WorldWideScience

Sample records for supercooled stratiform cloud

  1. Microphysical Effects of Cloud Seeding in Supercooled Stratiform Clouds Observed from NOAA Satellite

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Based on the satellite retrieval methodology, the spectral characteristics and cloud microphysical properties were analyzed that included brightness temperatures of Channels 4 and 5, and their brightness temperature difference (BTD), the particle effective radius of seeded cloud track caused by an operational cloud seeding and the microphysical effects of cloud seeding were revealed by the comparisons of their differences inside and outside the seeded track. The cloud track was actually a cloud channel reaching 1.5-km deep and 14-km wide lasting for more than 80 min. The effective radius of ambient clouds was 10-15μm, while that within the cloud track ranged from 15 to 26 μm. The ambient clouds were composed of supercooled droplets, and the composition of the cloud within the seeding track was ice. With respect to the rather stable reflectance of two ambient sides around the track, the visible spectral reflectance in the cloud track varied at least 10%, and reached a maximum of 35%, the reflectance of 3.7 μm in the seeded track relatively decreased at least 10%. As cloud seeding advanced, the width and depth were gradually increased. Simultaneously the cloud top temperature within the track became progressively warmer with respect to the ambient clouds,and the maximum temperature differences reached 4.2 and 3.9℃ at the first seeding position for Channels 4 and 5. In addition, the BTD in the track also increased steadily to a maximum of 1.4℃, compared with 0.2-0.4℃ of the ambient clouds. The evidence that the seeded cloud became thinner comes from the visible image showing a channel, the warming of the cloud tops, and the increase of BTD in the seeded track.The seeded cloud became thinner mainly because the cloud top descended and it lost water to precipitation throughout its depth. For this cloud seeding case, the glaciation became apparent at cloud tops about 22min after seeding. The formation of a cloud track in the supercooled stratiform clouds was

  2. Evaluating stratiform cloud base charge remotely

    Science.gov (United States)

    Harrison, R. Giles; Nicoll, Keri A.; Aplin, Karen L.

    2017-06-01

    Stratiform clouds acquire charge at their upper and lower horizontal boundaries due to vertical current flow in the global electric circuit. Cloud charge is expected to influence microphysical processes, but understanding is restricted by the infrequent in situ measurements available. For stratiform cloud bases below 1 km in altitude, the cloud base charge modifies the surface electric field beneath, allowing a new method of remote determination. Combining continuous cloud height data during 2015-2016 from a laser ceilometer with electric field mill data, cloud base charge is derived using a horizontal charged disk model. The median daily cloud base charge density found was -0.86 nC m-2 from 43 days' data. This is consistent with a uniformly charged region 40 m thick at the cloud base, now confirming that negative cloud base charge is a common feature of terrestrial layer clouds. This technique can also be applied to planetary atmospheres and volcanic plumes.Plain Language SummaryThe idea that clouds in the atmosphere can charge electrically has been appreciated since the time of Benjamin Franklin, but it is less widely recognized that it is not just thunderclouds which contain electric charge. For example, water droplets in simple layer clouds, that are abundant and often responsible for an overcast day, carry electric charges. The droplet charging arises at the upper and lower edges of the layer cloud. This occurs because the small droplets at the edges draw charge from the air outside the cloud. Understanding how strongly layer clouds charge is important in evaluating electrical effects on the development of such clouds, for example, how thick the cloud becomes and whether it generates rain. Previously, cloud charge measurement has required direct measurements within the cloud using weather balloons or aircraft. This work has monitored the lower cloud charge continuously using instruments placed at the surface beneath. From measurements made over 2 years, the

  3. Observational evidence of high ice concentration in a shallow convective cloud embedded in stratiform cloud over North China

    Science.gov (United States)

    Yang, Jiefan; Lei, Hengchi; Hou, Tuanjie

    2017-04-01

    In this study we observed the microphysical properties, including the vertical and horizontal distributions of ice particles, liquid water content and ice habit, in different regions of a slightly supercooled stratiform cloud. Using aircraft instrument and radar data, the cloud top temperature was recorded as higher than -15°C, behind a cold front, on 9 September 2015 in North China. During the flight sampling, the high ice number concentration area was located in the supercooled part of a shallow convective cloud embedded in a stratiform cloud, where the ambient temperature was around -3°C. In this area, the maximum number concentrations of particles with diameter greater than 100 μm and 500 μm ( N 100 and N 500) exceeded 300 L-1 and 30 L-1, respectively, and were related to large supercooled water droplets with diameter greater than 24 μm derived from cloud-aerosol spectrometer probe measurements. The ice particles types in this region were predominantly columnar, needle, graupel, and some freezing drops, suggesting that the occurrence of high ice number concentrations was likely related to the Hallett-Mossop mechanism, although many other ice multiplication processes cannot be totally ruled out. The maximum ice number concentration obtained during the first penetration was around two to three orders of magnitude larger than that predicted by the Demott and Fletcher schemes when assuming the cloud top temperature was around -15°C. During the second penetration conducted within the stratiform cloud, N 100 and N 500 decreased by a factor of five to ten, and the presence of columnar and needle-like crystals became very rare.

  4. Aerosol processing in stratiform clouds in ECHAM6-HAM

    Science.gov (United States)

    Neubauer, David; Lohmann, Ulrike; Hoose, Corinna

    2013-04-01

    Aerosol processing in stratiform clouds by uptake into cloud particles, collision-coalescence, chemical processing inside the cloud particles and release back into the atmosphere has important effects on aerosol concentration, size distribution, chemical composition and mixing state. Aerosol particles can act as cloud condensation nuclei. Cloud droplets can take up further aerosol particles by collisions. Atmospheric gases may also be transferred into the cloud droplets and undergo chemical reactions, e.g. the production of atmospheric sulphate. Aerosol particles are also processed in ice crystals. They may be taken up by homogeneous freezing of cloud droplets below -38° C or by heterogeneous freezing above -38° C. This includes immersion freezing of already immersed aerosol particles in the droplets and contact freezing of particles colliding with a droplet. Many clouds do not form precipitation and also much of the precipitation evaporates before it reaches the ground. The water soluble part of the aerosol particles concentrates in the hydrometeors and together with the insoluble part forms a single, mixed, larger particle, which is released. We have implemented aerosol processing into the current version of the general circulation model ECHAM6 (Stevens et al., 2013) coupled to the aerosol module HAM (Stier et al., 2005). ECHAM6-HAM solves prognostic equations for the cloud droplet number and ice crystal number concentrations. In the standard version of HAM, seven modes are used to describe the total aerosol. The modes are divided into soluble/mixed and insoluble modes and the number concentrations and masses of different chemical components (sulphate, black carbon, organic carbon, sea salt and mineral dust) are prognostic variables. We extended this by an explicit representation of aerosol particles in cloud droplets and ice crystals in stratiform clouds similar to Hoose et al. (2008a,b). Aerosol particles in cloud droplets are represented by 5 tracers for the

  5. Daytime Low Stratiform Cloud Detection on AVHRR Imagery

    Directory of Open Access Journals (Sweden)

    Jan Pawel Musial

    2014-06-01

    Full Text Available The near-real time retrieval of low stratiform cloud (LSC coverage is of vital interest for such disciplines as meteorology, transport safety, economy and air quality. Within this scope, a novel methodology is proposed which provides the LSC occurrence probability estimates for a satellite scene. The algorithm is suited for the 1 × 1 km Advanced Very High Resolution Radiometer (AVHRR data and was trained and validated against collocated SYNOP observations. Utilisation of these two combined data sources requires a formulation of constraints in order to discriminate cases where the LSC is overlaid by higher clouds. The LSC classification process is based on six features which are first converted to the integer form by step functions and combined by means of bitwise operations. Consequently, a set of values reflecting a unique combination of those features is derived which is further employed to extract the LSC occurrence probability estimates from the precomputed look-up vectors (LUV. Although the validation analyses confirmed good performance of the algorithm, some inevitable misclassification with other optically thick clouds were reported. Moreover, the comparison against Polar Platform System (PPS cloud-type product revealed superior classification accuracy. From the temporal perspective, the acquired results reported a presence of diurnal and annual LSC probability cycles over Europe.

  6. Two-moment bulk stratiform cloud microphysics in the GFDL AM3 GCM: description, evaluation, and sensitivity tests

    Directory of Open Access Journals (Sweden)

    M. Salzmann

    2010-03-01

    Full Text Available A new stratiform cloud scheme including a two-moment bulk microphysics module, a cloud cover parameterization allowing ice supersaturation, and an ice nucleation parameterization has been implemented into the recently developed GFDL AM3 general circulation model (GCM as part of an effort to treat aerosol-cloud-radiation interactions more realistically. Unlike the original scheme, the new scheme facilitates the study of cloud-ice-aerosol interactions via influences of dust and sulfate on ice nucleation. While liquid and cloud ice water path associated with stratiform clouds are similar for the new and the original scheme, column integrated droplet numbers and global frequency distributions (PDFs of droplet effective radii differ significantly. This difference is in part due to a difference in the implementation of the Wegener-Bergeron-Findeisen (WBF mechanism, which leads to a larger contribution from super-cooled droplets in the original scheme. Clouds are more likely to be either completely glaciated or liquid due to the WBF mechanism in the new scheme. Super-saturations over ice simulated with the new scheme are in qualitative agreement with observations, and PDFs of ice numbers and effective radii appear reasonable in the light of observations. Especially, the temperature dependence of ice numbers qualitatively agrees with in-situ observations. The global average long-wave cloud forcing decreases in comparison to the original scheme as expected when super-saturation over ice is allowed. Anthropogenic aerosols lead to a larger decrease in short-wave absorption (SWABS in the new model setup, but outgoing long-wave radiation (OLR decreases as well, so that the net effect of including anthropogenic aerosols on the net radiation at the top of the atmosphere (netradTOA = SWABS-OLR is of similar magnitude for the new and the original scheme.

  7. Statistical properties of the ice particle distribution in stratiform clouds

    Science.gov (United States)

    Delanoe, J.; Tinel, C.; Testud, J.

    2003-04-01

    This paper presents an extensive analysis of several microphysical data bases CEPEX, EUCREX, CLARE and CARL to determine statistical properties of the Particle Size Distribution (PSD). The data base covers different type of stratiform clouds : tropical cirrus (CEPEX), mid-latitude cirrus (EUCREX) and mid-latitude cirrus and stratus (CARL,CLARE) The approach for analysis uses the concept of normalisation of the PSD developed by Testud et al. (2001). The normalization aims at isolating three independent characteristics of the PSD : its "intrinsic" shape, the "average size" of the spectrum and the ice water content IWC, "average size" is meant the mean mass weighted diameter. It is shown that concentration should be normalized by N_0^* proportional to IWC/D_m^4. The "intrinsic" shape is defined as F(Deq/D_m)=N(Deq)/N_0^* where Deq is the equivalent melted diameter. The "intrinsic" shape is found to be very stable in the range 001.5, more scatter is observed, but future analysis should decide if it is representative of real physical variation or statistical "error" due to counting problem. Considering an overall statistics over the full data base, a large scatter of the N_0^* against Dm plot is found. But in the case of a particular event or a particular leg of a flight, the N_0^* vs. Dm plot is much less scattered and shows a systematic trend for decaying of N_0^* when Dm increases. This trend is interpreted as the manifestation of the predominance of the aggregation process. Finally an important point for cloud remote sensing is investigated : the normalised relationships IWC/N_0^* against Z/N_0^* is much less scattered that the classical IWC against Z the radar reflectivity factor.

  8. Polarized View of Supercooled Liquid Water Clouds

    Science.gov (United States)

    Alexandrov, Mikhail D.; Cairns, Brian; Van Diedenhoven, Bastiaan; Ackerman, Andrew S.; Wasilewski, Andrzej P.; McGill, Matthew J.; Yorks, John E.; Hlavka, Dennis L.; Platnick, Steven E.; Arnold, G. Thomas

    2016-01-01

    Supercooled liquid water (SLW) clouds, where liquid droplets exist at temperatures below 0 C present a well known aviation hazard through aircraft icing, in which SLW accretes on the airframe. SLW clouds are common over the Southern Ocean, and climate-induced changes in their occurrence is thought to constitute a strong cloud feedback on global climate. The two recent NASA field campaigns POlarimeter Definition EXperiment (PODEX, based in Palmdale, California, January-February 2013) and Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS, based in Houston, Texas in August- September 2013) provided a unique opportunity to observe SLW clouds from the high-altitude airborne platform of NASA's ER-2 aircraft. We present an analysis of measurements made by the Research Scanning Polarimeter (RSP) during these experiments accompanied by correlative retrievals from other sensors. The RSP measures both polarized and total reflectance in 9 spectral channels with wavelengths ranging from 410 to 2250 nm. It is a scanning sensor taking samples at 0.8deg intervals within 60deg from nadir in both forward and backward directions. This unique angular resolution allows for characterization of liquid water droplet size using the rainbow structure observed in the polarized reflectances in the scattering angle range between 135deg and 165deg. Simple parametric fitting algorithms applied to the polarized reflectance provide retrievals of the droplet effective radius and variance assuming a prescribed size distribution shape (gamma distribution). In addition to this, we use a non-parametric method, Rainbow Fourier Transform (RFT),which allows retrieval of the droplet size distribution without assuming a size distribution shape. We present an overview of the RSP campaign datasets available from the NASA GISS website, as well as two detailed examples of the retrievals. In these case studies we focus on cloud fields with spatial features

  9. Polarized View of Supercooled Liquid Water Clouds

    Science.gov (United States)

    Alexandrov, Mikhail D.; Cairns, Brian; Van Diedenhoven, Bastiaan; Ackerman, Andrew S.; Wasilewski, Andrzej P.; McGill, Matthew J.; Yorks, John E.; Hlavka, Dennis L.; Platnick, Steven E.; Arnold, G. Thomas

    2016-01-01

    Supercooled liquid water (SLW) clouds, where liquid droplets exist at temperatures below 0 C present a well known aviation hazard through aircraft icing, in which SLW accretes on the airframe. SLW clouds are common over the Southern Ocean, and climate-induced changes in their occurrence is thought to constitute a strong cloud feedback on global climate. The two recent NASA field campaigns POlarimeter Definition EXperiment (PODEX, based in Palmdale, California, January-February 2013) and Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS, based in Houston, Texas in August- September 2013) provided a unique opportunity to observe SLW clouds from the high-altitude airborne platform of NASA's ER-2 aircraft. We present an analysis of measurements made by the Research Scanning Polarimeter (RSP) during these experiments accompanied by correlative retrievals from other sensors. The RSP measures both polarized and total reflectance in 9 spectral channels with wavelengths ranging from 410 to 2250 nm. It is a scanning sensor taking samples at 0.8deg intervals within 60deg from nadir in both forward and backward directions. This unique angular resolution allows for characterization of liquid water droplet size using the rainbow structure observed in the polarized reflectances in the scattering angle range between 135deg and 165deg. Simple parametric fitting algorithms applied to the polarized reflectance provide retrievals of the droplet effective radius and variance assuming a prescribed size distribution shape (gamma distribution). In addition to this, we use a non-parametric method, Rainbow Fourier Transform (RFT),which allows retrieval of the droplet size distribution without assuming a size distribution shape. We present an overview of the RSP campaign datasets available from the NASA GISS website, as well as two detailed examples of the retrievals. In these case studies we focus on cloud fields with spatial features

  10. Factors controlling cloud microphysics, precipitation rate, and brightness temperature of tropical convective and stratiform clouds

    Science.gov (United States)

    Hashino, T.; Casella, D.; Mugnai, A.; Sano, P.; Smith, E. A.; Tripoli, G.

    2008-12-01

    This paper discusses factors controlling cloud microphysics, precipitation rate and brightness temperature of tropical convective and stratiform clouds. Tropical convective and stratiform clouds are important in radiative forcing of climates and distribution of precipitation over the ocean. The possible effects of climate change on these clouds are still not well understood. Recent studies show that the higher CCN concentration in a convective cloud can lead to more vigorous updrafts and a higher evaporation/precipitation ratio. The stronger updraft often means stronger downdraft and gust fronts, which can trigger convection nearby. This implies that increases in CCN concentration can result in an increase in area coverage and persistence of tropical cirrus and stratiform clouds. The increased cloudiness would then be expected to lower sensible and latent heat flux from the ocean by lowering sea surface temperature, affecting the future development of convective clouds. The sea surface temperature may also change in a local area due to change of ocean circulation in climate change scenarios. Satellite remote sensing is a powerful tool to study tropical and global precipitation distribution. Many physically-based passive-microwave (MW) satellite precipitation algorithms make use of cloud radiation databases (CRDs), which typically consist of microphysical profiles from cloud resolving model (CRMs) and simulated MW brightness temperature (Tb). Thus, it is important to validate Tb simulated by a CRM against the observed Tb. Also, it is important to study how any changes in the tropical clouds due to aerosols and sea surface temperature translate into the precipitation and brightness temperature. The case study chosen is KWAJEX campaign that took place from 23 July to 14 September 1999. Authors have developed microphysical physical framework (Advanced Microphysics Prediction System) to predict ice particle properties explicitly in a CRM (University of Wisconsin

  11. Evaluation of a stratiform cloud parameterization for general circulation models

    Energy Technology Data Exchange (ETDEWEB)

    Ghan, S.J.; Leung, L.R. [Pacific Northwest National Lab., Richland, WA (United States); McCaa, J. [Univ. of Washington, Seattle, WA (United States)

    1996-04-01

    To evaluate the relative importance of horizontal advection of cloud versus cloud formation within the grid cell of a single column model (SCM), we have performed a series of simulations with our SCM driven by a fixed vertical velocity and various rates of horizontal advection.

  12. Entrainment, Drizzle, and the Indirect Effect in Stratiform Clouds

    Science.gov (United States)

    Ackerman, Andrew

    2005-01-01

    Activation of some fraction of increased concentrations of sub-micron soluble aerosol particles lead to enhanced cloud droplet concentrations and hence smaller droplets, increasing their total cross sectional area and thus reflecting solar radiation more efficiently (the Twomey, or first indirect, effect). However, because of competition during condensational growth, droplet distributions tend to broaden as numbers increase, reducing the sensitivity of cloud albedo to droplet concentration on the order of 10%. Also, smaller droplets less effectively produce drizzle through collisions and coalescence, and it is widely expected (and found in large-scale models) that decreased precipitation leads to clouds with more cloud water on average (the so-called cloud lifetime, or second indirect, effect). Much of the uncertainty regarding the overall indirect aerosol effect stems from inadequate understanding of such changes in cloud water. Detailed simulations based on FIRE-I, ASTEX, and DYCOMS-II conditions show that suppression of precipitation from increased droplet concentrations leads to increased cloud water only when sufficient precipitation reaches the surface, a condition favored when the overlying air is-humid or droplet concentrations are very low. Otherwise, aerosol induced suppression of precipitation enhances entrainment of overlying dry air, thereby reducing cloud water and diminishing the indirect climate forcing.

  13. Investigation of riming within mixed-phase stratiform clouds using Weather Research and Forecasting (WRF) model

    Science.gov (United States)

    Hou, Tuanjie; Lei, Hengchi; Yang, Jiefan; Hu, Zhaoxia; Feng, Qiujuan

    2016-09-01

    In this study, we investigated stratiform precipitation associated with an upper-level westerly trough and a cold front over northern China between 30 Apr. and 1 May 2009. We employed the Weather Research and Forecasting (WRF) model (version 3.4.1) to perform high-resolution numerical simulations of rainfall. We also conducted simulations with two microphysics schemes and sensitivity experiments without riming of snow and changing cloud droplet number concentrations (CDNCs) to determine the effect of snow riming on cloud structure and precipitation. Then we compared our results with CloudSat, Doppler radar and rain gauge observations. The comparison with the Doppler radar observations suggested that the WRF model was quite successful in capturing the timing and location of the stratiform precipitation region. Further comparisons with the CloudSat retrievals suggested that both microphysics schemes overestimated ice and liquid water contents. The sensitivity experiments without riming of snow suggested that the presence or absence of riming significantly influenced the precipitation distribution, but only slightly affected total accumulated precipitation. Without riming of snow, the changes of updrafts from the two microphysics schemes were different due to a different consideration of ice particle capacitance and latent heat effect of riming on deposition. While sensitivity experiments with three different CDNC values of 100, 250 and 1000 cm- 3 suggested variations in snow riming rates, changing CDNC had little impact on precipitation.

  14. Numerical study for production of space charge within the stratiform cloud

    Indian Academy of Sciences (India)

    A K Srivastava; S N Tripathi

    2010-10-01

    One dimensional numerical model has been developed to predict the production of space charge and variations in other electrical parameters within the low level stratiform type of cloud having very weak vertical motion.Non-linear coupled differential equations which govern ion concentrations,charged and neutral droplet concentrations and electric field were used.Symmetry has been observed in all the electrical parameters within the cloud.The magnitude of average positive ion concentrations was observed to be high as compared to the negative ion concentrations,which is due to low scavenging rate of positive ions than the negative ions,highly attributed to their mobilities.The rate of scavenging of ions affects the concentration of charged droplets,which eventually influence the electric field and thus the space charge density within the cloud.Maximum electric field (max) was observed at middle of the cloud whereas minimum was observed at both the edges of the cloud.Minimum electric field (min) was found to be equal and constant (∼27Vm−1)for any drop concentration.Net positive and negative space charges were observed at the top and bottom of the cloud,respectively.The simulated results show some discrepancies to the natural condition, which are due to simulations made under some basic assumptions and limitations and that will be incorporated in the future studies for natural cloud condition.

  15. Dependency of stratiform precipitation on a two-moment cloud microphysical scheme in mid-latitude squall line

    Science.gov (United States)

    Baba, Yuya; Takahashi, Keiko

    2014-03-01

    Dependency of stratiform precipitation on a two-moment cloud microphysical scheme in mid-latitude squall line is investigated, using full one-moment, full two-moment and partial two-moment schemes. The results show that the effect of two-moment scheme for rain is consistent with those presented in preceding studies, but the effect is found to be dependent on two-moment scheme for ice water species (ice particles) which enhanced detrainment in convective region and increased rearward buoyancy fluxes. Use of the two-moment scheme for cloud water and cloud ice is found to have less direct impact on the formation of stratiform precipitation, but indirectly affects the precipitation by changing source number concentration of large liquid and ice particles. Two-moment treatment for graupel rather than snow is also found to have great impact on stratiform precipitation through the melting process. The horizontally narrow and vertically gradual graupel melting profile originated from its size distribution change causes suppression to the convective updraft in convective region, and thus increases horizontal rearward buoyancy from the convective to stratiform regions with enhanced growth of ice water species, resulting in an increase in stratiform precipitation. To simulate these features, two-moment treatment for graupel or diagnostic model for graupel intercept parameter considering size distribution change is required.

  16. Minimalist model of ice microphysics in mixed-phase stratiform clouds

    Science.gov (United States)

    Yang, F.; Ovchinnikov, M.; Shaw, R. A.

    2013-12-01

    The question of whether persistent ice crystal precipitation from supercooled layer clouds can be explained by time-dependent, stochastic ice nucleation is explored using an approximate, analytical model and a large-eddy simulation (LES) cloud model. The updraft velocity in the cloud defines an accumulation zone, where small ice particles cannot fall out until they are large enough, which will increase the residence time of ice particles in the cloud. Ice particles reach a quasi-steady state between growth by vapor deposition and fall speed at cloud base. The analytical model predicts that ice water content (wi) has a 2.5 power-law relationship with ice number concentration (ni). wi and ni from a LES cloud model with stochastic ice nucleation confirm the 2.5 power-law relationship, and initial indications of the scaling law are observed in data from the Indirect and Semi-Direct Aerosol Campaign. The prefactor of the power law is proportional to the ice nucleation rate and therefore provides a quantitative link to observations of ice microphysical properties. Ice water content (wi) and ice number concentration (ni) relationship from LES. a and c: Accumulation zone region; b and d: Selective accumulation zone region. Black lines in c and d are best fitted 2.5 slope lines. Colors in Figures a and b represent updraft velocity, while colors in c and d represent altitude. The cloud base and top are at about 600 m and 800 m, respectively. Ice water content (wi) and ice number concentration (ni) relationship for two ice nucleation rates. Blue points are from LES with low ice nucleation rate and red points with high ice nucleation rate. Solid and dashed lines are best fitted 2.5 slope lines.

  17. Influence of Subpixel Scale Cloud Top Structure on Reflectances from Overcast Stratiform Cloud Layers

    Science.gov (United States)

    Loeb, N. G.; Varnai, Tamas; Winker, David M.

    1998-01-01

    Recent observational studies have shown that satellite retrievals of cloud optical depth based on plane-parallel model theory suffer from systematic biases that depend on viewing geometry, even when observations are restricted to overcast marine stratus layers, arguably the closest to plane parallel in nature. At moderate to low sun elevations, the plane-parallel model significantly overestimates the reflectance dependence on view angle in the forward-scattering direction but shows a similar dependence in the backscattering direction. Theoretical simulations are performed that show that the likely cause for this discrepancy is because the plane-parallel model assumption does not account for subpixel, scale variations in cloud-top height (i.e., "cloud bumps"). Monte Carlo simulation, comparing ID model radiances to radiances from overcast cloud field with 1) cloud-top height variation, but constant cloud volume extinction; 2) flat tops but horizontal variations in cloud volume extinction; and 3) variations in both cloud top height and cloud extinction are performed over a approximately equal to 4 km x 4 km domain (roughly the size of an individual GAC AVHRR pixel). The comparisons show that when cloud-top height variations are included, departures from 1D theory are remarkably similar (qualitatively) to those obtained observationally. In contrast, when clouds are assumed flat and only cloud extinction is variable, reflectance differences are much smaller and do not show any view-angle dependence. When both cloud-top height and cloud extinction variations are included, however, large increases in cloud extinction variability can enhance reflectance difference. The reason 3D-1D reflectance differences are more sensitive to cloud-top height variations in the forward-scattering direction (at moderate to low, sun elevations) is because photons leaving the cloud field in that direction experience fewer scattering events (low-order scattering) and are restricted to the

  18. Radiative consequences of low-temperature infrared refractive indices for supercooled water clouds

    Directory of Open Access Journals (Sweden)

    P. M. Rowe

    2013-07-01

    Full Text Available Simulations of cloud radiative properties for climate modeling and remote sensing rely on accurate knowledge of the complex refractive index (CRI of water. Although conventional algorithms employ a temperature independent assumption (TIA, recent infrared measurements of supercooled water have demonstrated that the CRI becomes increasingly ice-like at lower temperatures. Here, we assess biases that result from ignoring this temperature dependence. We show that TIA-based cloud retrievals introduce spurious ice into pure, supercooled clouds, or underestimate cloud thickness and droplet size. TIA-based downwelling radiative fluxes are lower than those for the temperature-dependent CRI by as much as 1.7 W m−2 (in cold regions, while top-of-atmosphere fluxes are higher by as much as 3.4 W m−2 (in warm regions. Proper accounting of the temperature dependence of the CRI, therefore, leads to significantly greater local greenhouse warming due to supercooled clouds than previously predicted. The current experimental uncertainty in the CRI at low temperatures must be reduced to properly account for supercooled clouds in both climate models and cloud property retrievals.

  19. Radiative consequences of low-temperature infrared refractive indices for supercooled water clouds

    Directory of Open Access Journals (Sweden)

    P. M. Rowe

    2013-12-01

    Full Text Available Simulations of cloud radiative properties for climate modeling and remote sensing rely on accurate knowledge of the complex refractive index (CRI of water. Although conventional algorithms employ a temperature-independent assumption (TIA, recent infrared measurements of supercooled water have demonstrated that the CRI becomes increasingly ice-like at lower temperatures. Here, we assess biases that result from ignoring this temperature dependence. We show that TIA-based cloud retrievals introduce spurious ice into pure, supercooled clouds, or underestimate cloud optical thickness and droplet size. TIA-based downwelling radiative fluxes are lower than those for the temperature-dependent CRI by as much as 1.7 W m−2 (in cold regions, while top-of-atmosphere fluxes are higher by as much as 3.4 W m−2 (in warm regions. Proper accounting of the temperature dependence of the CRI, therefore, leads to significantly greater local greenhouse warming due to supercooled clouds than previously predicted. The current experimental uncertainty in the CRI at low temperatures must be reduced to account for supercooled clouds properly in both climate models and cloud-property retrievals.

  20. Two-moment Bulk Stratiform Cloud Microphysics in the Grid-point Atmospheric Model of IAP LASG (GAMIL)

    Institute of Scientific and Technical Information of China (English)

    SHI Xiangjun; WANG Bin; Xiaohong LIU; Minghuai WANG

    2013-01-01

    A two-moment bulk stratiform microphysics scheme,including recently developed physically-based droplet activation/ice nucleation parameterizations has been implemented into the Grid-point Atmospheric Model of IAP LASG (GAMIL) as an effort to enhance the model's capability to simulate aerosol indirect effects.Unlike the previous one-moment cloud microphysics scheme,the new scheme produces a reasonable representation of cloud particle size and number concentration.This scheme captures the observed spatial variations in cloud droplet number concentrations.Simulated ice crystal number concentrations in cirrus clouds qualitatively agree with in situ observations.The longwave and shortwave cloud forcings are in better agreement with observations.Sensitivity tests show that the column cloud droplet number concentrations calculated from two different droplet activation parameterizations are similar.However,ice crystal number concentration in mixed-phased clouds is sensitive to different heterogeneous ice nucleation formulations.The simulation with high ice crystal number concentration in mixed-phase clouds has less liquid water path and weaker cloud forcing.Furthermore,ice crystal number concentration in cirrus clouds is sensitive to different ice nucleation parameterizations.Sensitivity tests also suggest that the impact of pre-existing ice crystals on homogeneous freezing in old clouds should be taken into account.

  1. Numerical Simulation of Effects of Cloud Top Temperatures and Generating Cells on Secondary Ice Production in Stratiform Clouds with a Detailed Microphysical Model

    Institute of Scientific and Technical Information of China (English)

    2012-01-01

    This paper outlines a one-dimensional,heightdependent bin model with detailed microphysical processes in which ice splinters are produced by a riming process.The model is then applied to simulate the shift of particle size distribution effected by the secondary ice production process within clouds with different generating cells and cloud top temperatures.The result of model simulations reveals the general effects of cloud updrafts on increasing ice particle concentration by extending the residence time of ice particles in clouds and providing sufficiently large supercooled water droplets.The rimesplintering mechanism is more effective in clouds with lower ice seeding rates than those with higher rates.Evolutions of hydrometeor size distribution triggered by the rime-splintering mechanism indicate that the interaction between large ice particles and supercooled water drops adds a "second maximum" to the primary ice spectra.

  2. Comparison Between Computer Simulation of Transport and Diffusion of Cloud Seeding Material Within Stratiform Cloud and the NOAA-14 Satellite Cloud Track

    Institute of Scientific and Technical Information of China (English)

    YU Xing; DAI Jin; LEI Hengchi; FAN Peng

    2005-01-01

    A precipitation enhancement operation using an aircraft was conducted from 1415 to 1549 LST 14 March 2000 in Shaanxi Province. The NOAA-14 satellite data received at 1535 LST soon after the cloud seeding shows that a vivid cloud track appears on the satellite image. The length, average width and maximum width of the cloud track are 301 km, 8.3 and 11 km, respectively. Using a three-dimensional numerical model of transport and diffusion of seeding material within stratiform clouds, the spatial concentration distribution characteristics of seeding material at different times, especially at the satellite receiving time,are simulated. The model results at the satellite receiving time are compared with the features of the cloud track. The transported position of the cloud seeding material coincides with the position of the track. The width, shape and extent of diffusion of the cloud seeding material are similar to that of the cloud track.The spatial variation of width is consistent with that of the track. The simulated length of each segment of the seeding line accords with the length of every segment of the track. Each segment of the cloud track corresponds to the transport and diffusion of each segment of the seeding line. These results suggest that the cloud track is the direct physical reflection of cloud seeding at the cloud top. The comparison demonstrates that the numerical model of transport and diffusion can simulate the main characteristics of transport and diffusion of seeding material, and the simulated results are sound and trustworthy. The area, volume, width, depth, and lateral diffusive rate corresponding to concentrations 1, 4, and 10 L-1are simulated in order to understand the variations of influencing range.

  3. Measuring ice and liquid water content in moderately supercooled clouds with Cloudnet

    Science.gov (United States)

    Bühl, Johannes; Seifert, Patric; Myagkov, Alexander; Albert, Ansmann

    2016-04-01

    The interaction between ice nuclei and clouds is an important topic in weather and climate research. Recent laboratory experiments and field in-situ field campaigns present more and more detailed measurements of ice nucleating particles (INP) at temperatures close to 0°C. This brings moderately supercooled mixed-phase clouds into the focus of current cloud research. One current example is the European Union BACCHUS project. A major goal of BACCHUS is the analysis of the anthropogenic impact on ice nucleation. Within this project, we use the Leipzig Aerosol Cloud Remote Observations System (LACROS) and the Cloudnet framework in order to get quantitative insight into the formation of ice in mixed-phase layered clouds with cloud top temperature (CTT) from -40 to 0°C. Depolarization measurements from lidar and radar show a clear dependence between particle shape and the temperature under which the particles have been formed. The special focus of this work is on the CTT range from -10 to 0°C. An algorithm is presented to decide between ice and liquid water precipitation falling from the clouds showing that between 10% and 30% of all layered clouds show ice precipitation with CTT between -5 and 0°C. For these slightly supercooled clouds an average ice-water-content between 10e-7 and 10e-8 [kg per cubic meter] is found.

  4. A statistical subgrid-scale algorithm for precipitation formation in stratiform clouds in the ECHAM5 single column model

    Directory of Open Access Journals (Sweden)

    S. Jess

    2011-03-01

    Full Text Available Cloud properties are usually assumed to be homogeneous within the cloudy part of the grid-box, i.e. subgrid-scale inhomogeneities in cloud cover and/or microphysical properties are often neglected. However, precipitation formation is initiated by large particles. Thus mean values are not representative and could lead to a delayed onset of precipitation.

    For a more physical description of the subgrid-scale structure of clouds we introduce a new statistical sub-column algorithm to study the impact of cloud inhomogeneities on stratiform precipitation. Each model column is divided into N independent sub-columns with sub-boxes in each layer, which are completely clear or cloudy. The cloud cover is distributed over the sub-columns depending on the diagnosed cloud fraction. Mass and number concentrations of cloud droplets and ice crystals are distributed randomly over the cloudy sub-columns according to prescribed probability distributions. Shapes and standard deviations of the distributions are obtained from aircraft observations.

    We have implemented this sub-column algorithm into the ECHAM5 global climate model to take subgrid variability of cloud cover and microphysical properties into account. Simulations with the Single Column Model version of ECHAM5 were carried out for one period of the Mixed-Phase Polar Arctic Cloud Experiment (MPACE campaign as well as for the Eastern Pacific Investigation of climate Processes (EPIC campaign. Results with the new algorithm show an earlier onset of precipitation for the EPIC campaign and a higher conversion of liquid to ice for the MPACE campaign, which reduces the liquid water path in better agreement with the observations than the original version of the ECHAM5 model.

  5. Numerical simulation on microphysical mechanism of stratiform cloud precipitation in Hebei province%河北一次层状云系降水的微物理机制数值模拟与分析

    Institute of Scientific and Technical Information of China (English)

    王秀娟; 姜忠宝; 杨洁帆; 夏葳; 张超

    2014-01-01

    Microphysical structures and precipitation process of a stratiform cloud on May 1 ,2009 in middle-east of China were analyzed by a one-dimensional stratiform cloud model.The results indicate that this precipitation process is caused by stratiform cloud,and the vertical structure of stratiform cloud is consistent with Koo Chen-Chao′s three-layer cloud conceptual model and “seeder-feeder”cloud mechanism.In the first layer (upper layer from 4.7 km to 7.0 km),there are ice crystal particles and snowflake,and the latter is formed in the way of subli-mation and automatical conversion from ice crystal.In the second layer (middle layer from 2.6 km to 4.6 km), there are ice crystal particles,snowflake,graupel,supercooled water droplets and rain droplets,and they are influ-enced significantly by the Bergeron process.In the third layer (lower layer from 1.3 km to 2.5 km),there are mainly cloud droplets,rain droplets,the melting snow droplets and graupel droplets from upper layers.The graupel droplets contribute greatly to the formation of rain droplets.When the cloud system develops maturely,there is a certain“seeder-feeder”relationship among the different layers.For example,the first layer supplies snow and ice crystal parti-cles to the top of the second layer and the second layer sends graupel and snow particles to the top of the third layer.%利用一维层状云模式,详细分析了2009年5月1日中国中东部地区一次层状云系的微物理结构和降水过程。结果表明:此次降水为层状云系降水,云系垂直结构符合顾震潮3层概念模型和“播种云-供给云”机制,其中第一层(上层:4.7-7.0 km)存在冰雪晶,雪主要通过冰晶自动转化和凝华增长;第二层(中层:2.6-4.6 km)有冰晶、雪、霰、云水和雨滴,此层贝吉龙过程作用明显;第三层(下层:1.3-2.5 km)主要粒子为云滴、雨滴及从上层融化的雪和霰,霰的融化对雨滴的形成贡献最大

  6. Analysis of Cloud-resolving Simulations of a Tropical Mesoscale Convective System Observed during TWP-ICE: Vertical Fluxes and Draft Properties in Convective and Stratiform Regions

    Energy Technology Data Exchange (ETDEWEB)

    Mrowiec, Agnieszka A.; Rio, Catherine; Fridlind, Ann; Ackerman, Andrew; Del Genio, Anthony D.; Pauluis, Olivier; Varble, Adam; Fan, Jiwen

    2012-10-02

    We analyze three cloud-resolving model simulations of a strong convective event observed during the TWP-ICE campaign, differing in dynamical core, microphysical scheme or both. Based on simulated and observed radar reflectivity, simulations roughly reproduce observed convective and stratiform precipitating areas. To identify the characteristics of convective and stratiform drafts that are difficult to observe but relevant to climate model parameterization, independent vertical wind speed thresholds are calculated to capture 90% of total convective and stratiform updraft and downdraft mass fluxes. Convective updrafts are fairly consistent across simulations (likely owing to fixed large-scale forcings and surface conditions), except that hydrometeor loadings differ substantially. Convective downdraft and stratiform updraft and downdraft mass fluxes vary notably below the melting level, but share similar vertically uniform draft velocities despite differing hydrometeor loadings. All identified convective and stratiform downdrafts contain precipitation below ~10 km and nearly all updrafts are cloudy above the melting level. Cold pool properties diverge substantially in a manner that is consistent with convective downdraft mass flux differences below the melting level. Despite differences in hydrometeor loadings and cold pool properties, convective updraft and downdraft mass fluxes are linearly correlated with convective area, the ratio of ice in downdrafts to that in updrafts is ~0.5 independent of species, and the ratio of downdraft to updraft mass flux is ~0.5-0.6, which may represent a minimum evaporation efficiency under moist conditions. Hydrometeor loading in stratiform regions is found to be a fraction of hydrometeor loading in convective regions that ranges from ~10% (graupel) to ~90% (cloud ice). These findings may lead to improved convection parameterizations.

  7. The impact of humidity above stratiform clouds on indirect aerosol climate forcing.

    Science.gov (United States)

    Ackerman, Andrew S; Kirkpatrick, Michael P; Stevens, David E; Toon, Owen B

    2004-12-23

    Some of the global warming from anthropogenic greenhouse gases is offset by increased reflection of solar radiation by clouds with smaller droplets that form in air polluted with aerosol particles that serve as cloud condensation nuclei. The resulting cooling tendency, termed the indirect aerosol forcing, is thought to be comparable in magnitude to the forcing by anthropogenic CO2, but it is difficult to estimate because the physical processes that determine global aerosol and cloud populations are poorly understood. Smaller cloud droplets not only reflect sunlight more effectively, but also inhibit precipitation, which is expected to result in increased cloud water. Such an increase in cloud water would result in even more reflective clouds, further increasing the indirect forcing. Marine boundary-layer clouds polluted by aerosol particles, however, are not generally observed to hold more water. Here we simulate stratocumulus clouds with a fluid dynamics model that includes detailed treatments of cloud microphysics and radiative transfer. Our simulations show that the response of cloud water to suppression of precipitation from increased droplet concentrations is determined by a competition between moistening from decreased surface precipitation and drying from increased entrainment of overlying air. Only when the overlying air is humid or droplet concentrations are very low does sufficient precipitation reach the surface to allow cloud water to increase with droplet concentrations. Otherwise, the response of cloud water to aerosol-induced suppression of precipitation is dominated by enhanced entrainment of overlying dry air. In this scenario, cloud water is reduced as droplet concentrations increase, which diminishes the indirect climate forcing.

  8. Uncertainty in stratiform cloud optical thickness inferred from pyranometer measurements at the sea surface

    Directory of Open Access Journals (Sweden)

    Anna Rozwadowska

    2004-06-01

    Full Text Available The relative "plane-parallel" error in a mean cloud optical thickness retrieved from ground-based pyranometer measurements is estimated. The plane-parallel error is defined as the bias introduced by the assumption in the radiative transfer model used in cloud optical thickness retrievals that the atmosphere, including clouds, is horizontally homogeneous on the scale of an individual retrieval. The error is estimated for the optical thickness averaged over the whole domain, which simulates the mean cloud optical thickness obtained from a time series of irradiance measurements. The study is based on 3D Monte Carlo radiative transfer simulations for non-absorbing, all-liquid, layer clouds. Liquid water path distributions in the clouds are simulated by a bounded cascade fractal model. The sensitivity of the error is studied with respect to the following factors: averaging time of irradiance used in an individual retrieval, mean cloud optical thickness, cloud variability, cloud base height and solar zenith angle. In the simulations presented in this paper, the relative bias in the domain averaged cloud optical thickness retrieved from pyranometer measurements varies from +1% for optically thin clouds to nearly -20%. The highest absolute value of the relative bias is expected for thick and variable clouds with high bases (e.g. 1 km and retrievals based on long-term mean irradiances (averaging time of the order of several tens of minutes or hours. The bias can be diminished by using short-term irradiance averages, e.g. of one minute, and by limiting retrievals to low-level clouds.

  9. The Impact of humidity above stratiform clouds on indirect aerosol climate forcing

    Energy Technology Data Exchange (ETDEWEB)

    Ackerman, A S; Kirkpatrick, M P; Stevens, D E; Toon, O B

    2004-12-20

    Some of the global warming effect of anthropogenic greenhouse gases is offset by increased solar reflection from clouds with smaller droplets that form on increased numbers of cloud condensation nuclei in polluted air. The global magnitude of the resulting indirect aerosol climate forcing is estimated to be comparable (and opposed) to the anthropogenic carbon dioxide forcing, but estimates are highly uncertain because of complexities in characterizing the physical process that determine global aerosol and cloud populations and their interactions. Beyond reflecting sunlight more effectively, smaller droplets are less efficient at producing precipitation, and decreased precipitation is expected to result in increased cloud water and cloud cover, further increasing the indirect forcing. Yet polluted marine boundary-layer clouds are not generally observed to hold more water. Here we use model simulations of stratocumulus clouds to show that suppression of precipitation from increased droplet concentrations leads to increased cloud water only when sufficient precipitation reaches the surface, a condition favored when the overlying air is moist. Otherwise, aerosol induced suppression of precipitation enhances entrainment of overlying dry air, thereby reducing cloud water and diminishing the indirect climate forcing.

  10. Icing Characteristics of Low Altitude, Supercooled Layer Clouds. Revision

    Science.gov (United States)

    1980-05-01

    Buffalo (BUF), NY, the upper layer appeared to be cirrus or cirro- stratus which provided about 30% sky cover in the two northern quadrants at this time...Aircraft still below cloud base at this altitude and position 13 mi south of BUF at the completion of the final data run for the day. Aircraft starL - ing...Otherwise the sky was cloudless with good ve;tical and horizontal visibility during the transit into Ohio. At about 1530 E.S.T., near Belleaire, Ohio, the

  11. Detection of supercooled liquid water-topped mixed-phase clouds >from shortwave-infrared satellite observations

    Science.gov (United States)

    NOH, Y. J.; Miller, S. D.; Heidinger, A. K.

    2015-12-01

    Many studies have demonstrated the utility of multispectral information from satellite passive radiometers for detecting and retrieving the properties of cloud globally, which conventionally utilizes shortwave- and thermal-infrared bands. However, the satellite-derived cloud information comes mainly from cloud top or represents a vertically integrated property. This can produce a large bias in determining cloud phase characteristics, in particular for mixed-phase clouds which are often observed to have supercooled liquid water at cloud top but a predominantly ice phase residing below. The current satellite retrieval algorithms may report these clouds simply as supercooled liquid without any further information regarding the presence of a sub-cloud-top ice phase. More accurate characterization of these clouds is very important for climate models and aviation applications. In this study, we present a physical basis and preliminary results for the algorithm development of supercooled liquid-topped mixed-phase cloud detection using satellite radiometer observations. The detection algorithm is based on differential absorption properties between liquid and ice particles in the shortwave-infrared bands. Solar reflectance data in narrow bands at 1.6 μm and 2.25 μm are used to optically probe below clouds for distinction between supercooled liquid-topped clouds with and without an underlying mixed phase component. Varying solar/sensor geometry and cloud optical properties are also considered. The spectral band combination utilized for the algorithm is currently available on Suomi NPP Visible/Infrared Imaging Radiometer Suite (VIIRS), Himawari-8 Advanced Himawari Imager (AHI), and the future GOES-R Advance Baseline Imager (ABI). When tested on simulated cloud fields from WRF model and synthetic ABI data, favorable results were shown with reasonable threat scores (0.6-0.8) and false alarm rates (0.1-0.2). An ARM/NSA case study applied to VIIRS data also indicated promising

  12. Discrimination of micrometre-sized ice and super-cooled droplets in mixed-phase cloud

    Science.gov (United States)

    Hirst, E.; Kaye, P. H.; Greenaway, R. S.; Field, P.; Johnson, D. W.

    Preliminary experimental results are presented from an aircraft-mounted probe designed to provide in situ data on cloud particle shape, size, and number concentration. In particular, the probe has been designed to facilitate discrimination between super-cooled water droplets and ice crystals of 1-25 μm size within mixed-phase clouds and to provide information on cloud interstitial aerosols. The probe acquires spatial light scattering data from individual particles at throughput rates of several thousand particles per second. These data are logged at 100 ms intervals to allow the distribution and number concentration of each particle type to be determined with 10 m spatial resolution at a typical airspeed of 100 m s -1. Preliminary results from flight data recorded in altocumulus castellanus, showing liquid water phase, mixed phase, and ice phase are presented to illustrate the probe's particle discrimination capabilities.

  13. Effects of atmospheric dynamics and aerosols on the fraction of supercooled water clouds

    Science.gov (United States)

    Li, Jiming; Lv, Qiaoyi; Zhang, Min; Wang, Tianhe; Kawamoto, Kazuaki; Chen, Siyu; Zhang, Beidou

    2017-02-01

    Based on 8 years of (January 2008-December 2015) cloud phase information from the GCM-Oriented Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) Cloud Product (GOCCP), aerosol products from CALIPSO and meteorological parameters from the ERA-Interim products, the present study investigates the effects of atmospheric dynamics on the supercooled liquid cloud fraction (SCF) during nighttime under different aerosol loadings at global scale to better understand the conditions of supercooled liquid water gradually transforming to ice phase. Statistical results indicate that aerosols' effect on nucleation cannot fully explain all SCF changes, especially in those regions where aerosols' effect on nucleation is not a first-order influence (e.g., due to low ice nuclei aerosol frequency). By performing the temporal and spatial correlations between SCFs and different meteorological factors, this study presents specifically the relationship between SCF and different meteorological parameters under different aerosol loadings on a global scale. We find that the SCFs almost decrease with increasing of aerosol loading, and the SCF variation is closely related to the meteorological parameters but their temporal relationship is not stable and varies with the different regions, seasons and isotherm levels. Obviously negative temporal correlations between SCFs versus vertical velocity and relative humidity indicate that the higher vertical velocity and relative humidity the smaller SCFs. However, the patterns of temporal correlation for lower-tropospheric static stability, skin temperature and horizontal wind are relatively more complex than those of vertical velocity and humidity. For example, their close correlations are predominantly located in middle and high latitudes and vary with latitude or surface type. Although these statistical correlations have not been used to establish a certain causal relationship, our results may provide a unique point of view

  14. Numerical Simulation of Precipitation Enhancement by Stratiform Cloud Seeding Using a Mesoscale Model%层状云系催化增雨的中尺度模拟研究

    Institute of Scientific and Technical Information of China (English)

    赵震; 雷恒池

    2012-01-01

    利用PSU/NCAR中尺度模式MM5研究层状云碘化银催化后的区域外效应.在MM5中双参数显式云物理方案基础上,采用显式方法加入碘化银粒子的成核机制,建立碘化银粒子比含水量和数浓度预报方程.通过增加催化过程的程序模块,建立起一个中尺度人工催化系统.采用三重嵌套到3.3 km格距模拟了一次层状云系大范围降水,此个例-5℃到-10℃上碘化银催化试验结果表明碘化银在高空风的作用下向下风方输送并影响云内的微物理过程,碘化银持续作用时间为3h.大多数碘化银主要起凝华核作用,催化后冰晶增加主要靠凝华过程.催化后3h内在下风方区域80 km到240 km有10%~30%的增雨,出现催化区域外效应.%The Fifth-Generation Penn State/NCAR Mesoscale Model (MM5) was used to investigate the extra-area effects of silver iodide (Agl) seeding on stratiform clouds at the supercooled layer. A bulk two-moment microphysical scheme and the new software package for Agl were incorporated into MM5. Extra conservation equations were applied to trace the seeding agent, which was transported along the flow field and interacted with the supercooled cloud fields. In this study, the model was run for widespread precipitation caused by a stratiform cloud system using three nested grids, with a 3.3 km X 3.3 km horizontal resolution in the finest grid. The model results showed that seeding with Agl at the -5 ℃ to -10℃ levels had microphysical effects on the simulated clouds and that the simulation produced a seeding effect that lasted 3 h longer because of transport of the seeding agent by upper-level winds. Most of the Agl particles acted as deposition nuclei, and the deposition nucleation process contributed most to additional cloud ice formation. The results showed that more precipitation results from seeded than unseeded clouds, and the precipitation was redistributed downwind of the target. Augmented precipitation (varying

  15. Seminal role of stratiform clouds in large-scale aggregation of tropical rain in boreal summer monsoon intraseasonal oscillations

    Science.gov (United States)

    Kumar, Siddharth; Arora, Anika; Chattopadhyay, R.; Hazra, Anupam; Rao, Suryachandra A.; Goswami, B. N.

    2017-02-01

    Modification of the vertical structure of non-adiabatic heating by significant abundance of the stratiform rain in the tropics has been known to influence the large-scale circulation. However, the role of the stratiform rain on the space-time evolution of the observed Boreal summer monsoon intraseasonal oscillations (MISO) has so far been ignored. In the present study, we unravel a feedback mechanism through which the stratiform component of the rain leads to aggregation (organization) of rain on the MISO scale, making it an indispensable component of the MISO evolution dynamics. Using TRMM 3A25 monthly mean data (between 1998 and 2013), the ratio between convective and stratiform rain (RCS) is shown to be strongly related to the total rainfall. Further, composites of rainfall and circulation anomalies corresponding to high (low) values of RCS over the Central India or over the Equatorial Indian Ocean show spatial structures remarkably similar to that associated with the MISOs. Analyzing lead-lag relationship between the convective rain, the stratiform rain and the large scale moisture convergence with respect to peak active (break) spells from daily modern era retrospective-analysis for research and applications data, we unravel that the initial isolated convective elements spawn the stratiform rain which in turn modifies the vertical distribution of heating and leads to stronger large scale moisture convergence thereby producing more convective elements and more stratiform rain ultimately leading to aggregation of rain on the MISO scale. Our finding indicates that large and persisting systematic biases in simulating the summer monsoon rainfall over the Asian monsoon region by climate models are likely to be related to the systematic biases in simulating the MISOs which in turn are related to the serious underestimation of stratiform rain in most climate models.

  16. A study of the structure and microphysical processes of a precipitating stratiform cloud in Jilin%吉林一次降水层状云的结构和物理过程研究

    Institute of Scientific and Technical Information of China (English)

    侯团结; 胡朝霞; 雷恒池

    2011-01-01

    Based on airborne cloud particle probe observations, Doppler radar measurements and surface precipitation data, the macro-and micro-structure as well as precipitation mechanisms of one precipitating stratiform cloud occurring on 1 July 2004 in Jilin Province were studied comprehensively by using a one-dimensional stratiform cloud model. With those quantitative results, we had a further insight into the Koo Chenchao's three-layer cloud conceptual model and also got some new conclusions referring to the seeder-feeder processes. According to field observations, the non-uniform precipitation was produced by a typical stratiform cloud. The cloud structure could be explained well with the three-layer cloud model where the first layer is the ice crystal layer, including primarily small a-mounts of ice crystals. The mixed-phase layer (the second layer) , with altostratus and stratocumulus as the main cloud region, includes such processes as depositional growth, riming, aggregation and freezing of supercooled cloud water. And the remaining layer is the warm layer, in which obvious radar bright band was observed from Doppler radar.Based on the above observations, the numerical simulations of cloud structure and precipitation formation processes were conducted. The numerical results showed the presence of the three layer structure at the mature stage of cloud development. In the first layer (7.8 - 10.0 km), there was little ice and snow crystals which grew mainly by depositional growth. And in the second layer (3. 8 -7. 8 km) the ice and snow crystals falling partly from the first layer grew through the Bergeron process initially and later grew predominantly by riming processes. After that, the grown-up snow and graupel fell to the third layer. Therefore, the melting of snow and graupel combined with subsequent collection of cloud water was the main source of rain drop mass growth. Our results indicated that 50% - 60% of rain drop mass growth was associated with melting of

  17. Monte Carlo-based subgrid parameterization of vertical velocity and stratiform cloud microphysics in ECHAM5.5-HAM2

    Directory of Open Access Journals (Sweden)

    J. Tonttila

    2013-08-01

    Full Text Available A new method for parameterizing the subgrid variations of vertical velocity and cloud droplet number concentration (CDNC is presented for general circulation models (GCMs. These parameterizations build on top of existing parameterizations that create stochastic subgrid cloud columns inside the GCM grid cells, which can be employed by the Monte Carlo independent column approximation approach for radiative transfer. The new model version adds a description for vertical velocity in individual subgrid columns, which can be used to compute cloud activation and the subgrid distribution of the number of cloud droplets explicitly. Autoconversion is also treated explicitly in the subcolumn space. This provides a consistent way of simulating the cloud radiative effects with two-moment cloud microphysical properties defined at subgrid scale. The primary impact of the new parameterizations is to decrease the CDNC over polluted continents, while over the oceans the impact is smaller. Moreover, the lower CDNC induces a stronger autoconversion of cloud water to rain. The strongest reduction in CDNC and cloud water content over the continental areas promotes weaker shortwave cloud radiative effects (SW CREs even after retuning the model. However, compared to the reference simulation, a slightly stronger SW CRE is seen e.g. over mid-latitude oceans, where CDNC remains similar to the reference simulation, and the in-cloud liquid water content is slightly increased after retuning the model.

  18. Development and Testing of a Life Cycle Model and a Parameterization of Thin Mid-level Stratiform Clouds

    Energy Technology Data Exchange (ETDEWEB)

    Krueger, Steven K.

    2008-03-03

    We used a cloud-resolving model (a detailed computer model of cloud systems) to evaluate and improve the representation of clouds in global atmospheric models used for numerical weather prediction and climate modeling. We also used observations of the atmospheric state, including clouds, made at DOE's Atmospheric Radiation Measurement (ARM) Program's Climate Research Facility located in the Southern Great Plains (Kansas and Oklahoma) during Intensive Observation Periods to evaluate our detailed computer model as well as a single-column version of a global atmospheric model used for numerical weather prediction (the Global Forecast System of the NOAA National Centers for Environmental Prediction). This so-called Single-Column Modeling approach has proved to be a very effective method for testing the representation of clouds in global atmospheric models. The method relies on detailed observations of the atmospheric state, including clouds, in an atmospheric column comparable in size to a grid column used in a global atmospheric model. The required observations are made by a combination of in situ and remote sensing instruments. One of the greatest problems facing mankind at the present is climate change. Part of the problem is our limited ability to predict the regional patterns of climate change. In order to increase this ability, uncertainties in climate models must be reduced. One of the greatest of these uncertainties is the representation of clouds and cloud processes. This project, and ARM taken as a whole, has helped to improve the representation of clouds in global atmospheric models.

  19. Effects of cloud condensation nuclei and ice nucleating particles on precipitation processes and supercooled liquid in mixed-phase orographic clouds

    Energy Technology Data Exchange (ETDEWEB)

    Fan, Jiwen; Leung, L. Ruby; Rosenfeld, Daniel; DeMott, Paul J.

    2017-01-01

    How orographic mixed-phase clouds respond to the change in cloud condensation nuclei (CCN) and ice nucleating particles (INPs) are highly uncertain. The main snow production mechanism in warm and cold mixed-phase orographic clouds (referred to as WMOCs and CMOCs, respectively, distinguished here as those having cloud tops warmer and colder than -20°C) could be very different. We quantify the CCN and INP impacts on supercooled water content, cloud phases, and precipitation for a WMOC case and a CMOC case, with sensitivity tests using the same CCN and INP concentrations between the WMOC and CMOC cases. It was found that deposition plays a more important role than riming for forming snow in the CMOC case, while the role of riming is dominant in the WMOC case. As expected, adding CCN suppresses precipitation, especially in WMOCs and low INPs. However, this reverses strongly for CCN of 1000 cm-3 and larger. We found a new mechanism through which CCN can invigorate mixed-phase clouds over the Sierra Nevada and drastically intensify snow precipitation when CCN concentrations are high (1000 cm-3 or higher). In this situation, more widespread shallow clouds with a greater amount of cloud water form in the Central Valley and foothills west of the mountain range. The increased latent heat release associated with the formation of these clouds strengthens the local transport of moisture to the windward slope, invigorating mixed-phase clouds over the mountains, and thereby producing higher amounts of snow precipitation. Under all CCN conditions, increasing the INPs leads to decreased riming and mixed-phase fraction in the CMOC as a result of liquid-limited conditions, but has the opposite effects in the WMOC as a result of ice-limited conditions. However, precipitation in both cases is increased by increasing INPs due to an increase in deposition for the CMOC but enhanced riming and deposition in the WMOC. Increasing the INPs dramatically reduces

  20. Entrainment rate diurnal cycle in marine stratiform clouds estimated from geostationary satellite retrievals and a meteorological forecast model

    Science.gov (United States)

    Painemal, David; Xu, Kuan-Man; Palikonda, Rabindra; Minnis, Patrick

    2017-07-01

    The mean diurnal cycle of cloud entrainment rate (we) over the northeast Pacific region is for the first time computed by combining, in a mixed-layer model framework, the hourly composited GOES-15 satellite-based cloud top height (HT) tendency, advection, and large-scale vertical velocity (w) during May to September 2013, with horizontal winds and w taken from the European Centre for Medium-Range Weather Forecasts (ECMWF) model. The tendency term dominates the magnitude and phase of the we diurnal cycle, with a secondary role of w, and a modest advective contribution. The peak and minimum in we occur between 20:00-22:00 LT and 9:00-11:00 LT, respectively, in close agreement with the diurnal cycle of turbulence driven by cloud top longwave cooling. Uncertainties in HT and ECMWF fields are assessed with in situ observations and three meteorological reanalysis data sets. This study provides the basis for constructing nearly global climatologies of we by combining a suite of well-calibrated geostationary satellites.

  1. Super-cooled liquid water topped sub-arctic clouds and precipitation - investigation based on combination of ground-based in-situ and remote-sensing observations

    Science.gov (United States)

    Hirsikko, Anne; Brus, David; O'Connor, Ewan J.; Filioglou, Maria; Komppula, Mika; Romakkaniemi, Sami

    2017-04-01

    In the high and mid latitudes super-cooled liquid water layers are frequently observed on top of clouds. These layers are difficult to forecast with numerical weather prediction models, even though, they have strong influence on atmospheric radiative properties, cloud microphysical properties, and subsequently, precipitation. This work investigates properties of super-cooled liquid water layer topped sub-arctic clouds and precipitation observed with ground-based in-situ (cloud probes) and remote-sensing (a cloud radar, Doppler and multi-wavelength lidars) instrumentation during two-month long Pallas Cloud Experiment (PaCE 2015) in autumn 2015. Analysis is based on standard Cloudnet scheme supplemented with new retrieval products of the specific clouds and their properties. Combination of two scales of observation provides new information on properties of clouds and precipitation in the sub-arctic Pallas region. Current status of results will be presented during the conference. The authors acknowledge financial support by the Academy of Finland (Centre of Excellence Programme, grant no 272041; and ICINA project, grant no 285068), the ACTRIS2 - European Union's Horizon 2020 research and innovation programme under grant agreement No 654109, the KONE foundation, and the EU FP7 project BACCHUS (grant no 603445).

  2. Determination of Ice Crystal Growth Parameters in a Supercooled Cloud Tunnel.

    Science.gov (United States)

    1981-06-01

    quite well with the findings of Fukuta (1968) during his studies of the use of "vapor activated" metaldehyde as an ice nucleation agent. At other...Some remarks on ice nucleation by metaldehyde . Proc. Intl. Conf. on Cloud Phys., Toronto, 26 - 30 Aug. 1968, 1947-- - , 1969: Experimental studies on

  3. Cloud microphysical properties and parameterization of cloud droplet effective radius from aircraft measurements:aircraft observational results from a stratiform precipitation cloud%云微物理特性及云滴有效半径参数化:一次降水层状云的飞机观测资料结果

    Institute of Scientific and Technical Information of China (English)

    解小宁; 王昭生; 王红丽; 岳治国

    2016-01-01

    clouds, and its accurate paremeterization is also especially of importance to evaluate the aerosol indirect effect and can reduce the uncertity of the aerosol indirect effect.Materials and methods Here, we use an observed data about the cloud droplet size distribution, which is derived from aircraft measurements for a stratiform cloud in Yan’an area in September 17, 2003 (Northwest China). This cloud dropet data can dispaly the cloud microphysical properties including the droplet number concentration, the cloud water content, the cloud droplet radius, volume radius, effective radius, the cloud droplet relative dispersion, and the prefactor about the ratio of the effective radius and the volume radius. Additionally, using the analytical methods based on the deifnation of effective radius, we can analytically derive the theoretical parameterization of the cloud droplet effective radius interms of three size distribution funcions described as the Lognormal, the Gamma, and the Weibull expressions, which are usually employed in the numerical models based on the various scales.Results (1) We summarize the Maximum, Mean, Median, and STDEV (Standard Deviation) values about the cloud microphysical properties including the cloud droplet number concentration (Nc), the cloud water content (Qc), the cloud droplet radius (Rm), the volume radius (Rv), the effective radius (Re), the cloud droplet relative dispersion (ε), and theRe/Rv prefactorβ for this stratiform cloud in Yan’an area (Northwest China). (2) Based on the observed data about the cloud droplet number concentrationNc and the cloud droplet relative dispersionε, we can derive aε—Nc negative relationship asε = 0.579 − 7.42×10 − 4Nc+ 4.2×10 − 7Nc2, which represents the cloud droplet relative dispersion decreases with the increase in cloud droplet number concentration. Thisε—Nc relationship can be directly coupled to the numerical models to evaluated the cloud

  4. Mesoscale characteristics of monsoonal convection and associated stratiform precipitation

    Science.gov (United States)

    Keenan, Thomas D.; Rutledge, Steven A.

    1993-01-01

    Observations undertaken on 12 January 1990 at Darwin (Australia) are used to document the structure of a monsoonal rainband in a low convective available potential energy low-shear tropical environment. Dual-Doppler radar analyses are employed to investigate the structure and kinematics of the convective and stratiform regions. A system with the characteristics of a relatively short-lived squall line in which warm rain processes play a significant role in the production of precipitation is evident. Planetary boundary layer cold-pool production is important in the organization and motion of the system. A trailing stratiform region is evident with a mean updraft-downdraft circulation, but is composed of in situ decaying convective cells. A storm-relative mesoscale cyclonic circulation is also observed within the stratiform cloud. This vortex was maintained by thermodynamically induced midlevel convergence, convectively generated storm-scale circulations, and their interaction with the background monsoon flow.

  5. Remote Sensing of Supercooled Cloud Layers in Cold Climate Using Ground Based Integrated Sensors System and Comparison with Pilot Reports and model forecasts

    Science.gov (United States)

    Boudala, Faisal; Wu, Di; Gultepe, Ismail; Anderson, Martha; turcotte, marie-france

    2017-04-01

    In-flight aircraft icing is one of the major weather hazards to aviation . It occurs when an aircraft passes through a cloud layer containing supercooled drops (SD). The SD in contact with the airframe freezes on the surface which degrades the performance of the aircraft.. Prediction of in-flight icing requires accurate prediction of SD sizes, liquid water content (LWC), and temperature. The current numerical weather predicting (NWP) models are not capable of making accurate prediction of SD sizes and associated LWC. Aircraft icing environment is normally studied by flying research aircraft, which is quite expensive. Thus, developing a ground based remote sensing system for detection of supercooled liquid clouds and characterization of their impact on severity of aircraft icing one of the important tasks for improving the NWPs based predictions and validations. In this respect, Environment and Climate Change Canada (ECCC) in cooperation with the Department of National Defense (DND) installed a number of specialized ground based remote sensing platforms and present weather sensors at Cold Lake, Alberta that includes a multi-channel microwave radiometer (MWR), K-band Micro Rain radar (MRR), Ceilometer, Parsivel distrometer and Vaisala PWD22 present weather sensor. In this study, a number of pilot reports confirming icing events and freezing precipitation that occurred at Cold Lake during the 2014-2016 winter periods and associated observation data for the same period are examined. The icing events are also examined using aircraft icing intensity estimated using ice accumulation model which is based on a cylindrical shape approximation of airfoil and the Canadian High Resolution Regional Deterministic Prediction System (HRDPS) model predicted LWC, median volume diameter and temperature. The results related to vertical atmospheric profiling conditions, surface observations, and the Canadian High Resolution Regional Deterministic Prediction System (HRDPS) model

  6. Observations of Stratiform Lightning Flashes and Their Microphysical and Kinematic Environments

    Science.gov (United States)

    Lang, Timothy J.; Williams, Earle

    2017-01-01

    During the Midlatitude Continental Convective Clouds Experiment (MC3E), combined observations of clouds and precipitation were made from airborne and ground-based in situ and remote sensing platforms. These observations were coordinated for multiple mesoscale convective systems (MCSs) that passed over the MC3E domain in northern Oklahoma. Notably, during a storm on 20 May 2011 in situ and remote sensing airborne observations were made near the times and locations of stratiform positive cloud-to-ground (+CG) lightning flashes. These +CGs resulted from extremely large stratiform lightning flashes that were hundreds of km in length and lasted several seconds. This dataset provides an unprecedented look at kinematic and microphysical environments in the vicinity of large, powerful, and long-lived stratiform lightning flashes. We will use this dataset to understand the influence of low liquid water contents (LWCs) in the electrical charging of MCS stratiform regions.

  7. Cloud liquid water path and radiative feedbacks over the Southern Ocean

    Science.gov (United States)

    Bodas-Salcedo, A.; Andrews, T.; Karmalkar, A. V.; Ringer, M. A.

    2016-10-01

    Climate models show a robust shortwave negative feedback in the midlatitude oceans in climate change simulations. This feedback is commonly attributed to an increase in cloud optical depth due to ice to liquid phase change as the climate warms. Here we use a cyclone compositing technique to show that the models' cloud liquid water path (LWP) response is strongly dependent on cloud regime. The radiative and LWP responses are not as tightly coupled as a zonal-mean analysis would suggest, implying that the physical mechanisms that control the overall LWP response are not necessarily responsible for the radiative response. The area of the cyclone dominated by low-level stratiform and shallow convective clouds plays a dominant role in the radiative response. Since these are mostly supercooled liquid clouds, the strength of a negative cloud phase feedback in the real world should be smaller than the one predicted by current models.

  8. Seasonal Scale Convective-Stratiform Pricipitation Variabilities at Tropics

    Science.gov (United States)

    S, Sreekanth T.

    begin{center} Large Seasonal Scale Convective-Stratiform Pricipitation Variabilities at Tropics Sreekanth T S*, Suby Symon*, G. Mohan Kumar (1) and V Sasi Kumar (2) *Centre for Earth Science Studies, Akkulam, Thiruvananthapuram (1) D-330, Swathi Nagar, West Fort, Thiruvananthapuram 695023 (2) 32. NCC Nagar Peroorkada, Thiruvananthapuram ABSTRACT This study investigates the variabilities of convective and stratiform rainfall from 2011 to 2013 at a tropical coastal station in three seasons viz Pre-Monsoon (March-May), Monsoon (June-September) and Post-Monsoon (October-December). Understanding the climatological variability of these two dominant forms of precipitation and their implications in the total rainfall were the main objectives of this investigation. Variabilities in the frequency & duration of events, rain rate & total number of rain drops distribution in different events and the accumulated amount of rain water were analysed. Based on the ground & radar observations from optical & impact disdrometers, Micro Rain Radar and Atmospheric Electric Field Mill, precipitation events were classified into convective and stratiform in three seasons. Classification was done by the method followed by Testud et al (2001) and as an additional information electrical behaviour of clouds from Atmospheric Electric Field Mill is also used. Events which could not be included in both types were termed as 'mixed precipitation' and were included separately. Diurnal variability of the total rainfall in each seasons were also examined. For both convective and stratiform rainfall there exist distinct day-night differences. During nocturnal hours convective rain draged more attention. In all seasons almost 70% of rain duration and 60% of rain events of convective origin were confined to nocturnal hours. But stratiform rain was not affected by diurnal variations greatly because night time occurrences of stratiform duration and events were less than 50%. Also in Monsoon above 35% of

  9. Micro-Physical characterisation of Convective & Stratiform Rainfall at Tropics

    Science.gov (United States)

    Sreekanth, T. S.

    Large Micro-Physical characterisation of Convective & Stratiform Rainfall at Tropics begin{center} begin{center} Sreekanth T S*, Suby Symon*, G. Mohan Kumar (1) , and V Sasi Kumar (2) *Centre for Earth Science Studies, Akkulam, Thiruvananthapuram (1) D-330, Swathi Nagar, West Fort, Thiruvananthapuram 695023 (2) 32. NCC Nagar, Peroorkada, Thiruvananthapuram ABSTRACT Micro-physical parameters of rainfall such as rain drop size & fall speed distribution, mass weighted mean diameter, Total no. of rain drops, Normalisation parameters for rain intensity, maximum & minimum drop diameter from different rain intensity ranges, from both stratiform and convective rain events were analysed. Convective -Stratiform classification was done by the method followed by Testud et al (2001) and as an additional information electrical behaviour of clouds from Atmospheric Electric Field Mill was also used. Events which cannot be included in both types are termed as 'mixed precipitation' and identified separately. For the three years 2011, 2012 & 2013, rain events from both convective & stratiform origin are identified from three seasons viz Pre-Monsoon (March-May), Monsoon (June-September) and Post-Monsoon (October-December). Micro-physical characterisation was done for each rain events and analysed. Ground based and radar observations were made and classification of stratiform and convective rainfall was done by the method followed by Testud et al (2001). Radar bright band and non bright band analysis was done for confimation of stratifom and convective rain respectievely. Atmospheric electric field data from electric field mill is also used for confirmation of convection during convective events. Statistical analyses revealed that the standard deviation of rain drop size in higher rain rates are higher than in lower rain rates. Normalised drop size distribution is ploted for selected events from both forms. Inter relations between various precipitation parameters were analysed in three

  10. Thermal aspect of the diurnal variation of tropical convective and stratiform rainfall

    Institute of Scientific and Technical Information of China (English)

    Cui Xiao-Peng; Li Xiao-Fan

    2011-01-01

    The diurnal variation of radiation plays a key role in determining the diurnal variations of tropical oceanic convective and stratiform rainfall,and the examination of such a relationship requires a direct link between the radiation term in a heat budget and the surface rain rate in a cloud budget.Thus,the thermally related surface rainfall budgets derived from the combination of cloud and heat budgets are analysed with two-dimensional equilibrium cloud-resolving model simulation data to study the effects of sea surface temperature (SST) and cloud radiative,and microphysical processes on the diurnal variations of convective and stratiform rainfall.The results show that the increase in SST,the inclusion of diurnal variation of SST and the exclusion of cloud radiative processes increase negative diurnal anomalies of heat divergence over rainfall-free regions during the nighttime through changing the vertical structures of diurnal anomaly of radiation in the troposphere.The strengthened negative diurnal anomalies of heat divergence over rainfallfree regions enhance positive diurnal anomalies of heat divergence over convective regions,which intensifies the positive diurnal anomaly of convective rainfall.The exclusion of microphysical effects of ice clouds increases the negative diurnal anomaly of heat divergence over rainfall-free regions during the nighttime through reducing latent heat; this appears to enhance the positive diurnal anomaly of heat divergence over raining stratiform regions,and thus stratiform rainfall.

  11. Role of stratiform heating on the organization of convection over the monsoon trough

    Science.gov (United States)

    Ajayamohan, R. S.; Khouider, Boualem; Majda, Andrew J.; Deng, Qiang

    2016-12-01

    It has been recently demonstrated that stratiform heating plays a critical role in the scale-selection of organized tropical convection, in an aquaplanet version of a coarse-resolution atmospheric general circulation model coupled to a stochastic multicloud cumulus parameterization scheme. It is shown that Madden-Julian oscillation-like organization dominates when the model is tuned to produce strong and long lived stratiform heating while it gives rise to mostly convectively coupled waves in the case of weak and short lived stratiform clouds. The study is extended here to the case of an asymmetric forcing mimicking the migration of the intertropical convergence zone (ITCZ) during summer to understand the impact of changes in stratiform heating on the monsoon dynamics. Consistent with the equatorial ITCZ case, strong and long lived stratiform heating promotes northward and eastward moving intraseasonal disturbances while weak and short lived stratiform heating yields mostly westward propgating synoptic scale low pressure systems. Moreover, the underlying intraseasonal versus low pressure system activity seems to impact the strength and extend of the monsoon trough (MT). In the regime with intraseasonal activity the MT is much stronger and extends northward while in the low pressure system case MT is some what weaker in strength but extends further westward. In the low pressure dominated regime, the background vorticity and zonal wind profiles over the monsoon trough are consistent with the observations.

  12. Recent Improvements in Estimating Convective and Stratiform Rainfall in Amazonia

    Science.gov (United States)

    Negri, Andrew J.

    1999-01-01

    In this paper we present results from the application of a satellite infrared (IR) technique for estimating rainfall over northern South America. Our main objectives are to examine the diurnal variability of rainfall and to investigate the relative contributions from the convective and stratiform components. We apply the technique of Anagnostou et al (1999). In simple functional form, the estimated rain area A(sub rain) may be expressed as: A(sub rain) = f(A(sub mode),T(sub mode)), where T(sub mode) is the mode temperature of a cloud defined by 253 K, and A(sub mode) is the area encompassed by T(sub mode). The technique was trained by a regression between coincident microwave estimates from the Goddard Profiling (GPROF) algorithm (Kummerow et al, 1996) applied to SSM/I data and GOES IR (11 microns) observations. The apportionment of the rainfall into convective and stratiform components is based on the microwave technique described by Anagnostou and Kummerow (1997). The convective area from this technique was regressed against an IR structure parameter (the Convective Index) defined by Anagnostou et al (1999). Finally, rainrates are assigned to the Am.de proportional to (253-temperature), with different rates for the convective and stratiform

  13. Liquid and Ice Cloud Microphysics in the CSU General Circulation Model. Part III: Sensitivity to Modeling Assumptions.

    Science.gov (United States)

    Fowler, Laura D.; Randall, David A.

    1996-03-01

    The inclusion of cloud microphysical processes in general circulation models makes it possible to study the multiple interactions among clouds, the hydrological cycle, and radiation. The gaps between the temporal and spatial scales at which such cloud microphysical processes work and those at which general circulation models presently function force climate modelers to crudely parameterize and simplify the various interactions among the different water species (namely, water vapor, cloud water, cloud ice, rain, and snow) and to use adjustable parameters to which large-scale models can be highly sensitive. Accordingly, the authors have investigated the sensitivity of the climate, simulated with the Colorado State University general circulation model, to various aspects of the parameterization of cloud microphysical processes and its interactions with the cumulus convection and radiative transfer parameterizations.The results of 120-day sensitivity experiments corresponding to perpetual January conditions have been compared with those of a control simulation in order to 1 ) determine the importance of advecting cloud water, cloud ice, rain, and snow at the temporal and spatial scale resolutions presently used in the model; 2) study the importance of the formation of extended stratiform anvils at the tops of cumulus towers, 3) analyze the role of mixed-phase clouds in determining the partitioning among cloud water, cloud ice, rain, and snow and, hence, their impacts on the simulated cloud optical properties; 4) evaluate the sensitivity of the atmospheric moisture budget and precipitation rates to a change in the fall velocities of rain and snow; 5) determine the model's sensitivity to the prescribed thresholds of autoconversion of cloud water to rain and cloud ice to snow; and 6) study the impact of the collection of supercooled cloud water by snow, as well as accounting for the cloud optical properties of snow.Results are presented in terms of 30-day mean differences

  14. An Analysis of Thermally-Related Surface Rainfall Budgets Associated with Convective and Stratiform Rainfall

    Institute of Scientific and Technical Information of China (English)

    ZHOU Yushu; Xiaofan LI

    2011-01-01

    Both water vapor and heat processes play key roles in producing surface rainfall.While the water vapor effects of sea surface temperature and cloud radiative and microphysical processes on surface rainfall have been investigated in previous studies,the thermal effects on rainfall are analyzed in this study using a series of two-dimensional equilibrium cloud-resolving model experiments forced by zonally-uniform,constant,large-scale zonal wind and zero large-scale vertical velocity.The analysis of thermally-related surface rainfall budget reveals that the model domain mean surface rain rate is primarily associated with the mean infrared cooling rate.Convective rainfall and transport of hydrometeor concentration from convective regions to raining stratiform regions corresponds to the heat divergence over convective regions,whereas stratiform rainfall corresponds to the transport of hydrometeor concentration from convective regions and heat divergence over raining stratiform regions.The heat divergence over convective regions is mainly balanced by the heat convergence over rainfall-free regions,which is,in turn,offset by the radiative cooling over rainfall-free regions.The sensitivity experiments of rainfall to the effects of sea surface temperature and cloud radiative and microphysical processes show that the sea surface temperature and cloud processes affect convective rainfall through the changes in infrared cooling rate over rainfall-free regions and transport rate of heat from convective regions to rainfall-free regions.

  15. Supercooled liquids for pedestrians

    Science.gov (United States)

    Cavagna, Andrea

    2009-06-01

    When we lower the temperature of a liquid, at some point we meet a first order phase transition to the crystal. Yet, under certain conditions it is possible to keep the system in its metastable phase and to avoid crystallization. In this way the liquid enters in the supercooled phase. Supercooled liquids have a very rich phenomenology, which is still far from being completely understood. To begin with, there is the problem of how to prevent crystallization and how deeply the liquid can be supercooled before a metastability limit is hit. But by far the most interesting feature of supercooled liquids is the dynamic glass transition: when the temperature is decreased below a certain point, the relaxation time increases so much that a dramatic dynamical arrest intervenes and we are unable to equilibrate the system within reasonable experimental times. The glass transition is a phenomenon whose physical origin has stirred an enormous interest in the last hundred years. Why does it occur? Is it just a conventional reference point, or does it have a more profound physical meaning? Is it a purely dynamical event, or the manifestation of a true thermodynamic transition? What is the correlation length associated to the sharp increase of the relaxation time? Can we define a new kind of amorphous order? A shared theory of supercooled liquids and the glass transition does not yet exist and these questions are still largely open. Here, I will illustrate in the most elementary fashion the main phenomenological traits of supercooled liquids and discuss in a very partial way a few theoretical ideas on the subject.

  16. Toward the Characterization of Mixed-Phase Clouds Using Remote Sensing

    Science.gov (United States)

    Andronache, C.

    2015-12-01

    Mixed-phase clouds consist of a mixture of ice particles and liquid droplets at temperatures below 0 deg C. They are present in all seasons in many regions of the world, account for about 30% of the global cloud coverage, and are linked to cloud electrification and aircraft icing. The mix of ice particles, liquid droplets, and water vapor is unstable, and such clouds are thought to have a short lifetime. A characteristic parameter is the phase composition of mixed-phase clouds. It affects the cloud life cycle and the rate of precipitation. This parameter is important for cloud parameters retrievals by radar, lidar, and satellite and is relevant for climate modeling. The phase transformation includes the remarkable Wegener-Bergeron-Findeisen (WBF) process. The direction and the rate of the phase transformations depend on the local thermodynamic and microphysical properties. Cloud condensation nuclei (CCN) and ice nuclei (IN) particles determine to a large extent cloud microstructure and the dynamic response of clouds to aerosols. The complexity of dynamics and microphysics involved in mixed-phase clouds requires a set of observational and modeling tools that continue to be refined. Among these techniques, the remote sensing methods provide an increasing number of parameters, covering large regions of the world. Thus, a series of studies were dedicated to stratiform mixed-phase clouds revealing longer lifetime than previously thought. Satellite data and aircraft in situ measurements in deep convective clouds suggest that highly supercooled water often occurs in vigorous continental convective storms. In this study, we use cases of convective clouds to discuss the feasibility of mixed-phase clouds characterization and potential advantages of remote sensing.

  17. A STUDY OF REAL-TIME IDENTIFICATION OF SEEDABILITY OF COLD STRATIFORM CLOUDS%层状冷云人工增雨可播性实时识别技术研究

    Institute of Scientific and Technical Information of China (English)

    陶树旺; 刘卫国; 李念童; 王广河; 周毓荃; 胡志晋

    2001-01-01

    该文综合分析了4次层状冷云人工增雨过程的雷达回波、粒子测量系统(PMS)探测资料,以及GPS定位资料,提出应以PMS的FSSP-100探头探测的云中粒子浓度以及2D-C探头探测的云中大粒子浓度作为判别云中可播性的主要技术参量,并发展了层状冷云飞机人工增雨实时监测指挥技术。FSSP-100探测的粒子浓度不小于20/cm3的云区才具有一定的可播性。其中2D-C探测的大粒子浓度小于20/L时,可确定为强可播区,否则为可播区。%Based on integrated analysis of the cloud data obtained by digital radar,the particle measuring system (PMS) and the global positioning system (GPS), the main cloud physical parameters used to identify cloud seedability are proposed. Only when the relevant cloud particle concentration obtained by FSSP-100 probe of PMS is larger than 20/cm3, has the cloud area certain seedability. Furthermore, when the particle concentration obtained by 2D-C probe of PMS is less than 20/L, the cloud is highly seedable and otherwise it is seedable.

  18. Supercooled smectic nanoparticles

    DEFF Research Database (Denmark)

    Kuntsche, Judith; Westesen, K; Drechsler, M

    2004-01-01

    The possibility of preparing nanoparticles in the supercooled thermotropic liquid crystalline state from cholesterol esters with saturated acyl chains as well as the incorporation of model drugs into the dispersions was investigated using cholesteryl myristate (CM) as a model cholesterol ester....

  19. Supercooled Liquids and Glasses

    OpenAIRE

    1999-01-01

    In these lectures, which were presented at "Soft and Fragile Matter, Nonequilibrium Dynamics, Metastability and Flow" University of St. Andrews, 8 July - 22 July, 1999, I give an introduction to the physics of supercooled liquids and glasses and discuss some computer simulations done to investigate these systems.

  20. Supercooled smectic nanoparticles

    DEFF Research Database (Denmark)

    Kuntsche, Judith; Westesen, K; Drechsler, M

    2004-01-01

    The possibility of preparing nanoparticles in the supercooled thermotropic liquid crystalline state from cholesterol esters with saturated acyl chains as well as the incorporation of model drugs into the dispersions was investigated using cholesteryl myristate (CM) as a model cholesterol ester....

  1. Seeding Conditions of Precipitation Enhancement Revealed by Multiple Spectral Data of Satellite.Ⅱ: Super-cooled Layer Clouds%卫星遥感人工增雨作业条件Ⅱ:层状云

    Institute of Scientific and Technical Information of China (English)

    刘贵华; 余兴; 岳治国; 戴进; 徐小红; 朱延年

    2012-01-01

    通过卫星多光谱资料的定标,利用可见光反射率、3.7 μm和11 μm辐射亮温,反演了云顶粒子有效半径、云顶温度等云特征参数.运用图像合成技术,建立了反映云宏、微观特征的RGB合成图.利用发展的多光谱云微物理综合分析方法,通过极轨卫星分析了不同过冷层状云及其降水特征,结合增雨假设,总结出适宜人工增雨作业的卫星判据为:云厚大于1.5 km,云顶温度-5~-15℃时,有效半径小于25 μm;或云顶温度-15~-25℃时,有效半径小于15 μm.利用可见光反射率、云顶温度和有效半径多阈值建立人工增雨播云等级和分级显示.通过静止卫星跟踪云系演变,进一步确定播云部位和作业时机,指导人工增雨作业.%On the basis of calibration of multiple spectral satellite data, parameters of cloud properties such as particle effective radius and temperature of cloud tops were retrieved from the reflectance of visible channel and brightness temperature at 3.7 urn and 11 μm wavelengths. By means of imagery compositions such as code reflectance at visible and 3.7 μrn channels and a brightness temperature of 11 μm channel with primary colors of red, blue, and green (RGB), RGB composite imagery was developed to reflect the micro- and macrophysical properties of clouds. Multiple-spectral comprehensive methodology was used to analyze the microphysical properties and precipitation for super-cooled layer clouds via polar-orbit satellite data. On the basis of the assumption of precipitation enhancement and the analyzed results, the suitable criterion for rainfall enhancement for these types of clouds is summarized by the following parameters: Cloud thickness is greater than 1.5 km, and effective radius should be less than 25 μm when the temperature ranges between -5 ℃ and -15 ℃ and less than 15 μm when temperature is between -15 ℃ and -25 ℃. The classes of cloud seed ability for precipitation enhancement and

  2. Classification of Convective and Stratiform Cells in Meteorological Radar Images Using SVM Based on a Textural Analysis

    Institute of Scientific and Technical Information of China (English)

    Abdenasser Djafri; Boualem Haddad

    2014-01-01

    This contribution deals with the discrimination between stratiform and convective cells in meteorological radar images. This study is based on a textural analysis of the latter and their classification using a support vector machine (SVM). First, we apply different textural parameters such as energy, entropy, inertia, and local homogeneity. Through this experience, we identify the different textural features of both the stratiform and convective cells. Then, we use an SVM to find the best discriminating parameter between the two types of clouds. The main goal of this work is to better apply the Palmer and Marshall Z-R relations specific to each type of precipitation.

  3. Stratiform and Convective Precipitation Observed by Multiple Radars during the DYNAMO/AMIE Experiment

    Energy Technology Data Exchange (ETDEWEB)

    Deng, Min; Kollias, Pavlos; Feng, Zhe; Zhang, Chidong; Long, Charles N.; Kalesse, Heike; Chandra, Arunchandra; Kumar, Vickal; Protat, Alain

    2014-11-01

    The motivation for this research is to develop a precipitation classification and rain rate estimation method using cloud radar-only measurements for Atmospheric Radiation Measurement (ARM) long-term cloud observation analysis, which are crucial and unique for studying cloud lifecycle and precipitation features under different weather and climate regimes. Based on simultaneous and collocated observations of the Ka-band ARM zenith radar (KAZR), two precipitation radars (NCAR S-PolKa and Texas A&M University SMART-R), and surface precipitation during the DYNAMO/AMIE field campaign, a new cloud radar-only based precipitation classification and rain rate estimation method has been developed and evaluated. The resulting precipitation classification is equivalent to those collocated SMART-R and S-PolKa observations. Both cloud and precipitation radars detected about 5% precipitation occurrence during this period. The convective (stratiform) precipitation fraction is about 18% (82%). The 2-day collocated disdrometer observations show an increased number concentration of large raindrops in convective rain compared to dominant concentration of small raindrops in stratiform rain. The composite distributions of KAZR reflectivity and Doppler velocity also show two distinct structures for convective and stratiform rain. These indicate that the method produces physically consistent results for two types of rain. The cloud radar-only rainfall estimation is developed based on the gradient of accumulative radar reflectivity below 1 km, near-surface Ze, and collocated surface rainfall (R) measurement. The parameterization is compared with the Z-R exponential relation. The relative difference between estimated and surface measured rainfall rate shows that the two-parameter relation can improve rainfall estimation.

  4. Image Segmentation Method for Identifying Convective and Stratiform Rain using MSG SEVIRI Data

    Directory of Open Access Journals (Sweden)

    Mounir Sehad

    2014-06-01

    Full Text Available This paper provides a new method for the classification of rainfall areas in convective and stratiform rain using MSG/SEVIRI (Spinning Enhanced Visible and Infrared data. The proposed approach is based on spectral and temporal properties of clouds. The spectral parameters used are: brightness temperature (BT and brightness temperature differences (BTDs, and the temporal parameter (RCT10.8 is the rate of change of (BT in the 10.8µm channel over two consecutive images. The developed rain area classification technique (RACT-DN is based on two multilayer perceptron neural networks (MLP-D for daytime and MLP-N for nighttime which relies on the correlation of satellite data with convective and stratiform rain. The two algorithms (MLP-D and MLP-N are trained using as reference data from ground meteorological radar over northern Algeria. The results show that RACT-DN classifier gives accurate discrimination between convective and stratiform areas during daytime and nighttime.

  5. Proportions of convective and stratiform precipitation revealed in water isotope ratios

    Science.gov (United States)

    Aggarwal, Pradeep K.; Romatschke, Ulrike; Araguas-Araguas, Luis; Belachew, Dagnachew; Longstaffe, Frederick J.; Berg, Peter; Schumacher, Courtney; Funk, Aaron

    2016-08-01

    Tropical and midlatitude precipitation is fundamentally of two types, spatially limited and high-intensity convective or widespread and lower-intensity stratiform, owing to differences in vertical air motions and microphysical processes governing rain formation. These processes are difficult to observe or model and precipitation partitioning into rain types is critical for understanding how the water cycle responds to changes in climate. Here, we combine two independent data sets--convective and stratiform precipitation fractions, derived from the Tropical Rainfall Measuring Mission satellite or synoptic cloud observations, and stable isotope and tritium compositions of surface precipitation, derived from a global network--to show that isotope ratios reflect rain type proportions and are negatively correlated with stratiform fractions. Condensation and riming associated with boundary layer moisture produces higher isotope ratios in convective rain, along with higher tritium when riming in deep convection occurs with entrained air at higher altitudes. On the basis of our data, stable isotope ratios can be used to monitor changes in the character of precipitation in response to periodic variability or changes in climate. Our results also provide observational constraints for an improved simulation of convection in climate models and a better understanding of isotope variations in proxy archives, such as speleothems and tropical ice.

  6. Supercooled smectic nanoparticles

    DEFF Research Database (Denmark)

    Kuntsche, Judith; Koch, Michel H J; Fahr, Alfred

    2009-01-01

    , laser diffraction combined with polarizing intensity differential scattering, DSC and SAXS. The morphology of selected formulations was studied by freeze-fracture electron microscopy. All smectic nanoparticles with a mixed cholesterol ester matrix were stable against recrystallization when stored...... in the bulk was studied by polarizing light microscopy, differential scanning calorimetry (DSC) and small angle X-ray scattering (SAXS). Colloidal dispersions with pure and mixed cholesterol ester matrices were prepared by high-pressure melt homogenization and characterized by photon correlation spectroscopy...... administration of lipophilic drugs, the cytotoxicity of selected formulations was compared with that of a clinically used colloidal fat emulsion (Lipofundin MCT) in the murine fibroblast cell line L929 using the sulforhodamine B assay. The supercooled smectic nanoparticle formulations display a good overall cell...

  7. Simulating mixed-phase Arctic stratus clouds: Sensitivity to ice initiationmechanisms

    Energy Technology Data Exchange (ETDEWEB)

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

    2009-04-10

    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 October 9th-10th, which indicated the presence of a single-layer mixed-phase clouds. We performed several sets of 12-hour 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

  8. 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

  9. The Common Occurrence of Highly Supercooled Drizzle and Rain near the Coastal Regions of the Western United States

    Energy Technology Data Exchange (ETDEWEB)

    Rosenfeld, Daniel; Chemke, Rei; DeMott, Paul J.; Sullivan, Ryan C.; Rasmussen, R M.; McDonough, Frank; Comstock, Jennifer M.; Schmid, Beat; Tomlinson, Jason M.; Jonsson, Haf; Suski, Kaitlyn; Cazorla, Alberto; Prather, Kimberly

    2013-09-05

    The formation of highly supercooled rain was documented by aircraft observations in clouds at a wide range of conditions near the coastal region of the western United States. Several case studies are described in detail using combined cloud and aerosol measurements to document both the highly super-cooled condition and the relatively pristine aerosol conditions under which it forms. The case studies include: (1) Marine convective clouds over the coastal waters of northern California, as measured by cloud physics probes flown on a Gulfstream-1 aircraft during the CALWATER campaign in February and early March 2011. The clouds had extensive drizzle in their tops, which extended downward to the 0°C isotherm as supercooled rain. Ice multiplication was observed only in mature parts of the clouds where cloud water was already depleted. (2) Orographically triggered convective clouds in marine air mass over the foothills of the Sierra Nevada to the east of Sacramento, as measured in CALWATER. Supercooled rain was observed down to -21°C. No indications for ice multiplication were evident. (3) Orographic layer clouds over Yosemite National Park, also measured in CALWATER. The clouds had extensive drizzle at -21°C, which intensified with little freezing lower in the cloud, and (4) Supercooled drizzle drops in layer clouds near Juneau, Alaska, as measured by the Wyoming King Air as part of a FAA project to study aircraft icing in this region. Low concentrations of CCN was a common observation in all these clouds, allowing for the formation of clouds with small concentration of large drops that coalesced into supercooled drizzle and raindrops. Another common observation was the absence of ice nuclei and/or ice crystals in measurable concentrations was associated with the persistent supercooled drizzle and rain. Average ice crystal concentrations were 0.007 l-1 at the top of convective clouds at -12°C and 0.03 l-1 in the case of layer clouds at -21°C. In combination these

  10. Radiometric Observations of Supercooled Liquid Water within a Split Front over the Sierra Nevada.

    Science.gov (United States)

    Heggli, Mark F.; Reynolds, David W.

    1985-11-01

    A storm bearing close structural resemblance to a katafront was observed from the ground with microwave radiometry and a vertically pointing Ka-band radar over the Sierra Nevada of California. The onset and duration of supercooled liquid water was determined and matched to a split front model used to describe the synoptic features of a katafront. Results indicate that prior to the passage of the upper front no supercooled liquid water was observed. This portion of the storm provided the deepest cloud and coldest cloud tops. Supercooled liquid water was most prevalent after the upper front passage, and persisted until the suspected surface front passage. The duration of measured supercooled water was 16 hours.This information broadens the knowledge regarding the presence of supercooled liquid water, and thus possible seeding potential, within winter storms so that treatment can be confined to the period of storms amenable to cloud seeding. Future studies may well confirm the ease with which these periods can be predicted on an operational basis in the Sierra Nevada.

  11. Thermal conductivity of supercooled water.

    Science.gov (United States)

    Biddle, John W; Holten, Vincent; Sengers, Jan V; Anisimov, Mikhail A

    2013-04-01

    The heat capacity of supercooled water, measured down to -37°C, shows an anomalous increase as temperature decreases. The thermal diffusivity, i.e., the ratio of the thermal conductivity and the heat capacity per unit volume, shows a decrease. These anomalies may be associated with a hypothesized liquid-liquid critical point in supercooled water below the line of homogeneous nucleation. However, while the thermal conductivity is known to diverge at the vapor-liquid critical point due to critical density fluctuations, the thermal conductivity of supercooled water, calculated as the product of thermal diffusivity and heat capacity, does not show any sign of such an anomaly. We have used mode-coupling theory to investigate the possible effect of critical fluctuations on the thermal conductivity of supercooled water and found that indeed any critical thermal-conductivity enhancement would be too small to be measurable at experimentally accessible temperatures. Moreover, the behavior of thermal conductivity can be explained by the observed anomalies of the thermodynamic properties. In particular, we show that thermal conductivity should go through a minimum when temperature is decreased, as Kumar and Stanley observed in the TIP5P model of water. We discuss physical reasons for the striking difference between the behavior of thermal conductivity in water near the vapor-liquid and liquid-liquid critical points.

  12. Separation of convective and stratiform precipitation for a precipitation analysis of the local model of the German Weather Service

    Directory of Open Access Journals (Sweden)

    E. Reimer

    2007-04-01

    Full Text Available An improved independent precipitation data set with the horizontal resolution of 7×7 km grid over central Europe was generated (Free University of Berlin (FUB-precipitation analysis. For scale dependent evaluation of the Local model (LM of the German Weather service, the precipitation data were separated into convective and stratiform fractions. To analyse precipitation amounts an interpolation scheme is used which contains the data set of "present weather" (ww, rain gauges and cloud types from the WMO-network in hourly resolution from the year 1992 until 2004 together with satellite cloud types derived from Meteosat-7 data. The structural analyses of cloud classes from satellite data as well as clouds from the synoptic observations were used to develop a statistical interpolation procedure to build up an independent precipitation analysis in resolution corresponding to the LM grid.

  13. Thermodynamic geometry of supercooled water

    Science.gov (United States)

    May, Helge-Otmar; Mausbach, Peter; Ruppeiner, George

    2015-03-01

    The thermodynamic curvature scalar R is evaluated for supercooled water with a two-state equation of state correlated with the most recent available experimental data. This model assumes a liquid-liquid critical point. Our investigation extends the understanding of the thermodynamic behavior of R considerably. We show that R diverges to -∞ when approaching the assumed liquid-liquid critical point. This limit is consistent with all of the fluid critical point models known so far. In addition, we demonstrate a sign change of R along the liquid-liquid line from negative near the critical point to positive on moving away from the critical point in the low density "ice-like" liquid phase. We also trace out the Widom line in phase space. In addition, we investigate increasing correlation length in supercooled water and compare our results with recent published small angle x-ray scattering measurements.

  14. Aircraft observations of the vertical structure of stratiform precipitation relevant to microwave radiative transfer

    Energy Technology Data Exchange (ETDEWEB)

    Chang, A.T.C. (NASA Goddard Space Flight Center, Greenbelt, MD (United States)); Barnes, A.; Glass, M. (Phillips Lab., Hanscom AFB, MA (United States)); Kakar, R. (NASA Headquarters, Washington, DC (United States)); Wilheit, T.T. (Texas A M Univ., College Station (United States))

    1993-06-01

    The retrieval of rainfall intensity over the oceans from passive microwave observations is based on a radiative transfer model. direct rainfall observations of oceanic rainfall are virtually nonexistent making validation of the retrievals extremely difficult. Observations of the model assumptions provide an alternative approach for improving and developing confidence in the rainfall retrievals. In the winter of 1983, the NASA CV-990 aircraft was equipped with a payload suitable for examining several of the model assumptions. The payload included microwave and infrared radiometers, mirror hygrometers, temperature probes, and PMS probes. On two occasions the aircraft ascended on a spiral track through stratiform precipitation providing an opportunity to study the atmospheric parameters. The assumptions concerning liquid hydrometeors, water vapor, lapse rate, and nonprecipitating clouds were studied. Model assumptions seem to be supported by these observations. 23 refs., 7 figs.

  15. VHF signal power suppression in stratiform and convective precipitation

    Directory of Open Access Journals (Sweden)

    A. J. McDonald

    2006-03-01

    Full Text Available Previous studies have indicated that VHF clear-air radar return strengths are reduced during periods of precipitation. This study aims to examine whether the type of precipitation, stratiform and convective precipitation types are identified, has any impact on the relationships previously observed and to examine the possible mechanisms which produce this phenomenon. This study uses a combination of UHF and VHF wind-profiler data to define periods associated with stratiform and convective precipitation. This identification is achieved using an algorithm which examines the range squared corrected signal to noise ratio of the UHF returns for a bright band signature for stratiform precipitation. Regions associated with convective rainfall have been defined by identifying regions of enhanced range corrected signal to noise ratio that do not display a bright band structure and that are relatively uniform until a region above the melting layer.

    This study uses a total of 68 days, which incorporated significant periods of surface rainfall, between 31 August 2000 and 28 February 2002 inclusive from Aberystwyth (52.4° N, 4.1° W. Examination suggests that both precipitation types produce similar magnitude reductions in VHF signal power on average. However, the frequency of occurrence of statistically significant reductions in VHF signal power are very different. In the altitude range 2-4 km stratiform precipitation is related to VHF signal suppression approximately 50% of the time while in convective precipitation suppression is observed only 27% of the time. This statistical result suggests that evaporation, which occurs more often in stratiform precipitation, is important in reducing the small-scale irregularities in humidity and thereby the radio refractive index. A detailed case study presented also suggests that evaporation reducing small-scale irregularities in humidity may contribute to the observed VHF signal

  16. The Stratiform Region of an MCS on 19 June in TELEX 2004 Observed With Polarimetric and Doppler Radars, Electric Field Soundings, and a Lightning Mapping Array

    Science.gov (United States)

    Ramig, N.; Macgorman, D.; Rust, D.; Schuur, T.; Bruning, E.; Krehbiel, P.; Rison, W.; Hamlin, T.; Straka, J.; Payne, C.; Apostolakopoulos, I.; Biggerstaff, M. I.; Biermann, N.; Carey, L.

    2005-12-01

    Polarimetric and Doppler radar data, balloon-borne soundings of the electric field, and three-dimensional lightning mapping array data were acquired from a mesoscale convective system (MCS) on 19 June 2004 during the Thunderstorm Electrification and Lightning Experiment (TELEX). A total of 10 partial and complete vertical soundings through the storm were obtained from the flights of four instrumented balloons: two launched in the convective region, one in the transition zone, and one in the stratiform region. Each balloon recorded ascent and descent soundings and the transition zone balloon recorded an additional two partial soundings due to a downdraft. At times, multiple soundings were in progress simultaneously. This study focuses on the stratiform region of the MCS, which was sampled by the last two soundings of balloon three and both soundings of balloon four. A comparison of the electrical structure of the stratiform region of this MCS with that of previously published conceptual models suggests that, during at least part of the MCS's lifetime, its electrical structure was Type A, which is more complex than Type B. The main difference between these classifications is the number of charge regions in the cloud. A one-dimensional analysis with Gauss's law indicates six vertically stacked charge layers that alternated polarity within the stratiform region during balloon four's ascent. The vector electric field pattern verified the 1-D Gauss analysis and showed the electric field structure to be primarily horizontally stratified. The maximum magnitude of the electric field was approximately 105 kV/m. The second stratiform sounding sampled by balloon three began fifty minutes after the first stratiform sounding. It showed a very different electric field profile, consistent with neither Type A nor Type B electrical structure, perhaps because the sounding was far from the front of the MCS. There were only three charge layers as opposed to the four charge layers

  17. Drop Size Distribution - Based Separation of Stratiform and Convective Rain

    Science.gov (United States)

    Thurai, Merhala; Gatlin, Patrick; Williams, Christopher

    2014-01-01

    For applications in hydrology and meteorology, it is often desirable to separate regions of stratiform and convective rain from meteorological radar observations, both from ground-based polarimetric radars and from space-based dual frequency radars. In a previous study by Bringi et al. (2009), dual frequency profiler and dual polarization radar (C-POL) observations in Darwin, Australia, had shown that stratiform and convective rain could be separated in the log10(Nw) versus Do domain, where Do is the mean volume diameter and Nw is the scaling parameter which is proportional to the ratio of water content to the mass weighted mean diameter. Note, Nw and Do are two of the main drop size distribution (DSD) parameters. In a later study, Thurai et al (2010) confirmed that both the dual-frequency profiler based stratiform-convective rain separation and the C-POL radar based separation were consistent with each other. In this paper, we test this separation method using DSD measurements from a ground based 2D video disdrometer (2DVD), along with simultaneous observations from a collocated, vertically-pointing, X-band profiling radar (XPR). The measurements were made in Huntsville, Alabama. One-minute DSDs from 2DVD are used as input to an appropriate gamma fitting procedure to determine Nw and Do. The fitted parameters - after averaging over 3-minutes - are plotted against each other and compared with a predefined separation line. An index is used to determine how far the points lie from the separation line (as described in Thurai et al. 2010). Negative index values indicate stratiform rain and positive index indicate convective rain, and, moreover, points which lie somewhat close to the separation line are considered 'mixed' or 'transition' type precipitation. The XPR observations are used to evaluate/test the 2DVD data-based classification. A 'bright-band' detection algorithm was used to classify each vertical reflectivity profile as either stratiform or convective

  18. Improving Mixed-phase Cloud Parameterization in Climate Model with the ACRF Measurements

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Zhien [Univ. of Wyoming, Laramie, WY (United States)

    2016-12-13

    Mixed-phase cloud microphysical and dynamical processes are still poorly understood, and their representation in GCMs is a major source of uncertainties in overall cloud feedback in GCMs. Thus improving mixed-phase cloud parameterizations in climate models is critical to reducing the climate forecast uncertainties. This study aims at providing improved knowledge of mixed-phase cloud properties from the long-term ACRF observations and improving mixed-phase clouds simulations in the NCAR Community Atmosphere Model version 5 (CAM5). The key accomplishments are: 1) An improved retrieval algorithm was developed to provide liquid droplet concentration for drizzling or mixed-phase stratiform clouds. 2) A new ice concentration retrieval algorithm for stratiform mixed-phase clouds was developed. 3) A strong seasonal aerosol impact on ice generation in Arctic mixed-phase clouds was identified, which is mainly attributed to the high dust occurrence during the spring season. 4) A suite of multi-senor algorithms was applied to long-term ARM observations at the Barrow site to provide a complete dataset (LWC and effective radius profile for liquid phase, and IWC, Dge profiles and ice concentration for ice phase) to characterize Arctic stratiform mixed-phase clouds. This multi-year stratiform mixed-phase cloud dataset provides necessary information to study related processes, evaluate model stratiform mixed-phase cloud simulations, and improve model stratiform mixed-phase cloud parameterization. 5). A new in situ data analysis method was developed to quantify liquid mass partition in convective mixed-phase clouds. For the first time, we reliably compared liquid mass partitions in stratiform and convective mixed-phase clouds. Due to the different dynamics in stratiform and convective mixed-phase clouds, the temperature dependencies of liquid mass partitions are significantly different due to much higher ice concentrations in convective mixed phase clouds. 6) Systematic evaluations

  19. Quantitative comparisons of satellite observations and cloud models

    Science.gov (United States)

    Wang, Fang

    Microwave radiation interacts directly with precipitating particles and can therefore be used to compare microphysical properties found in models with those found in nature. Lower frequencies (minimization procedures but produce different CWP and RWP. The similarity in Tb can be attributed to comparable Total Water Path (TWP) between the two retrievals while the disagreement in the microphysics is caused by their different degrees of constraint of the cloud/rain ratio by the observations. This situation occurs frequently and takes up 46.9% in the one month 1D-Var retrievals examined. To attain better constrained cloud/rain ratios and improved retrieval quality, this study suggests the implementation of higher microwave frequency channels in the 1D-Var algorithm. Cloud Resolving Models (CRMs) offer an important pathway to interpret satellite observations of microphysical properties of storms. High frequency microwave brightness temperatures (Tbs) respond to precipitating-sized ice particles and can, therefore, be compared with simulated Tbs at the same frequencies. By clustering the Tb vectors at these frequencies, the scene can be classified into distinct microphysical regimes, in other words, cloud types. The properties for each cloud type in the simulated scene are compared to those in the observation scene to identify the discrepancies in microphysics within that cloud type. A convective storm over the Amazon observed by the Tropical Rainfall Measuring Mission (TRMM) is simulated using the Regional Atmospheric Modeling System (RAMS) in a semi-ideal setting, and four regimes are defined within the scene using cluster analysis: the 'clear sky/thin cirrus' cluster, the 'cloudy' cluster, the 'stratiform anvil' cluster and the 'convective' cluster. The relationship between Tb difference of 37 and 85 GHz and Tb at 85 GHz is found to contain important information of microphysical properties such as hydrometeor species and size distributions. Cluster

  20. Strain Pattern in Supercooled Liquids

    Science.gov (United States)

    Illing, Bernd; Fritschi, Sebastian; Hajnal, David; Klix, Christian; Keim, Peter; Fuchs, Matthias

    2016-11-01

    Investigations of strain correlations at the glass transition reveal unexpected phenomena. The shear strain fluctuations show an Eshelby-strain pattern [˜cos (4 θ ) /r2 ], characteristic of elastic response, even in liquids, at long times. We address this using a mode-coupling theory for the strain fluctuations in supercooled liquids and data from both video microscopy of a two-dimensional colloidal glass former and simulations of Brownian hard disks. We show that the long-ranged and long-lived strain signatures follow a scaling law valid close to the glass transition. For large enough viscosities, the Eshelby-strain pattern is visible even on time scales longer than the structural relaxation time τ and after the shear modulus has relaxed to zero.

  1. Survey of Techniques for Clearing Military Smoke Clouds

    Science.gov (United States)

    1979-05-01

    substances with a high ice nucleating capability (AgI, PbT 2 , CuS, metaldehyde ). Supercooled fog seeding by dry ice was successfully per- formed by...seeding with metaldehyde (Fukuta, 1969). In general, the seeding of supercooled fogs is one of the few fields in which cloud physicists gained an

  2. A Regional Ensemble Forecast System for Stratiform Precipitation Events in Northern China.Part Ⅰ: A Case Study

    Institute of Scientific and Technical Information of China (English)

    ZHU Jiangshan; Fanyou KONG; LEI Hengchi

    2012-01-01

    A single-model,short-range,ensemble forecasting system (Institute of Atmospheric Physics,Regional Ensemble Forecast System,IAP REFS) with 15-km grid spacing,configured with multiple initial conditions,multiple lateral boundary conditions,and multiple physics parameterizations with 11 ensemble members,was developed using the Weather and Research Forecasting Model Advanced Research modeling system for prediction of stratiform precipitation events in northern China.This is the first part of a broader research project to develop a novel cloud-seeding operational system in a probabilistic framework.The ensemble perturbations were extracted from selected members of the National Center for Environmental Prediction Global Ensemble Forecasting System (NCEP GEFS) forecasts,and an inflation factor of two was applied to compensate for the lack of spread in the GEFS forecasts over the research region.Experiments on an actual stratiform precipitation case that occurred on 5-7 June 2009 in northern China were conducted to validate the ensemble system.The IAP REFS system had reasonably good performance in predicting the observed stratiform precipitation system.The perturbation inflation enlarged the ensemble spread and alleviated the underdispersion caused by parent forecasts.Centering the extracted perturbations on higher-resolution NCEP Global Forecast System forecasts resulted in less ensemble mean root-mean-square error and better accuracy in probabilistic quantitative precipitation forecasts (PQPF).However,the perturbation inflation and recentering had less effect on near-surface-level variables compared to the mid-level variables,and its influence on PQPF resolution was limited as well.

  3. Drop Axis Ratio Distributions in Stratiform and Convective Rain

    Science.gov (United States)

    Thurai, M.; Bringi, V. N.; Petersen, W. A.; Schultz, C.

    2010-01-01

    A fully calibrated low profile 2D video disdrometer (2DVD) has been recording many different rainfall events in Northern Alabama (USA) since June 2007. An earlier publication reported drop shapes and axis ratio distributions determined for some of the events. For one of the cases examined, a noticeable shift in the 3.5 - 3.75 mm drop axis ratio distribution was noted. In this paper, we extend the earlier work by separating the 2DVD measurements into stratiform and convective rain. The separation is made possible by using the minute-by-minute drop size distribution (DSD) measured by the 2DVD. The 1-minute DSDs are fitted to a gamma distribution, and using a simple indexing technique which involves two of the fitted parameters, periods of convective and stratiform rain are separated for a given event. The output of the DSD indexing technique is qualitatively confirmed by comparing with simultaneous time series observations from a co-located UHF profiler which continuously records height profiles of reflectivity, Doppler mean and spectral width, all of which enable the identification of bright-band periods and, furthermore, periods of moderate and deep convection. Excellent consistency is found between the output of the DSD-based separation method and the profiler observations. Next, we utilize the output of DSD index-based separation method to flag the periods of severe convection for a given event. Drop axis ratios during the flagged periods are derived and compared with those during stratiform rain periods. Five cases have been considered. Axis ratio distributions do not show appreciable differences between stratiform and convective periods for four of the cases. The fifth case (the same case as reported earlier) shows a shift in the 3.5 - 3.75 mm drop axis ratios during a prolonged period of convection. The contoured shapes for these drops determined from the 2DVD camera data indicate the possibility of non-axisymmetric oscillations, compared with the contoured

  4. Prediction of cloud droplet number in a general circulation model

    Energy Technology Data Exchange (ETDEWEB)

    Ghan, S.J.; Leung, L.R. [Pacific Northwest National Lab., Richland, WA (United States)

    1996-04-01

    We have applied the Colorado State University Regional Atmospheric Modeling System (RAMS) bulk cloud microphysics parameterization to the treatment of stratiform clouds in the National Center for Atmospheric Research Community Climate Model (CCM2). The RAMS predicts mass concentrations of cloud water, cloud ice, rain and snow, and number concnetration of ice. We have introduced the droplet number conservation equation to predict droplet number and it`s dependence on aerosols.

  5. Evolution of the Total Lightning Activity in a Leading-Line and Trailing Stratiform Mesoscale Convective System over Beijing

    Institute of Scientific and Technical Information of China (English)

    LIU Dongxia; QIE Xiushu; XIONG Yajun; FENG Guili

    2011-01-01

    Data from the Beijing SAFIR 3000 lightning detection system and Doppler radar provided some insights into the three-dimensional lightning structure and evolution of a leading-line and trailing-stratiform (LLTS) mesoscale convective system (MCS) over Beijing on 31 July 2007. Most of the lightning in the LLTS-MCSwas intracloud (IC) lightning, while the mean ratio of positive cloud-to-ground (+CG) lightning to -CG lightning was 1:4, which was higher than the average value from previous studies. The majority of CG limhtning occurred in the convective region of the radar echo, particularly at the leading edge of the front.Little IC lightning and little +CG lightning occurred in the stratiform region. The distribution of the CG lightning indicated that the storm had a tilted dipole structure given the wind shear or the tripole charge structure. During the storm's development, most of the IC lightning occurred at an altitude of ~9.5 km;the lightning rate reached its maximum at 10.5 kmn, the altitude of IC lightning in the mature stage of the storm. When the thunderstorm began to dissipate, the altitude of the IC lightning decreased gradually. The spatial distribution of lightning was well correlated with the rainfall on the ground, although the peak value of rainfall appeared 75 min later than the peak lightning rate.

  6. Stratiform chromite deposit model: Chapter E in Mineral deposit models for resource assessment

    Science.gov (United States)

    Schulte, Ruth F.; Taylor, Ryan D.; Piatak, Nadine M.; Seal, Robert R., II

    2012-01-01

    A new descriptive stratiform chromite deposit model was prepared which will provide a framework for understanding the characteristics of stratiform chromite deposits worldwide. Previous stratiform chromite deposit models developed by the U.S. Geological Survey (USGS) have been referred to as Bushveld chromium, because the Bushveld Complex in South Africa is the only stratified, mafic-ultramafic intrusion presently mined for chromite and is the most intensely researched. As part of the on-going effort by the USGS Mineral Resources Program to update existing deposit models for the upcoming national mineral resource assessment, this revised stratiform chromite deposit model includes new data on the geological, mineralogical, geophysical, and geochemical attributes of stratiform chromite deposits worldwide. This model will be a valuable tool in future chromite resource and environmental assessments and supplement previously published models used for mineral resource evaluation.

  7. Comment on 'Modeling of Convective-Stratiform Precipitation Processes: Sensitivity to Partitioning Methods' by Matthias Steiner

    Science.gov (United States)

    Lang, Steve; Tao, W.-K.; Simpson, J.; Ferrier, B.

    2003-01-01

    Despite the obvious notion that the presence of hail or graupel is a good indication of convection, the model results show this does not provide an objective benchmark partly due to the unrealistic presence of small amounts of hail or graupel throughout the anvil in the model but mainly because of the significant amounts of hail or graupel, especially in the tropical TOGA COARE simulation, in the transition zone. Without use of a "transition" category, it is open to debate as how this region should best be defined, as stratiform or as convective. So, the presence of significant hail or graupel contents in this zone significantly degrades its use an objective benchmark for convection. The separation algorithm comparison was done in the context of a cloud-resolving model. These models are widely used and serve a variety of purposes especially with regard to retrieving information that cannot be directly measured by providing synthetic data sets that are consistent and complete. Separation algorithms are regularly applied in these models. However, as with any modeling system, these types 'of models are constantly being improved to overcome any known deficiencies and make them more accurate representations of observed systems. The presence of hail and graupel in the anvil and the bias towards heavy rainfall rates are two such examples of areas that need improvement. Since, both of these can effect the perceived performance of the separation algorithms, the Lang et al. (2003) study did not want to overstate the relative performance of any specific algorithms.

  8. Recent Trends of Summer Convective and Stratiform Precipitation in Mid-Eastern China

    Science.gov (United States)

    Fu, Yunfei; Chen, Fengjiao; Liu, Guosheng; Yang, Yuanjian; Yuan, Renmin; Li, Rui; Liu, Qi; Wang, Yu; Zhong, Lei; Sun, Liang

    2016-09-01

    Many studies have reported on the trends of precipitation in Mid-Eastern China (EC). However, the trends of convective and stratiform precipitation are still unknown. Here, we examine the trends of summer convective and stratiform precipitation in EC from 2002 to 2012 on the basis of the TRMM observations. Results revealed that the rain frequency (RF) for both convective and stratiform precipitation increased in majority regions of Southern EC (SEC), but decreased in Northwest part of Northern EC (NEC). The decreasing rate of RF for stratiform precipitation in NEC is twice as much as that for convective precipitation, while the increase of convective precipitation in SEC is more evident than stratiform precipitation. The rain rate (RR) exhibited a decreasing trend in most portions of EC for both convective and stratiform precipitation. In SEC, neither PW nor WVT has good ability in explaining the precipitation variability. However, in NEC, PW is closely correlated to convective RF and WVT is more closely related to stratiform RF.

  9. Observations of ice multiplication in a weakly convective cell embedded in supercooled mid-level stratus

    Directory of Open Access Journals (Sweden)

    J. Crosier

    2010-08-01

    Full Text Available Simultaneous observations of cloud microphysical properties were obtained by in-situ aircraft measurements and ground based Radar/Lidar. Widespread mid-level stratus cloud was present below a temperature inversion (~5 °C magnitude at 3.6 km altitude. Localised convection (peak updraft 1.5 m s−1 was observed 20 km west of the Radar station. This was associated with convergence at 2.5 km altitude. The convection was unable to penetrate the inversion capping the mid-level stratus.

    The mid-level stratus cloud was vertically thin (~400 m, horizontally extensive (covering 100 s of km and persisted for more than 24 h. The cloud consisted of supercooled water droplets and small concentrations of large (~1 mm stellar/plate like ice which slowly precipitated out. This ice was nucleated at temperatures greater than −12.2 °C and less than −10.0 °C, (cloud top and cloud base temperatures, respectively. No ice seeding from above the cloud layer was observed. This ice was formed by primary nucleation, either through the entrainment of efficient ice nuclei from above/below cloud, or by the slow stochastic activation of immersion freezing ice nuclei contained within the supercooled drops. Above cloud top significant concentrations of sub-micron aerosol were observed and consisted of a mixture of sulphate and carbonaceous material, a potential source of ice nuclei.

    Precipitation from the mid-level stratus evaporated before reaching the surface, whereas rates of up to 1 mm h−1 were observed below the convective feature. There is strong evidence for the Hallett-Mossop (HM process of secondary ice particle production leading to the formation of the precipitation observed. This includes (1 Ice concentrations in the convective feature were more than an order of magnitude greater than the concentration of primary ice in the overlaying stratus, (2 Large concentrations of small pristine columns were observed at the ~−5

  10. What am I? Supercooled droplet or ice?

    CERN Document Server

    Antonini, Carlo; Maitra, Tanmoy; Tiwari, Manish K; Poulikakos, Dimos

    2013-01-01

    In this fluid dynamics video we show the trick played by a supercooled liquid water drop against a superhydrophobic surface. The water drop shows a double personality, impacting onto the surface the first time while still in the liquid state, and then re-impacting as a frozen ice crystal.

  11. An airborne microwave radiometer and measurements of cloud liquid water

    Institute of Scientific and Technical Information of China (English)

    LEI Hengchi; JIN Dezhen; WEI Chong; SHEN Zhilai

    2003-01-01

    A single-channel (9.5 mm) airborne microwave radiometer with one antenna is developed. The retrieval methods and primary observation results of cloud liquid water and super-cooled cloud liquid water are discussed. The aircraft experiments show that the cloud liquid water and super-cooled liquid water can be sensitively monitored at some level of accuracy by the radiometer. The results of cloud liquid water content are reasonable and correspond well with the surface radar echo intensity. The design of the airborne radiometer and its retrieval methods are feasible, giving it application value.

  12. Dynamics of deeply supercooled interfacial water.

    Science.gov (United States)

    Swenson, Jan; Cerveny, Silvina

    2015-01-28

    In this review we discuss the relaxation dynamics of glassy and deeply supercooled water in different types of systems. We compare the dynamics of such interfacial water in ordinary aqueous solutions, hard confinements and biological soft materials. In all these types of systems the dielectric relaxation time of the main water process exhibits a dynamic crossover from a high-temperature non-Arrhenius temperature dependence to a low-temperature Arrhenius behavior. Moreover, at large enough water content the low-temperature process is universal and exhibits the same temperature behavior in all types of systems. However, the physical nature of the dynamic crossover is somewhat different for the different types of systems. In ordinary aqueous solutions it is not even a proper dynamic crossover, since the water relaxation decouples from the cooperative α-relaxation of the solution slightly above the glass transition in the same way as all secondary (β) relaxations of glass-forming materials. In hard confinements, the physical origin of the dynamic crossover is not fully clear, but it seems to occur when the cooperative main relaxation of water at high temperatures reaches a temperature where the volume required for its cooperative motion exceeds the size of the geometrically-confined water cluster. Due to this confinement effect the α-like main relaxation of the confined water seems to transform to a more local β-relaxation with decreasing temperature. Since this low-temperature β-relaxation is universal for all systems at high water content it is possible that it can be considered as an intrinsic β-relaxation of supercooled water, including supercooled bulk water. This possibility, together with other findings for deeply supercooled interfacial water, suggests that the most accepted relaxation scenarios for supercooled bulk water have to be altered.

  13. Global simulations of aerosol processing in clouds

    Directory of Open Access Journals (Sweden)

    C. Hoose

    2008-12-01

    Full Text Available An explicit and detailed representation of in-droplet and in-crystal aerosol particles in stratiform clouds has been introduced in the global aerosol-climate model ECHAM5-HAM. The new scheme allows an evaluation of the cloud cycling of aerosols and an estimation of the relative contributions of nucleation and collision scavenging, as opposed to evaporation of hydrometeors in the global aerosol processing by clouds. On average an aerosol particle is cycled through stratiform clouds 0.5 times. The new scheme leads to important changes in the simulated fraction of aerosol scavenged in clouds, and consequently in the aerosol wet deposition. In general, less aerosol is scavenged into clouds with the new prognostic treatment than what is prescribed in standard ECHAM5-HAM. Aerosol concentrations, size distributions, scavenged fractions and cloud droplet concentrations are evaluated and compared to different observations. While the scavenged fraction and the aerosol number concentrations in the marine boundary layer are well represented in the new model, aerosol optical thickness, cloud droplet number concentrations in the marine boundary layer and the aerosol volume in the accumulation and coarse modes over the oceans are overestimated. Sensitivity studies suggest that a better representation of below-cloud scavenging, higher in-cloud collision coefficients, or a reduced water uptake by seasalt aerosols could reduce these biases.

  14. Global simulations of aerosol processing in clouds

    Directory of Open Access Journals (Sweden)

    C. Hoose

    2008-07-01

    Full Text Available An explicit and detailed representation of in-droplet and in-crystal aerosol particles in stratiform clouds has been introduced in the global aerosol-climate model ECHAM5-HAM. The new scheme allows an evaluation of the cloud cycling of aerosols and an estimation of the relative contributions of nucleation and collision scavenging, as opposed to evaporation of hydrometeors in the global aerosol processing by clouds. On average an aerosol particle is cycled through stratiform clouds 0.5 times. The new scheme leads to important changes in the simulated fraction of aerosol scavenged in clouds, and consequently in the aerosol wet deposition. In general, less aerosol is scavenged into clouds with the new prognostic treatment than what is prescribed in standard ECHAM5-HAM. Aerosol concentrations, size distributions, scavenged fractions and cloud droplet concentrations are evaluated and compared to different observations. While the scavenged fraction and the aerosol number concentrations in the marine boundary layer are well represented in the new model, aerosol optical thickness, cloud droplet number concentrations in the marine boundary layer and the aerosol volume in the accumulation and coarse modes over the oceans are overestimated. Sensitivity studies suggest that a better representation of below-cloud scavenging, higher in-cloud collision coefficients, or a reduced water uptake by seasalt aerosols could reduce these biases.

  15. Mechanism of supercooled droplet freezing on surfaces

    Science.gov (United States)

    Jung, Stefan; Tiwari, Manish K.; Doan, N. Vuong; Poulikakos, Dimos

    2012-01-01

    Understanding ice formation from supercooled water on surfaces is a problem of fundamental importance and general utility. Superhydrophobic surfaces promise to have remarkable 'icephobicity' and low ice adhesion. Here we show that their icephobicity can be rendered ineffective by simple changes in environmental conditions. Through experiments, nucleation theory and heat transfer physics, we establish that humidity and/or the flow of a surrounding gas can fundamentally switch the ice crystallization mechanism, drastically affecting surface icephobicity. Evaporative cooling of the supercooled liquid can engender ice crystallization by homogeneous nucleation at the droplet-free surface as opposed to the expected heterogeneous nucleation at the substrate. The related interplay between droplet roll-off and rapid crystallization is also studied. Overall, we bring a novel perspective to icing and icephobicity, unveiling the strong influence of environmental conditions in addition to the accepted effects of the surface conditions and hydrophobicity.

  16. Gelation on heating of supercooled gelatin solutions.

    Science.gov (United States)

    Guigo, Nathanaël; Sbirrazzuoli, Nicolas; Vyazovkin, Sergey

    2012-04-23

    Diluted (1.0-1.5 wt%) aqueous gelatin solutions have been cooled to -10 °C at a cooling rate 20 °C min(-1) without freezing and detectable gelation. When heated at a constant heating rate (0.5 -2 °C min(-1)), the obtained supercooled solutions demonstrate an atypical process of gelation that has been characterized by regular and stochastically modulated differential scanning calorimetry (DSC) as well as by isoconversional kinetic analysis. The process is detectable as an exothermic peak in the total heat flow of regular DSC and in the nonreversing heat flow of stochastically modulated DSC. Isoconversional kinetic analysis applied to DSC data reveals that the effective activation energy of the process increases from approximately 75 to 200 kJ mol(-1) as a supercooled solution transforms to gel on continuous heating.

  17. The transient behavior of scaling in the atmosphere: stratiform/convective transition and applications to sub-grid scale statistics

    Science.gov (United States)

    Nogueira, M.; Barros, A. P.

    2014-12-01

    Multifractal behavior holds to a remarkable approximation over wide ranges of spatial scales in orographic rainfall and cloud fields. The scaling exponents characterizing this behavior are shown to be fundamentally transient with nonlinear dependencies on the particular atmospheric state and terrain forcing. In particular, a robust transition is found in the scaling parameters between non-convective (stable) and convective (unstable) regimes, with clear physical correspondence to the transition from stratiform to organized convective orographic precipitation. These results can explain two often reported scaling regimes for atmospheric wind, temperature and water observations. On the one hand, spectral slopes around 2-2.3 arise under non-convective or very weak convective conditions when the spatial patterns are dominated by large-scale gradients and landform. On the other hand, under convective conditions the scaling exponents generally fluctuate around 5/3, in agreement with the Kolmogorov turbulent regime accounting for the intermittency correction. High-resolution numerical weather prediction (NWP) models are able to reproduce the ubiquitous scaling behavior of observed atmospheric fields down to their effective resolution length-scale, below which the variability is misrepresented by the model. The effective resolution is shown to be a transient property dependent on the particular simulated conditions and NWP formulation, implying that a blunt decrease in grid spacing without adjusting numerical techniques may not lead to the improvements desired.Finally, the application of transient spatial scaling behavior for stochastic downscaling and sub-grid scale parameterization of cloud and rainfall fields is investigated. The proposed fractal methods are able to rapidly generate large ensembles of high-resolution statistically robust fields from the coarse resolution information alone, which can provide significant improvements for stochastic hydrological prediction

  18. Persistence of orographic mixed-phase clouds

    Science.gov (United States)

    Lohmann, U.; Henneberger, J.; Henneberg, O.; Fugal, J. P.; Bühl, J.; Kanji, Z. A.

    2016-10-01

    Mixed-phase clouds (MPCs) consist of ice crystals and supercooled water droplets at temperatures between 0 and approximately -38°C. They are thermodynamically unstable because the saturation vapor pressure over ice is lower than that over supercooled liquid water. Nevertheless, long-lived MPCs are ubiquitous in the Arctic. Here we show that persistent MPCs are also frequently found in orographic terrain, especially in the Swiss Alps, when the updraft velocities are high enough to exceed saturation with respect to liquid water allowing simultaneous growth of supercooled liquid droplets and ice crystals. Their existence is characterized by holographic measurements of cloud particles obtained at the high-altitude research station Jungfraujoch during spring 2012 and winter 2013 and simulations with the regional climate model COSMO (Consortium of Small-Scale Modeling).

  19. Observations of ice multiplication in a weakly convective cell embedded in supercooled mid-level stratus

    Directory of Open Access Journals (Sweden)

    J. Crosier

    2011-01-01

    Full Text Available Simultaneous observations of cloud microphysical properties were obtained by in-situ aircraft measurements and ground based Radar/Lidar. Widespread mid-level stratus cloud was present below a temperature inversion (~5 °C magnitude at 3.6 km altitude. Localised convection (peak updraft 1.5 m s−1 was observed 20 km west of the Radar station. This was associated with convergence at 2.5 km altitude. The convection was unable to penetrate the inversion capping the mid-level stratus.

    The mid-level stratus cloud was vertically thin (~400 m, horizontally extensive (covering 100 s of km and persisted for more than 24 h. The cloud consisted of supercooled water droplets and small concentrations of large (~1 mm stellar/plate like ice which slowly precipitated out. This ice was nucleated at temperatures greater than −12.2 °C and less than −10.0 °C, (cloud top and cloud base temperatures, respectively. No ice seeding from above the cloud layer was observed. This ice was formed by primary nucleation, either through the entrainment of efficient ice nuclei from above/below cloud, or by the slow stochastic activation of immersion freezing ice nuclei contained within the supercooled drops. Above cloud top significant concentrations of sub-micron aerosol were observed and consisted of a mixture of sulphate and carbonaceous material, a potential source of ice nuclei. Particle number concentrations (in the size range 0.1<D<3.0 μm were measured above and below cloud in concentrations of ~25 cm−3. Ice crystal concentrations in the cloud were constant at around 0.2 L−1. It is estimated that entrainment of aerosol particles into cloud cannot replenish the loss of ice nuclei from the cloud layer via precipitation.

    Precipitation from the mid-level stratus evaporated before reaching the surface, whereas rates of up to 1 mm h−1 were observed below the convective feature. There is strong

  20. Detecting charge in the base of layer clouds

    Science.gov (United States)

    Harrison, R. Giles

    2017-04-01

    Stratiform clouds are known to acquire charge at their upper and lower horizontal boundaries as a consequence of vertical current flow in the global atmospheric electric circuit, passing through the cloud. Balloon carried sensors have provided direct observations of this effect, but opportunities for measurements are limited. For cloud bases at low altitudes with substantial charge, there is a weak effect of the charge on the electric field measured at the surface. This allows the cloud base charge to be inferred. Using cloud and surface electric field measurements obtained at Reading during 2015 and 2016, the presence of cloud base charge has been inferred. For the charge to be detectable it is found that the cloud base needs to be below 1 km altitude, and that the stratiform cloud needs to persist for typically 12 hours. If the cloud altitude becomes too low (theoretical expectations requiring the layer cloud to be sufficiently extensive that the vertical current passes through, rather than around the cloud.

  1. New Mexico cloud super cooled liquid water survey final report 2009.

    Energy Technology Data Exchange (ETDEWEB)

    Beavis, Nick; Roskovensky, John K.; Ivey, Mark D.

    2010-02-01

    Los Alamos and Sandia National Laboratories are partners in an effort to survey the super-cooled liquid water in clouds over the state of New Mexico in a project sponsored by the New Mexico Small Business Assistance Program. This report summarizes the scientific work performed at Sandia National Laboratories during the 2009. In this second year of the project a practical methodology for estimating cloud super-cooled liquid water was created. This was accomplished through the analysis of certain MODIS sensor satellite derived cloud products and vetted parameterizations techniques. A software code was developed to analyze multiple cases automatically. The eighty-one storm events identified in the previous year effort from 2006-2007 were again the focus. Six derived MODIS products were obtained first through careful MODIS image evaluation. Both cloud and clear-sky properties from this dataset were determined over New Mexico. Sensitivity studies were performed that identified the parameters which most influenced the estimation of cloud super-cooled liquid water. Limited validation was undertaken to ensure the soundness of the cloud super-cooled estimates. Finally, a path forward was formulized to insure the successful completion of the initial scientific goals which include analyzing different of annual datasets, validation of the developed algorithm, and the creation of a user-friendly and interactive tool for estimating cloud super-cooled liquid water.

  2. Longwave indirect effect of mineral dusts on ice clouds

    Directory of Open Access Journals (Sweden)

    Q. Min

    2010-08-01

    Full Text Available In addition to microphysical changes in clouds, changes in nucleation processes of ice cloud due to aerosols would result in substantial changes in cloud top temperature as mildly supercooled clouds are glaciated through heterogenous nucleation processes. Measurements from multiple sensors on multiple observing platforms over the Atlantic Ocean show that the cloud effective temperature increases with mineral dust loading with a slope of +3.06 °C per unit aerosol optical depth. The macrophysical changes in ice cloud top distributions as a consequence of mineral dust-cloud interaction exert a strong cooling effect (up to 16 Wm−2 of thermal infrared radiation on cloud systems. Induced changes of ice particle size by mineral dusts influence cloud emissivity and play a minor role in modulating the outgoing longwave radiation for optically thin ice clouds. Such a strong cooling forcing of thermal infrared radiation would have significant impacts on cloud systems and subsequently on climate.

  3. Transport properties of supercooled confined water

    Science.gov (United States)

    Mallamace, F.; Branca, C.; Broccio, M.; Corsaro, C.; Gonzalez-Segredo, N.; Spooren, J.; Stanley, H. E.; Chen, S.-H.

    2008-07-01

    This article presents an overview of recent experiments performed on transport properties of water in the deeply supercooled region, a temperature region of fundamental importance in the science of water. We report data of nuclear magnetic resonance, quasi-elastic neutron scattering, Fourier-transform infrared spectroscopy, and Raman spectroscopy, studying water confined in nanometer-scale environments. When contained within small pores, water does not crystallise, and can be supercooled well below its homogeneous nucleation temperature Th. On this basis it is possible to carry out a careful analysis of the well known thermodynamical anomalies of water. Studying the temperature and pressure dependencies of water dynamics, we show that the liquid-liquid phase transition (LLPT) hypothesis represents a reliable model for describing liquid water. In this model, water in the liquid state is a mixture of two different local structures, characterised by different densities, namely the low density liquid (LDL) and the high-density liquid (HDL). The LLPT line should terminate at a special transition point: a low-T liquid-liquid critical point. We discuss the following experimental findings on liquid water: (i) a crossover from non-Arrhenius behaviour at high T to Arrhenius behaviour at low T in transport parameters; (ii) a breakdown of the Stokes-Einstein relation; (iii) the existence of a Widom line, which is the locus of points corresponding to maximum correlation length in the p-T phase diagram and which ends in the liquid-liquid critical point; (iv) the direct observation of the LDL phase; (v) a minimum in the density at approximately 70 K below the temperature of the density maximum. In our opinion these results represent the experimental proofs of the validity of the LLPT hypothesis.

  4. Evolution in Cloud Population Statistics of the MJO: From AMIE Field Observations to Global-Cloud Permitting Models Final Report

    Energy Technology Data Exchange (ETDEWEB)

    Kollias, Pavlos [McGill Univ., Montreal, QC (Canada). Atmospheric and Oceanic Sciences Dept.

    2017-02-09

    This is a multi-institutional, collaborative project using a three-tier modeling approach to bridge field observations and global cloud-permitting models, with emphases on cloud population structural evolution through various large-scale environments. Our contribution was in data analysis for the generation of high value cloud and precipitation products and derive cloud statistics for model validation. There are two areas in data analysis that we contributed: the development of a synergistic cloud and precipitation cloud classification that identify different cloud (e.g. shallow cumulus, cirrus) and precipitation types (shallow, deep, convective, stratiform) using profiling ARM observations and the development of a quantitative precipitation rate retrieval algorithm using profiling ARM observations. Similar efforts have been developed in the past for precipitation (weather radars), but not for the millimeter-wavelength (cloud) radar deployed at the ARM sites.

  5. Entropy-driven liquid-liquid separation in supercooled water

    OpenAIRE

    Holten, V.; Anisimov, M.A.

    2012-01-01

    Twenty years ago Poole et al. (Nature 360, 324, 1992) suggested that the anomalous properties of supercooled water may be caused by a critical point that terminates a line of liquid-liquid separation of lower-density and higher-density water. Here we present an explicit thermodynamic model based on this hypothesis, which describes all available experimental data for supercooled water with better quality and with fewer adjustable parameters than any other model suggested so far. Liquid water a...

  6. Supercooled water in austral summer in Prydz Bay,Antarctica

    Institute of Scientific and Technical Information of China (English)

    SHI Jiuxin; CHENG Yaoyao; JIAO Yutian; HOU Jiaqiang

    2011-01-01

    Supercooled water with temperatures below freezing point, was identified from hydrographic data obtained by Chinese and Australian expeditions to Prydz Bay, Antarctica, during the austral summer. The study shows that most supercooled waters occurred at depths of 63-271 m in the region north of the Amery Ice Shelf (AIS) front. The maximum supercooling was 0.16℃ below the in-situ freezing point. In temperature and salinity ranges of-2.14 - -1.96℃ and 34.39--34.46, respectively,the water was colder and fresher than peripheral shelf water. The supercooled water had less variability in the vertical profiles compared to shelf water. Based on analysis of their thermohaline features and spatial distribution, as well as the circulation pattern in Prydz Bay, we conclude that these supercooled waters originated from a cavity beneath the AIS and resulted from upwelling just outside of the AIS front. Water emerging from the ice shelf cools to an extremely low temperature (about -2.0℃) by additional cooling from the ice shelf, and becomes buoyant with the addition of melt water from the ice shelf base. When this water flows out of the ice shelf front, its upper boundary is removed, and thus it rises abruptly. Once the temperature of this water reaches below the freezing point, supercooling takes place. In summer, the seasonal pycnocline at ~100 m water depth acts as a barrier to upwelling and supercooling. The upwelling of ice shelf outflow water illuminates a unique mid-depth convection of the polar ocean.

  7. The transient behavior of Peltier junctions pulsed with supercooling

    Science.gov (United States)

    Mao, J. N.; Chen, H. X.; Jia, H.; Qian, X. L.

    2012-07-01

    There exists the transient thermoelectric supercooling effect that can be enhanced by keeping on increasing the Peltier cooling effect to compensate for the Joule heating effect and Fourier heat conduction effect arriving at the cold junction, in which a transient cold spike can be produced by superimposing an additional shaped current pulse of a large magnitude on the original steady-state optimum value. Most previous work on the transient supercooling mainly focused on the minimum supercooling temperature achievable and separately analyzed the beneficial or detrimental effects on the transient supercooling performance, which was not clarified quantitatively to what extent the interactional effects were on the enhancement of the transient supercooling performance. In this work, we systematically investigate a numerical solution involving time-dependent imposed voltage pulse and time-dependent thermal boundary conditions on the transient supercooling behavior as well as the response of characteristic time and cold-junction temperature distribution to the pulse operation parameters during the periods of pulse start-up, pulse-on time, and pulse-off time, which is served as a theoretical basis for exploiting the coupling interaction of the thermoelectric effects on the heat diffusion from or to the cold junction interrelated with the amount of the availably electrical conversion in the short time scale. Additionally, the advantage of certain pulse forms over others is described. The results indicate that Peltier supercooling capacity shows a decreasing monotonic trend in proportion to the total amount of electrical conversion, and the maximum coefficient of performance for cooling state is about 0.5 to be achieved at steady state. Taking advantage of the temporary Peltier effect focused electrical conversion as the additional cooling for a period long enough against the earlier arrival of the excessively Joule heating dominated heat accumulation is the key parameter

  8. Effects of PVA(Polyvinyl Alcohol) on Supercooling Phenomena of Water

    Science.gov (United States)

    Kumano, Hiroyuki; Saito, Akio; Okawa, Seiji; Takizawa, Hiroshi

    In this paper, effects of polymer additive on supercooling of water were investigated experimentally. Poly-vinyl alcohol (PVA) were used as the polymer, and the samples were prepared by dissolving PVA in ultra pure water. Concentration, degree of polymerization and saponification of PVA were varied as the experimental parameters. The sample was cooled, and the temperature at the instant when ice appears was measured. Since freezing of supercooled water is statistical phenomenon, many experiments were carried out and average degrees of supercooling were obtained for each experimental condition. As the result, it was found that PVA affects nucleation of supercooling and the degree of supercooling increases by adding the PVA. Especially, it is found that the average degree of supercooling increases and the standard deviation of average degree of supercooling decreases with increase of degree of saponification of PVA. However, the average degree of supercooling are independent of the degree of polymerization of PVA in the range of this study.

  9. Supercooling across first-order phase transitions in vortex matter

    Indian Academy of Sciences (India)

    P Chaddah; S B Roy

    2000-06-01

    Hysteresis in cycling through first-order phase transitions in vortex matter, akin to the well-studied phenomenon of supercooling of water, has been discussed in literature. Hysteresis can be seen while varying either temperature or magnetic field (and thus the density of vortices). Our recent work on phase transitions with two control variables shows that the observable region of metastability of the supercooled phase would depend on the path followed in - space, and will be larger when is lowered at constant compared to the case when is lowered at constant . We discuss the effect of isothermal field variations on metastable supercooled states produced by field-cooling. This path dependence is not a priori applicable to metastability caused by reduced diffusivity or hindered kinetics.

  10. On the potential energy landscape of supercooled liquids and glasses

    DEFF Research Database (Denmark)

    Rodney, D.; Schrøder, Thomas

    2011-01-01

    The activation-relaxation technique (ART), a saddle-point search method, is applied to determine the potential energy landscape around supercooled and glassy configurations of a three-dimensional binary Lennard-Jones system. We show a strong relation between the distribution of activation energies...... around a given glassy configuration and its history, in particular, the cooling rate used to produce the glass and whether or not the glass was plastically deformed prior to sampling. We also compare the thermally activated transitions found by ART around a supercooled configuration with the succession...... of transitions undergone by the same supercooled liquid during a time trajectory simulated by molecular dynamics. We find that ART is biased towards more heterogeneous transitions with higher activation energies and more broken bonds than the MD simulation....

  11. A Possible Explanation for the Z -R Parameter Inconsistency when Comparing Stratiform and Convective Rainfall

    Science.gov (United States)

    Lane, John; Kasparis, Takis; Michaelides, Silas

    2016-04-01

    The well-known Z -R power law Z = ARb uses two parameters, A and b, in order to relate rainfall rate R to measured weather radar reflectivity Z. A common method used by researchers is to compute Z and R from disdrometer data and then extract the A-bparameter pair from a log-linear line fit to a scatter plot of Z -R pairs. Even though it may seem far more truthful to extract the parameter pair from a fit of radar ZR versus gauge rainfall rate RG, the extreme difference in spatial and temporal sampling volumes between radar and rain gauge creates a slew of problems that can generally only be solved by using rain gauge arrays and long sampling averages. Disdrometer derived A - b parameters are easily obtained and can provide information for the study of stratiform versus convective rainfall. However, an inconsistency appears when comparing averaged A - b pairs from various researchers. Values of b range from 1.26 to 1.51 for both stratiform and convective events. Paradoxically the values of Afall into three groups: 150 to 200 for convective; 200 to 400 for stratiform; and 400 to 500 again for convective. This apparent inconsistency can be explained by computing the A - b pair using the gamma DSD coupled with a modified drop terminal velocity model, v(D) = αDβ - w, where w is a somewhat artificial constant vertical velocity of the air above the disdrometer. This model predicts three regions of A, corresponding to w 0, which approximately matches observed data.

  12. Numerical framework and performance of the new multiple-phase cloud microphysics scheme in RegCM4.5: precipitation, cloud microphysics, and cloud radiative effects

    Science.gov (United States)

    Nogherotto, Rita; Tompkins, Adrian Mark; Giuliani, Graziano; Coppola, Erika; Giorgi, Filippo

    2016-07-01

    We implement and evaluate a new parameterization scheme for stratiform cloud microphysics and precipitation within regional climate model RegCM4. This new parameterization is based on a multiple-phase one-moment cloud microphysics scheme built upon the implicit numerical framework recently developed and implemented in the ECMWF operational forecasting model. The parameterization solves five prognostic equations for water vapour, cloud liquid water, rain, cloud ice, and snow mixing ratios. Compared to the pre-existing scheme, it allows a proper treatment of mixed-phase clouds and a more physically realistic representation of cloud microphysics and precipitation. Various fields from a 10-year long integration of RegCM4 run in tropical band mode with the new scheme are compared with their counterparts using the previous cloud scheme and are evaluated against satellite observations. In addition, an assessment using the Cloud Feedback Model Intercomparison Project (CFMIP) Observational Simulator Package (COSP) for a 1-year sub-period provides additional information for evaluating the cloud optical properties against satellite data. The new microphysics parameterization yields an improved simulation of cloud fields, and in particular it removes the overestimation of upper level cloud characteristics of the previous scheme, increasing the agreement with observations and leading to an amelioration of a long-standing problem in the RegCM system. The vertical cloud profile produced by the new scheme leads to a considerably improvement of the representation of the longwave and shortwave components of the cloud radiative forcing.

  13. Characterization of clouds in Titan's tropical atmosphere

    Science.gov (United States)

    Griffith, C.A.; Penteado, P.; Rodriguez, S.; Le, Mouelic S.; Baines, K.H.; Buratti, B.; Clark, R.; Nicholson, P.; Jaumann, R.; Sotin, Christophe

    2009-01-01

    Images of Titan's clouds, possible over the past 10 years, indicate primarily discrete convective methane clouds near the south and north poles and an immense stratiform cloud, likely composed of ethane, around the north pole. Here we present spectral images from Cassini's Visual Mapping Infrared Spectrometer that reveal the increasing presence of clouds in Titan's tropical atmosphere. Radiative transfer analyses indicate similarities between summer polar and tropical methane clouds. Like their southern counterparts, tropical clouds consist of particles exceeding 5 ??m. They display discrete structures suggestive of convective cumuli. They prevail at a specific latitude band between 8??-20?? S, indicative of a circulation origin and the beginning of a circulation turnover. Yet, unlike the high latitude clouds that often reach 45 km altitude, these discrete tropical clouds, so far, remain capped to altitudes below 26 km. Such low convective clouds are consistent with the highly stable atmospheric conditions measured at the Huygens landing site. Their characteristics suggest that Titan's tropical atmosphere has a dry climate unlike the south polar atmosphere, and despite the numerous washes that carve the tropical landscape. ?? 2009. The American Astronomical Society.

  14. Thermodynamics and dynamics of supercooled water

    Science.gov (United States)

    Mazza, Marco G.

    This thesis employs methods of statistical mechanics and numerical simulations to study some aspects of the thermodynamic and dynamic behavior of liquid water. As liquid water is cooled down into the supercooled state, some regions of the sample show correlated molecular motion. Previously, only the translational motion has been the object of investigation. Given the importance of orientational dynamics for water, a question that naturally arises is whether the rotational molecular motion also shows heterogeneous dynamics. We show that the most rotationally mobile molecules tend to form clusters, "rotational heterogeneities", and we study their dependence upon observation time and temperature. Further, we show evidence that molecules belonging to dynamic heterogeneities are involved in bifurcated bonds. Since the presence of dynamic heterogeneities is increasingly important as the temperature is lowered, one would expect a signature of this phenomenon in dynamical quantities. We study the effect of dynamic heterogeneities on the origin of the breakdown of the Stokes--- Einstein and Stokes---Einstein---Debye relations for water. These relations link the diffusivity to temperature and viscosity. We study the separation of time scales of dynamic heterogeneities and the diffusive regime. We also consider different sets of mobility, slowest and fastest, for both translational and rotational heterogeneities. A long-standing problem in biology is the seemingly universal loss of biological activity of all biomolecules, a phenomenon termed the "protein glass transition". We explore the connection between the hypothesized liquid-liquid phase transition of water, and the protein glass transition. We find that the protein glass transition coincides with the crossing of the Widom line of hydration water. Many different scenarios have been proposed to rationalize water's thermodynamic anomalies. We study a tell model for water using the Wolff' cluster algorithm, which permits

  15. A systematic experimental study on the evaporation rate of supercooled water droplets at subzero temperatures and varying relative humidity

    Science.gov (United States)

    Ruberto, S.; Reutzsch, J.; Roth, N.; Weigand, B.

    2017-05-01

    Supercooled water droplets (SWD) are present in clouds at high altitude and subjected to very low temperatures and high relative humidity. These droplets exist in a metastable state. The understanding of the evaporation of SWD at these extreme conditions is of high interest to understand rain, snow, and hail generating mechanisms in clouds. This paper focuses on the experimental results of the measurements of the evaporation rates β of supercooled water droplets. For this purpose, single SWDs are trapped by means of optical levitation. During the evaporation process, the elastically scattered light in the forward regime is recorded and evaluated. Experiments have been performed for different relative humidities φ at three constant ambient temperatures, namely, {T_∞}=268.15; 263.15; 253.15 {{K}} ({t_∞} = -5; -10; -20°C). The experimental data agrees well with direct numerical simulations (DNS) carried out with the in-house code Free Surface 3D (FS3D) and shows that the use of a simplified model is permissible for these ambient conditions.

  16. Formation of modern and Paleozoic stratiform barite at cold methane seeps on continental margins

    Science.gov (United States)

    Torres, M.E.; Bohrmann, G.; Dube, T.E.; Poole, F.G.

    2003-01-01

    Stratiform (bedded) Paleozoic barite occurs as large conformable beds within organic- and chert-rich sediments; the beds lack major sulfide minerals and are the largest and most economically significant barite deposits in the geologic record. Existing models for the origin of bedded barite fail to explain all their characteristics: the deposits display properties consistent with an exhalative origin involving fluid ascent to the seafloor, but they lack appreciable polymetallic sulfide minerals and the corresponding strontium isotopic composition to support a hydrothermal vent source. A new mechanism of barite formation, along structurally controlled sites of cold fluid seepage in continental margins, involves barite remobilization in organic-rich, highly reducing sediments, transport of barium-rich fluids, and barite precipitation at cold methane seeps. The lithologic and depositional framework of Paleozoic and cold seep barite, as well as morphological, textural, and chemical characteristics of the deposits, and associations with chemosymbiotic fauna, all support a cold seep origin for stratiform Paleozoic barite. This understanding is highly relevant to paleoceanographic and paleotectonic studies, as well as to economic geology.

  17. Peculiar thermodynamics of the second critical point in supercooled water.

    Science.gov (United States)

    Bertrand, C E; Anisimov, M A

    2011-12-08

    On the basis of the principle of critical-point universality, we examine the peculiar thermodynamics of the liquid-liquid critical point in supercooled water. We show that the liquid-liquid criticality in water represents a special kind of critical behavior in fluids, intermediate between two limiting cases: the lattice gas, commonly used to model liquid-vapor transitions, and the lattice liquid, a weakly compressible liquid with an entropy-driven phase separation. While the ordering field in the lattice gas is associated with the chemical potential and the order parameter with the density, in the lattice liquid the ordering field is the temperature and the order parameter is the entropy. The behavior of supercooled water is much closer to lattice-liquid behavior than to lattice-gas behavior. Using new experimental data recently obtained by Mishima [J. Chem. Phys. 2010, 133, 144503], we have revised the parametric scaled equation of state, previously suggested by Fuentevilla and Anisimov [Phys. Rev. Lett. 2006, 97, 195702], and obtain a consistent description of the thermodynamic anomalies of supercooled water by adjusting linear backgrounds, one critical amplitude, and the critical pressure. We also show how the lattice-liquid description affects the finite-size scaling description of supercooled water in confined media.

  18. Hopping in a supercooled binary Lennard-Jones liquid

    DEFF Research Database (Denmark)

    Schrøder, Thomas; Dyre, Jeppe

    1998-01-01

    A binary Lennard–Jones liquid has been investigated by molecular dynamics at equilibrium supercooled conditions. At the lowest temperature investigated, hopping is present in the system as indicated by a secondary peak in 4r2Gs(r,t), where Gs(r,t) is the van Hove self correlation function...

  19. Entropy calculations for a supercooled liquid crystalline blue phase

    Energy Technology Data Exchange (ETDEWEB)

    Singh, U [Physics Department, University of the West Indies, PO Box 64, Bridgetown (Barbados)

    2007-01-15

    We observed, using polarized light microscopy, the supercooling of the blue phase (BPI) of cholesteryl proprionate and measured the corresponding liquid crystalline phase transition temperatures. From these temperatures and additional published data we have provided, for the benefit of undergraduate physics students, a nontraditional example involving entropy calculations for an irreversible transition.

  20. Evaluation of Cloud-Resolving Model Intercomparison Simulations Using TWP-ICE Observations: Precipitation and Cloud Structure

    Science.gov (United States)

    Varble, Adam; Fridlind, Ann M.; Zipser, Edward J.; Ackerman, Andrew S.; Chaboureau, Jean-Pierre; Fan, Jiwen; Hill, Adrian; McFarlane, Sally A.; Pinty, Jean-Pierre; Shipway, Ben

    2011-01-01

    The Tropical Warm Pool.International Cloud Experiment (TWP ]ICE) provided extensive observational data sets designed to initialize, force, and constrain atmospheric model simulations. In this first of a two ]part study, precipitation and cloud structures within nine cloud ]resolving model simulations are compared with scanning radar reflectivity and satellite infrared brightness temperature observations during an active monsoon period from 19 to 25 January 2006. Seven of nine simulations overestimate convective area by 20% or more leading to general overestimation of convective rainfall. This is balanced by underestimation of stratiform rainfall by 5% to 50% despite overestimation of stratiform area by up to 65% because of a preponderance of very low stratiform rain rates in all simulations. All simulations fail to reproduce observed radar reflectivity distributions above the melting level in convective regions and throughout the troposphere in stratiform regions. Observed precipitation ]sized ice reaches higher altitudes than simulated precipitation ]sized ice despite some simulations that predict lower than observed top ]of ]atmosphere infrared brightness temperatures. For the simulations that overestimate radar reflectivity aloft, graupel is the cause with one ]moment microphysics schemes whereas snow is the cause with two ]moment microphysics schemes. Differences in simulated radar reflectivity are more highly correlated with differences in mass mean melted diameter (Dm) than differences in ice water content. Dm is largely dependent on the mass ]dimension relationship and gamma size distribution parameters such as size intercept (N0) and shape parameter (m). Having variable density, variable N0, or m greater than zero produces radar reflectivities closest to those observed.

  1. Evaluation of Cloud-Resolving Model Intercomparison Simulations Using TWP-ICE Observations: Precipitation and Cloud Structure

    Energy Technology Data Exchange (ETDEWEB)

    Varble, Adam C.; Fridlind, Ann; Zipser, Ed; Ackerman, Andrew; Chaboureau, Jean-Pierre; Fan, Jiwen; Hill, Adrian; McFarlane, Sally A.; Pinty, Jean-Pierre; Shipway, Ben

    2011-06-24

    The Tropical Warm Pool - International Cloud Experiment (TWP-ICE) provided high quality model forcing and observational datasets through which detailed model and observational intercomparisons could be performed. In this first of a two part study, precipitation and cloud structures within nine cloud-resolving model simulations are compared with scanning radar reflectivity and satellite infrared brightness temperature observations during an active monsoon period from 19 to 25 January 2006. Most simulations slightly overestimate volumetric convective rainfall. Overestimation of simulated convective area by 50% or more in several simulations is somewhat offset by underestimation of mean convective rain rates. Stratiform volumetric rainfall is underestimated by 13% to 53% despite overestimation of stratiform area by up to 65% because stratiform rain rates in every simulation are much lower than observed. Although simulations match the peaked convective radar reflectivity distribution at low levels, they do not reproduce the peaked distributions observed above the melting level. Simulated radar reflectivity aloft in convective regions is too high in most simulations. 29 In stratiform regions, there is a large spread in model results with none resembling 30 observed distributions. Above the melting level, observed radar reflectivity decreases 31 more gradually with height than simulated radar reflectivity. A few simulations produce 32 unrealistically uniform and cold 10.8-μm infrared brightness temperatures, but several 33 simulations produce distributions close to observed. Assumed ice particle size 34 distributions appear to play a larger role than ice water contents in producing incorrect 35 simulated radar reflectivity distributions aloft despite substantial differences in mean 36 graupel and snow water contents across models. 37

  2. Evaluation of Cloud-Resolving Model Intercomparison Simulations Using TWP-ICE Observations: Precipitation and Cloud Structure

    Science.gov (United States)

    Varble, Adam; Fridlind, Ann M.; Zipser, Edward J.; Ackerman, Andrew S.; Chaboureau, Jean-Pierre; Fan, Jiwen; Hill, Adrian; McFarlane, Sally A.; Pinty, Jean-Pierre; Shipway, Ben

    2011-01-01

    The Tropical Warm Pool.International Cloud Experiment (TWP ]ICE) provided extensive observational data sets designed to initialize, force, and constrain atmospheric model simulations. In this first of a two ]part study, precipitation and cloud structures within nine cloud ]resolving model simulations are compared with scanning radar reflectivity and satellite infrared brightness temperature observations during an active monsoon period from 19 to 25 January 2006. Seven of nine simulations overestimate convective area by 20% or more leading to general overestimation of convective rainfall. This is balanced by underestimation of stratiform rainfall by 5% to 50% despite overestimation of stratiform area by up to 65% because of a preponderance of very low stratiform rain rates in all simulations. All simulations fail to reproduce observed radar reflectivity distributions above the melting level in convective regions and throughout the troposphere in stratiform regions. Observed precipitation ]sized ice reaches higher altitudes than simulated precipitation ]sized ice despite some simulations that predict lower than observed top ]of ]atmosphere infrared brightness temperatures. For the simulations that overestimate radar reflectivity aloft, graupel is the cause with one ]moment microphysics schemes whereas snow is the cause with two ]moment microphysics schemes. Differences in simulated radar reflectivity are more highly correlated with differences in mass mean melted diameter (Dm) than differences in ice water content. Dm is largely dependent on the mass ]dimension relationship and gamma size distribution parameters such as size intercept (N0) and shape parameter (m). Having variable density, variable N0, or m greater than zero produces radar reflectivities closest to those observed.

  3. Evaluation of Cloud-Resolving Model Intercomparison Simulations Using TWP-ICE Observations: Precipitation and Cloud Structure

    Energy Technology Data Exchange (ETDEWEB)

    Varble, Adam; Fridlind, Ann; Zipser, Edward J.; Ackerman, Andrew; Chaboureau, Jean-Pierre; Fan, Jiwen; Hill, Adrian; McFarlane, Sally A.; Pinty, Jean-Pierre; Shipway, Ben

    2011-10-04

    The Tropical Warm Pool – International Cloud Experiment (TWP-ICE) provided high quality model forcing and observational datasets through which detailed model and observational intercomparisons could be performed. In this first of a two part study, precipitation and cloud structures within nine cloud-resolving model simulations are compared with scanning radar reflectivity and satellite infrared brightness temperature observations during an active monsoon period from 19 to 25 January 2006. Most simulations slightly overestimate volumetric convective rainfall. Overestimation of simulated convective area by 50% or more in several simulations is somewhat offset by underestimation of mean convective rain rates. Stratiform volumetric rainfall is underestimated by 13% to 53% despite overestimation of stratiform area by up to 65% because stratiform rain rates in every simulation are much lower than observed. Although simulations match the peaked convective radar reflectivity distribution at low levels, they do not reproduce the peaked distributions observed above the melting level. Simulated radar reflectivity aloft in convective regions is too high in most simulations. In stratiform regions, there is a large spread in model results with none resembling observed distributions. Above the melting level, observed radar reflectivity decreases more gradually with height than simulated radar reflectivity. A few simulations produce unrealistically uniform and cold 10.8-μm infrared brightness temperatures, but several simulations produce distributions close to observed. Assumed ice particle size distributions appear to play a larger role than ice water contents in producing incorrect simulated radar reflectivity distributions aloft despite substantial differences in mean graupel and snow water contents across models.

  4. Arctic clouds in the ECMWF forecast model: an evaluation of cloud parameterization schemes

    Science.gov (United States)

    Sotiropoulou, Georgia; Sedlar, Joseph; Forbes, Richard; Tjernström, Michael

    2016-04-01

    The Arctic is experiencing significant changes and is an important part of the global climate, which needs to be understood and accurately represented in both climate and weather prediction models. Mixed-phase clouds are an integral part of the Arctic system, for precipitation and for their interactions with radiation and the local thermodynamics. Mixed-phase processes are often poorly represented in global models and many use an empirically based diagnostic partition between the liquid and ice phase that is dependent solely on temperature. However, increasingly more complex microphysical parameterizations are being implemented allowing a more physical representation of mixed-phase clouds. This study uses in situ observations from ASCOS campaign in the central Arctic to evaluate the impact of a change from a diagnostic to a prognostic parameterization of mixed-phase cloud and increased vertical resolution in the ECMWF Integrated Forecast System (IFS). The newer cloud scheme improves the representation of the vertical structure of mixed-phase clouds, with supercooled liquid water at cloud top and ice precipitating below, improved further with higher vertical resolution. Increased supercooled liquid water and decreased ice content are both in closer agreement with observations. However, these changes do not result in any substantial improvement in surface radiation and there remains a warm and moist bias in the lowest part of the atmosphere. Both schemes also fail to capture the transitions from overcast to cloud-free conditions. Moreover, whereas the observed cloud layer is frequently decoupled from the surface, in the model the cloud remains coupled to the surface most of the time. The changes to the cloud scheme are an important step forward in improving the representation of Arctic clouds, but improvements in other aspects such as boundary layer turbulence, cloud radiative properties, sensitivity to low aerosol concentrations and representation of the sea

  5. Summer Arctic Clouds in the ECMWF Forecast Model: an Evaluation of Cloud Parameterization Schemes

    Science.gov (United States)

    Sotiropoulou, G.; Sedlar, J.; Forbes, R.; Tjernstrom, M. K. H.

    2015-12-01

    The Arctic is experiencing significant changes and is an important part of the global climate, which needs to be understood and accurately represented in both climate and weather prediction models. Mixed-phase clouds are an integral part of the Arctic system, for precipitation and for their interactions with radiation and the local thermodynamics. Mixed-phase processes are often poorly represented in global models and many use an empirically based diagnostic partition between the liquid and ice phase that is dependent solely on temperature. However, increasingly more complex microphysical parameterizations are being implemented allowing a more physical representation of mixed-phase clouds. This study uses in situ observations from the ASCOS campaign in the central Arctic to evaluate the impact of a change from a diagnostic to a prognostic parameterization of mixed-phase clouds and increased vertical resolution in the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecast System (IFS). The newer cloud scheme improves the representation of the vertical structure of mixed-phase clouds, with supercooled liquid water at cloud top and ice precipitating below, improved further with higher vertical resolution. Increased supercooled liquid water and decreased ice content are both in closer agreement with observations. However, these changes do not result in any substantial improvement in surface radiation and there remains a warm and moist bias in the lowest part of the atmosphere. Both schemes also fail to capture the transitions from overcast to cloud-free conditions. Moreover, whereas the observed cloud layer is frequently decoupled from the surface, in the model the cloud remains coupled to the surface most of the time. The changes implemented to the cloud scheme are an important step forward in improving the representation of Arctic clouds, but improvements in other aspects such as boundary layer turbulence, cloud radiative properties

  6. Automatic cloud classification of whole sky images

    Directory of Open Access Journals (Sweden)

    A. Heinle

    2010-05-01

    Full Text Available The recently increasing development of whole sky imagers enables temporal and spatial high-resolution sky observations. One application already performed in most cases is the estimation of fractional sky cover. A distinction between different cloud types, however, is still in progress. Here, an automatic cloud classification algorithm is presented, based on a set of mainly statistical features describing the color as well as the texture of an image. The k-nearest-neighbour classifier is used due to its high performance in solving complex issues, simplicity of implementation and low computational complexity. Seven different sky conditions are distinguished: high thin clouds (cirrus and cirrostratus, high patched cumuliform clouds (cirrocumulus and altocumulus, stratocumulus clouds, low cumuliform clouds, thick clouds (cumulonimbus and nimbostratus, stratiform clouds and clear sky. Based on the Leave-One-Out Cross-Validation the algorithm achieves an accuracy of about 97%. In addition, a test run of random images is presented, still outperforming previous algorithms by yielding a success rate of about 75%, or up to 88% if only "serious" errors with respect to radiation impact are considered. Reasons for the decrement in accuracy are discussed, and ideas to further improve the classification results, especially in problematic cases, are investigated.

  7. Evolution in Cloud Population Statistics of the MJO. From AMIE Field Observations to Global-Cloud Permitting Models final report Version 1

    Energy Technology Data Exchange (ETDEWEB)

    Deng, Min [Univ. of Wyoming, Laramie, WY (United States)

    2016-01-08

    Methods of convective/stratiform precipitation classification and surface rain rate estimation based on the Atmospheric Radiation Measurement (ARM) program cloud radar measurements were developed and evaluated. Simultaneous and collocated observations of the Ka-band ARM zenith radar (KAZR), two scanning precipitation radars (NCAR S-PolKa and Texas A&M University SMART-R), and surface precipitation during the DYNAMO/AMIE field campaign were used. The motivation of this study is to apply the unique long-term ARM cloud radar observations without accompanying precipitation radars to the study of cloud lifecycle and precipitation features under different weather and climate regimes.

  8. Lower Cambrian Black Rock Series and Associated Stratiform Deposits in Southern China

    Institute of Scientific and Technical Information of China (English)

    陈南生; 范德廉; 等

    1990-01-01

    Widespread in more than ten provinces of southern China are the Lower Cambrian black argillaceous-arenaceous rock series consisting of black carbonaceous shales,black carbonaceousargillo-siliceous rocks,black carbonaceous silicolite and black silicolite and black carbonaceous argillaceous siltstone.The Ni,Mo,V,Cu,U,Ba,Ag,P contents of these series are usually several to tens of times higher than their average values in shales.As viewed from lithological sequence,element association and evolution,these black series can be diveided into two types.There occur a variety of deposits in the black rock series,such as phosphorite deposits,Ni-Mo-V polymetal deposits and "Stone coal" seams.According to ore composition,texture and structure,the phosphorite deposits fall into three types,i.e.,thick-bedded,lenticular and nodular,The Ni-Mo-V polymetal deposits,V deposits and reworked sedimentary CU-U-Cd polymetal deposits in terms of their element assiciation and ore genesis.As for the stratiform deposits in the black rock series,three mineralization stages have been recognized,i.e.,the formation of phosphorite deposits,of Ni-Mo polymetal deposits and of V-Cu-U-Cd polymetal deposits as well as of ":stone coal" seams.Evidence strongly suggests that lower organisms have played an important role in mineralization. Our studies indicate that the Lower Cambrian black argillaceous-arenaceous rock series in southern China and their associated stratiform deposits occur generally in the basal parts of a big sedimentary cycle,i.e.,the initial period of a transgression,or in the fine detrital-siliceous formation between two carbonate formatons,formed in a humid climatic zone between two arid ones.As for the environment of deposition,it is suggested that the Lower Cambrian black argillaceous-arenaceous rock series and associated stratiform deposits(excluding thick-bedded phosphorite deposits)were formed mainly in a restricted and poorly-fed sea basin of stagnant shallow water containing

  9. AREM Simulations of Cloud Features over Eastern China in February 2001

    Institute of Scientific and Technical Information of China (English)

    LI Yunying; YU Rucong; XU Youping; ZHOU Tianjun

    2005-01-01

    Based on the simulations of cloud features in February 2001 by the regional numerical weather prediction model-Advanced Regional Eta-coordinate Model (AREM), the dynamic and thermodynamic conditions for middle cloud formation over eastern China are studied. Diagnostic analysis partly confirms the previous suggestion that the middle stratiform clouds downstream of the Tibetan Plateau are maintained by the frictional and blocking effects of the plateau. In addition, it is found that the temperature inversion at plateau height over eastern China generated by the warm air advected from the plateau provides a favorable thermodynamic condition for middle clouds. Both diurnal variations of the mid-level divergence and the inversion over eastern China, which are determined by the atmospheric boundary activity over the Tibetan Plateau, dominate the cloud diurnal cycle. The middle cloud amount decreases and the cloud top falls in the daytime, but reverses at night. The comparison of cloud features between the simulations and the observations also proves that the AREM can well capture the distinctive continental stratiform cloud features downstream of the Tibetan Plateau.

  10. Generation of live offspring from vitrified embryos with synthetic polymers SuperCool X-1000 and SuperCool Z-1000.

    Science.gov (United States)

    Marco-Jimenez, F; Jimenez-Trigos, E; Lavara, R; Vicente, J S

    2014-01-01

    Ice growth and recrystallisation are considered important factors in determining vitrification outcomes. Synthetic polymers inhibit ice formation during cooling or warming of the vitrification process. The aim of this study was to assess the effect of adding commercially available synthetic polymers SuperCool X-1000 and SuperCool Z-1000 to vitrification media on in vivo development competence of rabbit embryos. Four hundred and thirty morphologically normal embryos recovered at 72 h of gestation were used. The vitrification media contained 20% dimethyl sulphoxide and 20% ethylene glycol, either alone or in combination with 1% of SuperCool X-1000 and 1% SuperCool. Our results show that embryos can be successfully vitrified using SuperCool X-1000 and SuperCool Z-1000 and when embryos are transferred, live offspring can be successfully produced. In conclusion, our results demonstrated that we succeeded for the first time in obtaining live offspring after vitrification of embryos using SuperCool X-1000 and SuperCool Z-1000 polymers.

  11. World production and possible recovery of cobalt from the Kupferschiefer stratiform copper ore

    Directory of Open Access Journals (Sweden)

    Pazik Paulina M.

    2016-01-01

    Full Text Available Cobalt is recognized as a strategic metal and also E-tech element, which is crucial for worlds development. An increasing demand for cobalt forces for searching of new resources that could be explored in European countries. There are many examples of cobalt recoveries, mostly from laterite and sulphide deposits. However, the accurate choice of the technology depends on many factors. The Kupferschiefer stratiform copper ore located in Poland is the biggest deposit of cobalt in Europe. Although KGHM Polska Miedz S.A. recovers many precious metals from this ore, cobalt is not recovered yet. This metal occurs as an accompanying element, mostly in the form of cobaltite (CaAsS, with the average content of 50–80 g/Mg. In this paper a possible recovery of cobalt from the Kupferschiefer ore, with the use of hydrometallurgical methods, was investigated.

  12. Cloud microphysical and rainfall responses to zonal perturbations of sea surface temperature:A cloud-resolving modeling study

    Institute of Scientific and Technical Information of China (English)

    Xiaopeng Cui; Xiaofan Li; Zhiping Zong

    2009-01-01

    The cloud microphysicai and rainfall responses to zonal perturbations of sea surface temperature (SST) are investigated by analyzing the equilibrium simulation data (from day 31-40) obtained from a series of two-dimensional cloud-resolving simulations with a zonal model domain of 768 km.Four experiments imposed by zonal SST perturbations of wavenumbers 1 (SST29ZI),2 (SST29Z2),4 (SST29Z4),and 8 (SST29Z8) are compared to the control experiment imposed by zonally uniform SST (SST29).The model domain mean SST is 29 ℃,and the two-dimensional cloud-resolving model with a cyclic lateral boundary is also imposed by zero vertical velocity and constant zonal wind.The time and model domain mean surface rain rates in SST29ZI,SST29Z2,and SST29Z8 are about 10% larger than those in SST29,whereas the mean surface rain rates in SST29Z4 and SST29 are similar.The analysis of mean surface rainfall budgets shows that local water vapor and hydrometeor changes play important roles in determining the differences and similarities in mean surface rain rate between the perturbation experiments and the control experiment.Both convective and stratiform rain rates are larger in SST29Z1 and SST29Z2 than in SST29 due to the smaller advection of rain from convective regions into raining stratiform regions and the larger vapor condensation rates associated with the larger water vapor convergence over raining stratiform regions in SST29ZI and SST29Z2.The convective rain rates are larger in SST29ZA and SST29Z8 than in SST29 because of the larger condensation rates associated with the larger water vapor convergence over convective regions in SST29Z4 and SST29Z8.The stratiform rain rates in SST29Z4 and SST29Z8 are smaller than in SST29 due to the smaller vapor condensation rates and smaller collection rates of cloud water by rain over raining stratiform regions in SST29Z4 and SST29Z8.(C) 2008 National Natural Science Foundation of China and Chinese Academy of Sciences.Published by Elsevier Limited

  13. Sulfur- and oxygen-isotopes in sediment-hosted stratiform barite deposits

    Science.gov (United States)

    Johnson, C.A.; Emsbo, P.; Poole, F.G.; Rye, R.O.

    2009-01-01

    Sulfur- and oxygen-isotope analyses have been obtained for sediment-hosted stratiform barite deposits in Alaska, Nevada, Mexico, and China to examine the environment of formation of this deposit type. The barite is contained in sedimentary sequences as old as Late Neoproterozoic and as young as Mississippian. If previously published data for other localities are considered, sulfur- and oxygen-isotope data are now available for deposits spanning a host-rock age range of Late Neoproterozoic to Triassic. On a ??34S versus ??18O diagram, many deposits show linear or concave-upward trends that project down toward the isotopic composition of seawater sulfate. The trends suggest that barite formed from seawater sulfate that had been isotopically modified to varying degrees. The ??34S versus ??18O patterns resemble patterns that have been observed in the modern oceans in pore water sulfate and water column sulfate in some anoxic basins. However, the closest isotopic analog is barite mineralization that occurs at fluid seeps on modern continental margins. Thus the data favor genetic models for the deposits in which barium was delivered by seafloor seeps over models in which barium was delivered by sedimentation of pelagic organisms. The isotopic variations within the deposits appear to reflect bacterial sulfate reduction operating at different rates and possibly with different electron donors, oxygen isotope exchange between reduction intermediates and H2O, and sulfate availability. Because they are isotopically heterogeneous, sediment-hosted stratiform barite deposits are of limited value in reconstructing the isotopic composition of ancient seawater sulfate.

  14. Detection and Analysis of High Ice Concentration Events and Supercooled Drizzle from IAGOS Commercial Aircraft

    Science.gov (United States)

    Gallagher, Martin; Baumgardner, Darrel; Lloyd, Gary; Beswick, Karl; Freer, Matt; Durant, Adam

    2016-04-01

    Hazardous encounters with high ice concentrations that lead to temperature and airspeed sensor measurement errors, as well as engine rollback and flameout, continue to pose serious problems for flight operations of commercial air carriers. Supercooled liquid droplets (SLD) are an additional hazard, especially for smaller commuter aircraft that do not have sufficient power to fly out of heavy icing conditions or heat to remove the ice. New regulations issued by the United States and European regulatory agencies are being implemented that will require aircraft below a certain weight class to carry sensors that will detect and warn of these types of icing conditions. Commercial aircraft do not currently carry standard sensors to detect the presence of ice crystals in high concentrations because they are typical found in sizes that are below the detection range of aircraft weather radar. Likewise, the sensors that are currently used to detect supercooled water do not respond well to drizzle-sized drops. Hence, there is a need for a sensor that can fill this measurement void. In addition, the forecast models that are used to predict regions of icing rely on pilot observations as the only means to validate the model products and currently there are no forecasts for the prevalence of high altitude ice crystals. Backscatter Cloud Probes (BCP) have been flying since 2011 under the IAGOS project on six Airbus commercial airliners operated by Lufthansa, Air France, China Air, Iberia and Cathay Pacific, and measure cloud droplets, ice crystals and aerosol particles larger than 5 μm. The BCP can detect these particles and measures an optical equivalent diameter (OED) but is not able to distinguish the type of particle, i.e. whether they are droplets, ice crystals, dust or ash. However, some qualification can be done based on measured temperature to discriminate between liquid water and ice. The next generation BCP (BCPD, Backscatter Cloud Probe with polarization detection) is

  15. Shear-accelerated crystallization in a supercooled atomic liquid.

    Science.gov (United States)

    Shao, Zhen; Singer, Jonathan P; Liu, Yanhui; Liu, Ze; Li, Huiping; Gopinadhan, Manesh; O'Hern, Corey S; Schroers, Jan; Osuji, Chinedum O

    2015-02-01

    A bulk metallic glass forming alloy is subjected to shear flow in its supercooled state by compression of a short rod to produce a flat disk. The resulting material exhibits enhanced crystallization kinetics during isothermal annealing as reflected in the decrease of the crystallization time relative to the nondeformed case. The transition from quiescent to shear-accelerated crystallization is linked to strain accumulated during shear flow above a critical shear rate γ̇(c)≈0.3 s(-1) which corresponds to Péclet number, Pe∼O(1). The observation of shear-accelerated crystallization in an atomic system at modest shear rates is uncommon. It is made possible here by the substantial viscosity of the supercooled liquid which increases strongly with temperature in the approach to the glass transition. We may therefore anticipate the encounter of nontrivial shear-related effects during thermoplastic deformation of similar systems.

  16. Slow dynamics of supercooled water confined in nanoporous silica materials

    Energy Technology Data Exchange (ETDEWEB)

    Liu, L [Department of Nuclear Engineering, 24-209 MIT, Cambridge, MA 02139 (United States); Faraone, A [Department of Nuclear Engineering, 24-209 MIT, Cambridge, MA 02139 (United States); Mou, C-Y [Department of Chemistry, National Taiwan University, Taipei, 106, Taiwan (China); Yen, C-W [Department of Chemistry, National Taiwan University, Taipei, 106, Taiwan (China); Chen, S-H [Department of Nuclear Engineering, 24-209 MIT, Cambridge, MA 02139 (United States)

    2004-11-17

    We review our incoherent quasielastic neutron scattering (QENS) studies of the dynamics of supercooled water confined in nanoporous silica materials. QENS data were analysed by using the relaxing cage model (RCM) previously developed by us. We first use molecular dynamics (MD) simulation of the extended simple point charge model (SPC/E) for bulk supercooled water to establish the validity of the RCM, which applies to both the translational and rotational motion of water molecules. We then assume that the dynamics of water molecules in the vicinity of a hydrophilic surface is similar to a bulk water at an equivalent lower supercooled temperature. This analogy was experimentally demonstrated in previous investigations of water in Vycor glasses and near hydrophilic protein surfaces. Studies were made of supercooled water in MCM-41-S (pore sizes 25, 18, and 14 A) and MCM-48-S (pore size 22 A) using three QENS spectrometers of respective energy resolutions 1, 30, and 60 {mu}eV, covering the temperature range from 325 to 200 K. Five quantities are extracted from the analysis: they are {beta}, the stretch exponent characterizing the {alpha}-relaxation; {beta}{gamma}, the exponent determining the power-law dependence of the relaxation time on Q; <{tau}{sub 0}>, the Q-independent pre-factor for the average translational relaxation time; <{tau}{sub R{sub 1}}>, the relaxation time for the first-order rotational correlation function; and <{tau}{sub R{sub 3}}>, the relaxation time for the second-order rotational correlation function. We discuss the temperature dependence of these parameters and note that, in particular, the dynamics is rapidly slowing down at temperature around 220 K, signalling the onset of a structural arrest transition of liquid water into an amorphous solid water.

  17. Volume analysis of supercooled water under high pressure

    OpenAIRE

    Duki, Solomon F.; Tsige, Mesfin

    2016-01-01

    Motivated by recent experimental findings on the volume of supercooled water at high pressure [O. Mishima, J. Chem. Phys. 133, 144503 (2010)] we performed atomistic molecular dynamics simulations study of bulk water in the isothermal-isobaric ensemble. Cooling and heating cycles at different isobars and isothermal compression at different temperatures are performed on the water sample with pressures that range from 0 to 1.0 GPa. The cooling simulations are done at temperatures that range from...

  18. Effects of poly-vinyl alcohol on supercooling phenomena of water

    Energy Technology Data Exchange (ETDEWEB)

    Kumano, Hiroyuki; Hirata, Tetsuo; Kudoh, Tomoya [Department of Mechanical Systems Engineering, Shinshu University, 4-17-1, Wakasato, Nagano City, 380-8553 (Japan)

    2009-05-15

    The effects of a polymer additive on the supercooling of water were investigated experimentally. Poly-vinyl alcohols (PVAs) were used as the additives, and samples were prepared by dissolving the PVA in water. Since the characteristics of PVA are decided by its degrees of polymerization and saponification, these were varied along with the concentration as the experimental parameters. Moreover, the effect of purity of the water was also considered. Each sample was cooled and the temperature at the instant when ice appeared was measured. Since the freezing of supercooled water is a statistical phenomenon, many experiments were carried out and the average degree of supercooling was obtained. It was found that PVA affects the nucleation of ice in supercooled water and the degree of supercooling increases with the addition of PVA even for water with low purity. The average degree of supercooling increases with an increase in the degree of saponification of PVA. (author)

  19. Mixing effects in the crystallization of supercooled quantum binary liquids

    Energy Technology Data Exchange (ETDEWEB)

    Kühnel, M.; Kalinin, A. [Institut für Kernphysik, J. W. Goethe-Universität, Max-von-Laue-Str. 1, 60438 Frankfurt am Main (Germany); Fernández, J. M.; Tejeda, G.; Moreno, E.; Montero, S. [Laboratory of Molecular Fluid Dynamics, Instituto de Estructura de la Materia, CSIC, Serrano 121, 28006 Madrid (Spain); Tramonto, F.; Galli, D. E. [Laboratorio di Calcolo Parallelo e di Simulazioni di Materia Condensata, Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, 20133 Milano (Italy); Nava, M. [Laboratorio di Calcolo Parallelo e di Simulazioni di Materia Condensata, Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, 20133 Milano (Italy); Computational Science, Department of Chemistry and Applied Biosciences, ETH Zurich, USI Campus, Via Giuseppe Buffi 13, CH-6900 Lugano (Switzerland); Grisenti, R. E. [Institut für Kernphysik, J. W. Goethe-Universität, Max-von-Laue-Str. 1, 60438 Frankfurt am Main (Germany); GSI - Helmholtzzentrum für Schwerionenforschung, Planckstr. 1, 64291 Darmstadt (Germany)

    2015-08-14

    By means of Raman spectroscopy of liquid microjets, we have investigated the crystallization process of supercooled quantum liquid mixtures composed of parahydrogen (pH{sub 2}) or orthodeuterium (oD{sub 2}) diluted with small amounts of neon. We show that the introduction of the Ne impurities affects the crystallization kinetics in terms of a significant reduction of the measured pH{sub 2} and oD{sub 2} crystal growth rates, similarly to what found in our previous work on supercooled pH{sub 2}-oD{sub 2} liquid mixtures [Kühnel et al., Phys. Rev. B 89, 180201(R) (2014)]. Our experimental results, in combination with path-integral simulations of the supercooled liquid mixtures, suggest in particular a correlation between the measured growth rates and the ratio of the effective particle sizes originating from quantum delocalization effects. We further show that the crystalline structure of the mixtures is also affected to a large extent by the presence of the Ne impurities, which likely initiate the freezing process through the formation of Ne-rich crystallites.

  20. A Comparison of TWP-ICE Observational Data with Cloud-Resolving Model Results

    Energy Technology Data Exchange (ETDEWEB)

    Fridlind, A. M.; Ackerman, Andrew; Chaboureau, Jean-Pierre; Fan, Jiwen; Grabowski, Wojciech W.; Hill, A.; Jones, T. R.; Khaiyer, M. M.; Liu, G.; Minnis, Patrick; Morrison, H.; Nguyen, L.; Park, S.; Petch, Jon C.; Pinty, Jean-Pierre; Schumacher, Courtney; Shipway, Ben; Varble, A. C.; Wu, Xiaoqing; Xie, Shaocheng; Zhang, Minghua

    2012-03-13

    Observations made during the TWP-ICE campaign are used to drive and evaluate thirteen cloud-resolving model simulations with periodic lateral boundary conditions. The simulations employ 2D and 3D dynamics, one- and two-moment microphysics, several variations on large-scale forcing, and the use of observationally derived aerosol properties to prognose droplet numbers. When domain means are averaged over a 6-day active monsoon period, all simulations reproduce observed surface precipitation rate but not its structural distribution. Simulated fractional areas covered by convective and stratiform rain are uncorrelated with one another, and are both variably overpredicted by up to a factor of {approx}2. Stratiform area fractions are strongly anticorrelated with outgoing longwave radiation (OLR) but are negligibly correlated with ice water path (IWP), indicating that ice spatial distribution controls OLR more than mean IWP. Overpredictions of OLR tend to be accompanied by underpredictions of reflected shortwave radiation (RSR). When there are two simulations differing only in microphysics scheme or large-scale forcing, the one with smaller stratiform area tends to exhibit greater OLR and lesser RSR by similar amounts. After {approx}10 days, simulations reach a suppressed monsoon period with a wide range of mean precipitable water vapor, attributable in part to varying overprediction of cloud-modulated radiative flux divergence compared with observationally derived values. Differences across the simulation ensemble arise from multiple sources, including dynamics, microphysics, and radiation treatments. Close agreement of spatial and temporal averages with observations may not be expected, but the wide spreads of predicted stratiform fraction and anticorrelated OLR indicate a need for more rigorous observation-based evaluation of the underlying micro- and macrophysical properties of convective and stratiform structures.

  1. Macquarie Island Cloud and Radiation Experiment (MICRE) Science Plan

    Energy Technology Data Exchange (ETDEWEB)

    Marchand, RT [University of Washington; Protat, A [Australian Bureau of Meterology; Alexander, SP [Australian Antarctic Division

    2015-12-01

    Clouds over the Southern Ocean are poorly represented in present day reanalysis products and global climate model simulations. Errors in top-of-atmosphere (TOA) broadband radiative fluxes in this region are among the largest globally, with large implications for modeling both regional and global scale climate responses (e.g., Trenberth and Fasullo 2010, Ceppi et al. 2012). Recent analyses of model simulations suggest that model radiative errors in the Southern Ocean are due to a lack of low-level postfrontal clouds (including clouds well behind the front) and perhaps a lack of supercooled liquid water that contribute most to the model biases (Bodas-Salcedo et al. 2013, Huang et al. 2014). These assessments of model performance, as well as our knowledge of cloud and aerosol properties over the Southern Ocean, rely heavily on satellite data sets. Satellite data sets are incomplete in that the observations are not continuous (i.e., they are acquired only when the satellite passes nearby), generally do not sample the diurnal cycle, and view primarily the tops of cloud systems (especially for the passive instruments). This is especially problematic for retrievals of aerosol, low-cloud properties, and layers of supercooled water embedded within (rather than at the top of) clouds, as well as estimates of surface shortwave and longwave fluxes based on these properties.

  2. Remobilisation features and structural control on ore grade distribution at the Konkola stratiform Cu-Co ore deposit, Zambia

    OpenAIRE

    Torremans, K.; Gauquie, J.; Boyce, A. J.; Barrie, C.D.; Sikazwe, O.; Muchez, P.H.

    2013-01-01

    The Konkola deposit is a high grade stratiform Cu–Co ore deposit in the Central African Copperbelt in Zambia. Economic mineralisation is confined to the Ore Shale formation, part of the Neoproterozoic metasedimentary rocks of the Katanga Supergroup. Petrographic study reveals that the copper–cobalt ore minerals are disseminated within the host rock, sometimes concentrated along bedding planes, often associated with dolomitic bands or clustered in cemented lenses and in layer-parallel and irre...

  3. Measurements of electric charge separated during the formation of rime by the accretion of supercooled droplets

    Directory of Open Access Journals (Sweden)

    E. E. Avila

    2009-11-01

    Full Text Available In these experiments, the electric charge carried by single particles ejected from the surface of a graupel particle growing by riming was measured. Simulated graupel pellets were grown by accretion of supercooled water drops, at temperatures ranging from −2 to −10°C in a wind tunnel at air velocities between 5 and 10 m s−1, with the goal of studying the charging of graupel pellets under conditions of secondary ice crystal production (Hallett-Mossop mechanism. The graupel, and induction rings upstream and downstream of the graupel, were connected to electrometers and analyzing circuits of sufficient sensitivity and speed to measure, correlate and display individual charging events. The results suggest that fewer than 1% of the ejected particles carry a measurable electric charge (>2 fC. Further, it was observed that the graupel pellets acquire a positive charge and the average charge of a single splinter ejected is −14 fC. This mechanism of ejection of charged particles seems adequate to account for a positive charge of around 1 pC that individual precipitation particles of mm-size could acquire in the lower part of the cloud, which in turn could contribute to the lower positive charge region of thunderstorms.

  4. Estimating seasonal variations in cloud droplet number concentration over the boreal forest from satellite observations

    Directory of Open Access Journals (Sweden)

    R. H. H. Janssen

    2011-08-01

    Full Text Available Seasonal variations in cloud droplet number concentration (NCD in low-level stratiform clouds over the boreal forest are estimated from MODIS observations of cloud optical and microphysical properties, using a sub-adiabatic cloud model to interpret vertical profiles of cloud properties. An uncertainty analysis of the cloud model is included to reveal the main sensitivities of the cloud model. We compared the seasonal cycle in NCD, obtained using 9 yr of satellite data, to surface concentrations of potential cloud activating aerosols, measured at the SMEAR II station at Hyytiälä in Finland. The results show that NCD and cloud condensation nuclei (CCN concentrations have no clear correlation at seasonal time scale. The fraction of aerosols that actually activate as cloud droplet decreases sharply with increasing aerosol concentrations. Furthermore, information on the stability of the atmosphere shows that low NCD is linked to stable atmospheric conditions. Combining these findings leads to the conclusion that cloud droplet activation for the studied clouds over the boreal forest is limited by convection. Our results suggest that it is important to take the strength of convection into account when studying the influence of aerosols from the boreal forest on cloud formation, although they do not rule out the possibility that aerosols from the boreal forest affect other types of clouds with a closer coupling to the surface.

  5. Hydrodynamic states in water below the temperature of the density maximum: the limit to supercooling

    NARCIS (Netherlands)

    van der Elsken, J.; van Boom, L.; Bot, A.

    1988-01-01

    Spectra of fluctuations in the total intensity of laser light deflected by supercooled water show that even under carefully controlled conditions large samples give convection when cooled below -0%. This is in agreement with the Rayleigh versus Prandtlnumber relation for supercooled water.

  6. Long term thermal energy storage with stable supercooled sodium acetate trihydrate

    DEFF Research Database (Denmark)

    Dannemand, Mark; Schultz, Jørgen M.; Johansen, Jakob Berg

    2015-01-01

    it expands and will cause a pressure built up in a closed chamber which might compromise stability of the supercooling. This can be avoided by having an air volume above the phase change material connected to an external pressure less expansion tank. Supercooled sodium acetate trihydrate at 20 °C stores up...

  7. Supercooling of rapidly expanding quark-gluon plasma

    CERN Document Server

    Zabrodin, E E; Csernai, László P; Stöcker, H; Greiner, W

    1998-01-01

    We reexamine the scenario of homogeneous nucleation of the quark-gluon plasma produced in ultra-relativistic heavy ion collisions. A generalization of the standard nucleation theory to rapidly expanding system is proposed. The nucleation rate is derived via the new scaling parameter $\\lambda_Z$. It is shown that the size distribution of hadronic clusters plays an important role in the dynamics of the phase transition. The longitudinally expanding system is supercooled to about 3-6%, then it is reheated, and the hadronization is completed within 6-10 fm/c, i.e. 5-10 times faster than it was estimated earlier, in a strongly nonequilibrium way.

  8. Hopping in a supercooled binary Lennard-Jones liquid

    DEFF Research Database (Denmark)

    Schrøder, Thomas; Dyre, Jeppe

    1998-01-01

    A binary Lennard–Jones liquid has been investigated by molecular dynamics at equilibrium supercooled conditions. At the lowest temperature investigated, hopping is present in the system as indicated by a secondary peak in 4r2Gs(r,t), where Gs(r,t) is the van Hove self correlation function....... To examine the dynamics of the system, we consider transitions between the inherent structures (local minima in the potential energy) along the trajectory. We conclude that the plateau in the mean square displacement found at lower temperatures is indeed a result of particles being trapped in local "cages...

  9. The freezing and supercooling of garlic (Allium sativum L.)

    Energy Technology Data Exchange (ETDEWEB)

    James, Christian; Seignemartin, Violaine; James, Stephen J. [Food Refrigeration and Process Engineering Research Centre (FRPERC), University of Bristol, Churchill Building, Langford, Bristol BS40 5DU (United Kingdom)

    2009-03-15

    This work shows that peeled garlic cloves demonstrate significant supercooling during freezing under standard conditions and can be stored at temperatures well below their freezing point (-2.7 C) without freezing. The nucleation point or 'metastable limit temperature' (the point at which ice crystal nucleation is initiated) of peeled garlic cloves was found to be between -7.7 and -14.6 C. Peeled garlic cloves were stored under static air conditions at temperatures between -6 and -9 C for up to 69 h without freezing, and unpeeled whole garlic bulbs and cloves were stored for 1 week at -6 C without freezing. (author)

  10. In-Situ Measurements of Cloud-Precipitation Microphysics in the East Asian Monsoon Region Since 1960

    Institute of Scientific and Technical Information of China (English)

    王东海; 尹金方; 翟国庆

    2015-01-01

    A large number of in-situ measurements of cloud-precipitation microphysical properties have been made since 1960, including measurements of particle size distribution, particle concentration, and liquid water content of clouds and rain. These measurements have contributed to considerable progress in understanding microphysical processes in clouds and precipitation and signifi cant improvements in parameterizations of cloud microphysics in numerical models. This work reviews key fi ndings regarding cloud-precipitation mi-crophysics over China. The total number concentrations of various particles vary signifi cantly, with certain characteristic spatial scales. The size distributions of cloud droplets in stratiform clouds can generally be fi t with gamma distributions, but the fi t parameters cover a wide range. Raindrop size distributions (RSDs) associated with stratiform clouds can be fi t with either exponential or gamma distributions, while RSDs associated with convective or mixed stratiform-cumuliform clouds are best fi t with gamma distributions. Concentrations of ice nuclei (IN) over China are higher than those observed over other regions, and increase exponentially as temperature decreases. The particle size distributions of ice crystals, snow crystals, and hailstones sampled at a variety of locations can be reliably approximated by using exponential distributions, while aerosol particle size distributions are best described as the sum of a modifi ed gamma distribution and a Junge power-law distribution. These results are helpful for evaluating and improving the fi delity of physical processes and hydrometeor fi elds simulated by microphysical parameterizations. The comprehensive summary and analysis of previous work presented here also provide useful guidelines for the design of future observational programs.

  11. Successful vitrification of mouse ovaries using less-concentrated cryoprotectants with Supercool X-1000 supplementation.

    Science.gov (United States)

    Tan, Xiuwen; Song, Enliang; Liu, Xiaomu; Liu, Guifen; Cheng, Haijian; Wan, Fachun

    2012-02-01

    The purpose of our study was to investigate the feasibility of using less-concentrated cryoprotectants supplemented with ice blocker Supercool X-1000 to vitrify ovarian tissues. Mouse ovaries were cryopreserved in different concentrations of vitrification solution alone or with Supercool X-1000, and fresh non-frozen ovaries were used as control. The proportions of morphological normality of follicles, normal GCs in follicular fluids and developing to blastocysts were higher in 12.5% ethylene glycol (EG) + 12.5% dimethylsulfoxide (DMSO) with Supercool X-1000 than those of treated in 10% EG + 10% DMSO or 15% EG + 15% DMSO alone or with Supercool X-1000. In conclusion, the inclusion of Supercool X-1000 in less-concentrated vitrification solution was effective to improve the efficiency and efficacy of cryopreservation of ovarian tissues.

  12. Impacts of Aerosol, Surface and Meteorological Conditions on Polar Cloud Properties: Use of In-Situ Cloud Probe Data

    Science.gov (United States)

    McFarquhar, Greg; Wu, Wei; Maahn, Maximilian

    2017-04-01

    Over the Southern Oceans, models from the Coupled Model Intercomparison Project 5 (CMIP5) almost universally underestimate sunlight reflected by near surface cloud in the Austral summer compared to Clouds and the Earth's Radiant Energy System (CERES) data. These and other biases in radiative fluxes over the Arctic are believed to be associated with the poorly modeled properties of low-level clouds that are frequently composed of supercooled water. Because changes in cloud macrophysical (heights, coverage) and microphysical (sizes, shapes and phases of particles) can alter the radiative impact of clouds, it is important to understand the processes that control cloud properties. In this presentation, in-situ microphysical observations obtained in prior arctic field campaigns (e.g., the Indirect and Semi-Direct Aerosol Campaign ISDAC, the Mixed-Phase Arctic Cloud Experiment M-PACE, and the Atmospheric Radiation Measurement Carbon Measurements Program-V ACME-V) are discussed. Strategies for comparing data collected in campaigns with different probes and processed with varying algorithms are introduced, along with procedures for using cloud probe data to refine assumptions about cloud properties in model schemes (e.g., size distributions, mass-dimension, and velocity-dimension relations) that affect rates at which mass and number are transferred between hydrometeor categories and hence estimates of latent and radiative heating, which feeds back on dynamics and hence cloud properties. Such observations from past arctic field experiments have enhanced our understanding of aerosol-cloud interactions acting in single-layer mixed phase clouds that are ubiquitous in the Arctic. But, it is still unknown what controls the amount of supercooled water in polar clouds (especially in frequently occurring complex multi-layer clouds), how probability distributions of cloud properties vary with aerosol loading and composition in different surface and meteorological conditions, and how

  13. Search Cloud

    Science.gov (United States)

    ... of this page: https://medlineplus.gov/cloud.html Search Cloud To use the sharing features on this ... of Top 110 zoster vaccine Share the MedlinePlus search cloud with your users by embedding our search ...

  14. Dynamical properties of confined supercooled water: an NMR study

    Science.gov (United States)

    Mallamace, Francesco; Broccio, Matteo; Corsaro, Carmelo; Faraone, Antonio; Liu, Li; Mou, Chung-Yuan; Chen, Sow-Hsin

    2006-09-01

    We report a set of dynamical data of confined water measured in a very deeply supercooled regime (290-190 K). Water is contained in silica matrices (MCM-41-S) which consist of 1D cylindrical pores with diameters d = 14,18 and 24 Å. When confined in these tubular pores, water does not crystallize, and can be supercooled well below 200 K. We use the NMR technique to obtain the characteristic proton relaxation time-constants (the spin-lattice relaxation time-constant T1 and the spin-spin relaxation time-constant T2) and a direct measurement of the self-diffusion coefficient in the whole temperature range. We give evidence of the existence of a fragile-to-strong dynamic crossover (FSC) at TL = 225 K from the temperature dependence of the self-diffusion coefficient. A combination of the NMR self-diffusion coefficient with the average translational relaxation time, as measured by quasi-elastic neutron scattering, shows a well defined decoupling of transport coefficients, i.e. the breakdown of the Stokes-Einstein relation, on approaching the crossover temperature TL.

  15. Dynamical properties of confined supercooled water: an NMR study

    Energy Technology Data Exchange (ETDEWEB)

    Mallamace, Francesco [Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Broccio, Matteo [Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Corsaro, Carmelo [Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Faraone, Antonio [Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Liu Li [Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Mou, C-Y [Department of Chemistry, National Taiwan University, Taipei, Taiwan (China); Chen, S-H [Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)

    2006-09-13

    We report a set of dynamical data of confined water measured in a very deeply supercooled regime (290-190 K). Water is contained in silica matrices (MCM-41-S) which consist of 1D cylindrical pores with diameters d = 14,18 and 24 A. When confined in these tubular pores, water does not crystallize, and can be supercooled well below 200 K. We use the NMR technique to obtain the characteristic proton relaxation time-constants (the spin-lattice relaxation time-constant T1 and the spin-spin relaxation time-constant T2) and a direct measurement of the self-diffusion coefficient in the whole temperature range. We give evidence of the existence of a fragile-to-strong dynamic crossover (FSC) at T{sub L} = 225 K from the temperature dependence of the self-diffusion coefficient. A combination of the NMR self-diffusion coefficient with the average translational relaxation time, as measured by quasi-elastic neutron scattering, shows a well defined decoupling of transport coefficients, i.e. the breakdown of the Stokes-Einstein relation, on approaching the crossover temperature T{sub L}.

  16. Entropy-driven liquid-liquid separation in supercooled water

    CERN Document Server

    Holten, V

    2012-01-01

    Twenty years ago Poole et al. (Nature 360, 324, 1992) suggested that the anomalous properties of supercooled water may be caused by a critical point that terminates a line of liquid-liquid separation of lower-density and higher-density water. Here we present an explicit thermodynamic model based on this hypothesis, which describes all available experimental data for supercooled water with better quality and with fewer adjustable parameters than any other model suggested so far. Liquid water at low temperatures is viewed as an 'athermal solution' of two molecular structures with different entropies and densities. Alternatively to popular models for water, in which the liquid-liquid separation is driven by energy, the phase separation in the athermal two-state water is driven by entropy upon increasing the pressure, while the critical temperature is defined by the 'reaction' equilibrium constant. In particular, the model predicts the location of density maxima at the locus of a near-constant fraction (about 0.1...

  17. Electrostatic levitation studies of supercooled liquids and metastable solid phases

    Science.gov (United States)

    Rustan, Gustav Errol

    A new laboratory has been developed at Iowa State University (ISU) to be used for the study of high temperature liquids and solids, with particular focus on the supercooling of liquids and their metastable solidification products. This new laboratory employs the electrostatic levitation (ESL) technique, in which a charged sample is suspended between a set of electrodes to achieve non-contact handling. Owing to the elimination of a crucible, high temperature processing of samples can be achieved with reduced levels of contamination and heterogeneous nucleation. Because of the reduction in heterogeneous nucleation, samples can be supercooled well below their equilibrium melting temperature, opening the door to a wide range of measurements on supercooled liquids. Measurements methods have been implemented for the characterization of thermophysical properties such as: volume/density, ratio of specific heat to total hemispherical emissivity, surface tension, viscosity, electrical resistivity, and magnetic susceptibility. For measurements of electrical resistivity and magnetic susceptibility, a new method has been developed at ISU based on the tunnel diode oscillator (TDO) technique. The TDO technique uses the negative differential resistance of a tunnel diode to drive an LC tank circuit into self-sustained oscillation at the resonant LC frequency. The LC tank is inductively coupled to the samples under study, and changes in the electrical resistivity or magnetic susceptibility of the sample are manifested as changes in the resonant frequency. By measuring the frequency shifts of the TDO, insights can be made into changes in the material's electrical and magnetic properties. This method has been validated by performing resistivity measurements on a sample of high purity Zr, and by performing measurements on the ferromagnetic transition in a low-carbon steel ball bearing. In addition to the development of the laboratory and its supporting instrumentation, an effort has

  18. A unified parameterization of clouds and turbulence using CLUBB and subcolumns in the Community Atmosphere Model

    Directory of Open Access Journals (Sweden)

    K. Thayer-Calder

    2015-06-01

    Full Text Available Most global climate models parameterize separate cloud types using separate parameterizations. This approach has several disadvantages, including obscure interactions between parameterizations and inaccurate triggering of cumulus parameterizations. Alternatively, a unified cloud parameterization uses one equation set to represent all cloud types. Such cloud types include stratiform liquid and ice cloud, shallow convective cloud, and deep convective cloud. Vital to the success of a unified parameterization is a general interface between clouds and microphysics. One such interface involves drawing Monte Carlo samples of subgrid variability of temperature, water vapor, cloud liquid, and cloud ice, and feeding the sample points into a microphysics scheme. This study evaluates a unified cloud parameterization and a Monte Carlo microphysics interface that has been implemented in the Community Atmosphere Model (CAM version 5.3. Results describing the mean climate and tropical variability from global simulations are presented. The new model shows a degradation in precipitation skill but improvements in short-wave cloud forcing, liquid water path, long-wave cloud forcing, precipitable water, and tropical wave simulation. Also presented are estimations of computational expense and investigation of sensitivity to number of subcolumns.

  19. Factors contributing to deep supercooling capability and cold survival in dwarf bamboo (Sasa senanensis leaf blades.

    Directory of Open Access Journals (Sweden)

    Masaya eIshikawa

    2015-01-01

    Full Text Available Wintering Sasa senanensis, dwarf bamboo, has been known to employ deep supercooling as the mechanism of cold hardiness in its most of the tissues from leaves to rhizomes. The unique cold hardiness mechanism of this plant was further characterized using current year leaf blades. Cold hardiness levels increased from August (LT20: –11 °C to December (LT20: –20 °C, which coincided with the initiation temperature of low temperature exotherms (LTE detected in differential thermal analyses. When leaf blades were stored at –5 °C for 1-14 days, there was no nucleation of the supercooled tissue units compartmentalized by the longitudinal and transverse veins either in summer or winter. However, only summer leaves suffered significant injury after prolonged supercooling of the tissue units. This may be a novel type of low temperature-induced injury in supercooled state at subfreezing temperatures. When winter leaf blades were maintained at the threshold temperature (-20 °C, a longer storage period (1-7 days increased lethal freezing of the supercooled tissue units. Within a wintering shoot, the second or third leaf blade from the top was most cold hardy and leaf blades at lower positions tended to suffer more injury due to lethal freezing of the supercooled units, which was not correlated with the leaf water content. LTE were shifted to higher temperatures (2-5 °C after a lethal freeze-thaw cycle. The results demonstrate that the tissue unit compartmentalized with longitudinal and transverse veins serves as the unit of supercooling and temperature- and time-dependent freezing of the units is lethal both in laboratory freeze tests and in the field. To establish such supercooling in the unit, structural ice barriers such as development of sclerenchyma and biochemical mechanisms to increase the stability of supercooling are considered important. We discussed these mechanisms in regard to ecological and physiological significance in winter survival.

  20. Airborne measurements of condensation nuclei and cloud condensation nuclei above the alpine foothills

    Energy Technology Data Exchange (ETDEWEB)

    Schaefer, B. [Inst. for Meteorology and Geophysics, Univ. of Frankfurt (Germany); Georgii, H.W. [Inst. for Meteorology and Geophysics, Univ. of Frankfurt (Germany)

    1994-11-01

    During the Cloud Experiment OberPfaffenhofen And TRAnsport (CLEOPATRA) in the summer 1992 airborne measurements of cloud condensation nuclei (CCN) and concentrations of condensation nuclei (CN) or total particle concentration have been determined. Flights were made in convective as well as in stratiform clouds. Enhancement of particle concentrations in the vicinity of clouds was observed in some but not all cases. Conditions pertaining to enhanced concentrations are examined. (orig.) [Deutsch] Im Sommer 1992 wurden im Rahmen des CLoud Experiment OberPfaffenhofen And TRAnsport (CLEOPATRA) Flugzeugmessungen von Wolkenkondensationskernen (CCN) und Kondensationskernen (CN) durchgefuehrt. Bei Fluegen in konvektiven und stratiformen Wolken wurde ein Anstieg von Partikeln im Wolkenrandbereich gemessen. Dieser Anstieg konnte allerdings nicht in allen Faellen beobachtet werden und war abhaengig von den Umgebungsbedingungen. (orig.)

  1. Evaluation of tropical cloud and precipitation statistics of CAM3 using CloudSat and CALIPSO data

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Y; Klein, S; Boyle, J; Mace, G G

    2008-11-20

    The combined CloudSat and CALIPSO satellite observations provide the first simultaneous measurements of cloud and precipitation vertical structure, and are used to examine the representation of tropical clouds and precipitation in the Community Atmosphere Model Version 3 (CAM3). A simulator package utilizing a model-to-satellite approach facilitates comparison of model simulations to observations, and a revised clustering method is used to sort the subgrid-scale patterns of clouds and precipitation into principal cloud regimes. Results from weather forecasts performed with CAM3 suggest that the model underestimates the horizontal extent of low and mid-level clouds in subsidence regions, but overestimates that of high clouds in ascending regions. CAM3 strongly overestimates the frequency of occurrence of the deep convection with heavy precipitation regime, but underestimates the horizontal extent of clouds and precipitation at low and middle levels when this regime occurs. This suggests that the model overestimates convective precipitation and underestimates stratiform precipitation consistent with a previous study that used only precipitation observations. Tropical cloud regimes are also evaluated in a different version of the model, CAM3.5, which uses a highly entraining plume in the parameterization of deep convection. While the frequency of occurrence of the deep convection with heavy precipitation regime from CAM3.5 forecasts decreases, the incidence of the low clouds with precipitation and congestus regimes increases. As a result, the parameterization change does not reduce the frequency of precipitating convection that is far too high relative to observations. For both versions of CAM, clouds and precipitation are overly reflective at the frequency of the CloudSat radar and thin clouds that could be detected by the lidar only are underestimated.

  2. Laboratory test of a prototype heat storage module based on stable supercooling of sodium acetate trihydrate

    DEFF Research Database (Denmark)

    Dannemand, Mark; Kong, Weiqiang; Fan, Jianhua;

    2015-01-01

    Laboratory test of a long term heat storage module utilizing the principle of stable supercooling of 199.5 kg of sodium acetate water mixture has been carried out. Avoiding phase separation of the incongruently melting salt hydrate by using the extra water principle increased the heat storage...... the supercooled sodium acetate water mixture was 194 kJ/kg of sodium acetate water mixture in the first test cycles dropping to 179 kJ/kg in the later test cycles. Instability of the supercooling occurred when the charging periods were short and in the last test cycles where the tube connecting the module...

  3. Effects of Artificial Supercooling Followed by Slow Freezing on the Microstructure and Qualities of Pork Loin

    OpenAIRE

    Kim, Yiseul; Hong, Geun-Pyo

    2016-01-01

    This study investigated the effects of artificial supercooling followed by still air freezing (SSF) on the qualities of pork loin. The qualities of pork frozen by SSF were compared with the fresh control (CT, stored at 4℃ for 24 h), slow freezing (SAF, still air freezing) and rapid freezing (EIF, ethanol immersion freezing) treatments. Compared with no supercooling phenomena of SAF and EIF, the extent of supercooling obtained by SSF treatment was 1.4℃. Despite that SSF was conducted with the ...

  4. Microphysical effects determine macrophysical response for aerosol impacts on deep convective clouds.

    Science.gov (United States)

    Fan, Jiwen; Leung, L Ruby; Rosenfeld, Daniel; Chen, Qian; Li, Zhanqing; Zhang, Jinqiang; Yan, Hongru

    2013-11-26

    Deep convective clouds (DCCs) play a crucial role in the general circulation, energy, and hydrological cycle of our climate system. Aerosol particles can influence DCCs by altering cloud properties, precipitation regimes, and radiation balance. Previous studies reported both invigoration and suppression of DCCs by aerosols, but few were concerned with the whole life cycle of DCC. By conducting multiple monthlong cloud-resolving simulations with spectral-bin cloud microphysics that capture the observed macrophysical and microphysical properties of summer convective clouds and precipitation in the tropics and midlatitudes, this study provides a comprehensive view of how aerosols affect cloud cover, cloud top height, and radiative forcing. We found that although the widely accepted theory of DCC invigoration due to aerosol's thermodynamic effect (additional latent heat release from freezing of greater amount of cloud water) may work during the growing stage, it is microphysical effect influenced by aerosols that drives the dramatic increase in cloud cover, cloud top height, and cloud thickness at the mature and dissipation stages by inducing larger amounts of smaller but longer-lasting ice particles in the stratiform/anvils of DCCs, even when thermodynamic invigoration of convection is absent. The thermodynamic invigoration effect contributes up to ~27% of total increase in cloud cover. The overall aerosol indirect effect is an atmospheric radiative warming (3-5 W m(-2)) and a surface cooling (-5 to -8 W m(-2)). The modeling findings are confirmed by the analyses of ample measurements made at three sites of distinctly different environments.

  5. 2H NMR studies of supercooled and glassy aspirin

    Science.gov (United States)

    Nath, R.; Nowaczyk, A.; Geil, B.; Bohmer, R.

    2007-11-01

    Acetyl salicylic acid, deuterated at the methyl group, was investigated using 2H-NMR in its supercooled and glassy states. Just above the glass transition temperature the molecular reorientations were studied using stimulated-echo spectroscopy and demonstrated a large degree of similarity with other glass formers. Deep in the glassy phase the NMR spectra look similar to those reported for the crystal [A. Detken, P. Focke, H. Zimmermann, U. Haeberlen, Z. Olejniczak, Z. T. Lalowicz, Z. Naturforsch. A 50 (1995) 95] and below 20 K they are indicative for rotational tunneling with a relatively large tunneling frequency. Measurements of the spin-lattice relaxation times for temperatures below 150 K reveal a broad distribution of correlation times in the glass. The dominant energy barrier characterizing the slow-down of the methyl group is significantly smaller than the well defined barrier in the crystal.

  6. Mechanism of supercooling in flower bud of Camellia oleifea

    Institute of Scientific and Technical Information of China (English)

    苏维埃; 潘良文

    1995-01-01

    It is the first time for MRI to be used in the research of flower buds supercooling. Directobservation on freezing course of living flower buds of Camellia yuhsienensis by MRI and tissue browning test showed that freezing order of the flower organs is bud axis, scale, petal, pistil and stamen. It is coincident with the direction of ice development from bud axes to flower organs upwards. The corresponding results from MRI and freezing-fixation showed that the water translocation from flower organs to axes and scales is carried on in the course of bud freezing. ’H spectral measurement of NMR was used to follow the decrease of unfrozen water in the buds during the cooling.

  7. A molecular dynamics study on surface properties of supercooled water

    Institute of Scientific and Technical Information of China (English)

    L(U) Yongjun; WEI Bingbo

    2006-01-01

    Molecular dynamics simulations were performed to study the surface properties of water in a temperature range from 228 to 293 K by using the extended simple point charge (SPC/E) and four-site TIP4P potentials. The calculated surface tension increases with the decrease of temperature, and moreover the slopes of the surface tension-temperature curves show a weak rise below 273 K, whereas no obvious anomalies appear near 228 K, which accords with the previous experiments. Compared with the measured values, the SPC/E potential shows a good agreement, and the TIP4P potential scription of the surface structure of supercooled water for the SPC/E. When simulating the orientational distributions of water molecules near the surface, the SPC/E potential produces higher ordering and larger surface potentials than the TIP4P potential.

  8. Dynamical Instability Causes the Demise of a Supercooled Tetrahedral Liquid

    Science.gov (United States)

    Gautam, Arvind Kumar; Pingua, Nandlal; Goyal, Aashish; Apte, Pankaj A.

    2017-09-01

    We investigate the relaxation mechanism of a supercooled tetrahedral liquid at its limit of stability using isothermal isobaric ( NPT) Monte Carlo simulations. In similarity with systems which are far from equilibrium but near the onset of jamming (O'Hern et al. in Phys Rev Lett 93:165702, 2004), we find that the relaxation is characterized by two time-scales: the decay of long-wavelength (slow) fluctuations of potential energy is controlled by the slope [partial (G/N)/partial φ ] of the Gibbs free energy ( G) at a unique value of per particle potential energy φ = φ _{{\\tiny mid}}. The short-wavelength (fast) fluctuations are controlled by the bath temperature T. The relaxation of the supercooled liquid is initiated with a dynamical crossover after which the potential energy fluctuations are biased towards values progressively lesser than φ _{{\\tiny mid}}. The dynamical crossover leads to the change of time-scale, i.e., the decay of long-wavelength potential energy fluctuations (intermediate stage of relaxation). Because of the condition [partial ^2 (G/N)/partial φ ^2 = 0] at φ = φ _{{\\tiny mid}}, the slope [partial (G/N)/partial φ ] has a unique value and governs the intermediate stage of relaxation, which ends just after the crossover. In the subsequent stage, there is a relatively rapid crystallization due to lack of long-wavelength fluctuations and the instability at φ _{{\\tiny mid}}, i.e., the condition that G decreases as configurations with potential energies lower than φ _{{\\tiny mid}} are accessed. The dynamical crossover point and the associated change in the time-scale of fluctuations is found to be consistent with the previous studies.

  9. Synergetic use of millimeter- and centimeter-wavelength radars for retrievals of cloud and rainfall parameters

    Directory of Open Access Journals (Sweden)

    S. Y. Matrosov

    2010-04-01

    Full Text Available A remote sensing approach for simultaneous retrievals of cloud and rainfall parameters in the vertical column above the US Department of Energy's (DOE Climate Research Facility at the Tropical Western Pacific (TWP Darwin site in Australia is described. This approach uses vertically pointing measurements from a DOE Ka-band radar and scanning measurements from a nearby C-band radar pointing toward the TWP Darwin site. Rainfall retrieval constraints are provided by data from a surface impact disdrometer. The approach is applicable to stratiform precipitating cloud systems when a separation between the liquid hydrometeor layer, which contains rainfall and liquid water clouds, and the ice hydrometeor layer is provided by the radar bright band. Absolute C-band reflectivities and Ka-band vertical reflectivity gradients in the liquid layer are used for retrievals of the mean layer rain rate and cloud liquid water path (CLWP. C-band radar reflectivities are also used to estimate ice water path (IWP in regions above the melting layer. The retrieval uncertainties of CLWP and IWP for typical stratiform precipitation systems are about 500–800 g m−2 (for CLWP and a factor of 2 (for IWP. The CLWP retrieval uncertainties increase with rain rate, so retrievals for higher rain rates may be impractical. The expected uncertainties of layer mean rain rate retrievals are around 20%, which, in part, is due to constraints available from the disdrometer data. The applicability of the suggested approach is illustrated for two characteristic events observed at the TWP Darwin site during the wet season of 2007. A future deployment of W-band radars at the DOE tropical Climate Research Facilities can improve CLWP estimation accuracies and provide retrievals for a wider range of stratiform precipitating cloud events.

  10. Synergetic use of millimeter and centimeter wavelength radars for retrievals of cloud and rainfall parameters

    Directory of Open Access Journals (Sweden)

    S. Y. Matrosov

    2010-01-01

    Full Text Available A remote sensing approach for simultaneous retrievals of cloud and rainfall parameters in the vertical column above the US Department of Energy's (DOE Climate Research Facility at the Tropical Western Pacific (TWP Darwin site in Australia is described. This approach uses vertically pointing measurements from a DOE Ka-band radar and scanning measurements from a nearby C-band radar pointing toward the TWP Darwin site. Rainfall retrieval constraints are provided by data from a surface impact disdrometer. The approach is applicable to stratiform precipitating cloud systems when a separation between the liquid hydrometeor layer, which contains rainfall and liquid water clouds, and the ice hydrometeor layer is provided by the radar bright band. Absolute C-band reflectivities and Ka-band vertical reflectivity gradients in the liquid layer are used for retrievals of the mean layer rain rate and cloud liquid water path (CLWP. C-band radar reflectivities are also used to estimate ice water path (IWP in regions above the melting layer. The retrieval uncertainties of CLWP and IWP for typical stratiform precipitation systems are about 500–800 g m−2 (for CLWP and a factor of 2 (for IWP. The CLWP retrieval uncertainties increase with rain rate, so retrievals for higher rain rates may be impractical. The expected uncertainties of layer mean rain rate retrievals are around 20%, which, in part, is due to constraints available from the disdrometer data. The applicability of the suggested approach is illustrated for two characteristic events observed at the TWP Darwin site during the wet season of 2007. A future deployment of W-band radars at the DOE tropical Climate Research Facilities can improve CLWP estimate accuracies and provide retrievals for a wider range of stratiform precipitating cloud events.

  11. Temperature measurement of supercooled droplet in icing phenomenon by means of dual-luminescent imaging

    Science.gov (United States)

    Tanaka, M.; Morita, K.; Mamori, H.; Fukushima, N.; Yamamoto, M.

    2017-08-01

    The collision of a supercooled water droplet with a surface result an object creates ice accretion on the surface. The icing problem in any cold environments leads to severe damages on aircrafts, and a lot of studies on prevention and prediction techniques for icing have been conducted so far. Therefore, it is very important to know the detail of freezing mechanism of supercooled water droplets to improve the anti-and de-icing devices and icing simulation codes. The icing mechanism of a single supercooled water droplet impacting on an object surface would give us great insights for the purpose. In the present study, we develop a dual-luminescent imaging technique to measure the time-resolved temperature of a supercooled water droplet impacting on the surface under different temperature conditions. We apply this technique to measure the exact temperature of a water droplet, and to discuss the detail of the freezing process.

  12. A phase space approach to supercooled liquids and a universal collapse of their viscosity

    CERN Document Server

    Weingartner, Nicholas B; Nogueira, Flavio S; Kelton, K F; Nussinov, Zohar

    2016-01-01

    A broad fundamental understanding of the mechanisms underlying the phenomenology of supercooled liquids has remained elusive, despite decades of intense exploration. When supercooled beneath its characteristic melting temperature, a liquid sees a sharp rise in its viscosity over a narrow temperature range, eventually becoming frozen on laboratory timescales. Explaining this immense increase in viscosity is one of the principle goals of condensed matter physicists. To that end, numerous theoretical frameworks have been proposed which explain and reproduce the temperature dependence of the viscosity of supercooled liquids. Each of these frameworks appears only applicable to specific classes of glassformers and each possess a number of variable parameters. Here we describe a classical framework for explaining the dynamical behavior of supercooled liquids based on statistical mechanical considerations, and possessing only a single variable parameter. This parameter varies weakly from liquid to liquid. Furthermore...

  13. Chemical Composition of the Tourmaline from Stratiform Tourmalinites of the Passagem de Mariana Gold Mine, Southeastern Quadrilátero Ferrífero (Minas Gerais, Brazil)

    OpenAIRE

    Gianna Maria Garda; Johann Hans Daniel Schorscher; Paulo Beljavskis; Marcos de Souza Mansueto; Margareth Sugano Navarro; Andrezza Alves Mota

    2009-01-01

    The Passagem de Mariana Mine in the southeastern part of the Quadrilátero Ferrífero, Minas Gerais, Brazil, is one ofthe oldest Brazilian gold mines. Gold is associated with stratiform tourmalinites and tourmaline-bearing quartz and carbonateveins and breccias. The highest gold contents (up to 200 g/t) have been recorded in the stratiform tourmalinites, whichbelong to the Batatal Formation (Caraça Group, Minas Supergroup). Three petrographic types of tourmaline have been defined and analyzed b...

  14. NASA Glenn Icing Research Tunnel: 2014 Cloud Calibration

    Science.gov (United States)

    VanZante, Judith Foss; Ide, Robert F.; Steen, Laura; Acosta, Waldo J.

    2014-01-01

    The results of the December 2013 to February 2014 Icing Research Tunnel full icing cloud calibration are being presented to the SAE AC-9C committee, as represented in the 2014 cloud calibration report. The calibration steps included establishing a uniform cloud and conducting drop size and liquid water content calibrations. The goal of the calibration was to develop a uniform cloud, and to generate a transfer function from the inputs of air speed, spray bar atomizing air pressure and water pressure to the outputs of median volumetric drop diameter and liquid water content. This was done for both 14 CFR Parts 25 and 29, Appendix C (typical icing) and soon-to-be released Appendix O (supercooled large drop) conditions.

  15. Fragile to strong crossover at the Widom line in supercooled aqueous solutions of NaCl

    Energy Technology Data Exchange (ETDEWEB)

    Gallo, P. [Dipartimento di Matematica e Fisica, Università Roma Tre, Via della Vasca Navale 84, I-00146 Rome, Italy and INFN, Sezione di Roma Tre, Via della Vasca Navale 84, I-00146 Rome (Italy); Corradini, D.; Rovere, M., E-mail: rovere@fis.uniroma3.it [Dipartimento di Matematica e Fisica, Università Roma Tre, Via della Vasca Navale 84, I-00146 Rome (Italy)

    2013-11-28

    We study by molecular dynamics simulations the dynamical properties of an aqueous solution of NaCl at a concentration of 0.67 mol/kg upon supercooling. In a previous study of the same ionic solution, we have located the liquid-liquid critical point (LLCP) and determined the Widom line connected to the liquid-liquid transition. We present here the results obtained from the study of the self-intermediate scattering function in a large range of temperatures and densities approaching the LLCP. The structural relaxation is in agreement with the mode coupling theory (MCT) in the region of mild supercooling. In the deeper supercooled region the α-relaxation time as function of temperature deviates from the MCT power law prediction showing a crossover from a fragile to a strong behavior. This crossover is found upon crossing the Widom line. The same trend was found in bulk water upon supercooling and it appears almost unchanged by the interaction with ions apart from a shift in the thermodynamic plane toward lower pressures and higher temperatures. These results show that the phenomenology of supercooled water transfers from bulk to solution where the study of the supercooled region is experimentally less difficult.

  16. Fragile to strong crossover at the Widom line in supercooled aqueous solutions of NaCl.

    Science.gov (United States)

    Gallo, P; Corradini, D; Rovere, M

    2013-11-28

    We study by molecular dynamics simulations the dynamical properties of an aqueous solution of NaCl at a concentration of 0.67 mol/kg upon supercooling. In a previous study of the same ionic solution, we have located the liquid-liquid critical point (LLCP) and determined the Widom line connected to the liquid-liquid transition. We present here the results obtained from the study of the self-intermediate scattering function in a large range of temperatures and densities approaching the LLCP. The structural relaxation is in agreement with the mode coupling theory (MCT) in the region of mild supercooling. In the deeper supercooled region the α-relaxation time as function of temperature deviates from the MCT power law prediction showing a crossover from a fragile to a strong behavior. This crossover is found upon crossing the Widom line. The same trend was found in bulk water upon supercooling and it appears almost unchanged by the interaction with ions apart from a shift in the thermodynamic plane toward lower pressures and higher temperatures. These results show that the phenomenology of supercooled water transfers from bulk to solution where the study of the supercooled region is experimentally less difficult.

  17. RACORO Continental Boundary Layer Cloud Investigations: 3. Separation of Parameterization Biases in Single-Column Model CAM5 Simulations of Shallow Cumulus

    Science.gov (United States)

    Lin, Wuyin; Liu, Yangang; Vogelmann, Andrew M.; Fridlind, Ann; Endo, Satoshi; Song, Hua; Feng, Sha; Toto, Tami; Li, Zhijin; Zhang, Minghua

    2015-01-01

    Climatically important low-level clouds are commonly misrepresented in climate models. The FAst-physics System TEstbed and Research (FASTER) Project has constructed case studies from the Atmospheric Radiation Measurement Climate Research Facility's Southern Great Plain site during the RACORO aircraft campaign to facilitate research on model representation of boundary-layer clouds. This paper focuses on using the single-column Community Atmosphere Model version 5 (SCAM5) simulations of a multi-day continental shallow cumulus case to identify specific parameterization causes of low-cloud biases. Consistent model biases among the simulations driven by a set of alternative forcings suggest that uncertainty in the forcing plays only a relatively minor role. In-depth analysis reveals that the model's shallow cumulus convection scheme tends to significantly under-produce clouds during the times when shallow cumuli exist in the observations, while the deep convective and stratiform cloud schemes significantly over-produce low-level clouds throughout the day. The links between model biases and the underlying assumptions of the shallow cumulus scheme are further diagnosed with the aid of large-eddy simulations and aircraft measurements, and by suppressing the triggering of the deep convection scheme. It is found that the weak boundary layer turbulence simulated is directly responsible for the weak cumulus activity and the simulated boundary layer stratiform clouds. Increased vertical and temporal resolutions are shown to lead to stronger boundary layer turbulence and reduction of low-cloud biases.

  18. NASA Glenn Icing Research Tunnel: 2014 Cloud Calibration Procedure and Results

    Science.gov (United States)

    Van Zante, Judith F.; Ide, Robert F.; Steen, Laura E.; Acosta, Waldo J.

    2014-01-01

    The results of the December 2013 to February 2014 Icing Research Tunnel full icing cloud calibration are presented. The calibration steps included establishing a uniform cloud and conducting drop size and liquid water content calibrations. The goal of the calibration was to develop a uniform cloud, and to generate a transfer function from the inputs of air speed, spray bar atomizing air pressure and water pressure to the outputs of median volumetric drop diameter and liquid water content. This was done for both 14 CFR Parts 25 and 29, Appendix C ('typical' icing) and soon-to-be released Appendix O (supercooled large drop) conditions.

  19. Cloud Governance

    DEFF Research Database (Denmark)

    Berthing, Hans Henrik

    Denne præsentation beskriver fordele og værdier ved anvendelse af Cloud Computing. Endvidere inddrager resultater fra en række internationale analyser fra ISACA om Cloud Computing.......Denne præsentation beskriver fordele og værdier ved anvendelse af Cloud Computing. Endvidere inddrager resultater fra en række internationale analyser fra ISACA om Cloud Computing....

  20. Raman Spectra and Nucleation Rates of Sulfuric Acid and Ammonium Sulfate Aerosols Supercooled with Respect to Ice

    Science.gov (United States)

    Knopf, D. A.; Koop, T.; Weers, U. G.; Krieger, U. K.; Peter, T.

    2001-12-01

    Sulfuric acid and ammonium sulfate aerosol particles can serve as ice condensation nuclei for the formation of upper tropospheric cirrus clouds. These clouds influence the global radiation budget by scattering of short wavelength (solar) radiation as well as by absorbing long wavelength (terrestrial) radiation. Knowledge of the thermodynamics and the nucleation rates of aerosols is fundamental for the understanding of formation processes of cirrus clouds. Here, we present a new investigation tool to observe phase transitions of aerosols supercooled with respect to ice. Confocal Raman microscopy is used to determine the phase changes and the morphology of the particles. Raman spectroscopy is employed to distinguish and to characterize the different phases inside the frozen particles. Single droplets with a diameter of typically 20-120 μ m are deposited on a hydrophobically coated Herasil-plate that is covered by a spacer and another plate. Since the gas phase volume of the cell is small compared to the liquid droplet volume the composition of the droplets remains fixed during temperature changes. The temperature of the droplets can be varied between 150-350~K. We present the first Raman spectra of aqueous H2SO4/H2O and (NH4)2SO4/H2O droplets for several concentrations and temperatures to the homogeneous ice nucleation limits. The analysis of the speciation of the components inside the droplets (e.g. sulfate vs. bisulfate ions) is compared to results from thermodynamic models. Evaluation of the freezing data gives upper limits for ice nucleation rates of droplets as a function of sulfuric acid or ammonium sulfate concentration.

  1. Simulations of Cloud-Radiation Interaction Using Large-Scale Forcing Derived from the CINDY/DYNAMO Northern Sounding Array

    Science.gov (United States)

    Wang, Shuguang; Sobel, Adam H.; Fridlind, Ann; Feng, Zhe; Comstock, Jennifer M.; Minnis, Patrick; Nordeen, Michele L.

    2015-01-01

    The recently completed CINDY/DYNAMO field campaign observed two Madden-Julian oscillation (MJO) events in the equatorial Indian Ocean from October to December 2011. Prior work has indicated that the moist static energy anomalies in these events grew and were sustained to a significant extent by radiative feedbacks. We present here a study of radiative fluxes and clouds in a set of cloud-resolving simulations of these MJO events. The simulations are driven by the large-scale forcing data set derived from the DYNAMO northern sounding array observations, and carried out in a doubly periodic domain using the Weather Research and Forecasting (WRF) model. Simulated cloud properties and radiative fluxes are compared to those derived from the S-PolKa radar and satellite observations. To accommodate the uncertainty in simulated cloud microphysics, a number of single-moment (1M) and double-moment (2M) microphysical schemes in the WRF model are tested. The 1M schemes tend to underestimate radiative flux anomalies in the active phases of the MJO events, while the 2M schemes perform better, but can overestimate radiative flux anomalies. All the tested microphysics schemes exhibit biases in the shapes of the histograms of radiative fluxes and radar reflectivity. Histograms of radiative fluxes and brightness temperature indicate that radiative biases are not evenly distributed; the most significant bias occurs in rainy areas with OLR less than 150 W/ cu sq in the 2M schemes. Analysis of simulated radar reflectivities indicates that this radiative flux uncertainty is closely related to the simulated stratiform cloud coverage. Single-moment schemes underestimate stratiform cloudiness by a factor of 2, whereas 2M schemes simulate much more stratiform cloud.

  2. Experimental evidence for supercooled brines, viscous liquids, and low temperature perchlorate glasses on Mars

    Science.gov (United States)

    Toner, J.; Catling, D. C.; Light, B.

    2013-12-01

    The presence of liquid water on the cold and dry surface of Mars is possible where concentrated salt solutions lower the freezing point of water. The eutectic temperature is the maximum equilibrium freezing point depression possible for a given salt solution, which ranges from near 0°C for carbonates and sulfates, to as low as -75°C for perchlorates. Although eutectic temperatures suggest a lower temperature limit for liquid water on Mars, salt solutions will typically supercool below their eutectic before crystallization occurs. We report on results investigating the magnitude of supercooling and its variation with salt composition and concentration for pure salt solutions and saturated soil solutions of MgSO4, MgCl2, NaCl, NaClO4, Mg(ClO4)2, and Ca(ClO4)2. We measured supercooling by monitoring solution temperatures during slow cooling and warming experiments. Our results indicate that supercooling is pervasive. Slowly cooled MgSO4, MgCl2, NaCl, and NaClO4 solutions typically supercool 5-15°C below their eutectic temperature before crystallizing. The addition of soil to these salt solutions has a variable effect on supercooling. Relative to the pure salt solutions, supercooling decreases in MgSO4 soil solutions, increases in MgCl2 soil solutions, and is similar in NaCl and NaClO4 soil solutions. Supercooling in MgSO4, MgCl2, NaCl, and NaClO4 solutions could marginally extend the duration of liquid water during relatively warm daytime temperatures in the Martian summer. Remarkably, we found that Mg(ClO4)2 and Ca(ClO4)2 solutions never crystallize during slow cooling, but remain in a supercooled, liquid state until forming an amorphous glass near -120°C. Even if soil is added to the solutions, which will induce crystallization in most salt solutions, a glass still forms during cooling. The large supercooling effect in Mg(ClO4)2 and Ca(ClO4)2 solutions has the potential to prevent water from freezing over diurnal and possibly annual cycles on Mars. Glasses are

  3. Cloud optics

    CERN Document Server

    Kokhanovsky, A

    2006-01-01

    Clouds affect the climate of the Earth, and they are an important factor in the weather. Therefore, their radiative properties must be understood in great detail. This book summarizes current knowledge on cloud optical properties, for example their ability to absorb, transmit, and reflect light, which depends on the clouds' geometrical and microphysical characteristics such as sizes of droplets and crystals, their shapes, and structures. In addition, problems related to the image transfer through clouds and cloud remote sensing are addressed in this book in great detail. This book can be an im

  4. Global anthropogenic aerosol effects on convective clouds in ECHAM5-HAM

    Directory of Open Access Journals (Sweden)

    U. Lohmann

    2008-04-01

    Full Text Available Aerosols affect the climate system by changing cloud characteristics in many ways. They act as cloud condensation and ice nuclei and may have an influence on the hydrological cycle. Here we investigate aerosol effects on convective clouds by extending the double-moment cloud microphysics scheme developed for stratiform clouds, which is coupled to the HAM double-moment aerosol scheme, to convective clouds in the ECHAM5 general circulation model. This enables us to investigate whether more, and smaller cloud droplets suppress the warm rain formation in the lower parts of convective clouds and thus release more latent heat upon freezing, which would then result in more vigorous convection and more precipitation. In ECHAM5, including aerosol effects in large-scale and convective clouds (simulation ECHAM5-conv reduces the sensitivity of the liquid water path increase with increasing aerosol optical depth in better agreement with observations and large-eddy simulation studies. In simulation ECHAM5-conv with increases in greenhouse gas and aerosol emissions since pre-industrial times, the geographical distribution of the changes in precipitation better matches the observed increase in precipitation than neglecting microphysics in convective clouds. In this simulation the convective precipitation increases the most suggesting that the convection has indeed become more vigorous.

  5. Impact of cloud-borne aerosol representation on aerosol direct and indirect effects

    Directory of Open Access Journals (Sweden)

    S. J. Ghan

    2006-01-01

    Full Text Available Aerosol particles attached to cloud droplets are much more likely to be removed from the atmosphere and are much less efficient at scattering sunlight than if unattached. Models used to estimate direct and indirect effects of aerosols employ a variety of representations of such cloud-borne particles. Here we use a global aerosol model with a relatively complete treatment of cloud-borne particles to estimate the sensitivity of simulated aerosol, cloud and radiation fields to various approximations to the representation of cloud-borne particles. We find that neglecting transport of cloud-borne particles introduces little error, but that diagnosing cloud-borne particles produces global mean biases of 20% and local errors of up to 40% for aerosol, droplet number, and direct and indirect radiative forcing. Aerosol number, aerosol optical depth and droplet number are significantly underestimated in regions and seasons where and when wet removal is primarily by stratiform rather than convective clouds (polar regions during winter, but direct and indirect effects are less biased because of the limited sunlight there and then. A treatment that predicts the total mass concentration of cloud-borne particles for each mode yields smaller errors and runs 20% faster than the complete treatment. The errors are much smaller than current estimates of uncertainty in direct and indirect effects of aerosols, which suggests that the treatment of cloud-borne aerosol is not a significant source of uncertainty in estimates of direct and indirect effects.

  6. Fractional Walden rule for electrolytes in supercooled disaccharide aqueous solutions.

    Science.gov (United States)

    Longinotti, M Paula; Corti, Horacio R

    2009-04-23

    The electrical conductivity of CsCl, KCl, Bu(4)NBr, and Bu(4)NI was studied in stable and supercooled (metastable) sucrose and trehalose aqueous solutions over a wide viscosity range. The results indicate that large positive deviations from the Walden rule occur in these systems due to the higher tendency of the ions to move in water-rich regions, as previously observed for NaCl and MgCl(2). The electrical molar conductivity viscosity dependence can be described with a fractional Walden rule (Lambdaeta(alpha) = constant), where alpha is a decoupling parameter which increases with ionic size and varies between 0.61 and 0.74 for all of the studied electrolytes. Using the electrical molar conductivity dependence of ion-ion interactions, an effective dielectric constant was calculated for a trehalose 39 wt% aqueous solution as a function of temperature. Above 278 K, the effective and the bulk solution dielectric constants are similar, but at lower temperatures, where the carbohydrate becomes less mobile than water, the effective dielectric constant approaches the dielectric constant of water. We also conclude that the solute-solvent dielectric friction contribution can be neglected, reinforcing the idea that the observed breakdown of the Walden rule is due to the existence of local microheterogeneities. The Walden plots for the studied ionic solutes show a decoupling similar to that found for the diffusion of water in the same solutions.

  7. Spatiotemporal heterogeneity of local free volumes in highly supercooled liquid

    Science.gov (United States)

    Shiba, Hayato; Kawasaki, Takeshi

    2013-11-01

    We discuss the spatiotemporal behavior of local density and its relation to dynamical heterogeneity in a highly supercooled liquid by using molecular dynamics simulations of a binary mixture with different particle sizes in two dimensions. To trace voids heterogeneously existing with lower local densities, which move along with the structural relaxation, we employ the minimum local density for each particle in a time window whose width is set along with the structural relaxation time. Particles subject to free volumes correspond well to the configuration rearranging region of dynamical heterogeneity. While the correlation length for dynamical heterogeneity grows with temperature decrease, no growth in the correlation length of heterogeneity in the minimum local density distribution takes place. A comparison of these results with those of normal mode analysis reveals that superpositions of lower-frequency soft modes extending over the free volumes exhibit spatial correlation with the broken bonds. This observation suggests a possibility that long-ranged vibration modes facilitate the interactions between fragile regions represented by free volumes, to induce dynamical correlations at a large scale.

  8. Simulation study of water and sugar dynamics in supercooled mixtures

    Science.gov (United States)

    Molinero, Valeria; Cagin, Tahir; Goddard, William A.

    2003-03-01

    Water dynamics in concentrated carbohydrate solutions is of utmost importance in food and pharmaceutical technology, where low water mobility is desirable to slow down chemical degradation and preserve biomolecules. We have studied the microscopic mechanism of water diffusion in binary and polydisperse malto-oligosaccharides and water mixtures by means of molecular dynamics simulations. The computations were performed with a coarse grain model (M3B), derived from atomistic simulations of water and malto-oligosaccharides. The use of the M3B model permits simulations of the order of 0.1 microsecond, thus allowing us to explore water dynamics from the liquid to the deep supercooled regime. The dynamics of water confined in the sugar matrix is slowed down with respect to bulk water. We found that at low moisture content and low temperature, ranslational diffusion of water and glucose rotation proceed through a hopping-diffusion mechanism. Moreover, we found water mobility to be heterogeneous: there is a broad distribution of time scales for different water molecules in the mixtures. We discuss whether there is a relationship between the heterogeneous structure of these mixtures in the sub-nanometer scale and the heterogeneous dynamics of water molecules.

  9. The Transient Supercooling Enhancement For A Pulsed Thermoelectric Cooler (TEC)

    OpenAIRE

    Mao, Jia-ni; Du, Jun-yan; Wang, Shi-fei; Zhou, Jing-wei; Wang, Yu-Gang

    2016-01-01

    Once TEC excitated by a high-voltage pulse, there exists a transient thermoelectric supercooling effect, which can be enhanced by keeping on increasing the Peltier cooling effect to compensate for the negative self-heating from the Joule heating effect and Fourier heat conduction effect. After superimposing an additional voltage pulse over a steady-state reference value in a short time scale, abrupt temperature drop will be produc...

  10. Thermodynamic scaling of molecular dynamics in supercooled ibuprofen.

    Science.gov (United States)

    Adrjanowicz, K; Wojnarowska, Z; Paluch, M; Pionteck, J

    2011-04-28

    It was shown recently that ibuprofen revealed a strong tendency to form hydrogen bonded aggregates such as dimers and trimers of either cyclic or linear geometry, which somehow seems to control molecular mobility of that drug [Brás et al. J. Phys. Chem. B2008, 112 (35), 11 087-11 099]. For such hydrogen-bonded liquids, superpositioning of dynamics under various temperature T, pressure P, and volume V conditions, when plotted versus the scaling function of T(-1)V(-γ) (where γ is a material constant), may not always be satisfying. In the present work, we have tested the validity of this scaling for supercooled ibuprofen. In order to do that, pressure-volume-temperature (PVT) measurements combined with isobaric and isothermal dielectric relaxation studies (pressure up to 310 MPa) were carried out. The scaling properties of the examined drug were derived from the fitting of the τ(α)(T,V) dependences to the modified Avramov equation and by analyzing in double logarithmic scale the T(g)(V(g)) dependences, where the glass transition temperature T(g) and volume V(g) were defined for various relaxation times. In view of the obtained results, we conjecture that for ibuprofen the thermodynamic scaling idea works but not perfectly. The slight departure from the scaling behavior is discussed in the context of the hydrogen bonding abilities of the examined system and compared with the results reported for other strongly associated liquids.

  11. The Transient Supercooling Enhancement For A Pulsed Thermoelectric Cooler (TEC)

    OpenAIRE

    Mao, Jia-ni; Du, Jun-yan; Wang, Shi-fei; Zhou, Jing-wei; Wang, Yu-Gang

    2016-01-01

    Once TEC excitated by a high-voltage pulse, there exists a transient thermoelectric supercooling effect, which can be enhanced by keeping on increasing the Peltier cooling effect to compensate for the negative self-heating from the Joule heating effect and Fourier heat conduction effect. After superimposing an additional voltage pulse over a steady-state reference value in a short time scale, abrupt temperature drop will be produc...

  12. Supercooling and cold energy storage characteristics of nano-media in ball-packed porous structures

    Directory of Open Access Journals (Sweden)

    Zhao Qunzhi

    2015-04-01

    Full Text Available The presented experiments aimed to study the supercooling and cold-energy storage characteristics of nanofluids and water-based nano-media in ball-packed porous structures (BPS. Titanium dioxide nanoparticles (TiO2 NPs measuring 20nm and 80nm were used as additives and sodium dodecyl benzene sulphonate (SDBS was used as anionic surfactant. The experiments used different concentrations of nanofluid, distilled with BPS of different spherical diameter and different concentrations of nano-media, and were conducted 20 times. Experimental results of supercooling were analysed by statistical methods. Results show that the average and peak supercooling degrees of nanofluids and nano-media in BPS are lower than those of distilled water. For the distilled water in BPS, the supercooling degree decreases on the whole with the decrease of the ball diameter. With the same spherical diameter (8mm of BPS, the supercooling degree of TiO2 NPs measuring 20nm is lower than the supercooling degree of distilled water in BPS. Step-cooling experiments of different concentrations of nanofluids and nano-media in BPS were also conducted. Results showed that phase transition time is reduced because of the presence of TiO2 NPs. The BPS substrate and the NPs enhance the heat transfer. Distilled water with a porous solid base and nanoparticles means the amount of cold-energy storage increases and the supercooling degree and the total time are greatly reduced. The phase transition time of distilled water is about 3.5 times that of nano-media in BPS.

  13. Behavior analysis of convective and stratiform rain using Markovian approach over Mediterranean region from meteorological radar data

    Directory of Open Access Journals (Sweden)

    M. Lazri

    2012-05-01

    Full Text Available The aim of this study is to analyze the chronological behavior of precipitation in the north of Algeria using a Markovian approach. The probabilistic approach presented here proposes to study the evolution of the rainfall phenomenon in two distinct study areas, one located in sea and other located in ground. The data that we have used are provided by the National Office of Meteorology in Algiers (ONM. They are a series of images collected by the meterological radar of Setif during the rainy season 2001/2002. A decision criterion is established and based on radar reflectivity in order to classify the precipitation events located in both areas. At each radar observation, a state of precipitations is classified, either convective (heavy precipitation or stratiform (average precipitation both for the "sea" and for the "ground". On the whole, a time series of precipitations composed of three states; S0 (no raining, S1 (stratiform precipitation and S2 (convective precipitation, is obtained for each of the two areas. Thereby, we studied and characterized the behavior of precipitation in time by a Markov chain of order one with three states. Transition probabilities Pij of state Si to state Sj are calculated. The results show that rainfall is well described by a Markov chain of order one with three states. Indeed, the stationary probabilities, which are calculated by using the Markovian model, and the actual probabilities are almost identical.

  14. Mechanism of Supercooled Water Droplet Breakup near the Leading Edge of an Airfoil

    Science.gov (United States)

    Veras-Alba, Belen; Palacios, Jose; Vargas, Mario; Ruggeri, Charles; Bartkus, Tadas P.

    2017-01-01

    This work presents the results of an experimental study on supercooled droplet deformation and breakup near the leading edge of an airfoil. The results are compared to prior room temperature droplet deformation results to explore the effects of droplet supercooling. The experiments were conducted in the Adverse Environment Rotor Test Stand (AERTS) at The Pennsylvania State University. An airfoil model placed at the end of the rotor blades mounted onto the hub in the AERTS chamber was moved at speeds ranging between 50 and 80 m/sec. The temperature of the chamber was set at -20°C. A monotonic droplet generator was used to produce droplets that fell from above, perpendicular to the path of the airfoil. The supercooled state of the droplets was determined by measurement of the temperature of the drops at various locations below the droplet generator exit. A temperature prediction code was also used to estimate the temperature of the droplets based on vertical velocity and the distance traveled by droplets from the droplet generator to the airfoil stagnation line. High speed imaging was employed to observe the interaction between the droplets and the airfoil. The high speed imaging provided droplet deformation information as the droplet approached the airfoil near the stagnation line. A tracking software program was used to measure the horizontal and vertical displacement of the droplet against time. It was demonstrated that to compare the effects of water supercooling on droplet deformation, the ratio of the slip velocity and the initial droplet velocity must be equal. A case with equal slip velocity to initial velocity ratios was selected for room temperature and supercooled droplet conditions. The airfoil velocity was 60 m/s and the slip velocity for both sets of data was 40 m/s. In these cases, the deformation of the weakly supercooled and warm droplets did not present different trends. The similar behavior for both environmental conditions indicates that water

  15. Comprehensive Radar Observations of Clouds and Precipitation over the Tibetan Plateau and Preliminary Analysis of Cloud Properties

    Institute of Scientific and Technical Information of China (English)

    2015-01-01

    ), and updrafts and downdrafts coexisted in the convective system. Supercooled water might exist in such kinds of deep convective system. The above measurements and preliminary analysis provide a basis for further study of cloud physics and precipitation process over the Tibetan Plateau. These observations are also valuable for modeling studies of cloud and precipitation physics as well as in the development of parameterization schemes in numerical prediction models.

  16. A phase space approach to supercooled liquids and a universal collapse of their viscosity

    Directory of Open Access Journals (Sweden)

    Nicholas Bryan Weingartner

    2016-11-01

    Full Text Available A broad fundamental understanding of the mechanisms underlying the phenomenology of supercooled liquids has remained elusive, despite decades of intense exploration. When supercooled beneath its characteristic melting temperature, a liquid sees a sharp rise in its viscosity over a narrow temperature range, eventually becoming frozen on laboratory timescales. Explaining this immense increase in viscosity is one of the principle goals of condensed matter physicists. To that end, numerous theoretical frameworks have been proposed which explain and reproduce the temperature dependence of the viscosity of supercooled liquids. Each of these frameworks appears only applicable to specific classes of glassformers and each possess a number of variable parameters. Here we describe a classical framework for explaining the dynamical behavior of supercooled liquids based on statistical mechanical considerations, and possessing only a single variable parameter. This parameter varies weakly from liquid to liquid. Furthermore, as predicted by this new classical theory and its earlier quantum counterpart, we find with the aid of a small dimensionless constant that varies in size from sim 0.05-0.12 , a universal (16 decade collapse of the viscosity data as a function of temperature. The collapse appears in all known types of glass forming supercooled liquids (silicates, metallic alloys, organic systems, chalcogenide, sugars, and water.

  17. Effect of drop size on the impact thermodynamics for supercooled large droplet in aircraft icing

    Science.gov (United States)

    Zhang, Chen; Liu, Hong

    2016-06-01

    Supercooled large droplet (SLD), which can cause abnormal icing, is a well-known issue in aerospace engineering. Although efforts have been exerted to understand large droplet impact dynamics and the supercooled feature in the film/substrate interface, respectively, the thermodynamic effect during the SLD impact process has not received sufficient attention. This work conducts experimental studies to determine the effects of drop size on the thermodynamics for supercooled large droplet impingement. Through phenomenological reproduction, the rapid-freezing characteristics are observed in diameters of 400, 800, and 1300 μm. The experimental analysis provides information on the maximum spreading rate and the shrinkage rate of the drop, the supercooled diffusive rate, and the freezing time. A physical explanation of this unsteady heat transfer process is proposed theoretically, which indicates that the drop size is a critical factor influencing the supercooled heat exchange and effective heat transfer duration between the film/substrate interface. On the basis of the present experimental data and theoretical analysis, an impinging heating model is developed and applied to typical SLD cases. The model behaves as anticipated, which underlines the wide applicability to SLD icing problems in related fields.

  18. Liquid Supercoolability and Synthesis Kinetics of Quinary Refractory High-entropy Alloy

    Science.gov (United States)

    Wang, W. L.; Hu, L.; Yang, S. J.; Wang, A.; Wang, L.; Wei, B.

    2016-11-01

    The high-entropy configuration of equiatomic multicomponent alloys opens an effective access to the development of advanced materials. Here we report the synthesis of a new quinary refractory WMoTaNbZr high-entropy alloy under electrostatic levitation condition. It showed a high liquidus temperature of 2686 K and achieved a maximum supercooling of 640 K (0.24 TL) at molten state. The containerless measurements revealed a linear increasing tendency for both its liquid state density and the specific heat to emissivity ratio versus alloy supercooling. A high-entropy body-centered cubic (HEB) phase dominated its phase constitution despite the formation of a negligible amount of solid solution (Zr) phase. The dendritic growth of HEB phase always governed the crystallization process, attained a fastest growth velocity of 13.5 m/s and displayed a power function relation to alloy supercooling. The high speed videographic research of recalescence phenomenon indicated Johnson-Mehl-Avrami type transition kinetics for its rapid solidification process. As supercooling increases, the microstructures of primary HEB phase were refined conspicuously and exhibited an obvious solute trapping effect of the segregative Zr component. Meanwhile, the Vickers hardness of HEB phase displayed the rising tendency with supercooling.

  19. A phase space approach to supercooled liquids and a universal collapse of their viscosity

    Science.gov (United States)

    Weingartner, Nicholas; Nogueira, Flavio; Pueblo, Chris; Kelton, Kenneth; Nussinov, Zohar

    2016-11-01

    A broad fundamental understanding of the mechanisms underlying the phenomenology of supercooled liquids has remained elusive, despite decades of intense exploration. When supercooled beneath its characteristic melting temperature, a liquid sees a sharp rise in its viscosity over a narrow temperature range, eventually becoming frozen on laboratory timescales. Explaining this immense increase in viscosity is one of the principle goals of condensed matter physicists. To that end, numerous theoretical frameworks have been proposed which explain and reproduce the temperature dependence of the viscosity of supercooled liquids. Each of these frameworks appears only applicable to specific classes of glassformers and each possess a number of variable parameters. Here we describe a classical framework for explaining the dynamical behavior of supercooled liquids based on statistical mechanical considerations, and possessing only a single variable parameter. This parameter varies weakly from liquid to liquid. Furthermore, as predicted by this new classical theory and its earlier quantum counterpart, we find with the aid of a small dimensionless constant that varies in size from ˜ 0.05-0.12, a universal (16 decade) collapse of the viscosity data as a function of temperature. The collapse appears in all known types of glass forming supercooled liquids (silicates, metallic alloys, organic systems, chalcogenide, sugars, and water).

  20. Antarctic clouds

    OpenAIRE

    Lachlan-Cope, Tom

    2010-01-01

    Sensitivity studies with global climate models show that, by their influence on the radiation balance, Antarctic clouds play a major role in the climate system, both directly at high southern latitudes and indirectly globally, as the local circulation changes lead to global teleconnections. Unfortunately, observations of cloud distribution in the Antarctic are limited and often of low quality because of the practical difficulty in observing clouds in the harsh Antarctic environment. The best ...

  1. Cloud Computing

    CERN Document Server

    Antonopoulos, Nick

    2010-01-01

    Cloud computing has recently emerged as a subject of substantial industrial and academic interest, though its meaning and scope is hotly debated. For some researchers, clouds are a natural evolution towards the full commercialisation of grid systems, while others dismiss the term as a mere re-branding of existing pay-per-use technologies. From either perspective, 'cloud' is now the label of choice for accountable pay-per-use access to third party applications and computational resources on a massive scale. Clouds support patterns of less predictable resource use for applications and services a

  2. Representation of Arctic mixed-phase clouds and the Wegener-Bergeron-Findeisen process in climate models: Perspectives from a cloud-resolving study

    Science.gov (United States)

    Fan, Jiwen; Ghan, Steven; Ovchinnikov, Mikhail; Liu, Xiaohong; Rasch, Philip J.; Korolev, Alexei

    2011-01-01

    Two types of Arctic mixed-phase clouds observed during the ISDAC and M-PACE field campaigns are simulated using a 3-dimensional cloud-resolving model (CRM) with size-resolved cloud microphysics. The modeled cloud properties agree reasonably well with aircraft measurements and surface-based retrievals. Cloud properties such as the probability density function (PDF) of vertical velocity (w), cloud liquid and ice, regimes of cloud particle growth, including the Wegener-Bergeron-Findeisen (WBF) process, and the relationships among properties/processes in mixed-phase clouds are examined to gain insights for improving their representation in General Circulation Models (GCMs). The PDF of the simulated w is well represented by a Gaussian function, validating, at least for arctic clouds, the subgrid treatment used in GCMs. The PDFs of liquid and ice water contents can be approximated by Gamma functions, and a Gaussian function can describe the total water distribution, but a fixed variance assumption should be avoided in both cases. The CRM results support the assumption frequently used in GCMs that mixed phase clouds maintain water vapor near liquid saturation. Thus, ice continues to grow throughout the stratiform cloud but the WBF process occurs in about 50% of cloud volume where liquid and ice co-exist, predominantly in downdrafts. In updrafts, liquid and ice particles grow simultaneously. The relationship between the ice depositional growth rate and cloud ice strongly depends on the capacitance of ice particles. The simplified size-independent capacitance of ice particles used in GCMs could lead to large deviations in ice depositional growth.

  3. Observations of Cloud Top Entrainment Instability Induced by Aircraft Wake Downwash

    Science.gov (United States)

    Walcek, C. J.

    2012-12-01

    Aircraft produce considerable turbulence and generate 20-80 m/s downward velocity impulses immediately below the airframe and wings. This downward-propagating air produces turbulent vortices that descend 100-300 meters before dissipating. If an aircraft flies very close to the tops of stratiform clouds, it can induce mixing between cloudy air and clear air pushed into the cloud from above cloud top. Here we present photographs and evidence that aircraft flying close to the tops of stable stratiform clouds can trigger the release of cloud-top entrainment instability (CTEI). Negatively-buoyant air can be produced as warm air forced into a cloud from above cloud top mixes with colder cloudy air, inducing evaporation and further cooling below the cloud temperature, thus initiating turbulent downdrafts that can propagate the CTEI mechanism that ultimately dissipates and evaporates the top several hundred meters near cloud top. Photographs taken from observation chase planes flying 1-2 km above another aircraft flying very close to cloud top show 50-100 m wide swaths cleared within 3-4 seconds after fly-over, and growth rates of 2-3 m/s lateral to the flight track are observed. Ultimately "canal cloud" or "hole punch" features 2-3 km wide are generated in 20-30 minutes following the flyover from this mechanism. Here the mechanism of aircraft downwash is reviewed, CTEI is described, and evidence of the importance of evaporation and entrainment is provided from unpublished results from the late 1940s-era "project CIRRUS" and more recent images of hole-punch and canal-clouds. Since the propagation of this turbulent process occurs in turbulent filaments of mixtures of clear and cloudy air, modeling this process will require resolutions of less than several meters, yet require simulation domains several 1000s of meters wide. Similarly, measurements of dissipated cloud regions induced by aircraft would require resolutions of several meters or 10s of Hz to unambiguously

  4. Thermal conductivity enhancement of sodium acetate trihydrate by adding graphite powder and the effect on stability of supercooling

    DEFF Research Database (Denmark)

    Johansen, Jakob Berg; Dannemand, Mark; Kong, Weiqiang

    2015-01-01

    Sodium acetate trihydrate and graphite powder mixtures have been evaluated to investigate the influence of the graphite powder on the stability of supercooling. A sodium acetate and water mixture mixed with graphite powder was successfully supercooled at ambient indoor temperatures for five month...

  5. An investigation on supercooling directional solidification process of Cu-Ni single phase alloy

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Supercooling directional solidification (SDS) is put forward by combination of melt supercooling and conventional solidification by application of supercooling inheritance. On the self-designed SDS equipment, SDS of Cu-Ni alloy was achieved successfully. The results are as follows: (ⅰ) The primary arm spacing is about 30 m m, the growth of secondary arms are strongly suppressed. The primary arm spacing is nearly the same as LMC method (GL=25 K/mm, V=500 m m/s), the primary stems are straight, fine and completed, with an inclination angle of about 5.8o. (ⅱ) A semi-quantitative T-T model is brought forward to describe the dendrite growth rate V vs. undercooling D T. The prediction of T-T model agrees well with experimental results. The formation of fine equiaxed dendrites, transition region and dendrite region can be explained successfully by D T-V-x relation of T-T model.

  6. Development of seasonal heat storage based on stable supercooling of a sodium acetate water mixture

    DEFF Research Database (Denmark)

    Furbo, Simon; Fan, Jianhua; Andersen, Elsa

    2012-01-01

    A number of heat storage modules for seasonal heat storages based on stable supercooling of a sodium acetate water mixture have been tested by means of experiments in a heat storage test facility. The modules had different volumes and designs. Further, different methods were used to transfer heat....... • The reliability of the supercooling was elucidated for the heat storage modules for different operation conditions. • The reliability of a cooling method used to start solidification of the supercooled sodium acetate water mixture was elucidated. The method is making use of boiling CO2 in a small tank in good...... to and from the sodium acetate water mixture in the modules. By means of the experiments: • The heat exchange capacity rates to and from the sodium acetate water mixture in the heat storage modules were determined for different volume flow rates. • The heat content of the heat storage modules were determined...

  7. Experimental investigations on cylindrical latent heat storage units with sodium acetate trihydrate composites utilizing supercooling

    DEFF Research Database (Denmark)

    Dannemand, Mark; Johansen, Jakob Berg; Kong, Weiqiang;

    2016-01-01

    unit was tested with 116.3 kg SAT with 0.5% Xanthan rubber as a thickening agent and 4.4% graphite powder. The heat exchange capacity rate during charge was significantly lower for the unit with SAT and Xanthan rubber compared to the unit with SAT and extra water. This was due to less convection......Latent heat storage units utilizing stable supercooling of sodium acetate trihydrate (SAT) composites were tested in a laboratory. The stainless steel units were 1.5 m high cylinders with internal heat exchangers of tubes with fins. One unit was tested with 116 kg SAT with 6% extra water. Another...... in the thickened phase change material after melting. The heat content in the fully charged state and the heat released after solidification of the supercooled SAT mixtures at ambient temperature was higher for the unit with the thickened SAT mixture. The heat discharged after solidification of the supercooled SAT...

  8. Experimental investigations on heat content of supercooled sodium acetate trihydrate by a simple heat loss method

    DEFF Research Database (Denmark)

    Kong, Weiqiang; Dannemand, Mark; Johansen, Jakob Berg

    2016-01-01

    Sodium acetate trihydrate is a phase change material that can be used for long term heat storage in solar heating systems because of its relatively high heat of fusion, a melting temperature of 58 °C and its ability to supercool stable. In practical applications sodium acetate trihydrate tend...... to suffer from phase separation which is the phenomenon where anhydrous salt settles to the bottom over time. This happens especially in supercooled state. The heat released from the crystallization of supercooled sodium acetate trihydrate with phase separation will be lower than the heat released from...... sodium acetate trihydrate without phase separation. Possible ways of avoiding or reducing the problem of phase separation were investigated. A wide variety of composites of sodium acetate trihydrate with additives including extra water, thickening agents, solid and liquid polymers have been...

  9. Measurements of Cloud Characteristics with a Ceilometer and Supporting Measurements with a Water Based Condensation Particle Counter

    Science.gov (United States)

    Vishnu, R.; Muralidas, S.; Mohankumar, G.; Varikoden, Hamza; v, Sasi Kumar; Sampath, S.; Vishnu, R.

    A Vaisala Laser Ceilometer which employs the LIDAR technique with a 910 nm laser diode for measurement of cloud base height, sky condition and vertical visibility was set up at a tropical coastal station Thiruvananthapuram (8.29° N, 76.59° E)at Kerala state, India. Measurements of cloud base height during different rain spells were made to understand the basic nature of cloud during different types of rain episodes such as convective and stratiform rains. Information on diurnal variation of cloud base height for different seasons has been obtained. The dominant altitude range of cloud occurrence is found to be below 1.5 km for clouds of all rainy seasons. The southwest monsoon clouds were dominant below 500 m also. The Ceilometer with its data on visibility also gave a picture of particles that can scatter the laser which includes water in liquid and ice phases. During dry weather conditions visibility below 1 km was found to be relatively low. To understand the cause of visibility change, a water based condensation nuclei counter manufactured by M/s TSI Inc, USA was employed and concentration monitored. An attempt was also made to get the cloud base height characteristics on a mountain slope to understand the orographic lifting of clouds due to mountain slope during different rainy seasons. At the mountain location data on cloud base measurements during cloud formation by orographic lifting of water vapour during thunderstorm months of the region is also presented and discussed.

  10. Managing Clouds in Cloud Platforms

    CERN Document Server

    Ahmat, Kamal A

    2010-01-01

    Managing cloud services is a fundamental challenge in todays virtualized environments. These challenges equally face both providers and consumers of cloud services. The issue becomes even more challenging in virtualized environments that support mobile clouds. Cloud computing platforms such as Amazon EC2 provide customers with flexible, on demand resources at low cost. However, they fail to provide seamless infrastructure management and monitoring capabilities that many customers may need. For instance, Amazon EC2 doesn't fully support cloud services automated discovery and it requires a private set of authentication credentials. Salesforce.com, on the other hand, do not provide monitoring access to their underlying systems. Moreover, these systems fail to provide infrastructure monitoring of heterogenous and legacy systems that don't support agents. In this work, we explore how to build a cloud management system that combines heterogeneous management of virtual resources with comprehensive management of phys...

  11. Evaluation of GISS SCM Simulated Cloud and Radiative Properties Using Both Surface and Satellite Observations

    Science.gov (United States)

    Kennedy, A. D.; Dong, X.; Xi, B.; Del Genio, A.; Wolf, A.; Minnis, P.; Khaiyer, M.; Doelling, D.; Nordeen, M.; Keyes, D.

    2009-05-01

    To evaluate the GISS SCM simulated cloud fractions, three years of surface and GOES satellite data have been collected at DOE ARM Southern Great Plains (SGP) site during 1999-2001. The GOES derived total and high cloud fractions from both 0.5° and 2.5° grid boxes are in excellent agreement with surface observations, suggesting that the ARM point observations can represent large areal observations. Compared to the ARM radar-lidar observed cloud fractions, the SCM simulated most mid-level clouds, overestimated low clouds, and underestimated total and high clouds with additional missed during the summer season. Further studies have revealed that the model simulated cloud fractions are strongly dependent on the large-scale synoptic pattern and its associated variables such as vertical motion and relative humidity. Because a significant amount of clouds over ARM SGP occur during synoptically quiescent conditions, the model has issues producing enough high cloud cover. This work suggests that alterations need to be made to the stratiform cloud scheme to better represent the sub-grid scale cloud variability in this case. The model simulated radiation budget is also evaluated with two years of collocated ARM surface radiation and CERES and GOES TOA radiation over the SGP site during March 2000-Dec. 2001. For this comparison, the model simulated surface and TOA radiation budgets agree well with surface and satellite observations (˜10 W m-2). Model simulated cloud optical depth, however, is about an order of magnitude higher than CERES/GOES retrievals, which may explain why the radiation budget is reasonable and yet total cloud fraction has a negative bias compared to observations. Further study is warranted to better understand how this impacts cloud radiative forcing.

  12. Effect of cloud microphysics on Indian summer monsoon precipitating clouds: A coupled climate modeling study

    Science.gov (United States)

    Hazra, Anupam; Chaudhari, Hemantkumar S.; Saha, Subodh K.; Pokhrel, Samir

    2017-04-01

    The quest for one of the most dominant processes controlling the large-scale circulations in the tropics is unraveled. The impact of cloud microphysical processes is known to have effects on rainfall and local atmospheric thermodynamics; however, its effect on the prevailing mean circulations is not yet studied. Two sets of coupled global climate model experiments (ICE and NO ICE microphysics) reveal that ice microphysics improves the strength of the Hadley circulation with respect to observation. Results pinpoint that ICE simulation enhances high cloud fraction (global tropics: 59%, India: 51%) and stratiform rain (global tropics: 5%, India: 15%) contribution. ICE and NO ICE cloud microphysics impacts differently on the outgoing longwave radiation (OLR), tropospheric temperature, and surface shortwave and longwave radiation. The effect of ice microphysics reduces OLR, which signifies deeper convection in the ICE run. The global annual average of the net radiation flux (shortwave and longwave) at the surface in ICE run (108.1 W/m2) is close to the observation (106 W/m2), which is overestimated in NO ICE run (112 W/m2). The result of apparent heat source term over the land and ocean surface eventually modifies regional Hadley circulation. Thus, the effect of ice microphysics in the global coupled model is important not only because of microphysics but also due to the radiation feedbacks. Therefore, better ice-phase microphysics is required in the new generation of climate forecast model, which may lead to improvements in the simulation of monsoon.

  13. Long term thermal energy storage with stable supercooled sodium acetate trihydrate

    DEFF Research Database (Denmark)

    Dannemand, Mark; Schultz, Jørgen M.; Johansen, Jakob Berg

    2015-01-01

    Utilizing stable supercooling of sodium acetate trihydrate makes it possible to store thermal energy partly loss free. This principle makes seasonal heat storage in compact systems possible. To keep high and stable energy content and cycling stability phase separation of the storage material must...... to 230 kJ/kg. TRNSYS simulations of a solar combi system including a storage with four heat storage modules of each 200 kg of sodium acetate trihydrate utilizing stable supercooling achieved a solar fraction of 80% for a low energy house in Danish climatic conditions....

  14. Cloud Control

    Science.gov (United States)

    Ramaswami, Rama; Raths, David; Schaffhauser, Dian; Skelly, Jennifer

    2011-01-01

    For many IT shops, the cloud offers an opportunity not only to improve operations but also to align themselves more closely with their schools' strategic goals. The cloud is not a plug-and-play proposition, however--it is a complex, evolving landscape that demands one's full attention. Security, privacy, contracts, and contingency planning are all…

  15. Cloud Cover

    Science.gov (United States)

    Schaffhauser, Dian

    2012-01-01

    This article features a major statewide initiative in North Carolina that is showing how a consortium model can minimize risks for districts and help them exploit the advantages of cloud computing. Edgecombe County Public Schools in Tarboro, North Carolina, intends to exploit a major cloud initiative being refined in the state and involving every…

  16. Cloud Computing

    CERN Document Server

    Mirashe, Shivaji P

    2010-01-01

    Computing as you know it is about to change, your applications and documents are going to move from the desktop into the cloud. I'm talking about cloud computing, where applications and files are hosted on a "cloud" consisting of thousands of computers and servers, all linked together and accessible via the Internet. With cloud computing, everything you do is now web based instead of being desktop based. You can access all your programs and documents from any computer that's connected to the Internet. How will cloud computing change the way you work? For one thing, you're no longer tied to a single computer. You can take your work anywhere because it's always accessible via the web. In addition, cloud computing facilitates group collaboration, as all group members can access the same programs and documents from wherever they happen to be located. Cloud computing might sound far-fetched, but chances are you're already using some cloud applications. If you're using a web-based email program, such as Gmail or Ho...

  17. Chemical composition of ambient aerosol, ice residues and cloud droplet residues in mixed-phase clouds: single particle analysis during the Cloud and Aerosol Characterization Experiment (CLACE 6

    Directory of Open Access Journals (Sweden)

    M. Kamphus

    2009-07-01

    Full Text Available Two different single particle mass spectrometers were operated in parallel at the Swiss High Alpine Research Station Jungfraujoch (JFJ, 3580 m a.s.l. during the Cloud and Aerosol Characterization Experiment (CLACE 6 in February and March 2007. During mixed phase cloud events ice crystals from 5 μm up to 20 μm were separated from large ice aggregates, non-activated, interstitial aerosol particles and supercooled droplets using an Ice-Counterflow Virtual Impactor (Ice-CVI. During one cloud period supercooled droplets were additionally sampled and analyzed by changing the Ice-CVI setup. The small ice particles and droplets were evaporated by injection into dry air inside the Ice-CVI. The resulting ice and droplet residues (IR and DR were analyzed for size and composition by two single particle mass spectrometers: a custom-built Single Particle Laser-Ablation Time-of-Flight Mass Spectrometer (SPLAT and a commercial Aerosol Time of Flight Mass Spectrometer (ATOFMS, TSI Model 3800. During CLACE 6 the SPLAT instrument characterized 355 individual ice residues that produced a mass spectrum for at least one polarity and the ATOFMS measured 152 particles. The mass spectra were binned in classes, based on the combination of dominating substances, such as mineral dust, sulfate, potassium and elemental carbon or organic material. The derived chemical information from the ice residues is compared to the JFJ ambient aerosol that was sampled while the measurement station was out of clouds (several thousand particles analyzed by SPLAT and ATOFMS and to the composition of the residues of supercooled cloud droplets (SPLAT: 162 cloud droplet residues analyzed, ATOFMS: 1094. The measurements showed that mineral dust particles were strongly enhanced in the ice particle residues. 57% of the SPLAT spectra from ice residues were dominated by signatures from mineral compounds, and 78% of the ATOFMS spectra. Sulfate and nitrate containing particles were strongly

  18. CSIR NLC mobile lidar observation of cirrus cloud

    CSIR Research Space (South Africa)

    Sivakumar, V

    2011-09-01

    Full Text Available and with less frequent content of super-cooled water. Apart from the cirrus cloud observations, the figure clearly illustrates the temporal evolution of the planetary boundary layer (PBL). At the beginning of the observation, the PBL is observed... at the height range just above 2 km and later it gradually decreased to 1.2 ? 1.5 km during the middle of the observation. Thereafter, a slow increase in the PBL is noted indicating the decrease in atmosphere stability. It is important to note here...

  19. Screaming Clouds

    Science.gov (United States)

    Fikke, Svein; Egill Kristjánsson, Jón; Nordli, Øyvind

    2017-04-01

    "Mother-of-pearl clouds" appear irregularly in the winter stratosphere at high northern latitudes, about 20-30 km above the surface of the Earth. The size range of the cloud particles is near that of visible light, which explains their extraordinary beautiful colours. We argue that the Norwegian painter Edvard Munch could well have been terrified when the sky all of a sudden turned "bloodish red" after sunset, when darkness was expected. Hence, there is a high probability that it was an event of mother-of-pearl clouds which was the background for Munch's experience in nature, and for his iconic Scream. Currently, the leading hypothesis for explaining the dramatic colours of the sky in Munch's famous painting is that the artist was captivated by colourful sunsets following the enormous Krakatoa eruption in 1883. After carefully considering the historical accounts of some of Munch's contemporaries, especially the physicist Carl Störmer, we suggest an alternative hypothesis, namely that Munch was inspired by spectacular occurrences of mother-of-pearl clouds. Such clouds, which have a wave-like structure akin to that seen in the Scream were first observed and described only a few years before the first version of this motive was released in 1892. Unlike clouds related to conventional weather systems in the troposphere, mother-of-pearl clouds appear in the stratosphere, where significantly different physical conditions prevail. This result in droplet sizes within the range of visible light, creating the spectacular colour patterns these clouds are famous for. Carl Störmer observed such clouds, and described them in minute details at the age of 16, but already with a profound interest in science. He later noted that "..these mother-of-pearl clouds was a vision of indescribable beauty!" The authors find it logical that the same vision could appear scaring in the sensible mind of a young artist unknown to such phenomena.

  20. An Integrated Method of Multiradar Quantitative Precipitation Estimation Based on Cloud Classification and Dynamic Error Analysis

    Directory of Open Access Journals (Sweden)

    Yong Huang

    2017-01-01

    Full Text Available Relationships between radar reflectivity factor and rainfall are different in various precipitation cloud systems. In this study, the cloud systems are firstly classified into five categories with radar and satellite data to improve radar quantitative precipitation estimation (QPE algorithm. Secondly, the errors of multiradar QPE algorithms are assumed to be different in convective and stratiform clouds. The QPE data are then derived with methods of Z-R, Kalman filter (KF, optimum interpolation (OI, Kalman filter plus optimum interpolation (KFOI, and average calibration (AC based on error analysis on the Huaihe River Basin. In the case of flood on the early of July 2007, the KFOI is applied to obtain the QPE product. Applications show that the KFOI can improve precision of estimating precipitation for multiple precipitation types.

  1. Towards improved understanding of cloud influence on polar surface energy budgets using CloudSat and CALIPSO observations

    Science.gov (United States)

    Kay, J. E.; L'Ecuyer, T. S.; McIlhattan, E.; Chepfer, H.; Morrison, A.

    2015-12-01

    The spaceborne radar CloudSat and the spaceborne lidar platform Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) have provided nearly a decade of groundbreaking observations of polar cloud and precipitation processes. Specifically relevant to this AGU session, the CloudSat 2B-FLXHR-LIDAR product (hereafter, 2BFLX) is an observationally constrained radiative flux and heating rate calculation that leverages constraints from A-train observations, including CloudSat+CALIPSO. The surface radiative fluxes calculated within 2BFLX represent an important advance because unlike top-of-atmosphere (TOA) fluxes, surface radiative fluxes cannot be directly measured by satellite, yet directly impact surface heating, sea ice melt, and ice sheet mass balance. In this presentation, we will highlight the influence of supercooled liquid on polar surface radiation budgets constrained within 2BFLX data. We will also use 2BFLX data in concert with the fully attenuated signal and cloud phase information from CALIPSO as an observational constraint on polar cloud-climate feedbacks in the Community Earth System Model (CESM).

  2. Surface Crystallization of Cloud Droplets: Implications for Climate Change and Ozone Depletion

    Science.gov (United States)

    Tabazadeh, A.; Djikaev, Y. S.; Reiss, H.; Gore, Warren J. (Technical Monitor)

    2002-01-01

    The process of supercooled liquid water crystallization into ice is still not well understood. Current experimental data on homogeneous freezing rates of ice nucleation in supercooled water droplets show considerable scatter. For example, at -33 C, the reported freezing nucleation rates vary by as much as 5 orders of magnitude, which is well outside the range of measurement uncertainties. Until now, experimental data on the freezing of supercooled water has been analyzed under the assumption that nucleation of ice took place in the interior volume of a water droplet. Here, the same data is reanalyzed assuming that the nucleation occurred "pseudoheterogeneously" at the air (or oil)-liquid water interface of the droplet. Our analysis suggest that the scatter in the nucleation data can be explained by two main factors. First, the current assumption that nucleation occurs solely inside the volume of a water droplet is incorrect. Second, because the nucleation process most likely occurs on the surface, the rates of nuclei formation could differ vastly when oil or air interfaces are involved. Our results suggest that ice freezing in clouds may initiate on droplet surfaces and such a process can allow for low amounts of liquid water (approx. 0.002 g per cubic meters) to remain supercooled down to -40 C as observed in the atmosphere.

  3. A 35-GHz Polarimetric Doppler Radar and Its Application for Observing Clouds Associated with Typhoon Nuri

    Institute of Scientific and Technical Information of China (English)

    ZHONG Lingzhi; LIU Liping; FENG Sheng; GE Runsheng; ZHANG Zhe

    2011-01-01

    Millimeter-wavelength radar has proved to be an effective instrument for cloud observation and research.In this study, 8-mm-wavelength cloud radar (MMCR) with Doppler and polarization capabilities was used to investigate cloud dynamics in China for the first time. Its design, system specifications, calibration,and application in measuring clouds associated with typhoon are discussed in this article. The cloud radar measurements of radar refiectivity (Z), Doppler velocity (Vr), velocity spectrum width (Sw) and the depolarization ratio (LDR) at vertical incidence were used to analyze the microphysical and dynamic processes of the cloud system and precipitation associated with Typhoon Nuri, which occurred in southern China in August 2008. The results show the refiectivity observed using MMCR to be consistent with the echo height and the melting-layer location data obtained by the nearby China S-band new-generation weather radar (SA),but the Ka-band MMCR provided more detailed structural information about clouds and weak precipitation data than did the SA radar. The variation of radar refiectivity and LDR in vertical structure reveals the transformation of particle phase from ice to water. The vertical velocity and velocity spectrum width of MMCR observations indicate an updraft and strong turbulence in the stratiform cloud layer. MMCR provides a valuable new technology for meteorological research in China.

  4. Securing Cloud from Cloud Drain

    Directory of Open Access Journals (Sweden)

    Niva Das

    2014-09-01

    Full Text Available Today, in the world of communication, connected systems is growing at a rapid pace. To accommodate this growth the need for computational power and storage is also increasing at a similar rate. Companies are investing a large amount of resources in buying, maintaining and ensuring availability of the system to their customers. To mitigate these issues, cloud computing is playing a major role [1]. The underlying concept of cloud computing dates back to the ‘50s but the term entering into widespread usage can be traced to 2006 when Amazon.com announced the Elastic Compute Cloud. In this paper, we will discuss about cloud security approaches. We have used the term “CloudDrain” to define data leakage in case of security compromise.

  5. Cluster analysis of midlatitude oceanic cloud regimes: mean properties and temperature sensitivity

    Directory of Open Access Journals (Sweden)

    N. D. Gordon

    2010-07-01

    Full Text Available Clouds play an important role in the climate system by reducing the amount of shortwave radiation reaching the surface and the amount of longwave radiation escaping to space. Accurate simulation of clouds in computer models remains elusive, however, pointing to a lack of understanding of the connection between large-scale dynamics and cloud properties. This study uses a k-means clustering algorithm to group 21 years of satellite cloud data over midlatitude oceans into seven clusters, and demonstrates that the cloud clusters are associated with distinct large-scale dynamical conditions. Three clusters correspond to low-level cloud regimes with different cloud fraction and cumuliform or stratiform characteristics, but all occur under large-scale descent and a relatively dry free troposphere. Three clusters correspond to vertically extensive cloud regimes with tops in the middle or upper troposphere, and they differ according to the strength of large-scale ascent and enhancement of tropospheric temperature and humidity. The final cluster is associated with a lower troposphere that is dry and an upper troposphere that is moist and experiencing weak ascent and horizontal moist advection.

    Since the present balance of reflection of shortwave and absorption of longwave radiation by clouds could change as the atmosphere warms from increasing anthropogenic greenhouse gases, we must also better understand how increasing temperature modifies cloud and radiative properties. We therefore undertake an observational analysis of how midlatitude oceanic clouds change with temperature when dynamical processes are held constant (i.e., partial derivative with respect to temperature. For each of the seven cloud regimes, we examine the difference in cloud and radiative properties between warm and cold subsets. To avoid misinterpreting a cloud response to large-scale dynamical forcing as a cloud response to temperature, we require horizontal and vertical

  6. Influences of in-cloud aerosol scavenging parameterizations on aerosol concentrations and wet deposition in ECHAM5-HAM

    Directory of Open Access Journals (Sweden)

    B. Croft

    2010-02-01

    Full Text Available A diagnostic cloud nucleation scavenging scheme, which determines stratiform cloud scavenging ratios for both aerosol mass and number distributions, based on cloud droplet, and ice crystal number concentrations, is introduced into the ECHAM5-HAM global climate model. This scheme is coupled with a size-dependent in-cloud impaction scavenging parameterization for both cloud droplet-aerosol, and ice crystal-aerosol collisions. The aerosol mass scavenged in stratiform clouds is found to be primarily (>90% scavenged by cloud nucleation processes for all aerosol species, except for dust (50%. The aerosol number scavenged is primarily (>90% attributed to impaction. 99% of this impaction scavenging occurs in clouds with temperatures less than 273 K. Sensitivity studies are presented, which compare aerosol concentrations, burdens, and deposition for a variety of in-cloud scavenging approaches: prescribed fractions, a more computationally expensive prognostic aerosol cloud processing treatment, and the new diagnostic scheme, also with modified assumptions about in-cloud impaction and nucleation scavenging. Our results show that while uncertainties in the representation of in-cloud scavenging processes can lead to differences in the range of 20–30% for the predicted annual, global mean aerosol mass burdens, and near to 50% for accumulation mode aerosol number burden, the differences in predicted aerosol mass concentrations can be up to one order of magnitude, particularly for regions of the middle troposphere with temperatures below 273 K where mixed and ice phase clouds exist. Different parameterizations for impaction scavenging changed the predicted global, annual mean number removal attributed to ice clouds by seven-fold, and the global, annual dust mass removal attributed to impaction by two orders of magnitude. Closer agreement with observations of black carbon profiles from aircraft (increases near to one order of magnitude for mixed phase clouds

  7. Revisiting the iris effect of tropical cirrus clouds with TRMM and A-Train satellite data

    Science.gov (United States)

    Choi, Yong-Sang; Kim, WonMoo; Yeh, Sang-Wook; Masunaga, Hirohiko; Kwon, Min-Jae; Jo, Hyun-Su; Huang, Lei

    2017-06-01

    Just as the iris of human eye controls the light influx (iris effect), tropical anvil cirrus clouds may regulate the Earth's surface warming by controlling outgoing longwave radiation. This study examines this possible effect with monthly satellite observations such as Tropical Rainfall Measuring Mission (TRMM) precipitation, Moderate Resolution Imaging Spectroradiometer cirrus fraction, and Clouds and the Earth's Radiant Energy System top-of-the-atmosphere radiative fluxes averaged over different tropical domains from March 2000 to October 2014. To confirm that high-level cirrus is relevant to this study, Cloud-Aerosol Lidar with Orthogonal Polarization high cloud observations were also analyzed from June 2006 to December 2015. Our analysis revealed that the increase in sea surface temperature in the tropical western Pacific tends to concentrate convective cloud systems. This concentration effect very likely induces the significant reduction of both stratiform rain rate and cirrus fraction, without appreciable change in the convective rain rate. This reduction of stratiform rain rate and cirrus fraction cannot be found over its subregion or the tropical eastern Pacific, where the concentration effect of anvil cirrus is weak. Consistently, over the tropical western Pacific, the higher ratio of convective rain rate to total rain rate (i.e., precipitation efficiency) significantly correlates with warmer sea surface temperature and lower cirrus fraction. The reduced cirrus eventually increased outgoing longwave radiation to a greater degree than absorbed solar radiation. Finally, the negative relationship between precipitation efficiency and cirrus fraction tends to correspond to a low global equilibrium climate sensitivity in the models in the Coupled Model Intercomparison Project Phase 5. This suggests that tropical anvil cirrus clouds exert a negative climate feedback in strong association with precipitation efficiency.

  8. The interdependence of continental warm cloud properties derived from unexploited solar background signal in ground-based lidar measurements

    Directory of Open Access Journals (Sweden)

    J. C. Chiu

    2014-04-01

    Full Text Available We have extensively analysed the interdependence between cloud optical depth, droplet effective radius, liquid water path (LWP and geometric thickness for stratiform warm clouds using ground-based observations. In particular, this analysis uses cloud optical depths retrieved from untapped solar background signal that is previously unwanted and needs to be removed in most lidar applications. Combining these new optical depth retrievals with radar and microwave observations at the Atmospheric Radiation Measurement (ARM Climate Research Facility in Oklahoma during 2005–2007, we have found that LWP and geometric thickness increase and follow a power-law relationship with cloud optical depth regardless of the presence of drizzle; LWP and geometric thickness in drizzling clouds can be generally 20–40% and at least 10% higher than those in non-drizzling clouds, respectively. In contrast, droplet effective radius shows a negative correlation with optical depth in drizzling clouds, while it increases with optical depth and reaches an asymptote of 10 μm in non-drizzling clouds. This asymptotic behaviour in non-drizzling clouds is found in both droplet effective radius and optical depth, making it possible to use simple thresholds of optical depth, droplet size, or a combination of these two variables for drizzle delineation. This paper demonstrates a new way to enhance ground-based cloud observations and drizzle delineations using existing lidar networks.

  9. Cloud migration

    CERN Document Server

    Höllwarth, Tobias

    2012-01-01

    This book is designed for managers and entrepreneurs, who are considering improving the economics and flexibility of their IT solutions and infrastructures. The book is also for readers who wish to learn more about the Cloud, but do not want to become specialists.This book discusses the technical, legal, fiscal, economic, organisational and environmental aspects of Cloud services. If you are looking for practical advice on vendor selection and certification, as well as real world Cloud project case studies, this is the book to consult.It is the result of a highly cooper

  10. Cloud Computing

    CERN Document Server

    Baun, Christian; Nimis, Jens; Tai, Stefan

    2011-01-01

    Cloud computing is a buzz-word in today's information technology (IT) that nobody can escape. But what is really behind it? There are many interpretations of this term, but no standardized or even uniform definition. Instead, as a result of the multi-faceted viewpoints and the diverse interests expressed by the various stakeholders, cloud computing is perceived as a rather fuzzy concept. With this book, the authors deliver an overview of cloud computing architecture, services, and applications. Their aim is to bring readers up to date on this technology and thus to provide a common basis for d

  11. Dynamics of hydrogen bonds in water and consequences for the unusual behaviour of supercooled water

    Indian Academy of Sciences (India)

    José Teixeira

    2008-10-01

    The dynamics of liquid water is evaluated by the coherent quasi-elastic scattering at two different momentum transfers, in order to discriminate hydrogen bond life-time from molecular dynamics. The results indicate a possible issue for the puzzle of the behaviour of supercooled water.

  12. Crystallization in diblock copolymer thin films at different degrees of supercooling

    DEFF Research Database (Denmark)

    Darko, C.; Botiz, I.; Reiter, G.

    2009-01-01

    The crystalline structures in thin films of polystyrene-b-poly(ethylene oxide) (PS-b-PEO) diblock copolymers were studied in dependence on the degree of supercooling. Atomic force microscopy showed that the crystalline domains (lamellae) consist of grains, which are macroscopic at low...

  13. Solidification of supercooled water in the vicinity of a solid wall

    Science.gov (United States)

    Schremb, Markus; Tropea, Cameron

    2016-11-01

    An experimental approach utilizing a Hele-Shaw cell for the investigation of the solidification of a supercooled liquid in contact with a solid wall is presented. The setup is based on an idea presented by Marín et al. [A. G. Marín et al., Phys. Rev. Lett. 113, 054301 (2014), 10.1103/PhysRevLett.113.054301], who investigated the planar freezing of a sessile drop without supercooling. This apparatus overcomes optical distortions present when observing the freezing of sessile drops, arising due to reflections and refraction of light on the drop surface. The facility is used to investigate the freezing process of water drops, supercooled down to -20∘C , and to qualitatively demonstrate that the growth behavior is uninfluenced by the use of the Hele-Shaw cell. Different features during freezing, which are known for sessile water drops, are also observed with the Hele-Shaw cell. The growth morphology within the first phase of solidification is categorized according to the initial drop supercooling. Furthermore, freezing velocities within this phase are related to data available in the literature for the growth of single ice dendrites.

  14. Hydrophobic Surfaces: Topography Effects on Wetting by Supercooled Water and Freezing Delay

    DEFF Research Database (Denmark)

    Heydari, Golrokh; Thormann, Esben; Järn, Mikael

    2013-01-01

    Hydrophobicity, and in particular superhydrophobicity, has been extensively considered to promote ice-phobicity. Dynamic contact angle measurements above 0 °C have been widely used to evaluate the water repellency. However, it is the wetting properties of supercooled water at subzero temperatures...

  15. Supercooling Suppression of Microencapsulated n-Alkanes by Introducing an Organic Gelator

    Institute of Scientific and Technical Information of China (English)

    ZHU Kong-ying; WANG Shuang; QI Heng-zhi; LI Hui; ZHAO Yun-hui; YUAN Xiao-yan

    2012-01-01

    Supercooling of the microencapsulated phase change materials(PCMs) during cooling usually happens.This phenomenon can interfere with heat transfer and is necessary to further overcome.In this study,melamine-formaldehyde microcapsules containing two n-alkane PCMs,namely,n-dodecane(C12) or n-tetradecane(C14)were prepared by in situ polymerization.A small amount of n-hexatriacontane(C36) was introduced as an organic gelator into the core of microcapsules to cope with the supercooling problem.Analyses demonstrate that supcrcooling of the microencapsulated C12 or C14 was significantly suppressed by adding 3%(mass fraction) C36,without changing the spherical morphology and dispersibility.It could be also found that the enthalpy of microencapsulated C12 or C14 containing C36 was similar to that of microencapsulated n-alkanes without C36,whereas the difference between onsets of crystallization and melting(degree of supercooling) is similar to that of those of pure n-alkanes,suggesting the remarkable suppression ability of the organic gelator on supercooling.

  16. Anomalous dependence of the heat capacity of supercooled water on pressure and temperature

    Directory of Open Access Journals (Sweden)

    I.A. Stepanov

    2014-01-01

    Full Text Available In some papers, dependences of the isobaric heat capacity of water versus pressure and temperature were obtained. It is shown that these dependences contradict both the dependence of heat capacity on temperature for supercooled water, and an important thermodynamic equation for the dependence of heat capacity on pressure. A possible explanation for this contradiction is proposed.

  17. Compressive Deformation Induced Nanocrystallization of a Supercooled Zr-Based Bulk Metallic Glass

    Institute of Scientific and Technical Information of China (English)

    GUO Xiao-Lin; SHAN De-Bin; MA Ming-Zhen; GUO Bin

    2008-01-01

    The nanocrystallization behaviour of a bulk Zr-based metallic glass subjected to compressive stress is investigated in the supercooled liquid region. Compared with annealing treatments without compressive stress, compressive deformation promotes the development of nucleation and suppresses the coarsening of nanocrystallites at high ternperatures.

  18. Predicting How Nanoconfinement Changes the Relaxation Time of a Supercooled Liquid

    DEFF Research Database (Denmark)

    Ingebrigtsen, Trond; Errington, Jeff; Truskett, Tom;

    2013-01-01

    asymmetric dumbbell-shaped molecules, which can be deeply supercooled without crystallizing. We find that the dimensionless structural relaxation times—spanning six decades as a function of temperature, density, and degree of confinement—collapse when plotted versus excess entropy. The data also collapse...

  19. Thermalization calorimetry: A simple method for investigating glass transition and crystallization of supercooled liquids

    DEFF Research Database (Denmark)

    Jakobsen, Bo; Sanz, Alejandro; Niss, Kristine;

    2016-01-01

    We present a simple method for fast and cheap thermal analysis on supercooled glass-forming liquids. This “Thermalization Calorimetry” technique is based on monitoring the temperature and its rate of change during heating or cooling of a sample for which the thermal power input comes from heat...

  20. Temperature-dependent bouncing of super-cooled water on teflon-coated superhydrophobic tungsten nanorods

    Energy Technology Data Exchange (ETDEWEB)

    Khedir, Khedir R.; Kannarpady, Ganesh K.; Ishihara, Hidetaka; Woo, Justin; Asar, Madhu P. [Center for Integrative Nanotechnology Sciences, University of Arkansas at Little Rock, 2801 South University Avenue, Little Rock, AR, 72204 (United States); Ryerson, Charles [Terrestrial and Cryospheric Sciences Branch Cold Regions, Research and Engineering Laboratory, U.S. Army Corps of Engineers, Hanover, NH 03755-1290 (United States); Biris, Alexandru S., E-mail: asbiris@ualr.edu [Center for Integrative Nanotechnology Sciences, University of Arkansas at Little Rock, 2801 South University Avenue, Little Rock, AR, 72204 (United States)

    2013-08-15

    The bouncing mechanism of warm and supercooled water droplets with temperatures ranging from 20 °C to −10 °C on the surface of superhydrophobic (SHP) tungsten nanorods (WNRs), held at a constant temperature of −10 °C, was investigated. The measurements were carried out inside a chamber kept at a low relative humidity of 20%. A considerable energy loss was observed mainly due to the increase in the viscous forces of the supercooled water droplet. The increase in the values of the capillary number, as a result of the variation in both viscosity and surface energy of the supercooled water droplet, has confirmed the significant role of viscous forces in the dissipation of bouncing energy. However, the contact time and contact line evolution of the supercooled water droplet on the surface remained unaffected by the decrease in its temperature at constant humidity. The calculations of the bouncing restitution and dissipated energy at various water droplet temperatures, using classical mechanics, were also carried out.

  1. An assessment of cloud top thermodynamic phase products obtained from A-Train passive and active sensors

    Directory of Open Access Journals (Sweden)

    S. Zeng

    2013-09-01

    Full Text Available The A-Train observations provide an unprecedented opportunity for the production of high quality dataset describing cloud properties. We illustrate in this study the use of one year of coincident POLDER (Polarization and Directionality of the Earth Reflectance, MODIS (MODerate Resolution Imaging Spectroradiometer and CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization observations to establish a reference dataset for the description of cloud top thermodynamic phase at global scale. We present the results of an extensive comparison between POLDER and MODIS cloud top phase products and discuss those in view of cloud vertical structure and optical properties derived simultaneously from collocated CALIOP active measurements. These results allow to identify and quantify potential biases present in the 3 considered dataset. Among those, we discuss the impacts of observation geometry, thin cirrus in multilayered and single layered cloud systems, supercooled liquid droplets, aerosols, fractional cloud cover and snow/ice or bright surfaces on global statistics of cloud phase derived from POLDER and MODIS passive measurements. Based on these analysis we define criteria for the selection of high confidence cloud phase retrievals which in turn can serve for the establishment of a reference cloud phase product. This high confidence joint product derived from POLDER/PARASOL and MODIS/Aqua can be used in the future as a benchmark for the evaluation of other cloud climatologies, for the assessment of cloud phase representation in models and the development of better cloud phase parametrization in the general circulation models (GCMs.

  2. Cloud Formation

    Science.gov (United States)

    Graham, Mark Talmage

    2004-05-01

    Cloud formation is crucial to the heritage of modern physics, and there is a rich literature on this important topic. In 1927, Charles T.R. Wilson was awarded the Nobel Prize in physics for applications of the cloud chamber.2 Wilson was inspired to study cloud formation after working at a meteorological observatory on top of the highest mountain in Scotland, Ben Nevis, and testified near the end of his life, "The whole of my scientific work undoubtedly developed from the experiments I was led to make by what I saw during my fortnight on Ben Nevis in September 1894."3 To form clouds, Wilson used the sudden expansion of humid air.4 Any structure the cloud may have is spoiled by turbulence in the sudden expansion, but in 1912 Wilson got ion tracks to show up by using strobe photography of the chamber immediately upon expansion.5 In the interim, Millikan's study in 1909 of the formation of cloud droplets around individual ions was the first in which the electron charge was isolated. This study led to his famous oil drop experiment.6 To Millikan, as to Wilson, meteorology and physics were professionally indistinct. With his meteorological physics expertise, in WWI Millikan commanded perhaps the first meteorological observation and forecasting team essential to military operation in history.7 But even during peacetime meteorology is so much of a concern to everyone that a regular news segment is dedicated to it. Weather is the universal conversation topic, and life on land could not exist as we know it without clouds. One wonders then, why cloud formation is never covered in physics texts.

  3. Influence of Nanoparticles and Graphite Foam on the Supercooling of Acetamide

    Directory of Open Access Journals (Sweden)

    Jia Yu

    2014-01-01

    Full Text Available Acetamide is a promising phase change materials (PCMs for thermal storage,but the large supercooling during the freezing process has limited its application. In this study, we prepared acetamide-SiO2 composites by adding nano-SiO2 into acetamide. This modified PCM was then impregnated into the porous graphite foam forming acetamide-SiO2-graphite foam form-stable composites. These composites were subjected to melting-solidification cycles 50 times; the time-temperature curves were tracked and recorded during these cycles. The time-temperature curves showed that, for the acetamide containing 2 wt. % SiO2, the supercooling phenomenon was eliminated and the material’s performance was stable for 50 cycles. The solidification temperature of the acetamide-SiO2-graphite foam samples was 65°C and the melting temperature was lowered to 65°C. The samples exhibited almost no supercooling and the presence of SiO2 had no significant effect on the melting-solidification temperature. The microscopic supercooling of the acetamide-SiO2 composite was measured using differential scanning calorimetry (DSC. The results indicated that when the content of SiO2 was 1 wt. to 2 wt. %, the supercooling could be reduced to less than 10°C and heat was sufficiently released during solidification. Finally, a set of algorithms was derived using MATLAB software for simulating the crystallization of samples based on the classical nucleation theory. The results of the simulation agreed with the experiment results.

  4. Mechanical responses and stress fluctuations of a supercooled liquid in a sheared non-equilibrium state.

    Science.gov (United States)

    Mizuno, H; Yamamoto, R

    2012-04-01

    A steady shear flow can drive supercooled liquids into a non-equilibrium state. Using molecular dynamics simulations under steady shear flow superimposed with oscillatory shear strain for a probe, non-equilibrium mechanical responses are studied for a model supercooled liquid composed of binary soft spheres. We found that even in the strongly sheared situation, the supercooled liquid exhibits surprisingly isotropic responses to oscillating shear strains applied in three different components of the strain tensor. Based on this isotropic feature, we successfully constructed a simple two-mode Maxwell model that can capture the key features of the storage and loss moduli, even for highly non-equilibrium state. Furthermore, we examined the correlation functions of the shear stress fluctuations, which also exhibit isotropic relaxation behaviors in the sheared non-equilibrium situation. In contrast to the isotropic features, the supercooled liquid additionally demonstrates anisotropies in both its responses and its correlations to the shear stress fluctuations. Using the constitutive equation (a two-mode Maxwell model), we demonstrated that the anisotropic responses are caused by the coupling between the oscillating strain and the driving shear flow. Due to these anisotropic responses and fluctuations, the violation of the fluctuation-dissipation theorem (FDT) is distinct for different components. We measured the magnitude of this violation in terms of the effective temperature. It was demonstrated that the effective temperature is notably different between different components, which indicates that a simple scalar mapping, such as the concept of an effective temperature, oversimplifies the true nature of supercooled liquids under shear flow. An understanding of the mechanism of isotropies and anisotropies in the responses and fluctuations will lead to a better appreciation of these violations of the FDT, as well as certain consequent modifications to the concept of an

  5. Dimethyl sulfide as a source of cloud condensation nuclei

    Energy Technology Data Exchange (ETDEWEB)

    Warren, S. [Univ. of Washington, Seattle, WA (United States)

    1995-09-01

    Cloud condensation nuclei (CCN) are predominantly sulfate particles, and over the oceans the major source of sulfur for these particles appears to be dimethyl sulfide, a gas produced by marine biota. The reflection of sunlight by marine stratiform clouds is a major feature of the Earth`s radiation budget, and these clouds will reflect more sunlight if their liquid water is distributed among more CCN, thus forming more (and smaller) droplets. These facts form the basis of a proposal that marine biogenic sulfur may be an important factor in determining the Earth`s climate. Key implications of this proposal are (1) the possibility of a biota-climate feedback loop if the production of biogenic sulfur is sensitive to changes in climate, (2) the possibility that anthropogenic sulfur emissions may be altering the global climate through this cloud-mediated mechanism, and (3) the possibility that anthropogenic pollution could alter climate by perturbing the sulfur-producing marine organisms. 3 refs., 1 fig.

  6. Breaking Through the Glass Ceiling: Recent Experimental Approaches to Probe the Properties of Supercooled Liquids near the Glass Transition.

    Energy Technology Data Exchange (ETDEWEB)

    Smith, R. Scott; Kay, Bruce D.

    2012-03-15

    Experimental measurements of the properties supercooled liquids at temperatures near their respective glass transition temperatures, Tg, are requisite for understanding the behavior of glasses and amorphous solids. Unfortunately, many supercooled molecular liquids rapidly crystallize at temperatures far above their Tg making such measurements difficult to nearly impossible. In this perspective we discuss some recent alternative approaches to obtain experimental data in the temperature regime near Tg. These new approaches may yield the additional experimental data necessary to test current theoretical models of the dynamical slowdown that occurs in supercooled liquids approaching the glass transition.

  7. Breaking Through the Glass Ceiling: Recent Experimental Approaches to Probe the Properties of Supercooled Liquids near the Glass Transition.

    Science.gov (United States)

    Smith, R Scott; Kay, Bruce D

    2012-03-15

    Experimental measurements of the properties of supercooled liquids at temperatures near their glass transition temperatures, Tg, are requisite for understanding the behavior of glasses and amorphous solids. Unfortunately, many supercooled molecular liquids rapidly crystallize at temperatures far above their Tg, making such measurements difficult to nearly impossible. In this Perspective, we discuss some recent alternative approaches to obtain experimental data in the temperature regime near Tg. These new approaches may yield the additional experimental data necessary to test current theoretical models of the dynamical slowdown that occurs in supercooled liquids approaching the glass transition.

  8. Retrievals of ice cloud microphysical properties of deep convective systems using radar measurements: Convective Cloud Microphysical Retrieval

    Energy Technology Data Exchange (ETDEWEB)

    Tian, Jingjing [Department of Atmospheric Sciences, University of North Dakota, Grand Forks North Dakota USA; Dong, Xiquan [Department of Atmospheric Sciences, University of North Dakota, Grand Forks North Dakota USA; Xi, Baike [Department of Atmospheric Sciences, University of North Dakota, Grand Forks North Dakota USA; Wang, Jingyu [Department of Atmospheric Sciences, University of North Dakota, Grand Forks North Dakota USA; Homeyer, Cameron R. [School of Meteorology, University of Oklahoma, Norman Oklahoma USA; McFarquhar, Greg M. [Department of Atmospheric Sciences, University of Illinois at Urbana-Champaign, Urbana Illinois USA; Fan, Jiwen [Pacific Northwest National Laboratory, Richland Washington USA

    2016-09-23

    This study presents new algorithms for retrieving ice cloud microphysical properties (ice water content (IWC) and median mass diameter (Dm)) for the stratiform and thick anvil regions of Deep Convective Systems (DCSs) using Next-Generation Radar (NEXRAD) reflectivity and recently developed empirical relationships from aircraft in situ measurements during the Midlatitude Continental Convective Clouds Experiment (MC3E). A classic DCS case on 20 May 2011 is used to compare the retrieved IWC profiles with other retrieval and cloud-resolving model simulations. The mean values of each retrieved and simulated IWC fall within one standard derivation of the other two. The statistical results from six selected cases during MC3E show that the aircraft in situ derived IWC and Dm are 0.47 ± 0.29 g m-3 and 2.02 ± 1.3 mm, while the mean values of retrievals have a positive bias of 0.16 g m-3 (34%) and a negative bias of 0.39 mm (19%). To validate the newly developed retrieval algorithms from this study, IWC and Dm are performed with other DCS cases during Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX) field campaign using composite gridded NEXRAD reflectivity and compared with in situ IWC and Dm from aircraft. A total of 64 1-min collocated aircraft and radar samples are available for comparisons, and the averages of radar retrieved and aircraft in situ measured IWCs are 1.22 g m-3 and 1.26 g m-3 with a correlation of 0.5, and their averaged Dm values are 2.15 and 1.80 mm. These comparisons have shown that the retrieval algorithms 45 developed during MC3E can retrieve similar ice cloud microphysical properties of DCS to aircraft in situ measurements during BAMEX with median errors of ~40% and ~25% for IWC and Dm retrievals, respectively. This is indicating our retrieval algorithms are suitable for other midlatitude continental DCS ice clouds, especially at stratiform rain and thick anvil regions. In addition, based on the averaged IWC and Dm values during MC3E and

  9. Radiation transfer in stratus clouds at the BSRN Payerne site

    Directory of Open Access Journals (Sweden)

    D. Nowak

    2008-06-01

    Full Text Available Clouds represent a major source of uncertainty in understanding climate change, because potential changes in the way they affect the atmospheric and surface energy budget are difficult to predict. It is therefore important to determine how clouds affect radiation. Stratiform clouds in particular have an important effect on climate as they cover large areas. This article presents results of radiation transfer calculations with MODTRANTM for well-defined stratus cloud cases detected at the meteorological station of Payerne, Switzerland. These stratus situations are selected in a data set covering the years from 2000 to 2005 with a method using data widely available at national meteorological observing stations. For 18 single layer stratus situations the shortwave radiation fluxes calculated with MODTRANTM are compared to surface observations from the Baseline Surface Radiation Network (BSRN site at Payerne and top of atmosphere (TOA observations from the Clouds and the Earth's Radiant Energy System (CERES experiment. A median bias on the order of 20 Wm−2 (<9% was found for the differences between modeled and observed reflected solar radiation at TOA. At the surface, good agreement is obtained by adjusting the vertical extinction in the modeled cloud layer within reasonable limits for a stratus cloud: The median bias of modeled minus observed shortwave downward radiation is well within instrument precision (<1%. The simultaneous agreement of modeled and observed radiation fluxes at the surface and TOA confirmed that radiation transfer in the atmosphere including a single cloud layer can be well simulated with MODTRANTM. Based on the present results, the absorbance was calculated within the stratus cloud layer (cloud base to cloud top. For the 18 single stratus layer situations the median absorbance is 0.07 [minimum 0.04, maximum 0.1], the median transmittance is 0.29 [0.15 0.39], and the median

  10. A study of cloud microphysics and precipitation over the Tibetan Plateau by radar observations and cloud-resolving model simulations: Cloud Microphysics over Tibetan Plateau

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Wenhua [State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing China; Pacific Northwest National Laboratory, Richland Washington USA; Sui, Chung-Hsiung [Department of Atmospheric Sciences, National Taiwan University, Taipei Taiwan; Fan, Jiwen [Pacific Northwest National Laboratory, Richland Washington USA; Hu, Zhiqun [State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing China; Zhong, Lingzhi [State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing China

    2016-11-27

    Cloud microphysical properties and precipitation over the Tibetan Plateau (TP) are unique because of the high terrains, clean atmosphere, and sufficient water vapor. With dual-polarization precipitation radar and cloud radar measurements during the Third Tibetan Plateau Atmospheric Scientific Experiment (TIPEX-III), the simulated microphysics and precipitation by the Weather Research and Forecasting model (WRF) with the Chinese Academy of Meteorological Sciences (CAMS) microphysics and other microphysical schemes are investigated through a typical plateau rainfall event on 22 July 2014. Results show that the WRF-CAMS simulation reasonably reproduces the spatial distribution of 24-h accumulated precipitation, but has limitations in simulating time evolution of precipitation rates. The model-calculated polarimetric radar variables have biases as well, suggesting bias in modeled hydrometeor types. The raindrop sizes in convective region are larger than those in stratiform region indicated by the small intercept of raindrop size distribution in the former. The sensitivity experiments show that precipitation processes are sensitive to the changes of warm rain processes in condensation and nucleated droplet size (but less sensitive to evaporation process). Increasing droplet condensation produces the best area-averaged rain rate during weak convection period compared with the observation, suggesting a considerable bias in thermodynamics in the baseline simulation. Increasing the initial cloud droplet size causes the rain rate reduced by half, an opposite effect to that of increasing droplet condensation.

  11. Mobile Clouds

    DEFF Research Database (Denmark)

    Fitzek, Frank; Katz, Marcos

    users in very different ways and for various purposes. The book provides many stimulating examples of resource-sharing applications. Enabling technologies for mobile clouds are also discussed, highlighting the key role of network coding. Mobile clouds have the potential to enhance communications...... of resource sharing takes a wider and deeper meaning, creating the foundations for a global real-time multidimensional resource pool, the underlying infrastructure for shareconomy. Above all, this is an inspiring book for anyone who is concerned about the future of wireless and mobile communications networks...... and their relationship with Social networks. Key Features: Provides fundamental ideas and promising concepts for exploiting opportunistic cooperation and cognition in wireless and mobile networks Gives clear definitions of mobile clouds from different perspectives Associates mobile and wireless networks with social...

  12. Cloud radiative properties and aerosol - cloud interaction

    Science.gov (United States)

    Viviana Vladutescu, Daniela; Gross, Barry; Li, Clement; Han, Zaw

    2015-04-01

    The presented research discusses different techniques for improvement of cloud properties measurements and analysis. The need for these measurements and analysis arises from the high errors noticed in existing methods that are currently used in retrieving cloud properties and implicitly cloud radiative forcing. The properties investigated are cloud fraction (cf) and cloud optical thickness (COT) measured with a suite of collocated remote sensing instruments. The novel approach makes use of a ground based "poor man's camera" to detect cloud and sky radiation in red, green, and blue with a high spatial resolution of 30 mm at 1km. The surface-based high resolution photography provides a new and interesting view of clouds. As the cloud fraction cannot be uniquely defined or measured, it depends on threshold and resolution. However as resolution decreases, cloud fraction tends to increase if the threshold is below the mean, and vice versa. Additionally cloud fractal dimension also depends on threshold. Therefore these findings raise concerns over the ability to characterize clouds by cloud fraction or fractal dimension. Our analysis indicate that Principal Component analysis may lead to a robust means of quantifying cloud contribution to radiance. The cloud images are analyzed in conjunction with a collocated CIMEL sky radiometer, Microwave Radiometer and LIDAR to determine homogeneity and heterogeneity. Additionally, MFRSR measurements are used to determine the cloud radiative properties as a validation tool to the results obtained from the other instruments and methods. The cloud properties to be further studied are aerosol- cloud interaction, cloud particle radii, and vertical homogeneity.

  13. Simultaneous radar and aircraft observations of mixed-phase cloud at the 100-m-scale

    Science.gov (United States)

    Field, P.; Hogan, R.; Brown, P.; Illingworth, A.; Choularton, T.; Kaye, P.; Hirst, E.; Greenaway, R.

    2003-04-01

    Determination of cloud phase is important for predicting the radiative impact of clouds. Previous work by some of the authors has shown that even the presence of thin (~100 m) supercooled liquid layers above and below ice cloud significantly increase the reflection of solar radiation to space. We present 100-m-scale in situ and simultaneous radar observations of mixed-phase clouds over the UK. Particle sphericity, as determined by the aircraft mounted Small Ice Detector, appears to be a good indication of phase in these types of cloud where any newly produced ice will quickly grow in highly ice supersaturated conditions into non-spherical particles. During 1-d aircraft transects the dominant phase of the cloud was determined in contiguous 100 m horizontal segments. The resulting structure reveals that mixed-phase clouds can exhibit alternating regions of ice and liquid of varying horizontal scale that may be the result of the 1-d transect of the aircraft intercepting undulating liquid layers or turbulent activity. High differential reflectivity signals measured by the radar can be indicative of the nearby presence of liquid water giving rise to highly ice saturated conditions conducive to the growth of pristine crystals with high axial ratios. Although this is the case for discrete cloud layers it is not always true within a deep frontal cloud.

  14. Possible Evidence for a New Form of Liquid Buried in the Surface Tension of Supercooled Water

    Science.gov (United States)

    Rogers, T. Ryan; Leong, Kai-Yang; Wang, Feng

    2016-09-01

    Contrary to the historical data, several recent experiments indicate that the surface tension of supercooled water follows a smooth extrapolation of the IAPWS equation in the supercooled regime. It can be seen, however, that a small deviation from the IAPWS equation is present in the recent experimental measurements. It is shown with simulations using the WAIL water potential that the small deviation in the experimental data is consistent with the tail of an exponential growth in surface tension as temperature decreases. The emergence temperature, Te, of a substantial deviation from the IAPWS equation is shown to be 227 K for the WAIL water and 235 K for real water. Since the 227 K Te is close to the Widom line in WAIL water, we argue that real water at 235 K approaches a similar crossover line at one atmospheric pressure.

  15. Thermalization calorimetry: A simple method for investigating glass transition and crystallization of supercooled liquids

    Directory of Open Access Journals (Sweden)

    Bo Jakobsen

    2016-05-01

    Full Text Available We present a simple method for fast and cheap thermal analysis on supercooled glass-forming liquids. This “Thermalization Calorimetry” technique is based on monitoring the temperature and its rate of change during heating or cooling of a sample for which the thermal power input comes from heat conduction through an insulating material, i.e., is proportional to the temperature difference between sample and surroundings. The monitored signal reflects the sample’s specific heat and is sensitive to exo- and endothermic processes. The technique is useful for studying supercooled liquids and their crystallization, e.g., for locating the glass transition and melting point(s, as well as for investigating the stability against crystallization and estimating the relative change in specific heat between the solid and liquid phases at the glass transition.

  16. Supercooling transition in phase separated manganite thin films: An electrical transport study

    Science.gov (United States)

    Singh, Sandeep; Kumar, Pawan; Siwach, P. K.; Tyagi, Pawan Kumar; Singh, H. K.

    2014-05-01

    The impact of variation in the relative fractions of the ferromagnetic metallic and antiferromagnetic/charge ordered insulator phases on the supercooling/superheating transition in strongly phase separated system, La5/8-yPryCa3/8MnO3 (y ≈ 0.4), has been studied employing magnetotransport measurements. Our study clearly shows that the supercooling transition temperature is non-unique and strongly depends on the magneto-thermodynamic path through which the low temperature state is accessed. In contrast, the superheating transition temperature remains constant. The thermo-magnetic hysteresis, the separation of the two transitions and the associated resistivity, all are functions of the relative fraction of the coexisting phases.

  17. Metastable Demixing of Supercooled Cu-Co and Cu-Fe Alloys in an Oxide Flux

    Science.gov (United States)

    Li, D.; Robinson, M. B.; Rathz, T. J.; Williams, G.

    1998-01-01

    A systematic study on the liquid separation in supercooled Cu-Co and Cu-Fe alloys was performed using a melt fluxing which permits high supercooling to be achieved. Moreover, this method renders it possible to directly measure binodal temperatures and establish metastable liquid miscibility gap (LMG). All phase-separated samples at compositions ranging from 10 to 80 wt pct Co or to 83 wt pct Fe were found to exhibit droplet-shaped morphologies, in spite of various droplet distributions. Uniformly dispersed microstructures were obtained as the minority component was less than 20 vol.%; while beyond this percentage, serious coarsening was brought about. Calculations of the miscibility gap in the Cu-Co system and Stokes movement velocity of Co and Fe droplets in Cu matrix were made to analyze the experimental results.

  18. Study on Supercooling Point and Freezing Point in Floral Organs of Apricot

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Under the environment of an artificial climate chamber, supercooling point (SCP) and freezing point (FP) in flower and young fruit at different development stages and freezing injuries of floral organs were studied. The apricot cultivars tested were Kety, Golden Sun and Honghebao. With the development of flower buds, SCP and FP increased, which indicated that their cold resistance decreased. SCP and FP varied with different floral organs. For different apricot cultivars, it was found that, the lower SCP or FP in floral organs was, the more resistant capacity the cultivar had, and the larger the temperature interval from SCP to FP was. SCP was not a constant value, but a range. Frequency distribution of SCP in petals was more dispersing than that in stamens and pistils. Floral organs could maintain a supercooling state to avoid ice formation, but they were sensitive to freezing. Once floral organs froze, they turned brown after thawing.

  19. The water supercooled regime as described by four common water models

    CERN Document Server

    Malaspina, David C; Pereyra, Rodolfo G; Szleifer, Igal; Carignano, Marcelo A

    2013-01-01

    The temperature scale of simple water models in general does not coincide with the natural one. Therefore, in order to make a meaningful evaluation of different water models a temperature rescaling is necessary. In this paper we introduce a rescaling using the melting temperature and the temperature corresponding to the maximum of the heat capacity to evaluate four common water models (TIP4P-Ew, TIP4P-2005, TIP5P-Ew and Six-Sites) in the supercooled regime. Although all the models show the same general qualitative behavior, the TIP5P-Ew appears as the best representation of the supercooled regime when the rescaled temperature is used. We also analyze, using thermodynamic arguments, the critical nucleus size for ice growth. Finally, we speculate on the possible reasons why atomistic models do not usually crystalize while the coarse grained mW model do crystallize.

  20. Mobile Clouds

    DEFF Research Database (Denmark)

    Fitzek, Frank; Katz, Marcos

    examples of mobile clouds applications, based on both existing commercial initiatives as well as proof-of-concept test-beds. Visions and prospects are also discussed, paving the way for further development. As mobile networks and social networks become more and more reliant on each other, the concept...

  1. Soft Clouding

    DEFF Research Database (Denmark)

    Søndergaard, Morten; Markussen, Thomas; Wetton, Barnabas;

    2012-01-01

    Soft Clouding is a blended concept, which describes the aim of a collaborative and transdisciplinary project. The concept is a metaphor implying a blend of cognitive, embodied interaction and semantic web. Furthermore, it is a metaphor describing our attempt of curating a new semantics of sound...

  2. Two-Dimensional Nucleation of Ice from Supercooled Water

    Science.gov (United States)

    Seeley, L. H.; Seidler, G. T.

    2001-03-01

    Heterogeneous nucleation is the initial formation of a stable phase from a metastable phase in the presence of a catalyzing surface. This ubiquitous process has consequences ranging from metallurgy to the formation of kidney stones. Heterogeneous nucleation of ice plays a central role in cloud formation, suggesting one possible connection between anthropogenic pollutants and global climate. A key topic in the theory of nucleation is the geometry of the critical nucleus. Standard nucleation theories generally predict a compact critical nucleus with a surface of roughly constant curvature. We report measurements of the temperature dependent nucleation rate of ice from water samples supporting aliphatic alcohol Langmuir films. We use classical nucleation theory to extract thermodynamic parameters from the measured nucleation rates. From these parameters we conclude that both the effective free energy barrier and the molecular kinetics of nucleation are dominated by the physics at the interface. Our results give self-consistent evidence that the geometry of the critical nucleus in this system is essentially two-dimensional.

  3. Evidence of the existence of the low-density liquid phase in supercooled, confined water

    OpenAIRE

    Mallamace, Francesco; Broccio, Matteo; Corsaro, Carmelo; Faraone, Antonio; Majolino, Domenico; Venuti, Valentina; Liu, Li; Mou, Chung-Yuan; Chen, Sow-Hsin

    2006-01-01

    By confining water in a nanoporous structure so narrow that the liquid could not freeze, it is possible to study properties of this previously undescribed system well below its homogeneous nucleation temperature TH = 231 K. Using this trick, we were able to study, by means of a Fourier transform infrared spectroscopy, vibrational spectra (HOH bending and OH-stretching modes) of deeply supercooled water in the temperature range 183 < T < 273 K. We observed, upon decreasing temperature, the bui...

  4. Quark-gluon plasma freeze-out from a supercooled state?

    CERN Document Server

    Csörgö, T

    1994-01-01

    The quark-gluon plasma, formed in the first 3 fm/c of the heavy ion collisions at RHIC and LHC, supercooles due to nucleation and develops soon a negative pressure in the bag model. The negative pressure yields mechanical instability which may lead to a sudden timelike deflagration to a (super)heated hadron gas. The resulting freeze-out times are shorter than those of the standard nucleation scenario.

  5. Behavior of Supercooled Aqueous Solutions Stemming from Hidden Liquid-Liquid Transition in Water

    OpenAIRE

    Biddle, John W.; Holten, Vincent; Anisimov, Mikhail A.

    2014-01-01

    A popular hypothesis that explains the anomalies of supercooled water is the existence of a metastable liquid-liquid transition hidden below the line of homogeneous nucleation. If this transition exists and if it is terminated by a critical point, the addition of a solute should generate a line of liquid-liquid critical points emanating from the critical point of pure metastable water. We have analyzed thermodynamic consequences of this scenario. In particular, we consider the behavior of two...

  6. Direct measurement of the surface dynamics of supercooled liquid-glycerol by optical scanning a film

    Institute of Scientific and Technical Information of China (English)

    Zhang Fang; Zhang Guo-Feng; Dong Shuang-Li; Sun Jian-Hu; Chen Rui-Yun; Xiao Lian-Tuan; Jia Suo-Tang

    2009-01-01

    The surface dynamics of supercooled liquid-glycerol is studied by scanning the thickness of the glycerol film with single photon detection. Measurements are performed at room temperature well above the glycerol's glass transition temperature. It is shown that the surface dynamics of the glycerol film is very sensitive to the temperature. The linear relationship between the thickness of the film and the viscosity predicted by the Vogel-Fulcher-Tammann-Hesse (VFTH) law is also presented experimentally.

  7. Liquid–liquid transition in supercooled water suggested by microsecond simulations

    OpenAIRE

    Li, Yaping; Li, Jicun; Wang, Feng

    2013-01-01

    The putative liquid–liquid phase transition in supercooled water has been used to explain many anomalous behaviors of water. However, no direct experimental verification of such a phase transition has been accomplished, and theoretical studies from different simulations contradict each other. We investigated the putative liquid–liquid phase transition using the Water potential from Adaptive Force Matching for Ice and Liquid (WAIL). The simulation reveals a first-order phase transition in the ...

  8. A comparison of ground and satellite observations of cloud cover to saturation pressure differences during a cold air outbreak

    Energy Technology Data Exchange (ETDEWEB)

    Alliss, R.J.; Raman, S. [North Carolina State Univ., Raleigh, NC (United States)

    1996-04-01

    The role of clouds in the atmospheric general circulation and the global climate is twofold. First, clouds owe their origin to large-scale dynamical forcing, radiative cooling in the atmosphere, and turbulent transfer at the surface. In addition, they provide one of the most important mechanisms for the vertical redistribution of momentum and sensible and latent heat for the large scale, and they influence the coupling between the atmosphere and the surface as well as the radiative and dynamical-hydrological balance. In existing diagnostic cloudiness parameterization schemes, relative humidity is the most frequently used variable for estimating total cloud amount or stratiform cloud amount. However, the prediction of relative humidity in general circulation models (GCMs) is usually poor. Even for the most comprehensive GCMs, the predicted relative humidity may deviate greatly from that observed, as far as the frequency distribution of relative humidity is concerned. Recently, there has been an increased effort to improve the representation of clouds and cloud-radiation feedback in GCMs, but the verification of cloudiness parameterization schemes remains a severe problem because of the lack of observational data sets. In this study, saturation pressure differences (as opposed to relative humidity) and satellite-derived cloud heights and amounts are compared with ground determinations of cloud cover over the Gulf Stream Locale (GSL) during a cold air outbreak.

  9. Real-time observation of the isothermal crystallization kinetics in a deeply supercooled liquid

    Science.gov (United States)

    Zanatta, M.; Cormier, L.; Hennet, L.; Petrillo, C.; Sacchetti, F.

    2017-01-01

    Below the melting temperature Tm, crystals are the stable phase of typical elemental or molecular systems. However, cooling down a liquid below Tm, crystallization is anything but inevitable. The liquid can be supercooled, eventually forming a glass below the glass transition temperature Tg. Despite their long lifetimes and the presence of strong barriers that produces an apparent stability, supercooled liquids and glasses remain intrinsically a metastable state and thermodynamically unstable towards the crystal. Here we investigated the isothermal crystallization kinetics of the prototypical strong glassformer GeO2 in the deep supercooled liquid at 1100 K, about half-way between Tm and Tg. The crystallization process has been observed through time-resolved neutron diffraction for about three days. Data show a continuous reorganization of the amorphous structure towards the alpha-quartz phase with the final material composed by crystalline domains plunged into a low-density, residual amorphous matrix. A quantitative analysis of the diffraction patterns allows determining the time evolution of the relative fractions of crystal and amorphous, that was interpreted through an empirical model for the crystallization kinetics. This approach provides a very good description of the experimental data and identifies a predator-prey-like mechanism between crystal and amorphous, where the density variation acts as a blocking barrier. PMID:28255173

  10. Effect of cloud microphysics on particle growth under mixed phase conditions

    Science.gov (United States)

    Pfitzenmaier, Lukas; Dufournet, Yann; Unal, Christine; Russchenberg, Herman; Myagkov, Alexander; Seifert, Patric

    2015-04-01

    Mixed phase clouds contain both ice particles and super-cooled cloud water droplets in the same volume of air. Currently, one of the main challenges is to observe and understand how ice particles grow by interacting with liquid water within the mixed-phase clouds. In the mid latitudes this process is one of the most efficient processes for precipitation formation. It is particularly important to understand under which conditions growth processes are most efficient within such clouds. The observation of microphysical cloud properties from the ground is one possible approach to study the liquid-ice interaction that play a role on the ice crystal growth processes. The study presented here is based on a ground-based multi-sensor technique. Dataset of this study was taken during the ACCEPT campaign (Analysis of the Composition of mixed-phase Clouds with Extended Polarization Techniques) at Cabauw The Netherlands, autumn 2014. Measurements with the Transportable Atmospheric RAdar (TARA), S-band precipitation radar profiler, from the Delft Technical University, and Ka-band cloud radar systems were performed in cooperation with the Leibniz Institute for Tropospheric Research (TROPOS), Leipzig, Germany. All the radar systems had full Doppler capabilities. In addition , TARA and one of the Ka-band radar systems had full polarimetric capabilities as well, in order to get information of the ice phase within mixed-phase cloud systems. Lidar, microwave radiometer and radiosonde measurements were combined to describe the liquid phase within such clouds. So a whole characterisation of microphysical processes within mixed-phase cloud systems could be done. This study shows how such a combination of instruments is used to: - Detect the liquid layer within the ice clouds - Describe the microphysical conditions for ice particle growth within mixed phase clouds based on cloud hydrometeor shape, size, number concentration obtained from measurements The project aims to observe

  11. Lidar investigation of tropical nocturnal boundary layer aerosols and cloud macrophysics

    Science.gov (United States)

    Manoj, M. G.; Devara, P. C. S.; Taraphdar, S.

    2013-10-01

    Observational evidence of two-way association between nocturnal boundary layer aerosols and cloud macrophysical properties over a tropical urban site is reported in this paper. The study has been conducted during 2008-09 employing a high space-time resolution polarimetric micro-pulse lidar over a tropical urban station in India. Firstly, the study highlights the crucial role of boundary layer aerosols and background meteorology on the formation and structure of low-level stratiform clouds in the backdrop of different atmospheric stability conditions. Turbulent mixing induced by the wind shear at the station, which is associated with a complex terrain, is found to play a pivotal role in the formation and structural evolution of nocturnal boundary layer clouds. Secondly, it is shown that the trapping of energy in the form of outgoing terrestrial radiation by the overlying low-level clouds can enhance the aerosol mixing height associated with the nocturnal boundary layer. To substantiate this, the long-wave heating associated with cloud capping has been quantitatively estimated in an indirect way by employing an Advanced Research Weather Research and Forecasting (WRF-ARW) model developed by National Center for Atmospheric Research (NCAR), Colorado, USA, and supplementary data sets; and differentiated against other heating mechanisms. The present investigation as well establishes the potential of lidar remote-sensing technique in exploring some of the intriguing aspects of the cloud-environment relationship.

  12. The formation of supercooled brines, viscous liquids, and low-temperature perchlorate glasses in aqueous solutions relevant to Mars

    Science.gov (United States)

    Toner, J. D.; Catling, D. C.; Light, B.

    2014-05-01

    Salt solutions on Mars can stabilize liquid water at low temperatures by lowering the freezing point of water. The maximum equilibrium freezing-point depression possible, known as the eutectic temperature, suggests a lower temperature limit for liquid water on Mars; however, salt solutions can supercool below their eutectic before crystallization occurs. To investigate the magnitude of supercooling and its variation with salt composition and concentration, we performed slow cooling and warming experiments on pure salt solutions and saturated soil-solutions of MgSO4, MgCl2, NaCl, NaClO4, Mg(ClO4)2, and Ca(ClO4)2. By monitoring solution temperatures, we identified exothermic crystallization events and determined the composition of precipitated phases from the eutectic melting temperature. Our results indicate that supercooling is pervasive. In general, supercooling is greater in more concentrated solutions and with salts of Ca and Mg. Slowly cooled MgSO4, MgCl2, NaCl, and NaClO4 solutions investigated in this study typically supercool 5-15 °C below their eutectic temperature before crystallizing. The addition of soil to these salt solutions has a variable effect on supercooling. Relative to the pure salt solutions, supercooling decreases in MgSO4 soil-solutions, increases in MgCl2 soil-solutions, and is similar in NaCl and NaClO4 soil-solutions. Supercooling in MgSO4, MgCl2, NaCl, and NaClO4 solutions could marginally extend the duration of liquid water during relatively warm daytime temperatures in the martian summer. In contrast, we find that Mg(ClO4)2 and Ca(ClO4)2 solutions do not crystallize during slow cooling, but remain in a supercooled, liquid state until forming an amorphous glass near -120 °C. Even if soil is added to the solutions, a glass still forms during cooling. The large supercooling effect in Mg(ClO4)2 and Ca(ClO4)2 solutions has the potential to prevent water from freezing over diurnal and possibly annual cycles on Mars. Glasses are also

  13. Cloud cover diurnal cycles in satellite data and regional climate model simulations

    Energy Technology Data Exchange (ETDEWEB)

    Pfeifroth, Uwe; Ahrens, Bodo [Frankfurt Univ., Frankfurt am Main (Germany). Inst. for Atmospheric and Environmental Sciences; Hollmann, Rainer [Deutscher Wetterdienst, Offenbach (Germany)

    2012-12-15

    The amount and diurnal cycle of cloud cover play an important role in the energy and water cycle of the earth-atmosphere system and influence the radiation budget of the earth. Due to its importance and the challenging nature of its quantification, cloud cover is considered the biggest uncertainty factor in climate modeling. There is a clear need for reliable cloud datasets suitable for climate model evaluation studies. This study analyzes two datasets of cloud cover and its diurnal cycle derived from satellite observations by the International Satellite Cloud Climatology Project (ISCCP) and by EUMETSAT's Satellite Application Facility on Climate Monitoring (CM SAF) in Africa and Europe. Two regions, Europe and the subtropical southern Atlantic Ocean, were identified as offering distinct cloud cover diurnal cycles reasonably observed by both satellite datasets. In these regions, simulations by the regional climate model COSMO-CLM (CCLM) were evaluated in terms of cloud cover and its diurnal cycle during the time period of 1990 to 2007. Results show that the satellite derived cloud diurnal cycles largely agree, while discrepancies occur under extreme conditions like in the Sahara region. The CCLM is able to simulate the diurnal cycle observed consistently in the two satellite datasets in the South-Atlantic ocean, but not in Europe. CCLM misses the afternoon maximum cloud cover in Summer in Europe, which implies deficiencies in the parameterization of convection and in the treatment of surface-atmosphere interactions. The simulation of the diurnal cycle of the more stratiform cloud cover over the subtropical Atlantic was satisfactory in CCLM. (orig.)

  14. Cloud management and security

    CERN Document Server

    Abbadi, Imad M

    2014-01-01

    Written by an expert with over 15 years' experience in the field, this book establishes the foundations of Cloud computing, building an in-depth and diverse understanding of the technologies behind Cloud computing. In this book, the author begins with an introduction to Cloud computing, presenting fundamental concepts such as analyzing Cloud definitions, Cloud evolution, Cloud services, Cloud deployment types and highlighting the main challenges. Following on from the introduction, the book is divided into three parts: Cloud management, Cloud security, and practical examples. Part one presents the main components constituting the Cloud and federated Cloud infrastructure(e.g., interactions and deployment), discusses management platforms (resources and services), identifies and analyzes the main properties of the Cloud infrastructure, and presents Cloud automated management services: virtual and application resource management services. Part two analyzes the problem of establishing trustworthy Cloud, discuss...

  15. Remobilisation features and structural control on ore grade distribution at the Konkola stratiform Cu-Co ore deposit, Zambia

    Science.gov (United States)

    Torremans, K.; Gauquie, J.; Boyce, A. J.; Barrie, C. D.; Dewaele, S.; Sikazwe, O.; Muchez, Ph.

    2013-03-01

    The Konkola deposit is a high grade stratiform Cu-Co ore deposit in the Central African Copperbelt in Zambia. Economic mineralisation is confined to the Ore Shale formation, part of the Neoproterozoic metasedimentary rocks of the Katanga Supergroup. Petrographic study reveals that the copper-cobalt ore minerals are disseminated within the host rock, sometimes concentrated along bedding planes, often associated with dolomitic bands or clustered in cemented lenses and in layer-parallel and irregular veins. The hypogene sulphide mineralogy consists predominantly of chalcopyrite, bornite and chalcocite. Based upon relationships with metamorphic biotite, vein sulphides and most of the sulphides in cemented lenses were precipitated during or after biotite zone greenschist facies metamorphism. New δ34S values of sulphides from the Konkola deposit are presented. The sulphur isotope values range from -8.7‰ to +1.4‰ V-CDT for chalcopyrite from all mineralising phases and from -4.4‰ to +2.0‰ V-CDT for secondary chalcocite. Similarities in δ34S for sulphides from different vein generations, earlier sulphides and secondary chalcocite can be explained by (re)mobilisation of S from earlier formed sulphide phases, an interpretation strongly supported by the petrographic evidence. Deep supergene enrichment and leaching occurs up to a km in depth, predominantly in the form of secondary chalcocite, goethite and malachite and is often associated with zones of high permeability. Detailed distribution maps of total copper and total cobalt contents of the Ore Shale formation show a close relationship between structural features and higher copper and lower cobalt contents, relative to other areas of the mine. Structural features include the Kirilabombwe anticline and fault zones along the axial plane and two fault zones in the southern limb of the anticline. Cobalt and copper behave differently in relation to these structural features. These structures are interpreted to have

  16. Cloud Computing

    DEFF Research Database (Denmark)

    Krogh, Simon

    2013-01-01

    The second half of the 20th century has been characterized by an explosive development in information technology (Maney, Hamm, & O'Brien, 2011). Processing power, storage capacity and network bandwidth have increased exponentially, resulting in new possibilities and shifting IT paradigms. In step...... with technological changes, the paradigmatic pendulum has swung between increased centralization on one side and a focus on distributed computing that pushes IT power out to end users on the other. With the introduction of outsourcing and cloud computing, centralization in large data centers is again dominating...... the IT scene. In line with the views presented by Nicolas Carr in 2003 (Carr, 2003), it is a popular assumption that cloud computing will be the next utility (like water, electricity and gas) (Buyya, Yeo, Venugopal, Broberg, & Brandic, 2009). However, this assumption disregards the fact that most IT production...

  17. Diagnosing Aircraft Icing Potential from Satellite Cloud Retrievals

    Science.gov (United States)

    Smith, William L., Jr.; Minnis, Patrick; Fleeger, Cecilia; Spangenberg, Douglas

    2013-01-01

    The threat for aircraft icing in clouds is a significant hazard that routinely impacts aviation operations. Accurate diagnoses and forecasts of aircraft icing conditions requires identifying the location and vertical distribution of clouds with super-cooled liquid water (SLW) droplets, as well as the characteristics of the droplet size distribution. Traditional forecasting methods rely on guidance from numerical models and conventional observations, neither of which currently resolve cloud properties adequately on the optimal scales needed for aviation. Satellite imagers provide measurements over large areas with high spatial resolution that can be interpreted to identify the locations and characteristics of clouds, including features associated with adverse weather and storms. This paper describes new techniques for interpreting cloud products derived from satellite data to infer the flight icing threat to aircraft. For unobscured low clouds, the icing threat is determined using empirical relationships developed from correlations between satellite imager retrievals of liquid water path and droplet size with icing conditions reported by pilots (PIREPS). For deep ice over water cloud systems, ice and liquid water content (IWC and LWC) profiles are derived by using the imager cloud properties to constrain climatological information on cloud vertical structure and water phase obtained apriori from radar and lidar observations, and from cloud model analyses. Retrievals of the SLW content embedded within overlapping clouds are mapped to the icing threat using guidance from an airfoil modeling study. Compared to PIREPS and ground-based icing remote sensing datasets, the satellite icing detection and intensity accuracies are approximately 90% and 70%, respectively, and found to be similar for both low level and deep ice over water cloud systems. The satellite-derived icing boundaries capture the reported altitudes over 90% of the time. Satellite analyses corresponding to

  18. The microphysics of clouds over the Antarctic Peninsula - Part 2: modelling aspects within Polar WRF

    Science.gov (United States)

    Listowski, Constantino; Lachlan-Cope, Tom

    2017-08-01

    The first intercomparisons of cloud microphysics schemes implemented in the Weather Research and Forecasting (WRF) mesoscale atmospheric model (version 3.5.1) are performed on the Antarctic Peninsula using the polar version of WRF (Polar WRF) at 5 km resolution, along with comparisons to the British Antarctic Survey's aircraft measurements (presented in part 1 of this work; Lachlan-Cope et al., 2016). This study follows previous works suggesting the misrepresentation of the cloud thermodynamic phase in order to explain large radiative biases derived at the surface in Polar WRF continent-wide (at 15 km or coarser horizontal resolution) and in the Polar WRF-based operational forecast model Antarctic Mesoscale Prediction System (AMPS) over the Larsen C Ice Shelf at 5 km horizontal resolution. Five cloud microphysics schemes are investigated: the WRF single-moment five-class scheme (WSM5), the WRF double-moment six-class scheme (WDM6), the Morrison double-moment scheme, the Thompson scheme, and the Milbrandt-Yau double-moment seven-class scheme. WSM5 (used in AMPS) and WDM6 (an upgrade version of WSM5) lead to the largest biases in observed supercooled liquid phase and surface radiative biases. The schemes simulating clouds in closest agreement to the observations are the Morrison, Thompson, and Milbrandt schemes for their better average prediction of occurrences of clouds and cloud phase. Interestingly, those three schemes are also the ones allowing for significant reduction of the longwave surface radiative bias over the Larsen C Ice Shelf (eastern side of the peninsula). This is important for surface energy budget consideration with Polar WRF since the cloud radiative effect is more pronounced in the infrared over icy surfaces. Overall, the Morrison scheme compares better to the cloud observation and radiation measurements. The fact that WSM5 and WDM6 are single-moment parameterizations for the ice crystals is responsible for their lesser ability to model the

  19. Cloud Interactions

    Science.gov (United States)

    2004-01-01

    [figure removed for brevity, see original site] Released 1 July 2004 The atmosphere of Mars is a dynamic system. Water-ice clouds, fog, and hazes can make imaging the surface from space difficult. Dust storms can grow from local disturbances to global sizes, through which imaging is impossible. Seasonal temperature changes are the usual drivers in cloud and dust storm development and growth. Eons of atmospheric dust storm activity has left its mark on the surface of Mars. Dust carried aloft by the wind has settled out on every available surface; sand dunes have been created and moved by centuries of wind; and the effect of continual sand-blasting has modified many regions of Mars, creating yardangs and other unusual surface forms. This image was acquired during mid-spring near the North Pole. The linear water-ice clouds are now regional in extent and often interact with neighboring cloud system, as seen in this image. The bottom of the image shows how the interaction can destroy the linear nature. While the surface is still visible through most of the clouds, there is evidence that dust is also starting to enter the atmosphere. Image information: VIS instrument. Latitude 68.4, Longitude 258.8 East (101.2 West). 38 meter/pixel resolution. Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time. NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara

  20. Evaluation of Cloud-Resolving and Limited Area Model Intercomparison Simulations Using TWP-ICE Observations. Part 2 ; Precipitation Microphysics

    Science.gov (United States)

    Varble, Adam; Zipser, Edward J.; Fridland, Ann M.; Zhu, Ping; Ackerman, Andrew S.; Chaboureau, Jean-Pierre; Fan, Jiwen; Hill, Adrian; Shipway, Ben; Williams, Christopher

    2014-01-01

    Ten 3-D cloud-resolving model (CRM) simulations and four 3-D limited area model (LAM) simulations of an intense mesoscale convective system observed on 23-24 January 2006 during the Tropical Warm Pool-International Cloud Experiment (TWP-ICE) are compared with each other and with observations and retrievals from a scanning polarimetric radar, colocated UHF and VHF vertical profilers, and a Joss-Waldvogel disdrometer in an attempt to explain a low bias in simulated stratiform rainfall. Despite different forcing methodologies, similar precipitation microphysics errors appear in CRMs and LAMs with differences that depend on the details of the bulk microphysics scheme used. One-moment schemes produce too many small raindrops, which biases Doppler velocities low, but produces rainwater contents (RWCs) that are similar to observed. Two-moment rain schemes with a gamma shape parameter (mu) of 0 produce excessive size sorting, which leads to larger Doppler velocities than those produced in one-moment schemes but lower RWCs. Two-moment schemes also produce a convective median volume diameter distribution that is too broad relative to observations and, thus, may have issues balancing raindrop formation, collision-coalescence, and raindrop breakup. Assuming a mu of 2.5 rather than 0 for the raindrop size distribution improves one-moment scheme biases, and allowing mu to have values greater than 0 may improve excessive size sorting in two-moment schemes. Underpredicted stratiform rain rates are associated with underpredicted ice water contents at the melting level rather than excessive rain evaporation, in turn likely associated with convective detrainment that is too high in the troposphere and mesoscale circulations that are too weak. A limited domain size also prevents a large, well-developed stratiform region like the one observed from developing in CRMs, although LAMs also fail to produce such a region.

  1. Evaluation of Cloud-Resolving and Limited Area Model Intercomparison Simulations Using TWP-ICE Observations. Part 2 ; Precipitation Microphysics

    Science.gov (United States)

    Varble, Adam; Zipser, Edward J.; Fridland, Ann M.; Zhu, Ping; Ackerman, Andrew S.; Chaboureau, Jean-Pierre; Fan, Jiwen; Hill, Adrian; Shipway, Ben; Williams, Christopher

    2014-01-01

    Ten 3-D cloud-resolving model (CRM) simulations and four 3-D limited area model (LAM) simulations of an intense mesoscale convective system observed on 23-24 January 2006 during the Tropical Warm Pool-International Cloud Experiment (TWP-ICE) are compared with each other and with observations and retrievals from a scanning polarimetric radar, colocated UHF and VHF vertical profilers, and a Joss-Waldvogel disdrometer in an attempt to explain a low bias in simulated stratiform rainfall. Despite different forcing methodologies, similar precipitation microphysics errors appear in CRMs and LAMs with differences that depend on the details of the bulk microphysics scheme used. One-moment schemes produce too many small raindrops, which biases Doppler velocities low, but produces rainwater contents (RWCs) that are similar to observed. Two-moment rain schemes with a gamma shape parameter (mu) of 0 produce excessive size sorting, which leads to larger Doppler velocities than those produced in one-moment schemes but lower RWCs. Two-moment schemes also produce a convective median volume diameter distribution that is too broad relative to observations and, thus, may have issues balancing raindrop formation, collision-coalescence, and raindrop breakup. Assuming a mu of 2.5 rather than 0 for the raindrop size distribution improves one-moment scheme biases, and allowing mu to have values greater than 0 may improve excessive size sorting in two-moment schemes. Underpredicted stratiform rain rates are associated with underpredicted ice water contents at the melting level rather than excessive rain evaporation, in turn likely associated with convective detrainment that is too high in the troposphere and mesoscale circulations that are too weak. A limited domain size also prevents a large, well-developed stratiform region like the one observed from developing in CRMs, although LAMs also fail to produce such a region.

  2. Evaluation of Cloud-resolving and Limited Area Model Intercomparison Simulations using TWP-ICE Observations. Part 2: Rain Microphysics

    Energy Technology Data Exchange (ETDEWEB)

    Varble, Adam; Zipser, Edward J.; Fridlind, Ann; Zhu, Ping; Ackerman, Andrew; Chaboureau, Jean-Pierre; Fan, Jiwen; Hill, Adrian; Shipway, Ben; Williams, Christopher R.

    2014-12-27

    Ten 3D cloud-resolving model (CRM) simulations and four 3D limited area model (LAM) simulations of an intense mesoscale convective system observed on January 23-24, 2006 during the Tropical Warm Pool – International Cloud Experiment (TWP-ICE) are compared with each other and with observations and retrievals from a scanning polarimetric radar, co-located UHF and VHF vertical profilers, and a Joss-Waldvogel disdrometer in an attempt to explain published results showing a low bias in simulated stratiform rainfall. Despite different forcing methodologies, similar precipitation microphysics errors appear in CRMs and LAMs with differences that depend on the details of the bulk microphysics scheme used. One-moment schemes produce too many small raindrops, which biases Doppler velocities low, but produces rain water contents (RWCs) that are similar to observed. Two-moment rain schemes with a gamma shape parameter (μ) of 0 produce excessive size sorting, which leads to larger Doppler velocities than those produced in one-moment schemes, but lower RWCs than observed. Two moment schemes also produce a convective median volume diameter distribution that is too broad relative to observations and thus, may have issues balancing raindrop formation, collision coalescence, and raindrop breakup. Assuming a μ of 2.5 rather than 0 for the raindrop size distribution improves one-moment scheme biases, and allowing μ to have values greater than 0 may improve two-moment schemes. Under-predicted stratiform rain rates are associated with under-predicted ice water contents at the melting level rather than excessive rain evaporation, in turn likely associated with convective detrainment that is too high in the troposphere and mesoscale circulations that are too weak. In addition to stronger convective updrafts than observed, limited domain size prevents a large, well-developed stratiform region from developing in CRMs, while a dry bias in ECMWF analyses does the same to the LAMs.

  3. Evaluation of cloud-resolving and limited area model intercomparison simulations using TWP-ICE observations: 2. Precipitation microphysics

    Science.gov (United States)

    Varble, Adam; Zipser, Edward J.; Fridlind, Ann M.; Zhu, Ping; Ackerman, Andrew S.; Chaboureau, Jean-Pierre; Fan, Jiwen; Hill, Adrian; Shipway, Ben; Williams, Christopher

    2014-12-01

    Ten 3-D cloud-resolving model (CRM) simulations and four 3-D limited area model (LAM) simulations of an intense mesoscale convective system observed on 23-24 January 2006 during the Tropical Warm Pool-International Cloud Experiment (TWP-ICE) are compared with each other and with observations and retrievals from a scanning polarimetric radar, colocated UHF and VHF vertical profilers, and a Joss-Waldvogel disdrometer in an attempt to explain a low bias in simulated stratiform rainfall. Despite different forcing methodologies, similar precipitation microphysics errors appear in CRMs and LAMs with differences that depend on the details of the bulk microphysics scheme used. One-moment schemes produce too many small raindrops, which biases Doppler velocities low, but produces rainwater contents (RWCs) that are similar to observed. Two-moment rain schemes with a gamma shape parameter (μ) of 0 produce excessive size sorting, which leads to larger Doppler velocities than those produced in one-moment schemes but lower RWCs. Two-moment schemes also produce a convective median volume diameter distribution that is too broad relative to observations and, thus, may have issues balancing raindrop formation, collision-coalescence, and raindrop breakup. Assuming a μ of 2.5 rather than 0 for the raindrop size distribution improves one-moment scheme biases, and allowing μ to have values greater than 0 may improve excessive size sorting in two-moment schemes. Underpredicted stratiform rain rates are associated with underpredicted ice water contents at the melting level rather than excessive rain evaporation, in turn likely associated with convective detrainment that is too high in the troposphere and mesoscale circulations that are too weak. A limited domain size also prevents a large, well-developed stratiform region like the one observed from developing in CRMs, although LAMs also fail to produce such a region.

  4. Integrating Cloud Processes in the Community Atmosphere Model, Version 5.

    Energy Technology Data Exchange (ETDEWEB)

    Park, S.; Bretherton, Christopher S.; Rasch, Philip J.

    2014-09-15

    This paper provides a description on the parameterizations of global cloud system in CAM5. Compared to the previous versions, CAM5 cloud parameterization has the following unique characteristics: (1) a transparent cloud macrophysical structure that has horizontally non-overlapped deep cumulus, shallow cumulus and stratus in each grid layer, each of which has own cloud fraction, mass and number concentrations of cloud liquid droplets and ice crystals, (2) stratus-radiation-turbulence interaction that allows CAM5 to simulate marine stratocumulus solely from grid-mean RH without relying on the stability-based empirical empty stratus, (3) prognostic treatment of the number concentrations of stratus liquid droplets and ice crystals with activated aerosols and detrained in-cumulus condensates as the main sources and evaporation-sedimentation-precipitation of stratus condensate as the main sinks, and (4) radiatively active cumulus. By imposing consistency between diagnosed stratus fraction and prognosed stratus condensate, CAM5 is free from empty or highly-dense stratus at the end of stratus macrophysics. CAM5 also prognoses mass and number concentrations of various aerosol species. Thanks to the aerosol activation and the parameterizations of the radiation and stratiform precipitation production as a function of the droplet size, CAM5 simulates various aerosol indirect effects associated with stratus as well as direct effects, i.e., aerosol controls both the radiative and hydrological budgets. Detailed analysis of various simulations revealed that CAM5 is much better than CAM3/4 in the global performance as well as the physical formulation. However, several problems were also identifed, which can be attributed to inappropriate regional tuning, inconsistency between various physics parameterizations, and incomplete model physics. Continuous efforts are going on to further improve CAM5.

  5. Influences of in-cloud aerosol scavenging parameterizations on aerosol concentrations and wet deposition in ECHAM5-HAM

    Directory of Open Access Journals (Sweden)

    B. Croft

    2009-10-01

    Full Text Available A diagnostic nucleation scavenging scheme, which determines stratiform cloud scavenging ratios for both aerosol mass and number distributions, based on cloud droplet, and ice crystal number concentrations, is introduced into the ECHAM5-HAM global climate model. This is coupled with a size-dependent in-cloud impaction scavenging parameterization for both cloud droplet-aerosol, and ice crystal-aerosol collisions. Sensitivity studies are presented, which compare aerosol concentrations, and deposition between a variety of in-cloud scavenging approaches, including prescribed fractions, several diagnostic schemes, and a prognostic aerosol cloud processing treatment that passes aerosol in-droplet and in-ice crystal concentrations between model time steps. For one sensitivity study, assuming 100% of the in-cloud aerosol is scavenged into the cloud droplets and ice crystals, the annual global mean accumulation mode number burden is decreased by 65%, relative to a simulation with prognostic aerosol cloud processing. Diagnosing separate nucleation scavenging ratios for aerosol number and mass distributions, as opposed to equating the aerosol mass scavenging to the number scavenging ratios, reduces the annual global mean sulfate burden by near to 10%. The annual global mean sea salt burden is 30% lower for the diagnostic approach, which does not carry aerosol in-droplet and in-crystal concentrations between model time-steps as compared to the prognostic scheme. Implementation of in-cloud impaction scavenging reduced the annual, global mean black carbon burden by 30% for the prognostic aerosol cloud processing scheme. Better agreement with observations of black carbon profiles from aircraft (changes near to one order of magnitude for mixed phase clouds, 210Pb surface layer concentrations and wet deposition, and the geographic distribution of aerosol optical depth are found for the new diagnostic scavenging as compared to prescribed ratio

  6. Polluting of Winter Convective Clouds upon Transition from Ocean Inland Over Central California: Contrasting Case Studies

    Energy Technology Data Exchange (ETDEWEB)

    Rosenfeld, Daniel; Chemke, Rei; Prather, Kimberly; Suski, Kaitlyn; Comstock, Jennifer M.; Schmid, Beat; Tomlinson, Jason M.; Jonsson, Haf

    2014-01-01

    In-situ aircraft measurements of aerosol chemical and cloud microphysical properties were conducted during the CalWater campaign in February and March 2011 over the Sierra Nevada Mountains and the coastal waters of central California. The main objective was to elucidate the impacts of aerosol properties on clouds and precipitation forming processes. In order to accomplish this, we compared contrasting cases of clouds that ingested aerosols from different sources. The results showed that clouds containing pristine oceanic air had low cloud drop concentrations and started to develop rain 500 m above their base. This occurred both over the ocean and over the Sierra Nevada, mainly in the early morning when the radiatively cooled stable continental boundary layer was decoupled from the cloud base. Supercooled rain dominated the precipitation that formed in growing convective clouds in the pristine air, up to the -21°C isotherm level. A contrasting situation was documented in the afternoon over the foothills of the Sierra Nevada, when the clouds ingested high pollution aerosol concentrations produced in the Central Valley. This led to slow growth of the cloud drop effective radius with height and suppressed and even prevented the initiation of warm rain while contributing to the development of ice hydrometeors in the form of graupel. Our results show that cloud condensation and ice nuclei were the limiting factors that controlled warm rain and ice processes, respectively, while the unpolluted clouds in the same air mass produced precipitation quite efficiently. These findings provide the motivation for deeper investigations into the nature of the aerosols seeding clouds.

  7. Martian Clouds

    Science.gov (United States)

    2004-01-01

    [figure removed for brevity, see original site] Released 28 June 2004 The atmosphere of Mars is a dynamic system. Water-ice clouds, fog, and hazes can make imaging the surface from space difficult. Dust storms can grow from local disturbances to global sizes, through which imaging is impossible. Seasonal temperature changes are the usual drivers in cloud and dust storm development and growth. Eons of atmospheric dust storm activity has left its mark on the surface of Mars. Dust carried aloft by the wind has settled out on every available surface; sand dunes have been created and moved by centuries of wind; and the effect of continual sand-blasting has modified many regions of Mars, creating yardangs and other unusual surface forms. This image was acquired during early spring near the North Pole. The linear 'ripples' are transparent water-ice clouds. This linear form is typical for polar clouds. The black regions on the margins of this image are areas of saturation caused by the build up of scattered light from the bright polar material during the long image exposure. Image information: VIS instrument. Latitude 68.1, Longitude 147.9 East (212.1 West). 38 meter/pixel resolution. Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time. NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip

  8. The retrieval of cloud microphysical properties using satellite measurements and an in situ database

    Directory of Open Access Journals (Sweden)

    Christophe Poix

    Full Text Available By combining AVHRR data from the NOAA satellites with information from a database of in situ measurements, large-scale maps can be generated of the microphysical parameters most immediately significant for the modelling of global circulation and climate. From the satellite data, the clouds can be classified into cumuliform, stratiform and cirrus classes and then into further sub-classes by cloud top temperature. At the same time a database of in situ measurements made by research aircraft is classified into the same sub-classes and a statistical analysis is used to derive relationships between the sub-classes and the cloud microphysical properties. These two analyses are then linked to give estimates of the microphysical properties of the satellite observed clouds. Examples are given of the application of this technique to derive maps of the probability of occurrence of precipitating clouds and of precipitating water content derived from a case study within the International Cirrus Experiment (ICE held in 1989 over the North Sea.

  9. Determination of the optical thickness and effective particle radius of clouds from transmitted solar radiation measurements

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    A method is presented for determining the optical thickness (τc) and effective particle radius (γe) of stratiform cloud layers from transmitted solar radiation measurements. A detailed study shows that the cloud optical thickness and effective particle radius of water clouds can be determined from transmission function rneasurements at 0.75 and 2.13 μm, provided that the scaled optical thickness τ'0.75 >1 and γe>5 μm. The wavelengths adopted by our study are similar to the channels of the moderate resolution imaging spectrometer (MODIS). The proposed method is invalid for optically thin clouds since transmission at 2.13 μm is less sensitive to γe. The retrieval errors of τ'γ.75 and γe monotonically decrease with increasing τc. For clouds having τ'0.75≥2, the retrieval errors of τ'0.75 and γe are below 10 % and 20 %, respectively. Transmissions at 0.75 and 1.65 μm can also be used to retrieve τc and γe.

  10. Properties of subvisible cirrus clouds formed by homogeneous freezing

    Directory of Open Access Journals (Sweden)

    B. Kärcher

    2002-04-01

    Full Text Available Number concentrations and mean sizes of ice crystals and derived microphysical and optical properties of subvisible cirrus clouds (SVCs formed by homogeneous freezing of supercooled aerosols are investigated as a function of temperature and updraft speed of adiabatically ascending air parcels. The properties of such clouds are insensitive to variations of the aerosol number and size distribution. Based on criteria constraining the optical extinction, sedimentation time, and existence time of SVCs, longer-lived (>10 min clouds, capable of exerting a measurable radiative or chemical impact, are generated within a narrow range of updraft speeds below 1 - 2 cm s -1 at temperatures below about 215K, with concentrations of ice crystals not exceeding 0.1 cm-3. The clouds do not reach an equilibrium state because the ice crystals sediment out of the formation layer typically before the supersaturation is removed. Given these results, it seems likely that a limited number (<0.1 cm-3 of effective heterogeneous freezing nuclei that nucleate ice below the homogeneous freezing threshold can control the formation and properties of SVCs, although homogeneous freezing nuclei are far more abundant.

  11. Cloud Computing (4)

    Institute of Scientific and Technical Information of China (English)

    Wang Bai; Xu Liutong

    2010-01-01

    @@ 8 Case Study Cloud computing is still a new phenomenon. Although many IT giants are developing their own cloud computing infrastructures,platforms, software, and services, few have really succeeded in becoming cloud computing providers.

  12. Blue skies for CLOUD

    CERN Multimedia

    2006-01-01

    Through the recently approved CLOUD experiment, CERN will soon be contributing to climate research. Tests are being performed on the first prototype of CLOUD, an experiment designed to assess cosmic radiation influence on cloud formation.

  13. Enhanced small-angle scattering connected to the Widom line in simulations of supercooled water.

    Science.gov (United States)

    Wikfeldt, K T; Huang, C; Nilsson, A; Pettersson, L G M

    2011-06-07

    We present extensive simulations on the TIP4P∕2005 water model showing significantly enhanced small-angle scattering (SAS) in the supercooled regime. The SAS is related to the presence of a Widom line (T(W)) characterized by maxima in thermodynamic response functions and Ornstein-Zernike correlation length. Recent experimental small-angle x-ray scattering data [Huang et al., J. Chem. Phys. 133, 134504 (2010)] are excellently reproduced, albeit with an increasing temperature offset at lower temperatures. Assuming the same origin of the SAS in experiment and model this suggests the existence of a Widom line also in real supercooled water. Simulations performed at 1000 bar show an increased abruptness of a crossover from dominating high-density (HDL) to dominating low-density (LDL) liquid and strongly enhanced SAS associated with crossing T(W), consistent with a recent determination of the critical pressure of TIP4P∕2005 at 1350 bar. Furthermore, good agreement with experimental isothermal compressibilities at 1000, 1500, and 2000 bar shows that the high pressure supercooled thermodynamic behavior of water is well described by TIP4P∕2005. Analysis of the tetrahedrality parameter Q reveals that the HDL-LDL structural transition is very sharp at 1000 bar, and that structural fluctuations become strongly coupled to density fluctuations upon approaching T(W). Furthermore, the tetrahedrality distribution becomes bimodal at ambient temperatures, an observation that possibly provides a link between HDL-LDL fluctuations and the structural bimodality in liquid water indicated by x-ray spectroscopic techniques. Computed x-ray absorption spectra are indeed found to show sensitivity to the tetrahedrality parameter.

  14. Evidence of the existence of the low-density liquid phase in supercooled, confined water.

    Science.gov (United States)

    Mallamace, Francesco; Broccio, Matteo; Corsaro, Carmelo; Faraone, Antonio; Majolino, Domenico; Venuti, Valentina; Liu, Li; Mou, Chung-Yuan; Chen, Sow-Hsin

    2007-01-09

    By confining water in a nanoporous structure so narrow that the liquid could not freeze, it is possible to study properties of this previously undescribed system well below its homogeneous nucleation temperature TH = 231 K. Using this trick, we were able to study, by means of a Fourier transform infrared spectroscopy, vibrational spectra (HOH bending and OH-stretching modes) of deeply supercooled water in the temperature range 183 < T < 273 K. We observed, upon decreasing temperature, the building up of a new population of hydrogen-bonded oscillators centered around 3,120 cm(-1), the contribution of which progressively dominates the spectra as one enters into the deeply supercooled regime. We determined that the fractional weight of this spectral component reaches 50% just at the temperature, TL approximately 225 K, where the confined water shows a fragile-to-strong dynamic cross-over phenomenon [Ito, K., Moynihan, C. T., Angell, C. A. (1999) Nature 398:492-494]. Furthermore, the fact that the corresponding OH stretching spectral peak position of the low-density-amorphous solid water occurs exactly at 3,120 cm(-1) [Sivakumar, T. C., Rice, S. A., Sceats, M. G. (1978) J. Chem. Phys. 69:3468-3476.] strongly suggests that these oscillators originate from existence of the low-density-liquid phase derived from the occurrence of the first-order liquid-liquid (LL) phase transition and the associated LL critical point in supercooled water proposed earlier by a computer molecular dynamics simulation [Poole, P. H., Sciortino, F., Essmann, U., Stanley, H. E. (1992) Nature 360:324-328].

  15. Wetting hysteresis induced by temperature changes: Supercooled water on hydrophobic surfaces.

    Science.gov (United States)

    Heydari, Golrokh; Sedighi Moghaddam, Maziar; Tuominen, Mikko; Fielden, Matthew; Haapanen, Janne; Mäkelä, Jyrki M; Claesson, Per M

    2016-04-15

    The state and stability of supercooled water on (super)hydrophobic surfaces is crucial for low temperature applications and it will affect anti-icing and de-icing properties. Surface characteristics such as topography and chemistry are expected to affect wetting hysteresis during temperature cycling experiments, and also the freezing delay of supercooled water. We utilized stochastically rough wood surfaces that were further modified to render them hydrophobic or superhydrophobic. Liquid flame spraying (LFS) was utilized to create a multi-scale roughness by depositing titanium dioxide nanoparticles. The coating was subsequently made non-polar by applying a thin plasma polymer layer. As flat reference samples modified silica surfaces with similar chemistries were utilized. With these substrates we test the hypothesis that superhydrophobic surfaces also should retard ice formation. Wetting hysteresis was evaluated using contact angle measurements during a freeze-thaw cycle from room temperature to freezing occurrence at -7°C, and then back to room temperature. Further, the delay in freezing of supercooled water droplets was studied at temperatures of -4°C and -7°C. The hysteresis in contact angle observed during a cooling-heating cycle is found to be small on flat hydrophobic surfaces. However, significant changes in contact angles during a cooling-heating cycle are observed on the rough surfaces, with a higher contact angle observed on cooling compared to during the subsequent heating. Condensation and subsequent frost formation at sub-zero temperatures induce the hysteresis. The freezing delay data show that the flat surface is more efficient in enhancing the freezing delay than the rougher surfaces, which can be rationalized considering heterogeneous nucleation theory. Thus, our data suggests that molecular flat surfaces, rather than rough superhydrophobic surfaces, are beneficial for retarding ice formation under conditions that allow condensation and frost

  16. Crystallization Behavior and Relaxation Dynamics of Supercooled S‑Ketoprofen and the Racemic Mixture along an Isochrone

    DEFF Research Database (Denmark)

    Adrjanowicz, Karolina; Kaminski, Kamil; Paluch, Marian

    2015-01-01

    In this paper, we study crystallization behavior and molecular dynamics in the supercooled liquid state of the pharmaceutically important compound ketoprofen at various thermodynamic conditions. Dielectric relaxation for a racemic mixture was investigated in a wide range of temperatures and press......In this paper, we study crystallization behavior and molecular dynamics in the supercooled liquid state of the pharmaceutically important compound ketoprofen at various thermodynamic conditions. Dielectric relaxation for a racemic mixture was investigated in a wide range of temperatures...... of pure enantiomers and their 50–50 equimolar mixture in the metastable supercooled liquid state. Crystallization kinetic studies revealed that at the same isochronal conditions the behavior of the S-enantiomer and R,S-racemic mixture of ketoprofen is entirely different. This was examined in the context...

  17. In-situ High-energy X-ray Diffraction Study of the Local Structure of Supercooled Liquid Si

    Science.gov (United States)

    Lee, G. W.; Kim, T. H.; Sieve, B.; Gangopadhyay, A. K.; Hyers, R. W.; Rathz, T. J.; Rogers, J. R.; Robinson, D. S.; Kelton, K. F.; Goldman, A. I.

    2005-01-01

    While changes in the coordination number for liquid silicon upon supercooling, signaling an underlying liquid-liquid phase transition, have been predicted, x-ray and neutron measurements have produced conflicting reports. In particular some studies have found an increase in the first shell coordination as temperature decreases in the supercooled regime, while others have reported increases in the coordination number with decreasing temperature. Employing the technique of electrostatic levitation coupled with high energy x-ray diffraction (125 keV), and rapid data acquisition (100ms collection times) using an area detector, we have obtained high quality structural data more deeply into the supercooled regime than has been possible before. No change in coordination number is observed in this temperature region, calling into question previous experimental claims of structural evidence for the existence of a liquid-liquid phase transition.

  18. Studies of a dynamic type ice storage system using supercooled water; Kareikyakusui riyo dainamikku gata shochikunetsu shisutemu no kenkyu

    Energy Technology Data Exchange (ETDEWEB)

    Ito, S.; Hashimoto, A.; Miura, N. [Kanagawa Inst. of Tech., Kanagawa (Japan); Ikemoto, Y.

    1999-11-25

    An ice storage system using supercooled water was constructed and the performance was tested. The system was consisted of a storage tank with the volume of 1.2 m{sup 3} in which slurry-ice was stared, a spiral double-tube heat exchanger 22 m long for making supercooled water by brine, a refrigerating machine of the rated capacity of 2.2 kW, reservoirs for cold and hot brine, heaters, and pumps. The system was able to be operated for more than 5 hours without freezing mostly if the degree of supercooling was less than about 2 degree C. The COPs based on the power of the refrigerating machine and system were about 1.3 and 0.7, respectively. (author)

  19. Chosen thermodynamic experiments: depression of the freezing point of water with salt and supercooled water

    OpenAIRE

    Krnc, Katja

    2014-01-01

    The diploma thesis presents two interesting thermodynamic experiments which were executed and described by Joseph Black in 18th Century. These are: depression of the freezing point of water with salt and supercooled water. We meet water in three states of matter in nature: in the state of ice, liquid water, and water steam. Phase crossing from water to ice (and vice versa from ice to water) is done with normal air pressure with the state temperature of 0°C. If we add certain matters to wat...

  20. Slow dynamics and local quasi-equilibrium-relaxation in supercooled colloidal systems

    Energy Technology Data Exchange (ETDEWEB)

    RubI, J M; SantamarIa-Holek, I; Perez-Madrid, A [Department de Fisica Fonamental, Facultat de Fisica, Universitat de Barcelona, Diagonal 647, 08028 Barcelona (Spain)

    2004-06-09

    We present a Fokker-Planck description of supercooled colloidal systems exhibiting slow relaxation dynamics. Assuming the existence of a local quasi-equilibrium state during the relaxation of the system, we derive a non-Markovian Fokker-Planck equation for the non-stationary conditional probability. A generalized Stokes-Einstein relation containing the temperature of the system at local quasi-equilibrium instead of the temperature of the bath is obtained. Our results explain experiments showing that the diffusion coefficient is not proportional to the inverse of the effective viscosity at frequencies related to the diffusion timescale.

  1. Experimental investigations on prototype heat storage units utilizing stable supercooling of sodium acetate trihydrate mixtures

    DEFF Research Database (Denmark)

    Dannemand, Mark; Dragsted, Janne; Fan, Jianhua;

    2016-01-01

    was filled with 220 kg SAT mixture thickened with 1% carboxymethyl cellulose. The heat exchange capacity rate during the charging of the unit with the extra water was significantly higher than for the unit with the thickening agent due to the different levels of convection. The SAT mixtures in the units were......Laboratory tests of two heat storage units based on the principle of stable supercooling of sodium acetate trihydrate (SAT) mixtures were carried out. One unit was filled with 199.5 kg of SAT with 9% extra water to avoid phase separation of the incongruently melting salt hydrate. The other unit...

  2. Breaking Kelvin-Helmholtz waves and cloud-top entrainment as revealed by K-band Doppler radar

    Science.gov (United States)

    Martner, Brooks E.; Ralph, F. Martin

    1993-01-01

    Radars have occasionally detected breaking Kelvin-Helmholtz (KH) waves under clear-air conditions in the atmospheric boundary layer and in the free troposphere. However, very few direct measurements of such waves within clouds have previously been reported and those have not clearly documented wave breaking. In this article, we present some of the most detailed and striking radar observations to date of breaking KH waves within clouds and at cloud top and discuss their relevance to the issue of cloud-top entrainment, which is believed to be important in convective and stratiform clouds. Aircraft observations reported by Stith suggest that vortex-like circulations near cloud top are an entrainment mechanism in cumuliform clouds. Laboratory and modeling studies have examined possibility that KH instability may be responsible for mixing at cloud top, but direct observations have not yet been presented. Preliminary analyses shown here may help fill this gap. The data presented in this paper were obtained during two field projects in 1991 that included observations from the NOAA Wave Propagation Laboratory's K-band Doppler radar (wavelength = 8.7 mm) and special rawinsonde ascents. The sensitivity (-30 dBZ at 10 km range), fine spatial resolution (375-m pulse length and 0.5 degrees beamwidth), velocity measurement precision (5-10 cm s-1), scanning capability, and relative immunity to ground clutter make it sensitive to non-precipitating and weakly precipitating clouds, and make it an excellent instrument to study gravity waves in clouds. In particular, the narrow beam width and short pulse length create scattering volumes that are cylinders 37.5 m long and 45 m (90 m) in diameter at 5 km (10 km) range. These characteristics allow the radar to resolve the detailed structure in breaking KH waves such as have been seen in photographic cloud images.

  3. Cloud-Top Entrainment in Stratocumulus Clouds

    Science.gov (United States)

    Mellado, Juan Pedro

    2017-01-01

    Cloud entrainment, the mixing between cloudy and clear air at the boundary of clouds, constitutes one paradigm for the relevance of small scales in the Earth system: By regulating cloud lifetimes, meter- and submeter-scale processes at cloud boundaries can influence planetary-scale properties. Understanding cloud entrainment is difficult given the complexity and diversity of the associated phenomena, which include turbulence entrainment within a stratified medium, convective instabilities driven by radiative and evaporative cooling, shear instabilities, and cloud microphysics. Obtaining accurate data at the required small scales is also challenging, for both simulations and measurements. During the past few decades, however, high-resolution simulations and measurements have greatly advanced our understanding of the main mechanisms controlling cloud entrainment. This article reviews some of these advances, focusing on stratocumulus clouds, and indicates remaining challenges.

  4. Silicon Photonics Cloud (SiCloud)

    DEFF Research Database (Denmark)

    DeVore, P. T. S.; Jiang, Y.; Lynch, M.;

    2015-01-01

    Silicon Photonics Cloud (SiCloud.org) is the first silicon photonics interactive web tool. Here we report new features of this tool including mode propagation parameters and mode distribution galleries for user specified waveguide dimensions and wavelengths.......Silicon Photonics Cloud (SiCloud.org) is the first silicon photonics interactive web tool. Here we report new features of this tool including mode propagation parameters and mode distribution galleries for user specified waveguide dimensions and wavelengths....

  5. Fragile-to-strong crossover in supercooled water: A comparison between TIP4P and TIP4P/2005 models

    Science.gov (United States)

    De Marzio, M.; Camisasca, G.; Rovere, M.; Gallo, P.

    2016-05-01

    We present recent simulation results on the dynamics of supercooled water with the TIP4P/2005 potential. We find that the dynamical behaviour of the translational motion of the molecules is well interpreted in terms of the Mode Coupling Theory, as it was found for supercooled TIP4P water. We compare the results of the two models and in particular we find also in TIP4P/2005 a crossover from a fragile to a strong regime. We connect this crossover to the crossing of the Widom line emanating from the liquid-liquid critical point.

  6. Design, Evaluation and GCM-Performance of a New Parameterization for Microphysics of Clouds with Relaxed Arakawa-Schubert Scheme (McRas)

    Science.gov (United States)

    Sud, Y. C.; Walker, G. K.

    1998-01-01

    A prognostic cloud scheme named McRAS (Microphysics of clouds with Relaxed Arakawa-Schubert Scheme) was developed with the aim of improving cloud-microphysics, and cloud-radiation interactions in GCMs. McRAS distinguishes convective, stratiform, and boundary-layer clouds. The convective clouds merge into stratiform clouds on an hourly time-scale, while the boundary-layer clouds do so instantly. The cloud condensate transforms into precipitation following the auto-conversion relations of Sundqvist that contain a parametric adaptation for the Bergeron-Findeisen process of ice crystal growth and collection of cloud condensate by precipitation. All clouds convect, advect, and diffuse both horizontally and vertically with a fully active cloud-microphysics throughout its life-cycle, while the optical properties of clouds are derived from the statistical distribution of hydrometeors and idealized cloud geometry. An evaluation of McRAS in a single column model (SCM) with the GATE Phase III data has shown that McRAS can simulate the observed temperature, humidity, and precipitation without discernible systematic errors. An evaluation with the ARM-CART SCM data in a cloud model intercomparison exercise shows reasonable but not an outstanding accurate simulation. Such a discrepancy is common to almost all models and is related, in part, to the input data quality. McRAS was implemented in the GEOS II GCM. A 50 month integration that was initialized with the ECMWF analysis of observations for January 1, 1987 and forced with the observed sea-surface temperatures and sea-ice distribution and vegetation properties (biomes, and soils), with prognostic soil moisture, snow-cover, and hydrology showed a very realistic simulation of cloud process, incloud water and ice, and cloud-radiative forcing (CRF). The simulated ITCZ showed a realistic time-mean structure and seasonal cycle, while the simulated CRF showed sensitivity to vertical distribution of cloud water which can be easily

  7. Automatic Cloud Bursting under FermiCloud

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Hao [Fermilab; Shangping, Ren [IIT; Garzoglio, Gabriele [Fermilab; Timm, Steven [Fermilab; Bernabeu, Gerard [Fermilab; Kim, Hyun Woo; Chadwick, Keith; Jang, Haengjin [KISTI, Daejeon; Noh, Seo-Young [KISTI, Daejeon

    1900-01-01

    Cloud computing is changing the infrastructure upon which scientific computing depends from supercomputers and distributed computing clusters to a more elastic cloud-based structure. The service-oriented focus and elasticity of clouds can not only facilitate technology needs of emerging business but also shorten response time and reduce operational costs of traditional scientific applications. Fermi National Accelerator Laboratory (Fermilab) is currently in the process of building its own private cloud, FermiCloud, which allows the existing grid infrastructure to use dynamically provisioned resources on FermiCloud to accommodate increased but dynamic computation demand from scientists in the domains of High Energy Physics (HEP) and other research areas. Cloud infrastructure also allows to increase a private cloud’s resource capacity through “bursting” by borrowing or renting resources from other community or commercial clouds when needed. This paper introduces a joint project on building a cloud federation to support HEP applications between Fermi National Accelerator Laboratory and Korea Institution of Science and Technology Information, with technical contributions from the Illinois Institute of Technology. In particular, this paper presents two recent accomplishments of the joint project: (a) cloud bursting automation and (b) load balancer. Automatic cloud bursting allows computer resources to be dynamically reconfigured to meet users’ demands. The load balance algorithm which the cloud bursting depends on decides when and where new resources need to be allocated. Our preliminary prototyping and experiments have shown promising success, yet, they also have opened new challenges to be studied

  8. Automatic Cloud Bursting under FermiCloud

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Hao [Fermilab; Shangping, Ren [IIT; Garzoglio, Gabriele [Fermilab; Timm, Steven [Fermilab; Bernabeu, Gerard [Fermilab; Kim, Hyun Woo; Chadwick, Keith; Jang, Haengjin [KISTI, Daejeon; Noh, Seo-Young [KISTI, Daejeon

    2013-01-01

    Cloud computing is changing the infrastructure upon which scientific computing depends from supercomputers and distributed computing clusters to a more elastic cloud-based structure. The service-oriented focus and elasticity of clouds can not only facilitate technology needs of emerging business but also shorten response time and reduce operational costs of traditional scientific applications. Fermi National Accelerator Laboratory (Fermilab) is currently in the process of building its own private cloud, FermiCloud, which allows the existing grid infrastructure to use dynamically provisioned resources on FermiCloud to accommodate increased but dynamic computation demand from scientists in the domains of High Energy Physics (HEP) and other research areas. Cloud infrastructure also allows to increase a private cloud’s resource capacity through “bursting” by borrowing or renting resources from other community or commercial clouds when needed. This paper introduces a joint project on building a cloud federation to support HEP applications between Fermi National Accelerator Laboratory and Korea Institution of Science and Technology Information, with technical contributions from the Illinois Institute of Technology. In particular, this paper presents two recent accomplishments of the joint project: (a) cloud bursting automation and (b) load balancer. Automatic cloud bursting allows computer resources to be dynamically reconfigured to meet users’ demands. The load balance algorithm which the cloud bursting depends on decides when and where new resources need to be allocated. Our preliminary prototyping and experiments have shown promising success, yet, they also have opened new challenges to be studied

  9. Evaluating Arctic cloud radiative effects simulated by NICAM with A-train

    Science.gov (United States)

    Hashino, Tempei; Satoh, Masaki; Hagihara, Yuichiro; Kato, Seiji; Kubota, Takuji; Matsui, Toshihisa; Nasuno, Tomoe; Okamoto, Hajime; Sekiguchi, Miho

    2016-06-01

    Evaluation of cloud radiative effects (CREs) in global atmospheric models is of vital importance to reduce uncertainties in weather forecasting and future climate projection. In this paper, we describe an effective way to evaluate CREs from a 3.5 km mesh global nonhydrostatic model by comparing it against A-train satellite data. The model is the Nonhydrostatic Icosahedral Atmospheric Model (NICAM), and its output is run through a satellite-sensor simulator (Joint Simulator for satellite sensors) to produce the equivalent CloudSat radar, CALIPSO lidar, and Aqua Clouds and the Earth's Radiant Energy System (CERES) data. These simulated observations are then compared to real observations from the satellites. We focus on the Arctic, which is a region experiencing rapid climate change over various surface types. The NICAM simulation significantly overestimates the shortwave CREs at top of atmosphere and surface as large as 24 W m-2 for the month of June. The CREs were decomposed into cloud fractions and footprint CREs of cloud types that are defined based on the CloudSat-CALIPSO cloud top temperature and maximum radar reflectivity. It turned out that the simulation underestimates the cloud fraction and optical thickness of mixed-phase clouds due to predicting too little supercooled liquid and predicting overly large snow particles with too little mass content. This bias was partially offset by predicting too many optically thin high clouds. Offline sensitivity experiments, where cloud microphysical parameters, surface albedo, and single scattering parameters are varied, support the diagnosis. Aerosol radiative effects and nonspherical single scattering of ice particles should be introduced into the NICAM broadband calculation for further improvement.

  10. The influence of extratropical cloud phase and amount feedbacks on climate sensitivity

    Science.gov (United States)

    Frey, William R.; Kay, Jennifer E.

    2017-07-01

    Global coupled climate models have large long-standing cloud and radiation biases, calling into question their ability to simulate climate and climate change. This study assesses the impact of reducing shortwave radiation biases on climate sensitivity within the Community Earth System Model (CESM). The model is modified by increasing supercooled cloud liquid to better match absorbed shortwave radiation observations over the Southern Ocean while tuning to reduce a compensating tropical shortwave bias. With a thermodynamic mixed-layer ocean, equilibrium warming in response to doubled CO2 increases from 4.1 K in the control to 5.6 K in the modified model. This 1.5 K increase in equilibrium climate sensitivity is caused by changes in two extratropical shortwave cloud feedbacks. First, reduced conversion of cloud ice to liquid at high southern latitudes decreases the magnitude of a negative cloud phase feedback. Second, warming is amplified in the mid-latitudes by a larger positive shortwave cloud feedback. The positive cloud feedback, usually associated with the subtropics, arises when sea surface warming increases the moisture gradient between the boundary layer and free troposphere. The increased moisture gradient enhances the effectiveness of mixing to dry the boundary layer, which decreases cloud amount and optical depth. When a full-depth ocean with dynamics and thermodynamics is included, ocean heat uptake preferentially cools the mid-latitude Southern Ocean, partially inhibiting the positive cloud feedback and slowing warming. Overall, the results highlight strong connections between Southern Ocean mixed-phase cloud partitioning, cloud feedbacks, and ocean heat uptake in a climate forced by greenhouse gas changes.

  11. Quasi-elastic neutron scattering studies of the slow dynamics of supercooled and glassy aspirin

    Science.gov (United States)

    Zhang, Yang; Tyagi, Madhusudan; Mamontov, Eugene; Chen, Sow-Hsin

    2012-02-01

    Aspirin, also known as acetylsalicylic acid (ASA), is not only a wonderful drug, but also a good glass former. Therefore, it serves as an important molecular system to study the near-arrest and arrested phenomena. In this paper, a high-resolution quasi-elastic neutron scattering (QENS) technique is used to investigate the slow dynamics of supercooled liquid and glassy aspirin from 410 down to 350 K. The measured QENS spectra can be analyzed with a stretched exponential model. We find that (i) the stretched exponent β(Q) is independent of the wavevector transfer Q in the measured Q range and (ii) the structural relaxation time τ(Q) follows a power-law dependence on Q. Consequently, the Q-independent structural relaxation time τ0 can be extracted for each temperature to characterize the slow dynamics of aspirin. The temperature dependence of τ0 can be fitted with the mode-coupling power law, the Vogel-Fulcher-Tammann equation and a universal equation for fragile glass forming liquids recently proposed by Tokuyama in the measured temperature range. The calculated dynamic response function χT(Q, t) using the experimentally determined self-intermediate scattering function of the hydrogen atoms of aspirin shows direct evidence of the enhanced dynamic fluctuations as the aspirin is increasingly supercooled, in agreement with the fixed-time mean squared displacement langx2rang and the non-Gaussian parameter α2 extracted from the elastic scattering.

  12. Orientational dynamics and energy landscape features of thermotropic liquid crystals: An analogy with supercooled liquids

    Indian Academy of Sciences (India)

    Biman Jana; Biman Bagchi

    2007-09-01

    Recent optical kerr effect (OKE) studies have revealed that orientational relaxation of rodlike nematogens near the isotropic-nematic (I-N) phase boundary and also in the nematic phase exhibit temporal power law decay at intermediate times. Such behaviour has drawn an intriguing analogy with supercooled liquids. Here, we have investigated the single-particle and collective orientational dynamics of a family of model system of thermotropic liquid crystals using extensive computer simulations. Several remarkable features of glassy dynamics are on display including non-exponential relaxation, dynamical heterogeneity, and non-Arrhenius temperature dependence of the orientational relaxation time. Over a temperature range near the I-N phase boundary, the system behaves like a fragile glass-forming liquid. Using proper scaling, we construct the usual relaxation time versus inverse temperature plot and explicitly demonstrate that one can successfully define a density dependent fragility of liquid crystals. The fragility of liquid crystals shows a temperature and density dependence which is remarkably similar to the fragility of glass forming supercooled liquids. Energy landscape analysis of inherent structures shows that the breakdown of the Arrhenius temperature dependence of relaxation rate occurs at a temperature that marks the onset of the growth of the depth of the potential energy minima explored by the system.

  13. Numerical investigation on super-cooled large droplet icing of fan rotor blade in jet engine

    Science.gov (United States)

    Isobe, Keisuke; Suzuki, Masaya; Yamamoto, Makoto

    2014-10-01

    Icing (or ice accretion) is a phenomenon in which super-cooled water droplets impinge and accrete on a body. It is well known that ice accretion on blades and vanes leads to performance degradation and has caused severe accidents. Although various anti-icing and deicing systems have been developed, such accidents still occur. Therefore, it is important to clarify the phenomenon of ice accretion on an aircraft and in a jet engine. However, flight tests for ice accretion are very expensive, and in the wind tunnel it is difficult to reproduce all climate conditions where ice accretion can occur. Therefore, it is expected that computational fluid dynamics (CFD), which can estimate ice accretion in various climate conditions, will be a useful way to predict and understand the ice accretion phenomenon. On the other hand, although the icing caused by super-cooled large droplets (SLD) is very dangerous, the numerical method has not been established yet. This is why SLD icing is characterized by splash and bounce phenomena of droplets and they are very complex in nature. In the present study, we develop an ice accretion code considering the splash and bounce phenomena to predict SLD icing, and the code is applied to a fan rotor blade. The numerical results with and without the SLD icing model are compared. Through this study, the influence of the SLD icing model is numerically clarified.

  14. Nature of large aggregates in supercooled aqueous solutions of sodium dodecyl sulfate

    Energy Technology Data Exchange (ETDEWEB)

    Franses, E.I. (Purdue Univ., West Lafayette, IN); Davis, H.T.; Miller, W.G.; Scriven, L.E.

    1980-09-18

    Preparations of 2.0 and 5.5 wt % sodium dodecyl sulfate (SDS) in 3.5 wt % (0.6 M) aqueous NaCl are equilibrium micellar solutions above 28/sup 0/C, the Krafft point of the surfactant at this salinity. These systems can be supercooled and remain transparent for hours and days. At 25/sup 0/C at equilibrium they are biphasic, a hydrated crystal phase and an aqueous salt solution phase containing only 0.01/sub 2/ wt % SDS. Conductimetry and /sup 13/C NMR show that these transparent supercooled systems are indeed supersaturated solutions and not microdispersions of the hydrated crystal. The time lag for the onset of nucleation of the crystals depends strongly on stirring details and probably on presence of gas-liquid interface. The big nonequilibrium aggregates present in the supersaturated systems resemble micelles in conductivity and molecular motion, and are likely to be metastable micelles as is presumed by Mazer, Benedek, and Carey. 21 references, 6 figures, 1 table.

  15. Behavior of supercooled aqueous solutions stemming from hidden liquid-liquid transition in water

    Science.gov (United States)

    Biddle, John W.; Holten, Vincent; Anisimov, Mikhail A.

    2014-08-01

    A popular hypothesis that explains the anomalies of supercooled water is the existence of a metastable liquid-liquid transition hidden below the line of homogeneous nucleation. If this transition exists and if it is terminated by a critical point, the addition of a solute should generate a line of liquid-liquid critical points emanating from the critical point of pure metastable water. We have analyzed thermodynamic consequences of this scenario. In particular, we consider the behavior of two systems, H2O-NaCl and H2O-glycerol. We find the behavior of the heat capacity in supercooled aqueous solutions of NaCl, as reported by Archer and Carter [J. Phys. Chem. B 104, 8563 (2000)], to be consistent with the presence of the metastable liquid-liquid transition. We elucidate the non-conserved nature of the order parameter (extent of "reaction" between two alternative structures of water) and the consequences of its coupling with conserved properties (density and concentration). We also show how the shape of the critical line in a solution controls the difference in concentration of the coexisting liquid phases.

  16. Behavior of supercooled aqueous solutions stemming from hidden liquid–liquid transition in water

    Energy Technology Data Exchange (ETDEWEB)

    Biddle, John W.; Holten, Vincent; Anisimov, Mikhail A., E-mail: anisimov@umd.edu [Institute for Physical Science and Technology and Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, Maryland 20742 (United States)

    2014-08-21

    A popular hypothesis that explains the anomalies of supercooled water is the existence of a metastable liquid–liquid transition hidden below the line of homogeneous nucleation. If this transition exists and if it is terminated by a critical point, the addition of a solute should generate a line of liquid–liquid critical points emanating from the critical point of pure metastable water. We have analyzed thermodynamic consequences of this scenario. In particular, we consider the behavior of two systems, H{sub 2}O-NaCl and H{sub 2}O-glycerol. We find the behavior of the heat capacity in supercooled aqueous solutions of NaCl, as reported by Archer and Carter [J. Phys. Chem. B 104, 8563 (2000)], to be consistent with the presence of the metastable liquid–liquid transition. We elucidate the non-conserved nature of the order parameter (extent of “reaction” between two alternative structures of water) and the consequences of its coupling with conserved properties (density and concentration). We also show how the shape of the critical line in a solution controls the difference in concentration of the coexisting liquid phases.

  17. Ice-lens formation and geometrical supercooling in soils and other colloidal materials

    CERN Document Server

    Style, Robert W; Cocks, Alan C F; Wettlaufer, John S

    2011-01-01

    We present a new, physically-intuitive model of ice-lens formation and growth during the freezing of soils and other dense, particulate suspensions. Motivated by experimental evidence, we consider the growth of an ice-filled crack in a freezing soil. At low temperatures, ice in the crack exerts large pressures on the crack walls that will eventually cause the crack to split open. We show that the crack will then propagate across the soil to form a new lens. The process is controlled by two factors: the cohesion of the soil, and the geometrical supercooling of the water in the soil; a new concept introduced to measure the energy available to form a new ice lens. When the supercooling exceeds a critical amount (proportional to the cohesive strength of the soil) a new ice lens forms. This condition for ice-lens formation and growth does not appeal to any ad hoc, empirical assumptions, and explains how periodic ice lenses can form with or without the presence of a frozen fringe. The proposed mechanism is in good ...

  18. Liquid-liquid transition in supercooled water suggested by microsecond simulations.

    Science.gov (United States)

    Li, Yaping; Li, Jicun; Wang, Feng

    2013-07-23

    The putative liquid-liquid phase transition in supercooled water has been used to explain many anomalous behaviors of water. However, no direct experimental verification of such a phase transition has been accomplished, and theoretical studies from different simulations contradict each other. We investigated the putative liquid-liquid phase transition using the Water potential from Adaptive Force Matching for Ice and Liquid (WAIL). The simulation reveals a first-order phase transition in the supercooled regime with the critical point at ~207 K and 50 MPa. Normal water is high-density liquid (HDL). Low-density liquid (LDL) emerges at lower temperatures. The LDL phase has a density only slightly larger than that of the ice-Ih and shows more long-range order than HDL. However, the transformation from LDL to HDL is spontaneous across the first-order phase transition line, suggesting the LDL configuration is not poorly formed nanocrystalline ice. It has been demonstrated in the past that the WAIL potential provides reliable predictions of water properties such as melting temperature and temperature of maximum density. Compared with other simple water potentials, WAIL is not biased by fitting to experimental properties, and simulation with this potential reflects the prediction of a high-quality first-principle potential energy surface.

  19. Optical Kerr effect of liquid and supercooled water: The experimental and data analysis perspective

    Science.gov (United States)

    Taschin, A.; Bartolini, P.; Eramo, R.; Righini, R.; Torre, R.

    2014-08-01

    The time-resolved optical Kerr effect spectroscopy (OKE) is a powerful experimental tool enabling accurate investigations of the dynamic phenomena in molecular liquids. We introduced innovative experimental and fitting procedures, that enable a safe deconvolution of sample response function from the instrumental function. This is a critical issue in order to measure the dynamics of liquid water. We report OKE data on water measuring intermolecular vibrations and the structural relaxation processes in an extended temperature range, inclusive of the supercooled states. The unpreceded data quality makes possible a solid comparison with few theoretical models: the multi-mode Brownian oscillator model, the Kubo's discrete random jump model, and the schematic mode-coupling model. All these models produce reasonable good fits of the OKE data of stable liquid water, i.e., over the freezing point. The features of water dynamics in the OKE data becomes unambiguous only at lower temperatures, i.e., for water in the metastable supercooled phase. We found that the schematic mode-coupling model provides the more rigorous and complete model for water dynamics, even if its intrinsic hydrodynamic approach does not give a direct access to the molecular information.

  20. Growth rate of crystalline ice and the diffusivity of supercooled water from 126 to 262 K

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Yuntao; Petrik, Nikolay G.; Smith, R. Scott; Kay, Bruce D.; Kimmel, Greg A.

    2016-12-12

    Understanding deeply supercooled water is key to unraveling many of water’s anomalous properties. However, this has proven difficult due to rapid and uncontrolled crystallization. Using a pulsed laser heating technique, we measure the growth rate of crystalline ice, G(T), for 180 K < T < 262 K, i.e. deep within water’s “no man’s land.” The self-diffusion of supercooled liquid water, D(T), is obtained from G(T) using the Wilson-Frenkel model of crystal growth. For T > 237 K, G(T) and D(T) have super-Arrhenius (“fragile”) temperature dependences, but both crossover to Arrhenius (“strong”) behavior with a large activation energy in “no man’s land.” The fact that G(T) and D(T) are smoothly varying rules out the hypothesis that liquid water’s properties have a singularity at or near 228 K. However the results are consistent with a previous prediction for D(T) that assumed no thermodynamic transitions occur in “no man’s land.

  1. Quasi-Elastic Neutron Scattering Studies of the Slow Dynamics of Supercooled and Glassy Aspirin

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yang [ORNL; Tyagi, M. [NCNR and University of Maryland; Mamontov, Eugene [ORNL; Chen, Sow-hsin H [ORNL

    2011-01-01

    Aspirin, also known as acetylsalicylic acid (ASA), is not only a wonderful drug, but also a good glass former. Therefore, it serves as an important molecular system to study the near-arrest and arrested phenomena. In this paper, a high-resolution quasi-elastic neutron scattering (QENS) technique is used to investigate the slow dynamics of supercooled liquid and glassy aspirin from 410 K down to 350 K. The measured QENS spectra can be analyzed with a stretched exponential model. We find that (i) the stretched exponent (Q) is independent of the wave vector transfer Q in the measured Q-range, and (ii) the structural relaxation time (Q) follows a power law dependence on Q. Consequently, the Q-independent structural relaxation time 0 can be extracted for each temperature to characterize the slow dynamics of aspirin. The temperature dependence of 0 can be fitted with the mode coupling power law, the Vogel-Fulcher-Tammann equation and a universal equation for fragile glass forming liquids recently proposed by M. Tokuyama in the measured temperature range. The calculated dynamic response function T(Q,t) using the experimentally determined self-intermediate scattering function of the hydrogen atoms of aspirin shows a direct evidence of the enhanced dynamic fluctuations as the aspirin is increasingly supercooled, in agreement with the fixed-time mean squared displacement x2 and non-Gaussian parameter 2 extracted from the elastic scattering.

  2. Quasi-Equilibrium States in the Tropics Simulated by a Cloud-Resolving Model. Part 1; Specific Features and Budget Analysis

    Science.gov (United States)

    Shie, C.-L.; Tao, W.-K.; Simpson, J.; Sui, C.-H.; Starr, David OC. (Technical Monitor)

    2001-01-01

    A series of long-term integrations using the two-dimensional Goddard Cumulus Ensemble (GCE) model were performed by altering imposed environmental components to produce various quasi-equilibrium thermodynamic states. Model results show that the genesis of a warm/wet quasi-equilibrium state is mainly due to either strong vertical wind shear (from nudging) or large surface fluxes (from strong surface winds), while a cold/dry quasi-equilibrium state is attributed to a remarkably weakened mixed-wind shear (from vertical mixing due to deep convection) along with weak surface winds. In general, latent heat flux and net large-scale temperature forcing, the two dominant physical processes, dominate in the beginning stage of the simulated convective systems, then considerably weaken in the final stage, which leads to quasi-equilibrium states. A higher thermodynamic regime is found to produce a larger rainfall amount, as convective clouds are the leading source of rainfall over stratiform clouds even though the former occupy much less area. Moreover, convective clouds are more likely to occur in the presence of strong surface winds (latent heat flux), while stratiform clouds (especially the well-organized type) are favored in conditions with strong wind shear (large-scale forcing). The convective systems, which consist of distinct cloud types due to the variation in horizontal winds, are also found to propagate differently. Accordingly, convective systems with mixed-wind shear generally propagate in the direction of shear, while the system with strong (multidirectional) wind shear propagates in a more complex way. Based on the results from the temperature (Q1) and moisture (Q2) budgets, cloud-scale eddies are found to act as a hydrodynamic 'vehicle' that cascades the heat and moisture vertically. Several other specific features such as atmospheric stability, CAPE, and mass fluxes are also investigated and found to be significantly different between diverse quasi

  3. Cloud Computing (1)

    Institute of Scientific and Technical Information of China (English)

    Wang Bai; Xu Liutong

    2010-01-01

    @@ Editor's Desk: Cloud computing is a topic of intense interest in the Internet field. Major IT giants have launched their own cloud computing products. This four-part lecture series will discuss cloud computing technology in the following aspects: The first part provides a brief description of the origin and characteristics of cloud computing from the users view of point; the other parts introduce typical applications of cloud computing, technically analyze the specific content within the cloud, its components, architecture and computational paradigm, compare cloud computing to other distributed computing technologies, and discuss its successful cases, commercial models, related technical and economic issues, and development trends.

  4. Cloud Computing (2)

    Institute of Scientific and Technical Information of China (English)

    Wang Bai; Xu Liutong

    2010-01-01

    @@ Editor's Desk: Cloud computing is a topic of intense interest in the Internet field. Major IT giants have launched their own cloud computing products. This four-part lecture series discusses cloud computing technology in the following aspects: The first part provided a brief description of the origin and characteristics of cloud computing from the users view of point; the other parts introduce typical applications of cloud computing, technically analyze the specific content within the cloud, its components, architecture and computational paradigm, compare cloud computing to other distributed computing technologies, and discuss its successful cases, commercial models, related technical and economic issues, and development trends.

  5. Cloud storage for dummies

    CERN Document Server

    Xu, Linda; Loughlin, Tanya

    2010-01-01

    Understand cloud computing and save your organization time and money! Cloud computing is taking IT by storm, but what is it and what are the benefits to your organization? Hitachi Data Systems' Cloud Storage For Dummies provides all the answers, With this book, you discover a clear explanation of cloud storage, and tips for how to choose the right type of cloud storage for your organization's needs. You also find out how cloud storage can free up valuable IT resources, saving time and money. Cloud Storage For Dummies presents useful information on setting up a

  6. Robots and sensor clouds

    CERN Document Server

    Shakshuki, Elhadi

    2016-01-01

    This book comprises four chapters that address some of the latest research in clouds robotics and sensor clouds. The first part of the book includes two chapters on cloud robotics. The first chapter introduces a novel resource allocation framework for cloud robotics and proposes a Stackelberg game model and the corresponding task oriented pricing mechanism for resource allocation. In the second chapter, the authors apply Cloud Computing for building a Cloud-Based 3D Point Cloud extractor for stereo images. Their objective is to have a dynamically scalable and applicable to near real-time scenarios.  .

  7. The Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study (SOCRATES): An Observational Campaign for Determining Role of Clouds, Aerosols and Radiation in Climate System

    Science.gov (United States)

    McFarquhar, G. M.; Wood, R.; Bretherton, C. S.; Alexander, S.; Jakob, C.; Marchand, R.; Protat, A.; Quinn, P.; Siems, S. T.; Weller, R. A.

    2014-12-01

    The Southern Ocean (SO) region is one of the cloudiest on Earth, and as such clouds determine its albedo and play a major role in climate. Evidence shows Earth's climate sensitivity and the Intertropical Convergence Zone location depend upon SO clouds. But, climate models are challenged by uncertainties and biases in the simulation of clouds, aerosols, and air-sea exchanges in this region which trace back to a poor process-level understanding. Due to the SO's remote location, there have been sparse observations of clouds, aerosols, precipitation, radiation and the air-sea interface apart from those from satellites. Plans for an upcoming observational program, SOCRATES, are outlined. Based on feedback on observational and modeling requirements from a 2014 workshop conducted at the University of Washington, a plan is described for obtaining a comprehensive dataset on the boundary-layer structure and associated vertical distributions of liquid and mixed-phase cloud and aerosol properties across a range of synoptic settings, especially in the cold sector of cyclonic storms. Four science themes are developed: improved climate model simulation of SO cloud and boundary layer structure in a rapidly varying synoptic setting; understanding seasonal and synoptic variability in SO cloud condensation and ice nucleus concentration and the role of local biogenic sources; understanding supercooled liquid and mixed-phase clouds and their impacts; and advancing retrievals of clouds, precipitation, aerosols, radiation and surface fluxes. Testable hypotheses for each theme are identified. The observational strategy consists of long-term ground-based observations from Macquarie Island and Davis, continuous data collection onboard Antarctic supply ships, satellite retrievals, and a dedicated field campaign covering 2 distinct seasons using in-situ and remote sensors on low- and high-altitude aircraft, UAVs, and a ship-borne platform. A timeline for these activities is proposed.

  8. The CLOUD experiment

    CERN Multimedia

    Maximilien Brice

    2006-01-01

    The Cosmics Leaving Outdoor Droplets (CLOUD) experiment as shown by Jasper Kirkby (spokesperson). Kirkby shows a sketch to illustrate the possible link between galactic cosmic rays and cloud formations. The CLOUD experiment uses beams from the PS accelerator at CERN to simulate the effect of cosmic rays on cloud formations in the Earth's atmosphere. It is thought that cosmic ray intensity is linked to the amount of low cloud cover due to the formation of aerosols, which induce condensation.

  9. Cloud Computing (3)

    Institute of Scientific and Technical Information of China (English)

    Wang Bai; Xu Liutong

    2010-01-01

    @@ Editor's Desk: In the preceding two parts of this series, several aspects of cloud computing-including definition, classification, characteristics, typical applications, and service levels-were discussed. This part continues with a discussion of Cloud Computing Oopen Architecture and Market-Oriented Cloud. A comparison is made between cloud computing and other distributed computing technologies, and Google's cloud platform is analyzed to determine how distributed computing is implemented in its particular model.

  10. Cloud Robotics Platforms

    Directory of Open Access Journals (Sweden)

    Busra Koken

    2015-01-01

    Full Text Available Cloud robotics is a rapidly evolving field that allows robots to offload computation-intensive and storage-intensive jobs into the cloud. Robots are limited in terms of computational capacity, memory and storage. Cloud provides unlimited computation power, memory, storage and especially collaboration opportunity. Cloud-enabled robots are divided into two categories as standalone and networked robots. This article surveys cloud robotic platforms, standalone and networked robotic works such as grasping, simultaneous localization and mapping (SLAM and monitoring.

  11. Freezing avoidance by supercooling in Olea europaea cultivars: the role of apoplastic water, solute content and cell wall rigidity.

    Science.gov (United States)

    Arias, Nadia S; Bucci, Sandra J; Scholz, Fabian G; Goldstein, Guillermo

    2015-10-01

    Plants can avoid freezing damage by preventing extracellular ice formation below the equilibrium freezing temperature (supercooling). We used Olea europaea cultivars to assess which traits contribute to avoid ice nucleation at sub-zero temperatures. Seasonal leaf water relations, non-structural carbohydrates, nitrogen and tissue damage and ice nucleation temperatures in different plant parts were determined in five cultivars growing in the Patagonian cold desert. Ice seeding in roots occurred at higher temperatures than in stems and leaves. Leaves of cold acclimated cultivars supercooled down to -13 °C, substantially lower than the minimum air temperatures observed in the study site. During winter, leaf ice nucleation and leaf freezing damage (LT50 ) occurred at similar temperatures, typical of plant tissues that supercool. Higher leaf density and cell wall rigidity were observed during winter, consistent with a substantial acclimation to sub-zero temperatures. Larger supercooling capacity and lower LT50 were observed in cold-acclimated cultivars with higher osmotically active solute content, higher tissue elastic adjustments and lower apoplastic water. Irreversible leaf damage was only observed in laboratory experiments at very low temperatures, but not in the field. A comparative analysis of closely related plants avoids phylogenetic independence bias in a comparative study of adaptations to survive low temperatures.

  12. Transcriptomic and proteomic analyses on the supercooling ability and mining of antifreeze proteins of the Chinese white wax scale insect.

    Science.gov (United States)

    Yu, Shu-Hui; Yang, Pu; Sun, Tao; Qi, Qian; Wang, Xue-Qing; Chen, Xiao-Ming; Feng, Ying; Liu, Bo-Wen

    2016-06-01

    The Chinese white wax scale insect, Ericerus pela, can survive at extremely low temperatures, and some overwintering individuals exhibit supercooling at temperatures below -30°C. To investigate the deep supercooling ability of E. pela, transcriptomic and proteomic analyses were performed to delineate the major gene and protein families responsible for the deep supercooling ability of overwintering females. Gene Ontology (GO) classification and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that genes involved in the mitogen-activated protein kinase, calcium, and PI3K-Akt signaling pathways and pathways associated with the biosynthesis of soluble sugars, sugar alcohols and free amino acids were dominant. Proteins responsible for low-temperature stress, such as cold acclimation proteins, glycerol biosynthesis-related enzymes and heat shock proteins (HSPs) were identified. However, no antifreeze proteins (AFPs) were identified through sequence similarity search methods. A random forest approach identified 388 putative AFPs in the proteome. The AFP gene ep-afp was expressed in Escherichia coli, and the expressed protein exhibited a thermal hysteresis activity of 0.97°C, suggesting its potential role in the deep supercooling ability of E. pela.

  13. Realisation of dynamic ice-making by supercooled water%过冷水动态制冰的研究

    Institute of Scientific and Technical Information of China (English)

    曲凯阳; 江亿

    2001-01-01

    Further studies based on the authors' earlier researches the conditions under which no fpeezing occur in the supercooler while sufficient supercooling of water is guaranteed.Establishes a stably opepeting experimental assembly. Water temperature at the entrance of the supercooler reaches as low as 0.45 ℃, and the water temperature drop in supercooler isabout 1℃.%在作者前期研究的基础上,进一步研究了保证过冷水动态制冰系统中过冷却器不发生结冰的条件,建立了能够稳定运行的过冷水动态制冰实验装置。水在过冷却器入口的最低温度为0.45℃,在过冷却器中的温降约为1.0℃。

  14. Elastic properties of Pd40Cu30Ni10P20 bulk glass in supercooled liquid region

    DEFF Research Database (Denmark)

    Nishiyama, N.; Inoue, A.; Jiang, Jianzhong

    2001-01-01

    In situ ultrasonic measurements for the Pd40Cu30Ni10P20 bulk glass in three states: Glassy solid, supercooled liquid, and crystalline, have been performed. It is found that velocities of both longitudinal and transverse waves and elastic moduli (shear modulus, bulk modulus, Young's modulus, and L...

  15. Evaluating the diurnal cycle in cloud top temperature from SEVIRI

    Directory of Open Access Journals (Sweden)

    S. Taylor

    2017-06-01

    diurnal cycle of cloud tops accurately in regions of stratiform cloud such as the southeast Atlantic Ocean and Europe, where cloud top temperature retrieval biases are small and exhibit limited spatial and temporal variability. Quantifying the diurnal cycle over the tropics and regions of desert is more difficult, as retrieval biases are larger and display significant diurnal variability. CLAAS-2 cloud top temperature data are found to be of limited skill in measuring the diurnal cycle accurately over desert regions. In tropical regions such as central Africa, the diurnal cycle can be described by the CLAAS-2 data to some extent, although retrieval biases appear to reduce the amplitude of the real diurnal cycle of cloud top temperatures. This is the first study to relate the diurnal variations in SEVIRI retrieval bias to observed diurnal cycles in cloud top temperature. Our results may be of interest to those in the observation and modelling communities when using cloud top properties data from SEVIRI, particularly for studies considering the diurnal cycle of convection.

  16. Evaluating the diurnal cycle in cloud top temperature from SEVIRI

    Science.gov (United States)

    Taylor, Sarah; Stier, Philip; White, Bethan; Finkensieper, Stephan; Stengel, Martin

    2017-06-01

    accurately in regions of stratiform cloud such as the southeast Atlantic Ocean and Europe, where cloud top temperature retrieval biases are small and exhibit limited spatial and temporal variability. Quantifying the diurnal cycle over the tropics and regions of desert is more difficult, as retrieval biases are larger and display significant diurnal variability. CLAAS-2 cloud top temperature data are found to be of limited skill in measuring the diurnal cycle accurately over desert regions. In tropical regions such as central Africa, the diurnal cycle can be described by the CLAAS-2 data to some extent, although retrieval biases appear to reduce the amplitude of the real diurnal cycle of cloud top temperatures. This is the first study to relate the diurnal variations in SEVIRI retrieval bias to observed diurnal cycles in cloud top temperature. Our results may be of interest to those in the observation and modelling communities when using cloud top properties data from SEVIRI, particularly for studies considering the diurnal cycle of convection.

  17. From pixels to patches: a cloud classification method based on bag of micro-structures

    Directory of Open Access Journals (Sweden)

    Q. Li

    2015-10-01

    Full Text Available Automatic cloud classification has attracted more and more attention with the increasing development of whole sky imagers, but it is still in progress for ground-based cloud observation. This paper proposes a new cloud classification method, named bag of micro-structures (BoMS. This method treats an all-sky image as a collection of micro-structures mapped from image patches, rather than a collection of pixels. And then it constructs an image representation with a weighted histogram of micro-structures. Lastly, a support vector machine (SVM classifier is applied on the image representation because SVM is appealing for sparse and high dimensional feature space. Five different sky conditions are identified: cirriform, cumuliform, stratiform, clear sky and mixed cloudiness that often appears in all-sky images but is seldom addressed in literature. BoMS is evaluated on a large dataset, which contains 5000 all-sky images that are captured by a total-sky cloud imager located in Tibet (29.25° N, 88.88° E. BoMS achieves an accuracy of 90.9 % for 10 fold cross-validation, and it outperforms the state-of-the-art method with an increase of about 19 %. Furthermore, influence of key parameters in BoMS are investigated to verify their robustness.

  18. Interactions Between Microphysics and Dynamics in Persistent Arctic Mixed Phase Clouds

    Science.gov (United States)

    Komurcu, M.; Harrington, J. Y.

    2011-12-01

    Mixed-phase clouds are commonly observed in the Arctic atmosphere, particularly during the transition and winter seasons. Inter-comparison of the results of the model simulations of cold season mixed-phase clouds show that the biggest spreads in model results occur in the simulated water contents which lead to negative radiation errors. Partitioning of the liquid water and ice is crucial in understanding the radiative influences of these clouds, and in turn their influences on the Arctic surface energy budget. Because ice growth occurs at the expense of liquid water droplets at cold temperatures of the Arctic during the cold season, the phase partitioning of water is partly controlled by the ice formation and growth processes. Therefore, in this study, we investigate and intercompare different ice formation mechanisms, ice crystal shapes and the number of available ice nuclei to understand the microphysical and dynamical interactions that allow for the formation and persistence of both liquid water and ice in long-lived mixed-phase clouds. We present results that attempt to separate the influences of microphysics and dynamics, with a view to understanding how dynamic processes affect the production and maintenance of supercooled liquid within Arctic cloud systems. We investigate how certain conditions that influence cloud circulations, such as changing the magnitudes of surface fluxes, or radiative forcing, can lead to the decoupling of the cloud and subcloud layers, and in turn possibly to the cessation of the cloud. To identify the conditions of decoupling, we develop a new ratio based on cloud circulations that is different from previous assessments of decoupling in the literature, which did not seem to work for Arctic clouds.

  19. The microphysics of clouds over the Antarctic Peninsula – Part 2: modelling aspects within Polar WRF

    Directory of Open Access Journals (Sweden)

    C. Listowski

    2017-08-01

    Full Text Available The first intercomparisons of cloud microphysics schemes implemented in the Weather Research and Forecasting (WRF mesoscale atmospheric model (version 3.5.1 are performed on the Antarctic Peninsula using the polar version of WRF (Polar WRF at 5 km resolution, along with comparisons to the British Antarctic Survey's aircraft measurements (presented in part 1 of this work; Lachlan-Cope et al., 2016. This study follows previous works suggesting the misrepresentation of the cloud thermodynamic phase in order to explain large radiative biases derived at the surface in Polar WRF continent-wide (at 15 km or coarser horizontal resolution and in the Polar WRF-based operational forecast model Antarctic Mesoscale Prediction System (AMPS over the Larsen C Ice Shelf at 5 km horizontal resolution. Five cloud microphysics schemes are investigated: the WRF single-moment five-class scheme (WSM5, the WRF double-moment six-class scheme (WDM6, the Morrison double-moment scheme, the Thompson scheme, and the Milbrandt–Yau double-moment seven-class scheme. WSM5 (used in AMPS and WDM6 (an upgrade version of WSM5 lead to the largest biases in observed supercooled liquid phase and surface radiative biases. The schemes simulating clouds in closest agreement to the observations are the Morrison, Thompson, and Milbrandt schemes for their better average prediction of occurrences of clouds and cloud phase. Interestingly, those three schemes are also the ones allowing for significant reduction of the longwave surface radiative bias over the Larsen C Ice Shelf (eastern side of the peninsula. This is important for surface energy budget consideration with Polar WRF since the cloud radiative effect is more pronounced in the infrared over icy surfaces. Overall, the Morrison scheme compares better to the cloud observation and radiation measurements. The fact that WSM5 and WDM6 are single-moment parameterizations for the ice crystals is responsible for their lesser

  20. Supercooled Water.

    Science.gov (United States)

    1983-03-01

    53) study by Egelstaff et al Emulsion samples have also been briefly studied but background difficulties have made resolution of the results...Angell, L., Angell, C. A. ., Phys. Chem. (to be published) 52. Bosio, L., Chen, S.-H., Teixeira, 3. Phys. Rev. A (in press) 53. Egelstaff , P. A., Polo, 3

  1. Cloud glaciation temperature estimation from passive remote sensing data with evolutionary computing

    Science.gov (United States)

    Carro-Calvo, L.; Hoose, C.; Stengel, M.; Salcedo-Sanz, S.

    2016-11-01

    The phase partitioning between supercooled liquid water and ice in clouds in the temperature range between 0 and -37°C influences their optical properties and the efficiency of precipitation formation. Passive remote sensing observations provide long-term records of the cloud top phase at a high spatial resolution. Based on the assumption of a cumulative Gaussian distribution of the ice cloud fraction as a function of temperature, we quantify the cloud glaciation temperature (CGT) as the 50th percentile of the fitted distribution function and its variance for different cloud top pressure intervals, obtained by applying an evolutionary algorithm (EA). EAs are metaheuristics approaches for optimization, used in difficult problems where standard approaches are either not applicable or show poor performance. In this case, the proposed EA is applied to 4 years of Pathfinder Atmospheres-Extended (PATMOS-x) data, aggregated into boxes of 1° × 1° and vertical layers of 5.5 hPa. The resulting vertical profile of CGT shows a characteristic sickle shape, indicating low CGTs close to homogeneous freezing in the upper troposphere and significantly higher values in the midtroposphere. In winter, a pronounced land-sea contrast is found at midlatitudes, with lower CGTs over land. Among this and previous studies, there is disagreement on the sign of the land-sea difference in CGT, suggesting that it is strongly sensitive to the detected and analyzed cloud types, the time of the day, and the phase retrieval method.

  2. Simulation and Interpretation of the Genesis of Tropical Storm Gert (2005) as Part of the NASA Tropical Cloud Systems and Processes Experiment

    Science.gov (United States)

    Braun, Scott A.; Montgomery, Michael T.; Mallen, Kevin

    2009-01-01

    Several hypotheses have been put forward for the how tropical cyclones (tropical storms and hurricanes in the Atlantic) first develop circulation at the surface, a key event that needs to occur before a storm can begin to draw energy from the warm ocean. One hypothesis suggests that the surface circulation forms from a "top-down" approach in which a storm s rotating circulation begins at middle levels of the atmosphere and builds down to the surface through processes related to light "stratiform" (horizontally extensive) precipitation. Another hypothesis suggests a bottom-up approach in which deep thunderstorm towers (convection) play the major role in spinning up the flow at the surface. These "hot towers" form in the area of the mid-level circulation and strongly concentrate this rotation at low levels within their updrafts. Merger of several of these hot towers then intensifies the surface circulation to the point in which a storm forms. This paper examines computer simulations of Tropical Storm Gert (2005), which formed in the Gulf of Mexico during the National Aeronautics and Space Administration s (NASA) Tropical Cloud Systems and Processes (TCSP) Experiment, to investigate the development of low-level circulation and, in particular, whether stratiform or hot tower processes were responsible for the storm s formation. Data from NASA satellites and from aircraft were used to show that the model did a good job of reproducing the formation and evolution of Gert. The simulation shows that a mix of both stratiform and convective rainfall occurred within Gert. While the stratiform rainfall clearly acted to increase rotation at middle levels, the diverging outflow beneath the stratiform rain worked against spinning up the low-level winds. The hot towers appeared to dominate the low-level flow, producing intense rotation within their cores and often being associated with significant pressure falls at the surface. Over time, many of these hot towers merged, with each

  3. Evaporative supercooling characteristics of single water droplet in ice-slurry production system with evaporative supercooled water%蒸发式过冷水制冰中单个水滴的蒸发过冷特性

    Institute of Scientific and Technical Information of China (English)

    闫俊海; 张小松

    2012-01-01

    To analyze the evaporation characteristics of single water droplet in low temperature and low humidity ratio air in ice production system with evaporative supercooled water, a mathematical model of evaporative supercooling process of single water droplet was proposed. The evaporation process of droplet in supercooling stage was simulated with theoretical model and the results are basically consistent with the experiment on suspended single water droplet, so it is feasible to predict the evaporative supercooling characteristics of small water droplet by the mathematical model. The influence of initial diameter and temperature of water droplet, air temperature, humidity ratio of air, and air velocity on the temperature of water droplet during its evaporative supercooling process was analyzed. The numerical results show that smaller diameter and lower temperature of water droplet and larger air velocity can increase the cooling rate of water droplet and shorten the supercooling time reaching steady state evaporation stage. Additionally, lowering the temperature or humidity ratio of air can not only improve the cooling rate of water droplet, but also increase the supercooling degree of water droplet reaching steady state evaporation stage. The investigation of evaporative supercooling process of water droplet can provide a foundation for improving the efficiency of ice production and optimal design for ice-making system with evaporative supercooled water.%为分析蒸发式过冷水制冰中单个水滴在此低温低湿空气环境中的蒸发特性,建立了水滴蒸发过冷过程的数理模型.通过悬挂水滴实验与模拟结果的对比,验证了模型的有效性.因此利用该数学模型预测微小直径水滴的蒸发特性是可行的.通过模拟计算获得了水滴初始直径、初始水温、空气温度、空气含湿量和空气流速对水滴蒸发过冷过程的影响.结果表明,水滴初始直径越小、温度越低或空气流速越大,

  4. Using Peltier cells to study solid-liquid-vapour transitions and supercooling

    Energy Technology Data Exchange (ETDEWEB)

    Torzo, Giacomo [ICIS-CNR and Physics Department of Padova University, Padova (Italy); Soletta, Isabella [Liceo Scientifico Fermi, Alghero (Italy); Branca, Mario [Chemical Department of Sassari University, Sassari (Italy)

    2007-05-15

    We propose an apparatus for teaching experimental thermodynamics in undergraduate introductory courses, using thermoelectric modules and a real-time data acquisition system. The device may be made at low cost, still providing an easy approach to the investigation of liquid-solid and liquid-vapour phase transitions and of metastable states (supercooling). The thermoelectric module (a technological evolution of the thermocouple) is by itself an interesting subject that offers a clear example of both thermo-electric (Seebeck effect) and electro-thermal (Peltier effect) energy transformation. We report here some cooling/heating measurements for several liquids and mixtures, including water, salt/water, ethanol/water and sodium acetate, showing how to evaluate the phenomena of freezing point depression and elevation, and how to evaluate the water latent heat.

  5. Using Peltier cells to study solid liquid vapour transitions and supercooling

    Science.gov (United States)

    Torzo, Giacomo; Soletta, Isabella; Branca, Mario

    2007-05-01

    We propose an apparatus for teaching experimental thermodynamics in undergraduate introductory courses, using thermoelectric modules and a real-time data acquisition system. The device may be made at low cost, still providing an easy approach to the investigation of liquid solid and liquid vapour phase transitions and of metastable states (supercooling). The thermoelectric module (a technological evolution of the thermocouple) is by itself an interesting subject that offers a clear example of both thermo-electric (Seebeck effect) and electro-thermal (Peltier effect) energy transformation. We report here some cooling/heating measurements for several liquids and mixtures, including water, salt/water, ethanol/water and sodium acetate, showing how to evaluate the phenomena of freezing point depression and elevation, and how to evaluate the water latent heat.

  6. The glass crossover from mean-field Spin-Glasses to supercooled liquids

    Science.gov (United States)

    Rizzo, Tommaso

    2016-03-01

    Stochastic-Beta-Relaxation provides a characterisation of the glass crossover in discontinuous Spin-Glasses and supercoooled liquid. Notably it can be derived through a rigorous computation from a dynamical Landau theory. In this paper, I will discuss the precise meaning of this connection in a language that does not require familiarity with statistical field theory. I will discuss finite-size corrections in mean-field Spin-Glass models and loop corrections in finite-dimensional models that are both described by the dynamical Landau theory considered. Then I will argue that the same Landau theory can be associated to supercooled liquid described by Mode-Coupling Theory invoking a physical principle of time-scale invariance.

  7. A maximum-entropy approach to the adiabatic freezing of a supercooled liquid.

    Science.gov (United States)

    Prestipino, Santi

    2013-04-28

    I employ the van der Waals theory of Baus and co-workers to analyze the fast, adiabatic decay of a supercooled liquid in a closed vessel with which the solidification process usually starts. By imposing a further constraint on either the system volume or pressure, I use the maximum-entropy method to quantify the fraction of liquid that is transformed into solid as a function of undercooling and of the amount of a foreign gas that could possibly be also present in the test tube. Upon looking at the implications of thermal and mechanical insulation for the energy cost of forming a solid droplet within the liquid, I identify one situation where the onset of solidification inevitably occurs near the wall in contact with the bath.

  8. Size dependence of volume and surface nucleation rates for homogeneous freezing of supercooled water droplets

    Directory of Open Access Journals (Sweden)

    T. Kuhn

    2009-10-01

    Full Text Available We investigated the relative roles of volume and surface nucleation in the freezing of water droplets. Nucleation experiments were carried out in a cryogenic laminar aerosol flow tube using supercooled liquid water aerosols with radii between about 1 and 3 μ m. Temperature- and size-dependent values of volume- and surface-based homogeneous nucleation rate between 234.8 and 236.2 K are derived with help of a microphysical model from aerosol compositions and size distributions based on infrared extinction measurements in the aerosol flow tube. The results show that the contribution from nucleation at the droplet surface increases with decreasing droplet radius and dominates over nucleation in the bulk droplet volume for droplets with radii smaller than approximately 5 μm. This is interpreted in terms of a lowered free energy of ice germ formation in the surface-based process and has implications for the parameterization of homogeneous ice nucleation in numerical models.

  9. Volume and structural analysis of super-cooled water under high pressure

    Science.gov (United States)

    Duki, Solomon F.; Tsige, Mesfin

    2012-02-01

    Motivated by recent experimental study of super-cooled water at high pressure [1], we performed atomistic molecular dynamic simulations study on bulk water molecules at isothermal-isobaric ensemble. These simulations are performed at temperatures that range from 40 K to 380 K using two different cooling rates, 10K/ns and 10K/5ns, and pressure that ranges from 1atm to 10000 atm. Our analysis for the variation of the volume of the bulk sample against temperature indicates a downward concave shape for pressures above certain values, as reported in [1]. The same downward concave behavior is observed at high pressure on the mean-squared-displacements (MSD) of the water molecules when the MSD is plotted against time. To get further insight on the effect of the pressure on the sample we have also performed a structural analysis of the sample.[4pt] [1] O. Mishima, J. Chem. Phys. 133, 144503 (2010);

  10. Water and its relatives: the stable, supercooled and particularly the stretched, regimes

    CERN Document Server

    Meadley, Stacey L

    2014-01-01

    While the water molecule is simple, its condensed phase liquid behavior is so complex that no consensus description has emerged despite three centuries of effort. Here we identify features of its behavior that are the most peculiar, hence suggest ways forward. We examine the properties of water at the boundaries of common experience, including stable states at high pressure, the supercooled state at normal and elevated pressure, and the stretched ("negative pressure") state, out to the limits of mechanical stability. The familiar anomalies at moderate pressures (viscosity and density (TMD) behavior, etc.), are not explained by H-bond breaking, according to common bond-breaking criteria. A comparison of data on the TMD, at both positive and negative pressures, with the predictions of popular pair potential models, shows dramatic discrepancies appearing in the stretched liquid domain. This prompts questions on the second critical point (TC2) hypothesis that has been guiding much current thinking. We turn to rel...

  11. Crystallization behavior of supercooled smectic cholesteryl myristate nanoparticles containing phospholipids as stabilizers

    DEFF Research Database (Denmark)

    Kuntsche, Judith; Koch, Michel; Drechsler, M;

    2005-01-01

    Supercooled smectic nanoparticles based on physiological cholesterol esters are under investigation as a potential novel carrier system for lipophilic drugs. The present study investigates the very complex crystallization behavior of such nanoparticles stabilized with the aid of phospholipids....... Phospholipid and phospholipid/bile salt stabilized cholesteryl myristate dispersions were prepared by high-pressure melt homogenization and characterized by particle size measurements, differential scanning calorimetry, X-ray diffraction and electron microscopy. To obtain fractions with very small smectic...... nanoparticles, selected dispersions were ultracentrifuged. A mixture of cholesteryl myristate and the phospholipid used for the stabilization of the dispersions was also investigated by light microscopy. The nanoparticles usually display a bimodal crystallization event which depends on the thermal treatment...

  12. Local structure of equilibrium and supercooled Ti-Zr-Ni liquids

    Energy Technology Data Exchange (ETDEWEB)

    Lee, G. W.; Gangopadhyay, A.; Hyers, R.; Rathz, T.; Rogers, J.; Robinson, D.; Goldman, A.; Kelton, K.

    2008-05-01

    Recently, we reported the results of experimental in situ high-energy x-ray diffraction studies of electrostatically levitated equilibrium and supercooled metallic elements and alloy liquids, showing evidence for icosahedral short-range ordering (ISRO). In this paper, these studies are extended to binary Ti-Zr and ternary Ti-Zr-Ni alloys. From a cluster-based analysis of the x-ray structure factors, it is concluded that ISRO in the binary alloys becomes progressively more dominant, and the coherence length of the order becomes longer, with the addition of Ni, especially near the concentration of 21 at. % Ni. The effect of chemical interactions among Ti/Zr-Ni and the atomic size on the stabilization of the ISRO is discussed.

  13. Stable glass transformation to supercooled liquid via surface-initiated growth front.

    Science.gov (United States)

    Swallen, Stephen F; Traynor, Katherine; McMahon, Robert J; Ediger, M D; Mates, Thomas E

    2009-02-13

    Highly stable glasses of tris-naphthylbenzene transform into a liquid when annealed above the glass transition temperature T_{g}. In contrast to the predictions of standard models, the observed transformation is spatially inhomogeneous. Secondary ion mass spectrometry experiments on isotopically labeled multilayer films show that the liquid grows into the stable glass with sharp growth fronts initiated at the free surface and at the interface with the substrate. For the free surface, the growth velocity is constant in time and has the same temperature dependence as self-diffusion in the equilibrium supercooled liquid. These stable glasses are packed so efficiently that surfaces and interfaces are required to initiate the transformation to the liquid even well above T_{g}.

  14. Electron Correlation Microscopy: A New Technique for Studying Local Atom Dynamics Applied to a Supercooled Liquid.

    Science.gov (United States)

    He, Li; Zhang, Pei; Besser, Matthew F; Kramer, Matthew Joseph; Voyles, Paul M

    2015-08-01

    Electron correlation microscopy (ECM) is a new technique that utilizes time-resolved coherent electron nanodiffraction to study dynamic atomic rearrangements in materials. It is the electron scattering equivalent of photon correlation spectroscopy with the added advantage of nanometer-scale spatial resolution. We have applied ECM to a Pd40Ni40P20 metallic glass, heated inside a scanning transmission electron microscope into a supercooled liquid to measure the structural relaxation time τ between the glass transition temperature T g and the crystallization temperature, T x . τ determined from the mean diffraction intensity autocorrelation function g 2(t) decreases with temperature following an Arrhenius relationship between T g and T g +25 K, and then increases as temperature approaches T x . The distribution of τ determined from the g 2(t) of single speckles is broad and changes significantly with temperature.

  15. Vibrating-Wire, Supercooled Liquid Water Content Sensor Calibration and Characterization Progress

    Science.gov (United States)

    King, Michael C.; Bognar, John A.; Guest, Daniel; Bunt, Fred

    2016-01-01

    NASA conducted a winter 2015 field campaign using weather balloons at the NASA Glenn Research Center to generate a validation database for the NASA Icing Remote Sensing System. The weather balloons carried a specialized, disposable, vibrating-wire sensor to determine supercooled liquid water content aloft. Significant progress has been made to calibrate and characterize these sensors. Calibration testing of the vibrating-wire sensors was carried out in a specially developed, low-speed, icing wind tunnel, and the results were analyzed. The sensor ice accretion behavior was also documented and analyzed. Finally, post-campaign evaluation of the balloon soundings revealed a gradual drift in the sensor data with increasing altitude. This behavior was analyzed and a method to correct for the drift in the data was developed.

  16. Deformation behavior of Zr-based bulk metallic glass and composite in the supercooled liquid region

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    A Zr-based bulk metallic glass (BMG) with a composition of (Zr75Cu25)78.5Ta4Ni10Al7.5 and a bulk metallic glass matrix composite (BMGC) with a composition of (Zr75Cu25)74.5Ta8Ni10Al7.5 have been prepared by copper-mold casting. The compres-sive deformation behavior of the BMG and BMGC was investigated in the super-cooled region at different temperatures and various strain rates ranging from 8×10-4s-1 to 8×10-2s-1. It was found that both the strain rate and test temperature signifi-cantly affect the deformation behavior of the two alloys. The deformation follows Newtonian flow at low strain rates but non-Newtonian flow at high strain rates. The deformation mechanism for the two kinds of alloys was discussed in terms of the transition state theory.

  17. Correlation between supercooled liquid relaxation and glass poisson’s ratio

    DEFF Research Database (Denmark)

    Sun, Q.J.; Hu, L.N.; Zhou, C.

    2015-01-01

    We report on a correlation between the supercooled liquid (SL) relaxation and glass Poisson’s ratio (v) by comparing the activation energy ratio (r) of the α and the slow β relaxations and the v values for both metallic and nonmetallic glasses. Poisson’s ratio v generally increases with an increase...... in the ratio r and this relation can be described by the empirical function v = 0.5 − A ∗ exp(−B ∗ r), where A and B are constants. This correlation might imply that glass plasticity is associated with the competition between the α and the slow β relaxations in SLs. The underlying physics of this correlation...

  18. Local order in a supercooled colloidal fluid observed by confocal microscopy

    CERN Document Server

    Gasser, U; Weitz, D A

    2003-01-01

    The local order in a supercooled monodisperse colloidal fluid is studied by direct imaging of the particles with a laser scanning confocal microscope. The local structure is analysed with a bond order parameter method, which allows one to discern simple structures that are relevant in this system. As expected for samples that crystallize eventually, a large fraction of the particles are found to sit in surroundings with dominant face-centred cubic or hexagonally close-packed character. Evidence for local structures that contain fragments of icosahedra is found, and, moreover, the icosahedral character increases with volume fraction phi, which indicates that it might play an important role at volume fractions near the glass transition.

  19. Local order in a supercooled colloidal fluid observed by confocal microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Gasser, U [Department of Physics and Division of Engineering and Applied Sciences, Harvard University, Cambridge, MA (United States); Schofield, Andrew [Department of Physics and Astronomy, University of Edinburgh, Edinburgh (United Kingdom); Weitz, D A [Department of Physics and Division of Engineering and Applied Sciences, Harvard University, Cambridge, MA (United States)

    2003-01-15

    The local order in a supercooled monodisperse colloidal fluid is studied by direct imaging of the particles with a laser scanning confocal microscope. The local structure is analysed with a bond order parameter method, which allows one to discern simple structures that are relevant in this system. As expected for samples that crystallize eventually, a large fraction of the particles are found to sit in surroundings with dominant face-centred cubic or hexagonally close-packed character. Evidence for local structures that contain fragments of icosahedra is found, and, moreover, the icosahedral character increases with volume fraction {phi}, which indicates that it might play an important role at volume fractions near the glass transition.

  20. Hybrid cloud for dummies

    CERN Document Server

    Hurwitz, Judith; Halper, Fern; Kirsch, Dan

    2012-01-01

    Understand the cloud and implement a cloud strategy for your business Cloud computing enables companies to save money by leasing storage space and accessing technology services through the Internet instead of buying and maintaining equipment and support services. Because it has its own unique set of challenges, cloud computing requires careful explanation. This easy-to-follow guide shows IT managers and support staff just what cloud computing is, how to deliver and manage cloud computing services, how to choose a service provider, and how to go about implementation. It also covers security and

  1. Secure cloud computing

    CERN Document Server

    Jajodia, Sushil; Samarati, Pierangela; Singhal, Anoop; Swarup, Vipin; Wang, Cliff

    2014-01-01

    This book presents a range of cloud computing security challenges and promising solution paths. The first two chapters focus on practical considerations of cloud computing. In Chapter 1, Chandramouli, Iorga, and Chokani describe the evolution of cloud computing and the current state of practice, followed by the challenges of cryptographic key management in the cloud. In Chapter 2, Chen and Sion present a dollar cost model of cloud computing and explore the economic viability of cloud computing with and without security mechanisms involving cryptographic mechanisms. The next two chapters addres

  2. Ice-lens formation and geometrical supercooling in soils and other colloidal materials

    KAUST Repository

    Style, Robert W.

    2011-10-14

    We present a physically intuitive model of ice-lens formation and growth during the freezing of soils and other dense, particulate suspensions. Motivated by experimental evidence, we consider the growth of an ice-filled crack in a freezing soil. At low temperatures, ice in the crack exerts large pressures on the crack walls that will eventually cause the crack to split open. We show that the crack will then propagate across the soil to form a new lens. The process is controlled by two factors: the cohesion of the soil and the geometrical supercooling of the water in the soil, a new concept introduced to measure the energy available to form a new ice lens. When the supercooling exceeds a critical amount (proportional to the cohesive strength of the soil) a new ice lens forms. This condition for ice-lens formation and growth does not appeal to any ad hoc, empirical assumptions, and explains how periodic ice lenses can form with or without the presence of a frozen fringe. The proposed mechanism is in good agreement with experiments, in particular explaining ice-lens pattern formation and surges in heave rate associated with the growth of new lenses. Importantly for systems with no frozen fringe, ice-lens formation and frost heave can be predicted given only the unfrozen properties of the soil. We use our theory to estimate ice-lens growth temperatures obtaining quantitative agreement with the limited experimental data that are currently available. Finally we suggest experiments that might be performed in order to verify this theory in more detail. The theory is generalizable to complex natural-soil scenarios and should therefore be useful in the prediction of macroscopic frost-heave rates. © 2011 American Physical Society.

  3. A Laboratory Study on the Phase Transition for Polar Stratospheric Cloud Particles

    Science.gov (United States)

    Teets, Edward H., Jr.

    1997-01-01

    The nucleation and growth of different phases of simulated polar stratospheric cloud (PSC) particles were investigated in the laboratory. Solutions and mixtures of solutions at concentrations 1 to 5 m (molality) of ammonium sulfate, ammonium bisulfate, sodium chloride, sulfuric acid, and nitric acid were supercooled to prescribed temperatures below their equilibrium melting point. These solutions were contained in small diameter glass tubing of volumes ranging from 2.6 to 0.04 ml. Samples were nucleated by insertion of an ice crystal, or in some cases by a liquid nitrogen cooled wire. Crystallization velocities were determined by timing the crystal growth front passages along the glass tubing. Solution mixtures containing aircraft exhaust (soot) were also examined. Crystallization rates increased as deltaT2, where deltaT is the supercooling for weak solutions (2 m or less). The higher concentrated solutions (greater than 3 m) showed rates significantly less than deltaT2. This reduced rate suggested an onset of a glass phase. Results were applied to the nucleation of highly concentrated solutions at various stages of polar stratospheric cloud development within the polar stratosphere.

  4. Cloud Processed CCN Affect Cloud Microphysics

    Science.gov (United States)

    Hudson, J. G.; Noble, S. R., Jr.; Tabor, S. S.

    2015-12-01

    Variations in the bimodality/monomodality of CCN spectra (Hudson et al. 2015) exert opposite effects on cloud microphysics in two aircraft field projects. The figure shows two examples, droplet concentration, Nc, and drizzle liquid water content, Ld, against classification of CCN spectral modality. Low ratings go to balanced separated bimodal spectra, high ratings go to single mode spectra, strictly monomodal 8. Intermediate ratings go merged modes, e.g., one mode a shoulder of another. Bimodality is caused by mass or hygroscopicity increases that go only to CCN that made activated cloud droplets. In the Ice in Clouds Experiment-Tropical (ICE-T) small cumuli with lower Nc, greater droplet mean diameters, MD, effective radii, re, spectral widths, σ, cloud liquid water contents, Lc, and Ld were closer to more bimodal (lower modal ratings) below cloud CCN spectra whereas clouds with higher Nc, smaller MD, re, σ, and Ld were closer to more monomodal CCN (higher modal ratings). In polluted stratus clouds of the MArine Stratus/Stratocumulus Experiment (MASE) clouds that had greater Nc, and smaller MD, re, σ, Lc, and Ld were closer to more bimodal CCN spectra whereas clouds with lower Nc, and greater MD, re, σ, Lc, and Ld were closer to more monomodal CCN. These relationships are opposite because the dominant ICE-T cloud processing was coalescence whereas chemical transformations (e.g., SO2 to SO4) were dominant in MASE. Coalescence reduces Nc and thus also CCN concentrations (NCCN) when droplets evaporate. In subsequent clouds the reduced competition increases MD and σ, which further enhance coalescence and drizzle. Chemical transformations do not change Nc but added sulfate enhances droplet and CCN solubility. Thus, lower critical supersaturation (S) CCN can produce more cloud droplets in subsequent cloud cycles, especially for the low W and effective S of stratus. The increased competition reduces MD, re, and σ, which inhibit coalescence and thus reduce drizzle

  5. Moving towards Cloud Security

    Directory of Open Access Journals (Sweden)

    Edit Szilvia Rubóczki

    2015-01-01

    Full Text Available Cloud computing hosts and delivers many different services via Internet. There are a lot of reasons why people opt for using cloud resources. Cloud development is increasing fast while a lot of related services drop behind, for example the mass awareness of cloud security. However the new generation upload videos and pictures without reason to a cloud storage, but only few know about data privacy, data management and the proprietary of stored data in the cloud. In an enterprise environment the users have to know the rule of cloud usage, however they have little knowledge about traditional IT security. It is important to measure the level of their knowledge, and evolve the training system to develop the security awareness. The article proves the importance of suggesting new metrics and algorithms for measuring security awareness of corporate users and employees to include the requirements of emerging cloud security.

  6. In the clouds

    NARCIS (Netherlands)

    Wassink, J.

    2012-01-01

    Clouds always used to be the least understood element of the weather system, but that is rapidly changing . Computer clouds increasingly correspond with those in the sky, which promises weather forecasts at street level and more accurate climate scenarios.

  7. Cloud Computing for radiologists.

    Science.gov (United States)

    Kharat, Amit T; Safvi, Amjad; Thind, Ss; Singh, Amarjit

    2012-07-01

    Cloud computing is a concept wherein a computer grid is created using the Internet with the sole purpose of utilizing shared resources such as computer software, hardware, on a pay-per-use model. Using Cloud computing, radiology users can efficiently manage multimodality imaging units by using the latest software and hardware without paying huge upfront costs. Cloud computing systems usually work on public, private, hybrid, or community models. Using the various components of a Cloud, such as applications, client, infrastructure, storage, services, and processing power, Cloud computing can help imaging units rapidly scale and descale operations and avoid huge spending on maintenance of costly applications and storage. Cloud computing allows flexibility in imaging. It sets free radiology from the confines of a hospital and creates a virtual mobile office. The downsides to Cloud computing involve security and privacy issues which need to be addressed to ensure the success of Cloud computing in the future.

  8. Variability of the TRMM-PR total and convective and stratiform rain fractions over the Indian region during the summer monsoon

    Science.gov (United States)

    Pokhrel, Samir; Sikka, D. R.

    2013-07-01

    Level 3 (3A25) TRMM Precipitation Radar (PR) data are used for 13 years period (1998-2010) to prepare climatology of TRMM PR derived near surface rain (Total rain) and rain fractions for the 4-months duration of Indian Summer Monsoon season (June-September) as well as for individual months. It is found that the total rain is contributed mostly (99 %) by two rain fractions i.e. stratiform and convective rain fractions for the season as well as on the monthly basis. It is also found that total rain estimates by PR are about 65 % of the gauge measured rain over continental India as well as on sub-regional basis. Inter-annual variability of TRMM-PR rain estimates for India mainland and its sub-regions as well as over the neighboring oceanic regions, in terms of coefficient of variability (CV) is discussed. The heaviest rain region over north Bay of Bengal (BoB) is found to have the lowest CV. Another sub-region of low CV lies over the eastern equatorial Indian ocean (EEIO). The CVs of total rain as well as its two major constituents are found to be higher on monthly basis compared to seasonal basis. Existence of a well known dipole between the EEIO and the north BoB is well recognized in PR data also. Significant variation in PR rainfall is found over continental India between excess and deficit monsoon seasons as well as between excess and deficit rainfall months of July and August. Examination of rainfall fractions between the BoB and Central India on year to year basis shows that compensation in rainfall fractions exists on monthly scale on both the regions. Also on the seasonal and monthly scales, compensation is observed in extreme monsoon seasons between the two regions. However, much less compensation is observed between the north BoB and EEIO belts in extreme rain months. This leads to speculation that the deficit and excess seasons over India may result from slight shift of the rainfall from Central India to the neighboring oceanic regions of north Bo

  9. Breaking through the Glass Ceiling: The Correlation Between the Self-Diffusivity in and Krypton Permeation through Deeply Supercooled Liquid Nanoscale Methanol Films

    Energy Technology Data Exchange (ETDEWEB)

    Smith, R. Scott; Matthiesen, Jesper; Kay, Bruce D.

    2010-03-28

    Molecular beam techniques, temperature-programmed desorption (TPD), and reflection absorption infrared spectroscopy (RAIRS) are used to explore the relationship between krypton permeation through and the self-diffusivity of supercooled liquid methanol at temperatures near (100-115 K) the glass transition temperature, Tg (103 K). Layered films, consisting of CH3OH and CD3OH, are deposited ontop of a monolayer of Kr on a graphene covered Pt(111) substrate at 25 K. Concurrent Kr TPD and RAIRS spectra are acquired during the heating of the composite film to temperatures above Tg. The CO vibrational stretch is sensitive to the local molecular environment and is used to determine the supercooled liquid diffusivity from the intermixing of the isotopic layers. We find that the Kr permeation and the diffusivity of the supercooled liquid are directly and quantitatively correlated. These results validate the rare gas permeation technique as a tool for probing the diffusivity of supercooled liquids.

  10. Breaking through the glass ceiling: The correlation between the self-diffusivity in and krypton permeation through deeply supercooled liquid nanoscale methanol films

    Science.gov (United States)

    Smith, R. Scott; Matthiesen, Jesper; Kay, Bruce D.

    2010-03-01

    Molecular beam techniques, temperature-programmed desorption (TPD), and reflection absorption infrared spectroscopy (RAIRS) are used to explore the relationship between krypton permeation through and the self-diffusivity of supercooled liquid methanol at temperatures (100-115 K) near the glass transition temperature, Tg (103 K). Layered films, consisting of CH3OH and CD3OH, are deposited on top of a monolayer of Kr on a graphene covered Pt(111) substrate at 25 K. Concurrent Kr TPD and RAIRS spectra are acquired during the heating of the composite film to temperatures above Tg. The CO vibrational stretch is sensitive to the local molecular environment and is used to determine the supercooled liquid diffusivity from the intermixing of the isotopic layers. We find that the Kr permeation and the diffusivity of the supercooled liquid are directly and quantitatively correlated. These results validate the rare-gas permeation technique as a tool for probing the diffusivity of supercooled liquids.

  11. Computer animation of clouds

    Energy Technology Data Exchange (ETDEWEB)

    Max, N.

    1994-01-28

    Computer animation of outdoor scenes is enhanced by realistic clouds. I will discuss several different modeling and rendering schemes for clouds, and show how they evolved in my animation work. These include transparency-textured clouds on a 2-D plane, smooth shaded or textured 3-D clouds surfaces, and 3-D volume rendering. For the volume rendering, I will present various illumination schemes, including the density emitter, single scattering, and multiple scattering models.

  12. Computer animation of clouds

    Energy Technology Data Exchange (ETDEWEB)

    Max, N.

    1994-01-28

    Computer animation of outdoor scenes is enhanced by realistic clouds. I will discuss several different modeling and rendering schemes for clouds, and show how they evolved in my animation work. These include transparency-textured clouds on a 2-D plane, smooth shaded or textured 3-D clouds surfaces, and 3-D volume rendering. For the volume rendering, I will present various illumination schemes, including the density emitter, single scattering, and multiple scattering models.

  13. Comparing Point Clouds

    Science.gov (United States)

    2004-04-01

    Point clouds are one of the most primitive and fundamental surface representations. A popular source of point clouds are three dimensional shape...acquisition devices such as laser range scanners. Another important field where point clouds are found is in the representation of high-dimensional...framework for comparing manifolds given by point clouds is presented in this paper. The underlying theory is based on Gromov-Hausdorff distances, leading

  14. Cloud computing strategies

    CERN Document Server

    Chorafas, Dimitris N

    2011-01-01

    A guide to managing cloud projects, Cloud Computing Strategies provides the understanding required to evaluate the technology and determine how it can be best applied to improve business and enhance your overall corporate strategy. Based on extensive research, it examines the opportunities and challenges that loom in the cloud. It explains exactly what cloud computing is, what it has to offer, and calls attention to the important issues management needs to consider before passing the point of no return regarding financial commitments.

  15. Governmental Cloud - Part of Cloud Computing

    Directory of Open Access Journals (Sweden)

    Cristian IVANUS

    2014-01-01

    Full Text Available Large IT (Information Technology companies propose cloud government's (G-Cloud development model through investment from the private sector, which will facilitate the access of users from public sector to the new generation IT services. Through the G-Cloud private operators that operate governmental cloud infrastructure by adding specific SaaS (Software as a Service functionalities, proposed model by big companies, supports public institutions in optimizing costs and increased operational efficiency, bringing tangible benefits in relation with citizens and thus with the whole society. These optimizations are achieved by moving the initial investment to the private sector, through type subscription model cost by eliminating dependency on human factors (technical and by providing a low cost [1]. This paper aims to bring to the attention of specialists, some aspects of Governmental Cloud from the European Union (EU countries to be understood and implemented in Romania.

  16. Security in the cloud.

    Science.gov (United States)

    Degaspari, John

    2011-08-01

    As more provider organizations look to the cloud computing model, they face a host of security-related questions. What are the appropriate applications for the cloud, what is the best cloud model, and what do they need to know to choose the best vendor? Hospital CIOs and security experts weigh in.

  17. On clocks and clouds

    Directory of Open Access Journals (Sweden)

    M. K. Witte

    2013-09-01

    Full Text Available Cumulus clouds exhibit a life cycle that consists of: (a the growth phase (increasing size, most notably in the vertical direction; (b the mature phase (growth ceases; any precipitation that develops is strongest during this period; and (c the dissipation phase (cloud dissipates because of precipitation and/or entrainment; no more dynamical support. Although radar can track clouds over time and give some sense of the age of a cloud, most aircraft in situ measurements lack temporal context. We use large eddy simulations of trade wind cumulus cloud fields from cases during the Barbados Oceanographic and Meteorological Experiment (BOMEX and Rain In Cumulus over the Ocean (RICO campaigns to demonstrate a potential cumulus cloud "clock". We find that the volume-averaged total water mixing ratio rt is a useful cloud clock for the 12 clouds studied. A cloud's initial rt is set by the subcloud mixed-layer mean rt and decreases monotonically from the initial value due primarily to entrainment. The clock is insensitive to aerosol loading, environmental sounding and extrinsic cloud properties such as lifetime and volume. In some cases (more commonly for larger clouds, multiple pulses of buoyancy occur, which complicate the cumulus clock by replenishing rt. The clock is most effectively used to classify clouds by life phase.

  18. Cloud Computing Explained

    Science.gov (United States)

    Metz, Rosalyn

    2010-01-01

    While many talk about the cloud, few actually understand it. Three organizations' definitions come to the forefront when defining the cloud: Gartner, Forrester, and the National Institutes of Standards and Technology (NIST). Although both Gartner and Forrester provide definitions of cloud computing, the NIST definition is concise and uses…

  19. Cloud Computing Explained

    Science.gov (United States)

    Metz, Rosalyn

    2010-01-01

    While many talk about the cloud, few actually understand it. Three organizations' definitions come to the forefront when defining the cloud: Gartner, Forrester, and the National Institutes of Standards and Technology (NIST). Although both Gartner and Forrester provide definitions of cloud computing, the NIST definition is concise and uses…

  20. On CLOUD nine

    CERN Multimedia

    2009-01-01

    The team from the CLOUD experiment - the world’s first experiment using a high-energy particle accelerator to study the climate - were on cloud nine after the arrival of their new three-metre diameter cloud chamber. This marks the end of three years’ R&D and design, and the start of preparations for data taking later this year.

  1. Response of the Nevzorov hot wire probe in Arctic clouds dominated by very large droplet sizes

    Directory of Open Access Journals (Sweden)

    A. Schwarzenboeck

    2009-05-01

    Full Text Available During the airborne research mission ASTAR 2004 (Arctic Study of Tropospheric Aerosols, Clouds and Radiation performed over the island of Svalbard in the Arctic a constant-temperature hot-wire Nevzorov Probe designed for aircraft measurements, has been used onboard the aircraft POLAR 2. The Nevzorov probe measured liquid water (LWC and total condensed water content (TWC in supercooled liquid and partly mixed phase clouds, respectively. As for other hotwire probes the calculation of LWC and/or TWC (and thus the ice water content IWC has to take into account the collection efficiencies of the two separate sensors for LWC and TWC which both react differently with respect to cloud phase and what is even more difficult to quantify with respect to the size of ice and liquid cloud particles. The study demonstrates that during pure liquid cloud sequences the ASTAR data set of the Nevzorov probe allowed to improve the quantification of the collection efficiency, particularly of the LWC probe part with respect to water. The improved quantification of liquid water content should lead to improved retrievals of IWC content. Simultaneous retrievals of LWC and IWC are correlated with the asymmetry factor derived from the Polar Nephelometer instrument.

  2. Intergalactic HI Clouds

    CERN Document Server

    Briggs, F H

    2005-01-01

    Neutral intergalactic clouds are so greatly out numbered by galaxies that their integral HI content is negligible in comparison to that contained in optically luminous galaxies. In fact, no HI cloud that is not associated with a galaxy or grouping of galaxies has yet been identified. This points to a causal relationship that relies on gravitational potentials that bind galaxies also being responsible for confining HI clouds to sufficient density that they can become self-shielding to the ionizing background radiation. Unconfined clouds of low density become ionized, but confined clouds find themselves vulnerable to instability and collapse, leading to star formation.

  3. Cloud Computing Bible

    CERN Document Server

    Sosinsky, Barrie

    2010-01-01

    The complete reference guide to the hot technology of cloud computingIts potential for lowering IT costs makes cloud computing a major force for both IT vendors and users; it is expected to gain momentum rapidly with the launch of Office Web Apps later this year. Because cloud computing involves various technologies, protocols, platforms, and infrastructure elements, this comprehensive reference is just what you need if you'll be using or implementing cloud computing.Cloud computing offers significant cost savings by eliminating upfront expenses for hardware and software; its growing popularit

  4. Cloud Computing Quality

    Directory of Open Access Journals (Sweden)

    Anamaria Şiclovan

    2013-02-01

    Full Text Available Cloud computing was and it will be a new way of providing Internet services and computers. This calculation approach is based on many existing services, such as the Internet, grid computing, Web services. Cloud computing as a system aims to provide on demand services more acceptable as price and infrastructure. It is exactly the transition from computer to a service offered to the consumers as a product delivered online. This paper is meant to describe the quality of cloud computing services, analyzing the advantages and characteristics offered by it. It is a theoretical paper.Keywords: Cloud computing, QoS, quality of cloud computing

  5. Cloud Computing Technologies

    Directory of Open Access Journals (Sweden)

    Sean Carlin

    2012-06-01

    Full Text Available This paper outlines the key characteristics that cloud computing technologies possess and illustrates the cloud computing stack containing the three essential services (SaaS, PaaS and IaaS that have come to define the technology and its delivery model. The underlying virtualization technologies that make cloud computing possible are also identified and explained. The various challenges that face cloud computing technologies today are investigated and discussed. The future of cloud computing technologies along with its various applications and trends are also explored, giving a brief outlook of where and how the technology will progress into the future.

  6. Free energy of formation of small ice nuclei near the Widom line in simulations of supercooled water.

    Science.gov (United States)

    Buhariwalla, Connor R C; Bowles, Richard K; Saika-Voivod, Ivan; Sciortino, Francesco; Poole, Peter H

    2015-05-01

    The ST2 interaction potential has been used in a large number of simulation studies to explore the possibility of a liquid-liquid phase transition (LLPT) in supercooled water. Using umbrella sampling Monte Carlo simulations of ST2 water, we evaluate the free energy of formation of small ice nuclei in the supercooled liquid in the vicinity of the Widom line, the region above the critical temperature of the LLPT where a number of thermodynamic anomalies occur. Our results show that in this region there is a substantial free-energy cost for the formation of small ice nuclei, demonstrating that the thermodynamic anomalies associated with the Widom line in ST2 water occur in a well-defined metastable liquid phase. On passing through the Widom line, we identify changes in the free energy to form small ice nuclei that illustrate how the thermodynamic anomalies associated with the LLPT may influence the ice nucleation process.

  7. Turbulent heat transfer as a control of platelet ice growth in supercooled under-ice ocean boundary layers

    Science.gov (United States)

    McPhee, Miles G.; Stevens, Craig L.; Smith, Inga J.; Robinson, Natalie J.

    2016-04-01

    Late winter measurements of turbulent quantities in tidally modulated flow under land-fast sea ice near the Erebus Glacier Tongue, McMurdo Sound, Antarctica, identified processes that influence growth at the interface of an ice surface in contact with supercooled seawater. The data show that turbulent heat exchange at the ocean-ice boundary is characterized by the product of friction velocity and (negative) water temperature departure from freezing, analogous to similar results for moderate melting rates in seawater above freezing. Platelet ice growth appears to increase the hydraulic roughness (drag) of fast ice compared with undeformed fast ice without platelets. Platelet growth in supercooled water under thick ice appears to be rate-limited by turbulent heat transfer and that this is a significant factor to be considered in mass transfer at the underside of ice shelves and sea ice in the vicinity of ice shelves.

  8. Pressure Induced Liquid-to-Liquid Transition in Zr-based Supercooled Melts and Pressure Quenched Glasses

    Energy Technology Data Exchange (ETDEWEB)

    Dmowski, W.; Gierlotka, S.; Wang, Z.; Yokoyama, Y.; Palosz, B.; Egami, T.

    2017-07-26

    Through high-energy x-ray diffraction and atomic pair density function analysis we find that Zr-based metallic alloy, heated to the supercooled liquid state under hydrostatic pressure and then quenched to room temperature, exhibits a distinct glassy structure. The PDF indicates that the Zr-Zr distances in this glass are significantly reduced compared to those quenched without pressure. Annealing at the glass transition temperature at ambient pressure reverses structural changes and the initial glassy state is recovered. This result suggests that pressure causes a liquid-to-liquid phase transition in this metallic alloy supercooled melt. Such a pressure induced transition is known for covalent liquids, but has not been observed for metallic liquids. The High Pressure Quenched glasses are stable in ambient conditions after decompression.

  9. CLOUD COMPUTING SECURITY

    Directory of Open Access Journals (Sweden)

    Ştefan IOVAN

    2016-05-01

    Full Text Available Cloud computing reprentes the software applications offered as a service online, but also the software and hardware components from the data center.In the case of wide offerd services for any type of client, we are dealing with a public cloud. In the other case, in wich a cloud is exclusively available for an organization and is not available to the open public, this is consider a private cloud [1]. There is also a third type, called hibrid in which case an user or an organization might use both services available in the public and private cloud. One of the main challenges of cloud computing are to build the trust and ofer information privacy in every aspect of service offerd by cloud computingle. The variety of existing standards, just like the lack of clarity in sustenability certificationis not a real help in building trust. Also appear some questions marks regarding the efficiency of traditionsecurity means that are applied in the cloud domain. Beside the economic and technology advantages offered by cloud, also are some advantages in security area if the information is migrated to cloud. Shared resources available in cloud includes the survey, use of the "best practices" and technology for advance security level, above all the solutions offered by the majority of medium and small businesses, big companies and even some guvermental organizations [2].

  10. Two-structure thermodynamics for the TIP4P/2005 model of water covering supercooled and deeply stretched regions

    Science.gov (United States)

    Biddle, John W.; Singh, Rakesh S.; Sparano, Evan M.; Ricci, Francesco; González, Miguel A.; Valeriani, Chantal; Abascal, José L. F.; Debenedetti, Pablo G.; Anisimov, Mikhail A.; Caupin, Frédéric

    2017-01-01

    One of the most promising frameworks for understanding the anomalies of cold and supercooled water postulates the existence of two competing, interconvertible local structures. If the non-ideality in the Gibbs energy of mixing overcomes the ideal entropy of mixing of these two structures, a liquid-liquid phase transition, terminated at a liquid-liquid critical point, is predicted. Various versions of the "two-structure equation of state" (TSEOS) based on this concept have shown remarkable agreement with both experimental data for metastable, deeply supercooled water and simulations of molecular water models. However, existing TSEOSs were not designed to describe the negative pressure region and do not account for the stability limit of the liquid state with respect to the vapor. While experimental data on supercooled water at negative pressures may shed additional light on the source of the anomalies of water, such data are very limited. To fill this gap, we have analyzed simulation results for TIP4P/2005, one of the most accurate classical water models available. We have used recently published simulation data, and performed additional simulations, over a broad range of positive and negative pressures, from ambient temperature to deeply supercooled conditions. We show that, by explicitly incorporating the liquid-vapor spinodal into a TSEOS, we are able to match the simulation data for TIP4P/2005 with remarkable accuracy. In particular, this equation of state quantitatively reproduces the lines of extrema in density, isothermal compressibility, and isobaric heat capacity. Contrary to an explanation of the thermodynamic anomalies of water based on a "retracing spinodal," the liquid-vapor spinodal in the present TSEOS continues monotonically to lower pressures upon cooling, influencing but not giving rise to density extrema and other thermodynamic anomalies.

  11. Non-contact property measurements of liquid and supercooled ceramics with a hybrid electrostatic-aerodynamic levitation furnace

    OpenAIRE

    Ishikawa, Takehiko; Yoda, Shinichi; Paradis, Paul-Francois; 石川 毅彦; 依田 真一

    2005-01-01

    The use of an hybrid pressurized electrostatic-aerodynamic levitation furnace and procedures developed by the Japan Aerospace Exploration Agency overcame the contamination problems associated with the processing of ceramics under extreme temperature conditions. This made possible property measurements over wide temperature ranges that cover the superheated as well as the supercooled states. In this study, samples of various ceramics were levitated and their densities were found as a function ...

  12. Community Cloud Computing

    CERN Document Server

    Marinos, Alexandros

    2009-01-01

    Cloud Computing is rising fast, with its data centres growing at an unprecedented rate. However, this has come with concerns over privacy, efficiency at the expense of resilience, and environmental sustainability, because of the dependence on Cloud vendors such as Google, Amazon and Microsoft. Our response is an alternative model for the Cloud conceptualisation, providing a paradigm for Clouds in the community, utilising networked personal computers for liberation from the centralised vendor model. Community Cloud Computing (C3) offers an alternative architecture, created by combing the Cloud with paradigms from Grid Computing, principles from Digital Ecosystems, and sustainability from Green Computing, while remaining true to the original vision of the Internet. It is more technically challenging than Cloud Computing, having to deal with distributed computing issues, including heterogeneous nodes, varying quality of service, and additional security constraints. However, these are not insurmountable challenge...

  13. Molecular dynamics of the supercooled pharmaceutical agent posaconazole studied via differential scanning calorimetry and dielectric and mechanical spectroscopies.

    Science.gov (United States)

    Adrjanowicz, K; Kaminski, K; Wlodarczyk, P; Grzybowska, K; Tarnacka, M; Zakowiecki, D; Garbacz, G; Paluch, M; Jurga, S

    2013-10-07

    This paper presents comprehensive studies on the molecular dynamics of a pharmaceutically important substance, posaconazole. In order to characterize relaxation dynamics in the supercooled liquid and glassy states, dielectric and mechanical spectroscopies were applied. Dielectric data have indicated multiple relaxation processes that appear above and below the glass transition temperature Tg (τα=100 s) of posaconazole. From the curvature of the dielectric log10(τα) versus inverse of temperature dependence, we determine so-called "fragility", being a very popular parameter for classifying the structural dynamics of supercooled liquids and polymers. From the calculations, we get m=150, which means that is one of the most fragile glass-forming liquids. In this paper, the relaxation dynamics of supercooled posaconazole extracted from the dielectric response function was also confronted with shear-mechanical relaxation. Finally, we have also presented a direct comparison of the fragility and the number of dynamically correlated molecules Nc determined from dynamic calorimetry curves and dielectric and mechanical spectroscopies, showing a clear deviation in the picture of glass-transition dynamics generated by calorimetric and spectroscopic techniques.

  14. Improvements of the experimental apparatus for measurement of the surface tension of supercooled liquids using horizontal capillary tube

    Directory of Open Access Journals (Sweden)

    Vinš Václav

    2016-01-01

    Full Text Available An experimental apparatus with a horizontal capillary tube for measurement of the surface tension of supercooled liquids, i.e. liquids in a metastable state below the equilibrium freezing point, was designed and tested in the previous study [V. Vinš et al., EPJ Web Conf. 92, 02108 (2015]. In this work, recent modifications of both the experimental setup and the measurement analysis are described. The main aim is to improve the accuracy and the reproducibility of measured surface tension and to achieve higher degrees of supercooling. Temperature probes measuring the temperature of cooling medium near the horizontal capillary tube were calibrated in the relevant temperature range from – 31 °C to + 45 °C. An additional pressure transducer was installed in the helium distribution setup at the position close to the capillary tube. The optical setup observing the liquid meniscus at the open end of the horizontal capillary tube together with the video analysis were thoroughly revised. The red laser illuminating the liquid meniscus, used at the original apparatus, was replaced by a fiber optic light source, which significantly improved the quality of the meniscus image. The modified apparatus was used for the measurement of surface tension of supercooled water at temperatures down to – 11 °C. The new data have a lower scatter compared to the previous horizontal measurements and show a good agreement with the other data obtained with a different measurement technique based on the modified capillary rise method.

  15. Midlatitude Continental Convective Clouds Experiment (MC3E)

    Energy Technology Data Exchange (ETDEWEB)

    Jensen, MP; Petersen, WA; Del Genio, AD; Giangrande, SE; Heymsfield, A; Heymsfield, G; Hou, AY; Kollias, P; Orr, B; Rutledge, SA; Schwaller, MR; Zipser, E

    2010-04-01

    Convective processes play a critical role in the Earth’s energy balance through the redistribution of heat and moisture in the atmosphere and subsequent impacts on the hydrologic cycle. Global observation and accurate representation of these processes in numerical models is vital to improving our current understanding and future simulations of Earth’s climate system. Despite improvements in computing power, current operational weather and global climate models are unable to resolve the natural temporal and spatial scales that are associated with convective and stratiform precipitation processes; therefore, they must turn to parameterization schemes to represent these processes. In turn, the physical basis for these parameterization schemes needs to be evaluated for general application under a variety of atmospheric conditions. Analogously, space-based remote sensing algorithms designed to retrieve related cloud and precipitation information for use in hydrological, climate, and numerical weather prediction applications often rely on physical “parameterizations” that reliably translate indirectly related instrument measurements to the physical quantity of interest (e.g., precipitation rate). Importantly, both spaceborne retrieval algorithms and model convective parameterization schemes traditionally rely on field campaign data sets as a basis for evaluating and improving the physics of their respective approaches. The Midlatitude Continental Convective Clouds Experiment (MC3E) will take place in central Oklahoma during the April–May 2011 period. The experiment is a collaborative effort between the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Climate Research Facility and the National Aeronautics and Space Administration’s (NASA) Global Precipitation Measurement (GPM) mission Ground Validation (GV) program. The field campaign leverages the unprecedented observing infrastructure currently available in the central United States

  16. Security Problems in Cloud Computing

    OpenAIRE

    Rola Motawie; Mahmoud M. El-Khouly; Samir Abou El-Seoud

    2016-01-01

    Cloud is a pool of computing resources which are distributed among cloud users. Cloud computing has many benefits like scalability, flexibility, cost savings, reliability, maintenance and mobile accessibility. Since cloud-computing technology is growing day by day, it comes with many security problems. Securing the data in the cloud environment is most critical challenges which act as a barrier when implementing the cloud. There are many new concepts that cloud introduces, such as resource sh...

  17. Cross-Cloud Testing Strategies Over Cloud Computing

    Directory of Open Access Journals (Sweden)

    Mr. Nageswararao,

    2014-06-01

    Full Text Available Cloud computing is the new paradigm to deliver all the hosted services over internet on demand. The ultimate goal of cloud computing paradigm is to realize computing as a utility. The cloud is rapidly maturing towards its goal to support a wide variety of enterprise and consumer services and real-world applications. Recently a movement towards cross cloud also called as multi-clouds or inters clouds or cloud-of-clouds has emerged which take advantage of multiple independent cloud provider offers for cloud resilience and dependability. This cross cloud represents the next logical wave in computing, enabling complex hybrid applications, cost and performance optimization, enhanced reliability, customer flexibility and lock-in avoidance. Providing testing as a service (TaaS in cross clouds become hot topics in industry. Testing heterogeneous e-commerce sites, Software as a Service solutions, and Cloud based applications is extremely challenging.

  18. Reconstruction of 3D Shapes of Opaque Cumulus Clouds from Airborne Multiangle Imaging: A Proof-of-Concept

    Science.gov (United States)

    Davis, A. B.; Bal, G.; Chen, J.

    2015-12-01

    Operational remote sensing of microphysical and optical cloud properties is invariably predicated on the assumption of plane-parallel slab geometry for the targeted cloud. The sole benefit of this often-questionable assumption about the cloud is that it leads to one-dimensional (1D) radiative transfer (RT)---a textbook, computationally tractable model. We present new results as evidence that, thanks to converging advances in 3D RT, inverse problem theory, algorithm implementation, and computer hardware, we are at the dawn of a new era in cloud remote sensing where we can finally go beyond the plane-parallel paradigm. Granted, the plane-parallel/1D RT assumption is reasonable for spatially extended stratiform cloud layers, as well as the smoothly distributed background aerosol layers. However, these 1D RT-friendly scenarios exclude cases that are critically important for climate physics. 1D RT---whence operational cloud remote sensing---fails catastrophically for cumuliform clouds that have fully 3D outer shapes and internal structures driven by shallow or deep convection. For these situations, the first order of business in a robust characterization by remote sensing is to abandon the slab geometry framework and determine the 3D geometry of the cloud, as a first step toward bone fide 3D cloud tomography. With this specific goal in mind, we deliver a proof-of-concept for an entirely new kind of remote sensing applicable to 3D clouds. It is based on highly simplified 3D RT and exploits multi-angular suites of cloud images at high spatial resolution. Airborne sensors like AirMSPI readily acquire such data. The key element of the reconstruction algorithm is a sophisticated solution of the nonlinear inverse problem via linearization of the forward model and an iteration scheme supported, where necessary, by adaptive regularization. Currently, the demo uses a 2D setting to show how either vertical profiles or horizontal slices of the cloud can be accurately reconstructed

  19. Observed microphysical changes in Arctic mixed-phase clouds when transitioning from sea ice to open ocean

    Science.gov (United States)

    Young, Gillian; Jones, Hazel M.; Choularton, Thomas W.; Crosier, Jonathan; Bower, Keith N.; Gallagher, Martin W.; Davies, Rhiannon S.; Renfrew, Ian A.; Elvidge, Andrew D.; Darbyshire, Eoghan; Marenco, Franco; Brown, Philip R. A.; Ricketts, Hugo M. A.; Connolly, Paul J.; Lloyd, Gary; Williams, Paul I.; Allan, James D.; Taylor, Jonathan W.; Liu, Dantong; Flynn, Michael J.

    2016-11-01

    changing sea ice cover and addresses the question of how the microphysics of Arctic stratiform clouds may change as the region warms and sea ice extent reduces.

  20. Secure Cloud Architecture

    Directory of Open Access Journals (Sweden)

    Kashif Munir

    2013-02-01

    Full Text Available Cloud computing is set of resources and services offered through the Internet. Cloud services are delivered from data centers located throughout the world. Cloud computing facilitates its consumers by providing virtual resources via internet. The biggest challenge in cloud computing is the security and privacy problems caused by its multi-tenancy nature and the outsourcing of infrastructure, sensitive data and critical applications. Enterprises are rapidly adopting cloud services for their businesses, measures need to be developed so that organizations can be assured of security in their businesses and can choose a suitable vendor for their computing needs. Cloud computing depends on the internet as a medium for users to access the required services at any time on pay-per-use pattern. However this technology is still in its initial stages of development, as it suffers from threats and vulnerabilities that prevent the users from trusting it. Various malicious activitiesfrom illegal users have threatened this technology such as data misuse, inflexible access control and limited monitoring. The occurrence of these threats may result into damaging or illegal access of critical and confidential data of users. In this paper we identify the most vulnerable security threats/attacks in cloud computing, which will enable both end users and vendors to know a bout the k ey security threats associated with cloud computing and propose relevant solution directives to strengthen security in the Cloud environment. We also propose secure cloud architecture for organizations to strengthen the security.

  1. The Cloud Radar System

    Science.gov (United States)

    Racette, Paul; Heymsfield, Gerald; Li, Lihua; Tian, Lin; Zenker, Ed

    2003-01-01

    Improvement in our understanding of the radiative impact of clouds on the climate system requires a comprehensive view of clouds including their physical dimensions, dynamical generation processes, and detailed microphysical properties. To this end, millimeter vave radar is a powerful tool by which clouds can be remotely sensed. The NASA Goddard Space Flight Center has developed the Cloud Radar System (CRS). CRS is a highly sensitive 94 GHz (W-band) pulsed-Doppler polarimetric radar that is designed to fly on board the NASA high-altitude ER-2 aircraft. The instrument is currently the only millimeter wave radar capable of cloud and precipitation measurements from above most all clouds. Because it operates from high-altitude, the CRS provides a unique measurement perspective for cirrus cloud studies. The CRS emulates a satellite view of clouds and precipitation systems thus providing valuable measurements for the implementation and algorithm validation for the upcoming NASA CloudSat mission that is designed to measure ice cloud distributions on the global scale using a spaceborne 94 GHz radar. This paper describes the CRS instrument and preliminary data from the recent Cirrus Regional Study of Tropical Anvils and Cirrus Layers - Florida Area Cirrus Experiment (CRYSTAL-FACE). The radar design is discussed. Characteristics of the radar are given. A block diagram illustrating functional components of the radar is shown. The performance of the CRS during the CRYSTAL-FACE campaign is discussed.

  2. Cloud, Aerosol, and Complex Terrain Interactions (CACTI) Preliminary Science Plan

    Energy Technology Data Exchange (ETDEWEB)

    Varble, Adam [Univ. of Utah, Salt Lake City, UT (United States); Nesbitt, Steve [Univ. of Illinois, Urbana-Champaign, IL (United States); Salio, Paola [Univ. of Buenos Aires (Argentina); Zipser, Edward [Univ. of Utah, Salt Lake City, UT (United States); van den Heever, Susan [Colorado State Univ., Fort Collins, CO (United States); McFarquhar, Greg [Univ. of Illinois, Urbana-Champaign, IL (United States); Kollias, Pavlos [Stony Brook Univ., NY (United States); Kreidenweis, Sonia [Colorado State Univ., Fort Collins, CO (United States); DeMott, Paul [Colorado State Univ., Fort Collins, CO (United States); Jensen, Michael [Brookhaven National Lab. (BNL), Upton, NY (United States); Houze, Jr., Robert [Univ. of Washington, Seattle, WA (United States); Rasmussen, Kristen [Colorado State Univ., Fort Collins, CO (United States); Leung, Ruby [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Romps, David [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Gochis, David [National Center for Atmospheric Research, Boulder, CO (United States); Avila, Eldo [National Univ. of Cordoba (Argentina); Williams, Christopher [Univ. of Colorado, Boulder, CO (United States); National Center for Atmospheric Research, Boulder, CO (United States)

    2017-02-01

    General circulation models and downscaled regional models exhibit persistent biases in deep convective initiation location and timing, cloud top height, stratiform area and precipitation fraction, and anvil coverage. Despite important impacts on the distribution of atmospheric heating, moistening, and momentum, nearly all climate models fail to represent convective organization, while system evolution is not represented at all. Improving representation of convective systems in models requires characterization of their predictability as a function of environmental conditions, and this characterization depends on observing many cases of convective initiation, non-initiation, organization, and non-organization. The Cloud, Aerosol, and Complex Terrain Interactions (CACTI) experiment in the Sierras de Córdoba mountain range of north-central Argentina is designed to improve understanding of cloud life cycle and organization in relation to environmental conditions so that cumulus, microphysics, and aerosol parameterizations in multi-scale models can be improved. The Sierras de Córdoba range has a high frequency of orographic boundary-layer clouds, many reaching congestus depths, many initiating into deep convection, and some organizing into mesoscale systems uniquely observable from a single fixed site. Some systems even grow upscale to become among the deepest, largest, and longest-lived in the world. These systems likely contribute to an observed regional trend of increasing extreme rainfall, and poor prediction of them likely contributes to a warm, dry bias in climate models downstream of the Sierras de Córdoba range in a key agricultural region. Many environmental factors influence the convective lifecycle in this region including orographic, low-level jet, and frontal circulations, surface fluxes, synoptic vertical motions influenced by the Andes, cloud detrainment, and aerosol properties. Local and long-range transport of smoke resulting from biomass burning as

  3. Experimental studies on seasonal heat storage based on stable supercooling of a sodium acetate water mixture

    DEFF Research Database (Denmark)

    Furbo, Simon; Dragsted, Janne; Fan, Jianhua

    2011-01-01

    to transfer heat to and from the module have been tested. Further, a solidification start method, based on a strong cooling of a small part of the salt water mixture in the module by boiling CO2 in a small brass tank in good thermal contact to the outer side of the module wall, has been tested. Tests......Laboratory tests of a 230 l seasonal heat storage module with a sodium acetate water mixture have been carried out. The aim of the tests is to elucidate how best to design a seasonal heat storage based on the salt water mixture, which supercools in a stable way. The module can be a part...... of a seasonal heat storage, that will be suitable for solar heating systems which can fully cover the yearly heat demand of Danish low energy buildings. The tested module has approximately the dimensions 2020 mm x 1285 mm x 80 mm. The module material is steel and the wall thickness is 2 mm. Different methods...

  4. Supercooling Self-Assembly of Magnetic Shelled Core/Shell Supraparticles.

    Science.gov (United States)

    Zheng, Xiaotong; Yan, Bingyun; Wu, Fengluan; Zhang, Jinlong; Qu, Shuxin; Zhou, Shaobing; Weng, Jie

    2016-09-14

    Molecular self-assembly has emerged as a powerful technique for controlling the structure and properties of core/shell structured supraparticles. However, drug-loading capacities and therapeutic effects of self-assembled magnetic core/shell nanocarriers with magnetic nanoparticles in the core are limited by the intervention of the outer organic or inorganic shell, the aggregation of superparamagnetic nanoparticles, the narrowed inner cavity, etc. Here, we present a self-assembly approach based on rebalancing hydrogen bonds between components under a supercooling process to form a new core/shell nanoscale supraparticle with magnetic nanoparticles as the shell and a polysaccharide as a core. Compared with conventional iron oxide nanoparticles, this magnetic shelled core/shell nanoparticle possesses an optimized inner cavity and a loss-free outer magnetic property. Furthermore, we find that the drug-loaded magnetic shelled nanocarriers showed interesting in vitro release behaviors at different pH conditions, including "swelling-broken", "dissociating-broken", and "bursting-broken" modes. Our experiments demonstrate the novel design of the multifunctional hybrid nanostructure and provide a considerable potential for the biomedical applications.

  5. A quantitative test of infrared optical constants for supercooled sulphuric and nitric acid droplet aerosols

    Directory of Open Access Journals (Sweden)

    R. Wagner

    2003-05-01

    Full Text Available In situ Fourier transform infrared (FTIR extinction spectra of supercooled H2SO4/H2O and HNO3/H2O solution droplets were recorded in the large coolable aerosol chamber AIDA (Aerosol Interactions and Dynamics in the Atmosphere of Forschungszentrum Karlsruhe for a range of aerosol compositions and at temperatures extending down to 192 K. The measured spectra were quantitatively analysed in terms of aerosol composition and mass concentration by using Mie theory in combination with published refractive index data as input parameters. Simultaneously, total sulphuric acid and nitric acid mass concentrations from filter analysis and total water concentrations measured with the Lyman-a hygrometer of Forschungszentrum Jülich were used to calculate the aerosol composition at thermodynamic equilibrium inside the aerosol chamber. By comparing these measured aerosol parameters with those retrieved from the analysis of the FTIR spectra, the accuracy of the literature data sets of refractive indices could be assessed. In summary, four data sets were tested in the H2SO4/H2O system as well as two data sets in the HNO3/H2O system, partly revealing significant discrepancies in the retrieved aerosol properties. Potential explanations for these differences are discussed in this paper.

  6. A nanosecond pulsed laser heating system for studying liquid and supercooled liquid films in ultrahigh vacuum

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Yuntao [Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA; Dibble, Collin J. [Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA; Petrik, Nikolay G. [Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA; Smith, R. Scott [Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA; Joly, Alan G. [Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA; Tonkyn, Russell G. [Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA; Kay, Bruce D. [Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA; Kimmel, Greg A. [Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA

    2016-04-26

    A pulsed laser heating system has been developed that enables investigations of the dynamics and kinetics of nanoscale liquid films and liquid/solid interfaces on the nanosecond timescale in ultrahigh vacuum (UHV). Details of the design, implementation and characterization of a nanosecond pulsed laser system for transiently heating nanoscale films are described. Nanosecond pulses from a Nd:YAG laser are used to rapidly heat thin films of adsorbed water or other volatile materials on a clean, well-characterized Pt(111) crystal in UHV. Heating rates of ~1010 K/s for temperature increases of ~100 – 200 K are obtained. Subsequent rapid cooling (~5 × 109 K/s) quenches the film, permitting in-situ, post-mortem analysis using a variety of surface science techniques. Lateral variations in the laser pulse energy are ~ ± 3% leading to a temperature uncertainty of ~ ± 5 K for a temperature jump of 200 K. Initial experiments with the apparatus demonstrate that crystalline ice films initially held at 90 K can be rapidly transformed into liquid water films with T > 273 K. No discernable recrystallization occurs during the rapid cooling back to cryogenic temperatures. In contrast, amorphous solid water films heated below the melting point rapidly crystallize. The nanosecond pulsed laser heating system can prepare nanoscale liquid and supercooled liquid films that persist for nanoseconds per heat pulse in an UHV environment, enabling experimental studies of a wide range of phenomena in liquids and at liquid/solid interfaces.

  7. Boson peak, Ioffe-Regel Crossover, and Liquid-Liquid phase transition in Supercooled Water

    Science.gov (United States)

    Kumar, Pradeep

    We have investigated the onset of Boson peak in a model of liquid water which exhibits a clear first-order phase transition between a low-density liquid phase and a high-density liquid phase of water at low temperature and high pressure. We find that the at low pressures, the onset of Boson peak coincides with the Widom-line of the system. At high pressures, the onset occurs at the transition temperature between the two liquids. Furthermore, we show that at both low and high pressure, the frequency of the Boson peak coincides with the Ioffe-Regel crossover of the transverse phonons, suggesting that the breakdown of Debye behavior is a general feature of Ioffe-Regel limit crossover in supercooled water. The frequency of the Boson peak is weakly pressure dependent and decreases with increasing pressure. Our work bridges gap between the experimental results on the Boson peak nanoconfined water and the behavior that one would expect from a bulk system.

  8. Size dependence of volume and surface nucleation rates for homogeneous freezing of supercooled water droplets

    Directory of Open Access Journals (Sweden)

    T. Kuhn

    2011-03-01

    Full Text Available The relative roles of volume and surface nucleation were investigated for the homogeneous freezing of pure water droplets. Experiments were carried out in a cryogenic laminar aerosol flow tube using supercooled water aerosols with maximum volume densities at radii between 1 and 3 μm. Temperature- and size-dependent values of volume- and surface-based homogeneous nucleation rates between 234.8 and 236.2 K were derived using a microphysical model and aerosol phase compositions and size distributions determined from infrared extinction measurements in the flow tube. The results show that the contribution from nucleation at the droplet surface increases with decreasing droplet radius and dominates over nucleation in the bulk droplet volume for droplets with radii smaller than approximately 5 μm. This is interpreted in terms of a lowered free energy of ice germ formation in the surface-based process. The implications of surface nucleation for the parameterization of homogeneous ice nucleation in numerical models are considered.

  9. Understanding the nonlinear dynamics of driven particles in supercooled liquids in terms of an effective temperature

    Energy Technology Data Exchange (ETDEWEB)

    Schroer, Carsten F. E., E-mail: c.schroer@uni-muenster.de [Institut für Physikalische Chemie, Westfälische Wilhelms-Universität Münster, Corrensstraße 28/30, 48149 Münster (Germany); NRW Graduate School of Chemistry, Wilhelm-Klemm-Straße 10, 48149 Münster (Germany); Heuer, Andreas, E-mail: andheuer@uni-muenster.de [Institut für Physikalische Chemie, Westfälische Wilhelms-Universität Münster, Corrensstraße 28/30, 48149 Münster (Germany); Center of Nonlinear Science, Corresstraße 2, 48149 Münster (Germany); Center for Multiscale Theory and Computation, Corrensstraße 40, 48149 Münster (Germany)

    2015-12-14

    In active microrheology, the mechanical properties of a material are tested by adding probe particles which are pulled by an external force. In case of supercooled liquids, strong forcing leads to a thinning of the host material which becomes more pronounced as the system approaches the glass transition. In this work, we provide a quantitative theoretical description of this thinning behavior based on the properties of the Potential Energy Landscape (PEL) of a model glass-former. A key role plays the trap-like nature of the PEL. We find that the mechanical properties in the strongly driven system behave the same as in a quiescent system at an enhanced temperature, giving rise to a well-characterized effective temperature. Furthermore, this effective temperature turns out to be independent of the chosen observable and individually shows up in the thermodynamic and dynamic properties of the system. Based on this underlying theoretical understanding, we can estimate its dependence on temperature and force by the PEL-properties of the quiescent system. We furthermore critically discuss the relevance of effective temperatures obtained by scaling relations for the description of out-of-equilibrium situations.

  10. Dynamic heterogeneity in crossover spin facilitated model of supercooled liquid and fractional Stokes-Einstein relation

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Seo-Woo; Kim, Soree; Jung, YounJoon, E-mail: yjjung@snu.ac.kr [Department of Chemistry, Seoul National University, Seoul 151-747 (Korea, Republic of)

    2015-06-28

    Kinetically constrained models have gained much interest as models that assign the origins of interesting dynamic properties of supercooled liquids to dynamical facilitation mechanisms that have been revealed in many experiments and numerical simulations. In this work, we investigate the dynamic heterogeneity in the fragile-to-strong liquid via Monte Carlo method using the model that linearly interpolates between the strong liquid-like behavior and the fragile liquid-like behavior by an asymmetry parameter b. When the asymmetry parameter is sufficiently small, smooth fragile-to-strong transition is observed both in the relaxation time and the diffusion constant. Using these physical quantities, we investigate fractional Stokes-Einstein relations observed in this model. When b is fixed, the system shows constant power law exponent under the temperature change, and the exponent has the value between that of the Frederickson-Andersen model and the East model. Furthermore, we investigate the dynamic length scale of our systems and also find the crossover relation between the relaxation time. We ascribe the competition between energetically favored symmetric relaxation mechanism and entropically favored asymmetric relaxation mechanism to the fragile-to-strong crossover behavior.

  11. Hard rhenium–boron–cobalt amorphous alloys with a wide supercooled liquid region

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Jianfeng, E-mail: jfwang316@zzu.edu.cn [School of Materials Science and Engineering, Zhengzhou University, Zhengzhou 450001 (China); Zhu, Shijie; Wang, Liguo; Guan, Shaokang [School of Materials Science and Engineering, Zhengzhou University, Zhengzhou 450001 (China); Li, Ran; Zhang, Tao [School of Materials Science and Engineering, Beihang University, Beijing 100191 (China)

    2015-10-01

    Novel Re–B–Co amorphous alloys with compositions of Re{sub 65−x}B{sub 35}Co{sub x} (at%, x=25, 30, 35, 40, 45, and 50) were fabricated by single-roller melt spinning. These alloys were found to exhibit a clear glass transition phenomenon. The width of supercooled liquid region (ΔT{sub x}) is in the range of 52–71 K. Such a large ΔT{sub x} allows us to produce amorphous alloy bulks by thermoplastic forming. The Vickers hardness is up to 19.10 GPa for the Re{sub 40}B{sub 35}Co{sub 25} alloy, which is close to that reported for some hard covalent crystals. Thus, the present alloys with a combination of large ΔT{sub x} and high hardness are expected to be used as a new type of structural materials. Furthermore, the relationships of hardness with glass transition temperature and Young's modulus were also discussed.

  12. Understanding the nonlinear dynamics of driven particles in supercooled liquids in terms of an effective temperature

    Science.gov (United States)

    Schroer, Carsten F. E.; Heuer, Andreas

    2015-12-01

    In active microrheology, the mechanical properties of a material are tested by adding probe particles which are pulled by an external force. In case of supercooled liquids, strong forcing leads to a thinning of the host material which becomes more pronounced as the system approaches the glass transition. In this work, we provide a quantitative theoretical description of this thinning behavior based on the properties of the Potential Energy Landscape (PEL) of a model glass-former. A key role plays the trap-like nature of the PEL. We find that the mechanical properties in the strongly driven system behave the same as in a quiescent system at an enhanced temperature, giving rise to a well-characterized effective temperature. Furthermore, this effective temperature turns out to be independent of the chosen observable and individually shows up in the thermodynamic and dynamic properties of the system. Based on this underlying theoretical understanding, we can estimate its dependence on temperature and force by the PEL-properties of the quiescent system. We furthermore critically discuss the relevance of effective temperatures obtained by scaling relations for the description of out-of-equilibrium situations.

  13. Molecular dynamics of supercooled ionic liquids studied by light scattering and dielectric spectroscopy

    Science.gov (United States)

    Pabst, Florian; Gabriel, Jan; Weigl, Peter; Blochowicz, Thomas

    2017-09-01

    We investigate molecular dynamics of two supercooled room temperature ionic liquids (RTILs) above of their glass transition temperature by means of dynamic light scattering and broadband dielectric spectroscopy from nanoseconds up to ≈105s . We show that a direct comparison of the raw data of these two techniques allows us to identify the reorientation of ions in the dielectric data, giving experimental evidence to a very recently proposed model of Gainaru et al. [1], stating that the conductivity process in ionic liquids takes place through a reorientational step of ions escaping their cage formed by surrounding counterions. Within this approach we can also understand the apparent decoupling of time constants from dielectric spectroscopy and light scattering, often found in ionic liquids, in a very natural way. Furthermore, as a consequence of knowing the reorientational part of the dielectric spectrum, we are able to show that two more processes contribute to these spectra, which are due to electrode polarization effects. The relative position of all three contributions vary among the systems and may overshadow each other, thus complicating the data analysis and favor misinterpretations.

  14. Liquid-liquid coexistence and crystallization in supercooled ST2 water

    Science.gov (United States)

    Martelli, Fausto; Palmer, Jeremy; Debenedetti, Pablo; Car, Roberto

    2014-03-01

    We have computed the free energy landscape of ST2 water in the supercooled regime (228.6 K and 2.4 kbar) using several state-of-the-art computational techniques, including umbrella sampling and metadynamics. Such results conclusively demonstrate coexistence between two liquid phases, a high-density liquid (HDL) and a low-density liquid (HDL), which are metastable with respect to cubic ice. We show that the three phases have distinct structural features characterized by the local structure index and ring statistics. We also find that ice nucleation, should it occur, does so from the low-density liquid. Interestingly, we find that the number of 6-member rings increases monotonically along the path from HDL to LDL, while non-monotonic behavior is observed near the saddle point along the LDL-ice Ic path. This behavior indicates a complex re-arrangement of the H-bond network, followed by progressive crystallization. DOE: DE-SC0008626 (F. M. and R.C.)

  15. Unraveling the microscopic pathway of homogeneous water crystallization at supercooled conditions from direct simulations

    Science.gov (United States)

    Martelli, Fausto; Palmer, Jeremy; Singh, Rakesh; Debenedetti, Pablo; Car, Roberto

    By means of unbiased classical molecular dynamics simulations, we identify the microscopic pathways of spontaneous homogeneous crystallization in supercooled ST2 water. By introducing a new order parameter, we are able to monitor formation/disruption of locally ordered regions characterized by small ice clusters with intermediate range order. When two of these regions are close each other, they percolate and form a larger ordered region. The process is slow enough to allow for polymorphic selection in favor of cubic ice (Ic). The formation of an ice nucleus requires percolation of many small clusters so that the transformations at the interface of the nucleus do not involve its core, thus guaranteeing the stability of the nucleus. The growth of the crystalline nucleus is fast and involves direct transformation of interfacial liquid molecules as well as percolation of small Ic/Ih clusters. The growth is too fast to allow conversion of Ih into Ic sites, originating the formation of a stacking fault in the final crystal. We recognize Euclidean structures in the oxygen configuration of the second shell in Ic and Ih clusters. This new point of view allows us to explain the source of the ordered stacking fault geometry.

  16. Discriminating raining from non-raining clouds at mid-latitudes using Meteosat Second Generation daytime data

    Directory of Open Access Journals (Sweden)

    B. Thies

    2007-11-01

    Full Text Available A new method for the delineation of precipitation during daytime using multispectral satellite data is proposed. The approach is not only applicable to the detection of mainly convective precipitation by means of the commonly used relation between infrared cloud top temperature and rainfall probability but enables also the detection of stratiform precipitation (e.g. in connection with mid-latitude frontal systems. The presented scheme is based on the conceptual model that precipitating clouds are characterized by a combination of particles large enough to fall, an adequate vertical extension (both represented by the cloud water path (cwp, and the existence of ice particles in the upper part of the cloud. The technique considers the VIS0.6 and the NIR1.6 channel to gain information about the cloud water path. Additionally, the channel differences ΔT8.7-10.8 and ΔT10.8-12.1 are considered to supply information about the cloud phase. Rain area delineation is realized by using a minimum threshold of the rainfall confidence. To obtain a statistical transfer function between the rainfall confidence and the channel differences, the value combination of the four variables is compared to ground based radar data. The retrieval is validated against independent radar data not used for deriving the transfer function and shows an encouraging performance as well as clear improvements compared to existing optical retrieval techniques using only IR thresholds for cloud top temperature.

  17. Evaluation of microphysics and precipitation-type frequencies in long-term three-dimensional cloud-resolving model simulations using passive and active microwave sensors from the TRMM satellite

    Science.gov (United States)

    Matsui, T.; Zeng, X.; Tao, W.; Lang, S.; Zhang, M.; Masunaga, H.

    2007-12-01

    With significant improvements in computational power over the last decades, cloud-resolving model (CRM) simulations can now be conducted on larger scales for longer time periods to better understand cloud- precipitation systems. However, even after the decadal development of CRMs, there are many uncertainties in cloud microphysics processes and cloud-precipitation structures due to the lack of routine observations. Therefore, we need to establish a practical CRM evaluation framework using frequent observations from satellites. This evaluation framework consists of i) multi-satellite simulators and ii) the construction of statistical composites that can be used to effectively evaluate cloud-precipitation systems. First, simulated cloud- precipitation structures and microphysics processes are converted to satellite-consistent radar reflectivity and microwave brightness temperature using microwave and radar simulators in the Satellite Data Simulator Unit (SDSU). Second, the CRM-computed and satellite-observed radar reflectivities and microwave brightness temperatures are used to construct two statistical composites. One combines TRMM (Tropical Rainfall Measuring Mission) PR (precipitation radar) 13.8-GHz radar echo-top heights and TRMM VIRS (visible/infrared scanner) 10.8-micron brightness temperatures. This composite categorizes precipitating clouds into shallow warm, cumulus congestus, deep stratiform, and deep convective clouds. The other composite combines multi- frequency TMI (TRMM microwave imager) brightness temperatures. The combination of low- and high-frequency channels reveals the performance of the model cloud microphysics in terms of liquid and ice precipitation amounts. In this study, long-term CRM simulations are performed using the Goddard Cumulus Ensemble (GCE) model for three cases: ARM TWP-ICE (Tropical Warm Pool International Cloud Experiment), SCSMEX (South China Sea Monsoon Experiment), and KWAJEX (Kwajalein Experiment). Results from the proposed

  18. Entangled Cloud Storage

    DEFF Research Database (Denmark)

    Ateniese, Giuseppe; Dagdelen, Özgür; Damgård, Ivan Bjerre

    2012-01-01

    Entangled cloud storage enables a set of clients {P_i} to “entangle” their files {f_i} into a single clew c to be stored by a (potentially malicious) cloud provider S. The entanglement makes it impossible to modify or delete significant part of the clew without affecting all files in c. A clew...... recover their files. We provide theoretical foundations for entangled cloud storage, introducing the notion of an entangled encoding scheme that guarantees strong security requirements capturing the properties above. We also give a concrete construction based on privacy-preserving polynomial interpolation......, along with protocols for using the encoding scheme in practice. Protocols for cloud storage find application in the cloud setting, where clients store their files on a remote server and need to be ensured that the cloud provider will not delete their data illegitimately. Current solutions, e.g., based...

  19. Encyclopedia of cloud computing

    CERN Document Server

    Bojanova, Irena

    2016-01-01

    The Encyclopedia of Cloud Computing provides IT professionals, educators, researchers and students with a compendium of cloud computing knowledge. Authored by a spectrum of subject matter experts in industry and academia, this unique publication, in a single volume, covers a wide range of cloud computing topics, including technological trends and developments, research opportunities, best practices, standards, and cloud adoption. Providing multiple perspectives, it also addresses questions that stakeholders might have in the context of development, operation, management, and use of clouds. Furthermore, it examines cloud computing's impact now and in the future. The encyclopedia presents 56 chapters logically organized into 10 sections. Each chapter covers a major topic/area with cross-references to other chapters and contains tables, illustrations, side-bars as appropriate. Furthermore, each chapter presents its summary at the beginning and backend material, references and additional resources for further i...

  20. Cloud Robotics Model

    Directory of Open Access Journals (Sweden)

    Gyula Mester

    2015-01-01

    Full Text Available Cloud Robotics was born from the merger of service robotics and cloud technologies. It allows robots to benefit from the powerful computational, storage, and communications resources of modern data centres. Cloud robotics allows robots to take advantage of the rapid increase in data transfer rates to offload tasks without hard real time requirements. Cloud Robotics has rapidly gained momentum with initiatives by companies such as Google, Willow Garage and Gostai as well as more than a dozen active research projects around the world. The presentation summarizes the main idea, the definition, the cloud model composed of essential characteristics, service models and deployment models, planning task execution and beyond. Finally some cloud robotics projects are discussed.

  1. CLOUD Experiment - How it works -

    CERN Multimedia

    Jasper Kirkby

    2016-01-01

    A brief tour of the CLOUD experiment at CERN, and its scientific aims. CLOUD uses a special cloud chamber to study the possible link between galactic cosmic rays and cloud formation. The results should contribute much to our fundamental understanding of aerosols and clouds, and their affect on climate.

  2. Considerations for Cloud Security Operations

    OpenAIRE

    Cusick, James

    2016-01-01

    Information Security in Cloud Computing environments is explored. Cloud Computing is presented, security needs are discussed, and mitigation approaches are listed. Topics covered include Information Security, Cloud Computing, Private Cloud, Public Cloud, SaaS, PaaS, IaaS, ISO 27001, OWASP, Secure SDLC.

  3. Cryptographic Cloud Storage

    Science.gov (United States)

    Kamara, Seny; Lauter, Kristin

    We consider the problem of building a secure cloud storage service on top of a public cloud infrastructure where the service provider is not completely trusted by the customer. We describe, at a high level, several architectures that combine recent and non-standard cryptographic primitives in order to achieve our goal. We survey the benefits such an architecture would provide to both customers and service providers and give an overview of recent advances in cryptography motivated specifically by cloud storage.

  4. CLOUD COMPUTING SECURITY

    Directory of Open Access Journals (Sweden)

    DANISH JAMIL,

    2011-04-01

    Full Text Available It is no secret that cloud computing is becoming more and more popular today and is ever increasing inpopularity with large companies as they share valuable resources in a cost effective way. Due to this increasingdemand for more clouds there is an ever growing threat of security becoming a major issue. This paper shalllook at ways in which security threats can be a danger to cloud computing and how they can be avoided.

  5. Geodesics on Point Clouds

    OpenAIRE

    Hongchuan Yu; Zhang, Jian J.; Zheng Jiao

    2014-01-01

    We present a novel framework to compute geodesics on implicit surfaces and point clouds. Our framework consists of three parts, particle based approximate geodesics on implicit surfaces, Cartesian grid based approximate geodesics on point clouds, and geodesic correction. The first two parts can effectively generate approximate geodesics on implicit surfaces and point clouds, respectively. By introducing the geodesic curvature flow, the third part produces smooth and accurate geodesic solution...

  6. Cloud Detection with MATLAB

    OpenAIRE

    P. Shrivastava

    2013-01-01

    The accurate detection of clouds in satellite imagery is important in research and operational applications. Cloud cover influences the distribution of solar radiation reaching the ground where it is absorbed. Resulting fluxes of sensible and latent heat are critical to the accurate characterization of boundary layer behavior and mesoscale circulations that often lead to convective development. Therefore the spatial and temporal variation in cloud cover can greatly affect regional an...

  7. High Ice Water Content at Low Radar Reflectivity near Deep Convection. Part I ; Consistency of In Situ and Remote-Sensing Observations with Stratiform Rain Column Simulations

    Science.gov (United States)

    Fridlind, A. M.; Ackerman, A. S.; Grandin, A.; Dezitter, F.; Weber, M.; Strapp, J. W.; Korolev, A. V.; Williams, C. R.

    2015-01-01

    Occurrences of jet engine power loss and damage have been associated with flight through fully glaciated deep convection at -10 to -50 degrees Centigrade. Power loss events commonly occur during flight through radar reflectivity (Zeta (sub e)) less than 20-30 decibels relative to Zeta (dBZ - radar returns) and no more than moderate turbulence, often overlying moderate to heavy rain near the surface. During 2010-2012, Airbus carried out flight tests seeking to characterize the highest ice water content (IWC) in such low-radar-reflectivity regions of large, cold-topped storm systems in the vicinity of Cayenne, Darwin, and Santiago. Within the highest IWC regions encountered, at typical sampling elevations (circa 11 kilometers), the measured ice size distributions exhibit a notably narrow concentration of mass over area-equivalent diameters of 100-500 micrometers. Given substantial and poorly quantified measurement uncertainties, here we evaluate the consistency of the Airbus in situ measurements with ground-based profiling radar observations obtained under quasi-steady, heavy stratiform rain conditions in one of the Airbus-sampled locations. We find that profiler-observed radar reflectivities and mean Doppler velocities at Airbus sampling temperatures are generally consistent with those calculated from in situ size-distribution measurements. We also find that column simulations using the in situ size distributions as an upper boundary condition are generally consistent with observed profiles of radar reflectivity (Ze), mean Doppler velocity (MDV), and retrieved rain rate. The results of these consistency checks motivate an examination of the microphysical pathways that could be responsible for the observed size-distribution features in Ackerman et al. (2015).

  8. Core of Cloud Computing

    Directory of Open Access Journals (Sweden)

    Prof. C.P.Chandgude

    2017-04-01

    Full Text Available Advancement in computing facilities marks back from 1960’s with introduction of mainframes. Each of the computing has one or the other issues, so keeping this in mind cloud computing was introduced. Cloud computing has its roots in older technologies such as hardware virtualization, distributed computing, internet technologies, and autonomic computing. Cloud computing can be described with two models, one is service model and second is deployment model. While providing several services, cloud management’s primary role is resource provisioning. While there are several such benefits of cloud computing, there are challenges in adopting public clouds because of dependency on infrastructure that is shared by many enterprises. In this paper, we present core knowledge of cloud computing, highlighting its key concepts, deployment models, service models, benefits as well as security issues related to cloud data. The aim of this paper is to provide a better understanding of the cloud computing and to identify important research directions in this field

  9. CLOUD TECHNOLOGY IN EDUCATION

    Directory of Open Access Journals (Sweden)

    Alexander N. Dukkardt

    2014-01-01

    Full Text Available This article is devoted to the review of main features of cloud computing that can be used in education. Particular attention is paid to those learning and supportive tasks, that can be greatly improved in the case of the using of cloud services. Several ways to implement this approach are proposed, based on widely accepted models of providing cloud services. Nevertheless, the authors have not ignored currently existing problems of cloud technologies , identifying the most dangerous risks and their impact on the core business processes of the university. 

  10. Cloud Computing: An Overview

    Science.gov (United States)

    Qian, Ling; Luo, Zhiguo; Du, Yujian; Guo, Leitao

    In order to support the maximum number of user and elastic service with the minimum resource, the Internet service provider invented the cloud computing. within a few years, emerging cloud computing has became the hottest technology. From the publication of core papers by Google since 2003 to the commercialization of Amazon EC2 in 2006, and to the service offering of AT&T Synaptic Hosting, the cloud computing has been evolved from internal IT system to public service, from cost-saving tools to revenue generator, and from ISP to telecom. This paper introduces the concept, history, pros and cons of cloud computing as well as the value chain and standardization effort.

  11. JINR cloud infrastructure evolution

    Science.gov (United States)

    Baranov, A. V.; Balashov, N. A.; Kutovskiy, N. A.; Semenov, R. N.

    2016-09-01

    To fulfil JINR commitments in different national and international projects related to the use of modern information technologies such as cloud and grid computing as well as to provide a modern tool for JINR users for their scientific research a cloud infrastructure was deployed at Laboratory of Information Technologies of Joint Institute for Nuclear Research. OpenNebula software was chosen as a cloud platform. Initially it was set up in simple configuration with single front-end host and a few cloud nodes. Some custom development was done to tune JINR cloud installation to fit local needs: web form in the cloud web-interface for resources request, a menu item with cloud utilization statistics, user authentication via Kerberos, custom driver for OpenVZ containers. Because of high demand in that cloud service and its resources over-utilization it was re-designed to cover increasing users' needs in capacity, availability and reliability. Recently a new cloud instance has been deployed in high-availability configuration with distributed network file system and additional computing power.

  12. A cloud storage overlay to aggregate heterogeneous cloud services

    OpenAIRE

    Machado, Guilherme Sperb; Bocek, Thomas; Ammann, Michael; Stiller, Burkhard

    2013-01-01

    Many Cloud services provide generic (e.g., Amazon S3 or Dropbox) or data-specific Cloud storage (e.g., Google Picasa or SoundCloud). Although both Cloud storage service types have the data storage in common, they present heterogeneous characteristics: different interfaces, accounting and charging schemes, privacy and security levels, functionality and, among the data-specific Cloud storage services, different data type restrictions. This paper proposes PiCsMu (Platform-independent Cloud Stora...

  13. Relationships between cloud-to-ground flashes and hydrometeors in a thunderstorm in Fujian province

    Science.gov (United States)

    Zhang, Tinglong; Zhao, Guo; Wei, Changxiong; Gao, Yi; Yu, Hai; Zhou, Fangcong

    2017-02-01

    A local severe thunderstorm, occurring near the coastal region in Fujian province, China, was chosen to study the relationships between hydrometeors and cloud-to-ground (CG) flash activities. This thunderstorm case study was carried out by using vehicle-mounted X-band dual-polarization radar on August 28, 2009. On the basis of polarimetric parameters, the hydrometeors were identified by fuzzy logic hydrometeor classification (FLHC). The results show that the thunderstorm grew into a squall line with a maximum flash rate of 85 fl/5 min in mature stage. Negative CG constituted approximately 97.3% of total CG flashes. More than 90% of the CG flashes occurred in the convective regions, and less than 10% occurred in the stratiform region. The strong echo volume in convective region had a positive linear correlation with the CG flashes rate. Seven types of hydrometeors, namely, rain (RN), aggregates (AG), low-density graupel (LDG), high-density graupel (HDG), vertically aligned ice crystals (VI), drizzle-light rain (DR), and ice crystals (IC), have been classified; the first five of the hydrometeors are predominant in the thunderstorm. RN is located mainly in regions warmer than 0 °C; the HDG is located in the middle and lower regions colder than 0 °C; and LDG and VI mainly appear in the upper portion of the thunderstorm. The ice hydrometeors seemly had a close relation with CG flashes because the total CG flash rates had a strong positive correlation with the grid number of AG, LDG, HDG, and VI in the convective region. However, the sufficient ice hydrometeors did not produce frequent CG flashes in the stratiform region. It suggests that the dynamic structure is also very important for triggering lightning flashes.

  14. Intercomparison study and optical asphericity measurements of small ice particles in the CERN CLOUD experiment

    Directory of Open Access Journals (Sweden)

    L. Nichman

    2017-09-01

    separate perfectly spherical ice particles from supercooled droplets. Correlation analysis of bulk averaged path depolarisation measurements and single particle measurements of these clouds showed higher R2 values at high concentrations and small diameters, but these results require further confirmation. We find that none of these instruments were able to determine unambiguously the phase of the small particles. These results have implications for the interpretation of atmospheric measurements and parametrisations for modelling, particularly for low particle number concentration clouds.

  15. Intercomparison study and optical asphericity measurements of small ice particles in the CERN CLOUD experiment

    Science.gov (United States)

    Nichman, Leonid; Järvinen, Emma; Dorsey, James; Connolly, Paul; Duplissy, Jonathan; Fuchs, Claudia; Ignatius, Karoliina; Sengupta, Kamalika; Stratmann, Frank; Möhler, Ottmar; Schnaiter, Martin; Gallagher, Martin

    2017-09-01

    spherical ice particles from supercooled droplets. Correlation analysis of bulk averaged path depolarisation measurements and single particle measurements of these clouds showed higher R2 values at high concentrations and small diameters, but these results require further confirmation. We find that none of these instruments were able to determine unambiguously the phase of the small particles. These results have implications for the interpretation of atmospheric measurements and parametrisations for modelling, particularly for low particle number concentration clouds.

  16. Preparation and Supercooling Modification of Salt Hydrate Phase Change Materials Based on CaCl₂·2H₂O/CaCl₂.

    Science.gov (United States)

    Xu, Xiaoxiao; Dong, Zhijun; Memon, Shazim Ali; Bao, Xiaohua; Cui, Hongzhi

    2017-06-23

    Salt hydrates have issues of supercooling when they are utilized as phase change materials (PCMs). In this research, a new method was adopted to prepare a salt hydrate PCM (based on a mixture of calcium chloride dihydrate and calcium chloride anhydrous) as a novel PCM system to reduce the supercooling phenomenon existing in CaCl₂·6H₂O. Six samples with different compositions of CaCl₂ were prepared. The relationship between the performance and the proportion of calcium chloride dihydrate (CaCl₂·2H₂O) and calcium chloride anhydrous (CaCl₂) was also investigated. The supercooling degree of the final PCM reduced with the increase in volume of CaCl₂·2H₂O during its preparation. The PCM obtained with 66.21 wt % CaCl₂·2H₂O reduced the supercooling degree by about 96.8%. All six samples, whose ratio of CaCl₂·2H₂O to (CaCl₂ plus CaCl₂·2H₂O) was 0%, 34.03%, 53.82%, 76.56%, 90.74%, and 100% respectively, showed relatively higher enthalpy (greater than 155.29 J/g), and have the possibility to be applied in buildings for thermal energy storage purposes. Hence, CaCl₂·2H₂O plays an important role in reducing supercooling and it can be helpful in adjusting the solidification enthalpy. Thereafter, the influence of adding different percentages of Nano-SiO₂ (0.1 wt %, 0.3 wt %, 0.5 wt %) in reducing the supercooling degree of some PCM samples was investigated. The test results showed that the supercooling of the salt hydrate PCM in Samples 6 and 5 reduced to 0.2 °C and 0.4 °C respectively. Finally, the effect of the different cooling conditions, including frozen storage (-20 °C) and cold storage (5 °C), that were used to prepare the salt hydrate PCM was considered. It was found that both cooling conditions are effective in reducing the supercooling degree of the salt hydrate PCM. With the synergistic action of the two materials, the performance and properties of the newly developed PCM systems were better especially in terms of reducing

  17. Supercool纤维牛仔面料的开发与生产实践%DEVELOPMENT AND PRODUCTION PRACTICE OF SUPERCOOL DENIM

    Institute of Scientific and Technical Information of China (English)

    成海量; 张增强

    2015-01-01

    以48.6 tex赛络纺棉纱、48.6 tex赛络纺竹节纱为经纱,33.3 tex Supercool 吸湿排汗纤维为纬纱开发吸湿排汗牛仔面料。介绍了Supercool纤维的特性, Supercool纤维牛仔面料的规格设计、生产工艺流程,及各工序重要参数的选择和关键生产技术,指出了Supercool纤维牛仔面料开发的基本思路和产品的应用前景。%Taking 48. 6 tex Siro spun yarn plus 48. 6 tex Siro spun slub yarn as warp yarn and 33. 3 tex Supercool, moisture absorption and sweat discharge fiber as weft yarn to develop and porduce the moisture absorption and sweat discharge denim fabric. The article introduced the characteristics of the Supercool fiber, the specification designing of the Supercool Denim, production process, the selection of important parameters in each process and the key to production technology , and pointed out the basic idea of developing the Supercool Denim and the application prospect of the product.

  18. Aqueous phase oxidation of sulphur dioxide by ozone in cloud droplets

    Science.gov (United States)

    Hoyle, C. R.; Fuchs, C.; Järvinen, E.; Saathoff, H.; Dias, A.; El Haddad, I.; Gysel, M.; Coburn, S. C.; Tröstl, J.; Bernhammer, A.-K.; Bianchi, F.; Breitenlechner, M.; Corbin, J. C.; Craven, J.; Donahue, N. M.; Duplissy, J.; Ehrhart, S.; Frege, C.; Gordon, H.; Höppel, N.; Heinritzi, M.; Kristensen, T. B.; Molteni, U.; Nichman, L.; Pinterich, T.; Prévôt, A. S. H.; Simon, M.; Slowik, J. G.; Steiner, G.; Tomé, A.; Vogel, A. L.; Volkamer, R.; Wagner, A. C.; Wagner, R.; Wexler, A. S.; Williamson, C.; Winkler, P. M.; Yan, C.; Amorim, A.; Dommen, J.; Curtius, J.; Gallagher, M. W.; Flagan, R. C.; Hansel, A.; Kirkby, J.; Kulmala, M.; Möhler, O.; Stratmann, F.; Worsnop, D. R.; Baltensperger, U.

    2016-02-01

    The growth of aerosol due to the aqueous phase oxidation of sulfur dioxide by ozone was measured in laboratory-generated clouds created in the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber at the European Organization for Nuclear Research (CERN). Experiments were performed at 10 and -10 °C, on acidic (sulfuric acid) and on partially to fully neutralised (ammonium sulfate) seed aerosol. Clouds were generated by performing an adiabatic expansion - pressurising the chamber to 220 hPa above atmospheric pressure, and then rapidly releasing the excess pressure, resulting in a cooling, condensation of water on the aerosol and a cloud lifetime of approximately 6 min. A model was developed to compare the observed aerosol growth with that predicted using oxidation rate constants previously measured in bulk solutions. The model captured the measured aerosol growth very well for experiments performed at 10 and -10 °C, indicating that, in contrast to some previous studies, the oxidation rates of SO2 in a dispersed aqueous system can be well represented by using accepted rate constants, based on bulk measurements. To the best of our knowledge, these are the first laboratory-based measurements of aqueous phase oxidation in a dispersed, super-cooled population of droplets. The measurements are therefore important in confirming that the extrapolation of currently accepted reaction rate constants to temperatures below 0 °C is correct.

  19. An Example of Canal Formation in a Thick Cloud Induced by Massive Seeding Using Liquid Carbon Dioxide

    Institute of Scientific and Technical Information of China (English)

    2015-01-01

    The purpose of this experiment is to show that massive cloud seeding is eff ective in mitigating the damage caused by heavy snowfall. In order to show its eff ect, we attempted to form a canal in a thick convective cloud by massive seeding, and left the parts that were not infl uenced by the seeding as a reference to show that the canal was formed by the massive seeding only. The seeding was carried out by using an aircraft. The seeding rate and air speed of the aircraft were 35 g s−1 and 115 m s−1, respectively. The fl ight course for seeding was selected to be parallel to the wind direction to ensure that the dispersed liquid carbon dioxide did not infl uence both sides of the course. The results show that a part of the radar echo observed from onboard beneath the seeding track was weakened and divided the radar echo into two parts 20 minutes after the cloud top and the bottom were seeded, and distribution of rainfall rate on the ground from the target cloud was confi rmed to be divided into two parts 24 minutes after the seeding. The target cloud was torn along the seeding track, and we could see the sea surface through the break in the cloud. Canal formation occurred in the cloud along the seeding track. Clouds and snowfall were left on both sides of the canal. The results show that supercooled liquid cloud particles along the seeding track evaporated to form larger precipitable particles which grew and fell rapidly.

  20. VMware vCloud security

    CERN Document Server

    Sarkar, Prasenjit

    2013-01-01

    VMware vCloud Security provides the reader with in depth knowledge and practical exercises sufficient to implement a secured private cloud using VMware vCloud Director and vCloud Networking and Security.This book is primarily for technical professionals with system administration and security administration skills with significant VMware vCloud experience who want to learn about advanced concepts of vCloud security and compliance.

  1. The California Molecular Cloud

    CERN Document Server

    Lada, Charles J; Alves, Joao F

    2009-01-01

    We present an analysis of wide-field infrared extinction maps of a region in Perseus just north of the Taurus-Auriga dark cloud complex. From this analysis we have identified a massive, nearby, but previously unrecognized, giant molecular cloud (GMC). From comparison of foreground star counts with Galactic models we derive a distance of 450 +/- 23 parsecs to the cloud. At this distance the cloud extends over roughly 80 pc and has a mass of approximately 10^5 solar masses, rivaling the Orion (A) Molecular Cloud as the largest and most massive GMC in the solar neighborhood. Although surprisingly similar in mass and size to the more famous Orion Molecular Cloud (OMC) the newly recognized cloud displays significantly less star formation activity with more than an order of magnitude fewer young stellar objects than found in the OMC, suggesting that both the level of star formation and perhaps the star formation rate in this cloud are an order of magnitude or more lower than in the OMC. Analysis of extinction maps ...

  2. On Cloud Nine

    Science.gov (United States)

    McCrea, Bridget; Weil, Marty

    2011-01-01

    Across the U.S., innovative collaboration practices are happening in the cloud: Sixth-graders participate in literary salons. Fourth-graders mentor kindergarteners. And teachers use virtual Post-it notes to advise students as they create their own television shows. In other words, cloud computing is no longer just used to manage administrative…

  3. Cloud speed sensor

    Directory of Open Access Journals (Sweden)

    V. Fung

    2013-10-01

    Full Text Available Changing cloud cover is a major source of solar radiation variability and poses challenges for the integration of solar energy. A compact and economical system that measures cloud motion vectors to estimate power plant ramp rates and provide short term solar irradiance forecasts is presented. The Cloud Speed Sensor (CSS is constructed using an array of luminance sensors and high-speed data acquisition to resolve the progression of cloud passages across the sensor footprint. An embedded microcontroller acquires the sensor data and uses a cross-correlation algorithm to determine cloud motion vectors. The CSS was validated against an artificial shading test apparatus, an alternative method of cloud motion detection from ground measured irradiance (Linear Cloud Edge, LCE, and a UC San Diego Sky Imager (USI. The CSS detected artificial shadow directions and speeds to within 15 and 6% accuracy, respectively. The CSS detected (real cloud directions and speeds without average bias and with average weighted root mean square difference of 22° and 1.9 m s−1 when compared to USI and 33° and 1.5 m s−1 when compared to LCE results.

  4. Clouds in Planetary Atmospheres

    Science.gov (United States)

    West, R.; Murdin, P.

    2000-11-01

    What are clouds? The answer to that question is both obvious and subtle. In the terrestrial atmosphere clouds are familiar as vast collections of small water drops or ice crystals suspended in the air. In the atmospheres of Venus, Mars, Jupiter, Saturn, Saturn's moon Titan, Uranus, Neptune, and possibly Pluto, they are composed of several other substances including sulfuric acid, ammonia, hydroge...

  5. Emissions from Ships with respect to Their Effects on Clouds.

    Science.gov (United States)

    Hobbs, Peter V.; Garrett, Timothy J.; Ferek, Ronald J.; Strader, Scott R.; Hegg, Dean A.; Frick, Glendon M.; Hoppel, William A.; Gasparovic, Richard F.; Russell, Lynn M.; Johnson, Douglas W.; O'Dowd, Colin; Durkee, Philip A.; Nielsen, Kurt E.; Innis, George

    2000-08-01

    Emissions of particles, gases, heat, and water vapor from ships are discussed with respect to their potential for changing the microstructure of marine stratiform clouds and producing the phenomenon known as `ship tracks.' Airborne measurements are used to derive emission factors of SO2 and NO from diesel-powered and steam turbine-powered ships, burning low-grade marine fuel oil (MFO); they were 15-89 and 2-25 g kg1 of fuel burned, respectively. By contrast a steam turbine-powered ship burning high-grade navy distillate fuel had an SO2 emission factor of 6 g kg1.Various types of ships, burning both MFO and navy distillate fuel, emitted from 4 × 1015 to 2 × 1016 total particles per kilogram of fuel burned (4 × 1015-1.5 × 1016 particles per second). However, diesel-powered ships burning MFO emitted particles with a larger mode radius (0.03-0.05 m) and larger maximum sizes than those powered by steam turbines burning navy distillate fuel (mode radius 0.02 m). Consequently, if the particles have similar chemical compositions, those emitted by diesel ships burning MFO will serve as cloud condensation nuclei (CCN) at lower supersaturations (and will therefore be more likely to produce ship tracks) than the particles emitted by steam turbine ships burning distillate fuel. Since steam turbine-powered ships fueled by MFO emit particles with a mode radius similar to that of diesel-powered ships fueled by MFO, it appears that, for given ambient conditions, the type of fuel burned by a ship is more important than the type of ship engine in determining whether or not a ship will produce a ship track. However, more measurements are needed to test this hypothesis.The particles emitted from ships appear to be primarily organics, possibly combined with sulfuric acid produced by gas-to-particle conversion of SO2. Comparison of model results with measurements in ship tracks suggests that the particles from ships contain only about 10% water-soluble materials. Measurements of the

  6. A nanosecond pulsed laser heating system for studying liquid and supercooled liquid films in ultrahigh vacuum.

    Science.gov (United States)

    Xu, Yuntao; Dibble, Collin J; Petrik, Nikolay G; Smith, R Scott; Joly, Alan G; Tonkyn, Russell G; Kay, Bruce D; Kimmel, Greg A

    2016-04-28

    A pulsed laser heating system has been developed that enables investigations of the dynamics and kinetics of nanoscale liquid films and liquid/solid interfaces on the nanosecond time scale in ultrahigh vacuum (UHV). Details of the design, implementation, and characterization of a nanosecond pulsed laser system for transiently heating nanoscale films are described. Nanosecond pulses from a Nd:YAG laser are used to rapidly heat thin films of adsorbed water or other volatile materials on a clean, well-characterized Pt(111) crystal in UHV. Heating rates of ∼10(10) K/s for temperature increases of ∼100-200 K are obtained. Subsequent rapid cooling (∼5 × 10(9) K/s) quenches the film, permitting in-situ, post-heating analysis using a variety of surface science techniques. Lateral variations in the laser pulse energy are ∼±2.7% leading to a temperature uncertainty of ∼±4.4 K for a temperature jump of 200 K. Initial experiments with the apparatus demonstrate that crystalline ice films initially held at 90 K can be rapidly transformed into liquid water films with T > 273 K. No discernable recrystallization occurs during the rapid cooling back to cryogenic temperatures. In contrast, amorphous solid water films heated below the melting point rapidly crystallize. The nanosecond pulsed laser heating system can prepare nanoscale liquid and supercooled liquid films that persist for nanoseconds per heat pulse in an UHV environment, enabling experimental studies of a wide range of phenomena in liquids and at liquid/solid interfaces.

  7. A nanosecond pulsed laser heating system for studying liquid and supercooled liquid films in ultrahigh vacuum

    Science.gov (United States)

    Xu, Yuntao; Dibble, Collin J.; Petrik, Nikolay G.; Smith, R. Scott; Joly, Alan G.; Tonkyn, Russell G.; Kay, Bruce D.; Kimmel, Greg A.

    2016-04-01

    A pulsed laser heating system has been developed that enables investigations of the dynamics and kinetics of nanoscale liquid films and liquid/solid interfaces on the nanosecond time scale in ultrahigh vacuum (UHV). Details of the design, implementation, and characterization of a nanosecond pulsed laser system for transiently heating nanoscale films are described. Nanosecond pulses from a Nd:YAG laser are used to rapidly heat thin films of adsorbed water or other volatile materials on a clean, well-characterized Pt(111) crystal in UHV. Heating rates of ˜1010 K/s for temperature increases of ˜100-200 K are obtained. Subsequent rapid cooling (˜5 × 109 K/s) quenches the film, permitting in-situ, post-heating analysis using a variety of surface science techniques. Lateral variations in the laser pulse energy are ˜±2.7% leading to a temperature uncertainty of ˜±4.4 K for a temperature jump of 200 K. Initial experiments with the apparatus demonstrate that crystalline ice films initially held at 90 K can be rapidly transformed into liquid water films with T > 273 K. No discernable recrystallization occurs during the rapid cooling back to cryogenic temperatures. In contrast, amorphous solid water films heated below the melting point rapidly crystallize. The nanosecond pulsed laser heating system can prepare nanoscale liquid and supercooled liquid films that persist for nanoseconds per heat pulse in an UHV environment, enabling experimental studies of a wide range of phenomena in liquids and at liquid/solid interfaces.

  8. Communication: Towards first principles theory of relaxation in supercooled liquids formulated in terms of cooperative motion.

    Science.gov (United States)

    Freed, Karl F

    2014-10-14

    A general theory of the long time, low temperature dynamics of glass-forming fluids remains elusive despite the almost 20 years since the famous pronouncement by the Nobel Laureate P. W. Anderson, "The deepest and most interesting unsolved problem in solid state theory is probably the theory of the nature of glass and the glass transition" [Science 267, 1615 (1995)]. While recent work indicates that Adam-Gibbs theory (AGT) provides a framework for computing the structural relaxation time of supercooled fluids and for analyzing the properties of the cooperatively rearranging dynamical strings observed in low temperature molecular dynamics simulations, the heuristic nature of AGT has impeded general acceptance due to the lack of a first principles derivation [G. Adam and J. H. Gibbs, J. Chem. Phys. 43, 139 (1965)]. This deficiency is rectified here by a statistical mechanical derivation of AGT that uses transition state theory and the assumption that the transition state is composed of elementary excitations of a string-like form. The strings are assumed to form in equilibrium with the mobile particles in the fluid. Hence, transition state theory requires the strings to be in mutual equilibrium and thus to have the size distribution of a self-assembling system, in accord with the simulations and analyses of Douglas and co-workers. The average relaxation rate is computed as a grand canonical ensemble average over all string sizes, and use of the previously determined relation between configurational entropy and the average cluster size in several model equilibrium self-associating systems produces the AGT expression in a manner enabling further extensions and more fundamental tests of the assumptions.

  9. Cold tolerance and supercooling capacity in overwintering adults of elm leaf beetle Xanthogaleruca luteola (Coleoptera: Chrysomelidae).

    Science.gov (United States)

    Soudi, Sh; Moharramipour, S

    2011-12-01

    Elm leaf beetle, Xanthogaleruca luteola (Muller) is one of the key pests of elm trees all over the world, and survives winter in reproductive diapause in sheltered locations. Seasonal variation of whole body supercooling points (SCPs), LT50 (temperature at which 50% of the test individuals die) and survival rate after exposure to subzero temperatures were determined in field collected adults during October 2008 to May 2009 and October 2009 to May 2010. The SCP of adults decreased significantly from October (median=-13.8°C) to January (median=-20.7°C) in first year, relatively similar results was observed in the second year. The lowest LT50 was observed in overwintering adults collected in January (-16.81°C) in the first year and December (-15.59°C) in the second year. Mortality at -15°C for 24 h was >70% in early autumn in both years whereas it decreased to lower than 45% in early winter, the highest mortality (100%) was observed in adults collected in May in both years. Cold acclimated adults (30 d, 5°C) in November 2008 exhibited significantly higher SCP (-12.21±0.64°C) than nonacclimated adults (-15.57±1.35°C). A 30-d exposure to 5°C caused >20% mortality in November, while <9% mortality was observed in adults collected in December and January 2008. Overwintering adults died upon freezing and the lower lethal temperatures were within the range of SCP, indicating that X. luteola is a freeze intolerant insect.

  10. Solar variability and clouds

    CERN Document Server

    Kirkby, Jasper

    2000-01-01

    Satellite observations have revealed a surprising imprint of the 11- year solar cycle on global low cloud cover. The cloud data suggest a correlation with the intensity of Galactic cosmic rays. If this apparent connection between cosmic rays and clouds is real, variations of the cosmic ray flux caused by long-term changes in the solar wind could have a significant influence on the global energy radiation budget and the climate. However a direct link between cosmic rays and clouds has not been unambiguously established and, moreover, the microphysical mechanism is poorly understood. New experiments are being planned to find out whether cosmic rays can affect cloud formation, and if so how. (37 refs).

  11. Cloud computing basics

    CERN Document Server

    Srinivasan, S

    2014-01-01

    Cloud Computing Basics covers the main aspects of this fast moving technology so that both practitioners and students will be able to understand cloud computing. The author highlights the key aspects of this technology that a potential user might want to investigate before deciding to adopt this service. This book explains how cloud services can be used to augment existing services such as storage, backup and recovery. Addressing the details on how cloud security works and what the users must be prepared for when they move their data to the cloud. Also this book discusses how businesses could prepare for compliance with the laws as well as industry standards such as the Payment Card Industry.

  12. Prebiotic chemistry in clouds

    Science.gov (United States)

    Oberbeck, Verne R.; Marshall, John; Shen, Thomas

    1991-01-01

    The chemical evolution hypothesis of Woese (1979), according to which prebiotic reactions occurred rapidly in droplets in giant atmospheric reflux columns was criticized by Scherer (1985). This paper proposes a mechanism for prebiotic chemistry in clouds that answers Scherer's concerns and supports Woese's hypothesis. According to this mechanism, rapid prebiotic chemical evolution was facilitated on the primordial earth by cycles of condensation and evaporation of cloud drops containing clay condensation nuclei and nonvolatile monomers. For example, amino acids supplied by, or synthesized during entry of meteorites, comets, and interplanetary dust, would have been scavenged by cloud drops containing clay condensation nuclei and would be polymerized within cloud systems during cycles of condensation, freezing, melting, and evaporation of cloud drops.

  13. Cloud Computing Quality

    Directory of Open Access Journals (Sweden)

    Anamaria Şiclovan

    2013-02-01

    Full Text Available

    Cloud computing was and it will be a new way of providing Internet services and computers. This calculation approach is based on many existing services, such as the Internet, grid computing, Web services. Cloud computing as a system aims to provide on demand services more acceptable as price and infrastructure. It is exactly the transition from computer to a service offered to the consumers as a product delivered online. This paper is meant to describe the quality of cloud computing services, analyzing the advantages and characteristics offered by it. It is a theoretical paper.

    Keywords: Cloud computing, QoS, quality of cloud computing

  14. Cloud computing security.

    Energy Technology Data Exchange (ETDEWEB)

    Shin, Dongwan; Claycomb, William R.; Urias, Vincent E.

    2010-10-01

    Cloud computing is a paradigm rapidly being embraced by government and industry as a solution for cost-savings, scalability, and collaboration. While a multitude of applications and services are available commercially for cloud-based solutions, research in this area has yet to fully embrace the full spectrum of potential challenges facing cloud computing. This tutorial aims to provide researchers with a fundamental understanding of cloud computing, with the goals of identifying a broad range of potential research topics, and inspiring a new surge in research to address current issues. We will also discuss real implementations of research-oriented cloud computing systems for both academia and government, including configuration options, hardware issues, challenges, and solutions.

  15. CLOUD COMPUTING AND SECURITY

    Directory of Open Access Journals (Sweden)

    Asharani Shinde

    2015-10-01

    Full Text Available This document gives an insight into Cloud Computing giving an overview of key features as well as the detail study of exact working of Cloud computing. Cloud Computing lets you access all your application and documents from anywhere in the world, freeing you from the confines of the desktop thus making it easier for group members in different locations to collaborate. Certainly cloud computing can bring about strategic, transformational and even revolutionary benefits fundamental to future enterprise computing but it also offers immediate and pragmatic opportunities to improve efficiencies today while cost effectively and systematically setting the stage for the strategic change. As this technology makes the computing, sharing, networking easy and interesting, we should think about the security and privacy of information too. Thus the key points we are going to be discussed are what is cloud, what are its key features, current applications, future status and the security issues and the possible solutions.

  16. Persistent Supercooling of Reproductive Shoots Is Enabled by Structural Ice Barriers Being Active Despite an Intact Xylem Connection

    Science.gov (United States)

    Pfaller, Kristian; Wagner, Johanna

    2016-01-01

    Extracellular ice nucleation usually occurs at mild subzero temperatures in most plants. For persistent supercooling of certain plant parts ice barriers are necessary to prevent the entry of ice from already frozen tissues. The reproductive shoot of Calluna vulgaris is able to supercool down to below -22°C throughout all developmental stages (shoot elongation, flowering, fruiting) despite an established xylem conductivity. After localization of the persistent ice barrier between the reproductive and vegetative shoot at the base of the pedicel by infrared differential thermal analysis, the currently unknown structural features of the ice barrier tissue were anatomically analyzed on cross and longitudinal sections. The ice barrier tissue was recognized as a 250 μm long constriction zone at the base of the pedicel that lacked pith tissue and intercellular spaces. Most cell walls in this region were thickened and contained hydrophobic substances (lignin, suberin, and cutin). A few cell walls had what appeared to be thicker cellulose inclusions. In the ice barrier tissue, the area of the xylem was as much as 5.7 times smaller than in vegetative shoots and consisted of tracheids only. The mean number of conducting units in the xylem per cross section was reduced to 3.5% of that in vegetative shoots. Diameter of conducting units and tracheid length were 70% and 60% (respectively) of that in vegetative shoots. From vegetative shoots water transport into the ice barrier must pass pit membranes that are likely impermeable to ice. Pit apertures were about 1.9 μm x 0.7 μm, which was significantly smaller than in the vegetative shoot. The peculiar anatomical features of the xylem at the base of the pedicel suggest that the diameter of pores in pit membranes could be the critical constriction for ice propagation into the persistently supercooled reproductive shoots of C. vulgaris. PMID:27632365

  17. Static and dynamic length scales in supercooled liquids: insights from molecular dynamics simulations of water and tri-propylene oxide.

    Science.gov (United States)

    Klameth, F; Henritzi, P; Vogel, M

    2014-04-14

    We perform molecular dynamics simulations to study static and dynamic length scales in molecular supercooled liquids, in particular, water. For a determination of these scales, we use equilibrium configurations and pin appropriate subsets of molecules so as to obtain random matrices, cylindrical pores, and slit confinements. Static length scales ξ(s) are determined by analyzing overlap correlation functions for various fractions of pinned molecules or distances to the confining walls. For water in all confinements and for propylene oxide trimers in random geometry, a linear increase of ξ(s) with inverse temperature is found. Dynamic length scales ξ(d) are determined by analogous analysis of fraction-dependent or position-resolved correlation times of structural relaxation. While ξ(d) continuously grows upon cooling in the cylindrical and slit confinements, we find no evidence for a temperature dependence in random matrices, implying that molecular dynamics in parsed volumes is qualitatively different from that in bulk liquids. Finally, we study possible connections between the growth of the static and dynamic length scales and the slowdown of the structural relaxation of the supercooled bulk liquids. For water, we observe a linear relation between ln τ(α) and ξ(s)²/T in the whole accessible range down to the critical temperature of mode-coupling theory, T(c). In the weakly supercooled regime, the same relation holds also for ξ(d), as obtained from cylindrical and slit confinements, but deviations from this behavior are observed near T(c). The results are discussed in connection with random first-order theory and experimental studies of liquid dynamics in nanoscopic confinements and binary mixtures.

  18. Critical elements in sediment-hosted deposits (clastic-dominated Zn-Pb-Ag, Mississippi Valley-type Zn-Pb, sedimentary rock-hosted Stratiform Cu, and carbonate-hosted Polymetallic Deposits): A review: Chapter 12

    Science.gov (United States)

    Marsh, Erin; Hitzman, Murray W.; Leach, David L.

    2016-01-01

    Some sediment-hosted base metal deposits, specifically the clastic-dominated (CD) Zn-Pb deposits, carbonate-hosted Mississippi Valley-type (MVT) deposits, sedimentary-rock hosted stratiform copper deposits, and carbonate-hosted polymetallic (“Kipushi type”) deposits, are or have been important sources of critical elements including Co, Ga, Ge, and Re. The generally poor data concerning trace element concentrations in these types of sediment-hosted ores suggest that there may be economically important concentrations of critical elements yet to be recognized.

  19. Supercooling of the disordered vortex lattice in Bi(2)Sr(2)CaCu(2)O(8+delta)

    Science.gov (United States)

    van Der Beek CJ; Colson; Indenbom; Konczykowski

    2000-05-01

    Time-resolved local induction measurements near the vortex lattice order-disorder transition in optimally doped Bi(2)Sr(2)CaCu(2)O(8+delta) crystals show that the high-field, disordered phase can be quenched to fields as low as half the transition field. Over an important range of fields, the electrodynamical behavior of the vortex system is governed by the coexistence of ordered and disordered vortex phases in the sample. We interpret the results as supercooling of the high-field phase and the possible first-order nature of the order-disorder transition at the "second magnetization peak."

  20. Structural crossover in a supercooled metallic liquid and the link to a liquid-to-liquid phase transition

    Science.gov (United States)

    Lan, S.; Blodgett, M.; Kelton, K. F.; Ma, J. L.; Fan, J.; Wang, X.-L.

    2016-05-01

    Time-resolved synchrotron measurements were carried out to capture the structure evolution of an electrostatically levitated metallic-glass-forming liquid during free cooling. The experimental data shows a crossover in the liquid structure at ˜1000 K, about 115 K below the melting temperature and 150 K above the crystallization temperature. The structure change is characterized by a dramatic growth in the extended-range order below the crossover temperature. Molecular dynamics simulations have identified that the growth of the extended-range order was due to an increased correlation between solute atoms. These results provide structural evidence for a liquid-to-liquid-phase-transition in the supercooled metallic liquid.

  1. NMR evidence of a sharp change in a measure of local order in deeply supercooled confined water

    OpenAIRE

    Mallamace, F.; Corsaro, C.; Broccio, M.; Branca, C.; González-Segredo, N.; Spooren, J.; Chen, S. -H.; Stanley, H. E.

    2008-01-01

    Using NMR, we measure the proton chemical shift δ, of supercooled nanoconfined water in the temperature range 195 K < T < 350 K. Because δ is directly connected to the magnetic shielding tensor, we discuss the data in terms of the local hydrogen bond geometry and order. We argue that the derivative −(∂ ln δ/∂T)P should behave roughly as the constant pressure specific heat CP(T), and we confirm this argument by detailed comparisons with literature values of CP(T) in the range 290–370 K. We fin...

  2. Numerical and experimental verification of a theoretical model of ripple formation in ice growth under supercooled water film flow

    Energy Technology Data Exchange (ETDEWEB)

    Ueno, K; Farzaneh, M [NSERC/Hydro-Quebec/UQAC Industrial Chair on Atmospheric Icing of Power Network Equipment (CIGELE) and Canada Research Chair on Engineering of Power Network Atmospheric Icing (INGIVRE), Universite du Quebec a Chicoutimi, 555 Boulevard de l' Universite, Chicoutimi, Quebec, G7H 2B1 (Canada); Yamaguchi, S [Snow and Ice Research Center, National Research Institute for Earth Science and Disaster Prevention, Nagaoka, 940-0821 (Japan); Tsuji, H [Research Institute for Applied Mechanics, Kyushu University, Kasuga, Fukuoka, 816-8580 (Japan)], E-mail: kazuto.ueno@uqac.ca

    2010-04-15

    Little is known about morphological instability of a solidification front during the crystal growth of a thin film of flowing supercooled liquid with a free surface: for example, the ring-like ripples on the surface of icicles. The length scale of the ripples is nearly 1 cm. Two theoretical models for the ripple formation mechanism have been proposed. However, these models lead to quite different results because of differences in the boundary conditions at the solid-liquid interface and liquid-air surface. The validity of the assumption used in the two models is numerically investigated and some of the theoretical predictions are compared with experiments.

  3. Retrieving latent heating vertical structure from cloud and precipitation Profiles—Part I: Warm rain processes

    Science.gov (United States)

    Min, Qilong; Li, Rui; Wu, Xiaoqing; Fu, Yunfei

    2013-06-01

    An exploratory study on physical based latent heat (LH) retrieval algorithm is conducted by parameterizing the physical linkages of hydrometeor profiles of cloud and precipitation to the major processes related to the phase change of atmospheric water. Specifically, rain events are segregated into three rain types: warm, convective, and stratiform, based on their dynamical and thermodynamical characteristics. As the first of the series, only the warm rain LH algorithm is presented and evaluated here. The major microphysical processes of condensation and evaporation for warm rain are parameterized through traditional rain growth theory, with the aid of Cloud Resolving Model (CRM) simulations. The evaluation or the self-consistency tests indicate that the physical based retrievals capture the fundamental LH processes associated with the warm rain life cycle. There is no significant systematic bias in terms of convection strength, illustrated by the month-long CRM simulation as the mesoscale convective systems (MCSs) experience from initial, mature, to decay stages. The overall monthly-mean LH comparison showed that the total LH, as well as condensation heating and evaporation cooling components, agree with the CRM simulation.

  4. Response of the Nevzorov hot wire probe in clouds dominated by droplet conditions in the drizzle size range

    Directory of Open Access Journals (Sweden)

    A. Schwarzenboeck

    2009-12-01

    Full Text Available During the airborne research mission ASTAR 2004 (Arctic Study of Tropospheric Aerosols, Clouds and Radiation performed over the island of Svalbard in the Arctic a constant-temperature hot-wire Nevzorov Probe designed for aircraft measurements, has been used onboard the aircraft POLAR 2. The Nevzorov probe measured liquid water (LWC and total condensed water content (TWC in supercooled liquid and partly mixed phase clouds, respectively. As for other hotwire probes the calculation of LWC and/or TWC (and thus the ice water content IWC has to take into account the collection efficiencies of the two separate sensors for LWC and TWC which both react differently with respect to cloud phase and what is even more difficult to quantify with respect to the size of ice and liquid cloud particles. The study demonstrates that during pure liquid cloud sequences the ASTAR data set of the Nevzorov probe allowed to improve the quantification of the collection efficiency, particularly of the LWC probe part with respect to water. The improved quantification of liquid water content should lead to improved retrievals of IWC content. Simultaneous retrievals of LWC and IWC are correlated with the asymmetry factor derived from the Polar Nephelometer instrument.

  5. Re-Os systematics and age of pyrite associated with stratiform Zn-Pb mineralization in the Howards Pass district, Yukon and Northwest Territories, Canada

    Science.gov (United States)

    Kelley, Karen D.; Selby, David; Falck, Hendrik; Slack, John F.

    2016-05-01

    Stratiform Zn-Pb deposits hosted in unmetamorphosed carbonaceous and siliceous mudstones of the Ordovician to Silurian Duo Lake Formation define the Howards Pass district in Yukon Territory and Northwest Territories, western Canada. Collectively, the deposits are amongst the largest in the world, containing drill-indicated and inferred resources of 423 Mt at 4.84 % Zn and 1.59 % Pb. Sulphide textures include (a) fine-scale laminations of sphalerite, galena, and pyrite from rock; (b) layers of coarse sulphide that are structurally controlled by microfolds; and (c) veins that cut bedding and sulphide laminations. The finely interlaminated nature of sulphides with mudstone has been used as evidence for syngenetic mineralizing processes, whereas paleomagnetic data determined on coarse layered sulphides suggest a Middle Jurassic age of mineralization. Here, we present new rhenium-osmium (Re-Os) isotopic data for 12 pyrite separates obtained from 4 laminated sulphide-rich samples from the XY Central (XYC) and Don (DON) deposits and for 1 unmineralized organic-rich mudstone ˜20 m stratigraphically below the sulphide-bearing zone. Pyrite separates that lack mudstone inclusions ("pure") from the XYC deposit contain 2.2 to 4.0 ppb Re and 93.4 to 123.4 ppt Os; pure pyrite from the DON deposit is significantly more enriched in Re and Os (34-37 ppb Re; 636.8-694.9 ppt Os). The 187Re/188Os values of pure pyrite separates from the XYC and DON deposits range from 137.6 to 197 and 182.1 to 201.4, respectively. Regression of all pure pyrite Re-Os data from both deposits yields an isochron age of 442 ± 14 Ma (MSWD = 7.4) and an initial 187Os/188Os (Osi) value of 0.71 ± 0.07. The Re-Os age indicates that the early phase of pyrite precipitation (and by inference, sphalerite and galena) occurred during the early Silurian, consistent with biostratigraphic ages of the host rocks. The Osi value of ˜0.8 for earliest Silurian seawater recorded from organic-rich shale in the basal

  6. Molecular Cloud Evolution

    CERN Document Server

    Vazquez-Semadeni, Enrique

    2010-01-01

    I describe the scenario of molecular cloud (MC) evolution that has emerged over the past decade or so. MCs can start out as cold atomic clouds formed by compressive motions in the warm neutral medium (WNM) of galaxies. Such motions can be driven by large-scale instabilities, or by local turbulence. The compressions induce a phase transition to the cold neutral medium (CNM) to form growing cold atomic clouds, which in their early stages may constitute thin CNM sheets. Several dynamical instabilities soon destabilize a cloud, rendering it turbulent. For solar neighborhood conditions, a cloud is coincidentally expected to become molecular, magnetically supercritical, and gravitationally dominated at roughly the same column density, $N \\sim 1.5 \\times 10^21 \\psc \\approx 10 \\Msun$ pc$^{-2}$. At this point, the cloud begins to contract gravitationally. However, before its global collapse is completed ($\\sim 10^7$ yr later), the nonlinear density fluctuations within the cloud, which have shorter local free-fall time...

  7. Interstellar molecular clouds

    Science.gov (United States)

    Bally, J.

    1986-04-01

    The physical properties of the molecular phase of the interstellar medium are studied with regard to star formation and the structure of the Galaxy. Most observations of molecular clouds are made with single-dish, high-surface precision radio telescopes, with the best resolution attainable at 0.2 to 1 arcmin; the smallest structures that can be resolved are of order 10 to the 17th cm in diameter. It is now believed that: (1) most of the mass of the Galaxy is in the form of giant molecular clouds; (2) the largest clouds and those responsible for most massive star formation are concentrated in spiral arms; (3) the molecular clouds are the sites of perpetual star formation, and are significant in the chemical evolution of the Galaxy; (4) giant molecular clouds determine the evolution of the kinematic properties of galactic disk stars; (5) the total gas content is diminishing with time; and (6) most clouds have supersonic internal motions and do not form stars on a free-fall time scale. It is concluded that though progress has been made, more advanced instruments are needed to inspect the processes operating within stellar nurseries and to study the distribution of the molecular clouds in more distant galaxies. Instruments presently under construction which are designed to meet these ends are presented.

  8. Cloud Computing Law

    CERN Document Server

    Millard, Christopher

    2013-01-01

    This book is about the legal implications of cloud computing. In essence, ‘the cloud’ is a way of delivering computing resources as a utility service via the internet. It is evolving very rapidly with substantial investments being made in infrastructure, platforms and applications, all delivered ‘as a service’. The demand for cloud resources is enormous, driven by such developments as the deployment on a vast scale of mobile apps and the rapid emergence of ‘Big Data’. Part I of this book explains what cloud computing is and how it works. Part II analyses contractual relationships between cloud service providers and their customers, as well as the complex roles of intermediaries. Drawing on primary research conducted by the Cloud Legal Project at Queen Mary University of London, cloud contracts are analysed in detail, including the appropriateness and enforceability of ‘take it or leave it’ terms of service, as well as the scope for negotiating cloud deals. Specific arrangements for public sect...

  9. Cloud Scheduler: a resource manager for distributed compute clouds

    CERN Document Server

    Armstrong, P; Bishop, A; Charbonneau, A; Desmarais, R; Fransham, K; Hill, N; Gable, I; Gaudet, S; Goliath, S; Impey, R; Leavett-Brown, C; Ouellete, J; Paterson, M; Pritchet, C; Penfold-Brown, D; Podaima, W; Schade, D; Sobie, R J

    2010-01-01

    The availability of Infrastructure-as-a-Service (IaaS) computing clouds gives researchers access to a large set of new resources for running complex scientific applications. However, exploiting cloud resources for large numbers of jobs requires significant effort and expertise. In order to make it simple and transparent for researchers to deploy their applications, we have developed a virtual machine resource manager (Cloud Scheduler) for distributed compute clouds. Cloud Scheduler boots and manages the user-customized virtual machines in response to a user's job submission. We describe the motivation and design of the Cloud Scheduler and present results on its use on both science and commercial clouds.

  10. Cloud Computing: A study of cloud architecture and its patterns

    Directory of Open Access Journals (Sweden)

    Mandeep Handa,

    2015-05-01

    Full Text Available Cloud computing is a general term for anything that involves delivering hosted services over the Internet. Cloud computing is a paradigm shift following the shift from mainframe to client–server in the early 1980s. Cloud computing can be defined as accessing third party software and services on web and paying as per usage. It facilitates scalability and virtualized resources over Internet as a service providing cost effective and scalable solution to customers. Cloud computing has evolved as a disruptive technology and picked up speed with the presence of many vendors in cloud computing space. The evolution of cloud computing from numerous technological approaches and business models such as SaaS, cluster computing, high performance computing, etc., signifies that the cloud IDM can be considered as a superset of all the corresponding issues from these paradigms and many more. In this paper we will discuss Life cycle management, Cloud architecture, Pattern in Cloud IDM, Volatility of Cloud relations.

  11. Cloud Optical Properties from the Multi-Filter Shadowband Radiometer (MFRSRCLDOD): An ARM Value-Added Product

    Energy Technology Data Exchange (ETDEWEB)

    Turner, DD; Lo, C; Min, Q

    2004-12-01

    The Min and Harrison algorithm has been incorporated into an ARM Value-Added Product (VAP) called MFRSR CLDOD. This version of the VAP (1Min) uses the diffuse transmission at 415 nm from the MFRSR. Therefore, the results are only valid for “horizontally homogeneous” stratiform clouds with optical depths larger than approximately 7. The retrieval assumes a single cloud layer consisting solely of liquid water drops. As specified by Min and Harrison (1996), the wavelength at 415 nm was chosen due to the lack of gaseous absorption and the relatively constant surface albedo (in the absence of snow) at this wavelength. The MFRSR CLDOD VAP (henceforth referred to as “the VAP”) retrieves cloud optical depth (τ) from the MFRSR measurements. If the LWP is available from a coincident MWR observation, then the droplet effective radius (re) can be determined. Knowledge of the estimated re can be used to improve the estimate of τ because there is a slight dependence on the extinction coefficient, single scattering albedo, and asymmetry parameter on effective radius at this wavelength. However, if the MWR’s LWP is not available, then the VAP assumes that re = 8.0 μm. The primary output from the VAP is τ and re.

  12. Investigating mixed phase clouds using a synergy of ground based remote sensing measurements

    Science.gov (United States)

    Gierens, Rosa; Kneifel, Stefan; Löhnert, Ulrich

    2017-04-01

    obtained from a Doppler wind lidar. Furthermore, the Cloudnet scheme (www.cloud-net.org), that combines radar, lidar and microwave radiometer observations with a forecast model to provide a best estimate of cloud properties, is used for identifying mixed phase clouds. The continuous measurements carried out at AWIPEV make it possible to characterize the macro- and micro- physical properties of mixed-phase clouds on a long-term, statistical basis. The Arctic observations are compared to a 5-year observational data set from Jülich Observatory for Cloud Evolution (JOYCE) in Western Germany. The occurrence of different types of clouds (with focus on mixed-phase and super-cooled clouds), the distribution of ice and liquid within the clouds, the turbulent environment as well as the temperatures where the different phases are occurring are investigated.

  13. Polar stratospheric cloud evolution and chlorine activation measured by CALIPSO and MLS, and modeled by ATLAS

    Science.gov (United States)

    Nakajima, Hideaki; Wohltmann, Ingo; Wegner, Tobias; Takeda, Masanori; Pitts, Michael C.; Poole, Lamont R.; Lehmann, Ralph; Santee, Michelle L.; Rex, Markus

    2016-03-01

    We examined observations of polar stratospheric clouds (PSCs) by CALIPSO, and of HCl and ClO by MLS along air mass trajectories, to investigate the dependence of the inferred PSC composition on the temperature history of the air parcels and the dependence of the level of chlorine activation on PSC composition. Several case studies based on individual trajectories from the Arctic winter 2009/2010 were conducted, with the trajectories chosen such that the first processing of the air mass by PSCs in this winter occurred on the trajectory. Transitions of PSC composition classes were observed to be highly dependent on the temperature history. In cases of a gradual temperature decrease, nitric acid trihydrate (NAT) and super-cooled ternary solution (STS) mixture clouds were observed. In cases of rapid temperature decrease, STS clouds were first observed, followed by NAT/STS mixture clouds. When temperatures dropped below the frost point, ice clouds formed and then transformed into NAT/STS mixture clouds when temperature increased above the frost point. The threshold temperature for rapid chlorine activation on PSCs is approximately 4 K below the NAT existence temperature, TNAT. Furthermore, simulations of the ATLAS chemistry and transport box model along the trajectories were used to corroborate the measurements and show good agreement with the observations. Rapid chlorine activation was observed when an air mass encountered PSCs. Usually, chlorine activation was limited by the amount of available ClONO2. Where ClONO2 was not the limiting factor, a large dependence on temperature was evident.

  14. July 2012 Greenland melt extent enhanced by low-level liquid clouds.

    Science.gov (United States)

    Bennartz, R; Shupe, M D; Turner, D D; Walden, V P; Steffen, K; Cox, C J; Kulie, M S; Miller, N B; Pettersen, C

    2013-04-04

    Melting of the world's major ice sheets can affect human and environmental conditions by contributing to sea-level rise. In July 2012, an historically rare period of extended surface melting was observed across almost the entire Greenland ice sheet, raising questions about the frequency and spatial extent of such events. Here we show that low-level clouds consisting of liquid water droplets ('liquid clouds'), via their radiative effects, played a key part in this melt event by increasing near-surface temperatures. We used a suite of surface-based observations, remote sensing data, and a surface energy-balance model. At the critical surface melt time, the clouds were optically thick enough and low enough to enhance the downwelling infrared flux at the surface. At the same time they were optically thin enough to allow sufficient solar radiation to penetrate through them and raise surface temperatures above the melting point. Outside this narrow range in cloud optical thickness, the radiative contribution to the surface energy budget would have been diminished, and the spatial extent of this melting event would have been smaller. We further show that these thin, low-level liquid clouds occur frequently, both over Greenland and across the Arctic, being present around 30-50 per cent of the time. Our results may help to explain the difficulties that global climate models have in simulating the Arctic surface energy budget, particularly as models tend to under-predict the formation of optically thin liquid clouds at supercooled temperatures--a process potentially necessary to account fully for temperature feedbacks in a warming Arctic climate.

  15. Polar Stratospheric Cloud evolution and chlorine activation measured by CALIPSO and MLS, and modelled by ATLAS

    Science.gov (United States)

    Nakajima, H.; Wohltmann, I.; Wegner, T.; Takeda, M.; Pitts, M. C.; Poole, L. R.; Lehmann, R.; Santee, M. L.; Rex, M.

    2015-08-01

    We examined observations of polar stratospheric clouds (PSCs) by CALIPSO and of HCl, ClO and HNO3 by MLS along air mass trajectories to investigate the dependence of the inferred PSC composition on the temperature history of the air parcels, and the dependence of the level of chlorine activation on PSC composition. Several case studies based on individual trajectories from the Arctic winter 2009/10 were conducted, with the trajectories chosen such that the first processing of the air mass by PSCs in this winter occurred on the trajectory. Transitions of PSC composition classes were observed to be highly dependent on the temperature history. In cases of a gradual temperature decrease, nitric acid trihydrate (NAT) and super-cooled ternary solution (STS) mixture clouds were observed. In cases of rapid temperature decrease, STS clouds were first observed, followed by NAT/STS mixture clouds. When temperatures dropped below the frost point, ice clouds formed, and then transformed into NAT/STS mixture clouds when temperature increased above the frost point. The threshold temperature for rapid chlorine activation on PSCs is approximately 4 K below the NAT existence temperature, TNAT. Furthermore, simulations of the ATLAS chemistry and transport box model along the trajectories were used to corroborate the measurements and show good agreement with the observations. Rapid chlorine activation was observed when an airmass encountered PSCs. The observed and modelled dependence of the rate of chlorine activation on the PSC composition class was small. Usually, chlorine activation was limited by the amount of available ClONO2. Where ClONO2 was not the limiting factor, a large dependence on temperature was evident.

  16. Polar Stratospheric Cloud evolution and chlorine activation measured by CALIPSO and MLS, and modelled by ATLAS

    Directory of Open Access Journals (Sweden)

    H. Nakajima

    2015-08-01

    Full Text Available We examined observations of polar stratospheric clouds (PSCs by CALIPSO and of HCl, ClO and HNO3 by MLS along air mass trajectories to investigate the dependence of the inferred PSC composition on the temperature history of the air parcels, and the dependence of the level of chlorine activation on PSC composition. Several case studies based on individual trajectories from the Arctic winter 2009/10 were conducted, with the trajectories chosen such that the first processing of the air mass by PSCs in this winter occurred on the trajectory. Transitions of PSC composition classes were observed to be highly dependent on the temperature history. In cases of a gradual temperature decrease, nitric acid trihydrate (NAT and super-cooled ternary solution (STS mixture clouds were observed. In cases of rapid temperature decrease, STS clouds were first observed, followed by NAT/STS mixture clouds. When temperatures dropped below the frost point, ice clouds formed, and then transformed into NAT/STS mixture clouds when temperature increased above the frost point. The threshold temperature for rapid chlorine activation on PSCs is approximately 4 K below the NAT existence temperature, TNAT. Furthermore, simulations of the ATLAS chemistry and transport box model along the trajectories were used to corroborate the measurements and show good agreement with the observations. Rapid chlorine activation was observed when an airmass encountered PSCs. The observed and modelled dependence of the rate of chlorine activation on the PSC composition class was small. Usually, chlorine activation was limited by the amount of available ClONO2. Where ClONO2 was not the limiting factor, a large dependence on temperature was evident.

  17. A cybernetics Social Cloud

    OpenAIRE

    Chang, V

    2015-01-01

    © 2015 Elsevier Inc. This paper proposes a Social Cloud, which presents the system design, development and analysis. The technology is based on the BOINC open source software, our hybrid Cloud, Facebook Graph API and our development in a new Facebook API, SocialMedia. The creation of SocialMedia API with its four functions can ensure a smooth delivery of Big Data processing in the Social Cloud, with four selected examples provided. The proposed solution is focused on processing the contacts w...

  18. Cloud Computing Services Accounting

    Directory of Open Access Journals (Sweden)

    Igor Ruiz-Agundez

    2012-06-01

    Full Text Available Cloud computing provides a new promising parading to offer services. It brings the opportunity to develop new business models in the Internet. Classic accounting solutions fail to full fill the new requirements of these services due to their structural design. To understand these new constrains, we study the different actors and processes that interact in the Internet Economics. Specifically, we focus on cloud computing introducing a methodology that allows the deployment of cloud services. Further, we present an Infrastructure as a Service (IaaS use case that applies the proposed system.

  19. Trusted cloud computing

    CERN Document Server

    Krcmar, Helmut; Rumpe, Bernhard

    2014-01-01

    This book documents the scientific results of the projects related to the Trusted Cloud Program, covering fundamental aspects of trust, security, and quality of service for cloud-based services and applications. These results aim to allow trustworthy IT applications in the cloud by providing a reliable and secure technical and legal framework. In this domain, business models, legislative circumstances, technical possibilities, and realizable security are closely interwoven and thus are addressed jointly. The book is organized in four parts on "Security and Privacy", "Software Engineering and

  20. Cloud computing basics for librarians.

    Science.gov (United States)

    Hoy, Matthew B

    2012-01-01

    "Cloud computing" is the name for the recent trend of moving software and computing resources to an online, shared-service model. This article briefly defines cloud computing, discusses different models, explores the advantages and disadvantages, and describes some of the ways cloud computing can be used in libraries. Examples of cloud services are included at the end of the article.

  1. Taxonomy of cloud computing services

    NARCIS (Netherlands)

    Hoefer, C.N.; Karagiannis, G.

    2010-01-01

    Cloud computing is a highly discussed topic, and many big players of the software industry are entering the development of cloud services. Several companies want to explore the possibilities and benefits of cloud computing, but with the amount of cloud computing services increasing quickly, the need

  2. Taxonomy of cloud computing services

    NARCIS (Netherlands)

    Hoefer, C.N.; Karagiannis, Georgios

    2010-01-01

    Cloud computing is a highly discussed topic, and many big players of the software industry are entering the development of cloud services. Several companies want to explore the possibilities and benefits of cloud computing, but with the amount of cloud computing services increasing quickly, the need

  3. Simulation of polar stratospheric clouds in the chemistry-climate-model EMAC via the submodel PSC

    Directory of Open Access Journals (Sweden)

    O. Kirner

    2011-03-01

    Full Text Available The submodel PSC of the ECHAM5/MESSy Atmospheric Chemistry model (EMAC has been developed to simulate the main types of polar stratospheric clouds (PSC. The parameterisation of the supercooled ternary solutions (STS, type 1b PSC in the submodel is based on Carslaw et al. (1995b, the thermodynamic approach to simulate ice particles (type 2 PSC on Marti and Mauersberger (1993. For the formation of nitric acid trihydrate (NAT particles (type 1a PSC two different parameterisations exist. The first is based on an instantaneous thermodynamic approach from Hanson and Mauersberger (1988, the second is new implemented and considers the growth of the NAT particles with the aid of a surface growth factor based on Carslaw et al. (2002. It is possible to choose one of this NAT parameterisation in the submodel. This publication explains the background of the submodel PSC and the use of the submodel with the goal of simulating realistic PSC in EMAC.

  4. Formation of mixed-phase particles during the freezing of polar stratospheric ice clouds.

    Science.gov (United States)

    Bogdan, Anatoli; Molina, Mario J; Tenhu, Heikki; Mayer, Erwin; Loerting, Thomas

    2010-03-01

    Polar stratospheric clouds (PSCs) are extremely efficient at catalysing the transformation of photostable chlorine reservoirs into photolabile species, which are actively involved in springtime ozone-depletion events. Why PSCs are such efficient catalysts, however, is not well understood. Here, we investigate the freezing behaviour of ternary HNO₃-H₂SO₄-H₂O droplets of micrometric size, which form type II PSC ice particles. We show that on freezing, a phase separation into pure ice and a residual solution coating occurs; this coating does not freeze but transforms into glass below ∼150 K. We find that the coating, which is thicker around young ice crystals, can still be approximately 30 nm around older ice crystals of diameter about 10 µm. These results affect our understanding of PSC microphysics and chemistry and suggest that chlorine-activation reactions are better studied on supercooled HNO₃-H₂SO₄-H₂O solutions rather than on a pure ice surface.

  5. Cloud Computing (2/2)

    CERN Document Server

    CERN. Geneva

    2012-01-01

    Cloud computing, the recent years buzzword for distributed computing, continues to attract and keep the interest of both the computing and business world. These lectures aim at explaining "What is Cloud Computing?" identifying and analyzing it's characteristics, models, and applications. The lectures will explore different "Cloud definitions" given by different authors and use them to introduce the particular concepts. The main cloud models (SaaS, PaaS, IaaS), cloud types (public, private, hybrid), cloud standards and security concerns will be presented. The borders between Cloud Computing and Grid Computing, Server Virtualization, Utility Computing will be discussed and analyzed.

  6. IBM SmartCloud essentials

    CERN Document Server

    Schouten, Edwin

    2013-01-01

    A practical, user-friendly guide that provides an introduction to cloud computing using IBM SmartCloud, along with a thorough understanding of resource management in a cloud environment.This book is great for anyone who wants to get a grasp of what cloud computing is and what IBM SmartCloud has to offer. If you are an IT specialist, IT architect, system administrator, or a developer who wants to thoroughly understand the cloud computing resource model, this book is ideal for you. No prior knowledge of cloud computing is expected.

  7. Cloud Computing (1/2)

    CERN Document Server

    CERN. Geneva

    2012-01-01

    Cloud computing, the recent years buzzword for distributed computing, continues to attract and keep the interest of both the computing and business world. These lectures aim at explaining "What is Cloud Computing?" identifying and analyzing it's characteristics, models, and applications. The lectures will explore different "Cloud definitions" given by different authors and use them to introduce the particular concepts. The main cloud models (SaaS, PaaS, IaaS), cloud types (public, private, hybrid), cloud standards and security concerns will be presented. The borders between Cloud Computing and Grid Computing, Server Virtualization, Utility Computing will be discussed and analyzed.

  8. Nature of the anomalies in the supercooled liquid state of the mW model of water

    CERN Document Server

    Holten, Vincent; Molinero, Valeria; Anisimov, Mikhail A

    2013-01-01

    The thermodynamic properties of the supercooled liquid state of the mW model of water show anomalous behavior. Like in real water, the heat capacity and compressibility sharply increase upon supercooling. One of the possible explanations of these anomalies, the existence of a second (liquid-liquid) critical point, is not supported by simulations for this particular model. In this work, we reproduce the anomalies of the mW model with two thermodynamic scenarios: one based on a non-ideal "mixture" with two different types of local order of the water molecules, and one based on weak crystallization theory. We show that both descriptions accurately reproduce the model's basic thermodynamic properties. However, the coupling constant required for fitting the power laws implied by weak crystallization theory is found not to be physically meaningful. For the two-state approach, the direct computation of the low-density fraction of molecules in the mW model is in agreement with the prediction of the phenomenological e...

  9. NASA/FAA/NCAR Supercooled Large Droplet Icing Flight Research: Summary of Winter 1996-1997 Flight Operations

    Science.gov (United States)

    Miller, Dean; Ratvasky, Thomas; Bernstein, Ben; McDonough, Frank; Strapp, J. Walter

    1998-01-01

    During the winter of 1996-1997, a flight research program was conducted at the NASA-Lewis Research Center to study the characteristics of Supercooled Large Droplets (SLD) within the Great Lakes region. This flight program was a joint effort between the National Aeronautics and Space Administration (NASA), the National Center for Atmospheric Research (NCAR), and the Federal Aviation Administration (FAA). Based on weather forecasts and real-time in-flight guidance provided by NCAR, the NASA-Lewis Icing Research Aircraft was flown to locations where conditions were believed to be conducive to the formation of Supercooled Large Droplets aloft. Onboard instrumentation was then used to record meteorological, ice accretion, and aero-performance characteristics encountered during the flight. A total of 29 icing research flights were conducted, during which "conventional" small droplet icing, SLD, and mixed phase conditions were encountered aloft. This paper will describe how flight operations were conducted, provide an operational summary of the flights, present selected experimental results from one typical research flight, and conclude with practical "lessons learned" from this first year of operation.

  10. Supercooling capacity and cold hardiness of the adults of the sycamore lace bug, corythucha ciliata (Hemiptera:Tingidae).

    Science.gov (United States)

    Ju, Rui-Ting; Wang, Feng; Xiao, Yu-Yu; Li, Bo

    2010-01-01

    Supercooling point (SCP) of female adults of Corythucha ciliata was significantly lower than that of male adults, with an average being -11.49 degrees C and -9.54 degrees C, respectively. Low temperature survival of adults of different ages indicated that there were differences in cold survival ability among age groups of adults. Nonlinear regression analysis found that the response of C. ciliata adults to exposure time under different low temperature regimes (above -5 degrees C) was best fitted by a logistic equation. Both low temperature and exposure time had significant effects on mortality of adults. Temperatures above 5 degrees C did not prevent C. ciliata adults from surviving. C. ciliata was shown to be a freeze-intolerant but chill-tolerant insect. C. ciliata could tolerate subzero temperatures by supercooling. Temperature around -8 degres C is a critical point for successful overwintering of C. ciliata adults, which can establish in the whole areas where Platanus trees are planted in China.

  11. Dynamics of supercooled liquid and plastic crystalline ethanol: Dielectric relaxation and AC nanocalorimetry distinguish structural α- and Debye relaxation processes

    Science.gov (United States)

    Chua, Y. Z.; Young-Gonzales, A. R.; Richert, R.; Ediger, M. D.; Schick, C.

    2017-07-01

    Physical vapor deposition has been used to prepare glasses of ethanol. Upon heating, the glasses transformed into the supercooled liquid phase and then crystallized into the plastic crystal phase. The dynamic glass transition of the supercooled liquid is successfully measured by AC nanocalorimetry, and preliminary results for the plastic crystal are obtained. The frequency dependences of these dynamic glass transitions observed by AC nanocalorimetry are in disagreement with conclusions from previously published dielectric spectra of ethanol. Existing dielectric loss spectra have been carefully re-evaluated considering a Debye peak, which is a typical feature in the dielectric loss spectra of monohydroxy alcohols. The re-evaluated dielectric fits reveal a prominent dielectric Debye peak, a smaller and asymmetrically broadened peak, which is identified as the signature of the structural α-relaxation and a Johari-Goldstein secondary relaxation process. This new assignment of the dielectric processes is supported by the observation that the AC nanocalorimetry dynamic glass transition temperature, Tα, coincides with the dielectric structural α-relaxation process rather than the Debye process. The combined results from dielectric spectroscopy and AC nanocalorimetry on the plastic crystal of ethanol suggest the occurrence of a Debye process also in the plastic crystal phase.

  12. Heterogeneous nucleation from a supercooled ionic liquid on a carbon surface

    Science.gov (United States)

    He, Xiaoxia; Shen, Yan; Hung, Francisco R.; Santiso, Erik E.

    2016-12-01

    Classical molecular dynamics simulations were used to study the nucleation of the crystal phase of the ionic liquid [dmim+][Cl-] from its supercooled liquid phase, both in the bulk and in contact with a graphitic surface of D = 3 nm. By combining the string method in collective variables [Maragliano et al., J. Chem. Phys. 125, 024106 (2006)], with Markovian milestoning with Voronoi tessellations [Maragliano et al., J. Chem. Theory Comput. 5, 2589-2594 (2009)] and order parameters for molecular crystals [Santiso and Trout, J. Chem. Phys. 134, 064109 (2011)], we computed minimum free energy paths, the approximate size of the critical nucleus, the free energy barrier, and the rates involved in these nucleation processes. For homogeneous nucleation, the subcooled liquid phase has to overcome a free energy barrier of ˜85 kcal/mol to form a critical nucleus of size ˜3.6 nm, which then grows into the monoclinic crystal phase. This free energy barrier becomes about 42% smaller (˜49 kcal/mol) when the subcooled liquid phase is in contact with a graphitic disk, and the critical nucleus formed is about 17% smaller (˜3.0 nm) than the one observed for homogeneous nucleation. The crystal formed in the heterogeneous nucleation scenario has a structure that is similar to that of the bulk crystal, with the exception of the layers of ions next to the graphene surface, which have larger local density and the cations lie with their imidazolium rings parallel to the graphitic surface. The critical nucleus forms near the graphene surface separated only by these layers of ions. The heterogeneous nucleation rate (˜4.8 × 1011 cm-3 s-1) is about one order of magnitude faster than the homogeneous rate (˜6.6 × 1010 cm-3 s-1). The comp