisely, the central 400 pc), which contains a large concentration of CO molecules. The H 2 /CO abundance and the cosmic-ray density in the galactic centre are discussed and compared to the findings for the galactic disk. In various analyses in this thesis a likelihood-ratio method is applied for parameter estimation and hypothesis testing. A general description of this method is added as an appendix. (Auth.)

  10. Reassigning hydrogen-bond centering in dense ice

    International Nuclear Information System (INIS)

    Benoit, Magali; Romero, Aldo H.; Marx, Dominik

    2002-01-01

    Hydrogen bonds in H 2 O ice change dramatically upon compression. Thereby a hydrogen-bonded molecular crystal, ice VII, is transformed to an atomic crystal, ice X. Car-Parrinello simulations reproduce the features of the x-ray diffraction spectra up to about 170 GPa but allow for analysis in real space. Starting from molecular ice VII with static orientational disorder, dynamical translational disordering occurs first via creation of ionic defects, which results in a systematic violation of the ice rules. As a second step, the transformation to an atomic solid and thus hydrogen-bond centering occurs around 110 GPa at 300 K and no novel phase is found up to at least 170 GPa

  11. Load Shifting and Storage of Cooling Energy through Ice Bank or Ice Slurry Systems: modelling and experimental analysis

    Energy Technology Data Exchange (ETDEWEB)

    Grozdek, Marino

    2009-10-15

    Ice based Cool Thermal Energy Storage (CTES) systems have attracted much attention during last few decades. The reasons are mainly of economical and environmental nature. Compared to conventional refrigeration and air-conditioning systems without cool thermal energy storage, implementation of CTES will increase environmental standards and overall efficiency of the energy systems as it contributes to the phase-out of synthetic refrigerants and reduces peak loads in electricity grids. For the application of a cool thermal energy storages in refrigeration installations and HVAC systems in industry and building sector, it is necessary to have appropriate design tools in order to sufficiently accurate predict their performance. In this thesis theoretical and experimental investigations of two ice based cool thermal energy storage systems, namely static, indirect, external melt, ice-on-coil, i.e. ice bank system and dynamic, ice slurry cool thermal energy storage system are carried out. An ice bank storage technology for cooling purposes is known for a long time. The main drawbacks which are hindering its wider use are the system complexity, high first costs, system efficiency which is highly dependant on design, control and monitoring of the system, etc. On the other hand, ice slurry technology was not well studied until recently, while in the current scientific literature there are still differences between results and conclusions reported by different investigators. The aim of the present thesis is to extend the knowledge in the field of ice based CTES systems, thereby contributing in the development and wider utilization of those systems. In the first part of the thesis a computer application, named 'BankaLeda' is presented. It enables simulation of an ice bank system performance. In order to verify developed simulation model an experimental evaluation has been performed. Field measurements have been conducted on a two module silo which was installed as a

  12. Controls on Arctic sea ice from first-year and multi-year ice survival rates

    Science.gov (United States)

    Armour, K.; Bitz, C. M.; Hunke, E. C.; Thompson, L.

    2009-12-01

    The recent decrease in Arctic sea ice cover has transpired with a significant loss of multi-year (MY) ice. The transition to an Arctic that is populated by thinner first-year (FY) sea ice has important implications for future trends in area and volume. We develop a reduced model for Arctic sea ice with which we investigate how the survivability of FY and MY ice control various aspects of the sea-ice system. We demonstrate that Arctic sea-ice area and volume behave approximately as first-order autoregressive processes, which allows for a simple interpretation of September sea-ice in which its mean state, variability, and sensitivity to climate forcing can be described naturally in terms of the average survival rates of FY and MY ice. This model, used in concert with a sea-ice simulation that traces FY and MY ice areas to estimate the survival rates, reveals that small trends in the ice survival rates explain the decline in total Arctic ice area, and the relatively larger loss of MY ice area, over the period 1979-2006. Additionally, our model allows for a calculation of the persistence time scales of September area and volume anomalies. A relatively short memory time scale for ice area (~ 1 year) implies that Arctic ice area is nearly in equilibrium with long-term climate forcing at all times, and therefore observed trends in area are a clear indication of a changing climate. A longer memory time scale for ice volume (~ 5 years) suggests that volume can be out of equilibrium with climate forcing for long periods of time, and therefore trends in ice volume are difficult to distinguish from its natural variability. With our reduced model, we demonstrate the connection between memory time scale and sensitivity to climate forcing, and discuss the implications that a changing memory time scale has on the trajectory of ice area and volume in a warming climate. Our findings indicate that it is unlikely that a “tipping point” in September ice area and volume will be

  13. Cosmic ray diffusion in a violent interstellar medium

    International Nuclear Information System (INIS)

    Bykov, A.M.; Toptygin, I.N.

    1985-01-01

    A variety of the avaiable observational data on the cosmic ray (CR) spectrum, anisotropy and composition are in good agreement with a suggestion on the diffusion propagation of CR with energy below 10(15) eV in the interstellar medium. The magnitude of the CR diffusion coefficient and its energy dependence are determined by interstellar medium (ISM) magnetic field spectra. Direct observational data on magnetic field spectra are still absent. A theoretical model to the turbulence generation in the multiphase ISM is resented. The model is based on the multiple generation of secondary shocks and concomitant large-scale rarefactions due to supernova shock interactions with interstellar clouds. The distribution function for ISM shocks are derived to include supernova statistics, diffuse cloud distribution, and various shock wave propagation regimes. This permits calculation of the ISM magnetic field fluctuation spectrum and CR diffusion coefficient for the hot phase of ISM

  14. The Ingenious Theory of Interstellar Trade

    Science.gov (United States)

    Radhakrishnan, Arun; Ganapathy, Rohan M.

    This paper extends interplanetary trade theory to an interstellar setting. It is chiefly concerned with the following question: How should interest charges on goods in transit be computed when the goods travel at speeds close to the actual speed of light? This is a problem because the time taken in transit will appear less to an observer travelling with the goods than to a stationary observer. An innovative and ingenious solution is derived from the economic theory, and two useless but TRUE theorems are proved. The interstellar trade would happen in such a way that two time frames must be considered namely that of the stationary observer whose time runs faster compared to the time frame of the observer in transit The interest in a given trade is purely based on the time taken for the debtor to pay the amount, once the goods have been delivered by the seller. But, in case of interstellar trade, the interest to be calculated in between two time frames would lead to the question of which time frame to be considered and moreover, the time taken for the goods to reach the destination is signicantly prolonged compared to the interplanetary trade, which means, even the slightest variations in the interest rate would be magnied. Apart from this, various new factors arise while calculating the interest. The factors include the time value of money, and the risk of variation in demand for goods, the risk of interspace accidents causing loss of the goods and the rate of perish-ability in case of organic goods. The first two factors considered, for which the time frame of the stationary observer is considered and the factors such as the risk of accidents and the rate of perish-ability of the goods are considered based on the time frame of the observer in transit's point of view. The reasons for such considerations and various assumptions on these concepts are dealt in this paper. The theorems that are formulated in this paper would provide the interstellar traders a basic

  15. Nebulae and interstellar matter

    International Nuclear Information System (INIS)

    1987-01-01

    The South African Astronomical Observatory (SAAO) has investigated the IRAS source 1912+172. This source appears to be a young planetary nebula with a binary central star. During 1986 SAAO has also studied the following: hydrogen deficient planetary nebulae; high speed flows in HII regions, and the wavelength dependence of interstellar polarization. 2 figs

  16. Modelling interstellar structures around Vela X-1

    Science.gov (United States)

    Gvaramadze, V. V.; Alexashov, D. B.; Katushkina, O. A.; Kniazev, A. Y.

    2018-03-01

    We report the discovery of filamentary structures stretched behind the bow-shock-producing high-mass X-ray binary Vela X-1 using the SuperCOSMOS H-alpha Survey and present the results of optical spectroscopy of the bow shock carried out with the Southern African Large Telescope. The geometry of the detected structures suggests that Vela X-1 has encountered a wedge-like layer of enhanced density on its way and that the shocked material of the layer partially outlines a wake downstream of Vela X-1. To substantiate this suggestion, we carried out 3D magnetohydrodynamic simulations of interaction between Vela X-1 and the layer for three limiting cases. Namely, we run simulations in which (i) the stellar wind and the interstellar medium (ISM) were treated as pure hydrodynamic flows, (ii) a homogeneous magnetic field was added to the ISM, while the stellar wind was assumed to be unmagnetized, and (iii) the stellar wind was assumed to possess a helical magnetic field, while there was no magnetic field in the ISM. We found that although the first two simulations can provide a rough agreement with the observations, only the third one allowed us to reproduce not only the wake behind Vela X-1, but also the general geometry of the bow shock ahead of it.

  17. Photochirogenesis: Photochemical Models on the Origin of Biomolecular Homochirality

    Directory of Open Access Journals (Sweden)

    Cornelia Meinert

    2010-05-01

    Full Text Available Current research focuses on a better understanding of the origin of biomolecular asymmetry by the identification and detection of the possibly first chiral molecules that were involved in the appearance and evolution of life on Earth. We have reasons to assume that these molecules were specific chiral amino acids. Chiral amino acids have been identified in both chondritic meteorites and simulated interstellar ices. Present research reasons that circularly polarized electromagnetic radiation was identified in interstellar environments and an asymmetric interstellar photon-molecule interaction might have triggered biomolecular symmetry breaking. We review on the possible prebiotic interaction of ‘chiral photons’ in the form of circularly polarized light, with early chiral organic molecules. We will highlight recent studies on enantioselective photolysis of racemic amino acids by circularly polarized light and experiments on the asymmetric photochemical synthesis of amino acids from only one C and one N containing molecules by simulating interstellar environments. Both approaches are based on circular dichroic transitions of amino acids that will be presented as well.

  18. A dirty window diffuse and translucent molecular gas in the interstellar medium

    CERN Document Server

    Magnani, Loris

    2017-01-01

    This book provides an introduction to the physics of interstellar gas in the Galaxy. It deals with the diffuse interstellar medium which supplies a complex environment for exploring the neutral gas content of a galaxy like the Milky Way and the techniques necessary for studying this non-stellar component. After an initial exposition of the phases of the interstellar medium and the role of gas in a spiral galaxy, the authors discuss the transition from atomic to molecular gas. They then consider basic radiative transfer and molecular spectroscopy with particular emphasis on the molecules useful for studying low-density molecular gas. Observational techniques for investigating the gas and the dust component of the diffuse interstellar medium throughout the electromagnetic spectrum are explored emphasizing results from the recent Herschel and Planck missions. A brief exposition on dust in the diffuse interstellar medium is followed by a discussion of molecular clouds in general and high-latitude molecular clouds...

  19. Investigation of land ice-ocean interaction with a fully coupled ice-ocean model: 2. Sensitivity to external forcings

    Science.gov (United States)

    Goldberg, D. N.; Little, C. M.; Sergienko, O. V.; Gnanadesikan, A.; Hallberg, R.; Oppenheimer, M.

    2012-06-01

    A coupled ice stream-ice shelf-ocean cavity model is used to assess the sensitivity of the coupled system to far-field ocean temperatures, varying from 0.0 to 1.8°C, as well as sensitivity to the parameters controlling grounded ice flow. A response to warming is seen in grounding line retreat and grounded ice loss that cannot be inferred from the response of integrated melt rates alone. This is due to concentrated thinning at the ice shelf lateral margin, and to processes that contribute to this thinning. Parameters controlling the flow of grounded ice have a strong influence on the response to sub-ice shelf melting, but this influence is not seen until several years after an initial perturbation in temperatures. The simulated melt rates are on the order of that observed for Pine Island Glacier in the 1990s. However, retreat rates are much slower, possibly due to unrepresented bedrock features.

  20. Northern Alaskan land surface response to reduced Arctic sea ice extent

    Energy Technology Data Exchange (ETDEWEB)

    Higgins, Matthew E. [University of Colorado, Cooperative Institute for Research in Environmental Sciences, Boulder, CO (United States); Cassano, John J. [University of Colorado, Cooperative Institute for Research in Environmental Sciences, Department of Atmospheric and Oceanic Sciences, Boulder, CO (United States)

    2012-05-15

    With Arctic sea ice extent at near-record lows, an improved understanding of the relationship between sea ice and the land surface is warranted. We examine the land surface response to changing sea ice by first conducting a simulation using the Community Atmospheric Model version 3.1 with end of the twenty-first century sea ice extent. This future atmospheric response is then used to force the Weather and Research Forecasting Model version 3.1 to examine the terrestrial land surface response at high resolution over the North Slope of Alaska. Similar control simulations with twentieth century sea ice projections are also performed, and in both simulations only sea ice extent is altered. In the future sea ice extent experiment, atmospheric temperature increases significantly due to increases in latent and sensible heat flux, particularly in the winter season. Precipitation and snow pack increase significantly, and the increased snow pack contributes to warmer soil temperatures for most seasons by insulating the land surface. In the summer, however, soil temperatures are reduced due to increased albedo. Despite warmer near-surface atmospheric temperatures, it is found that spring melt is delayed throughout much of the North Slope due to the increased snow pack, and the growing season length is shortened. (orig.)