WorldWideScience

Sample records for high latitude wind

  1. High Altitude Bird Migration at Temperate Latitudes: A Synoptic Perspective on Wind Assistance

    OpenAIRE

    2013-01-01

    At temperate latitudes the synoptic patterns of bird migration are strongly structured by the presence of cyclones and anticyclones, both in the horizontal and altitudinal dimensions. In certain synoptic conditions, birds may efficiently cross regions with opposing surface wind by choosing a higher flight altitude with more favourable wind. We observed migratory passerines at mid-latitudes that selected high altitude wind optima on particular nights, leading to the formation of structured mig...

  2. High-latitude Conic Current Sheets in the Solar Wind

    Science.gov (United States)

    Khabarova, Olga V.; Malova, Helmi V.; Kislov, Roman A.; Zelenyi, Lev M.; Obridko, Vladimir N.; Kharshiladze, Alexander F.; Tokumaru, Munetoshi; Sokół, Justyna M.; Grzedzielski, Stan; Fujiki, Ken'ichi

    2017-02-01

    We provide observational evidence for the existence of large-scale cylindrical (or conic-like) current sheets (CCSs) at high heliolatitudes. Long-lived CCSs were detected by Ulysses during its passages over the South Solar Pole in 1994 and 2007. The characteristic scale of these tornado-like structures is several times less than a typical width of coronal holes within which the CCSs are observed. CCS crossings are characterized by a dramatic decrease in the solar wind speed and plasma beta typical for predicted profiles of CCSs. Ulysses crossed the same CCS at different heliolatitudes at 2-3 au several times in 1994, as the CCS was declined from the rotation axis and corotated with the Sun. In 2007, a CCS was detected directly over the South Pole, and its structure was strongly highlighted by the interaction with comet McNaught. Restorations of solar coronal magnetic field lines reveal the occurrence of conic-like magnetic separators over the solar poles in both 1994 and 2007. Such separators exist only during solar minima. Interplanetary scintillation data analysis confirms the presence of long-lived low-speed regions surrounded by the typical polar high-speed solar wind in solar minima. Energetic particle flux enhancements up to several MeV/nuc are observed at edges of the CCSs. We built simple MHD models of a CCS to illustrate its key features. The CCSs may be formed as a result of nonaxiality of the solar rotation axis and magnetic axis, as predicted by the Fisk-Parker hybrid heliospheric magnetic field model in the modification of Burger and coworkers.

  3. Small-scale anisotropy and intermittency in high and low-latitude solar wind

    CERN Document Server

    Bigazzi, A; Gama, S M A; Velli, M

    2004-01-01

    We analyze low and high--latitude fast solar wind data from the Ulysses spacecraft from 1992 to 1994 using a a systematic method to analyse the anisotropic content of the magnetic field fluctuations. We investigate all available frequencies, 1-10^{-6} Hz, for both high and low--latitudes datasets and are able to quantify the relative importance of the anisotropic versus the isotropic fluctuations. We analyse, up to sixth order, longitudinal, transverse and mixed magnetic field correlations. Our results show that strongly intermittent and anisotropic events are present in the solar wind plasma at high frequencies/small scales, indicating the absence of a complete recovery of isotropy. Anisotropic scaling properties are compatible for high and low--latitude data, suggesting a universal behaviour in spite of the different rate of evolution of the fast solar wind streams in the two environments.

  4. Solar wind entry into the high-latitude terrestrial magnetosphere during geomagnetically quiet times.

    Science.gov (United States)

    Shi, Q Q; Zong, Q-G; Fu, S Y; Dunlop, M W; Pu, Z Y; Parks, G K; Wei, Y; Li, W H; Zhang, H; Nowada, M; Wang, Y B; Sun, W J; Xiao, T; Reme, H; Carr, C; Fazakerley, A N; Lucek, E

    2013-01-01

    An understanding of the transport of solar wind plasma into and throughout the terrestrial magnetosphere is crucial to space science and space weather. For non-active periods, there is little agreement on where and how plasma entry into the magnetosphere might occur. Moreover, behaviour in the high-latitude region behind the magnetospheric cusps, for example, the lobes, is poorly understood, partly because of lack of coverage by previous space missions. Here, using Cluster multi-spacecraft data, we report an unexpected discovery of regions of solar wind entry into the Earth's high-latitude magnetosphere tailward of the cusps. From statistical observational facts and simulation analysis we suggest that these regions are most likely produced by magnetic reconnection at the high-latitude magnetopause, although other processes, such as impulsive penetration, may not be ruled out entirely. We find that the degree of entry can be significant for solar wind transport into the magnetosphere during such quiet times.

  5. Equatorwards Expansion of Unperturbed, High-Latitude Fast Solar Wind

    CERN Document Server

    Dorrian, Gareth; Fallows, Richard; Bisi, Mario

    2012-01-01

    We use dual-site radio observations of interplanetary scintillation (IPS) with extremely long baselines (ELB) to examine meridional flow characteristics of the ambient fast solar wind at plane-of-sky heliocentric distances of 24-85 solar radii (R\\odot). Our results demonstrate an equatorwards deviation of 3-4{\\deg} in the bulk fast solar wind flow direction over both northern and southern solar hemispheres during different times in the declining phase of Solar Cycle 23.

  6. Relative Contributions of Heating and Momentum Forcing to High-Latitude Lower Thermospheric Winds

    Science.gov (United States)

    Kwak, Y. S.; Richmond, A. D.

    2015-12-01

    At high latitudes the thermospheric dynamics are gov­erned by various heat and momentum sources. Recently several modeling studies have been attempt­ed to understand the physical process that control the high-latitude lower thermospheric dynamics. Kwak and Richmond [2007] and Kwak et al. [2007] studied the momentum forcing bal­ance that are mainly responsible for maintaining the high-latitude lower thermospheric wind system by using the National Center for Atmospheric Research Thermo­sphere Ionosphere Electrodynamics General Circulation Model (NCAR TIE-GCM). Kwak and Richmond [2014] analyzed the divergence and vorticity of the high-latitude neutral wind field in the lower thermosphere during the south­ern summertime. In this study, we extend previous works by Kwak and Rich­mond [2007, 2014] and Kwak et al. [2007], which helped to better understand the physical processes maintaining thermospheric dynamics at high latitudes, and here perform a "term analysis of the potential vorticity equation" for the high-latitude neu­tral wind field in the lower thermosphere, on the basis of numerical simulations using the NCAR TIE-GCM. These analyses can provide insight into the relative strength of the heating and the momentum forcing responsible for driving rotational winds at the high-latitude lower thermosphere. The heating is the net heat including the heat transfer by downward molecular and eddy heat conduction, the absorption of solar ultraviolet (UV) and extreme ultraviolet (EUV) ra­diation, auroral heating by particles, Joule dissipation of ionospheric currents, release of chemical energy by the atomic oxygen recombination, and radiative CO2, NO and O infrared emissions. The momentum forcing is associated with the viscous force and the frictional drag force from convecting ions.

  7. Winds in the high-latitude lower thermosphere: Dependence on the interplanetary magnetic field

    DEFF Research Database (Denmark)

    Richmond, A.D.; Lathuillere, C.; Vennerstrøm, Susanne

    2003-01-01

    [1] Wind observations in the summertime lower thermosphere at high southern latitudes, measured by the Wind Imaging Interferometer (WINDII) on the Upper Atmosphere Research Satellite, are statistically analyzed in magnetic coordinates and correlated with the interplanetary magnetic field (IMF......) to determine influences of IMF-dependent ionospheric convection on the winds. Effects are clearly detectable down to 105 km altitude. Above 125 km the wind patterns show considerable similarity with ionospheric convection patterns, and the speed of the averaged neutral wind in the polar cap often exceeds 300 m....../s. The correlation between the IMF B-z component and the diurnal harmonic of the winds is generally best when the IMF is averaged over the preceding 1-4.5 hours. The magnetic-zonal-mean zonal wind below 120 km correlates best with the IMF B-y component when the latter is averaged over approximately the preceding 20...

  8. Effects of magnetospheric lobe cell convection on dayside upper thermospheric winds at high latitudes

    Science.gov (United States)

    Zhang, B.; Wang, W.; Wu, Q.; Knipp, D.; Kilcommons, L.; Brambles, O. J.; Liu, J.; Wiltberger, M.; Lyon, J. G.; Häggström, I.

    2016-08-01

    This paper investigates a possible physical mechanism of the observed dayside high-latitude upper thermospheric wind using numerical simulations from the coupled magnetosphere-ionosphere-thermosphere (CMIT) model. Results show that the CMIT model is capable of reproducing the unexpected afternoon equatorward winds in the upper thermosphere observed by the High altitude Interferometer WIND observation (HIWIND) balloon. Models that lack adequate coupling produce poleward winds. The modeling study suggests that ion drag driven by magnetospheric lobe cell convection is another possible mechanism for turning the climatologically expected dayside poleward winds to the observed equatorward direction. The simulation results are validated by HIWIND, European Incoherent Scatter, and Defense Meteorological Satellite Program. The results suggest a strong momentum coupling between high-latitude ionospheric plasma circulation and thermospheric neutral winds in the summer hemisphere during positive IMF Bz periods, through the formation of magnetospheric lobe cell convection driven by persistent positive IMF By. The CMIT simulation adds important insight into the role of dayside coupling during intervals of otherwise quiet geomagnetic activity

  9. Comparison of high-latitude thermospheric meridional winds II: combined FPI, radar and model climatologies

    Energy Technology Data Exchange (ETDEWEB)

    Griffin, E.M.; Aruliah, A.; Mueller-Wodarg, I.C.F.; Aylward, A. [Atmospheric Physics Lab., Univ. Coll. London, London (United Kingdom)

    2004-07-01

    The climatological behaviour of the thermospheric meridional wind above Kiruna, Sweden (67.4 N, 20.4 E) has been investigated for seasonal and solar cycle dependence using six different techniques, comprising both model and experimental sources. Model output from both the empirical Horizontal Wind Model (HWM) (Hedin et al., 1988) and the numerical coupled thermosphere and ionosphere model (CTIM) are compared to the measured behaviour at kiruna, as a single site example. The empirical International Reference Ionosphere (IRI) model is used as input to an implementation of servo theory, to provide another climatology combining empirical input with a theoretical framework. The experimental techniques have been introduced in a companion paper in this issue and provide climatologies from direct measurements, using fabry-perot interferometers (FPI), together with 2 separate techniques applied to the European incoherent scatter radar (EISCAT) database to derive neutral winds. One of these techniques uses the same implementation of servo theory as has been used with the IRI model. Detailed comparisons for each season and solar activity category allow for conclusions to be drawn as to the major influences on the climatological behaviour of the wind at this latitude. Comparison of the incoherent scatter radar (ISR) derived neutral winds with FPI, empirical model and numerical model winds is important to our understanding and judgement of the validity of the techniques used to derive thermospheric wind databases. The comparisons also test model performance and indicate possible reasons for differences found between the models. In turn, the conclusions point to possible improvements in their formulation. In particular it is found that the empirical models are over-reliant on mid-latitude data in their formulation, and fail to provide accurate estimates of the winds at high-latitudes. (orig.)

  10. Comparison of high-latitude thermospheric meridional winds I: optical and radar experimental comparisons

    Energy Technology Data Exchange (ETDEWEB)

    Griffin, E.M.; Mueller-Wodarg, I.C.F.; Aruliah, A.; Aylward, A. [Atmospheric Physics Lab., Univ. Coll. London, London (United Kingdom)

    2004-07-01

    Thermospheric neutral winds at Kiruna, Sweden (67.4 N, 20.4 E) are compared using both direct optical fabry-perot interferometer (FPI) measurements and those derived from European incoherent scatter radar (EISCAT) measurements. This combination of experimental data sets, both covering well over a solar cycle of data, allows for a unique comparison of the thermospheric meridional component of the neutral wind as observed by different experimental techniques. Uniquely in this study the EISCAT measurements are used to provide winds for comparison using two separate techniques: the most popular method based on the work of Salah and Holt (1974) and the meridional wind model (MWM) (Miller et al., 1997) application of servo theory. The balance of forces at this location that produces the observed diurnal pattern are investigated using output from the coupled thermosphere and ionosphere (CTIM) numerical model. Along with detailed comparisons from short periods the climatological behaviour of the winds have been investigated for seasonal and solar cycle dependence using the experimental techniques. While there are features which are consistent between the 3 techniques, such as the evidence of the equinoctial asymmetry, there are also significant differences between the techniques both in terms of trends and absolute values. It is clear from this and previous studies that the high-latitude representation of the thermospheric neutral winds from the empirical horizontal wind model (HWM), though improved from earlier versions, lacks accuracy in many conditions. The relative merits of each technique are discussed and while none of the techniques provides the perfect data set to address model performance at high-latitude, one or more needs to be included in future HWM reformulations. (orig.)

  11. Winds in the high-latitude lower thermosphere: Dependence on the interplanetary magnetic field

    DEFF Research Database (Denmark)

    Richmond, A.D.; Lathuillere, C.; Vennerstrøm, Susanne

    2003-01-01

    -side cyclonic vortex that responds more strongly to B-z variations. The dependence of the wind on the IMF is nonlinear, especially with respect to IMF B-z. For positive B-z the difference winds are largely confined to the polar cap, while for negative B-z the difference winds extend to subauroral latitudes...... of similar to20 hours, a B-y-dependent magnetic-zonal-mean zonal wind generally exists, with maximum wind speeds at 80 magnetic latitude, typically 10 m/s at 105 km, increasing to about 60 m/s at 123 km and 80 m/s at 200 km. In the southern hemisphere the wind is cyclonic when the time-averaged B...

  12. High-latitude plasma convection from Cluster EDI: variances and solar wind correlations

    Directory of Open Access Journals (Sweden)

    M. Förster

    2007-07-01

    Full Text Available Based on drift velocity measurements of the EDI instruments on Cluster during the years 2001–2006, we have constructed a database of high-latitude ionospheric convection velocities and associated solar wind and magnetospheric activity parameters. In an earlier paper (Haaland et al., 2007, we have described the method, consisting of an improved technique for calculating the propagation delay between the chosen solar wind monitor (ACE and Earth's magnetosphere, filtering the data for periods of sufficiently stable IMF orientations, and mapping the EDI measurements from their high-altitude positions to ionospheric altitudes. The present paper extends this study, by looking at the spatial pattern of the variances of the convection velocities as a function of IMF orientation, and by performing sortings of the data according to the IMF magnitude in the GSM y-z plane, |ByzIMF|, the estimated reconnection electric field, Er,sw, the solar wind dynamic pressure, Pdyn, the season, and indices characterizing the ring current (Dst and tail activity (ASYM-H. The variability of the high-latitude convection shows characteristic spatial patterns, which are mirror symmetric between the Northern and Southern Hemispheres with respect to the IMF By component. The latitude range of the highest variability zone varies with IMF Bz similar to the auroral oval extent. The magnitude of convection standard deviations is of the same order as, or even larger than, the convection magnitude itself. Positive correlations of polar cap activity are found with |ByzIMF| and with Er,sw, in particular. The strict linear increase for small magnitudes of Er,sw starts to deviate toward a flattened increase above about 2 mV/m. There is also a weak positive correlation with Pdyn. At

  13. First observations of simultaneous interhemispheric conjugate high-latitude thermospheric winds

    Science.gov (United States)

    Kosch, M. J.; Anderson, C.; Yiu, H.-C. I.; Kellerman, A. C.; Makarevich, R. A.; Aruliah, A.; Conde, M.; Griffin, E.; Davies, T.; McWhirter, I.; Dyson, P. L.

    2010-09-01

    We report the first observations of simultaneous high-latitude interhemispheric F region neutral wind fields by combining the 630 nm optical measurements from two scanning Doppler imagers (SDIs) and three Fabry-Perot interferometers (FPIs) for a period exceeding 5 h. From the Southern Hemisphere, a SDI at Mawson and a FPI at Davis, both in Antarctica, are geomagnetically mapped onto the Northern Hemisphere. These data are combined in the Northern Hemisphere with a SDI at Longyearbyen, Svalbard, and two FPIs near Kiruna in Sweden and Sodankyla in Finland. Geomagnetic conditions were moderate (Kp = 3--3+) and steady although the interplanetary magnetic field Bz component did change polarity several times. There is good agreement between the conjugate 630 nm optical intensities and wind vectors where the two SDIs' fields of view overlap. All wind field vectors are overlaid onto the northern Super Dual Auroral Radar Network ion convection contours. Qualitatively, the agreement between neutral and ion flow is remarkably good throughout the study interval, even down to mesoscale spatial size.

  14. High Altitude Bird Migration at Temperate Latitudes: A Synoptic Perspective on Wind Assistance

    NARCIS (Netherlands)

    Dokter, A.M.; Shamoun-Baranes, J.; Kemp, M.U.; Tijm, S.; Holleman, I.

    2013-01-01

    At temperate latitudes the synoptic patterns of bird migration are strongly structured by the presence of cyclones and anticyclones, both in the horizontal and altitudinal dimensions. In certain synoptic conditions, birds may efficiently cross regions with opposing surface wind by choosing a higher

  15. The geomagnetic cutoff rigidities at high latitudes for different solar wind and geomagnetic conditions

    Energy Technology Data Exchange (ETDEWEB)

    Chu, W. [Chinese Academy of Sciences, Beijing (China). State Key Lab. of Space Weather; Univ. of Chinese Academy of Sciences, Beijing (China). College of Earth Sciences; Qin, G. [Chinese Academy of Sciences, Beijing (China). State Key Lab. of Space Weather

    2016-04-01

    Studying the access of the cosmic rays (CRs) into the magnetosphere is important to understand the coupling between the magnetosphere and the solar wind. In this paper we numerically studied CRs' magnetospheric access with vertical geomagnetic cutoff rigidities using the method proposed by Smart and Shea (1999). By the study of CRs' vertical geomagnetic cutoff rigidities at high latitudes we obtain the CRs' window (CRW) whose boundary is determined when the vertical geomagnetic cutoff rigidities drop to a value lower than a threshold value. Furthermore, we studied the area of CRWs and found out they are sensitive to different parameters, such as the z component of interplanetary magnetic field (IMF), the solar wind dynamic pressure, AE index, and Dst index. It was found that both the AE index and Dst index have a strong correlation with the area of CRWs during strong geomagnetic storms. However, during the medium storms, only AE index has a strong correlation with the area of CRWs, while Dst index has a much weaker correlation with the area of CRWs. This result on the CRW can be used for forecasting the variation of the cosmic rays during the geomagnetic storms.

  16. Dayside magnetic ULF power at high latitudes: A possible long-term proxy for the solar wind velocity?

    DEFF Research Database (Denmark)

    Vennerstrøm, Susanne

    1999-01-01

    We examine the occurrence of dayside high-latitude magnetic variations with periods between 2 and 10 min statistically using data from around 20 magnetic stations in Greenland, Scandinavia, and Canada, many of which have been in operation for a full solar cycle. We derive time series of the power...... in the 5-10 min band for the auroral stations. We find the results encouraging for the use of dayside spectral band power at high-latitude stations as a tool for investigating past solar wind variations....

  17. Solar wind effect on Joule heating in the high-latitude ionosphere

    Science.gov (United States)

    Cai, L.; Aikio, A. T.; Nygrén, T.

    2014-12-01

    The effect of solar wind on several electrodynamic parameters, measured simultaneously by the European Incoherent Scatter (EISCAT) radars in Tromsø (TRO, 66.6° cgmLat) and on Svalbard (ESR, 75.4° cgmLat), has been evaluated statistically. The main emphasis is on Joule heating rate QJ, which has been estimated by taking into account the neutral wind. In addition, a generally used proxy QE, which is the Pedersen conductance times the electric field squared, has been calculated. The most important findings are as follows. (i) The decrease in Joule heating in the afternoon-evening sector due to winds reported by Aikio et al. (2012) requires southward interplanetary magnetic field (IMF) conditions and a sufficiently high solar wind electric field. The increase in the morning sector takes place for all IMF directions within a region where the upper E neutral wind has a large equatorward component and the F region plasma flow is directed eastward. (ii) At ESR, an afternoon hot spot of Joule heating centered typically at 14-15 magnetic local time (MLT) is observed during all IMF conditions. Enhanced Pedersen conductances within the hot spot region are observed only for the IMF Bz + /By- conditions, and the corresponding convection electric field values within the hot spot are smaller than during the other IMF conditions. Hence, the hot spot represents a region of persistent magnetospheric electromagnetic energy input, and the median value is about 3 mW/m2. (iii) For the southward IMF conditions, the MLT-integrated QE for By- is twice the value for By+ at TRO. This can plausibly be explained by the higher average solar wind electric field values for By-.

  18. High-latitude lower thermospheric neutral winds at EISCAT and Sondrestrom during LTCS 1

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, R.M. (Univ. of Michigan, Ann Arbor (USA)); Virdi, T.S. (Univ. Coll. of Wales, Aberystwyth (England))

    1991-02-01

    The incoherent scatter radar located at Soendre Stroemfjord, Greenland (67{degree}N, 51{degree}W, 74.5{degree}{Lambda}) and the EISCAT incoherent scatter facility located in northern Scandinavia (69.5{degree}N, 19{degree}E, 66.3{degree}{Lambda}) both obtained E and F region measurements during the first campaign of the Lower Thermosphere Coupling Study (LTCS 1, September 21-25, 1987). Neutral winds deduced from these measurements have been analyzed for their mean flow and tidal components. A number of the altitude profiles for the mean winds and the diurnal and semidiurnal wave components at the two radar locations show similar variations with height, indicating that latitudinal rather than longitudinal effects are dominant in determining the observed wind field. Diurnal tidal amplitudes and phases are reasonably well represented by theoretical model results (Forbes, 1982). The semidiurnal amplitudes and phases, although somewhat consistent between the two radars, are not well represented in equinox tidal model results (Forbes and Vial, this issue). Results from both radars indicate a vertical wavelength for the zonal semidiurnal oscillation of approximately 60 km. During a period of impulsive magnetospheric forcing (September 22-23), winds deduced from measurements at both radars show enhanced eastward flows near midnight accompanied by equatorward winds at Sondrestrom. Comparison with the results of a National Center for Atmospheric Research thermosphere-ionosphere general circulation model (TIGCM) simulation of the LTCS 1 interval shows generally better agreement with the observations at EISCAT than at Sondrestrom.

  19. The High-latitude Electric Potential Disparity and Hemispheric Differences in the Upper Thermospheric Neutral Wind Circulation

    Science.gov (United States)

    Foerster, M.; Haaland, S.; Cnossen, I.

    2014-12-01

    We present statistical studies of both the high-latitude ionospheric potential pattern deduced from long-term observations of the Cluster Electron Drift Instrument (EDI) and upper thermospheric neutral wind circulation patterns in the Northern (NH) and Southern Hemisphere (SH) obtained from accelerometers on board of low-Earth orbiting satellites like CHAMP during about the same time interval. The cross-polar cap potential difference during southward IMF conditions appears to be on average slightly (~7%) larger in the SH compared with the NH, while the neutral wind magnitude and vorticity amplitude are mostly larger in the NH than in the SH, especially during high solar activity conditions. We attribute such behaviour to peculiarities of the hemispheres due to the non-dipolar portions of Earth's main magnetic field that constitute substantial differences between the geomagnetic field configurations of both hemispheres. They cause in particular different magnetic field flux densities in the opposite polar regions and different offsets of the invariant poles with respect to the rotation axis of the Earth. The pole is presently displaced almost twice the distance in the SH compared to the NH, which has substantial implications for the coupled magnetosphere-ionosphere-thermosphere system under the influence of external drivers. To analyse this behaviour, we have run several numerical simulations using the first-principle Coupled Magnetosphere-Ionosphere-Thermosphere (CMIT) model under various seasonal conditions. The survey of both the numerical simulation results and the observations confirm prominent asymmetries between the two hemispheres for these parameters.

  20. Solar wind transport into magnetosphere caused by magnetic reconnection at high latitude magnetopause during northward IMF: Cluster-DSP conjunction observations

    Institute of Scientific and Technical Information of China (English)

    YAN GuangQing; SHEN Chao; LIU ZhenXing; M. DUNLOP; E. LUOEK; H. REME; C. M. OARR; ZHANG TieLong

    2008-01-01

    An event of Cluster-Double Star conjunction observations of magnetic reconnec-tion at high latitude magnetopause nightside of both cusps and solar wind trans-port into magnetosphere caused by such reconnection process has been investi-gated. During northward IMF, Cluster/SC1 observed accelerated flows and ion heating associated with magnetic reconnection at high latitude magnetopause night$1de of southern cusp. And Double Star observed cold dense solar wind plasma transported into dayside magnetosphere. The analysis on such conjunction observations shows that: (1) during northward IMF, magnetic reconnection occurs at high latitude nightside of southern cusp, accompanied by accelerated flows that are observed by Cluster/SC1; (2) the direction of the accelerated flows, with its sunward component Vx, dawnward component Vy, northward component Vz, is quite consistent with the theoretical anticipation under the condition of northward IMF with dawnward component By; (3) reconnection can heat plasma more in par-allel direction than in perpendicular direction, to a level of about 4 keV; (4) with reconnection taking place at high latitude magnetopause nightside of the southern cusp, TC-1 observed cold and dense plasma transported into magnetosphere; (5) by reconnection at high latitude magnetopause nightside of both cusps, solar wind flux tube can be captured by magnetosphere and pulled into dayside magneto-sphere.

  1. Solar wind transport into magnetosphere caused by magnetic reconnection at high latitude magnetopause during northward IMF: Cluster-DSP conjunction observations

    Institute of Scientific and Technical Information of China (English)

    M.; DUNLOP; E.; LUCEK; H.; RME; C.; M.; CARR

    2008-01-01

    An event of Cluster-Double Star conjunction observations of magnetic reconnec-tion at high latitude magnetopause nightside of both cusps and solar wind trans-port into magnetosphere caused by such reconnection process has been investi-gated. During northward IMF, Cluster/SC1 observed accelerated flows and ion heating associated with magnetic reconnection at high latitude magnetopause nightside of southern cusp. And Double Star observed cold dense solar wind plasma transported into dayside magnetosphere. The analysis on such conjunction observations shows that: (1) during northward IMF, magnetic reconnection occurs at high latitude nightside of southern cusp, accompanied by accelerated flows that are observed by Cluster/SC1; (2) the direction of the accelerated flows, with its sunward component Vx, dawnward component Vy, northward component Vz, is quite consistent with the theoretical anticipation under the condition of northward IMF with dawnward component By; (3) reconnection can heat plasma more in par-allel direction than in perpendicular direction, to a level of about 4 keV; (4) with reconnection taking place at high latitude magnetopause nightside of the southern cusp, TC-1 observed cold and dense plasma transported into magnetosphere; (5) by reconnection at high latitude magnetopause nightside of both cusps, solar wind flux tube can be captured by magnetosphere and pulled into dayside magneto-sphere. This event presents further observational evidence for magnetic reconnec-tion at high latitude magnetopause nightside of both cusps as an important mech-anism of sol-ar w-ind transport into magnetosphere.

  2. High Latitude Mottling on Jupiter

    Science.gov (United States)

    2000-01-01

    The familiar banded appearance of Jupiter at low and middle latitudes gradually gives way to a more mottled appearance at high latitudes in this striking true color image taken Dec. 13, 2000, by NASA's Cassini spacecraft.The intricate structures seen in the polar region are clouds of different chemical composition, height and thickness. Clouds are organized by winds, and the mottled appearance in the polar regions suggests more vortex-type motion and winds of less vigor at higher latitudes.The cause of this difference is not understood. One possible contributor is that the horizontal component of the Coriolis force, which arises from the planet's rotation and is responsible for curving the trajectories of ocean currents and winds on Earth, has its greatest effect at high latitudes and vanishes at the equator. This tends to create small, intense vortices at high latitudes on Jupiter. Another possibility may lie in that fact that Jupiter overall emits nearly as much of its own heat as it absorbs from the Sun, and this internal heat flux is very likely greater at the poles. This condition could lead to enhanced convection at the poles and more vortex-type structures. Further analysis of Cassini images, including analysis of sequences taken over a span of time, should help us understand the cause of equator-to-pole differences in cloud organization and evolution.By the time this picture was taken, Cassini had reached close enough to Jupiter to allow the spacecraft to return images with more detail than what's possible with the planetary camera on NASA's Earth-orbiting Hubble Space Telescope. The resolution here is 114 kilometers (71 miles) per pixel. This contrast-enhanced, edge-sharpened frame was composited from images take at different wavelengths with Cassini's narrow-angle camera, from a distance of 19 million kilometers (11.8 million miles). The spacecraft was in almost a direct line between the Sun and Jupiter, so the solar illumination on Jupiter is almost full

  3. Tidi Observations Relating to High Latitude Aeronomy

    Science.gov (United States)

    Gell, D.; Niciejewski, R.; Killeen, T.; Wu, Q.; Skinner, W.; Solomon, S.; Ortland, D.; Kafkalidis, J.; Gablehouse, D.; Johnson, R.

    2003-12-01

    Unique observations of the horizontal neutral winds at high latitudes in the altitude range 60 to 180 km have been performed by TIDI (Thermosphere Ionosphere Doppler Interferometer) since January 2002. The satellite orbit is such that the TIDI field of view includes latitudes to both the north pole and the south pole. Though high latitude neutral wind measurements have been obtained from space with the DE-2 satellite and the UARS satellite, TIDI is the first instrument to sample the mesosphere and the lower thermosphere up to and including both polar regions on a long-term basis. Ground based studies have previously reported a strong semi-diurnal tide in the mesosphere over Resolute, Canada. This paper will describe the climatology that has been obtained by the TIDI instrument since early 2002 for high latitudes. The precession rate of TIMED supports two month averaging of data sets in order to sample all local solar time.

  4. Generation of the lower-thermospheric vertical wind estimated with the EISCAT KST radar at high latitudes during periods of moderate geomagnetic disturbance

    Directory of Open Access Journals (Sweden)

    S. Oyama

    2008-06-01

    Full Text Available Lower-thermospheric winds at high latitudes during moderately-disturbed geomagnetic conditions were studied using data obtained with the European Incoherent Scatter (EISCAT Kiruna-Sodankylä-Tromsø (KST ultrahigh frequency (UHF radar system on 9–10 September 2004. The antenna-beam configuration was newly designed to minimize the estimated measurement error of the vertical neutral-wind speed in the lower thermosphere. This method was also available to estimate the meridional and zonal components. The vertical neutral-wind speed at 109 km, 114 km, and 120 km heights showed large upward motions in excess of 30 m s−1 in association with an ionospheric heating event. Large downward speeds in excess of −30 m s−1 were also observed before and after the heating event. The meridional neutral-wind speed suddenly changed its direction from equatorward to poleward when the heating event began, and then returned equatorward coinciding with a decrease in the heating event. The magnetometer data from northern Scandinavia suggested that the center of the heated region was located about 80 km equatorward of Tromsø. The pressure gradient caused the lower-thermospheric wind to accelerate obliquely upward over Tromsø in the poleward direction. Acceleration of the neutral wind flowing on a vertically tilted isobar produced vertical wind speeds larger by more than two orders of magnitude than previously predicted, but still an order of magnitude smaller than observed speeds.

  5. Geomagnetic response to IMF and solar wind over different latitudes

    Science.gov (United States)

    Aslam, A. M.; Tripathi, Sharad Chandra; Mansoori, Azad Ahmad; Waheed, Malik Abdul

    2016-07-01

    In this paper a study on the response of geomagnetic field characteristics to the solar wind variation during three solar cycles (SC 21, SC 22, SC 23) have been conducted in a long term scale. The difference in the response of two different latitudinal characteristic indices has been investigated. For the purpose we have considered the high latitude index AE and the mid-latitude aa index and both gives the knowledge about the perturbations in the geomagnetic field conditions. Eventually we can infer the idea about the ionospheric current system changes in response to the solar wind conditions. The variation found in the AE and aa indices have been found to follow a 11 year cycle as similar to the sunspot variation. Also the correlation between the annual means of the solar wind parameters velocity V, magnetic filed B and the composite parameters BV and BV ^{2 } have been calculated . A difference was found between the correlations obtained for the AE and aa indices. We could also see that the difference in correlation follows a cyclic pattern i.e. the large difference is found during the solar maxima while a small difference is observed during the minima.

  6. A latitude-dependent wind model for Mira's cometary head

    CERN Document Server

    Raga, A C; De Colle, F; Esquivel, A; Kajdic, P; Rodríguez-González, A; Velázquez, P F

    2008-01-01

    We present a 3D numerical simulation of the recently discovered cometary structure produced as Mira travels through the galactic ISM. In our simulation, we consider that Mira ejects a steady, latitude-dependent wind, which interacts with a homogeneous, streaming environment. The axisymmetry of the problem is broken by the lack of alignment between the direction of the relative motion of the environment and the polar axis of the latitude-dependent wind. With this model, we are able to produce a cometary head with a ``double bow shock'' which agrees well with the structure of the head of Mira's comet. We therefore conclude that a time-dependence in the ejected wind is not required for reproducing the observed double bow shock.

  7. Corotating Interaction Regions at High Latitudes

    Science.gov (United States)

    Kunow, H.; Lee, M. A.; Fisk, L. A.; Forsyth, R. J.; Heber, B.; Horbury, T. S.; Keppler, E.; Kóta, J.; Lou, Y.-Q.; McKibben, R. B.; Paizis, C.; Potgieter, M. S.; Roelof, E. C.; Sanderson, T. R.; Simnett, G. M.; von Steiger, R.; Tsurutani, B. T.; Wimmer-Schweingruber, R. F.; Jokipii, J. R.

    1999-07-01

    Ulysses observed a stable strong CIR from early 1992 through 1994 during its first journey into the southern hemisphere. After the rapid latitude scan in early 1995, Ulysses observed a weaker CIR from early 1996 to mid-1997 in the northern hemisphere as it traveled back to the ecliptic at the orbit of Jupiter. These two CIRs are the observational basis of the investigation into the latitudinal structure of CIRs. The first CIR was caused by an extension of the northern coronal hole into the southern hemisphere during declining solar activity, whereas the second CIR near solar minimum activity was caused by small warps in the streamer belt. The latitudinal structure is described through the presentation of three 26-day periods during the southern CIR. The first at ˜24°S shows the full plasma interaction region including fast and slow wind streams, the compressed shocked flows with embedded stream interface and heliospheric current sheet (HCS), and the forward and reverse shocks with associated accelerated ions and electrons. The second at 40°S exhibits only the reverse shock, accelerated particles, and the 26-day modulation of cosmic rays. The third at 60°S shows only the accelerated particles and modulated cosmic rays. The possible mechanisms for the access of the accelerated particles and the CIR-modulated cosmic rays to high latitudes above the plasma interaction region are presented. They include direct magnetic field connection across latitude due to stochastic field line weaving or to systematic weaving caused by solar differential rotation combined with non-radial expansion of the fast wind. Another possible mechanism is particle diffusion across the average magnetic field, which includes stochastic field line weaving. A constraint on connection to a distant portion of the CIR is energy loss in the solar wind, which is substantial for the relatively slow-moving accelerated ions. Finally, the weaker northern CIR is compared with the southern CIR. It is weak

  8. Latitude-dependent effects in the stellar wind of Eta Carinae

    CERN Document Server

    Smith, N; Gull, T R; Ishibashi, K; Hillier, J; Smith, Nathan; Davidson, Kris; Gull, Theodore R.; Ishibashi, Kazunori; Hillier, John

    2003-01-01

    The Homunculus reflection nebula around eta Carinae provides a rare opportunity to observe the spectrum of a star from multiple latitudes. We present STIS spectra of several positions in the Homunculus, showing directly that eta Car has an aspherical stellar wind. P Cygni absorption in Balmer lines depends on latitude, with high velocities and strong absorption near the poles. Stronger absorption at high latitudes is surprising, and it suggests higher mass flux toward the poles, perhaps resulting from radiative driving with equatorial gravity darkening on a rotating star. Reflected profiles of He I lines are more puzzling, offering clues to the wind geometry and ionization structure. During eta Car's high-excitation state in March 2000, the wind was fast and dense at the poles, with higher ionization at low latitudes. Older STIS data obtained since 1998 reveal that this global stellar-wind geometry changes during eta Car's 5.5 year cycle, and may suggest that this star's spectroscopic events are shell ejectio...

  9. The SDSS High Latitude Cloud Survey

    Science.gov (United States)

    McGehee, P. M.

    2009-01-01

    The high latitude clouds (|b| > 30) are primarily translucent molecular clouds and diffuse Galactic cirrus with the majority of them seen at high latitude simply due to their proximity to the Sun. The rare exceptions are those, like the Draco and other intermediate or high velocity clouds, found significantly above or below the Galactic plane. To date, star formation has only been verified in MBM 12 and MBM 20, which are two of the densest high latitude molecular clouds. We present results from an ongoing study of high latitude clouds based on the Sloan Digital Sky Survey (SDSS) and the Two Micron All-Sky Survey (2MASS). This study consists of two major efforts, the first (described here) to provide a 3-D mapping of the interstellar dust using a color-excess technique, the second to identify candidate low-mass Classical T Tauri stars in the field.

  10. Climatologies of nighttime upper thermospheric winds measured by ground-based Fabry-Perot interferometers during geomagnetically quiet conditions: 2. High-latitude circulation and interplanetary magnetic field dependence

    DEFF Research Database (Denmark)

    Emmert, J.T.; Hernandez, G.; Jarvis, M.J.;

    2006-01-01

    Stromfjord (67 degrees N, 51 degrees W), and Thule (77 degrees N, 68 degrees W). We examine the wind patterns as a function of magnetic local time and latitude, solar cycle, day of year, and the dawn-dusk and north-south components of the interplanetary magnetic field (IMF B-y and B-z). In magnetic...... at latitudes as low as that of Millstone Hill ( magnetic latitude 53 degrees N). Quiet time Bz effects are negligible except over the magnetic polar cap station of Thule....

  11. Assessment of Plasma Transport and Convection at High Latitudes

    Science.gov (United States)

    1984-01-01

    The high-latitude ionosphere is strongly coupled to the thermosphere and magnetosphere. The magnetospheric coupling occurs via electric fields, field-aligned currents, and particle precipitation. Owing to the interaction of the shocked solar wind with the geomagnetic field, an electric potential difference is generated across the tail of the magnetosphere, with the resulting electric field pointing from dawn to dusk. Energetic particle precipitation from the magnetosphere in the auroral region leads to the creation of ionization and to electron, ion, and neutral gas heating. In order to assess the current understanding of plasma transport and convection at high latitudes, it is necessary to take account of the strong coupling between the ionosphere, thermosphere, and magnetosphere.

  12. Spacecraft design project: High latitude communications satellite

    Science.gov (United States)

    Josefson, Carl; Myers, Jack; Cloutier, Mike; Paluszek, Steve; Michael, Gerry; Hunter, Dan; Sakoda, Dan; Walters, Wes; Johnson, Dennis; Bauer, Terry

    1989-01-01

    The spacecraft design project was part of AE-4871, Advanced Spacecraft Design. The project was intended to provide experience in the design of all major components of a satellite. Each member of the class was given primary responsibility for a subsystem or design support function. Support was requested from the Naval Research Laboratory to augment the Naval Postgraduate School faculty. Analysis and design of each subsystem was done to the extent possible within the constraints of an eleven week quarter and the design facilities (hardware and software) available. The project team chose to evaluate the design of a high latitude communications satellite as representative of the design issues and tradeoffs necessary for a wide range of satellites. The High-Latitude Communications Satellite (HILACS) will provide a continuous UHF communications link between stations located north of the region covered by geosynchronous communications satellites, i.e., the area above approximately 60 N latitude. HILACS will also provide a communications link to stations below 60 N via a relay Net Control Station (NCS), which is located with access to both the HILACS and geosynchronous communications satellites. The communications payload will operate only for that portion of the orbit necessary to provide specified coverage.

  13. Comparing High-latitude Ionospheric and Thermospheric Lagrangian Coherent Structures

    Science.gov (United States)

    Wang, N.; Ramirez, U.; Flores, F.; Okic, D.; Datta-Barua, S.

    2015-12-01

    Lagrangian Coherent Structures (LCSs) are invisible boundaries in time varying flow fields that may be subject to mixing and turbulence. The LCS is defined by the local maxima of the finite time Lyapunov exponent (FTLE), a scalar field quantifying the degree of stretching of fluid elements over the flow domain. Although the thermosphere is dominated by neutral wind processes and the ionosphere is governed by plasma electrodynamics, we can compare the LCS in the two modeled flow fields to yield insight into transport and interaction processes in the high-latitude IT system. For obtaining thermospheric LCS, we use the Horizontal Wind Model 2014 (HWM14) [1] at a single altitude to generate the two-dimensional velocity field. The FTLE computation is applied to study the flow field of the neutral wind, and to visualize the forward-time Lagrangian Coherent Structures in the flow domain. The time-varying structures indicate a possible thermospheric LCS ridge in the auroral oval area. The results of a two-day run during a geomagnetically quiet period show that the structures are diurnally quasi-periodic, thus that solar radiation influences the neutral wind flow field. To find the LCS in the high-latitude ionospheric drifts, the Weimer 2001 [2] polar electric potential model and the International Geomagnetic Reference Field 11 [3] are used to compute the ExB drift flow field in ionosphere. As with the neutral winds, the Lagrangian Coherent Structures are obtained by applying the FTLE computation. The relationship between the thermospheric and ionospheric LCS is analyzed by comparing overlapping FTLE maps. Both a publicly available FTLE solver [4] and a custom-built FTLE computation are used and compared for validation [5]. Comparing the modeled IT LCSs on a quiet day with the modeled IT LCSs on a storm day indicates important factors on the structure and time evolution of the LCS.

  14. Magnotospheric imaging of high latitude ion outflows

    Directory of Open Access Journals (Sweden)

    D. E. Garrido

    Full Text Available High latitude ion outflows mostly consist of upward streaming O+ and He+ emanating from the ionosphere. At heights above 1000 km, these flows consist of cold and hot components which resonantly scatter solar extreme ultraviolet (EUV light, however, the ion populations respond differently to Doppler shifting resulting from the large relative velocities between the ions and the Sun. The possibility of optical detection of the Doppler effect on the scattering rate will be discussed for the O+ (83.4 nm ions. We have contrasted the EUV solar resonance images of these outflows by simulations of the 30.4 nm He+ and 83.4 nm O+ emissions for both quiet and disturbed geomagnetic conditions. Input data for the 1000 km level has been obtained from the EICS instrument aboard the Dynamics Explorer satellite. Our results show emission rates of 50 and 56 milli-Rayleighs at 30.4 nm for quiet and disturbed conditions and 65 and 75 milli-Rayleighs at 83.4 nm for quiet and disturbed conditions, respectively, obtained for a polar orbiting satellite and viewing radially outward. We also find that an imager at an equatorial distance of 9 RE or more is in a favourable position for detecting ion outflows, particularly when the plasmapause is depressed in latitude. However, an occultation disk is necessary to obscure the bright plasmaspheric emissions.

  15. Latitude migration of solar activity at high latitudes

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Utilized here is the Carte Synoptique solar filament archive,namely the catalogue of solar filaments from March 1919 to December 1989,corresponding to solar rotation numbers 876 to 1823 to study Iatitudinal migration of solar activity at high Iatitudes.Except the well-known poleward migration of solar activity from middle Iatitudes to the poles,an equatorward migration is found from the solar poles toward middle Iatitudes(about 40°)within a normal cycle,which iS neglected before,and the time interval for the former migration(4.4 years)is about 2.2 years shorter than that for the latter(6.6 years),indicating that the change from one migration to the other takes place around the maximum time of a normal cycle.In the future,a dynamo model should represent the migration from the poles toward middle Iatitudes of the Sun,besides the migration in"butterfly diagrams"and the"rush to the poles".The traditional extended activity cycle is actually a part of the period of the successive migration from the poles toward the solar equator.

  16. Pc3 activity at low geomagnetic latitudes - A comparison with solar wind observations

    Science.gov (United States)

    Villante, U.; Lepidi, S.; Vellante, M.; Lazarus, A. J.; Lepping, R. P.

    1992-10-01

    On an hourly time-scale the different roles of the solar wind and interplanetary magnetic field (IMF) parameters on ground micropulsation activity can be better investigated than at longer time-scales. A long-term comparison between ground measurements made at L'Aquila and IMP 8 observations confirms the solar wind speed as the key parameter for the onset of pulsations even at low latitudes, although additional control of the energy transfer from the interplanetary medium to the earth's magnetosphere is clearly exerted by the cone angle. Above about 20 mHz the frequency of pulsations is confirmed to be closely related to the IMF magnitude while, in agreement with model predictions, the IMF magnitude is related to the amplitude of the local fundamental resonant mode. We provide an interesting example in which high resolution measurements simultaneously obtained in the foreshock region and on the ground show that external transversal fluctuations do not penetrate deep into the low latitude magnetosphere.

  17. High latitude electromagnetic plasma wave emissions

    Science.gov (United States)

    Gurnett, D. A.

    1983-01-01

    The principal types of electromagnetic plasma wave emission produced in the high latitude auroral regions are reviewed. Three types of radiation are described: auroral kilometric radiation, auroral hiss, and Z mode radiation. Auroral kilometric radiation is a very intense radio emission generated in the free space R-X mode by electrons associated with the formation of discrete auroral arcs in the local evening. Theories suggest that this radiation is an electron cyclotron resonance instability driven by an enhanced loss cone in the auroral acceleration region at altitudes of about 1 to 2 R sub E. Auroral hiss is a somewhat weaker whistler mode emission generated by low energy (100 eV to 10 keV) auroral electrons. The auroral hiss usually has a V shaped frequency time spectrum caused by a freqency dependent beaming of the whistler mode into a conical beam directed upward or downward along the magnetic field.

  18. Seasonal variabilities of low-latitude mesospheric winds

    Directory of Open Access Journals (Sweden)

    R. Rajaram

    Full Text Available Observations of mesospheric winds over a period of four years with the partial reflection radar at Tirunelveli (8.7°N, 77.8°E, India, are presented in this study. The emphasis is on describing seasonal variabilities in mean zonal and meridional winds in the altitude region 70–98 km. The meridional winds exhibit overall transequatorial flow associated with differential heating in the Northern and Southern Hemispheres. At lower altitudes (70–80 km the mean zonal winds reveal easterly flow during summer and westerly flow during winter, as expected from a circulation driven by solar forcing. In the higher altitude regime (80–98 km and at all altitudes during equinox periods, the mean zonal flow is subjected to the semi-annual oscillation (SAO. The interannual variability detected in the occurrence of SAO over Tirunelveli has also been observed in the data sets obtained from the recent UARS satellite mission. Harmonic analysis results over a period of two years indicate the presence of long-period oscillations in the mean zonal wind at specific harmonic periods near 240, 150 and 120 days. Results presented in this study are discussed in the context of current understanding of equatorial wave propagation.

    Key words. Meteorological and atmospheric dynamics · General circulation · Middle atmosphere dynamics · waves and tides.

  19. Response of thermosphere density to high-latitude forcing

    Science.gov (United States)

    Yamazaki, Y.; Kosch, M. J.; Vickers, H.; Sutton, E. K.; Ogawa, Y.

    2014-12-01

    Solar wind-magnetospheric disturbances cause enhancements in the energy input to the high-latitude upper atmosphere through particle precipitation and Joule heating. As the upper atmosphere is heated and expanded during geomagnetically disturbed periods, the neutral density in the thermosphere increases at a fixed altitude. Conversely, the thermosphere contracts during the recovery phase of the disturbance, resulting in a decrease of the density. The main objectives of this study are (1) to determine the morphology of the global thermospheric density response to high-latitude forcing, and (2) to determine the recovery speed of the thermosphere density after geomagnetic disturbances. For (1), we use thermospheric density data measured by the Challenging Minisatellite Payload (CHAMP) satellite during 2000-2010. It is demonstrated that the density enhancement during disturbed periods occurs first in the dayside cusp region, and the density at other regions slowly follows it. The reverse process is observed when geomagnetic activity ceases; the density enhancement in the cusp region fades away first, then the global density slowly goes back to the quiet level. For (2), we analyze EISCAT Svalbard radar and Tromso UHF radar data to estimate thermospheric densities during the recovery phase of geomagnetic disturbances. We attempt to determine the time constant for the density recovery both inside and outside the cusp region.

  20. Bayesian Image Classification At High Latitudes

    Science.gov (United States)

    Bulgin, Claire E.; Eastwood, Steinar; Merchant, Chris J.

    2013-12-01

    The European Space Agency created the Climate Change Initiative (CCI) to maximize the usefulness of Earth Observations to climate science. Sea Surface Temperature (SST) is an essential climate variable to which satellite observations make a crucial contribution, and is one of the projects within the CCI program. SST retrieval is dependent on successful cloud clearing and identification of clear-sky pixels over ocean. At high latitudes image classification is more difficult due to the presence of sea-ice. Newly formed ice has a temperature close to the freezing point of water and a dark surface making it difficult to distinguish from open ocean using data at visible and infrared wavelengths. Similarly, melt ponds on the sea-ice surface make image classification more difficult. We present here a three- way Bayesian classifier for the AATSR instrument classifying pixels as ‘clear-sky over ocean', ‘clear-sky over ice' or ‘cloud' using the 0.6, 1.6, 11 and 12 micron channels. We demonstrate the ability of the classifier to successfully identify sea-ice and consider the potential for generating an ice surface temperature record from AATSR which could be extended using data from SLSTR.

  1. Turbulence in high latitude molecular clouds

    Science.gov (United States)

    Shore, S. N.; Larosa, T. N.; Magnani, L.; Chastain, R. J.; Costagliola, F.

    We summarize a continuing investigation of turbulence in high-latitude translucent molecular clouds. These low mass (~ 50 M(solar), nearby (~ 100 pc), non-star forming clouds appear to be condensing out of the atomic cirrus and must be forced by external dynamical processes, since they lack internal sources, for which we can distinguish the injection scale for the turbulence. We have now mapped three clouds -- MBM 3, MBM 16, and MBM 40 -- with high spatial (0.03 pc) and velocity resolution (<0.08 km/s) in 12CO(1-0) 13CO(1-0) (NRAO 12m and FCRAO). All three clouds show evidence for large-shear flows and we propose that the turbulent motions are powered by shear-flow instability. The densest gas is structured into filaments but the velocity profiles do not change in going across a filament indicating that shocks are not compressing the gas. The density field is more likely the result of thermal instability. The velocity-size relationship, a commonly used diagnostic of ISM turbulence, does not hold in these clouds: the linewidth does not increase with region size. The centroid velocity probability distribution function (PDF) is a more precise measure of turbulence. In these clouds the PDFs exhibit broad wings, consistent with a Lorentzian distribution and showing evidence non-Gaussian correlated processes. This is a clear signature of intermittency. We have also begun a mapping survey of CS (1-0), CS (2-1), H2CO, and HCO+ at Arecibo and OSO and willdiscuss results for the Polaris flare and L1512. We will also discusssome implications of these studies for the turbulent dissipation in these systems.

  2. Magnetospheric effects in atmospheric electricity at high latitudes

    Science.gov (United States)

    Shumilov, O. I.; Kasatkina, E. A.; Frank-Kamenetsky, A. V.; Raspopov, O. M.; Vasiljev, A. N.; Struev, A. G.

    2003-04-01

    Measurements of the vertical atmospheric electric field (Ez) made at auroral station Apatity (geomagnetic latitude: 63.8) and polar cap station Vostok, Antarctica (geomagnetic latitude: -89.3) in 2001-2002 have been analyzed. The measurements were made by a high-latitude computer-aided complex installed at Apatity in 2001. It consists of three spatially placed microbarographs for measurements of atmospheric waves, a device for air conductivity measurement and a device for measurement of vertical component of the atmospheric electric field. The computer-aided system permits to get information with a frequency of five times per second. The ground level atmospheric electric field was found to have systematic local diurnal and seasonal variations. Diurnal variations of atmospheric potential gradient were found to have a departure from the Carnegie curve. A distinct difference in the diurnal variation of atmospheric electric field has been observed also between disturbed (Kp>30) and extremely quiet (Kplatitude electric field variations appear to be the result of solar wind-magnetosphere-ionosphere coupling. Besides, we have found the similarity between the diurnal course of the atmospheric electric field under the quiet geomagnetic conditions and the diurnal variation of galactic cosmic rays. These results have been explained in terms of calculated effective Bz component of the interpalnetary magnetic field arising due to variation of the geomagnetic dipole axis inclination during the Earth's rotation. The results of analysis of the influence of extreme weather conditions (rain, snow, snowstorm, stormclouds, thunderstorms, lightning) on atmospheric electricity (electric field and conductivity) are also discussed. This work was supported by EC (grant INTAS 97-31008) and RFBR (grant 01-05-64850).

  3. Pioneer and Voyager observations of the solar wind at large heliocentric distances and latitudes

    Science.gov (United States)

    Gazis, P. R.; Mihalov, J. D.; Barnes, A.; Lazarus, A. J.; Smith, E. J.

    1989-01-01

    Data obtained from the electrostatic analyzers aboard the Pioneer 10 and 11 spacecraft and from the Faraday cup aboard Voyager 2 were used to study spatial gradients in the distant solar wind. Prior to mid-1985, both spacecraft observed nearly identical solar wind structures. After day 150 of 1985, the velocity structure at Voyager 2 became flatter, and the Voyager 2 velocities were smaller than those observed by Pioneer 11. It is suggested that these changes in the solar wind at low latitudes may be related to a change which occurred in the coronal hole structure in early 1985.

  4. Cosmology with the WFIRST High Latitude Survey

    Science.gov (United States)

    Dore, Olivier

    Cosmic acceleration is the most surprising cosmological discovery in many decades. Testing and distinguishing among possible explanations requires cosmological measurements of extremely high precision that probe the full history of cosmic expansion and structure growth. The WFIRST-AFTA mission, as described in the Science Definition Team (SDT) reports (Spergel 2013, 2015), has the ability to improve these measurements by 1-2 orders of magnitude compared to the current state of the art, while simultaneously extending their redshift grasp, greatly improving control of systematic effects, and taking a unified approach to multiple probes that provide complementary physical information and cross-checks of cosmological results. We have assembled a team with the expertise and commitment needed to address the stringent challenges of the WFIRST dark energy program through the Project's formulation phase. After careful consideration, we have elected to address investigations A (Galaxy Redshift Survey) and C (Weak Lensing and Cluster Growth) of the WFIRST SIT NRA with a unified team, because the two investigations are tightly linked at both the technical level and the theoretical modeling level. The imaging and spectroscopic elements of the High Latitude Survey (HLS) will be realized as an integrated observing program, and they jointly impose requirements on instrument and telescope performance, operations, and data transfer. The methods for simulating and interpreting weak lensing and galaxy clustering observations largely overlap, and many members of our team have expertise in both areas. The team PI, Olivier Dore, is a cosmologist with a broad expertise in cosmic microwave background and large scale structures. Yun Wang and Chris Hirata will serve as Lead Co-Investigators for topics A and C, respectively. Many members of our team have been involved with the design and requirements of a dark energy space mission for a decade or more, including the Co-Chair and three

  5. CHIRALITY OF HIGH-LATITUDE FILAMENTS OVER SOLAR CYCLE 23

    Energy Technology Data Exchange (ETDEWEB)

    Yeates, A. R. [Department of Mathematical Sciences, Durham University, Durham, DH1 3LE (United Kingdom); Mackay, D. H., E-mail: anthony.yeates@durham.ac.uk, E-mail: duncan@mcs.st-and.ac.uk [School of Mathematics and Statistics, University of St Andrews, St Andrews, KY16 9SS (United Kingdom)

    2012-07-10

    A non-potential quasi-static evolution model coupling the Sun's photospheric and coronal magnetic fields is applied to the problem of filament chirality at high latitudes. For the first time, we run a continuous 15 year simulation, using bipolar active regions determined from US National Solar Observatory, Kitt Peak magnetograms between 1996 and 2011. Using this simulation, we are able to address the outstanding question of whether magnetic helicity transport from active latitudes can overcome the effect of differential rotation at higher latitudes. Acting alone, differential rotation would produce high-latitude filaments with opposite chirality to the majority type in each hemisphere. We find that differential rotation can indeed lead to opposite chirality at high latitudes, but only for around 5 years of the solar cycle following the polar field reversal. At other times, including the rising phase, transport of magnetic helicity from lower latitudes overcomes the effect of in situ differential rotation, producing the majority chirality even on the polar crowns at polar field reversal. These simulation predictions will allow for future testing of the non-potential coronal model. The results indicate the importance of long-term memory and helicity transport from active latitudes when modeling the structure and topology of the coronal magnetic field at higher latitudes.

  6. On multifractality of high-latitude geomagnetic fluctuations

    Directory of Open Access Journals (Sweden)

    Z. Vörös

    Full Text Available In order to contribute to the understanding of solar wind-magnetosphere interactions the multifractal scaling properties of high-latitude geomagnetic fluctuations observed at the Thule observatory have been studied. Using the local observatory data and the present experimental knowledge only it seems hard to characterize directly the, presumably intermittent, mesoscale energy accumulation and dissipation processes taking place at the magnetotail, auroral region, etc. Instead a positive probability measure, describing the accumulated local geomagnetic signal energy content at the given time scales has been introduced and its scaling properties have been studied. There is evidence for the multifractal nature of the so defined intermittent field ε, a result obtained by using the recently introduced technique of large deviation multifractal spectra. This technique allows us to describe the geomagnetic fluctuations locally in time by means of singularity exponents α, which represent a generalization of the local degree of differentiability and characterize the power-law scaling dependence of the introduced measure on resolution. A global description of the geomagnetic fluctuations is insured by the spectrum of exponents f(α which represents a rate function quantifying the deviations of the observed singularities α from the expected value. The results show that there exists a multifractal counterpart of the previously reported spectral break and different types of f(α spectra describe the fluctuations in direct dissipation or loading-unloading regimes of the solar wind-magnetosphere interaction. On the time scale of substorms and storms the multi-fractal structure of the loading-unloading mode fluctuations seems to be analogous to the simple multiplicative P-model, while the f(α spectra in direct dissipation regime are close but not equal to the features of a uniform distribution. Larger deviations from the multiplicative

  7. Distance to the northern high-latitude HI shells

    CERN Document Server

    Puspitarini, Lucky

    2012-01-01

    A detailed 3D distribution of interstellar matter in the solar neighborhood is increasingly necessary. As part of a 3D mapping program, we aim at assigning a precise distance to the high-latitude HI gas in particular the northern part (b \\geq 55^{circ}) of the shell associated with the conspicuous radio continuum Loop I. This shell is thought to be the expanding boundary of an interstellar bubble inflated and recently reheated by the strong stellar winds of the nearby Scorpius-Centaurus OB. We recorded high-resolution spectra of 30 A-type target stars located at various distances in the direction of the northern part of Loop I. Interstellar NaI 5889-5895 and CaII K-H 3934-3968 {\\AA} are modeled and compared with the HI emission spectra from the LAB Survey. About two-thirds of our stellar spectra possess narrow interstellar lines. Narrow lines are located at the velocity of the main, low-velocity Loop 1 HI shell ([-6,+1] km/s in the LSR). Using Hipparcos distances to the target stars, we show that the closest ...

  8. Magnetic latitude dependence of oxygen charge states in the global magnetosphere: Insights into solar wind-originating ion injection

    Science.gov (United States)

    Allen, R. C.; Livi, S. A.; Vines, S. K.; Goldstein, J.

    2016-10-01

    Understanding the sources and subsequent evolution of plasma in a magnetosphere holds intrinsic importance for magnetospheric dynamics. Previous studies have investigated the balance of ionospheric-originating heavy ions (low charge state) from those of solar wind origin (high charge state) in the magnetosphere of Earth. These studies have suggested a variety of entry mechanisms for solar wind ions to penetrate into the magnetosphere. Following from recently published distributions for oxygen charge states observed by the Polar spacecraft, this paper investigates oxygen charge state flux distributions versus L shell and magnetic latitude. By showing these distributions in this frame, and binning by various proxies for magnetospheric dynamics (Dst, AE, VSW∗BZ, Pdyn), insight has been gained into the underlying physics at play for oxygen injection. Ionospheric-originating oxygen is observed to depend predominantly on Dst, whereas solar wind-originating oxygen is observed to have a strong dependence on solar wind dynamic pressure (Pdyn) at the flanks and on VSW∗BZ at the dayside. This suggests that both Kelvin-Helmholtz instabilities and reconnection play major roles in solar wind ion penetration into a magnetosphere. Additionally, the near-Earth magnetotail reconnection site does not seem to be a major injection site of solar wind-originating plasma in the 1 to 200 keV/e energy range.

  9. Exchange across the shelf break at high southern latitudes

    Directory of Open Access Journals (Sweden)

    J. M. Klinck

    2010-01-01

    Full Text Available Exchange of water across the Antarctic shelf break has considerable scientific and societal importance due to its effects on circulation and biology of the region, conversion of water masses as part of the global overturning circulation and basal melt of glacial ice and the consequent effect on sea level rise. The focus in this paper is the onshore transport of warm, oceanic Circumpolar Deep Water (CDW; export of dense water from these shelves is equally important, but has been the focus of other recent papers and will not be considered here. A variety of physical mechanisms are described which could play a role in this onshore flux. The relative importance of some processes are evaluated by simple calculations. A numerical model for the Ross Sea continental shelf is used as an example of a more comprehensive evaluation of the details of cross-shelf break exchange. In order for an ocean circulation model simulate these processes at high southern latitudes, it needs to have high spatial resolution, realistic geometry and bathymetry. Grid spacing smaller than the first baroclinic radius deformation (a few km is required to adequately represent the circulation. Because of flow-topography interactions, bathymetry needs to be represented at these same small scales. Atmospheric conditions used to force these circulation models also need to be known at a similar small spatial resolution (a few km in order to represent orographically controlled winds (coastal jets and katabatic winds. Significantly, time variability of surface winds strongly influences the structure of the mixed layer. Daily, if not more frequent, surface fluxes must be imposed for a realistic surface mixed layer. Sea ice and ice shelves are important components of the coastal circulation. Ice isolates the ocean from exchange with the atmosphere, especially in the winter. Melting and freezing of both sea ice and glacial ice influence salinity and thereby the character of shelf water

  10. Exchange across the shelf break at high southern latitudes

    Directory of Open Access Journals (Sweden)

    J. M. Klinck

    2010-05-01

    Full Text Available Exchange of water across the Antarctic shelf break has considerable scientific and societal importance due to its effects on circulation and biology of the region, conversion of water masses as part of the global overturning circulation and basal melt of glacial ice and the consequent effect on sea level rise. The focus in this paper is the onshore transport of warm, oceanic Circumpolar Deep Water (CDW; export of dense water from these shelves is equally important, but has been the focus of other recent papers and will not be considered here. A variety of physical mechanisms are described which could play a role in this onshore flux. The relative importance of some processes are evaluated by simple calculations. A numerical model for the Ross Sea continental shelf is used as an example of a more comprehensive evaluation of the details of cross-shelf break exchange. In order for an ocean circulation model to simulate these processes at high southern latitudes, it needs to have high spatial resolution, realistic geometry and bathymetry. Grid spacing smaller than the first baroclinic radius of deformation (a few km is required to adequately represent the circulation. Because of flow-topography interactions, bathymetry needs to be represented at these same small scales. Atmospheric conditions used to force these circulation models also need to be known at a similar small spatial resolution (a few km in order to represent orographically controlled winds (coastal jets and katabatic winds. Significantly, time variability of surface winds strongly influences the structure of the mixed layer. Daily, if not more frequent, surface fluxes must be imposed for a realistic surface mixed layer. Sea ice and ice shelves are important components of the coastal circulation. Ice isolates the ocean from exchange with the atmosphere, especially in the winter. Melting and freezing of both sea ice and glacial ice influence salinity and thereby the character of shelf

  11. Comparison of high-latitude thermospheric meridionalwinds II: combined FPI, radar and model Climatologies

    Directory of Open Access Journals (Sweden)

    E. M. Griffin

    2004-03-01

    Full Text Available The climatological behaviour of the thermospheric meridional wind above Kiruna, Sweden (67.4°N, 20.4°E has been investigated for seasonal and solar cycle dependence using six different techniques, comprising both model and experimental sources. Model output from both the empirical Horizontal Wind Model (HWM (Hedin et al., 1988 and the numerical Coupled Thermosphere and Ionosphere Model (CTIM are compared to the measured behaviour at Kiruna, as a single site example. The empirical International Reference Ionosphere (IRI model is used as input to an implementation of servo theory, to provide another climatology combining empirical input with a theoretical framework. The experimental techniques have been introduced in a companion paper in this issue and provide climatologies from direct measurements, using Fabry-Perot Interferometers (FPI, together with 2 separate techniques applied to the European Incoherent Scatter radar (EISCAT database to derive neutral winds. One of these techniques uses the same implementation of servo theory as has been used with the IRI model. Detailed comparisons for each season and solar activity category allow for conclusions to be drawn as to the major influences on the climatological behaviour of the wind at this latitude. Comparison of the incoherent scatter radar (ISR derived neutral winds with FPI, empirical model and numerical model winds is important to our understanding and judgement of the validity of the techniques used to derive thermospheric wind databases. The comparisons also test model performance and indicate possible reasons for differences found between the models. In turn, the conclusions point to possible improvements in their formulation. In particular it is found that the empirical models are over-reliant on mid-latitude data in their formulation, and fail to provide accurate estimates of the winds at high-latitudes.

    Key words. Meteorology and atmospheric dynamics (thermospheric dynamics

  12. Climate response to imposed solar radiation reductions in high latitudes

    OpenAIRE

    M. C. MacCracken; H.-J. Shin; Caldeira, K; G. A. Ban-Weiss

    2012-01-01

    Increasing concentrations of greenhouse gases are the primary contributor to the 0.8 °C increase in the global average temperature since the late 19th century, shortening cold seasons and lengthening warm seasons. The warming is amplified in polar regions, causing retreat of sea ice, snow cover, permafrost, mountain glaciers, and ice sheets, while also modifying mid-latitude weather, amplifying global sea level rise, and initiating high-latitude carbon feedbacks. Model simulations in which we...

  13. A study of magnetic fluctuations and their anomalous scaling in the solar wind: the Ulysses fast-latitude scan

    Directory of Open Access Journals (Sweden)

    c. Pagel

    2001-01-01

    Full Text Available The solar wind is a highly turbulent and intermittent medium at frequencies between 10-4 and 10-1 Hz. Power spectra are used to look at fluctuations in the components of the magnetic field at high frequencies over a wide range of latitudes. Results show steady turbulence in the polar regions of the Sun and a more varied environment in the equatorial region. The magnetic field fluctuations exhibit anomalous scaling at high frequencies. Various models have been proposed in an attempt to better understand the scaling nature of such fluctuations in neutral fluid turbulence. We have used the Ulysses fast latitude scan data to perform a wide ranging comparison of three such models on the solar wind magnetic field data: the well-known P model, in both its Kolmogorov and Kraichnan forms, the lognormal cascade model and a model adapted from atmospheric physics, the G infinity model. They were tested by using fits to graphs of the structure function exponents g(q, by making a comparison with a non-linear measure of the deviation of g(q from the non-intermittent straight line, and by using extended self similarity technique, over a large range of helio-latitudes. Tests of all three models indicated a high level of intermittency in the fast solar wind, and showed a varied structure in the slow wind, with regions of apparently little intermittency next to regions of high intermittency, implying that the slow wind has no uniform origin. All but one of the models performed well, with the lognormal and Kolmogorov P model performing the best over all the tests, indicating that inhomogeneous energy transfer in the cascade is a good description. The Kraichnan model performed relatively poorly, and the overall results show that the Kraichnan model of turbulence is not well supported over the frequency and distance ranges of our data set. The G infinity model fitted the results surprisingly well and showed that there may very well be important universal geometrical

  14. Revisiting the question: Does high-latitude solar activity lead low-latitude solar activity in time phase?

    Energy Technology Data Exchange (ETDEWEB)

    Kong, D. F.; Qu, Z. N. [Yunnan Observatories, Chinese Academy of Sciences, Kunming 650011 (China); Guo, Q. L., E-mail: kdf@ynao.ac.cn [College of Mathematics Physics and Information Engineering, Jiaxing University, Jiaxing 314001 (China)

    2014-05-01

    Cross-correlation analysis and wavelet transform methods are used to investigate whether high-latitude solar activity leads low-latitude solar activity in time phase or not, using the data of the Carte Synoptique solar filaments archive from 1919 March to 1989 December. From the cross-correlation analysis, high-latitude solar filaments have a time lead of 12 Carrington solar rotations with respect to low-latitude ones. Both the cross-wavelet transform and wavelet coherence indicate that high-latitude solar filaments lead low-latitude ones in time phase. Furthermore, low-latitude solar activity is better correlated with high-latitude solar activity of the previous cycle than with that of the following cycle, which is statistically significant. Thus, the present study confirms that high-latitude solar activity in the polar regions is indeed better correlated with the low-latitude solar activity of the following cycle than with that of the previous cycle, namely, leading in time phase.

  15. Climate response to imposed solar radiation reductions in high latitudes

    Directory of Open Access Journals (Sweden)

    M. C. MacCracken

    2012-07-01

    Full Text Available Increasing concentrations of greenhouse gases are the primary contributor to the 0.8 °C increase in the global average temperature since the late 19th century, shortening cold seasons and lengthening warm seasons. The warming is amplified in polar regions, causing retreat of sea ice, snow cover, permafrost, mountain glaciers, and ice sheets, while also modifying mid-latitude weather, amplifying global sea level rise, and initiating high-latitude carbon feedbacks. Model simulations in which we reduced solar insolation over high latitudes not only cooled those regions, but also drew energy from lower latitudes, exerting a cooling influence over much of the hemisphere in which the reduction was imposed. Our simulations, which used the National Center for Atmospheric Research's CAM3.1 atmospheric model coupled to a slab ocean, indicated that, on a normalized basis, high-latitude reductions in absorbed solar radiation have a significantly larger cooling influence than equivalent solar reductions spread evenly over the Earth. This amplified influence occurred because high-latitude surface cooling preferentially increased sea ice fraction and, therefore, surface albedo, leading to a larger deficit in the radiation budget at the top of the atmosphere than from an equivalent global reduction in solar radiation. Reductions in incoming solar radiation in one polar region (either north or south resulted in increased poleward energy transport during that hemisphere's cold season and shifted the Inter-Tropical Convergence Zone (ITCZ away from that pole, whereas equivalent reductions in both polar regions tended to leave the ITCZ approximately in place. Together, these results suggest that, until emissions reductions are sufficient to limit the warming influence of greenhouse gas concentrations, polar reductions in solar radiation, if they can be efficiently and effectively implemented, might, because of fewer undesirable side effects than for global solar

  16. Upper mesospheric lunar tides over middle and high latitudes during sudden stratospheric warming events

    Science.gov (United States)

    Chau, J. L.; Hoffmann, P.; Pedatella, N. M.; Matthias, V.; Stober, G.

    2015-04-01

    In recent years there have been a series of reported ground- and satellite-based observations of lunar tide signatures in the equatorial and low latitude ionosphere/thermosphere around sudden stratospheric warming (SSW) events. This lower atmosphere/ionosphere coupling has been suggested to be via the E region dynamo. In this work we present the results of analyzing 6 years of hourly upper mesospheric winds from specular meteor radars over a midlatitude (54°N) station and a high latitude (69°N) station. Instead of correlating our results with typical definitions of SSWs, we use the definition of polar vortex weaking (PVW) used by Zhang and Forbes. This definition provides a better representation of the strength in middle atmospheric dynamics that should be responsible for the waves propagating to the E region. We have performed a wave decomposition on hourly wind data in 21 day segments, shifted by 1 day. In addition to the radar wind data, the analysis has been applied to simulations from Whole Atmosphere Community Climate Model Extended version and the thermosphere-ionosphere-mesosphere electrodynamics general circulation model. Our results indicate that the semidiurnal lunar tide (M2) enhances in northern hemispheric winter months, over both middle and high latitudes. The time and magnitude of M2 are highly correlated with the time and associated zonal wind of PVW. At middle/high latitudes, M2 in the upper mesosphere occurs after/before the PVW. At both latitudes, the maximum amplitude of M2 is directly proportional to the strength of PVW westward wind. We have found that M2 amplitudes could be comparable to semidiurnal solar tide amplitudes, particularly around PVW and equinoxes. Besides these general results, we have also found peculiarities in some events, particularly at high latitudes. These peculiarities point to the need of considering the longitudinal features of the polar stratosphere and the upper mesosphere and lower thermosphere regions. For

  17. Solar cosmic ray measurements at high heliocentric latitudes. [proposed space missions of solar probes to study solar physics

    Science.gov (United States)

    Anderson, K. A.

    1976-01-01

    A brief review is presented of what might result from a program of solar cosmic ray observations on 'out-of-the-ecliptic' spacecraft. The following topics are discussed: (1) The magnetic fields of the sun at high latitudes, (2) propagation of fast charged particles in the solar corona and in interplanetary space at high latitudes, (3) origin of interplanetary particle populations and the solar wind, (4) other particle phenomena in interplanetary space (e.g., acceleration of shock waves), and (5) effect of spacecraft mission characteristics on solar cosmic ray studies at high latitudes. Maps of polar coronal magnetic fields are shown.

  18. Operational high latitude surface irradiance products from polar orbiting satellites

    Science.gov (United States)

    Godøy, Øystein

    2016-12-01

    It remains a challenge to find an adequate approach for operational estimation of surface incoming short- and longwave irradiance at high latitudes using polar orbiting meteorological satellite data. In this presentation validation results at a number of North Atlantic and Arctic Ocean high latitude stations are presented and discussed. The validation results have revealed that although the method works well and normally fulfil the operational requirements, there is room for improvement. A number of issues that can improve the estimates at high latitudes have been identified. These improvements are partly related to improved cloud classification using satellite data and partly related to improved handling of multiple reflections over bright surfaces (snow and sea ice), especially in broken cloud conditions. Furthermore, the availability of validation sites over open ocean and sea ice is a challenge.

  19. Simulation studies of high-latitude magnetospheric boundary dynamics

    Institute of Scientific and Technical Information of China (English)

    PU; Zuyin; SHI; Quanqi; XIAO; Chijie; FU; Suiyan; ZHANG; Hu

    2004-01-01

    Magnetic reconnection at the high-latitude magnetopause is studied using 2.5-dimensional Hail-MHD simulation. Concentric flow vortices and magnetic islands appear when both Hall effect and sheared flow are considered. Plasma mixing across the magnetopause occurs in the presence of the flow vortices. Reconnected structure generated in the vicinity of the subsolar point changes its geometry with increasing flow shear while moving to high latitudes. In the presence of flow shear, with the Hail-MHD reconnection a higher reconnection rate than with the traditional MHD is obtained. The out-of-plane components of flow and magnetic field produced by the Hall current are redistributed under the action of the flow shear, which makes the plasma transport across the boundaries more complicated. The simulation results provide some help in understanding the dynamic processes at the high latitude magnetopause.

  20. Wind structure during mid-latitude storms and its application in Wind Energy

    DEFF Research Database (Denmark)

    Larsén, Xiaoli Guo; Du, Jianting; Bolanos, Rodolfo

    2015-01-01

    . The numerical modeling is done through an atmosphere-wave coupled system, where the atmospheric model is the Weather Research and Forecasting (WRF) model and the wave model is the Simulating WAves Nearshore (SWAN) model. Measurements from offshore stations, Horns Rev and the FINO platform, as well as satellite...... of model setups (domain, initial time and resolution) and input data (large scale atmospheric forcing and bathymetry data). The wind structures were both examined for open sea and fetch limited conditions....

  1. Star Formation and Molecular Clouds at High Galactic Latitude

    Science.gov (United States)

    McGehee, P. M.

    2008-12-01

    In this chapter we review the young stars and molecular clouds found at high Galactic latitudes (|b| ≥ 30°). These are mostly associated with two large-scale structures on the sky, the Gould Belt and the Taurus star formation region, and a handful of molecular clouds including MBM 12 and MBM 20 which, as a population, consist of the nearest star formation sites to our Sun. There are also a few young stars that are found in apparent isolation far from any molecular cloud. The high latitude clouds are primarily translucent molecular clouds and diffuse Galactic cirrus with the majority of them seen at high latitude simply due to their proximity to the Sun. The rare exceptions are those, like the Draco and other intermediate or high velocity clouds, found significantly above or below the Galactic plane. We review the processes that result in star formation within these low density and extraplanar environments as well as the mechanisms for production of isolated T Tauri stars. We present and discuss the known high-latitude stellar nurseries and young stellar objects.

  2. Beryllium-10 concentrations in water samples of high northern latitudes

    Energy Technology Data Exchange (ETDEWEB)

    Strobl, C.; Eisenhauer, A.; Schulz, V.; Baumann, S.; Mangini, A. [Heidelberger Akademie der Wissenschaften, Heildelberg (Germany); Kubik, P.W. [Paul Scherrer Inst. (PSI), Villigen (Switzerland)

    1997-09-01

    {sup 10}Be concentrations in the water column of high northern latitudes were not available so far. We present different {sup 10}Be profiles from the Norwegian-Greenland Sea, the Arctic Ocean, and the Laptev Sea. (author) 3 fig., 3 refs.

  3. Comparison of high-latitude thermospheric meridionalwinds I: optical and radar experimental comparisons

    Directory of Open Access Journals (Sweden)

    E. M. Griffin

    2004-03-01

    Full Text Available Thermospheric neutral winds at Kiruna, Sweden (67.4°N, 20.4°E are compared using both direct optical Fabry-Perot Interferometer (FPI measurements and those derived from European incoherent scatter radar (EISCAT measurements. This combination of experimental data sets, both covering well over a solar cycle of data, allows for a unique comparison of the thermospheric meridional component of the neutral wind as observed by different experimental techniques. Uniquely in this study the EISCAT measurements are used to provide winds for comparison using two separate techniques: the most popular method based on the work of Salah and Holt (1974 and the Meridional Wind Model (MWM (Miller et al., 1997 application of servo theory. The balance of forces at this location that produces the observed diurnal pattern are investigated using output from the Coupled Thermosphere and Ionosphere (CTIM numerical model. Along with detailed comparisons from short periods the climatological behaviour of the winds have been investigated for seasonal and solar cycle dependence using the experimental techniques. While there are features which are consistent between the 3 techniques, such as the evidence of the equinoctial asymmetry, there are also significant differences between the techniques both in terms of trends and absolute values. It is clear from this and previous studies that the high-latitude representation of the thermospheric neutral winds from the empirical Horizontal Wind Model (HWM, though improved from earlier versions, lacks accuracy in many conditions. The relative merits of each technique are discussed and while none of the techniques provides the perfect data set to address model performance at high-latitude, one or more needs to be included in future HWM reformulations.

    Key words. Meteorology and atmospheric dynamics (thermospheric dynamics, Ionosphere (ionosphere-atmosphere interactions, auroral ionosphere

  4. High latitude dust pathways from Iceland: implications for aeolian inputs to oceans and cryosphere

    Science.gov (United States)

    Bullard, J. E.; Baddock, M.; Mockford, T.; Thorsteinsson, T.

    2016-12-01

    Recent research has suggested that dust emission from source areas found in the high latitudes (≥50°N and ≥40°S) may contribute at least 5% to the global dust budget. Although this amount is low compared to that from sub-tropical dust sources, the relative impact of dust emission at high latitudes may well be magnified by its regional significance. High latitude regions lie away from the transport corridors of dust from the major sub-tropical dust belt, thus sources at higher latitudes have the potential to be especially important providers of mineral aerosol to (their) proximal cryospheric, terrestrial and marine systems. To examine the distribution of dust from a prominent high latitude dust source, this study employed forward air parcel trajectory modelling over a 20 year period, quantifying dust trajectories from source areas in the north and south of Iceland. The majority of multi-year dust transport studies have relied upon daily-run trajectories over their decadal study periods. This research differs from these because it only analyses trajectories generated when dust was known to be in suspension at the origin, based on meteorological observations. We demonstrate that the potential for Icelandic dust to be transported over the Greenland Ice Sheet is considerably overestimated by generic transport climatologies when compared with those specifically associated with dust. Modeled transport patterns illustrate the strong influence of seasonality as a primary control on dust emission and its transport from Iceland. Snow cover means dust activity is suppressed for a longer duration in the north of Iceland, and while winds are weakest in summer, the delivery of dust to Atlantic and sub-arctic oceans is greatest and broadest in that season. These findings illustrate the influence of drivers unique to high latitude environments, and their importance in understanding the aeolian systems operating there.

  5. Excitation of the ionospheric resonance cavity by neutral winds at middle latitudes

    Directory of Open Access Journals (Sweden)

    V. V. Surkov

    2004-09-01

    Full Text Available A new mechanism for the ionospheric Alfvén resonator (IAR excitation at middle latitudes is considered. It is shown that the ionosphere wind system in this region is capable of sustaining the generation of geomagnetic perturbations that can be detected by ground magnetometers. The general IAR dispersion relation describing the linear coupling of the shear Alfvén and fast magnetosonic/compressional modes is obtained. The dependence of the IAR eigenfrequencies and damping rates on the perpendicular wave number and on the ground conductivity during the day- and nighttime conditions is analyzed both analytically and numerically. In order to demonstrate the IAR excitation by neutral winds the power spectra of the geomagnetic perturbation on the ground surface are calculated. Furthermore, it is found that Kolmogorov spectra of the ionospheric turbulent neutral winds and the IAR eigenfrequencies lie in the same frequency range that make it possible to enhance the IAR excitation. The relevance of the developed theoretical model to the ground-based observations is stressed.

  6. High-Latitude Ionospheric Structuring at Kilometer Scales

    Science.gov (United States)

    Bust, G. S.; Datta-Barua, S.; Su, Y.; Deshpande, K.; Hampton, D.

    2014-12-01

    Ionospheric observations in the polar and auroral zones have been made regularly with radar chains and optical imaging at larger spatio-temporal cadence. However, the observation of kilometer scale variations at sub-second cadence has not been practically realizable until recently. Quantifying the irregularities at these sizes and scales is necessary for an understanding of the dynamics leading to fine scale phenomena in the high latitude environment. We present measurements of kilometer-scale plasma variations made at the northern auroral zone using an array of specialized Global Positioning System (GPS) receivers. These 6 CASES receivers (plus 1 from ASTRA, LLC) are sited at the Poker Flat Research Range, Alaska, and have been collecting data since late 2013. The array monitors for ionospheric scintillations, fluctuations in phase and amplitude of the GPS L-band signals received due to ionospheric variations. The array spans 2 km east-west and about 1 km north-south, with a variety of intermediate baseline lengths down to about 200 m. In addition to measuring amplitude and phase scintillation with the S4 and sigma_phi indices at 100-s cadence, these receivers also record 100 Hz raw power and phase measurements from GPS baseband signal processing. These low-rate data are publicly available for download through a web portal at http://apollo.tbc.iit.edu/~spaceweather/ with high rate available upon request. A detailed case study is presented from the December 8, 2013, 0300-0400 UT time period. During this period several interesting scintillation periods were observed. We use array cross-correlation processing methods to first estimate direct ground parameters of the array including a) estimate the 2D drift velocity on the ground; b) estimate a de-correlation (or turbulent) speed; and c) parameters of correlation elliptical coordinates (axial ratio and tilt angle). We then use these results and cross-correlation measurements to derive the ground 2D spatial spectrum of

  7. Simultaneous high- and low-latitude reconnection: ESR and DMSP observations

    Directory of Open Access Journals (Sweden)

    F. Pitout

    Full Text Available We present EISCAT Svalbard Radar and DMSP observations of a double cusp during an interval of predominantly northward IMF on 26 November 2000. In the cusp region, the ESR dish, pointing northward, recorded sun-ward ionospheric flow at high latitudes (above 82° GL, indicating reconnection occuring in the magnetospheric lobe. Meanwhile, the same dish also recorded bursts of poleward flow, indicative of bursty reconnection at the subsolar magnetopause. Within this time interval, the DMSP F13 satellite passed in the close vicinity of the Svalbard archipelago. The particle measurement on board exhibited a double cusp structure in which two oppositely oriented ion dispersions are recorded. We interpret this set of data in terms of simultaneous merging at low- and high-latitude magnetopause. We discuss the conditions for which such simultaneous high-latitude and low-latitude reconnection can be anticipated. We also discuss the consequences of the presence of two X-lines in the dayside polar ionosphere.

    Key words. Magnetospheric physics (solar wind-magnetosphere interactions – Ionosphere (polar ionosphere; plasma convection

  8. High-Latitude Ionospheric Dynamics During Conditions of Northward IMF

    Science.gov (United States)

    Sharber, J. R.

    1996-01-01

    In order to better understand the physical processes operating during conditions of northward interplanetary magnetic field (IMF), in situ measurements from the Dynamics Explorer-2 (low altitude) polar satellite and simultaneous observations from the auroral imager on the Dynamics Explorer-1 (high altitude) satellite were used to investigate the relationships between optical emissions, particle precipitation, and convective flows in the high-latitude ionosphere. Field aligned current and convective flow patterns during IMF north include polar cap arcs, the theta aurora or transpolar arc, and the 'horse-collar' aurora. The initial part of the study concentrated on the electrodynamics of auroral features in the horse-collar aurora, a contracted but thickened emission region in which the dawn and dusk portions can spread to very high latitudes, while the latter part focused on the evolution of one type of IMF north auroral pattern to another, specifically the quiet-time horse-collar pattern to a theta aurora.

  9. Star Formation and Molecular Clouds at High Galactic Latitude

    CERN Document Server

    McGehee, Peregrine M

    2008-01-01

    In this chapter we review the young stars and molecular clouds found at high Galactic latitudes $(|b| \\ge 30^\\circ)$. These are mostly associated with two large-scale structures on the sky, the Gould Belt and the Taurus star formation region, and a handful of molecular clouds including MBM 12 and MBM 20 which, as a population, consist of the nearest star formation sites to our Sun. There are also a few young stars that are found in apparent isolation far from any molecular cloud. The high latitude clouds are primarily translucent molecular clouds and diffuse Galactic cirrus with the majority of them seen at high latitude simply due to their proximity to the Sun. The rare exceptions are those, like the Draco and other intermediate or high velocity clouds, found significantly above or below the Galactic plane. We review the processes that result in star formation within these low density and extraplanar environments as well as the mechanisms for production of isolated T Tauri stars. We present and discuss the k...

  10. The High Latitude D Region During Electron Precipitation Events

    Science.gov (United States)

    Hargreaves, J. K.; Collis, P. N.; Korth, A.

    1984-01-01

    The fluxes of energetic electrons entering the high-latitude atmosphere during auroral radio absorption events and their effect on the electron density in the auroral D region are discussed. An attempt was made to calculate the radio absorption during precipitation events from the fluxes of energetic electrons measured at geosynchronous orbit, and then to consider the use of absorption measurements to indicate the magnetospheric particle fluxes, the production rates, and electron densities in the D region.

  11. High latitude D region during electron precipitation events

    Energy Technology Data Exchange (ETDEWEB)

    Hargreaves, J.K.; Collis, P.N.; Korth, A.

    1984-05-01

    The fluxes of energetic electrons entering the high-latitude atmosphere during auroral radio absorption events and their effect on the electron density in the auroral D region are discussed. An attempt was made to calculate the radio absorption during precipitation events from the fluxes of energetic electrons measured at geosynchronous orbit, and then to consider the use of absorption measurements to indicate the magnetospheric particle fluxes, the production rates, and electron densities in the D region.

  12. Boundary Current and Mixing Processes in The High Latitude Oceans

    Science.gov (United States)

    2016-06-07

    Boundary Current and Mixing Processes in The High Latitude Oceans Robin D. Muench Earth & Space Research 1910 Fairview Ave E., Ste 210 Seattle...Thorpe and Ozmidov length scales. Journal of Geophysical Research , 87, 9601-9613. Galbraith, P.S., and D.E. Kelley, 1996: Identifying overturns in...and near Marguerite Bay during winter 2003: A SO GLOBEC study. Deep-Sea Research 2, 54. Padman, L., S.L. Howard, and R.D. Muench, 2006a: Internal

  13. Simulation of equatorial and high-latitude jets on Jupiter in a deep convection model.

    Science.gov (United States)

    Heimpel, Moritz; Aurnou, Jonathan; Wicht, Johannes

    2005-11-10

    The bands of Jupiter represent a global system of powerful winds. Broad eastward equatorial jets are flanked by smaller-scale, higher-latitude jets flowing in alternating directions. Jupiter's large thermal emission suggests that the winds are powered from within, but the zonal flow depth is limited by increasing density and electrical conductivity in the molecular hydrogen-helium atmosphere towards the centre of the planet. Two types of planetary flow models have been explored: shallow-layer models reproduce multiple high-latitude jets, but not the equatorial flow system, and deep convection models only reproduce an eastward equatorial jet with two flanking neighbours. Here we present a numerical model of three-dimensional rotating convection in a relatively thin spherical shell that generates both types of jets. The simulated flow is turbulent and quasi-two-dimensional and, as observed for the jovian jets, simulated jet widths follow Rhines' scaling theory. Our findings imply that Jupiter's latitudinal transition in jet width corresponds to a separation between the bottom-bounded flow structures in higher latitudes and the deep equatorial flows.

  14. Physiological and behavioral adaptations in bats living at high latitudes.

    Science.gov (United States)

    Boyles, Justin G; McGuire, Liam P; Boyles, Esmarie; Reimer, Jesika P; Brooks, Christopher A C; Rutherford, Robert W; Rutherford, Teresa A; Whitaker, John O; McCracken, Gary F

    2016-10-15

    Widespread animals at the extremes of the species' distribution experience ecological constraints different than individuals in the core of the distribution. For example, small endotherms at very high latitudes face short summers with cool temperatures and a lack of true darkness. In particular, insectivorous bats at high latitudes may experience constraints because of their unique life history traits, and may have different energy requirements than bats at lower latitudes. To evaluate the extent of these differences, we estimated an energy budget and refueling rates for reproductively active female little brown bats (Myotis lucifugus) roosting in buildings in eastern Alaska (~63°N). Physiological parameters (torpor use and metabolic rates) and daily energy expenditures (25.7±5.3kJd(-1)) were similar to, or slightly lower than, conspecifics at lower latitudes. Northern little brown bats foraged for less time than southerly conspecifics, but measurements of plasma β-hydroxybutyrate concentrations suggest that northern bats refuel at a rate considerably higher than those to the south. It appears that high refueling rates (and therefore foraging intensity) involve a dietary shift to orb-weaver spiders, which are abundant and likely offer higher energetic benefit than the small, flying insects consumed by individuals in other parts of the distribution. Environmental factors may limit species' distributions, but our results provide an example of a population at the limit of their geographic range that has compensated for environmental challenges by adopting unique behavioral strategies while the underlying physiology (including daily energy expenditure) remains similar to populations at the core of the species' range. Copyright © 2016 Elsevier Inc. All rights reserved.

  15. Energy-Efficient Office Buildings at High Latitudes

    Energy Technology Data Exchange (ETDEWEB)

    Lerum, V.

    1996-12-31

    This doctoral thesis describes a method for energy efficient office building design at high latitudes and cold climates. The method combines daylighting, passive solar heating, solar protection, and ventilative cooling. The thesis focuses on optimal design of an equatorial-facing fenestration system. A spreadsheet framework linking existing simplified methods is used. The daylight analysis uses location specific data on frequency distribution of diffuse daylight on vertical surfaces to estimate energy savings from optimal window and room configurations in combination with a daylight-responsive electric lighting system. The passive solar heating analysis is a generalization of a solar load ratio method adapted to cold climates by combining it with the Norwegian standard NS3031 for winter months when the solar savings fraction is negative. The emphasis is on very high computational efficiency to permit rapid and comprehensive examination of a large number of options early in design. The procedure is illustrated for a location in Trondheim, Norway, testing the relative significance of various design improvement options relative to a base case. The method is also tested for two other locations in Norway, at latitudes 58 and 70 degrees North. The band of latitudes between these limits covers cities in Alaska, Canada, Greenland, Iceland, Scandinavia, Finland, Russia, and Northern Japan. A comprehensive study of the ``whole building approach`` shows the impact of integrated daylighting and low-energy design strategies. In general, consumption of lighting electricity may be reduced by 50-80%, even at extremely high latitudes. The reduced internal heat from electric lights is replaced by passive solar heating. 113 refs., 85 figs., 25 tabs.

  16. Assessing high wind energy penetration

    DEFF Research Database (Denmark)

    Tande, J.O.

    1995-01-01

    In order to convincingly promote installing wind power capacity as a substantial part of the energy supply system, a set of careful analyses must be undertaken. This paper applies a case study concentrated on assessing the cost/benefit of high wind energy penetration. The case study considers...... expanding the grid connected wind power capacity in Praia, the capital of Cape Verde. The currently installed 1 MW of wind power is estimated to supply close to 10% of the electric energy consumption in 1996. Increasing the wind energy penetration to a higher level is considered viable as the project...... with the existing wind power, supply over 30% of the electric consumption in 1996. Applying the recommended practices for estimating the cost of wind energy, the life-cycle cost of this 2.4 MW investment is estimated at a 7% discount rate and a 20 year lifetime to 0.26 DKK/kW h....

  17. Mountain biodiversity patterns at low and high latitudes.

    Science.gov (United States)

    Molau, Ulf

    2004-11-01

    This paper presents an overview of mountain biodiversity at a multitude of scales in space, time, and function. Even though species richness is usually the focal component in nature conservation, genetic diversity within species is equally important. The small-scale distribution of species in the tropical Andes, as exemplified by the plant genera Calceolaria and Bartsia, contrasts against the situation in high-latitude mountains, e.g., the Scandes, where species have wide ranges and many are circumpolar. Recent studies on alpine plants based on molecular methods show that the intraspecific genetic diversity tends to increase with latitude, a situation brought about by the glaciation history with repeated contraction-expansion episodes of species' distributions. In tropical mountains, species distributions are geographically much narrower, often as a result of relatively recent, local speciation. Thus, whereas species richness in mountains decreases from the Equator towards the poles, genetic diversity shows the opposite trend. Finally, a comparison of ecosystem diversity in low- and high-latitude mountain ranges (tropical Andes vs. Scandes) shows that the landscapes differ profoundly with regard to timberline ecotones, snow distribution, and climate variables, and are subject to widely different impacts of global change

  18. Ionosphere Scintillation at Low and High Latitudes (Modelling vs Measurement)

    Science.gov (United States)

    Béniguel, Yannick

    2016-04-01

    This paper will address the problem of scintillations characteristics, focusing on the parameters of interest for a navigation system. Those parameters are the probabilities of occurrence of simultaneous fading, the bubbles surface at IPP level, the cycle slips and the fades duration statistics. The scintillation characteristics obtained at low and high latitudes will be compared. These results correspond to the data analysis performed after the ESA Monitor ionosphere measurement campaign [1], [2]. A second aspect of the presentation will be the modelling aspect. It has been observed that the phase scintillation dominates at high latitudes while the intensity scintillation dominates at low latitudes. The way it can be reproduced and implemented in a propagation model (e.g. GISM model [3]) will be presented. Comparisons of measurements with results obtained by modelling will be presented on some typical scenarios. References [1] R. Prieto Cerdeira, Y. Beniguel, "The MONITOR project: architecture, data and products", Ionospheric Effects Symposium, Alexandria (Va), May 2011 [2] Y. Béniguel, R Orus-Perez , R. Prieto-Cerdeira , S. Schlueter , S. Scortan, A. Grosu "MONITOR 2: ionospheric monitoring network in support to SBAS and other GNSS and scientific purposes", IES Conference, Alexandria (Va), May 2015-05-22 [3] Y. Béniguel, P. Hamel, "A Global Ionosphere Scintillation Propagation Model for Equatorial Regions", Journal of Space Weather Space Climate, 1, (2011), doi: 10.1051/swsc/2011004

  19. Momentum transfer at the high-latitude magnetopause and boundary layers

    Directory of Open Access Journals (Sweden)

    E. J. Lund

    2008-08-01

    Full Text Available How and where momentum is transferred from the solar wind to the magnetosphere and ionosphere is one of the key problems of space physics. Much of this transfer occurs through direct reconnection on the dayside, particularly when the IMF is southward. However, momentum transfer also occurs at higher latitudes via Alfvén waves on old open field lines, even for southward IMF. This momentum is transferred to the ionosphere via field-aligned currents (FACs, and the flow channel associated with these FACs produces a Hall current which causes magnetic variations at high latitude (the Svalgaard-Mansurov effect. We show examples where such momentum transfer is observed with multiple spacecraft and ground-based instruments.

  20. High-Latitude Topside Ionospheric Vertical Electron Density Profile Changes in Response to Large Magnetic Storms

    Science.gov (United States)

    Benson, Robert F.; Fainberg, Joseph; Osherovich, Vladimir A.; Truhlik, Vladimir; Wang, Yongli; Bilitza, Dieter; Fung, Shing F.

    2016-01-01

    Large magnetic-storm-induced changes were detected in high-latitude topside vertical electron density profiles Ne(h) in a database of profiles and digital topside ionograms, from the International Satellites for Ionospheric Studies (ISIS) program, that enabled Ne(h) profiles to be obtained in nearly the same region of space before, during, and after a major magnetic storm (Dst -100nT). Storms where Ne(h) profiles were available in the high-latitude Northern Hemisphere had better coverage of solar wind parameters than storms with available Ne(h) profiles in the high-latitude Southern Hemisphere. Large Ne(h) changes were observed during all storms, with enhancements and depletions sometimes near a factor of 10 and 0.1, respectively, but with substantial differences in the responses in the two hemispheres. Large spatial andor temporal Ne(h) changes were often observed during Dst minimum and during the storm recovery phase. The storm-induced Ne(h) changes were the most pronounced and consistent in the Northern Hemisphere in that large enhancements were observed during winter nighttime and large depletions during winter and spring daytime. The limited available cases suggested that these Northern Hemisphere enhancements increased with increases of the time-shifted solar wind velocity v, magnetic field B, and with more negative values of the B components except for the highest common altitude (1100km) of the profiles. There was also some evidence suggesting that the Northern Hemisphere depletions were related to changes in the solar wind parameters. Southern Hemisphere storm-induced enhancements and depletions were typically considerably less with depletions observed during summer nighttime conditions and enhancements during summer daytime and fall nighttime conditions.

  1. Joule heating hot spot at high latitudes in the afternoon sector

    Science.gov (United States)

    Cai, L.; Aikio, A. T.; Milan, S. E.

    2016-07-01

    The afternoon Joule heating hot spot has been studied statistically by using the EISCAT Svalbard Radar (ESR) measurements at 75.4° Corrected Geomagnetic latitude (CGMLAT) and the OMNI solar wind data base. For a small subset of events, the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) field-aligned current distributions have been available. The main results are as follows. Afternoon Joule heating hot spots are associated with high values of ionospheric electric fields and slightly enhanced Pedersen conductances. The Joule heating hot spot values are larger in summer than in winter, which can be explained by the higher Pedersen conductances during summer than winter. The afternoon Joule heating hot spots are located close to the reversals of the large-scale field-aligned current systems. The most common location is close to the Region 1/Region 2 boundary and those events are associated with sunward convecting F region plasma. In a few cases, the hot spots take place close to the Region 1/Region 0 boundary and then the ionospheric plasma is convecting antisunward. The hot spots may occur both during slow (450 km/s) speed solar wind conditions. During slow-speed solar wind events, the dominant interplanetary magnetic field (IMF) direction is southward, which is the general requirement for the low-latitude magnetic merging at the dayside magnetopause. During high-speed solar wind, also northward IMF conditions appear, but those are associated with large values of the IMF |By| component, making again the dayside magnetopause merging possible. Finally, the measured afternoon hot spot Joule heating rates are not a linear function of the solar wind energy coupling function.

  2. Use of radio occultation to probe the high latitude ionosphere

    Directory of Open Access Journals (Sweden)

    A. J. Mannucci

    2015-02-01

    Full Text Available We have explored the use of COSMIC data to provide valuable scientific information on the ionospheric impacts of energetic particle precipitation during geomagnetic storms. Ionospheric electron density in the E region, and hence ionospheric conductivity, is significantly altered by precipitating particles from the magnetosphere. This has global impacts on the thermosphere-ionosphere because of the important role of conductivity on high latitude Joule heating. Two high-speed stream (HSS and two coronal mass ejection (CME storms are examined with the COSMIC data. We find clear correlation between geomagnetic activity and electron density retrievals from COSMIC. At nighttime local times, the number of profiles with maximum electron densities in the E layer (below 200 km altitude is well correlated with geomagnetic activity. We interpret this to mean that electron density increases due to precipitation are captured by the COSMIC profiles. These "E layer dominant ionosphere" (ELDI profiles have geomagnetic latitudes that are consistent with climatological models of the auroral location. For the two HSS storms, that occurred in May of 2011 and 2012, a strong hemispheric asymmetry is observed, with nearly all the ELDI profiles found in the southern, less sunlit, hemisphere. Stronger aurora and precipitation have been observed before in winter hemispheres, but the degree of asymmetry deserves further study. For the two CME storms, occurring in July and November of 2012, large increases in the number of ELDI profiles are found starting in the storm's main phase but continuing for several days into the recovery phase. Analysis of the COSMIC profiles was extended to all local times for the July 2012 CME storm by relaxing the ELDI criterion and instead visually inspecting all profiles above 50° magnetic latitude for signatures of precipitation in the E region. For nine days during the July 2012 period, we find a signature of precipitation occurs nearly

  3. Postmidnight ionospheric troughs in summer at high latitudes

    Science.gov (United States)

    Voiculescu, M.; Nygrén, T.; Aikio, A. T.; Vanhamäki, H.; Pierrard, V.

    2016-12-01

    In this article we identify possible mechanisms for the formation of postmidnight ionospheric troughs during summer, in sunlit plasma. Four events were identified in measurements of European Incoherent Scatter and ESR radars during CP3 experiments, when the ionosphere was scanned in a meridional plan. The spatial and temporal variation of plasma density, ion, and electron temperatures were analyzed for each of the four events. Super Dual Auroral Radar Network plasma velocity measurements were added, when these were available. For all high-latitude troughs the ion temperatures are high at density minima (within the trough), at places where the convection plasma velocity is eastward and high. There is no significant change in electron temperature inside the trough, regardless of its temporal evolution. We find that troughs in sunlit plasma form in two steps: the trough starts to form when energetic electron precipitation leads to faster recombination in the F region, and it deepens when entering a region with high eastward flow, producing frictional heating and further depleting the plasma. The high-latitude plasma convection plays an important role in formation and evolution of troughs in the postmidnight sector in sunlit plasma. During one event a second trough is identified at midlatitudes, with different characteristics, which is most likely produced by a rapid subauroral ion drift in the premidnight sector.

  4. Impacts of high-latitude volcanic eruptions on ENSO and AMOC.

    Science.gov (United States)

    Pausata, Francesco S R; Chafik, Leon; Caballero, Rodrigo; Battisti, David S

    2015-11-10

    Large volcanic eruptions can have major impacts on global climate, affecting both atmospheric and ocean circulation through changes in atmospheric chemical composition and optical properties. The residence time of volcanic aerosol from strong eruptions is roughly 2-3 y. Attention has consequently focused on their short-term impacts, whereas the long-term, ocean-mediated response has not been well studied. Most studies have focused on tropical eruptions; high-latitude eruptions have drawn less attention because their impacts are thought to be merely hemispheric rather than global. No study to date has investigated the long-term effects of high-latitude eruptions. Here, we use a climate model to show that large summer high-latitude eruptions in the Northern Hemisphere cause strong hemispheric cooling, which could induce an El Niño-like anomaly, in the equatorial Pacific during the first 8-9 mo after the start of the eruption. The hemispherically asymmetric cooling shifts the Intertropical Convergence Zone southward, triggering a weakening of the trade winds over the western and central equatorial Pacific that favors the development of an El Niño-like anomaly. In the model used here, the specified high-latitude eruption also leads to a strengthening of the Atlantic Meridional Overturning Circulation (AMOC) in the first 25 y after the eruption, followed by a weakening lasting at least 35 y. The long-lived changes in the AMOC strength also alter the variability of the El Niño-Southern Oscillation (ENSO).

  5. Small-scale characteristics of extremely high latitude aurora

    Directory of Open Access Journals (Sweden)

    J. A. Cumnock

    2009-09-01

    Full Text Available We examine 14 cases of an interesting type of extremely high latitude aurora as identified in the precipitating particles measured by the DMSP F13 satellite. In particular we investigate structures within large-scale arcs for which the particle signatures are made up of a group of multiple distinct thin arcs. These cases are chosen without regard to IMF orientation and are part of a group of 87 events where DMSP F13 SSJ/4 measures emissions which occur near the noon-midnight meridian and are spatially separated from both the dawnside and duskside auroral ovals by wide regions with precipitating particles typical of the polar cap. For 73 of these events the high-latitude aurora consists of a continuous region of precipitating particles. We focus on the remaining 14 of these events where the particle signatures show multiple distinct thin arcs. These events occur during northward or weakly southward IMF conditions and follow a change in IMF By. Correlations are seen between the field-aligned currents and plasma flows associated with the arcs, implying local closure of the FACs. Strong correlations are seen only in the sunlit hemisphere. The convection associated with the multiple thin arcs is localized and has little influence on the large-scale convection. This also implies that the sunward flow along the arcs is unrelated to the overall ionospheric convection.

  6. Silicon-carbon interactions in high latitude watersheds

    Science.gov (United States)

    Humborg, C.; Morth, C.; Struyf, E.; Conley, D. J.

    2008-12-01

    Changes in climate and hydrology in high latitude regions could liberate large amounts of previously inactive organic carbon (OC) during a prolonging thawing period, and new studies have shown that a great deal of this organic C is remineralized as CO2 during its transport to the sea. However, OC (with its origin in atmospheric carbon) and dissolved silicate (DSi) concentrations in taiga and tundra rivers are intimately linked, and higher concentrations of weathering products are found in taiga and tundra rivers with a higher percentage of peat in their watersheds. It appears that the weathering regime of taiga and tundra watersheds is tightly linked to carbon-silicon interactions, in which carbon acts both as a weathering agent (soil CO2 from degradation of OC) and as a weathering product (DSi and bicarbonate). Whereas respiration of OC can be regarded as a positive feedback to global warming, weathering can be regarded as a negative feedback to global warming since atmospheric CO2 is converted to bicarbonate and thereby locked into the aquatic phase for geological time scales. Thus, bicarbonate export may compensate for significant amounts of exported OC thereby reducing the positive feedback to atmospheric CO2. However, the silicon-carbon interactions are not straight forward as suggested by classical inverse modelling,using the stochiometry of rock forming minerals as base, since high latitude wetlands contain a massive stock of amorphous silica (diatoms and phytoliths) buffering the actual DSi export, suggesting that the Si cycle is to a large extent biologically controlled.

  7. Probabilistic forecasting of ionospheric scintillation and GNSS receiver signal tracking performance at high latitudes

    Directory of Open Access Journals (Sweden)

    Paul Prikryl

    2013-06-01

    Full Text Available At high latitudes, phase scintillation occurs predominantly on the dayside in the ionospheric footprint of the magnetospheric cusp, and in the nightside auroral oval. A new technique of probabilistic forecasting of phase scintillation occurrence relative to the arrival time of high-speed solar wind from coronal holes and interplanetary coronal mass ejections has recently been proposed [Prikryl et al. 2012]. Cumulative probability distribution functions for the phase-scintillation occurrence that are obtained can be specified for low (below-median and high (above-median values of various solar wind plasma parameters. Recent advances in modeling of high-speed solar wind and coronal mass ejections, combined with the probabilistic forecasting of scintillation, will lead to improved operational space weather forecasting applications. Scintillation forecasting and mitigation techniques need to be developed to avoid potential costly failures of technology-based Global Navigation Satellite Systems in the near future, in particular during the upcoming solar maximum. The Global Navigation Satellite Systems receiver-tracking performance during severe scintillation conditions can be assessed by the analysis of receiver phase-locked-loop jitter. Tracking jitter maps [Sreeja et al. 2011] offers a potentially useful tool to provide users with expected tracking conditions, if based on scintillation predictions as proposed above. Scintillation indices are obtained from L1 GPS data collected with the Canadian High Arctic Ionospheric Network. Combined with high rate amplitude and phase data, they can be used as input to receiver tracking models to develop scintillation mitigation techniques.

  8. High-latitude geomagnetic studies (22-23 millihertz)

    Energy Technology Data Exchange (ETDEWEB)

    Wolfe, A. (AT T Bell Laboratories, Murray Hill, NJ (USA) City Univ. of New York, Brooklyn (USA)); Lanzerotti, L.J.; Maclennan, C.C.; Medford, L.V. (AT T Bell Laboratories, Murray Hill, NJ (USA))

    1988-01-01

    Geomagnetic field measurements were initiated at Iqaluit (formerly Frobisher Bay) in the Northwest Territories of Canada during July 1985 (Wolfe et al. 1986). This site was selected because it was calculated to be in the conjugate area to the Amundsen-Scott South Pole Station where extensive geomagnetic research has been conducted. The principal scientific objectives are to study the conjugacy of high-latitude magnetic fluctuations observed at Iqaluit and South Pole (L{approximately}13). In this report, the authors extend the previous report of Wolfe et al. (1987) and comment upon the conjugacy of the stations for magnetic field fluctuations in the Pc3 (22-33 millihertz) hydromagnetic regime and upon the penetration of hydromagnetic energy deeper into the magnetosphere on the local dayside.

  9. The CH fraction of Carbon stars at high Galactic latitudes

    CERN Document Server

    Goswami, Aruna; Shantikumar, N S

    2009-01-01

    CH stars form a distinct class of objects with characteristic properties like iron deficiency, enrichment of carbon and overabundance in heavy elements. These properties can provide strong observational constraints for theoretical computation of nucleosynthesis at low-metallicity. An important question is the relative surface density of CH stars which can provide valuable inputs to our understanding on the role of low to intermediate-mass stars in the early Galactic chemical evolution. Spectroscopic characterization provides an effective way of identifying CH stars. The present analysis is aimed at a quantitative assessment of the fraction of CH stars in a sample of stars using a set of spectral classification criteria. The sample consists of 92 objects selected from a collection of candidate Faint High Latitude Carbon stars from the Hamburg/ESO survey. Medium resolution (R ~ 1300) spectra for these objects were obtained using OMR at VBO, Kavalur and HFOSC at HCT, IAO, Hanle, during 2007 - 2009 spanning a wav...

  10. Daylighting in linear atrium buildings at high latitudes

    Energy Technology Data Exchange (ETDEWEB)

    Matusiak, Barbara

    1998-12-31

    This thesis proposes new criteria for visual comfort based on knowledge of visual perception and a method for estimating the modelling ability of light by using inter-reflection calculations. Simplified calculations are presented for the daylight factor in linear building structures, using the projected solid angle principle, for uniform sky and for CIE overcast sky conditions. The calculations are compared with experimental results. Simple diagrams are created based on calculations of the mean daylight factor in rooms adjacent to a narrow street. These diagrams and presented formulas and tables can be used as a simple design tool. Daylighting strategies for linear atrium buildings at high latitudes are developed and examined. These strategies are divided into three groups: (1) the atrium space and facades as light conductor/reflector, (2) the glass roof as a light conductor, and (3) light reflectors on the neighbouring roof. The atrium space and facade strategies are subdivided into passive and active. The strategies connected to the glazed roof includes different configurations of glazing: horizontal, single pitched, double pitched, and the use of laser cut panels and prismatic panels in the glazed roof. The shapes of reflectors on the neighbouring roof are a flat reflector, a parabolic reflector and a parabolic concentrator. Strategies from all three groups are examined on a physical model of scale 1:20 in the artificial sky of mirror box type. Simulations with artificial sun have also been done. The results from model studies are compared with computer simulations. All the active daylighting systems designed for use in the atrium space or on the atrium facades have a huge potential for use in atrium buildings. From the strategies connected with the glazed roof the negatively sloped glass is found to be the best alternative for glazed roofs at high latitudes. Among the roof reflectors, the flat one performs best. 82 refs., 122 figs., 27 tabs.

  11. Large-amplitude ULF waves at high latitudes

    Science.gov (United States)

    Guido, T.; Tulegenov, B.; Streltsov, A. V.

    2014-11-01

    We present results from the statistical study of ULF waves detected by the fluxgate magnetometer in Gakona, Alaska during several experimental campaigns conducted at the High Frequency Active Auroral Research Program (HAARP) facility in years 2011-2013. We analyzed frequencies of ULF waves recorded during 26 strongly disturbed geomagnetic events (substorms) and compared them with frequencies of ULF waves detected during magnetically quiet times. Our analysis demonstrates that the frequency of the waves carrying most of the power in almost all these events is less than 1 mHz. We also analyzed data from the ACE satellite, measuring parameters of the solar wind in the L1 Lagrangian point between Earth and Sun, and found that in several occasions there is a strong correlation between oscillations of the magnetic field in the solar wind and oscillations detected on the ground. We also found several cases when there is no correlation between signals detected on ACE and on the ground. This finding suggests that these frequencies correspond to the fundamental eigenfrequency of the coupled magnetosphere-ionosphere system, and the amplitude of these waves can reach significant magnitude when the system is driven by the external driver (for example, the solar wind) with this particular frequency. When the frequency of the driver does not match the frequency of the system, the waves still are observed, but their amplitudes are much smaller.

  12. Highly Alfvenic Slow Solar Wind

    Science.gov (United States)

    Roberts, D. Aaron

    2010-01-01

    It is commonly thought that fast solar wind tends to be highly Alfvenic, with strong correlations between velocity and magnetic fluctuations, but examples have been known for over 20 years in which slow wind is both Alfvenic and has many other properties more typically expected of fast solar wind. This paper will present a search for examples of such flows from more recent data, and will begin to characterize the general characteristics of them. A very preliminary search suggests that such intervals are more common in the rising phase of the solar cycle. These intervals are important for providing constraints on models of solar wind acceleration, and in particular the role waves might or might not play in that process.

  13. Importance of post-shock streams and sheath region as drivers of intense magnetospheric storms and high-latitude activity

    Directory of Open Access Journals (Sweden)

    K. E. J. Huttunen

    2004-04-01

    Full Text Available Magnetic disturbances in the Earth's magnetosphere can be very different depending on the type of solar wind driver. We have determined the solar wind causes for intense magnetic storms (Dst<-100nT over a 6-year period from the beginning of 1997 to the end of 2002, using observations by the WIND and ACE spacecraft. We have taken into consideration whether the storm was caused by the sheath region or by the following interplanetary coronal mass ejection (ICME. We also divided ICMEs into those having a magnetic cloud structure and those without such a structure. We found that post-shock streams and sheath regions caused the largest fraction of intense magnetic storms. We present four periods of magnetospheric activity in more detail. One of the events was caused by a magnetic cloud (10-11 August 2000 and the rest (13-14 July 2000, 8-9 June 2000 and 17-18 April 2001 by sheath regions and post-shock streams. We have used several magnetic indices to monitor the low- and high-latitude magnetospheric response to these different solar wind structures. Two of the events are interesting examples where at first strong high-latitude activity took place and the low-latitude response followed several hours later. These events demonstrate that low- and high-latitude activity do not always occur concurrently and the level of activity may be very different. According to the examples shown the evolution of the pressure-corrected Dst index was more difficult to model for a sheath region or a post-shock stream driven storm than for a storm caused by a magnetic cloud.

  14. Projected changes of the low-latitude north-western Pacific wind-driven circulation under global warming

    Science.gov (United States)

    Duan, Jing; Chen, Zhaohui; Wu, Lixin

    2017-05-01

    Based on the outputs of 25 models participating in the Coupled Model Intercomparison Project Phase 5, the projected changes of the wind-driven circulation in the low-latitude north-western Pacific are evaluated. Results demonstrate that there will be a decrease in the mean transport of the North Equatorial Current (NEC), Mindanao Current, and Kuroshio Current in the east of the Philippines, accompanied by a northward shift of the NEC bifurcation Latitude (NBL) off the Philippine coast with over 30% increase in its seasonal south-north migration amplitude. Numerical simulations using a 1.5-layer nonlinear reduced-gravity ocean model show that the projected changes of the upper ocean circulation are predominantly determined by the robust weakening of the north-easterly trade winds and the associated wind stress curl under the El Niño-like warming pattern. The changes in the wind forcing and intensified upper ocean stratification are found equally important in amplifying the seasonal migration of the NBL.

  15. An atmospheric blast/thermal model for the formation of high-latitude pedestal craters

    Science.gov (United States)

    Wrobel, Kelly; Schultz, Peter; Crawford, David

    2006-10-01

    Although tenuous, the atmosphere of Mars affects the evolution of impact-generated vapor. Early-time vapor from a vertical impact expands symmetrically, directly transferring a small percentage of the initial kinetic energy of impact to the atmosphere. This energy, in turn, induces a hemispherical shock wave that propagates outward as an intense airblast (due to high-speed expansion of vapor) followed by a thermal pulse of extreme atmospheric temperatures (from thermal energy of expansion). This study models the atmospheric response to such early-time energy coupling using the CTH hydrocode written at Sandia National Laboratories. Results show that the surface surrounding a 10 km diameter crater (6 km "apparent" diameter) on Mars will be subjected to intense winds (˜200 m/s) and extreme atmospheric temperatures. These elevated temperatures are sufficient to melt subsurface volatiles at a depth of several centimeters for an ice-rich substrate. Ensuing surface signatures extend to distal locations (˜4 apparent crater diameters for a case of 0.1% energy coupling) and include striations, thermally armored surfaces, and/or ejecta pedestals—all of which are exhibited surrounding the freshest high-latitude craters on Mars. The combined effects of the atmospheric blast and thermal pulse, resulting in the generation of a crater-centered erosion-resistant armored surface, thus provide a new, very plausible formation model for high-latitude Martian pedestal craters.

  16. High-latitude plasma convection during Northward IMF as derived from in-situ magnetospheric Cluster EDI measurements

    Directory of Open Access Journals (Sweden)

    M. Förster

    2008-09-01

    Full Text Available In this study, we investigate statistical, systematic variations of the high-latitude convection cell structure during northward IMF. Using 1-min-averages of Cluster/EDI electron drift observations above the Northern and Southern polar cap areas for six and a half years (February 2001 till July 2007, and mapping the spatially distributed measurements to a common reference plane at ionospheric level in a magnetic latitude/MLT grid, we obtained regular drift patterns according to the various IMF conditions. We focus on the particular conditions during northward IMF, where lobe cells at magnetic latitudes >80° with opposite (sunward convection over the central polar cap are a permanent feature in addition to the main convection cells at lower latitudes. They are due to reconnection processes at the magnetopause boundary poleward of the cusp regions. Mapped EDI data have a particular good coverage within the central part of the polar cap, so that these patterns and their dependence on various solar wind conditions are well verified in a statistical sense. On average, 4-cell convection pattern are shown as regular structures during periods of nearly northward IMF with the tendency of a small shift toward negative clock angles. The positions of these high-latitude convection foci are within 79° to 85° magnetic latitude and 09:00–15:00 MLT. The MLT positions are approximately symmetric ±2 h about 11:30 MLT, i.e. slightly offset from midday toward prenoon hours, while the maximum (minimum potential of the high-latitude cells is at higher magnetic latitudes near their maximum potential difference at ≈−10° to −15° clock angle for the North (South Hemisphere. With increasing clock angle distances from ≈IMFBz+, a gradual transition occurs from the 4-cell pattern via a 3-cell to the common 2-cell convection pattern, in the course of which one of the medium-scale high-latitude dayside cells diminishes and disappears while the

  17. Autonomous, continuously recording broadband seismic stations at high-latitude

    Science.gov (United States)

    Beaudoin, B.; Parker, T.; Bonnett, B.; Tytgat, G.; Anderson, K.; Fowler, J.

    2009-04-01

    IRIS PASSCAL is in the third year of an NSF funded development and acquisition effort to establish a pool of cold-hardened seismic stations specifically for high-latitude broadband deployments. We have two complete years of field trials and have successfully recorded continuous seismic data during both years with data recovery rates of ~90%. Our design is premised on a 2W autonomous system recording to local media, capable of lasting two years without service. The system is composed of four new design elements: a heavily insulated station enclosure; a state-of-health (SOH) Iridium modem; a light weight, easily deployed solar panel mount; and a power system that includes power switching between primary (Lithium Thionyl Chloride) and secondary batteries. The station enclosures have proved most critical in keeping our data acquisition systems operating within manufacturer specifications and primary batteries within a 50-70% efficiency range. Enclosures with 2.5cm-thick vacuum panels and 5cm of foam insulation have kept interior enclosure temperatures 25-30°C above background (typically below -50°C). This austral summer we are deploying version three of our enclosures. Significant changes in the design include thicker vacuum panels (5cm), more robust construction, and simplified cable routing. An important aspect of our station design is easy installation and minimal weight. To simplify installation our station enclosures are packed with datalogger, SOH communications and batteries in the lab or base camp, so that access to the internal components is not necessary at the remote site. Bulkhead connectors allow a user to fully interact with the system without ever having to open the enclosure. Solar panel mounts are also fully constructed prior to deployment. Once on site, digging two large holes (one for the enclosure and one for the broadband seismometer) and constructing the site takes roughly 2 hours. A station designed to record continuously for 12-14 months is

  18. Small-scale fluctuations in barium drifts at high latitudes and associated Joule heating effects

    Science.gov (United States)

    Hurd, L. D.; Larsen, M. F.

    2016-01-01

    Most previous estimates of Joule heating rates, especially the contribution of small-scale structure in the high-latitude ionosphere, have been based on incoherent scatter or coherent scatter radar measurements. An alternative estimate can be found from the plasma drifts obtained from ionized barium clouds released from sounding rockets. We have used barium drift data from three experiments to estimate Joule heating rates in the high-latitude E region for different magnetic activity levels. In particular, we are interested in the contribution of small-scale plasma drift fluctuations, corresponding to equivalent electric field fluctuations, to the local Joule heating rate on scales smaller than those typically resolved by radar or other measurements. Since Joule heating is a Lagrangian quantity, the inherently Lagrangian estimates provided by the chemical tracer measurements are a full description of the effects of electric field variance and neutral winds on the heating, differing from the Eulerian estimates of the type provided by ground-based measurements. Results suggest that the small-scale contributions to the heating can be more than a factor of 2 greater than the mean field contribution regardless of geomagnetic conditions, and at times the small-scale contribution is even larger. The high-resolution barium drift measurements, moreover, show that the fine structure in the electric field can be more variable than previous studies have reported for similar conditions. The neutral winds also affect the heating, altering the height-integrated Joule heating rates by as much as 12%, for the cases studied here, and modifying the height distribution of the heating profile as well.

  19. High-latitude controls of thermocline nutrients and low latitude biological productivity.

    Science.gov (United States)

    Sarmiento, J L; Gruber, N; Brzezinski, M A; Dunne, J P

    2004-01-01

    The ocean's biological pump strips nutrients out of the surface waters and exports them into the thermocline and deep waters. If there were no return path of nutrients from deep waters, the biological pump would eventually deplete the surface waters and thermocline of nutrients; surface biological productivity would plummet. Here we make use of the combined distributions of silicic acid and nitrate to trace the main nutrient return path from deep waters by upwelling in the Southern Ocean and subsequent entrainment into subantarctic mode water. We show that the subantarctic mode water, which spreads throughout the entire Southern Hemisphere and North Atlantic Ocean, is the main source of nutrients for the thermocline. We also find that an additional return path exists in the northwest corner of the Pacific Ocean, where enhanced vertical mixing, perhaps driven by tides, brings abyssal nutrients to the surface and supplies them to the thermocline of the North Pacific. Our analysis has important implications for our understanding of large-scale controls on the nature and magnitude of low-latitude biological productivity and its sensitivity to climate change.

  20. Two dimensional hydrodynamic modeling of a high latitude braided river

    Science.gov (United States)

    Humphries, E.; Pavelsky, T.; Bates, P. D.

    2014-12-01

    Rivers are a fundamental resource to physical, ecologic and human systems, yet quantification of river flow in high-latitude environments remains limited due to the prevalence of complex morphologies, remote locations and sparse in situ monitoring equipment. Advances in hydrodynamic modeling and remote sensing technology allow us to address questions such as: How well can two-dimensional models simulate a flood wave in a highly 3-dimensional braided river environment, and how does the structure of such a flood wave differ from flow down a similar-sized single-channel river? Here, we use the raster-based hydrodynamic model LISFLOOD-FP to simulate flood waves, discharge, water surface height, and velocity measurements over a ~70 km reach of the Tanana River in Alaska. In order to use LISFLOOD-FP a digital elevation model (DEM) fused with detailed bathymetric data is required. During summer 2013, we surveyed 220,000 bathymetric points along the study reach using an echo sounder system connected to a high-precision GPS unit. The measurements are interpolated to a smooth bathymetric surface, using Topo to Raster interpolation, and combined with an existing five meter DEM (Alaska IfSAR) to create a seamless river terrain model. Flood waves are simulated using varying complexities in model solvers, then compared to gauge records and water logger data to assess major sources of model uncertainty. Velocity and flow direction maps are also assessed and quantified for detailed analysis of braided channel flow. The most accurate model output occurs with using the full two-dimensional model structure, and major inaccuracies appear to be related to DEM quality and roughness values. Future work will intercompare model outputs with extensive ground measurements and new data from AirSWOT, an airborne analog for the Surface Water and Ocean Topography (SWOT) mission, which aims to provide high-resolution measurements of terrestrial and ocean water surface elevations globally.

  1. A Study of Steady Magnetospheric Convection Using High Latitude Magnetometers

    Science.gov (United States)

    de Silva, J. T.; Erickson, K. N.; Engebretson, M. J.; Murr, D. L.; Hughes, W. J.

    2001-05-01

    Magnetometer data from the MACCS and CANOPUS arrays in northern North America have been analyzed during two of the intervals of steady magnetospheric convection identified by the GEM community, January 29-30 and February 3-4, 1998. These intervals were characterized by extended periods of southward interplanetary magnetic field (negative IMF Bz), and by the absence of substorms. The patterns of ionospheric current flow on the dayside were found to be in general agreement with the disturbance current system, SD, originally described by Silsbee and Vestine [1942]. This indicates that during extended periods of southward IMF the convection on the dayside is the same whether or not there are substorms. When plasma flow patterns measured by the SuperDARN auroral radar network were available for comparison, these patterns agreed with the patterns inferred from magnetometers. Further study will investigate convection patterns on the nightside, and a similar study of convection for the southern high latitude region will be conducted using data from Antarctic stations.

  2. Discovery of an Apparent High Latitude Galactic Supernova Remnant

    CERN Document Server

    Fesen, Robert; Black, Christine; Koeppel, Ari

    2015-01-01

    Deep H$\\alpha$ images of a faint emission complex 4.0 x 5.5 degrees in angular extent and located far off the Galactic plane at l = 70.0 degrees, b=-21.5 degrees reveal numerous thin filaments suggestive of a supernova remnant's shock emission. Low dispersion optical spectra covering the wavelength range 4500 - 7500 A show only Balmer line emissions for one filament while three others show a Balmer dominated spectrum along with weak [N I] 5198, 5200 A, [O I] 6300, 6364 A, [N II] 6583 A, [S II] 6716, 6731 A and in one case [O III] 5007 A line emission. Many of the brighter H$\\alpha$ filaments are visible in near UV GALEX images presumably due to C III] 1909 A line emission. ROSAT All Sky Survey images of this region show a faint crescent shaped X-ray emission nebula coincident with the portion of the H$\\alpha$ nebulosity closest to the Galactic plane. The presence of long, thin Balmer dominated emission filaments with associated UV emission and coincident X-ray emission suggests this nebula is a high latitude ...

  3. The single event upset environment for avionics at high latitude

    Energy Technology Data Exchange (ETDEWEB)

    Sims, A.J.; Dyer, C.S.; Peerless, C.L. (Defence Research Agency, Farnborough (United Kingdom). Space and Communications Dept.); Johansson, K.; Pettersson, H. (SAAB Military Aircraft, Linkoeping (Sweden)); Farren, J. (AEA Technology, Oxfordshire (United Kingdom). Harwell Lab.)

    1994-12-01

    Modern avionic systems for civil and military applications are becoming increasingly reliant upon embedded microprocessors and associated memory devices. The phenomenon of single event upset (SEU) is well known in space systems and designers have generally been careful to use SEU tolerant devices or to implement error detection and correction (EDAC) techniques where appropriate. In the past, avionics designers have had no reason to consider SEU effects but is clear that the more prevalent use of memory devices combined with increasing levels of IC integration will make SEU mitigation an important design consideration for future avionic systems. To this end, it is necessary to work towards producing models of the avionics SEU environment which will permit system designers to choose components and EDAC techniques which are based on predictions of SEU rates correct to much better than an order of magnitude. Measurements of the high latitude SEU environment at avionics altitude have been made on board a commercial airliner. Results are compared with models of primary and secondary cosmic rays and atmospheric neutrons. Ground based SEU tests of static RAMs are used to predict rates in flight.

  4. Birkeland current effects on high-latitude groundmagnetic field perturbations

    CERN Document Server

    Laundal, K M; Lehtinen, N; Gjerloev, J W; Østgaard, N; Tenfjord, P; Reistad, J P; Snekvik, K; Milan, S E; Ohtani, S; Anderson, B J

    2016-01-01

    Magnetic perturbations on ground at high latitudes are directly associated only with the divergence-free component of the height-integrated horizontal ionospheric current, $\\textbf{J}_{\\perp,df}$. Here we show how $\\textbf{J}_{\\perp,df}$ can be expressed as the total horizontal current $\\textbf{J}_\\perp$ minus its curl-free component, the latter being completely determined by the global Birkeland current pattern. Thus in regions where $\\textbf{J}_\\perp = 0$, the global Birkeland current distribution alone determines the local magnetic perturbation. We show with observations from ground and space that in the polar cap, the ground magnetic field perturbations tend to align with the Birkeland current contribution in darkness but not in sunlight. We also show that in sunlight, the magnetic perturbations are typically such that the equivalent overhead current is anti-parallel to the convection, indicating that the Hall current system dominates. Thus the ground magnetic field in the polar cap relates to different c...

  5. MBM 12: young protoplanetary discs at high galactic latitude

    CERN Document Server

    Meeus, G; Henning, T; Bouwman, J; Chen, C; Lawson, W; Apai, D; Pascucci, I; Sicilia-Aguilar, A

    2009-01-01

    (abridged) We present Spitzer infrared observations to constrain disc and dust evolution in young T Tauri stars in MBM 12, a star-forming cloud at high latitude with an age of 2 Myr and a distance of 275 pc. The region contains 12 T Tauri systems, with primary spectral types between K3 and M6; 5 are weak-line and the rest classical T Tauri stars. We first use MIPS and literature photometry to compile spectral energy distributions for each of the 12 members in MBM 12, and derive their IR excesses. The IRS spectra are analysed with the newly developed two-layer temperature distribution (TLTD) spectral decomposition method. For the 7 T Tauri stars with a detected IR excess, we analyse their solid-state features to derive dust properties such as mass-averaged grain size, composition and crystallinity. We find a spatial gradient in the forsterite to enstatite range, with more enstatite present in the warmer regions. The fact that we see a radial dependence of the dust properties indicates that radial mixing is not...

  6. Molecular cores of the high-latitude cloud MBM 40

    Science.gov (United States)

    Chol Minh, Y. C. Young; Kim, Hyun-Goo; Lee, Youngung; Park, Hyeran; Kim, Kwang-Tae; Park, Yong-Sun; Joon Kim, Sang

    2003-11-01

    Towards the high-latitude cloud MBM 40, we identify 3 dense molecular cores of M˜0.2-0.5 M ⊙, and sizes of ˜0.2 pc in diameter embedded in the H I cloud of ˜8 M ⊙ which is observed to be extended along the northeast-southwest direction. The molecular cloud is located almost perpendicularly to the H I emission. We confirm the previous result of Magnani et al. that MBM 40 is not a site for new star formations. We found a very poor correlation between the H I and the IRAS 100 μm emissions, but the CO (1-0) and 100 μm emissions show a better correlation of WCO/ I100=1±0.2 K km s -1 (MJy sr -1) -1. This ratio is larger by a factor of ≥5 than in dense dark clouds, which may indicate that the CO is less depleted in MBM 40 than in dense dark clouds.

  7. Kinematics and chemistry of faint high latitude dwarf carbon stars

    Science.gov (United States)

    Yoon, Jinmi; Beers, Timothy C.; Dietz, Sarah; Lee, Young Sun; Placco, Vinicius M.

    2017-01-01

    The diffuse halo system of the Milky Way is complex, and has been shown to comprise at least two main components: a near-zero net rotation inner-halo and a more rapidly rotating outer-halo component. Studies of the ancient, very metal-poor stars in the Galactic halo system are crucial for understanding its early formation history. The so-called carbon-enhanced metal-poor (CEMP) stars are an important subset of the stars in the halo system, which exhibit distinctive kinematic and chemical signatures that can be used to constrain the star-formation histories and assembly of the various Galactic components.We have examined the sample of main-sequence dwarf and other faint high Galactic latitude carbon-enhanced stars from the Sloan Digital Sky Survey studied by Green (2013). As noted by Green, many of these starsexhibit high proper motions, which have been later claimed to be related to possible binary ejection models Plant et al. (2016). By use of the CEMP sub-classification approach of Yoon et al. (2016), we investigate whether the kinematics of these stars might instead result from their membership in the inner/outer halo populations of the Galaxy.ReferencesGreen, P. 2013, ApJ, 765, 12Plant, K. et al. 2016, AAS 227.34115Yoon, J. et al. 2016, ApJ, in pressAcknowledgementThis work was supported in part by the National Science Foundation under Grant No. PHY-1430152 (JINA Center for the Evolution of the Elements).

  8. Modulation of Low-Latitude West Wind on Abnormal Track and Intensity of Tropical Cyclone Nargis (2008) in the Bay of Bengal

    Institute of Scientific and Technical Information of China (English)

    LI Wei-Wei; WANG Chunzai; WANG Dongxiao; YANG Lei; DENG Yi

    2012-01-01

    Tropical cyclone (TC) Nargis (2008) made landfall in Myanmar on 02 May 2008,bringing a storm surge,major flooding,and resulting in a significant death toll. TC Nargis (2008) displayed abnormal features,including rare eastward motion in its late stage,rapid intensification before landing.Using reanalysis data and a numerical model,we investigated how a low-latitude westerly wind modulated TC Nargis' (2008) track and provided favorable atmospheric conditions for its rapid intensification.More importantly,we found a possible counterbalance effect of flows from the two hemispheres on the TC track in the Bay of Bengal.Our analysis indicates that a strong westerly wind burst across the Bay of Bengal,resulting in TC Nargis' (2008) eastward movement after its recurvature.This sudden enhancement of westerly wind was mainly due to the rapidly intensified mid-level cross-equatorial flow.Our results show that a high-pressure system in the Southern Hemisphere induced this strong,mid-level,cross-equatorial flow.During the rapid intensification period of TC Nargis (2008),this strong and broad westerly wind also transported a large amount of water vapor to TC Nargis (2008).Sufficient water vapor gave rise to continuously high and increased mid-level relative humidity,which was favorable to TC Nargis' (2008) intensification.Condensation of water vapor increased the energy supply,which eventuated the intensification of TC Nargis (2008) to a category 4 on the Saffir-Simpson scale.

  9. Abrupt climate change and high to low latitude teleconnections as simulated in climate models

    DEFF Research Database (Denmark)

    Cvijanovic, Ivana

    High to low latitude atmospheric teleconnections have been a topic of increasing scientific interest since it was shown that high latitude extratropical forcing can induce tropical precipitation shifts through atmosphere-surface ocean interactions. In this thesis, several aspects of high to low l...

  10. EDITORIAL: Northern Hemisphere high latitude climate and environmental change

    Science.gov (United States)

    Groisman, Pavel; Soja, Amber

    2007-10-01

    High Northern Hemisphere latitudes are undergoing rapid and significant change associated with climate warming. Climatic change in this region interacts with and affects the rate of the global change through atmospheric circulation, biogeophysical, and biogeochemical feedbacks. Changes in the surface energy balance, hydrologic cycle, and carbon budget feedback to regional and global weather and climate systems. Two-thirds of the Northern Hemisphere high latitude land mass resides in Northern Eurasia (~20% of the global land mass), and this region has undergone sweeping socio-economic change throughout the 20th century. How this carbon-rich, cold region component of the Earth system functions as a regional entity and interacts with and feeds back to the greater global system is to a large extent unknown. To mitigate the deficiencies in understanding these feedbacks, which may in turn hamper our understanding of the global change rates and patterns, an initiative was formed. Three years ago the Northern Eurasia Earth Science Partnership Initiative (NEESPI) was established to address large-scale and long-term manifestations of climate and environmental change in this region. The NEESPI Science Plan and its Executive Summary have been published at the NEESPI web site (neespi.org). Since 2004, NEESPI participants have been able to seed several waves of research proposals to international and national funding agencies and institutions and also contribute to the International Polar Year. Currently, NEESPI is widely recognized and endorsed by several Earth System Science Partnership (ESSP) programmes and projects: the International Geosphere and Biosphere Programme, the World Climate Research Programme through the Global Energy and Water Cycle Experiment and Climate and Cryosphere Projects, the Global Water System Project, Global Carbon Project, Global Land Project, and the Integrated Land Ecosystem—Atmosphere Processes Study. Through NEESPI, more than 100 individually

  11. Under-Ice Operations with AUVS in High Latitudes

    Science.gov (United States)

    Ferguson, J.; Kaminski, C. D.

    2012-12-01

    In 2010 and 2011, ISE Explorer Autonomous Underwater Vehicles (AUV), built for Natural Resources Canada (NRCan), were deployed to Canada's high Arctic. The mission was to undertake under-ice bathymetric surveys supporting Canada's submission under the United Nations Convention on the Law of the Sea (UNCLOS). During these deployments several under-ice records were broken and several new technologies were demonstrated. The NRCan AUV is a 5000 meter depth rated vehicle, with several innovative additions to make it suitable for arctic survey work. Most notable are a depth rated variable ballast system, a 1300 Hz long-range homing system, and under-ice charging and data transfer capabilities. The Explorer's range was extended to approximately 450 km by adding a hull section to accommodate extra batteries. The scientific payload onboard included a Seabird SBE49 Conductivity-Temperature-Depth (CTD) sensor, Knudsen singlebeam echosounder, and a Kongsberg Simrad EM2000 multibeam echosounder. In 2010, operations were conducted from an ice camp near Borden Island (78°14'N, 112°39'W) operating through an ice hole. Following several test missions, the AUV spent 10 days surveying under ice before being successfully recovered. In total, close to 1100 km of under-ice survey was undertaken at depths to 3160 meters. A further set of operations was carried out in August and September 2011 from the Canadian Icebreaker CCGS Louis St. Laurent operating with the American Icebreaker USCGS Healy. Here the operations were much further north to latitudes of 88°30' N and to depths of 3500 meters. In this paper, the 2010 ice camp and the 2011 icebreaker missions are described, with an outline of technology developments that were undertaken, the preparations that were necessary for the success of the missions and finally, the outcome of the missions themselves.

  12. Occurrence of polar mesosphere summer echoes at very high latitudes

    Directory of Open Access Journals (Sweden)

    M. Zecha

    2009-03-01

    Full Text Available Observations of polar mesosphere summer echoes (PMSE have been carried out during the summer periodes 1999–2001 and 2003–2004 at the very high latitude of 78° N using the SOUSY Svalbard Radar (53.5 MHz at Longyearbyen. Although the measurements could not be done continuously in these seasons, PMSE have been detected over more than 6600 h of 9300 h of observation time overall. Using this data base, particular PMSE occurrence characteristics have been determined. PMSE at Svalbard appear from the middle of May to the end of August with an almost permanent total occurrence in June and July. Diurnal variations are observable in the height-depend occurrence rates and in PMSE thickness, they show a maximum around 09:00–10:00 UTC and a minimum around 21:00–22:00 UTC. PMSE occur nearly exclusively between a height of 80 km and 92 km with a maximum near 85 km. However, PMSE appear not simultaneously over the entire height range, the mean vertical PMSE extension is around 4–6 km in June and July. Furthermore, typically PMSE are separated into several layers, and only 30% of all PMSE are single layers. The probability of multiple layers is greater in June and July than at the beginning and the end of the PMSE season and shows a marked 5-day-variation. The same variation is noticeable in the seasonal dependence of the PMSE occurrence and the PMSE thickness. We finally discuss potential geophysical processes to explain our observational results.

  13. High-Latitude Topside Ionospheric Vertical Electron-Density-Profile Changes in Response to Large Magnetic Storms

    Science.gov (United States)

    Benson, Robert F.; Fainberg, Joseph; Osherovich, Vladimir A.; Truhlik, Vladimir; Wang, Yongli; Bilitza, Dieter; Fung, Shing F.

    2015-01-01

    Large magnetic-storm induced changes have been detected in high-latitude topside vertical electron-density profiles Ne(h). The investigation was based on the large database of topside Ne(h) profiles and digital topside ionograms from the International Satellites for Ionospheric Studies (ISIS) program available from the NASA Space Physics Data Facility (SPDF) at http://spdf.gsfc.nasa.gov/isis/isis-status.html. This large database enabled Ne(h) profiles to be obtained when an ISIS satellite passed through nearly the same region of space before, during, and after a major magnetic storm. A major goal was to relate the magnetic-storm induced high-latitude Ne(h) profile changes to solar-wind parameters. Thus an additional data constraint was to consider only storms where solar-wind data were available from the NASA/SPDF OMNIWeb database. Ten large magnetic storms (with Dst less than -100 nT) were identified that satisfied both the Ne(h) profile and the solar-wind data constraints. During five of these storms topside ionospheric Ne(h) profiles were available in the high-latitude northern hemisphere and during the other five storms similar ionospheric data were available in the southern hemisphere. Large Ne(h) changes were observed during each one of these storms. Our concentration in this paper is on the northern hemisphere. The data coverage was best for the northern-hemisphere winter. Here Ne(h) profile enhancements were always observed when the magnetic local time (MLT) was between 00 and 03 and Ne(h) profile depletions were always observed between 08 and 10 MLT. The observed Ne(h) deviations were compared with solar-wind parameters, with appropriate time shifts, for four storms.

  14. High-latitude electromagnetic and particle energy flux during an event with sustained strongly northward IMF

    Directory of Open Access Journals (Sweden)

    H. Korth

    2005-06-01

    Full Text Available We present a case study of a prolonged interval of strongly northward orientation of the interplanetary magnetic field on 16 July 2000, 16:00-19:00 UT to characterize the energy exchange between the magnetosphere and ionosphere for conditions associated with minimum solar wind-magnetosphere coupling. With reconnection occurring tailward of the cusp under northward IMF conditions, the reconnection dynamo should be separated from the viscous dynamo, presumably driven by the Kelvin-Helmholtz (KH instability. Thus, these conditions are also ideal for evaluating the contribution of a viscous interaction to the coupling process. We derive the two-dimensional distribution of the Poynting vector radial component in the northern sunlit polar ionosphere from magnetic field observations by the constellation of Iridium satellites together with drift meter and magnetometer observations from the Defense Meteorological Satellite Program (DMSP F13 and F15 satellites. The electromagnetic energy flux is then compared with the particle energy flux obtained from auroral images taken by the far-ultraviolet (FUV instrument on the Imager for Magnetopause to Aurora Global Exploration (IMAGE spacecraft. The electromagnetic energy input to the ionosphere of 51 GW calculated from the Iridium/DMSP observations is eight times larger than the 6 GW due to particle precipitation all poleward of 78° MLAT. This result indicates that the energy transport is significant, particularly as it is concentrated in a small region near the magnetic pole, even under conditions traditionally considered to be quiet and is dominated by the electromagnetic flux. We estimate the contributions of the high and mid-latitude dynamos to both the Birkeland currents and electric potentials finding that high-latitude reconnection accounts for 0.8 MA and 45kV while we attribute <0.2MA and ~5kV to an interaction at lower latitudes having the sense of a viscous interaction. Given that these

  15. Dense gas in high-latitude molecular clouds

    Energy Technology Data Exchange (ETDEWEB)

    Reach, W.R.; Pound, M.W.; Wilner, D.J. (Univ. of California, Berkeley (United States)); Lee, Y.

    1992-01-01

    The authors have surveyed high-latitude molecular clouds (MBM 12, 7, 55, 40) in spectral lines that are believed to be dense-gas' tracers due to the high H[sub 2] volume density required for collisional excitation. An extensive CS (2-1) line map of MBM 12 revealed emission that is not confined to clumps. Less than 20% of the integrated line emission from the cloud originates in clearly identified clumps with size between 0.2 pc and 0.02 pc in the integrated line map. The bulk of the emission originates from a relatively smooth horseshoe' structure about 0.1 pc wide and 1 pc long. The CS (2-1) map correlates with the published Bell Labs [sup 13] CO map, with significant [sup 13] CO emission even where the CS emission is undetectable. Within the central core, the C[sup 18]O(1-0) and CS(2-1) lines are positively correlated with significant scatter. There is some indication of higher CS/[sup 13]CO in the cores than the horseshoe'. The observed correlations suggest that both the diffuse CS and [sup 13]CO originate from either numerous, unresolved clumps, or the diffuse parts of the cloud. High-spatial-resolution observations of HCO[sup +] from MBM 12 obtained with the BIMA Hat Creek array demonstrated that the main core emission is primarily on spatial scales greater than 0.004 pc. It appears that the authors have resolved most of the spatial structure of the dense-gas' tracers and have found that the emission is primarily diffuse. To understand the excitation mechanism of the CS rotational levels, a multitransitional study of the 1-0, 2-1, and 3-2 lines is being performed. The CS excitation may be governed by electron collisions in regions with H[sub 2] column densities an order of magnitude lower than the critical density' of [approx gt] 2 [times] 10[sup 4] cm[sup -3]. If electron collisions are populating the CS levels, then the CS and [sup 13]CO lines can both be produced in the outer parts of the cloud, explaining their positive correlation

  16. High-latitude poynting flux from combined Iridium and SuperDARN data

    Directory of Open Access Journals (Sweden)

    C. L. Waters

    2004-09-01

    Full Text Available Field-aligned currents convey stress between the magnetosphere and ionosphere, and the associated low altitude magnetic and electric fields reflect the flow of electromagnetic energy to the polar ionosphere. We introduce a new technique to measure the global distribution of high latitude Poynting flux, S||, by combining electric field estimates from the Super Dual Auroral Radar Network (SuperDARN with magnetic perturbations derived using magnetometer data from the Iridium satellite constellation. Spherical harmonic methods are used to merge the data sets and calculate S|| for any magnetic local time (MLT from the pole to 60° magnetic latitude (MLAT. The effective spatial resolutions are 2° MLAT, 2h MLT, and the time resolution is about one hour due to the telemetry rate of the Iridium magnetometer data. The technique allows for the assessment of high-latitude net S|| and its spatial distribution on one hour time scales with two key advantages: (1 it yields the net S|| including the contribution of neutral winds; and (2 the results are obtained without recourse to estimates of ionosphere conductivity. We present two examples, 23 November 1999, 14:00-15:00 UT, and 11 March 2000, 16:00-17:00 UT, to test the accuracy of the technique and to illustrate the distributions of S|| that it gives. Comparisons with in-situ S|| estimates from DMSP satellites show agreement to a few mW/m2 and in the locations of S|| enhancements to within the technique's resolution. The total electromagnetic energy flux was 50GW for these events. At auroral latitudes, S|| tends to maximize in the morning and afternoon in regions less than 5° in MLAT by two hours in MLT having S||=10 to 20mW/m2 and total power up to 10GW. The power poleward of the Region 1 currents is about one

  17. Vulnerability of high-latitude soil organic carbon in North America to disturbance

    Science.gov (United States)

    Guido Grosse; Jennifer Harden; Merritt Turetsky; A. David McGuire; Philip Camill; Charles Tarnocai; Steve Frolking; Edward Schuur; Torre Jorgenson; Sergei Marchenko; Vladimir Romanovsky; Kimberly P. Wickland; Nancy French; Mark Waldrop; Laura Bourgeau-Chavez; Robert G. Streigl

    2011-01-01

    This synthesis addresses the vulnerability of the North American high-latitude soil organic carbon (SOC) pool to climate change. Disturbances caused by climate warming in arctic, subarctic, and boreal environments can result in significant redistribution of C among major reservoirs with potential global impacts. We divide the current northern high-latitude SOC pools...

  18. Investigation of High-Latitude Phenomena Using Polar Data and Global Simulations

    Science.gov (United States)

    Russell, Christopher T.; Hoffman, Robert (Technical Monitor)

    2001-01-01

    The goal of this one-year project was to use data from the Polar satellite in conjunction with global simulations of Earth's magnetosphere to investigate phenomena in the high-latitude magnetosphere. Specifically, we addressed reconnection at the cusp during periods of northward interplanetary magnetic field (IMF), and the effects of substorms on the high-latitude magnetosphere.

  19. Long-term variations of the mesospheric wind field at mid-latitudes

    Directory of Open Access Journals (Sweden)

    D. Keuer

    2007-08-01

    Full Text Available Continuous MF radar observations at the station Juliusruh (54.6° N; 13.4° E have been analysed for the time interval between 1990 and 2005, to obtain information about solar activity-induced variations, as well as long-term trends in the mesospheric wind field. Using monthly median values of the zonal and the meridional prevailing wind components, as well as of the amplitude of the semidiurnal tide, regression analyses have been carried out with a dependence on solar activity and time. The solar activity causes a significant amplification of the zonal winds during summer (increasing easterly winds and winter (increasing westerly winds. The meridional wind component is positively correlated with the solar activity during summer but during winter the correlation is very small and non significant. Also, the solar influence upon the amplitude of the semidiurnal tidal component is relatively small (in dependence on height partly positive and partly negative and mostly non-significant.

    The derived trends in the zonal wind component during summer are below an altitude of about 83 km negative and above this height positive. During the winter months the trends are nearly opposite compared with the trends in summer (transition height near 86 km. The trends in the meridional wind components are below about 85 km positive in summer (significant and near zero (nonsignificant in winter; above this height during both seasons negative trends have been detected. The trends in the semidiurnal tidal amplitude are at all heights positive, but only partly significant.

    The detected trends and solar cycle dependencies are compared with other experimental results and model calculations. There is no full agreement between the different results, probably caused by different measuring techniques and evaluation methods used. Also, different heights and observation periods investigated may contribute to the detected differences.

  20. HIgh-Latitude Neutral Hydrogen Shells identified in GALFA-HI

    Science.gov (United States)

    Sallmen, Shauna; Taylor, Rebecca; Korpela, Eric J.; Goldston Peek, Joshua Eli; Babler, Brian

    2017-08-01

    Supernovae and stellar winds are important processes in the development and evolution of galaxies. Due to these effects in generations of stars, the interstellar medium (ISM) is turbulent, multiphase, and filled with complex interacting structures. HI (neutral hydrogen) shells are formed when hot, expanding bubbles sweep up shells of neutral material. These shells gradually cool, slow down, and mix with the surrounding interstellar material, but we still lack a complete, detailed picture of the physical state and evolution of gas in our Galaxy's ISM. Studies of numerous shells at different stages of evolution are needed, but biases in search techniques and limitations of data quality and coverage have hindered our efforts. The Galactic Arecibo L-band Feed Array (GALFA) 21-cm survey of the Arecibo sky provides have uniquely high angular resolution except within a few degrees of the Galactic plane. A visual search of these data can therefore identify new structures with small angular diameter at high Galactic latitudes, at all stages of evolution. We present the results of a partial search of these data, focusing on high Galactic latitudes. For each potential shell, the location, velocity, angular size, and velocity range were determined, as well as estimates of the shell wall completeness and persistence of shell completeness, shape, and location across its velocity range. To date, we have identified over 100 potential new shells, ranging in size from 0.1 to 4.5 degrees. Approximately 2/3 of these are smaller than 2 degrees in diameter, a size range that was significantly underrepresented in previous searches. The statistical properties of these newly found shells will be presented, along with details on selected examples.

  1. Millennial-scale interhemispheric asymmetry of low-latitude precipitation: Speleothem evidence and possible high-latitude forcing

    Science.gov (United States)

    Wang, Xianfeng; Edwards, R. Lawrence; Auler, Augusto S.; Cheng, Hai; Ito, Emi

    During the last glacial period, global climate was characterized by numerous millennial-scale abrupt changes. Mechanisms of these events, however, are not yet resolved. Here, we use phasing information between climate records from different localities to distinguish between mechanisms. We establish a 90,000 year-long oxygen isotopic record of cave calcite, with our previously reported and newly obtained data from Caverna Botuverá, southern Brazil. The record was precisely dated with uranium-series methods. Using independent absolute-dated chronologies, we compare the southern Brazil record with contemporaneous oxygen isotopic records of cave calcite from eastern China and the record of speleothem growth periods from northeastern Brazil. Our record anti-correlates remarkably with the eastern China profile, while it correlates positively with the northeastern Brazil one, on both millennial and orbital scales. Thus, rainfall patterns are antiphased between southern Brazil and eastern China but in-phase between the two Brazilian regions. The in-phase Brazilian relationship argues against a Super El Niño-Southern Oscillation (Super-ENSO) mechanism as modern rainfall at these sites is out of phase during ENSO years. Rather, the relationship among the three records is likely related to displacement in the mean position of the intertropical convergence zone and associated asymmetry in Hadley circulation, which leads to an interhemispheric anti-phasing of rainfall between the southern and northern low latitudes. The abrupt climate events during the last glacial-interglacial cycle are probably triggered by meridional overturning circulation changes initiated in the high latitudes and then amplified through air-sea dynamics, resulting in the observed pattern of low-latitude precipitation.

  2. Solar Wind Activity Dependence of the Occurrence of Field-Line Resonance at low Latitudes (L~1.3)

    Science.gov (United States)

    Takasaki, S.; Kawano, H.; Tanaka, Y.; Yoshikawa, A.; Seto, M.; Iijima, M.; Yumoto, K.

    2002-12-01

    It is known that the field line resonance (FLR below) is caused by hydromagnetic waves in the magnetosphere. The fundamental field line eigenfrequency can be expressed by the magnetic field line length, the magnetic field intensity, and the plasma density at the magnetic field line. We can measure the fundamental field line eigenfrequency by ground-based observation. The field line length and the magnetic field intensity can be calculated from some magnetic field model (such as the IGRF model) of the magnetosphere. Then, it is possible that the plasma density at the magnetic field line is determined by these factors. The final aim of this study is to monitor and study time-dependent changes in the plasmaspheric plasma distributions by using ground magnetic field observations. For this purpose, we are working in the following three research phases. The first phase is to confirm the possibility of identifying FLR at low-latitudes (L~1.3). The second phase is to examine the correlation between FLR and solar wind parameters. The third phase is to estimate the plasma density from the FLR data, and monitor the density in a continuous manner. We are now in the third phase, and we report here the results of the first two phase. In the first phase, in order to investigate features of FLR close to the Earth, we installed three magnetometers in Japan at L~1.3 (at Kawatabi, Zaou, and Iitate), and started observing ULF geomagnetic pulsations. Each adjacent stations are separated in latitude by 50 to 100 km. The magnetic field data from these stations and Kakioka geomagnetic observatory, Japan, were analyzed by using the amplitude-ratio method and the cross-phase method. As a result, we identified FLR events whose frequency decreased with decreasing geomagnetic latitude; we infer that this feature was caused by heavy ion mass loading to low-L field lines. In the second phase, we studied the dependence of the occurrence probability of the above-identified FLR events on solar wind

  3. MBM 12: young protoplanetary discs at high galactic latitude

    Science.gov (United States)

    Meeus, G.; Juhász, A.; Henning, Th.; Bouwman, J.; Chen, C.; Lawson, W.; Apai, D.; Pascucci, I.; Sicilia-Aguilar, A.

    2009-04-01

    We present Spitzer infrared observations to constrain disc and dust evolution in young T Tauri stars in MBM 12, a star-forming cloud at high latitude with an age of 2 Myr and a distance of 275 pc. The region contains 12 T Tauri systems, with primary spectral types between K3 and M6; 5 are weak-line and the rest classical T Tauri stars. We first use MIPS and literature photometry to compile spectral energy distributions for each of the 12 members in MBM 12, and derive their IR excesses. Of the 8 stars that are detected with MIPS (spectral types between K3 and M5), only 1 lacks an IR excess - the other 7 all have an IR excess that can be attributed to a disc. This means that in MBM 12, for the detected spectral types K3-M5, we have a very high disc fraction rate, about 90%. Furthermore, 3 of those 7 excess sources are candidate transitional discs. The four lowest-mass systems in the cloud, with spectral types of M5-M6, were undetected by Spitzer. Their upper limits indicate that they either have a transitional disc, or no disc at all. The IRS spectra are analysed with the newly developed two-layer temperature distribution (TLTD) spectral decomposition method. For the 7 T Tauri stars with a detected IR excess, we analyse their solid-state features to derive dust properties such as mass-averaged grain size, composition and crystallinity. The mass-averaged grain size we determine from the 10 micron feature has a wide range, between 0.4 and 6 μm. This grain size is much smaller in the longer-wavelength region: between 0.1 and 1.5 μm. We find that later-type objects have larger grain sizes, as was already shown by earlier studies. Furthermore, we find a wide range in mass fraction of the crystalline grains, between 3 and (at least) 30%, with no relation to the spectral type nor grain size. We do find a spatial gradient in the forsterite to enstatite range, with more enstatite present in the warmer regions. The fact that we see a radial dependence of the dust properties

  4. 75 FR 47301 - Cedro Hill Wind LLC; Butler Ridge Wind Energy Center, LLC; High Majestic Wind Energy Center, LLC...

    Science.gov (United States)

    2010-08-05

    ...; EG10-36-000; EG10-37-000; EG10-38-000] Cedro Hill Wind LLC; Butler Ridge Wind Energy Center, LLC; High Majestic Wind Energy Center, LLC; Wessington Wind Energy Center, LLC; Juniper Canyon Wind Power LLC; Loraine Windpark Project, LLC; White Oak Energy LLC; Meadow Lake Wind Farm III LLC; Meadow Lake Wind Farm...

  5. ENSO response to high-latitude volcanic eruptions: the role of the initial conditions

    Science.gov (United States)

    Pausata, Francesco S. R.; Caballero, Rodrigo; Battisti, David S.

    2016-04-01

    Large volcanic eruptions can have major impacts on global climate affecting both atmospheric and ocean circulation through changes in atmospheric chemical composition and optical properties. The residence time of volcanic aerosol from strong eruptions is around 2-3 years and attention has consequently focused on their short-term impacts, and in particular on tropical eruptions. The long-term, ocean-mediated response has been less studied and large uncertainties remain. Moreover, studies have largely focused on tropical eruptions; high-latitude eruptions have drawn less attention because their impacts have been thought to be merely hemispheric rather than global and no study has hitherto investigated the long-term effects of such eruptions. Here we use a climate model to show that large summer high-latitude eruptions in the Northern Hemisphere could cause an El Niño-like anomaly in the equatorial Pacific during the first 8-9 months after the start of the eruption owing to a strong hemispheric cooling. The hemispherically asymmetric cooling shifts the Inter-Tropical Convergence Zone southwards, triggering a weakening of the trade winds over the western and central equatorial Pacific that leads to an El Niño-like anomaly. However, the El Niño-like anomaly strongly depends on the initial ENSO state: a 3-time larger response is shown when the climate system is going towards a La Niña compared to when is going towards an El Niño. Finally, the eruption also leads to a strengthening of the Atlantic Meridional Overturning Circulation (AMOC) in the first twenty-five years after the eruption, followed by a weakening lasting at least 35 years. The long-lived changes in the AMOC strength also alter the variability of El Niño-Southern Oscillation.

  6. Intraseasonal variability of air temperature over the mid-high latitude Eurasia in boreal winter

    Science.gov (United States)

    Yang, Shuangyan; Li, Tim

    2016-10-01

    The intraseasonal oscillation (ISO) of air temperature over the mid- and high-latitude Eurasia in boreal winter was investigated by NCEP-NCAR reanalysis data. It is found that the intraseasonal temperature disturbances exhibit maximum variability near the surface in the region of 50°-75°N, 80°‒120°E and they propagate southeastwards at average zonal and meridional phase speeds of 3.2 and 2.5 m s-1, respectively. The low-level temperature signal is tightly coupled with upper-tropospheric height anomalies, and both propagate southeastward in a similar phase speed. A diagnosis of the temperature budget reveals that the southeastward propagation is primarily attributed to the advection of the temperature anomaly by the mean wind. A wave activity flux analysis indicates that the southeastward propagating wave train is likely a result of Rossby wave energy propagation. The source of the Rossby wave train appears at the high latitude Europe/Atlantic sector, where maximum wave activity flux convergence resides. During its southeastward journey, the ISO perturbation gains energy from the mean flow through both kinetic and potential energy conversions. A physics-based empirical model was constructed to predict the intraseasonal temperature anomaly over southeast China. The major predictability source is the southeastward-propagating ISO signal. The data for 1979‒2003 were used as a training period to construct the empirical model. A 10-yr (2004‒2013) independent forecast shows that the model attains a useful skill of up to 25 days.

  7. Millennial-scale interhemispheric asymmetry of low-latitude precipitation: speleothem evidences and possible high-latitude forcing

    Science.gov (United States)

    Wang, X.; Auler, A.; Edwards, R.; Cheng, H.; Ito, E.

    2006-12-01

    A high resolution oxygen isotopic record of cave calcite, spanning the last 90,000 years, was obtained from Caverna Botuverá, southern Brazil. The record broadly follows local insolation changes and shows significant millennial-scale variation with amplitudes as large as 3 per mil. Tests for equilibrium conditions show that oxygen isotopic variations are a direct reflection of changes in rainwater values and temperatures at this low- latitude location. Established with independent absolute-dated uranium series chronologies, our record anti- correlates remarkably with the contemporaneous oxygen isotopic records of cave calcite from eastern China (anti-phase precipitation changes), but positively correlates with the record of speleothem growth periods from northeastern Brazil (in-phase precipitation changes) on millennial time scales. These observations suggest that a rainfall seesaw may have existed between the southern and northern low latitudes on millennial time scales in the past. This interhemipheric anti-phasing of rainfall is probably caused by feedbacks between North Atlantic thermohaline circulation and the intertropical convergence. The interplays affect not only North Atlantic climate but also result in the displacement of the mean position of the intertropical convergence zone and associated asymmetry of the Hadley cell. The Brazilian speleothem records further indicate that millennial-scale abrupt climate change is largely tied to meridional shifts rather than zonal shifts, and are therefore unlikely to have been triggered by tropical Walker circulation changes.

  8. Polar conic current sheets as sources and channels of energetic particles in the high-latitude heliosphere

    Science.gov (United States)

    Khabarova, Olga; Malova, Helmi; Kislov, Roman; Zelenyi, Lev; Obridko, Vladimir; Kharshiladze, Alexander; Tokumaru, Munetoshi; Sokół, Justyna; Grzedzielski, Stan; Fujiki, Ken'ichi; Malandraki, Olga

    2017-04-01

    The existence of a large-scale magnetically separated conic region inside the polar coronal hole has been predicted by the Fisk-Parker hybrid heliospheric magnetic field model in the modification of Burger and co-workers (Burger et al., ApJ, 2008). Recently, long-lived conic (or cylindrical) current sheets (CCSs) have been found from Ulysses observations at high heliolatitudes (Khabarova et al., ApJ, 2017). The characteristic scale of these structures is several times lesser than the typical width of coronal holes, and the CCSs can be observed at 2-3 AU for several months. CCS crossings in 1994 and 2007 are characterized by sharp decreases in the solar wind speed and plasma beta typical for predicted profiles of CCSs. In 2007, a CCS was detected directly over the South Pole and strongly highlighted by the interaction with comet McNaught. The finding is confirmed by restorations of solar coronal magnetic field lines that reveal the occurrence of conic-like magnetic separators over the solar poles both in 1994 and 2007. Interplanetary scintillation data analysis also confirms the existence of long-lived low-speed regions surrounded by the typical polar high-speed solar wind in solar minima. The occurrence of long-lived CCSs in the high-latitude solar wind could shed light on how energetic particles reach high latitudes. Energetic particle enhancements up to tens MeV were observed by Ulysses at edges of CCSs both in 1994 and 2007. In 1994 this effect was clearer, probably due to technical reasons. Accelerated particles could be produced either by magnetic reconnection at the edges of a CCS in the solar corona or in the solar wind. We discuss the role of high-latitude CCSs in propagation of energetic particles in the heliosphere and revisit previous studies of energetic particle enhancements at high heliolatitudes. We also suggest that the existence of a CCS can modify the distribution of the solar wind as a function of heliolatitude and consequently impact ionization

  9. Climatology of northern polar latitude MLT dynamics: mean winds and tides

    Directory of Open Access Journals (Sweden)

    G. Kishore Kumar

    2010-10-01

    Full Text Available Mean winds and tides in the northern polar Mesosphere and Lower Thermosphere (MLT have been studied using meteor radars located at Resolute Bay (75° N, 95° W and Yellowknife (62.5° N, 114.3° W. The measurements for Resolute Bay span almost 12 years from July 1997 to February 2009 and the Yellowknife data cover 7 years from June 2002 to October 2008. The analysis reveals similar wind flow over both sites with a difference in magnitude. The summer zonal flow is westward at lower heights, eastward at upper heights and the winter zonal flow is eastward at all heights. The winter meridional flow is poleward and sometimes weakly equatorward, while non winter months show equatorward flow, with a strong equatorward jet during mid-summer months. The zonal and meridional winds show strong interannual variation with a dominant annual variation as well as significant latitudinal variation. Year to year variability in both zonal and meridional winds exists, with a possible solar cycle dependence. The diurnal, semidiurnal and terdiurnal tides also show large interannual variability and latitudinal variation. The diurnal amplitudes are dominated by an annual variation. The climatological monthly mean winds are compared with CIRA 86, GEWM and HWM07 and the climatological monthly mean amplitudes and phases of diurnal and semidiurnal tides are compared with GSWM00 predictions. The GEWM shows better agreement with observations than the CIRA 86 and HWM07. The GSWM00 model predictions need to be modified above 90 km. The agreements and disagreements between observations and models are discussed.

  10. Opportunities for high wind energy penetration

    DEFF Research Database (Denmark)

    Tande, J.O.; Hansen, J.C.

    1997-01-01

    Wind power is today a mature technology, which at windy locations, is economically competitive to conventional power generation technologies. This and growing global environmental concerns have led governments to encourage and plan for wind energy development, a typical aim being 10% of electricity...... consumption. The successful operation of the three major power systems of Cape Verde, with a total wind energy penetration of about 15% since December 1994, demonstrates that power systems can be operated with high penetration of wind energy by adding simple control and monitoring systems only. Thorough...... analyses conclude that expanding to even above 15% wind energy penetration in the Cape Verde power systems is economical. Worldwide, numerous locations with favorable wind conditions and power systems similar to the Capeverdean provide good opportunities for installing wind farms and achieving high wind...

  11. Some aspects of the geomagnetic response to solar wind pressure variations: a case study at low and middle latitudes

    Directory of Open Access Journals (Sweden)

    U. Villante

    2004-06-01

    Full Text Available We examined geomagnetic field observations at low and middle latitudes in the Northern Hemisphere during a 50-min interval (12 May 1999, characterized by a complex behaviour of the solar wind dynamic pressure. For the entire interval, the aspects of the geomagnetic response can be organized into four groups of events which show common characteristics for the H and D components, respectively. The correspondence between the magnetospheric field and the ground components reveals different aspects of the geomagnetic response in different magnetic local time (MLT sectors. For the H component, the correspondence is highly significant in the dusk and night sectors; in the dawn and prenoon sectors it shows a dramatic change across a separation line that extends approximately between (6 MLT, 35° and (13 MLT, 60°. For the D component, the correspondence has significant values in the dawn and prenoon regions. We propose a new approach to the experimental data analysis which reveals that, at each station, the magnetospheric field has a close correspondence with the geomagnetic field projection along an axis (M1 that progressively rotates from north/south (night events to east/west orientation (dawn events. When projected along M1, the geomagnetic signals can be interpreted in terms of a one-dimensional pattern that mostly reflects the field behaviour observed at geostationary orbit. Several features appear more evident in this perspective, and the global geomagnetic response to the SW pressure variations appears much clearer than in other representations. In particular, the MLT dependence of the geomagnetic response is much smaller than that one estimated by previous investigations. A clear latitudinal dependence emerges in the dusk sector. The occurrence of low frequency waves at ~2.8mHz can be interpreted in terms of global magnetospheric modes driven by the SW pulse. This event occurred in the recovery phase after the day

  12. Wind-profiler observations of gravity waves produced by convection at mid-latitudes

    Directory of Open Access Journals (Sweden)

    Y. G. Choi

    2006-01-01

    Full Text Available This work presents a case study which includes regions of large rapidly varying vertical velocities observed by a VHF wind-profiler at Aberystwyth (52.4° N, 4.1° W. Analysis indicates that this region is associated with gravity waves above the tropopause level and simultaneous regions of convective activity below the tropopause level. This case study also suggests that convective activity can be identified effectively by finding periods of large uncertainties on the derived velocities. These regions are hypothesized to be related to regions of small-scale inhomogeneity in the wind field. Examination suggests that the large vertical velocity fluctuations above these convective regions are short period gravity wave packets as expected from theory. In addition the vertical flux of the horizontal momentum associated with the gravity waves also displays the pattern of reversal observed in previous studies.

  13. Ocean acidification at high latitudes: potential effects on functioning of the Antarctic bivalve Laternula elliptica

    National Research Council Canada - National Science Library

    Cummings, Vonda; Hewitt, Judi; Van Rooyen, Anthony; Currie, Kim; Beard, Samuel; Thrush, Simon; Norkko, Joanna; Barr, Neill; Heath, Philip; Halliday, N Jane; Sedcole, Richard; Gomez, Antony; McGraw, Christina; Metcalf, Victoria

    2011-01-01

    Ocean acidification is a well recognised threat to marine ecosystems. High latitude regions are predicted to be particularly affected due to cold waters and naturally low carbonate saturation levels...

  14. CO J = 3 -> 2 observations of translucent and high-latitude molecular clouds

    NARCIS (Netherlands)

    Dishoeck, van E.F.; Phillips, T.G.; Black, J.H.; Gredel, R.

    1991-01-01

    Measurements were carried out on the CO J = 3-2 emission line at 345 GHz from a number of translucent and high-latitude molecular clouds, as well as on the J = 2-1 and J = 1-0 lines of both the (C-12)O and (C-13)O. It is shown that the physical conditions in the high-latitude clouds are very similar

  15. On the wave number 2 eastward propagating quasi 2 day wave at middle and high latitudes

    Science.gov (United States)

    Gu, Sheng-Yang; Liu, Han-Li; Pedatella, N. M.; Dou, Xiankang; Liu, Yu

    2017-04-01

    The temperature and wind data sets from the ensemble data assimilation version of the Whole Atmosphere Community Climate Model + Data Assimilation Research Testbed (WACCM + DART) developed at the National Center for Atmospheric Research (NCAR) are utilized to study the seasonal variability of the eastward quasi 2 day wave (QTDW) with zonal wave number 2 (E2) during 2007. The aliasing ratio of E2 from wave number 3 (W3) in the synoptic WACCM data set is a constant value of 4 × 10-6% due to its uniform sampling pattern, whereas the aliasing is latitudinally dependent if the WACCM fields are sampled asynoptically based on the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) sampling. The aliasing ratio based on SABER sampling is 75% at 40°S during late January, where and when W3 peaks. The analysis of the synoptic WACCM data set shows that the E2 is in fact a winter phenomenon, which peaks in the stratosphere and lower mesosphere at high latitudes. In the austral winter period, the amplitudes of E2 can reach 10 K, 20 m/s, and 30 m/s for temperature, zonal, and meridional winds, respectively. In the boreal winter period, the wave perturbations are only one third as strong as those in austral winter. Diagnostic analysis also shows that the mean flow instabilities in the winter upper mesosphere polar region provide sources for the amplification of E2. This is different from the westward QTDWs, whose amplifications are related to the summer easterly jet. In addition, the E2 also peaks at lower altitude than the westward modes.

  16. UBVR polarimetry of high-galactic latitude carbon stars

    Directory of Open Access Journals (Sweden)

    J. M. López

    2011-01-01

    Full Text Available Presentamos polarimetría y fotometría en las bandas UBVR, en el periodo de un año, de ocho estrellas de carbón de alta latitud galáctica: V Hya, CZ Hya, R For, R Lep, Y Cvn, T Dra, RV Aqr y RT Cap. La polarización observada alcanza su máximo valor en la banda U y es muy variable en el tiempo. Similarmente, la polarización en la banda B es muy variable pero sus valores son siempre inferiores a los obtenidos en la banda U. El origen y la variabilidad de la polarización en estas bandas puede explicarse como el resultado de la dispersión de la radiación de la estrella central en las regiones interiores de la envolvente circunestelar donde los granos de polvo y las moléculas son creados, destruidos y mezclados por ondas de choque.

  17. A filament of energetic particles near the high-latitude dawn magnetopause

    Science.gov (United States)

    Lui, A. T. Y.; Williams, D. J.; Mcentire, R. W.; Christon, S. P.; Jacquey, C.; Angelopoulos, V.; Yamamoto, T.; Kokubun, S.; Frank, L. A.; Ackerson, K. L.

    1994-01-01

    The Geotail satelite detected a filament of tailward-streaming energetic particles spatially separated from the boundary layer of energetic particles at the high-latitude dawn magnetopause at a downstream distance of approximately 80 R(sub E) on October 27, 1992. During this event, the composition and charge states of energetic ions at energies above approximately 10 keV show significant intermix of ions from solar wind and ionospheric sources. Detailed analysis leads to the deduction that the filament was moving southward towards the neutral sheet at an average speed of approximately 80 km/s, implying an average duskward electric field of approximately 1 mV/m. Its north-south dimension was approximately 1 R(sub E) and it was associated with an earthward directed field-aligned current of approximately 5 mA/m. The filament was separated from the energetic particle boundary layer straddling the magnetopause by approximately 0.8 R(sub E) and was inferred to be detached from the boundary layer at downstream distance beyond approximately 70 R(sub E) in the distant tail.

  18. Latitudinal distribution of the solar wind properties in the low- and high-pressure regimes: Wind observations

    Directory of Open Access Journals (Sweden)

    C. Lacombe

    Full Text Available The solar wind properties depend on λ, the heliomagnetic latitude with respect to the heliospheric current sheet (HCS, more than on the heliographic latitude. We analyse the wind properties observed by Wind at 1 AU during about 2.5 solar rotations in 1995, a period close to the last minimum of solar activity. To determine λ, we use a model of the HCS which we fit to the magnetic sector boundary crossings observed by Wind. We find that the solar wind properties mainly depend on the modulus |λ|. But they also depend on a local parameter, the total pressure (magnetic pressure plus electron and proton thermal pressure. Furthermore, whatever the total pressure, we observe that the plasma properties also depend on the time: the latitudinal gradients of the wind speed and of the proton temperature are not the same before and after the closest HCS crossing. This is a consequence of the dynamical stream interactions. In the low pressure wind, at low |λ|, we find a clear maximum of the density, a clear minimum of the wind speed and of the proton temperature, a weak minimum of the average magnetic field strength, a weak maximum of the average thermal pressure, and a weak maximum of the average β factor. This overdense sheet is embedded in a density halo. The latitudinal thickness is about 5° for the overdense sheet, and 20° for the density halo. The HCS is thus wrapped in an overdense sheet surrounded by a halo, even in the non-compressed solar wind. In the high-pressure wind, the plasma properties are less well ordered as functions of the latitude than in the low-pressure wind; the minimum of the average speed is seen before the HCS crossing. The latitudinal thickness of the high-pressure region is about 20°. Our observations are qualitatively consistent with the numerical model of Pizzo for the deformation of the heliospheric current sheet and plasma sheet.

    Key words: Interplanetary physics (solar wind

  19. High-latitude ionospheric outflows characterized through analytic formulas

    Science.gov (United States)

    Zeng, W.; Horwitz, J. L.

    2008-12-01

    Recent advances involving multi-fluid treatments have begun to allow the prospect of global magnetospheric models to simulate the dynamics of multiple ion species, such as various ion species originating from sources in the solar wind and terrestrial ionosphere. Such opportunities for the dynamic treatment of ionospheric ions within the magnetosphere portend a need for realistic accessible methods of estimating ionospheric outflows as linked plasma sources for these global models. Toward this end, in this presentation, the results of numerous physics-based simulations of ionospheric plasma outflows under varied driving agents are distilled in terms of relatively compact analytic expressions. The simulations are conducted with the UT Arlington Dynamic Fluid (DyFK) ionospheric plasma transport code. These analytic expressions for O+ and H+ densities, temperatures and flow velocities are obtained at the 3 RE altitudes corresponding to typical inner boundary levels for certain current global magnetospheric models. These O+ and H+ parameters are expressed as functions of precipitation electron energy flux levels, characteristic energy levels of the precipitating electrons, the peak spectral wave densities for low-frequency electrostatic waves which transversely heat ionospheric ions, and solar zenith angle.

  20. Boundary-Layer Development and Low-level Baroclinicity during High-Latitude Cold-Air Outbreaks: A Simple Model

    Science.gov (United States)

    Chechin, Dmitry G.; Lüpkes, Christof

    2017-01-01

    A new quasi-analytical mixed-layer model is formulated describing the evolution of the convective atmospheric boundary layer (ABL) during cold-air outbreaks (CAO) over polar oceans downstream of the marginal sea-ice zones. The new model is superior to previous ones since it predicts not only temperature and mixed-layer height but also the height-averaged horizontal wind components. Results of the mixed-layer model are compared with dropsonde and aircraft observations carried out during several CAOs over the Fram Strait and also with results of a 3D non-hydrostatic (NH3D) model. It is shown that the mixed-layer model reproduces well the observed ABL height, temperature, low-level baroclinicity and its influence on the ABL wind speed. The mixed-layer model underestimates the observed ABL temperature only by about 10 %, most likely due to the neglect of condensation and subsidence. The comparison of the mixed-layer and NH3D model results shows good agreement with respect to wind speed including the formation of wind-speed maxima close to the ice edge. It is concluded that baroclinicity within the ABL governs the structure of the wind field while the baroclinicity above the ABL is important in reproducing the wind speed. It is shown that the baroclinicity in the ABL is strongest close to the ice edge and slowly decays further downwind. Analytical solutions demonstrate that the e-folding distance of this decay is the same as for the decay of the difference between the surface temperature of open water and of the mixed-layer temperature. This distance characterizing cold-air mass transformation ranges from 450 to 850 km for high-latitude CAOs.

  1. Boundary-Layer Development and Low-level Baroclinicity during High-Latitude Cold-Air Outbreaks: A Simple Model

    Science.gov (United States)

    Chechin, Dmitry G.; Lüpkes, Christof

    2016-08-01

    A new quasi-analytical mixed-layer model is formulated describing the evolution of the convective atmospheric boundary layer (ABL) during cold-air outbreaks (CAO) over polar oceans downstream of the marginal sea-ice zones. The new model is superior to previous ones since it predicts not only temperature and mixed-layer height but also the height-averaged horizontal wind components. Results of the mixed-layer model are compared with dropsonde and aircraft observations carried out during several CAOs over the Fram Strait and also with results of a 3D non-hydrostatic (NH3D) model. It is shown that the mixed-layer model reproduces well the observed ABL height, temperature, low-level baroclinicity and its influence on the ABL wind speed. The mixed-layer model underestimates the observed ABL temperature only by about 10 %, most likely due to the neglect of condensation and subsidence. The comparison of the mixed-layer and NH3D model results shows good agreement with respect to wind speed including the formation of wind-speed maxima close to the ice edge. It is concluded that baroclinicity within the ABL governs the structure of the wind field while the baroclinicity above the ABL is important in reproducing the wind speed. It is shown that the baroclinicity in the ABL is strongest close to the ice edge and slowly decays further downwind. Analytical solutions demonstrate that the e -folding distance of this decay is the same as for the decay of the difference between the surface temperature of open water and of the mixed-layer temperature. This distance characterizing cold-air mass transformation ranges from 450 to 850 km for high-latitude CAOs.

  2. High Voltage Power Transmission for Wind Energy

    Science.gov (United States)

    Kim, Young il

    The high wind speeds and wide available area at sea have recently increased the interests on offshore wind farms in the U.S.A. As offshore wind farms become larger and are placed further from the shore, the power transmission to the onshore grid becomes a key feature. Power transmission of the offshore wind farm, in which good wind conditions and a larger installation area than an onshore site are available, requires the use of submarine cable systems. Therefore, an underground power cable system requires unique design and installation challenges not found in the overhead power cable environment. This paper presents analysis about the benefit and drawbacks of three different transmission solutions: HVAC, LCC/VSC HVDC in the grid connecting offshore wind farms and also analyzed the electrical characteristics of underground cables. In particular, loss of HV (High Voltage) subsea power of the transmission cables was evaluated by the Brakelmann's theory, taking into account the distributions of current and temperature.

  3. Morphological features of Triassic and Late Cretaceous high-latitude radiolarian assemblages (comparative analysis)

    Science.gov (United States)

    Bragin, Nikita; Bragina, Liubov

    2010-05-01

    High-latitude radiolarian assemblages of Mesozoic represent particular interest for Boreal-Tethyan correlation of Mesozoic as well as for their paleobiogeography. Radiolarians are the only planktonic protists that present both in low- and high-latitude Mesozoic sections, therefore they have high importance. The aim of this work is to distinguish common and different features of Triassic and Late Cretaceous high-latitude assemblages of Radiolaria during their comparative analysis. We use material from Triassic of Omolon Massif (NE Siberia) (Bragin, Egorov, 2001) and Kotel'nyi Island (Arctic) (Bragin, Bragina, 2009; Bragin, in press) and Late Cretaceous of Western Siberia (Amon, 2000) and Kamchatka Peninsula (Vishnevskaya, 2005; Bragina, 1991). The main trends of radiolarian assemblages from these sections are: quantitative domination of some taxa, presence of characteristic high-latitude taxa that are absent or very rare in low-latitude regions, and relatively low taxonomic diversity with absence of many high taxa and many morphotypes. We made following conclusions after comparative analysis: 1. Triassic assemblages are dominated by morphotypes with bipolar main spines (Pseudostylosphaera and similar forms), and by pylomate forms (Glomeropyle). Genus Glomeropyle has bipolar distribution pattern and it is typically high-latitude taxon. Late Cretaceous assemblages are dominated by forms with bipolar three-bladed main spines (Amphisphaera, Protoxiphotractus, Stylosphaera), by prunoid morphotypes (Amphibrachium, Prunobrachium), discoid spongy forms (Orbiculiforma, Spongodiscus) by three-rayed (Paronaella, Spongotripus), four-rayed (Crucella, Histiastrum) and multirayed stauraxon forms (Pentinastrum, Multastrum). Pylomate forms (Spongopyle) are present in the Late Cretaceous high-latitude assemblages but not so common. 2. Spherical forms with spines that possess apophyses (Kahlerosphaera, Dumitricasphaera) are common for Triassic high-latitude areas, but not present in

  4. Artificial periodic irregularities in the high-latitude ionosphere excited by the HAARP facility

    Science.gov (United States)

    Bakhmetieva, N. V.; Grach, S. M.; Sergeev, E. N.; Shindin, A. V.; Milikh, G. M.; Siefring, C. L.; Bernhardt, P. A.; McCarrick, M.

    2016-07-01

    We present results of the new observations of artificial periodic irregularities (APIs) in the ionosphere using the High Frequency Active Auroral Research Program (HAARP) heating facility carried out in late May and early June 2014.The objective of this work is to detect API using high-latitude facility and analyze possible differences of the temporal and spatial variations of the API echoes in the high (HAARP) and middle (Sura) latitudes. Irregularities were created by the powerful wave of X mode and were sounded using the short probing pulses signals of X mode. API echoes were observed in the D, E, and F regions of the ionosphere. Amplitudes and characteristic times of the API echoes were measured. The API growth and decay times at HAARP (high latitudes) observed were similar to those at the Sura heating facility (midlatitudes).

  5. High-Latitude Molecular Clouds as (Gamma)-ray Sources for GLAST

    Energy Technology Data Exchange (ETDEWEB)

    Torres, D F; Dame, T M; Digel, S W

    2005-01-05

    For about two decades, a population of relative small and nearby molecular clouds has been known to exist at high Galactic latitudes. Lying more than 10{sup o} from the Galactic plane, these clouds have typical distances of {approx}150 pc, angular sizes of {approx}1{sup o}, and masses of order tens of solar masses. These objects are passive sources of high-energy {gamma}-rays through cosmic ray-gas interactions. Using a new wide-angle CO survey of the northern sky, we show that typical high-latitude clouds are not bright enough in {gamma}-rays to have been detected by EGRET, but that of order 100 of them will be detectable by the Large Area Telescope (LAT) on GLAST. Thus, we predict a new steady population of {gamma}-ray sources at high Galactic latitudes, perhaps the most numerous after active galactic nuclei.

  6. GPS phase scintillation at high latitudes during the geomagnetic storm of 17-18 March 2015

    Science.gov (United States)

    Prikryl, P.; Ghoddousi-Fard, R.; Weygand, J. M.; Viljanen, A.; Connors, M.; Danskin, D. W.; Jayachandran, P. T.; Jacobsen, K. S.; Andalsvik, Y. L.; Thomas, E. G.; Ruohoniemi, J. M.; Durgonics, T.; Oksavik, K.; Zhang, Y.; Spanswick, E.; Aquino, M.; Sreeja, V.

    2016-10-01

    The geomagnetic storm of 17-18 March 2015 was caused by the impacts of a coronal mass ejection and a high-speed plasma stream from a coronal hole. The high-latitude ionosphere dynamics is studied using arrays of ground-based instruments including GPS receivers, HF radars, ionosondes, riometers, and magnetometers. The phase scintillation index is computed for signals sampled at a rate of up to 100 Hz by specialized GPS scintillation receivers supplemented by the phase scintillation proxy index obtained from geodetic-quality GPS data sampled at 1 Hz. In the context of solar wind coupling to the magnetosphere-ionosphere system, it is shown that GPS phase scintillation is primarily enhanced in the cusp, the tongue of ionization that is broken into patches drawn into the polar cap from the dayside storm-enhanced plasma density, and in the auroral oval. In this paper we examine the relation between the scintillation and auroral electrojet currents observed by arrays of ground-based magnetometers as well as energetic particle precipitation observed by the DMSP satellites. Equivalent ionospheric currents are obtained from ground magnetometer data using the spherical elementary currents systems technique that has been applied over the ground magnetometer networks in North America and North Europe. The GPS phase scintillation is mapped to the poleward side of strong westward electrojet and to the edge of the eastward electrojet region. Also, the scintillation was generally collocated with fluxes of energetic electron precipitation observed by DMSP satellites with the exception of a period of pulsating aurora when only very weak currents were observed.

  7. Climatology of rapid geomagnetic variations at high latitudes over two solar cycles

    Directory of Open Access Journals (Sweden)

    A. Viljanen

    2011-10-01

    Full Text Available We investigate the characteristics of rapid geomagnetic variations at high latitudes based on the occurrence of large time derivatives of the horizontal magnetic field (dH/dt exceeding 1 nT s−1. Analysis of IMAGE magnetometer data from North Europe in 1983–2010, covering more than two solar cycles, confirms and specifies several previous findings. We show that dH/dt activity is high around the midnight and early morning hours, and nearly vanishes at noon and early afternoon. This happens during all seasons, although the midnight maximum is nearly invisible during summer. As indicated by modelled ionospheric equivalent currents, large dH/dt values occur predominantly during westward ionospheric electrojets. Before and around midnight, dH/dt tends to be north-south oriented, whereas in the morning hours, its direction is more west-east directed. dH/dt tends to be more strictly north-south oriented during winter than other seasons. The seasonal occurrence of large dH/dt values is similar to the variation of the maximum amplitude of westward equivalent currents. The yearly fraction of east-west directed large dH/dt vectors at the Kilpisjärvi station (MLAT 65.88 varies from 31 to 47 % without any clear correlation with the general geomagnetic activity nor with the yearly averages of solar wind parameters.

  8. Interhemispheric differences and solar cycle effects of the high-latitude ionospheric convection patterns deduced from Cluster EDI observations

    Science.gov (United States)

    Förster, Matthias; Haaland, Stein

    2015-04-01

    Here, we present a study of ionospheric convection at high latitudes that is based on satellite measurements of the Electron Drift Instrument (EDI) on-board the Cluster satellites, which were obtained over a full solar cycle (2001-2013). The mapped drift measurements are covering both hemispheres and a variety of different solar wind and interplanetary magnetic field (IMF) conditions. The large amount of data allows us to perform more detailed statistical studies. We show that flow patterns and polar cap potentials can differ between the two hemispheres on statistical average for a given IMF orientation. In particular, during southward directed IMF conditions, and thus enhanced energy input from the solar wind, we find that the southern polar cap has a higher cross polar cap potential. We also find persistent north-south asymmetries which cannot be explained by external drivers alone. Much of these asymmetries can probably be explained by significant differences in the strength and configuration of the geomagnetic field between the Northern and Southern Hemisphere. Since the ionosphere is magnetically connected to the magnetosphere, this difference will also be reflected in the magnetosphere in the form of different feedback from the two hemispheres. Consequently, local ionospheric conditions and the geomagnetic field configuration are important for north-south asymmetries in large regions of geospace. The average convection is higher during periods with high solar activity. Although local ionospheric conditions may play a role, we mainly attribute this to higher geomagnetic activity due to enhanced solar wind - magnetosphere interactions.

  9. Low- and Mid-High Latitude Components of the East Asian Winter Monsoon and Their Reflecting Variations in Winter Climate over Eastern China

    Institute of Scientific and Technical Information of China (English)

    LIU Ge; JI Li-Ren; SUN Shu-Qing; XIN Yu-Fei

    2012-01-01

    The present study defines a low-latitude component (regionally averaged winter 1000-hPa V-winds over 10 25°N, 105 135°E) and a mid-high-latitude component (regionally averaged winter 1000-hPa V-winds over 30 50°N, 110 125°E) of the East Asian winter monsoon (EAWM), which are denoted as EAWM-L and EAWM-M, respectively. The study examines the variation characteristics, reflecting variations in winter climate over eastern China, and associated atmospheric circulations corresponding to the two components. The main results are as follows: 1) the EAWM-L and EAWM-M have consistent variation in some years but opposite variations in other years; 2) the EAWM-M index mainly reflects the extensive temperature variability over eastern China, while the EAWM-L index better reflects the variation in winter precipitation over most parts of eastern China; and 3) corresponding to the variation in the EAWM-M index, anomalous winds over the mid-high latitudes of East Asia modulate the southward invasion of cold air from the high latitudes and accordingly affect temperatures over eastern China. In combination with the variation in the EAWM-L index, anomalous low-latitudinal winds regulate the water vapor transport from tropical oceans to eastern China, resulting in anomalous winter precipitation. These pronounced differences between the EAWM-L and the EAWM-M suggest that it is necessary to explore the monsoons' individual features and effects in the EAWM study.

  10. Alternative Coordinate Systems for High Latitude Ionospheric Plasma Studies.

    Science.gov (United States)

    2014-09-26

    only a small fraction of this energy flux is directly coupled into the magnetosphere system. However, it has been suggested that a high altitude...upon numerical error arising frori off-center differencing . To complete the mesh in three dimensions, the contours of of Figure 2 must he rotated

  11. Green house gas flux at high latitudes - constraints and susceptibility to a changing climate

    Science.gov (United States)

    Nilsson, M. B.

    2015-12-01

    High latitude boreal forests and peatlands contribute importantly to the land-atmosphere exchange of both carbon dioxide and methane. High latitude biomes are also identified as most vulnerable to changing climate. High latitudes are characterized by a strong seasonality in incoming solar radiation, weather conditions and biogeochemical processes. The strong seasonality in incoming solar radiation, not to change in response to a changing climate, constitute firm constraints on how changes in air temperature, evapotranspiration and precipitation will affect biogeochemical processes underlying the land atmosphere exchange of green house gases. Timing of the soil frost thaw and plant phenology thus constitutes two master controls on how fluxes of both CO2 and CH4 will be affected by weather conditions. In addition also the wintertime conditions importantly affect GHG fluxes both during winter time as well as during the succeeding summer. Examples will primarily be given for peatlands and coniferous forests.

  12. High-latitude ocean ventilation and its role in Earth's climate transitions.

    Science.gov (United States)

    Naveira Garabato, Alberto C; MacGilchrist, Graeme A; Brown, Peter J; Evans, D Gwyn; Meijers, Andrew J S; Zika, Jan D

    2017-09-13

    The processes regulating ocean ventilation at high latitudes are re-examined based on a range of observations spanning all scales of ocean circulation, from the centimetre scales of turbulence to the basin scales of gyres. It is argued that high-latitude ocean ventilation is controlled by mechanisms that differ in fundamental ways from those that set the overturning circulation. This is contrary to the assumption of broad equivalence between the two that is commonly adopted in interpreting the role of the high-latitude oceans in Earth's climate transitions. Illustrations of how recognizing this distinction may change our view of the ocean's role in the climate system are offered.This article is part of the themed issue 'Ocean ventilation and deoxygenation in a warming world'. © 2017 The Authors.

  13. Climatology of GNSS ionospheric scintillation at high latitudes

    OpenAIRE

    Spogli, Luca; Alfonsi, Lucilla; De Franceschi, Giorgiana; Romano, Vincenzo; Aquino, Marcio H. O.; Dodson, Alan

    2010-01-01

    The ionosphere is characterized by a highly variable degree of ionization maintained by a wide range of solar radiation and by electrons and protons originating from Sun. This plasma is under the permanent solar forcing, and interacts with the geomagnetic and interplanetary magnetic fields. The ionosphere shows diurnal and seasonal variations, together with a 11-year period variability related to the solar cycle. Sporadic events due to the intermittent behaviour of the Sun are superimposed to...

  14. Quantifying the Impact of Icelandic Dust Storms on High-Latitude Aerosol

    Science.gov (United States)

    Browse, Jo; Dorsi, Kelly; Dagsson Waldhauserova, Pavla; Murray, Ben

    2017-04-01

    Using a combination of observations, meteorological climatologies and modelling we have developed an Icelandic dust storm emission inventory. Here we present results from a global modelling study quantifying the contribution of Icelandic dust to high-latitude: ice nucleating particles (INP), cloud condensation nuclei (CCN) and PM2.5. Our results suggest that Icelandic dust cannot explain the formation and persistence of summertime mixed-phase Arctic marine clouds, as summertime marine clouds are too warm for Icelandic dust to serve as INP. However, in colder regions (such as Greenland) Icelandic dust may sporadically contribute to INP. The contribution of Icelandic dust to high-latitude CCN was shown to be complex. Indeed, our results indicate a decrease in high-latitude CCN in the aftermath of Icelandic dust storms. This decrease is due to the short-term increase of the Arctic atmospheric condensation sink and the resulting suppression of nucleation processes (a significant source of Arctic summertime CCN). Finally, Icelandic dust storms are shown to significantly contribute to high-latitude summertime PM2.5 (and PM10) both during (˜100 {μ}gm-3) and in the aftermath (˜10 {μ}gm-3) of dust events. Our results suggest that Icelandic dust storms (neglected in most global climate models) may in the short term increase aerosol optical depth (strongly correlated to PM2.5) at high latitudes. Additionally, Icelandic dust storms are likely to contribute to poor air quality as well as reduced visibility in the Arctic boundary layer. Thus, we argue for the adoption of high-latitude dust emissions in climate and NWP models.

  15. AO/NAO Response to Climate Change. 2; Relative Importance of Low- and High-Latitude Temperature Changes

    Science.gov (United States)

    Rind, D.; Perlwitz, J.; Lonergan, P.; Lerner, J.

    2005-01-01

    Using a variety of GCM experiments with various versions of the GISS model, we investigate how different aspects of tropospheric climate changes affect the extratropical Arctic Oscillation (AO)/North Atlantic Oscillation (NAO) circulation indices. The results show that low altitude changes in the extratropical latitudinal temperature gradient can have a strong impact on eddy forcing of the extratropical zonal wind, in the sense that when this latitudinal temperature gradient increases, it helps force a more negative AO/NAO phase. In addition, local conditions at high latitudes can stabilize/destabilize the atmosphere, inducing negative/positive phase changes. To the extent that there is not a large temperature change in the tropical upper troposphere (either through reduced tropical sensitivity at the surface, or limited transport of this change to high levels), the changes in the low level temperature gradient can provide the dominate influence on the extratropical circulation, so that planetary wave meridional refraction and eddy angular momentum transport changes become uncorrelated with potential vorticity transports. In particular, the climate change that produces the most positive NAO phase change would have substantial warming in the tropical upper troposphere over the Pacific Ocean, with high latitude warming in the North Atlantic. An increase in positive phase of these circulation indices is still more likely than not, but it will depend on the degree of tropical and high latitude temperature response and the transport of low level warming into the upper troposphere. These are aspects that currently differ among the models used for predicting the effects of global warning, contributing to the lack of consensus of future changes in the AO/NAO.

  16. GPS phase scintillation at high latitudes during the geomagnetic storm of 17-18 March 2015

    DEFF Research Database (Denmark)

    Prikryl, P.; Ghoddousi-Fard, R.; Weygand, J. M.

    2016-01-01

    The geomagnetic storm of 17–18 March 2015 was caused by the impacts of a coronal mass ejection and a high-speed plasma stream from a coronal hole. The high-latitude ionosphere dynamics is studied using arrays of ground-based instruments including GPS receivers, HF radars, ionosondes, riometers...

  17. Abrupt climate change and high to low latitude teleconnections as simulated in climate models

    DEFF Research Database (Denmark)

    Cvijanovic, Ivana

    of the present day atmospheric mid-latitude energy transport compared to that of the Last Glacial Maximum, suggesting its ability to reorganize more easily and thereby dampen high latitude temperature anomalies that could arise from changes in the oceanic transport. The role of tropical SSTs in the tropical...... precipitation shifts was further re-examined in idealized simulations with the fixed tropical sea surface temperatures, showing that the SST changes are fundamental to the tropical precipitation shifts. Regarding the high latitude energy loss, it was shown that the main energy compensation comes from...... the southern tropics, with the energy gain originating from the cloud radiative feedbacks, temperature and longwave water vapor feedbacks. Extended consideration of the various scenarios that can induce the southward precipitation shifts showed that the Southern Hemisphere warming simulations, in addition...

  18. Propagation of short-period gravity waves at high-latitudes during the MaCWAVE winter campaign

    Directory of Open Access Journals (Sweden)

    K. Nielsen

    2006-07-01

    Full Text Available As part of the MaCWAVE (Mountain and Convective Waves Ascending Vertically winter campaign an all-sky monochromatic CCD imager has been used to investigate the properties of short-period mesospheric gravity waves at high northern latitudes. Sequential measurements of several nightglow emissions were made from Esrange, Sweden, during a limited period from 27–31 January 2003. Coincident wind measurements over the altitude range (~80–100 km using two meteor radar systems located at Esrange and Andenes have been used to perform a novel investigation of the intrinsic properties of five distinct wave events observed during this period. Additional lidar and MSIS model temperature data have been used to investigate their nature (i.e. freely propagating or ducted. Four of these extensive wave events were found to be freely propagating with potential source regions to the north of Scandinavia. No evidence was found for strong orographic forcing by short-period waves in the airglow emission layers. The fifth event was most unusual exhibiting an extensive, but much smaller and variable wavelength pattern that appeared to be embedded in the background wind field. Coincident wind measurements indicated the presence of a strong shear suggesting this event was probably due to a large-scale Kelvin-Helmholtz instability.

  19. BVOC ecosystem flux measurements at a high latitude wetland site

    Directory of Open Access Journals (Sweden)

    T. Holst

    2010-02-01

    Full Text Available In this study, we present summertime concentrations and fluxes of biogenic volatile organic compounds (BVOCs measured at a sub-arctic wetland in northern Sweden using a disjunct eddy-covariance (DEC technique based on a proton transfer reaction mass spectrometer (PTR-MS. The vegetation at the site was dominated by Sphagnum, Carex and extit{Eriophorum} spp. The measurements reported here cover a period of 50 days (1 August to 19 September 2006, approximately one half of the growing season at the site, and allowed to investigate the effect of day-to-day variation in weather as well as of vegetation senescence on daily BVOC fluxes, and on their temperature and light responses. The sensitivity drift of the DEC system was assessed by comparing H3O+-ion cluster formed with water molecules (H3O+(H2O at m37 with water vapour concentration measurements made using an adjacent humidity sensor, and the applicability of the DEC method was analysed by a comparison of sensible heat fluxes for high frequency and DEC data obtained from the sonic anemometer. These analyses showed no significant PTR-MS sensor drift over a period of several weeks and only a small flux-loss due to high-frequency spectrum omissions. This loss was within the range expected from other studies and the theoretical considerations.

    Standardised (20 °C and 1000 μmol m−2 s−1 PAR summer isoprene emission rates found in this study of 329 μg C m−2 (ground area h−1 were comparable with findings from more southern boreal forests, and fen-like ecosystems. On a diel scale, measured fluxes indicated a stronger temperature dependence than emissions from temperate or (subtropical ecosystems. For the first time, to our knowledge, we report ecosystem methanol fluxes from a sub-arctic ecosystem. Maximum daytime emission fluxes were around 270 μg m−2 h−1

  20. BVOC ecosystem flux measurements at a high latitude wetland site

    Directory of Open Access Journals (Sweden)

    T. Holst

    2008-12-01

    Full Text Available In this study, we present summertime concentrations and fluxes of biogenic volatile organic compounds (BVOCs measured at a sub-arctic wetland in northern Sweden using a disjunct eddy-covariance (DEC technique based on a proton transfer reaction mass spectrometer (PTR-MS. The vegetation at the site was dominated by Sphagnum, Carex and Eriophorum spp. The performance of the DEC system was assessed by comparing H3O+-ion cluster formed with water molecules (H3O+(H2O at m37 with water vapour concentration measurements made using an adjacent humidity sensor, and from a comparison of sensible heat fluxes for high frequency and DEC data obtained from the sonic anemometer. These analyses showed no significant PTR-MS sensor drift over a period of several weeks and only a small flux-loss due to high-frequency spectrum omissions. This loss was within the range expected from other studies and the theoretical considerations.

    Standardised (20°C and 1000 μmol m−2 s−1 PAR summer isoprene emission rates of 323 μg C m−2 (ground area h−1 were comparable with findings from more southern boreal forests, and fen-like ecosystems. On a diel scale, measured fluxes indicated a stronger temperature dependence when compared with emissions from temperate or (subtropical ecosystems. For the first time, to our knowledge, we report ecosystem methanol fluxes from a sub-arctic ecosystem. Maximum daytime emission fluxes were around 270 μg m−2 h−1 (ca. 100 μg C m−2 h-1 and measurements indicated some nocturnal deposition.

    The measurements reported here covered a period of 50 days (1 August to 19 September 2006, approximately one half of the growing season at the site, and allowed to investigate the effect of vegetation senescence on daily BVOC fluxes and on their temperature and light

  1. Projecting crop yield in northern high latitude area.

    Science.gov (United States)

    Matsumura, Kanichiro

    2014-01-01

    Changing climatic conditions on seasonal and longer time scales influence agricultural production. Improvement of soil and fertilizer is a strong factor in agricultural production, but agricultural production is influenced by climate conditions even in highly developed countries. It is valuable if fewer predictors make it possible to conduct future projections. Monthly temperature and precipitation, wintertime 500hPa geopotential height, and the previous year's yield are used as predictors to forecast spring wheat yield in advance. Canadian small agricultural divisions (SAD) are used for analysis. Each SAD is composed of a collection of Canadian Agricultural Regions (CAR) of similar weather and growing conditions. Spring wheat yields in each CAR are forecast from the following variables: (a) the previous year's yield, (b) earlier stages of the growing season's climate conditions and, (c) the previous year's wintertime northern hemisphere 500hPa geopotential height field. Arctic outflow events in the Okanagan Valley in Canada are associated with episodes of extremely low temperatures during wintertime. Principal component analysis (PCA) is applied for wintertime northern hemisphere 500hPa geopotential height anomalies. The spatial PCA mode1 is defined as Arctic Oscillation and it influences prevailing westerlies. The prevailing westerlies meanders and influences climatic conditions. The spatial similarity between wintertime top 5 Arctic outflow event year's composites of 500hPa geopotential height anomalies and mode 3's spatial pattern is found. Mode 3's spatial pattern looks like the Pacific/North American (PNA) pattern which describes the variation of atmospheric circulation pattern over the Pacific Ocean and North America. Climate conditions from April to June, May to July, mode 3's time coefficients, and previous year's yield are used for forecasting spring wheat yield in each SAD. Cross-validation procedure which generates eight sets of models for the eight

  2. High-latitude ionospheric response to a sudden impulse event during northward IMF conditions

    DEFF Research Database (Denmark)

    Moretto, T.; Ridley, A.J.; Engebretson, M.J.

    2000-01-01

    A high-density structure under northward interplanetary magnetic field B-z conditions is identified at the Wind and IMP 8 satellites, both in the solar wind on August 22, 1995. A compression of the magnetosphere is observed by the GOES 7 magnetometer within a few minutes of the pressure increase ...

  3. The effects of coronal mass ejection on galactic cosmic rays in the high latitude heliosphere: Observations from Ulysses` first orbit

    Energy Technology Data Exchange (ETDEWEB)

    Bothmer, V.; Heber, B.; Kunow, H.; Mueller-Mellin, R.; Wibberenz, G. [Univ. of Kiel (Germany). Institut fuer Kernphysik; Gosling, J.T. [Los Alamos National Lab., NM (United States); Balogh, A. [Imperial College, London (United Kingdom). Blackett Lab.; Raviart, A. [CEA, Gif-sur-Yvette (France). Service d`Astrophysique; Paizis, C. [Univ. di Milano (Italy). Istituto di Fisica Cosmica CNR

    1997-10-01

    During its first solar orbit the Ulysses spacecraft detected several coronal mass ejections (CMEs) at high heliographic latitudes. The authors present first observations on the effects of these high latitude CMEs on galactic cosmic rays (GCRs) using measurements from the Kiel Electron Telescope (KET) which is part of the Cosmic Ray and Solar Particle Investigation (COSPIN) experiment, the Los Alamos SWOOPS (Solar Wind Observations Over the Poles of the Sun) experiment and the magnetic field experiments. They find the passage of these CMEs over the spacecraft to be associated with short term decreases of GCR intensities The relatively weak shocks in these events, driven by the CMEs` over-expansion, had no strong influence on the GCRs. The intensity minimums of GCRs occurred on closed magnetic field lines inside the CMEs themselves as indicated by bidirectional fluxes of suprathermal electrons. Short episodes of intensity increases of GCRs inside CMEs at times when the bidirectional fluxes of suprathermal electrons disappeared, can be interpreted as evidence that GCRs can easily access the interior of those CMEs in which open magnetic field lines are embedded.

  4. High-Resolution Wind Measurements for Offshore Wind Energy Development

    Science.gov (United States)

    Nghiem, Son V.; Neumann, Gregory

    2011-01-01

    A mathematical transform, called the Rosette Transform, together with a new method, called the Dense Sampling Method, have been developed. The Rosette Transform is invented to apply to both the mean part and the fluctuating part of a targeted radar signature using the Dense Sampling Method to construct the data in a high-resolution grid at 1-km posting for wind measurements over water surfaces such as oceans or lakes.

  5. Improved monitoring of vegetation dynamics at very high latitudes: a new method using MODIS NDVI

    NARCIS (Netherlands)

    Beck, P.S.A.; Atzberger, C.; Hogda, K.A.; Johansen, B.; Skidmore, A.K.

    2006-01-01

    Current models of vegetation dynamics using the normalized vegetation index (NDVI) time series perform poorly for high-latitude environments. This is due partly to specific attributes of these environments, such as short growing season, long periods of darkness in winter, persistence of snow cover,

  6. A FUSE Survey of Interstellar Molecular Hydrogen toward High-Latitude AGN

    CERN Document Server

    Gillmon, K; Tumlinson, J; Danforth, C; Gillmon, Kristen; Tumlinson, Jason; Danforth, Charles

    2006-01-01

    We report results from a FUSE survey of interstellar molecular hydrogen (H2) along 45 sight lines to AGN at high Galactic latitudes (|b| > 20 degrees). Most (39 of 45) of the sight lines show detectable Galactic H2 absorption from Lyman and Werner bands between 1000 and 1126 A, with column densities ranging from N(H2) = 10^(14.17-19.82) cm^-2. In the northern Galactic hemisphere, we identify many regions of low column, N(H2) 54 degrees. These `"H2 holes" provide valuable, uncontaminated sight lines for extragalactic UV spectroscopy, and a few may be related to the "Northern Chimney" (low Na I absorption) and "Lockman Hole" with low N(HI). A comparison of high-latitude H2 with 139 OB-star sight lines surveyed in the Galactic disk suggests that high-latitude and disk H2 clouds may have different rates of heating, cooling, and UV excitation. For rotational states J = 0 and 1, the mean excitation temperature at high latitude, = 124 +/- 8 K, is somewhat above that in the Galactic disk, = 86 +/- 20 K. For J = 2-...

  7. Detection of CH and CH+ in a high latitude molecular cloud

    NARCIS (Netherlands)

    Vries, de C.P.; Dishoeck, van E.F.

    1988-01-01

    Interstellar absorption lines of CH and CH(+) have been detected toward the star HD 210121, which is located behind a previously unknown high-latitude cloud. The CH observations and the measured extinction toward the star provide independent measures of the H2 column density along the line of sight,

  8. High-latitude forcing of diatom productivity in the southern Agulhas Plateauduring the past 350kyr

    NARCIS (Netherlands)

    Romero, O.E.; Kim, J.-H.; Bárcena, M.A.; Hall, I.R.; Zahn, R.; Schneider, R.

    2015-01-01

    The hydrography of the Indian-Atlantic Ocean gateway has been connected to high-latitude climate dynamics by oceanic and atmospheric teleconnections on orbital and suborbital timescales. A wealth of sedimentary records aiming at reconstructing the late Pleistocene paleoceanography around the souther

  9. Morphology and phenomenology of the high-latitude E and F regions

    Science.gov (United States)

    Hunsucker, R. D.

    1979-01-01

    Results obtained at high latitude observatories on the behavior of E and F region ionization are presented including a bibliography. Behavior of E and F region ionization during day and night for quiet and disturbed conditions in the auroral and polar regions is described. Daily, seasonal and sunspot variations are also outlined.

  10. Analysis of High-Latitude lonospheric Processes During HSS and CME-Induced Geomagnetic Storms

    DEFF Research Database (Denmark)

    Durgonics, Tibor; Komjathy, Attila; Verkhoglyadova, Olga

    For the first time we compared ionospheric effects of HSS and CME-driven storms at high-latitudes. There were similarities and also differences observed in the development of the storms. (1) Both type of storms exhibited clear negative phase, which resulted in an increase of TOI-breaking-down int...

  11. Oceanic mesoscale turbulence drives large biogeochemical interannual variability at middle and high latitudes

    Digital Repository Service at National Institute of Oceanography (India)

    Levy, M.; Resplandy, L.; Lengaigne, M.

    at middle and high latitudes. We used a 1/54◦idealized biogeochemical model with a seasonally repeating atmospheric forcing such that there was no external source of interannual variability. At the scale of moorings, our experiment suggested that internal...

  12. High-latitude oceanic variability associated with the 18.6-year nodal tide

    Science.gov (United States)

    Royer, Thomas C.

    1993-03-01

    Ocean temperatures in the upper 250 m in the northern North Pacific (60°N, 149°W) increased by more than 1°C from 1972 to 1986 but are now decreasing. Subsurface temperature anomalies are well correlated (˜0.58) with the air temperature anomalies at Sitka, Alaska; hence the coastal air temperatures can be used as a proxy data set to extend the ocean temperature time series back to 1828. Up to 30% of the low-frequency variance can be accounted for with the 18.6-year nodal signal. Additionally, spectral analysis of these air temperature variations indicates a significant low-frequency peak in the range of the 18.6-year signal. Similar low-frequency signals have been reported for Hudson Bay air temperatures since 1700, for sea surface temperatures in the North Atlantic from 1876 to 1939, and for sea level in the high-latitude southern hemisphere. The water column temperature variations presented here are the first evidence that the upper ocean is responding to this very long period tidal forcing. An enhanced high-latitude response to the 18.6-year forcing is predicted by equilibrium tide theory, and it should be most evident at latitudes poleward of about 50°. These low-frequency ocean-atmosphere variations must be considered in high-latitude assessments of global climate change, since they are of the same magnitude as many of the predicted global changes.

  13. Climate Effects on High Latitude Daphnia via Food Quality and Thresholds

    Science.gov (United States)

    Przytulska, Anna; Bartosiewicz, Maciej; Rautio, Milla; Dufresne, France; Vincent, Warwick F.

    2015-01-01

    Climate change is proceeding rapidly at high northern latitudes and may have a variety of direct and indirect effects on aquatic food webs. One predicted effect is the potential shift in phytoplankton community structure towards increased cyanobacterial abundance. Given that cyanobacteria are known to be a nutritionally poor food source, we hypothesized that such a shift would reduce the efficiency of feeding and growth of northern zooplankton. To test this hypothesis, we first isolated a clone of Daphnia pulex from a permafrost thaw pond in subarctic Québec, and confirmed that it was triploid but otherwise genetically similar to a diploid, reference clone of the same species isolated from a freshwater pond in southern Québec. We used a controlled flow-through system to investigate the direct effect of temperature and indirect effect of subarctic picocyanobacteria (Synechococcus) on threshold food concentrations and growth rate of the high latitude clone. We also compared the direct effect of temperature on both Daphnia clones feeding on eukaryotic picoplankton (Nannochloropsis). The high latitude clone had a significantly lower food threshold for growth than the temperate clone at both 18 and 26°C, implying adaptation to lower food availability even under warmer conditions. Polyunsaturated fatty acids were present in the picoeukaryote but not the cyanobacterium, confirming the large difference in food quality. The food threshold for growth of the high latitude Daphnia was 3.7 (18°C) to 4.2 (26°C) times higher when fed Synechococcus versus Nannochloropsis, and there was also a significant negative effect of increased temperature and cyanobacterial food on zooplankton fatty acid content and composition. The combined effect of temperature and food quality on the performance of the high latitude Daphnia was greater than their effects added separately, further indicating the potentially strong indirect effects of climate warming on aquatic food web processes. PMID

  14. The Sensitivity of Model Ozone to Advective and Photochemical Processes in the High Latitude Winter Lower Stratosphere

    Science.gov (United States)

    Douglass, A.; Kawa, S. R.; Einaudi, Franco (Technical Monitor)

    2000-01-01

    Three dimensional chemistry and transport models (CTMs) contain a set of coupled continuity equations which describe the evolution of constituents such as ozone and other minor species which affect ozone. Both advection and photochemical processes contribute to constituent evolution, and a CTM provides a means to evaluate these contributions separately. Such evaluation is particularly useful when both terms are important to the modeled tendency. An example is the ozone tendency in the high latitude winter lower stratosphere, where advection tends to increase ozone, and catalytic processes involving chlorine radicals tend to decrease ozone. The Goddard three dimensional chemistry and transport model uses meteorological fields from the Goddard Earth Observing System Data Assimilation System, thus the modeled ozone evolution may reproduce the observed evolution and provide a test of the model representation of photochemical processes if the transport is shown to be modeled appropriately. We have investigated the model advection further using diabatic trajectory calculations. For long lived constituents such as N2O, the model field for a particular time on a potential temperature surface is compared with a field produced by calculating 15 day back trajectories for a fixed latitude longitude grid, and mapping model N2O at the terminus of the back trajectories onto the initial grid. This provides a quantitative means to evaluate two aspects of the CTM transport: one, the model horizontal gradient between middle latitudes and the polar vortex is compared with the gradient produced using the non-diffusive trajectory calculation; two, the model vertical advection, which is produced by the divergence of the horizontal winds, is compared with the vertical transport expected from diabatic cooling.

  15. Geologic isolation of nuclear waste at high latitudes: the role of ice sheets

    Science.gov (United States)

    Person, M.; McIntosh, J.; Iverson, N.; Neuzil, C.E.; Bense, V.

    2012-01-01

    Geologic isolation of high-level nuclear waste from the biosphere requires special consideration in countries at high latitudes (>40°N) owing to the possibility of future episodes of continental glaciation (Talbot 1999). It is now widely recognized that Pleistocene continental glaciations have had a profound effect on rates of sediment erosion (Cuffey & Paterson 2010) and deformation including tectonic thrusting (Pedersen 2005) as well as groundwater flow (Person et al. 2007; Lemieux et al. 2008a,b,c). In addition, glacial mechanical loads may have generated anomalous, or fossil, pore pressures within certain clay-rich confining units (e.g. Vinard et al. 2001). Because high-level nuclear wastes must be isolated from the biosphere as long as 1 million years (McMurry et al. 2003), the likelihood of one or more continental ice sheets overrunning high-latitude sites must be considered.

  16. Role of neutral wind and storm time electric fields inferred from the storm time ionization distribution at low latitudes: in-situ measurements by Indian satellite SROSS-C2

    Directory of Open Access Journals (Sweden)

    P. Subrahmanyam

    2005-11-01

    Full Text Available Recently, there has been a renewal of interest in the study of the effects of solar weather events on the ionization redistribution and irregularity generation. The observed changes at low and equatorial latitudes are rather complex and are noted to be a function of location, the time of the storm onset and its intensity, and various other characteristics of the geomagnetic storms triggered by solar weather events. At these latitudes, the effects of geomagnetic storms are basically due to (a direct penetration of the magnetospheric electric fields to low latitudes, (b development of disturbance dynamo, (c changes in atmospheric neutral winds at ionospheric level and (d changes in neutral composition triggered by the storm time atmospheric heating.

    In the present study an attempt is made to further understand some of the observed storm time effects in terms of storm time changes in zonal electric fields and meridional neutral winds. For this purpose, observations made by the Retarding Potential Analyzer (RPA payload on board the Indian satellite SROSS-C2 are examined for four prominent geomagnetic storm events that occurred during the high solar activity period of 1997-2000. Available simultaneous observations, from the GPS satellite network, are also used. The daytime passes of SROSS-C2 have been selected to examine the redistribution of ionization in the equatorial ionization anomaly (EIA region. In general, EIA is observed to be weakened 12-24 h after the main phase onset (MPO of the storm. The storm time behaviour inferred by SROSS-C2 and the GPS satellite network during the geomagnetic storm of 13 November 1998, for which simultaneous observations are available, is found to be consistent. Storm time changes in the delay of received GPS signals are noted to be ~1-3 m, which is a significant component of the total delay observed on a quiet day.

    An attempt is made to identify and

  17. Rapid sympatry explains greater color pattern divergence in high latitude birds.

    Science.gov (United States)

    Martin, Paul R; Montgomerie, Robert; Lougheed, Stephen C

    2010-02-01

    Latitudinal variation in patterns of evolution has fascinated biologists for over a century, but our understanding of latitudinal differences in evolutionary processes-such as selection and drift-remains limited. Here, we test for, and find, accelerated evolution of color patterns in bird taxa that breed at higher latitudes compared with those breeding in the tropics, analyzing data from seven diverse avian families. Most important, we show that the extent of overlap of species' breeding ranges (degree of sympatry) explains the elevated rate of color pattern evolution at higher latitudes. We suggest that the dynamic shifts in breeding ranges that accompanied climatic changes during the last 3 million years (Milankovitch Oscillations) resulted in more rapid and more frequent secondary contact at high latitudes. We argue that sympatry among diverging clades causes greater divergence of color traits in birds at higher latitudes through sexual, social, or ecological character displacement that accelerate rates of evolution, and through the selective elimination of weakly differentiated lineages that hybridize and fuse in sympatry (differential fusion).

  18. North-South Asymmetries in Earth's Magnetic Field: Effects on High-Latitude Geospace

    CERN Document Server

    Laundal, K M; Milan, S E; Haaland, S E; Coxon, J; Pedatella, N M; Förster, M; Reistad, J P

    2016-01-01

    The solar-wind magnetosphere interaction primarily occurs at altitudes where the dipole component of Earth's magnetic field is dominating. The disturbances that are created in this interaction propagate along magnetic field lines and interact with the ionosphere-thermosphere system. At ionospheric altitudes, the Earth's field deviates significantly from a dipole. North-South asymmetries in the magnetic field imply that the magnetosphere ionosphere-thermosphere (M-I-T) coupling is different in the two hemispheres. In this paper we review the primary differences in the magnetic field at polar latitudes, and the consequences that these have for the M-I-T coupling. We focus on two interhemispheric differences which are thought to have the strongest effects: 1) A difference in the offset between magnetic and geographic poles in the Northern and Southern Hemispheres, and 2) differences in the magnetic field strength at magnetically conjugate regions. These asymmetries lead to differences in plasma convection, neutr...

  19. Cusp observation at Saturn's high-latitude magnetosphere by the Cassini spacecraft

    Science.gov (United States)

    Jasinski, J. M.; Arridge, C. S.; Lamy, L.; Leisner, J. S.; Thomsen, M. F.; Mitchell, D. G.; Coates, A. J.; Radioti, A.; Jones, G. H.; Roussos, E.; Krupp, N.; Grodent, D.; Dougherty, M. K.; Waite, J. H.

    2014-03-01

    We report on the first analysis of magnetospheric cusp observations at Saturn by multiple in situ instruments onboard the Cassini spacecraft. Using this we infer the process of reconnection was occurring at Saturn's magnetopause. This agrees with remote observations that showed the associated auroral signatures of reconnection. Cassini crossed the northern cusp around noon local time along a poleward trajectory. The spacecraft observed ion energy-latitude dispersions—a characteristic signature of the terrestrial cusp. This ion dispersion is "stepped," which shows that the reconnection is pulsed. The ion energy-pitch angle dispersions suggest that the field-aligned distance from the cusp to the reconnection site varies between ˜27 and 51 RS. An intensification of lower frequencies of the Saturn kilometric radiation emissions suggests the prior arrival of a solar wind shock front, compressing the magnetosphere and providing more favorable conditions for magnetopause reconnection.

  20. Persistent influence of ice sheet melting on high northern latitude climate during the early Last Interglacial

    Directory of Open Access Journals (Sweden)

    A. Govin

    2011-10-01

    Full Text Available Although the Last Interglacial (LIG is often considered as a possible analogue for future climate in high latitudes, its precise climate evolution and associated causes remain uncertain. Here we compile high-resolution marine sediment records from the North Atlantic, Labrador Sea, Norwegian Sea and the Southern Ocean. We document a delay in the establishment of peak interglacial conditions in the North Atlantic, Labrador and Norwegian Seas as compared to the Southern Ocean. In particular, we observe a persistent iceberg melting at high northern latitudes at the beginning of the LIG. It suggests that the input of meltwater has maintained (1 colder and fresher surface-water conditions in the North Atlantic, Labrador and Norwegian Seas and (2 weaker ventilation of North Atlantic deep waters during the early LIG (129–125.5 ka compared to the late LIG. Results from an ocean-atmosphere coupled model with insolation as a sole forcing for three key periods of the LIG show that insolation variations alone lead to warmer North Atlantic surface waters and stronger Atlantic overturning during the early LIG (126 ka than the late LIG (122 ka. Hence insolation variations alone do not explain the delay in peak interglacial conditions observed at high northern latitudes. When freshwater input is interactively computed at 126 ka in response to the high boreal summer insolation, the model simulates colder, fresher North Atlantic surface waters and weaker Atlantic overturning during the early LIG (126 ka compared to the late LIG (122 ka. This result indicates that both insolation variations and ice sheet melting have to be considered to reproduce the LIG climate evolution and supports our hypothesis that optimal thermal and deep ocean circulation conditions at high northern latitudes develop during the late LIG only, when the freshwater supply has already ceased.

  1. High Energy Processes in Pulsar Wind Nebulae

    CERN Document Server

    Bednarek, W

    2006-01-01

    Young pulsars produce relativistic winds which interact with matter ejected during the supernova explosion and the surrounding interstellar gas. Particles are accelerated to very high energies somewhere in the pulsar winds or at the shocks produced in collisions of the winds with the surrounding medium. As a result of interactions of relativistic leptons with the magnetic field and low energy radiation (of synchrotron origin, thermal, or microwave background), the non-thermal radiation is produced with the lowest possible energies up to $\\sim$100 TeV. The high energy (TeV) gamma-ray emission has been originally observed from the Crab Nebula and recently from several other objects. Recent observations by the HESS Cherenkov telescopes allow to study for the first time morphology of the sources of high energy emission, showing unexpected spectral features. They might be also interpreted as due to acceleration of hadrons. However, theory of particle acceleration in the PWNe and models for production of radiation ...

  2. Engineering challenges of operating year-round portable seismic stations at high-latitude

    Science.gov (United States)

    Beaudoin, Bruce; Carpenter, Paul; Hebert, Jason; Childs, Dean; Anderson, Kent

    2017-04-01

    Remote portable seismic stations are, in most cases, constrained by logistics and cost. High latitude operations introduce environmental, technical and logistical challenges that require substantially more engineering work to ensure robust, high quality data return. Since 2006, IRIS PASSCAL has been funded by NSF to develop, deploy, and maintain a pool of polar specific seismic stations. Here, we describe our latest advancements to mitigate the challenges of high-latitude, year-round station operation. The IRIS PASSCAL program has supported high-latitude deployments since the late 1980s. These early deployments were largely controlled source, summer only experiments. In early 2000 PASSCAL users began proposing year-round deployments of broadband stations in some of the harshest environments on the planet. These early year-round deployments were stand-alone (no telemetry) stations largely designed to operate during summer months and then run as long as possible during the winter with hopes the stations would revive come following summer. In 2006 and in collaboration with UNAVCO, we began developing communications, power systems, and enclosures to extend recording to year-round. Since this initial effort, PASSCAL continued refinement to power systems, enclosure design and manufacturability, and real-time data communications. Several sensor and data logger manufacturers have made advances in cold weather performance and delivered newly designed instruments that have furthered our ability to successfully run portable stations at high-latitude with minimal logistics - reducing size and weight of instruments and infrastructure. All PASSCAL polar engineering work is openly shared through our website: www.passcal.nmt.edu/content/polar

  3. Modeling of the dynamics of wind to power conversion including high wind speed behavior

    DEFF Research Database (Denmark)

    Litong-Palima, Marisciel; Bjerge, Martin Huus; Cutululis, Nicolaos Antonio

    2016-01-01

    of power system studies, but the idea of the proposed wind turbine model is to include the main dynamic effects in order to have a better representation of the fluctuations in the output power and of the fast power ramping especially because of high wind speed shutdowns of the wind turbine. The high wind......This paper proposes and validates an efficient, generic and computationally simple dynamic model for the conversion of the wind speed at hub height into the electrical power by a wind turbine. This proposed wind turbine model was developed as a first step to simulate wind power time series...... for power system studies. This paper focuses on describing and validating the single wind turbine model, and is therefore neither describing wind speed modeling nor aggregation of contributions from a whole wind farm or a power system area. The state-of-the-art is to use static power curves for the purpose...

  4. Parallel Gene Expression Differences between Low and High Latitude Populations of Drosophila melanogaster and D. simulans.

    Science.gov (United States)

    Zhao, Li; Wit, Janneke; Svetec, Nicolas; Begun, David J

    2015-05-01

    Gene expression variation within species is relatively common, however, the role of natural selection in the maintenance of this variation is poorly understood. Here we investigate low and high latitude populations of Drosophila melanogaster and its sister species, D. simulans, to determine whether the two species show similar patterns of population differentiation, consistent with a role for spatially varying selection in maintaining gene expression variation. We compared at two temperatures the whole male transcriptome of D. melanogaster and D. simulans sampled from Panama City (Panama) and Maine (USA). We observed a significant excess of genes exhibiting differential expression in both species, consistent with parallel adaptation to heterogeneous environments. Moreover, the majority of genes showing parallel expression differentiation showed the same direction of differential expression in the two species and the magnitudes of expression differences between high and low latitude populations were correlated across species, further bolstering the conclusion that parallelism for expression phenotypes results from spatially varying selection. However, the species also exhibited important differences in expression phenotypes. For example, the genomic extent of genotype × environment interaction was much more common in D. melanogaster. Highly differentiated SNPs between low and high latitudes were enriched in the 3' UTRs and CDS of the geographically differently expressed genes in both species, consistent with an important role for cis-acting variants in driving local adaptation for expression-related phenotypes.

  5. Energy release in high latitudes during the dissipation of ionospheric currents

    Energy Technology Data Exchange (ETDEWEB)

    Faermark, D.S.; Levitin, A.E.; Fel' dshtejn, Ya.I.; Belov, B.A.; Gajdukov, V.Yu.; Afonina, R.G.; Demidova, Yu.Z.

    Space-time distributions of Joule heating in the ionosphere for both summer and equinox seasons at different parameters of the interplanetary medium are obtained. It is shown, that in high latitudes there is a continuous Joule dissipation on which additional sources of energy release (qsub(j)) are superimposed. These sources are controlled by the Bsub(z) and Bsub(y) components of the interplanetary magnetic field (IMF) vector. In the region of high latitudes (PHI > or approximately 60 deg) there is a continuous Joule dissipation of ionospheric currents. Near the aurora borealis oval the maxima of qsub(j) (Bsub(z)=Bsub(y)=0) in the evening and morning sectors constitute: in summer season approximately 1-2 mW/mS; in the equinox season approximately 4-8 mW/mS. In the polar cap region, a continuous Joule dissipation with high values qsub(j) (Bsub(z)=Bsub(y)=0) is observed in the morning sector. Constantly existing Joule dissipation ensures a heat influx of approximately (2 - 4) x 10 W to the high-latitude ionosphere irrespectively of a year season.

  6. Analysis of High-Latitude lonospheric Processes During HSS and CME-Induced Geomagnetic Storms

    DEFF Research Database (Denmark)

    Durgonics, Tibor; Komjathy, Attila; Verkhoglyadova, Olga

    For the first time we compared ionospheric effects of HSS and CME-driven storms at high-latitudes. There were similarities and also differences observed in the development of the storms. (1) Both type of storms exhibited clear negative phase, which resulted in an increase of TOI......-breaking-down into patches and a decrease in patch formation in general throughout the Greenland sector. The negative phase developed as the PCN-index started to increase indicated energy input into the polarcap. (2) The rate of PCN increase was clearly different for the two types of storms. (3) The impact of the physical...... processes responsible for the negative phase have less pronounced impact on the diurnal TEC variations than on patch formation. We also investigated and assessed storm influences on airborne navigation at high-latitudes in order to determine the possible cause of the radio communication disturbances...

  7. Diffuse Galactic Gamma Rays at Intermediate and High Latitudes, Constraints on ISM Properties

    CERN Document Server

    Tavakoli, Maryam; Evoli, Carmelo; Ullio, Piero

    2011-01-01

    The spectral data on the diffuse Galactic gamma-rays, at medium and high latitudes (|b| > 10) and energies of 1-100 GeV, recently published by the Fermi Collaboration are used to produce a novel study on the gamma-ray emissivity in the Galaxy. We focus on analyzing the properties of propagation of cosmic rays (CRs), using the publicly available DRAGON code. We critically address some of the models for the interstellar HI and H2 gas distributions commonly used in the literature, as well as test a variety of propagation models. Each model assumes a distinct global profile for the diffusion and the re-acceleration of CRs. Fitting propagation parameters to well measured local CRs such as, the B/C ratio, protons, antiprotons and electron, positron fluxes, we evaluate the gamma-ray spectra at medium and high latitudes in order to place further constraints on these propagation models.

  8. The X-ray shadow of the high-latitude molecular cloud MBM 12

    Science.gov (United States)

    Snowden, S. L.; Mccammon, D.; Verter, F.

    1993-01-01

    ROSAT XRT/PSPC observations show a deep shadow cast by the high-latitude molecular cloud MBM 12 in the 3/4 keV diffuse background. Modeling of the shadow implies that less than 20 percent of the typical high-latitude 3/4 keV diffuse background intensity is emitted in front of the cloud (D = 60-70 pc). A weaker shadow consistent with the lower optical depth at higher energies was observed in the 1.5 keV band. Since little shadowing was seen in the 1/4 keV band, this observation places strong constraints on the amount of 0.5-2 keV emission that is intermixed with the source of the observed 1/4 keV flux.

  9. High-latitude truncation errors of box-type primitive equation models

    Science.gov (United States)

    Kalnay-Rivas, E.

    1976-01-01

    The 'box-type' finite-difference method includes a weighted average of the pressure gradient with weights proportional to the surface of the grid walls. It is shown that this averaging introduces first-order truncation errors near the poles. An example is shown in which the relative error is of zero order and the scheme produces large distortions in the solution at high latitudes.

  10. Soil-frost-enabled soil-moisture-precipitation feedback over northern high latitudes

    Science.gov (United States)

    Hagemann, Stefan; Blome, Tanja; Ekici, Altug; Beer, Christian

    2016-07-01

    Permafrost or perennially frozen ground is an important part of the terrestrial cryosphere; roughly one quarter of Earth's land surface is underlain by permafrost. The currently observed global warming is most pronounced in the Arctic region and is projected to persist during the coming decades due to anthropogenic CO2 input. This warming will certainly have effects on the ecosystems of the vast permafrost areas of the high northern latitudes. The quantification of such effects, however, is still an open question. This is partly due to the complexity of the system, including several feedback mechanisms between land and atmosphere. In this study we contribute to increasing our understanding of such land-atmosphere interactions using an Earth system model (ESM) which includes a representation of cold-region physical soil processes, especially the effects of freezing and thawing of soil water on thermal and hydrological states and processes. The coupled atmosphere-land models of the ESM of the Max Planck Institute for Meteorology, MPI-ESM, have been driven by prescribed observed SST and sea ice in an AMIP2-type setup with and without newly implemented cold-region soil processes. Results show a large improvement in the simulated discharge. On the one hand this is related to an improved snowmelt peak of runoff due to frozen soil in spring. On the other hand a subsequent reduction in soil moisture enables a positive feedback to precipitation over the high latitudes, which reduces the model's wet biases in precipitation and evapotranspiration during the summer. This is noteworthy as soil-moisture-atmosphere feedbacks have previously not been the focus of research on the high latitudes. These results point out the importance of high-latitude physical processes at the land surface for regional climate.

  11. The Relationship Between N(Htotal) and E(B-V) at High Galactic Latitude

    Science.gov (United States)

    Doppel, Jessica Erin; Magnani, Loris A.

    2017-06-01

    We studied the gas-to-dust ratio at high Galactic latitudes (|b| ≥ 20° and 30°). The gas content was measured by the column density of atomic hydrogen from the Leiden/Argentine/Bonn survey and the dust by E(B-V) from the Schlafly et al. (2014) compilation. We do not see significant variation as a function of galactic quadrant or hemisphere. Our results are similar to other studies that used different techniques for deriving N(HI), N(H2), or E(B-V). Like Liszt (2013), we see a higher slope [N(HI)/E(B-V)] if we choose only those points with E(B-V) ≤ 0.1 mag. We also see the break in slope he noted at 0.08 mag. We examined lines of sight that coincided with the Georgia/Harvard Smithsonian CfA high-latitude CO(1-0) surveys. Although at |b| ≥ 30° there were only about 200 CO detections, those points lie systematically below our best fit lines to the data. We can convert the CO line intensities to N(H2) and determine a global CO-H2 conversion factor for the high latitude sky.

  12. High-Power Wind Turbine: Performance Calculation

    Directory of Open Access Journals (Sweden)

    Goldaev Sergey V.

    2015-01-01

    Full Text Available The paper is devoted to high-power wind turbine performance calculation using Pearson’s chi-squared test the statistical hypothesis on distribution of general totality of air velocities by Weibull-Gnedenko. The distribution parameters are found by numerical solution of transcendental equation with the definition of the gamma function interpolation formula. Values of the operating characteristic of the incomplete gamma function are defined by numerical integration using Weddle’s rule. The comparison of the calculated results using the proposed methodology with those obtained by other authors found significant differences in the values of the sample variance and empirical Pearson. The analysis of the initial and maximum wind speed influence on performance of the high-power wind turbine is done

  13. A Geochemical and Sedimentary Record of High Southern Latitude Holocene Climate Evolution from Lago Fagnano, Tierra del Fuego

    Energy Technology Data Exchange (ETDEWEB)

    Moy, C M; Dunbar, R B; Guilderson, T P; Waldmann, N; Mucciarone, D A; Recasens, C; Austin, J A; Anselmetti, F S

    2010-11-19

    Situated at the southern margin of the hemispheric westerly wind belt and immediately north of the Antarctic Polar Frontal zone, Tierra del Fuego is well-positioned to monitor coupled changes in the ocean-atmosphere system of the high southern latitudes. Here we describe a Holocene paleoclimate record from sediment cores obtained from Lago Fagnano, a large lake in southern Tierra del Fuego at 55{sup o}S, to investigate past changes in climate related to these two important features of the global climate system. We use an AMS radiocarbon chronology for the last 8,000 years based on pollen concentrates, thereby avoiding contamination from bedrock-derived lignite. Our chronology is consistent with a tephrochronologic age date for deposits from the middle Holocene Volcan Hudson eruption. Combining bulk organic isotopic ({delta}{sup 13}C and {delta}{sup 15}N) and elemental (C and N) parameters with physical sediment properties allow us to better understand sediment provenance and transport mechanisms and to interpret Holocene climate and tectonic change during the last 8,000 years. Co-variability and long-term trends in C/N ratio, carbon accumulation rate, and magnetic susceptibility reflect an overall Holocene increase in the delivery of terrestrial organic and lithogenic material to the deep eastern basin. We attribute this variability to westerly wind-derived precipitation. Increased wind strength and precipitation in the late Holocene drives the Nothofagus forest eastward and enhances run-off and terrigenous inputs to the lake. Superimposed on the long-term trend are a series of abrupt 9 negative departures in C/N ratio, which constrain the presence of seismically-driven mass flow events in the record. We identify an increase in bulk {delta}{sup 13}C between 7,000 and 5,000 cal yr BP that we attribute to enhanced aquatic productivity driven by warmer summer temperatures. The Lago Fagnano {delta}{sup 13}C record shows similarities with Holocene records of sea surface

  14. A geochemical and sedimentary record of high southern latitude Holocene climate evolution from Lago Fagnano, Tierra del Fuego

    Science.gov (United States)

    Moy, Christopher M.; Dunbar, Robert B.; Guilderson, Thomas P.; Waldmann, Nicolas; Mucciarone, David A.; Recasens, Cristina; Ariztegui, Daniel; Austin, James A.; Anselmetti, Flavio S.

    2011-02-01

    Situated at the southern margin of the hemispheric westerly wind belt and immediately north of the Antarctic Polar Frontal zone, Tierra del Fuego is well-positioned to monitor coupled changes in the ocean-atmosphere system of the high southern latitudes. Here we describe a Holocene paleoclimate record from sediment cores obtained from Lago Fagnano, a large lake in southern Tierra del Fuego at 55°S, to investigate past changes in climate related to these two important features of the global climate system. We use an AMS radiocarbon chronology for the last 8000 yr based on pollen concentrates, thereby avoiding contamination from bedrock-derived lignite. Our chronology is consistent with a tephrochronologic age date for deposits from the middle Holocene Volcán Hudson eruption. Combining bulk organic isotopic (δ13C and δ15N) and elemental (C and N) parameters with physical sediment properties allows us to better understand sediment provenance and transport mechanisms and to interpret Holocene climate and tectonic change during the last 8000 yr. Co-variability and long-term trends in C/N ratio, carbon accumulation rate, and magnetic susceptibility reflect an overall Holocene increase in the delivery of terrestrial organic and lithogenic material to the deep eastern basin. We attribute this variability to westerly wind-derived precipitation. Increased wind strength and precipitation in the late Holocene drives the Nothofagus forest eastward and enhances run-off and terrigenous inputs to the lake. Superimposed on the long-term trend are a series of abrupt 9 negative departures in C/N ratio, which constrain the presence of seismically-driven mass flow events in the record. We identify an increase in bulk δ13C between 7000 and 5000 cal yr BP that we attribute to enhanced aquatic productivity driven by warmer summer temperatures. The Lago Fagnano δ13C record shows similarities with Holocene records of sea surface temperature from the mid-latitude Chilean continental

  15. Electrodynamic coupling of high and low latitudes: Observations on May 27, 1993

    DEFF Research Database (Denmark)

    Kobea, A.T.; Richmond, A.D.; Emery, B.A.

    2000-01-01

    The penetration of disturbance electric fields from the polar region to the magnetic equator on the dayside of the Earth is examined with geomagnetic data on May 27, 1993. First, we examine a dayside equatorial disturbance that followed the rapid recovery of magnetic activity from a storm...... and that has the characteristics of overshielding caused by persistent region-2 field-aligned currents. It lasted similar to 3 hours. Second, we analyze a series of fluctuations with periods of 25-75 min, to determine the variations of amplitude and phase with magnetic latitude and magnetic local time....... The fluctuations were highly coherent at all latitudes between the magnetic equator and the auroral zone, but the coherency decreased in the polar cap. A northward fluctuation at the equator during midday hours accompanied auroral zone fluctuations that were southward before noon, eastward around noon...

  16. High-latitude ionospheric convection during strong interplanetary magnetic field B-y

    DEFF Research Database (Denmark)

    Huang, C.S.; Sofko, G.J.; Murr, D.

    1999-01-01

    An unusual high-latitude ionospheric pattern was observed on March 23, 1995. ionospheric convection appeared as clockwise merging convection cell focused at 84 degrees magnetic latitude around 1200 MLT. No signature of the viscous convection cell in the afternoon sector was observed....... The interplanetary magnetic field (IMF) conditions corresponding to the occurrence of the ionospheric convection were B-x approximate to 1 nT, B-y approximate to 10 nT, and B-z ... conditions. It is found that the location of the convection cell focus in this event is at least two hours earlier than those previously observed and about 5 hours earlier than that predicted by the MHD model. The observations may have some significant implications on the antiparallel merging theory....

  17. The mid-high latitude whistler mode chorus waves observed around substorm onsets

    Institute of Scientific and Technical Information of China (English)

    YANG JunYing; CAO JinBin; YAN ChunXiao; LI LiuYuan; MA YuDuan

    2008-01-01

    Using the data of LFEW/TC-2, we studied the dawn side chorus around substorm onsets during a strong geomagnetic storm in November 2004. During this storm, LFEW/TC-2 observed 14 dawnside chorus events. Nine of them were associated with substorms and occurred within 40 min around the substorm onsets. The fre-quencies of waves have a very good correlation with the half equatorial electron cyclotron frequencies. Chorus can be excited in the region near magnetic equato-rial plane and then propagate to the mid and high latitudes. When the wave fre-quencies reach the local lower hybrid frequencies, chorus can be reflected due to the lower hybrid resonance. The time delay between the chorus and its echo is about 28 min. Previous observations show that the chorus can propagate at most to the magnetic latitudes of 40°. LFEW/TC-2 found for the first time that the chorus in space could propagate to the magnetic latitude of 70°. Since most of the previous chorus observatlons are made close to the magnetic equatorial plane, our results are Important for the studies of excitation and propagation of whistler mode wave, and relevant relativistic electron acceleration in the magnetosphere.

  18. High-latitude propagation studies using a meridional chain of LF/MF/HF receivers

    Directory of Open Access Journals (Sweden)

    J. LaBelle

    2004-04-01

    Full Text Available For over a decade, Dartmouth College has operated programmable radio receivers at multiple high-latitude sites covering the frequency range 100-5000kHz with about a 1-s resolution. Besides detecting radio emissions of auroral origin, these receivers record characteristics of the ionospheric propagation of natural and man-made signals, documenting well-known effects, such as the diurnal variation in the propagation characteristics of short and long waves, and also revealing more subtle effects. For example, at auroral zone sites in equinoctial conditions, the amplitudes of distant transmissions on MF/HF frequencies are often enhanced by a few dB just before they fade away at dawn. The polarization and/or direction of the arrival of ionospherically propagating signals in the lower HF range (3-5MHz show a consistent variation between pre-midnight, post-midnight, and pre-dawn conditions. As is well known, magnetic storms and substorms dramatically affect ionospheric propagation; data from multiple stations spanning the invariant latitude range 67-79° reveal spatial patterns of propagation characteristics associated with magnetic storms and substorms. For example, in the hours preceding many isolated substorms, favorable propagation conditions occur at progressively lower latitudes as a function of time preceding the substorm onset. For some of these effects, explanations follow readily from elementary ionospheric physics, but understanding others requires further investigation.

    Key words. Magnetospheric physics (annual phenomena – Radio science (ionosphere propagation; radio-wave propagation6

  19. The mid-high latitude whistler mode chorus waves observed around substorm onsets

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Using the data of LFEW/TC-2, we studied the dawn side chorus around substorm onsets during a strong geomagnetic storm in November 2004. During this storm, LFEW/TC-2 observed 14 dawnside chorus events. Nine of them were associated with substorms and occurred within 40 min around the substorm onsets. The fre-quencies of waves have a very good correlation with the half equatorial electron cyclotron frequencies. Chorus can be excited in the region near magnetic equato-rial plane and then propagate to the mid and high latitudes. When the wave fre-quencies reach the local lower hybrid frequencies, chorus can be reflected due to the lower hybrid resonance. The time delay between the chorus and its echo is about 28 min. Previous observations show that the chorus can propagate at most to the magnetic latitudes of 40°. LFEW/ TC-2 found for the first time that the chorus in space could propagate to the magnetic latitude of 70°. Since most of the previous chorus observations are made close to the magnetic equatorial plane, our results are important for the studies of excitation and propagation of whistler mode wave, and relevant relativistic electron acceleration in the magnetosphere.

  20. Testing the applicability of neural networks as a gap-filling method using CH4 flux data from high latitude wetlands

    DEFF Research Database (Denmark)

    Dengel, S.; Zona, D.; Sachs, T.;

    2013-01-01

    no consensus on CH4 gap-filling methods, and methods applied are still study-dependent and often carried out on low resolution, daily data. In the current study, we applied artificial neural networks to six distinctively different CH4 time series from high latitudes, explain the method and test its...... pressure, solar radiation, wind direction (indicator of source location) and in addition the lagged effect of water table depth and precipitation. In keeping with the principle of parsimony, we included up to five of these variables traditionally measured at CH4 flux measurement sites. Fuzzy sets were...

  1. Carbon dioxide in northern high latitude oceans: Anthropogenic increase and air-sea flux variability

    Energy Technology Data Exchange (ETDEWEB)

    Omar, Abdirahman M.

    2003-07-01

    The aim of this thesis is to further our knowledge of carbon dioxide in the northern high latitude oceans (northern North Atlantic, Barents Sea, and Arctic Ocean) by studying the anthropogenic change in the oceanic CO2, the inter-annual variability of the air-sea CO2 flux, and the relationship between this variability and changes in other oceanic processes. An introductory chapter and four papers are presented. Descriptions of the seawater carbonate system parameters, air-sea exchange of CO2, and related processes are given in the introduction chapter. The anthropogenic increase in partial pressure of CO2 (pCO2) in the surface water of the Barents Sea is evaluated in paper I. The effect of alternations of the Barents Sea climate between cold and warm modes on the annual cycles of seawater fugacity and air-sea flux of CO2 is investigated in paper II. Oceanic uptake of atmospheric CO2 associated with the seasonal formation of sea ice in Storfjorden and the implication for the entire Arctic Ocean is studied in paper III. An assessment of the variations of the air-sea flux of CO2 in the northern North Atlantic for 20 winters (1981-2001) is carried out in paper IV. PCO2 in the surface water of the Barents Sea is shown to have increased parallel with the atmospheric pCO2 between 1967 and 2000-2001 (paper I). This was determined by comparing seawater pCO2 from 1967 with that from 2000-2001. The former was estimated from surface seawater temperature (SST) while the latter was computed from data of total dissolved inorganic carbon and alkalinity. A procedure which accounts for the natural variability was applied and the difference between seawater pC02 of 1967 and that of 2000-2001 is attributed to the uptake of excess CO2. In the Atlantic sector of the Barents Sea, the surface seawater fugacity of CO2 (fCO s''w) is shown to be lower than the atmospheric fCO2 throughout the year, implying that the area is an annual sink of atmospheric CO2 (paper II). Additionally

  2. Persistent influence of ice sheet melting on high northern latitude climate during the early Last Interglacial

    Directory of Open Access Journals (Sweden)

    A. Govin

    2012-03-01

    Full Text Available Although the Last Interglacial (LIG is often considered as a possible analogue for future climate in high latitudes, its precise climate evolution and associated causes remain uncertain. Here we compile high-resolution marine sediment records from the North Atlantic, Labrador Sea, Norwegian Sea and the Southern Ocean. We document a delay in the establishment of peak interglacial conditions in the North Atlantic, Labrador and Norwegian Seas as compared to the Southern Ocean. In particular, we observe a persistent iceberg melting at high northern latitudes at the beginning of the LIG. It is associated with (1 colder and fresher surface-water conditions in the North Atlantic, Labrador and Norwegian Seas, and (2 a weaker ventilation of North Atlantic deep waters during the early LIG (129–125 ka compared to the late LIG. Results from an ocean-atmosphere coupled model with insolation as a sole forcing for three key periods of the LIG show warmer North Atlantic surface waters and stronger Atlantic overturning during the early LIG (126 ka than the late LIG (122 ka. Hence, insolation variations alone do not explain the delay in peak interglacial conditions observed at high northern latitudes. Additionally, we consider an idealized meltwater scenario at 126 ka where the freshwater input is interactively computed in response to the high boreal summer insolation. The model simulates colder, fresher North Atlantic surface waters and weaker Atlantic overturning during the early LIG (126 ka compared to the late LIG (122 ka. This result suggests that both insolation and ice sheet melting have to be considered to reproduce the climatic pattern that we identify during the early LIG. Our model-data comparison also reveals a number of limitations and reinforces the need for further detailed investigations using coupled climate-ice sheet models and transient simulations.

  3. High resolution climatological wind measurements for wind energy applications

    Energy Technology Data Exchange (ETDEWEB)

    Bergstroem, H. [Uppsala Univ. (Sweden). Dept. of Meteorology

    1996-12-01

    Measurements with a combined cup anemometer/wind vane instrument, developed at the Department of Meteorology in Uppsala, is presented. The instrument has a frequency response of about 1 Hz, making it suitable not only for mean wind measurements, but also for studies of atmospheric turbulence. It is robust enough to be used for climatological purposes. Comparisons with data from a hot-film anemometer show good agreement, both as regards standard deviations and the spectral decomposition of the turbulent wind signal. The cup anemometer/wind vane instrument is currently used at three sites within the Swedish wind energy research programme. These measurements are shortly described, and a few examples of the results are given. 1 ref, 10 figs

  4. The Structure of Galactic Gas at High Latitudes: The Southern Polar Cap

    Science.gov (United States)

    Gosachinskii, I. V.; Il'in, G. N.; Prozorov, V. A.

    2004-04-01

    We analyze the angular structure of the 21-cm interstellar neutral hydrogen emission at six and seven declinations in the northern (published previously) and southern polar caps of the Galaxy (Galactic latitudes from -40 deg to -90 deg), respectively, with an extent of 90 deg in right ascension. The RATAN-600 radio telescope has a beam width averaged over these regions of 2.0' x 30'. One-dimensional power spectra for the angular distribution of interstellar neutral hydrogen emission were computed in each 6.3-km/s-wide spectral channel by using the standard Fast Fourier Transform (FFT) code and were smoothed over 1 hour in right ascension. The Galactic latitude dependence of the mean parameters for the sky distribution of H I line emission at high latitudes was found to correspond to the distribution of gas in the form of a flat layer only in the northern region, while in the southern cap, the gas distribution is much less regular. In addition, the mean H I radial velocities are negative everywhere (-3.7 +/- 3.0 km/s in the north and -6.0+/-2.4 km/s in the south). The power spectra of the angular fluctuations in the range of angular periods from 10' to 6 deg appear as power laws. However, the spectral indices change greatly over the sky: from -3 to -1.2; on average, as the Galactic latitude increases and the H I column density decreases, the fluctuation spectrum of the interstellar gas emission becomes flatter. In the northern polar region, this behavior is much more pronounced, which probably stems from the fact that the gas column density in the south is generally a factor of 2 or 3 higher than that in the north. Therefore, the spectra are, on average, also steeper in the south, but the dependence on Galactic latitude is weaker. Using simulations, we show that the observed power-law spectrum of the H I emission distribution can be obtained in terms of not only a turbulent, but also a cloud model of interstellar gas if we use our previous spectra of the diameters

  5. Density and temperature of energetic electrons in the Earth's magnetotail derived from high-latitude GPS observations during the declining phase of the solar cycle

    Directory of Open Access Journals (Sweden)

    M. H. Denton

    2011-10-01

    Full Text Available Single relativistic-Maxwellian fits are made to high-latitude GPS-satellite observations of energetic electrons for the period January 2006–November 2010; a constellation of 12 GPS space vehicles provides the observations. The derived fit parameters (for energies ~0.1–1.0 MeV, in combination with field-line mapping on the nightside of the magnetosphere, provide a survey of the energetic electron density and temperature distribution in the magnetotail between McIlwain L-values of L=6 and L=22. Analysis reveals the characteristics of the density-temperature distribution of energetic electrons and its variation as a function of solar wind speed and the Kp index. The density-temperature characteristics of the magnetotail energetic electrons are very similar to those found in the outer electron radiation belt as measured at geosynchronous orbit. The energetic electron density in the magnetotail is much greater during increased geomagnetic activity and during fast solar wind. The total electron density in the magnetotail is found to be strongly correlated with solar wind speed and is at least a factor of two greater for high-speed solar wind (VSW=500–1000 km s−1 compared to low-speed solar wind (VSW=100–400 km s−1. These results have important implications for understanding (a how the solar wind may modulate entry into the magnetosphere during fast and slow solar wind, and (b if the magnetotail is a source or a sink for the outer electron radiation belt.

  6. On the solar cycle dependence of winds and planetary waves as seen from mid-latitude D1 LF mesopause region wind measurements

    Directory of Open Access Journals (Sweden)

    C. Jacobi

    Full Text Available At the Collm Observatory of the University of Leipzig LF D1 low-frequency total reflection night-time wind measurements have been carried out continuously for more than two decades. Using a multiple regression analysis to derive prevailing winds, tides and the quasi-2-day wave from the half-hourly mean values of the horizontal wind components, monthly mean values of mesopause wind parameters are obtained that can be analysed with respect to long-term trends and influences of solar variability. The response of the prevailing wind to the 11-year solar cycle differs throughout the year. While in winter no significant correlation between the zonal prevailing wind and solar activity is found, in spring and summer a negative correlation between the TWC can be seen from the measurements. This is connected with stronger vertical gradients of the zonal prevailing wind during solar maximum than during solar minimum. Since the amplitude of the quasi-2-day wave is dependent on the zonal mean wind vertical gradient, this is connected with a positive correlation between solar activity and quasi-two-day wave activity.

    Key words. Meteorology and atmospheric dynamics · Middle atmosphere dynamics Multiple regression analysis Quasi-2-day wave

  7. Phenology and cover of plant growth forms predict herbivore habitat selection in a high latitude ecosystem.

    Science.gov (United States)

    Iversen, Marianne; Fauchald, Per; Langeland, Knut; Ims, Rolf A; Yoccoz, Nigel G; Bråthen, Kari Anne

    2014-01-01

    The spatial and temporal distribution of forage quality is among the most central factors affecting herbivore habitat selection. Yet, for high latitude areas, forage quantity has been found to be more important than quality. Studies on large ungulate foraging patterns are faced with methodological challenges in both assessing animal movements at the scale of forage distribution, and in assessing forage quality with relevant metrics. Here we use first-passage time analyses to assess how reindeer movements relate to forage quality and quantity measured as the phenology and cover of growth forms along reindeer tracks. The study was conducted in a high latitude ecosystem dominated by low-palatable growth forms. We found that the scale of reindeer movement was season dependent, with more extensive area use as the summer season advanced. Small-scale movement in the early season was related to selection for younger stages of phenology and for higher abundances of generally phenologically advanced palatable growth forms (grasses and deciduous shrubs). Also there was a clear selection for later phenological stages of the most dominant, yet generally phenologically slow and low-palatable growth form (evergreen shrubs). As the summer season advanced only quantity was important, with selection for higher quantities of one palatable growth form and avoidance of a low palatable growth form. We conclude that both forage quality and quantity are significant predictors to habitat selection by a large herbivore at high latitude. The early season selectivity reflected that among dominating low palatability growth forms there were palatable phenological stages and palatable growth forms available, causing herbivores to be selective in their habitat use. The diminishing selectivity and the increasing scale of movement as the season developed suggest a response by reindeer to homogenized forage availability of low quality.

  8. Linking Sediment Microbial Communities to Carbon Cycling in High-Latitude Lakes

    Science.gov (United States)

    Emerson, J. B.; Varner, R. K.; Johnson, J. E.; Owusu-Dommey, A.; Binder, M.; Woodcroft, B. J.; Wik, M.; Freitas, N. L.; Boyd, J. A.; Crill, P. M.; Saleska, S. R.; Tyson, G. W.; Rich, V. I.

    2015-12-01

    It is well recognized that thawing permafrost peatlands are likely to provide a positive feedback to climate change via CH4 and CO2 emissions. High-latitude lakes in these landscapes have also been identified as sources of CH4 and CO2 loss to the atmosphere. To investigate microbial contributions to carbon loss from high-latitude lakes, we characterized sediment geochemistry and microbiota via cores collected from deep and shallow regions of two lakes (Inre Harrsjön and Mellersta Harrsjön) in Arctic Sweden in July, 2012. These lakes are within the Stordalen Mire long-term ecological area, a focal site for investigating the impacts of climate change-related permafrost thaw, and the lakes in this area are responsible for ~55% of the CH4 loss from this hydrologically interconnected system. Across 40 samples from 4 to 40 cm deep within four sediment cores, Illumina 16S rRNA gene sequencing revealed that the sedimentary microbiota was dominated by candidate phyla OP9 and OP8 (Atribacteria and Aminicenantes, respectively, including putative fermenters and anaerobic respirers), predicted methanotrophic Gammaproteobacteria, and predicted methanogenic archaea from the Thermoplasmata Group E2 clade. We observed some overlap in community structure with nearby peatlands, which tend to be dominated by methanogens and Acidobacteria. Sediment microbial communities differed significantly between lakes, by overlying lake depth (shallow vs. deep), and by depth within a core, with each trend corresponding to parallel differences in biogeochemical measurements. Overall, our results support the potential for significant microbial controls on carbon cycling in high-latitude lakes associated with thawing permafrost, and ongoing metagenomic analyses of focal samples will yield further insight into the functional potential of these microbial communities and their dominant members.

  9. EISCAT Observations of Main Ionization Troughs in the High-Latitude Ionosphere

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    F-region electron density depletions associated with main ionization troughs in the high-latitude ionosphere are studied using EISCAT CP3 data of meridian scanning experiments. The troughs in our observations are found to appear mainly in dusk sector, extending from late afternoon to pre-midnight, with higher occurrence rate during equinox and winter. Simultaneous ion drift velocity in F-region shows that the main trough minimm is mostly located at the equator ward edge of the plasma convection flow, rather than in the r~ion where the largest ion flow are observed.

  10. On the solar cycle variation in the barometer coefficients of high latitude neutron monitors

    Science.gov (United States)

    Kusunose, M.; Ogita, N.

    1985-01-01

    Evaluation of barometer coefficients of neutron monitors located at high latitudes has been performed by using the results of the spherical harmonic analysis based on the records from around twenty stations for twelve years from January 1966 to December 1977. The average of data at eight stations, where continuous records are available for twelve years, show that the absolute value of barometer coefficient is in positive correlation with the cosmic ray neutron intensity. The variation rate of the barometer coefficient to the cosmic ray neutron intensity is influenced by the changes in the cutoff rigidity and in the primary spectrum.

  11. Circulation in the high-latitude thermosphere due to electric fields and Joule heating

    Science.gov (United States)

    Heaps, M. G.; Megill, L. R.

    1975-01-01

    Electric fields in the earth's upper atmosphere are capable of setting the neutral atmosphere in motion via ion-neutral collisions as well as pressure gradients from resultant Joule heating. By means of simple models for the high-latitude thermosphere and electric fields a simplified set of coupled equations is solved which show that moderate electric fields, when present for a period of several hours, are capable of displacing the neutral atmosphere of the order of 50 km in the vertical, a few hundred kilometers in the north-south direction and over 1000 km in the east-west direction.

  12. Response of High Latitude Coralline Algae to pCO2 and Thermal Stress

    Science.gov (United States)

    Garlick-Ott, K.; Williams, B.; Chan, P. T. W.; Westfield, I. T.; Rasher, D.; Ries, J. B.; Adey, W.; Halfar, J.

    2016-12-01

    The impacts of recent and future anthropogenic increases in atmospheric pCO2 causing ocean acidification and temperature on high-latitude oceans, and the marine organisms that inhabit them, are varied and poorly understood. The ecologically important crustose coralline alga Clathromorphum compactum may be particularly vulnerable to ocean acidification due to the relatively high solubility of its high Mg-calcite skeleton . This species of coralline algae is abundant throughout coastal mid-to-high latitude areas of the northern hemisphere, and calcifies annually-banded skeletons with longevities of up to 650 years. Here we used micro-computed tomography (micro-CT) to evaluate the impact of decreasing seawater pH and increasing temperature on skeletal density of algal specimens cultured in a fully crossed pCO2 (280, 400, 700, 2800 µatm) and temperature (6.5, 8.7, 12.4 °C) laboratory experiment. To examine the natural variability in coralline algal skeletal density, additional long-lived wild C. compactum specimens were collected along a latitudinal transect extending from the Gulf of Maine to the Canadian Arctic Archipelago. Density time series generated from the wild specimens spans the past several decades to century, and were used to evaluate other environmental parameters that may influence the skeletal density of coralline algae. This research will evaluate the resiliency of this alga to future environmental change.

  13. Cusp observation at Saturn's high-latitude magnetosphere by the Cassini spacecraft.

    Science.gov (United States)

    Jasinski, J M; Arridge, C S; Lamy, L; Leisner, J S; Thomsen, M F; Mitchell, D G; Coates, A J; Radioti, A; Jones, G H; Roussos, E; Krupp, N; Grodent, D; Dougherty, M K; Waite, J H

    2014-03-16

    We report on the first analysis of magnetospheric cusp observations at Saturn by multiple in situ instruments onboard the Cassini spacecraft. Using this we infer the process of reconnection was occurring at Saturn's magnetopause. This agrees with remote observations that showed the associated auroral signatures of reconnection. Cassini crossed the northern cusp around noon local time along a poleward trajectory. The spacecraft observed ion energy-latitude dispersions-a characteristic signature of the terrestrial cusp. This ion dispersion is "stepped," which shows that the reconnection is pulsed. The ion energy-pitch angle dispersions suggest that the field-aligned distance from the cusp to the reconnection site varies between ∼27 and 51 RS . An intensification of lower frequencies of the Saturn kilometric radiation emissions suggests the prior arrival of a solar wind shock front, compressing the magnetosphere and providing more favorable conditions for magnetopause reconnection. We observe evidence for reconnection in the cusp plasma at SaturnWe present evidence that the reconnection process can be pulsed at SaturnSaturn's cusp shows similar characteristics to the terrestrial cusp.

  14. Ionospheric variations during sudden stratospheric warming in the high- and mid-latitude regions

    Science.gov (United States)

    Yasyukevich, Anna; Voeykov, Sergey; Mylnikova, Anna

    2017-04-01

    The ionospheric dynamic in the high- and middle-latitude regions during the periods of sudden stratospheric warmings (SSW) was studied by using the international network of phase dual-frequency GPS/GLONASS receivers and the vertical sounding data. Twelve SSW events that occurred in the Northern Hemisphere 2006 through 2013 were considered. In order to identify the possible response of the ionosphere to SSW events, we carried out the analysis of the total electron (TEC) and the F2-layer maximum electron density (NmF2) deviations from the background level. We have also studied changes of the level of total electron content (TEC) wave-like variations characterized by a special index WTEC. The index reflects the intensity of medium- and large-scale traveling ionospheric disturbances. The dynamics of the high- and middle-latitude ionosphere at the points near the SSW areas was found to differ from the regular. For a large number of events, it is shown that, despite quiet geomagnetic conditions, a noticeable decrease in the NmF2 and TEC values (by 5-10% relative to the background level) is observed during the SSW evolution and maximum stages. On the contrary, for 10-20 days after the SSW maxima, NmF2 and TEC significantly exceed the monthly averaged values. Moreover, these electron density changes are observed for both strong and weak stratospheric warmings, and are recorded mainly during daytime. The observed SSW effects in the polar and mid-latitude ionosphere are assumed to be probably associated with the changes in the neutral composition at the thermospheric heights that affect the F2-layer electron density. The study is supported by the Russian Foundation for Basic Research under Grant No. 16-35-60018, as well as by the RF President Grant of Public Support for RF Leading Scientific Schools (NSh-6894.2016.5).

  15. Ozone trends at northern mid- and high latitudes – a European perspective

    Directory of Open Access Journals (Sweden)

    Y. Orsolini

    2008-05-01

    Full Text Available The EU CANDIDOZ project investigated the chemical and dynamical influences on decadal ozone trends focusing on the Northern Hemisphere. High quality long-term ozone data sets, satellite-based as well as ground-based, and the long-term meteorological reanalyses from ECMWF and NCEP are used together with advanced multiple regression models and atmospheric models to assess the relative roles of chemistry and transport in stratospheric ozone changes. This overall synthesis of the individual analyses in CANDIDOZ shows clearly one common feature in the NH mid latitudes and in the Arctic: an almost monotonic negative trend from the late 1970s to the mid 1990s followed by an increase. In most trend studies, the Equivalent Effective Stratospheric Chlorine (EESC which peaked in 1997 as a consequence of the Montreal Protocol was observed to describe ozone loss better than a simple linear trend. Furthermore, all individual analyses point to changes in dynamical drivers, such as the residual circulation (responsible for the meridional transport of ozone into middle and high latitudes playing a key role in the observed turnaround. The changes in ozone transport are associated with variations in polar chemical ozone loss via heterogeneous ozone chemistry on PSCs (polar stratospheric clouds. Synoptic scale processes as represented by the new equivalent latitude proxy, by conventional tropopause altitude or by 250 hPa geopotential height have also been successfully linked to the recent ozone increases in the lowermost stratosphere. These show significant regional variation with a large impact over Europe and seem to be linked to changes in tropospheric climate patterns such as the North Atlantic Oscillation. Some influence in recent ozone increases was also attributed to the rise in solar cycle number 23. Changes from the late 1970s to the mid 1990s were found in a number of characteristics of the Arctic vortex. However, only one trend was found when more recent

  16. High resolution wind measurements for offshore wind energy development

    Science.gov (United States)

    Nghiem, Son Van (Inventor); Neumann, Gregory (Inventor)

    2013-01-01

    A method, apparatus, system, article of manufacture, and computer readable storage medium provide the ability to measure wind. Data at a first resolution (i.e., low resolution data) is collected by a satellite scatterometer. Thin slices of the data are determined. A collocation of the data slices are determined at each grid cell center to obtain ensembles of collocated data slices. Each ensemble of collocated data slices is decomposed into a mean part and a fluctuating part. The data is reconstructed at a second resolution from the mean part and a residue of the fluctuating part. A wind measurement is determined from the data at the second resolution using a wind model function. A description of the wind measurement is output.

  17. Coverage, Diversity, and Functionality of a High-Latitude Coral Community (Tatsukushi, Shikoku Island, Japan)

    Science.gov (United States)

    Denis, Vianney; Mezaki, Takuma; Tanaka, Kouki; Kuo, Chao-Yang; De Palmas, Stéphane; Keshavmurthy, Shashank; Chen, Chaolun Allen

    2013-01-01

    Background Seawater temperature is the main factor restricting shallow-water zooxanthellate coral reefs to low latitudes. As temperatures increase, coral species and perhaps reefs may move into higher-latitude waters, increasing the chances of coral reef ecosystems surviving despite global warming. However, there is a growing need to understand the structure of these high-latitude coral communities in order to analyze their future dynamics and to detect any potential changes. Methodology/Principal Findings The high-latitude (32.75°N) community surveyed was located at Tatsukushi, Shikoku Island, Japan. Coral cover was 60±2% and was composed of 73 scleractinian species partitioned into 7 functional groups. Although only 6% of species belonged to the ‘plate-like’ functional group, it was the major contributor to species coverage. This was explained by the dominance of plate-like species such as Acropora hyacinthus and A. solitaryensis. Comparison with historical data suggests a relatively recent colonization/development of A. hyacinthus in this region and a potential increase in coral diversity over the last century. Low coverage of macroalgae (2% of the benthic cover) contrasted with the low abundance of herbivorous fishes, but may be reasonably explained by the high density of sea urchins (12.9±3.3 individuals m−2). Conclusions/Significance The structure and composition of this benthic community are relatively remarkable for a site where winter temperature can durably fall below the accepted limit for coral reef development. Despite limited functionalities and functional redundancy, the current benthic structure might provide a base upon which a reef could eventually develop, as characterized by opportunistic and pioneer frame-building species. In addition to increasing seawater temperatures, on-going management actions and sea urchin density might also explain the observed state of this community. A focus on such ‘marginal’ communities should be a

  18. The Canada-France Ecliptic Plane Survey (CFEPS) - High Latitude Component

    CERN Document Server

    Petit, J-M; Gladman, B J; Jones, R L; Parker, J Wm; Van Laerhoven, C; Pike, R; Nicholson, P; Bieryla, A; Ashby, M L N; Lawler, S M

    2016-01-01

    We report the orbital distribution of the Trans-Neptunian objects (TNOs) discovered during the High Ecliptic Latitude (HiLat) extension of the Canada-France Ecliptic Plane Survey (CFEPS), conducted from June 2006 to July 2009. The HiLat component was designed to address one of the shortcomings of ecliptic surveys (like CFEPS), their lack of sensitivity to high-inclination objects. We searched 701~deg$^2$ of sky ranging from 12$^\\circ$ to 85$^\\circ$ ecliptic latitude and discovered \\lKBO TNOs, with inclinations between 15$^\\circ$ to 104$^\\circ$. This survey places a very strong constraint on the inclination distribution of the hot component of the classical Kuiper Belt, ruling out any possibility of a large intrinsic fraction of highly inclined orbits. Using the parameterization of \\citet{2001AJ....121.2804B}, the HiLat sample combined with CFEPS imposes a width $14^\\circ \\le \\sigma \\le 15.5^\\circ$, with a best match for $\\sigma = 14.5^\\circ$. HiLat discovered the first retrograde TNO, 2008~KV$_{42}$, with an ...

  19. Geomagnetic secular variations of high-latitude glaciomarine sediments: data from the Kola Peninsula, northwestern Russia

    Science.gov (United States)

    Bakhmutov, V.; Yevzerov, V.; Kolka, V.

    1994-08-01

    Geological, radiocarbon and paleomagnetic investigations of paleobays were carried out in the northwestern part of the Kola Peninsula (the Pechenga and Shuonijoki river valleys). The period from 10.3 to 9.5 kyear ago was characterized by the accumulation of glaciomarine sediments while the period 8.6-9.5 kyear was characterized by marine ones. Ca. 8.6 kyear marks the beginning of the formation of marine sediment transgression series. The clay sequences, accumulated in paleobays during a few hundred years, are an important object for studying the ancient geomagnetic field secular variations at high latitudes. Paleomagnetic signals in three outcrops from Pechenga river valley (69.5°N) record high-latitudinal inclination and declination variations in the time interval 8.5-10.0 kyear ago which correlate well with the secular variations of Early Holocene lacustrine deposits in the northern part of Ladoga Lake (61.5°N). A characteristic feature of the paleosecular variations at high latitudes is the proximity VGP to the observation point. Near to vertical inclination with declination variation amplitudes up to 150 took place ca. 9700-9500 year ago. The geomagnetic pole drifted south or crossed the Kola Peninsula at that time. The inclination and declination variations may be used in correlating the Early Holocene marine and lacustrine deposits in adjacent regions.

  20. Dust, Gas, and Star Formation in the MBM 18--19 High-Latitude Cloud Complex

    Science.gov (United States)

    Larson, Kristen A.; Reed, Cyrus M.

    Projected on the plane of the sky, the MBM 19 molecular cloud extends from the MBM 18 high-latitude cloud toward the Taurus star-forming regions. We present a new CO(J = 1--0) map of MBM 19 that shows clumpy emission with line intensities above 3 K in some regions despite low, relatively smooth 100 micron emission and modest visual extinction. This map complements data that show extremely high polarization efficiency of dust aligned along the bridge axis and low values of the ratio of total-to-selective extinction throughout the complex. In addition, several ongoing searches for spectral signatures of young stars have found evidence for star formation associated with MBM 18--19. We discuss variation in the molecular gas fraction and dust-to-gas ratio estimates, as well as the implications all these data have for understanding star formation in the region. Results of this study and others like it will provide insight into dust and gas of the translucent interstellar medium and star formation at high galactic latitude. This research was supported by the American Astronomical Society's Small Research Grant Program.

  1. High-Latitude Magnetic Reconnection in Sub-Alfvenic Flow as Observed by Interball Tail on 29 May 1996

    Science.gov (United States)

    Smirnov, V. N.; Avanov, L. A.; Waite, J.; Fuselier, S.; Vaisberg, O. L.; Six, N. Frank (Technical Monitor)

    2002-01-01

    The Interball/Tail spacecraft crossed the high latitude magnetopause near the cusp region under stable northward IMF conditions on 29 May 1996, with magnetic local time and magnetic latitude approx. 7.3 hours, approx. 65.4 degrees, respectively. The Interball Tail spacecraft observed quasi-steady reconnection and a relatively stable reconnection site at high latitudes. Observed sunward plasma flow and tangential stress balance indicated that reconnection occurred poleward of the magnetic cusp, above the spacecraft location. The spacecraft observed sub-alfvenic flow in the magnetosheath region adjacent to the magnetopause current layer near the reconnection site indicating that the reconnection site may have moved in the sunward direction. These observations suggest that the region of sub-alfvenic flow and stable, quasi-steady reconnection extend to very high latitudes under northward IMF conditions which is not consistent with the gas dynamic model predictions.

  2. Early Cretaceous vegetation and climate change at high latitude: palynological evidence from Isachsen Formation, Arctic Canada

    Science.gov (United States)

    Galloway, Jennifer M.; Tullius, Dylan N.; Evenchick, Carol A.; Swindles, Graeme T.; Hadlari, Thomas; Embry, Ashton

    2015-04-01

    expansion of mixed lowland communities. Our paleoclimate inferences for this Canadian high latitude region are consistent with reconstructions from lower latitudes, suggesting at least hemispherical expression of Valanginian cooling and a subsequent warming event in the Hauterivian that influenced polar vegetation. This work demonstrates the utility of a multivariate statistical approach to palynology to provide insight into the composition and dynamics of ecosystems and climate of high latitude regions during the Early Cretaceous.

  3. Influence of high-latitude geomagnetic pulsations on recordings of broadband force-balanced seismic sensors

    Directory of Open Access Journals (Sweden)

    E. Kozlovskaya

    2012-08-01

    Full Text Available Seismic broadband sensors with electromagnetic feedback are sensitive to variations of surrounding magnetic field, including variations of geomagnetic field. Usually, the influence of the geomagnetic field on recordings of such seismometers is ignored. It might be justified for seismic observations at middle and low latitudes. The problem is of high importance, however, for observations in Polar Regions (above 60° geomagnetic latitude, where magnitudes of natural magnetic disturbances may be two or even three orders larger. In our study we investigate the effect of ultra-low frequency (ULF magnetic disturbances, known as geomagnetic pulsations, on the STS-2 seismic broadband sensors. The pulsations have their sources and, respectively, maximal amplitudes in the region of the auroral ovals, which surround the magnetic poles in both hemispheres at geomagnetic latitude (GMLAT between 60° and 80°. To investigate sensitivity of the STS-2 seismometer to geomagnetic pulsations, we compared the recordings of permanent seismic stations in northern Finland to the data of the magnetometers of the IMAGE network located in the same area. Our results show that temporary variations of magnetic field with periods of 40–150 s corresponding to regular Pc4 and irregular Pi2 pulsations are seen very well in recordings of the STS-2 seismometers. Therefore, these pulsations may create a serious problem for interpretation of seismic observations in the vicinity of the auroral oval. Moreover, the shape of Pi2 magnetic disturbances and their periods resemble the waveforms of glacial seismic events reported originally by Ekström (2003. The problem may be treated, however, if combined analysis of recordings of co-located seismic and magnetic instruments is used.

  4. Genetic affinities between trans-oceanic populations of non-buoyant macroalgae in the high latitudes of the Southern Hemisphere.

    Directory of Open Access Journals (Sweden)

    Ceridwen I Fraser

    Full Text Available Marine biologists and biogeographers have long been puzzled by apparently non-dispersive coastal taxa that nonetheless have extensive transoceanic distributions. We here carried out a broad-scale phylogeographic study to test whether two widespread Southern Hemisphere species of non-buoyant littoral macroalgae are capable of long-distance dispersal. Samples were collected from along the coasts of southern Chile, New Zealand and several subAntarctic islands, with the focus on high latitude populations in the path of the Antarctic Circumpolar Current or West Wind Drift. We targeted two widespread littoral macroalgal species: the brown alga Adenocystisutricularis (Ectocarpales, Heterokontophyta and the red alga Bostrychiaintricata (Ceramiales, Rhodophyta. Phylogenetic analyses were performed using partial mitochondrial (COI, chloroplast (rbcL and ribosomal nuclear (LSU / 28S DNA sequence data. Numerous deeply-divergent clades were resolved across all markers in each of the target species, but close phylogenetic relationships - even shared haplotypes - were observed among some populations separated by large oceanic distances. Despite not being particularly buoyant, both Adenocystisutricularis and Bostrychiaintricata thus show genetic signatures of recent dispersal across vast oceanic distances, presumably by attachment to floating substrata such as wood or buoyant macroalgae.

  5. Impact of future Arctic shipping on high-latitude black carbon deposition (Invited)

    Science.gov (United States)

    Corbett, J. J.; Browse, J.; Carslaw, K. S.; Schmidt, A.

    2013-12-01

    The retreat of Arctic sea-ice has led to renewed calls to exploit Arctic shipping routes. The diversion of ship traffic through the Arctic will shorten shipping routes and possibly reduce global shipping emissions. However, deposition of black carbon (BC) aerosol emitted by additional Arctic ships could cause a reduction in the albedo of snow and ice, accelerating snow-melt and sea-ice loss. We use recently compiled Arctic shipping emission inventories for 2004 and 2050 together with a global aerosol microphysics model GLOMAP coupled to the chemical transport model TOMCAT to quantify the contribution of future Arctic shipping to high-latitude BC deposition. Emission rates of SOx (SO2 and SO4) and particulate matter (PM) were estimated for 2050 under both business-as-usual and high-growth scenarios. BC particles are assumed to be water-insoluble at emission but can become active in cloud drop formation through soluble material accumulation. After BC particles become cloud-active they are more efficiently wet scavenged, which accounts for 80% of modeled BC deposition. Current-day Arctic shipping contributes 0.3% to the BC mass deposited north of 60N (250 Gg). About 50% of modelled BC deposition is on open ocean, suggesting that current Arctic ship traffic may not significantly contribute to BC deposition on central Arctic sea ice. However, 6 - 8% of deposited BC on the west coast of Greenland originates from local ship traffic. Moreover, in-Arctic shipping contributes some 32% to high-latitude ship-sourced deposition despite accounting for less than 1.0% of global shipping emissions. This suggests that control of in-Arctic shipping BC emissions could yield greater decrease in high-latitude BC deposition than a similar control strategy applied only to the extra-Arctic shipping industry. Arctic shipping in 2050 will contribute less than 1% to the total BC deposition north of 60N due to the much greater relative contribution of BC transported from non-shipping sources

  6. High-latitude energy input and its impact on the thermosphere

    Science.gov (United States)

    Lu, G.; Richmond, A. D.; Lühr, H.; Paxton, L.

    2016-07-01

    This paper presents a quantitative assessment of high-latitude energy input and its partitioning in the polar cap by synthesizing various space and ground-based observations during the 17 January 2005 geomagnetic storm. It was found that Joule heating is the primary form of magnetospheric energy input, especially during active times when the hemispheric-integrated Joule heating can be an order of magnitude larger than the hemispheric-integrated auroral power. Most of magnetospheric energy is dissipated in the auroral zone rather than in the polar cap. On average, only about 22-25% of the total hemispheric energy input is dissipated into the polar cap region bordered by the convection reversal boundary (CRB) and the poleward auroral flux boundary (FXB). The impact of high-latitude energy input was also investigated to unveil the causal relationship between Joule heating and the formation of polar cap mass density anomalies. Our numerical simulation demonstrated that thermosphere dynamics readily redistributes composition, temperature, and mass through upwelling and atmospheric gravity waves. The polar cap mass density anomalies observed by the CHAMP satellite during the storm were largely a result of large-scale atmospheric gravity waves. Therefore, an increase in local thermospheric mass density does not necessarily mean there is direct energy input.

  7. Inorganic carbon in a high latitude estuary-fjord system in Canada's eastern Arctic

    Science.gov (United States)

    Turk, D.; Bedard, J. M.; Burt, W. J.; Vagle, S.; Thomas, H.; Azetsu-Scott, K.; McGillis, W. R.; Iverson, S. J.; Wallace, D. W. R.

    2016-09-01

    Rapidly changing conditions in the Arctic can have a significant impact on biogeochemical cycles and can be particularly important in high latitude estuary-fjord systems with abundant and diverse freshwater sources. This study provides a first look into the inorganic carbon system and its relation to freshwater sources in Cumberland Sound in the east coast of Baffin Island, Nunavut, Canada. These data contribute to the very limited set of inorganic carbon measurements in high latitude estuary-fjord systems. During the ice-free conditions in August 2011, the meteoric freshwater fractions (MW) in the upper 40 m ranged from 11 to 21% and no sea ice melt (SIM) was present in the Sound. Surface waters were undersaturated with pCO2 (260 and 300 μatm), and DIC and TA ranged between 1779 and 1966 μmol DIC kg-1, and 1922 and 2140 μmol TA kg-1, respectively. Aragonite saturation (ΩAr) state ranged from 1.9 in the surface to 1.4 in the subsurface waters. Data show decreasing TA and ΩAr with increasing MW fraction and suggest that Cumberland Sound waters would become aragonite undersaturated (ΩAr melt. In August 2012, MW fractions at the surface were between 8 and 11.5%, and SIM between 7 and 23%. Significant interannual variability of summertime SIM could potentially result in ΩAr undersaturation.

  8. The role played by thermal feedback in heated Farley-Buneman waves at high latitudes

    Directory of Open Access Journals (Sweden)

    J.-P. St.-Maurice

    Full Text Available It is becoming increasingly clear that electron thermal effects have to be taken into account when dealing with the theory of ionospheric instabilities in the high-latitude ionosphere. Unfortunately, the mathematical complexity often hides the physical processes at work. We follow the limiting cases of a complex but systematic generalized fluid approach to get to the heart of the thermal processes that affect the stability of E region waves during electron heating events. We try to show as simply as possible under what conditions thermal effects contribute to the destabilization of strongly field-aligned (zero aspect angle Farley-Buneman modes. We show that destabilization can arise from a combination of (1 a reduction in pressure gradients associated with temperature fluctuations that are out of phase with density fluctuations, and (2 thermal diffusion, which takes the electrons from regions of enhanced temperatures to regions of negative temperature fluctuations, and therefore enhanced densities. However, we also show that, contrary to what has been suggested in the past, for modes excited along the E0×B direction thermal feedback decreases the growth rate and raises the threshold speed of the Farley-Buneman instability. The increase in threshold speed appears to be important enough to explain the generation of `Type IV' waves in the high-latitude ionosphere.

    Key words: Ionosphere (auroral ionosphere; iono- spheric irregularities; plasma waves and instabilities

  9. Searches for Angular Extension in High Latitude Fermi-LAT Sources

    Science.gov (United States)

    Caputo, Regina; di Mauro, Mattia; Meyer, Manuel; Wells, Brendan; Wood, Matthew; Fermi-LAT Collaboration

    2017-01-01

    We present a comprehensive search for angular extension in high-latitude gamma-ray sources detected by the Fermi Large Area Telescope (LAT) using the 4-year LAT Point Source Catalog (3FGL). The majority of high-latitude LAT sources are extragalactic blazars that appear point-like within the LAT angular resolution. However, there are physics scenarios that predict populations of spatially extended sources. In one scenario, electron-positron pair cascades from gamma rays produced in blazars are deflected in the Intergalactic Magnetic Field (IGMF) producing extended emission, or ``pair halos''. The detection of a pair halo component around a LAT-detected blazar would provide a measurement of the strength and coherence length scale of the IGMF. In another scenario, the annihilation or decay of Weakly Interacting Massive Particles, a candidate for dark matter (DM), in Milky Way subhalos would appear as a population of unassociated gamma-ray sources with an angular extension. The detection of spatial extension in nearby sub halos could provide compelling evidence for a DM interpretation and would serve as an independent cross-check against other DM searches. We report on the angular extension catalog based on 7.5 years of Pass 8 data and discuss the implications of these results.

  10. Changes in Arctic vegetation amplify high-latitude warming through the greenhouse effect.

    Science.gov (United States)

    Swann, Abigail L; Fung, Inez Y; Levis, Samuel; Bonan, Gordon B; Doney, Scott C

    2010-01-26

    Arctic climate is projected to change dramatically in the next 100 years and increases in temperature will likely lead to changes in the distribution and makeup of the Arctic biosphere. A largely deciduous ecosystem has been suggested as a possible landscape for future Arctic vegetation and is seen in paleo-records of warm times in the past. Here we use a global climate model with an interactive terrestrial biosphere to investigate the effects of adding deciduous trees on bare ground at high northern latitudes. We find that the top-of-atmosphere radiative imbalance from enhanced transpiration (associated with the expanded forest cover) is up to 1.5 times larger than the forcing due to albedo change from the forest. Furthermore, the greenhouse warming by additional water vapor melts sea-ice and triggers a positive feedback through changes in ocean albedo and evaporation. Land surface albedo change is considered to be the dominant mechanism by which trees directly modify climate at high-latitudes, but our findings suggest an additional mechanism through transpiration of water vapor and feedbacks from the ocean and sea-ice.

  11. Evolutionary dynamics at high latitudes: speciation and extinction in polar marine faunas.

    Science.gov (United States)

    Clarke, Andrew; Crame, J Alistair

    2010-11-27

    Ecologists have long been fascinated by the flora and fauna of extreme environments. Physiological studies have revealed the extent to which lifestyle is constrained by low temperature but there is as yet no consensus on why the diversity of polar assemblages is so much lower than many tropical assemblages. The evolution of marine faunas at high latitudes has been influenced strongly by oceanic cooling during the Cenozoic and the associated onset of continental glaciations. Glaciation eradicated many shallow-water habitats, especially in the Southern Hemisphere, and the cooling has led to widespread extinction in some groups. While environmental conditions at glacial maxima would have been very different from those existing today, fossil evidence indicates that some lineages extend back well into the Cenozoic. Oscillations of the ice-sheet on Milankovitch frequencies will have periodically eradicated and exposed continental shelf habitat, and a full understanding of evolutionary dynamics at high latitude requires better knowledge of the links between the faunas of the shelf, slope and deep-sea. Molecular techniques to produce phylogenies, coupled with further palaeontological work to root these phylogenies in time, will be essential to further progress.

  12. High latitude cooling associated with landscape changes from North American boreal forest fires

    Directory of Open Access Journals (Sweden)

    B. M. Rogers

    2012-09-01

    Full Text Available Fires in the boreal forests of North America are generally stand-replacing, killing the majority of trees and initiating succession that may last over a century. Functional variation during succession can affect local surface energy budgets and, potentially, regional climate. Burn area across Alaska and Canada has increased in the last few decades and is projected to be substantially higher by the end of the 21st century because of a warmer climate with longer growing seasons. Here we simulated the changes in forest composition due to altered burn area using a stochastic model of fire occurrence, historical fire data from national inventories, and succession trajectories derived from remote sensing. When coupled to an Earth system model, younger vegetation from increased burning cooled the high-latitude atmosphere, primarily in the winter and spring, with noticeable feedbacks from the ocean and sea ice. Results from multiple scenarios suggest that a doubling of burn area would result in surface cooling of 0.23 ± 0.09 °C and 0.43 ± 0.12 °C for winter–spring and February–April time periods, respectively. This could provide a negative feedback to high-latitude terrestrial warming during winter on the order of 4–6% for a doubling, and 14–23% for a quadrupling, of burn area. Further work is needed to integrate all the climate drivers from boreal forest fires, including aerosols and greenhouse gasses.

  13. Dinosaurs on the North Slope, Alaska: High latitude, latest cretaceous environments

    Science.gov (United States)

    Brouwers, E.M.; Clemens, W.A.; Spicer, R.A.; Ager, T.A.; Carter, L.D.; Sliter, W.V.

    1987-01-01

    Abundant skeletal remains demonstrate that lambeosaurine hadrosaurid, tyrannosaurid, and troodontid dinosaurs lived on the Alaskan North Slope during late Campanian-early Maestrichtian time (about 66 to 76 million years ago) in a deltaic environment dominated by herbaceous vegetation. The high ground terrestrial plant community was a mild- to cold-temperate forest composed of coniferous and broad leaf trees. The high paleolatitude (about 70?? to 85?? North) implies extreme seasonal variation in solar insolation, temperature, and herbivore food supply. Great distances of migration to contemporaneous evergreen floras and the presence of both juvenile and adult hadrosaurs suggest that they remained at high latitudes year-round. This challenges the hypothesis that short-term periods of darkness and temperature decrease resulting from a bolide impact caused dinosaurian extinction.

  14. Holocene temperature evolution in the Northern Hemisphere high latitudes - Model-data comparisons

    Science.gov (United States)

    Zhang, Yurui; Renssen, Hans; Seppä, Heikki; Valdes, Paul J.

    2017-10-01

    Heterogeneous Holocene climate evolutions in the Northern Hemisphere high latitudes are primarily determined by orbital-scale insolation variations and melting ice sheets. Previous inter-model comparisons have revealed that multi-simulation consistencies vary spatially. We, therefore, compared multiple model results with proxy-based reconstructions in Fennoscandia, Greenland, north Canada, Alaska and Siberia. Our model-data comparisons reveal that data and models generally agree in Fennoscandia, Greenland and Canada, with the early-Holocene warming and subsequent gradual decrease to 0 ka BP (hereinafter referred as ka). In Fennoscandia, simulations and pollen data suggest a 2 °C warming by 8 ka, but this is less expressed in chironomid data. In Canada, a strong early-Holocene warming is suggested by both the simulations and pollen results. In Greenland, the magnitude of early-Holocene warming ranges from 6 °C in simulations to 8 °C in δ18O-based temperatures. Simulated and reconstructed temperatures are mismatched in Alaska. Pollen data suggest strong early-Holocene warming, while the simulations indicate constant Holocene cooling, and chironomid data show a stable trend. Meanwhile, a high frequency of Alaskan peatland initiation before 9 ka can reflect a either high temperature, high soil moisture or large seasonality. In high-latitude Siberia, although simulations and proxy data depict high Holocene temperatures, these signals are noisy owing to a large spread in the simulations and between pollen and chironomid results. On the whole, the Holocene climate evolutions in most regions (Fennoscandia, Greenland and Canada) are well established and understood, but important questions regarding the Holocene temperature trend and mechanisms remain for Alaska and Siberia.

  15. High-latitude ion temperature climatology during the International Polar Year 2007–2008

    Directory of Open Access Journals (Sweden)

    Yamazaki Y.

    2016-01-01

    Full Text Available This article presents the results of an ion temperature climatology study that examined ionospheric measurements from the European Incoherent SCATter (EISCAT Svalbard Radar (ESR: 78.2° N, 16.0° E and the Poker Flat Incoherent Scatter Radar (PFISR: 65.1° N, 212.6° E during the year-long campaign of the International Polar Year (IPY from March 2007 to February 2008. These observations were compared with those of the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIE-GCM, as well as the International Reference Ionosphere 2012 (IRI-2012. Fairly close agreement was found between the observations and TIE-GCM results. Numerical experiments revealed that the daily variation in the high-latitude ion temperature, about 100–200 K, is mainly due to ion frictional heating. The ion temperature was found to increase in response to elevated geomagnetic activity at both ESR and PFISR, which is consistent with the findings of previous studies. At ESR, a strong response occurred during the daytime, which was interpreted as a result of dayside-cusp heating. Neither TIE-GCM nor IRI-2012 reproduced the strong geomagnetic activity response at ESR, underscoring the need for improvement in both models at polar latitudes.

  16. Epithermal Neutron Evidence for a Diurnal Surface Hydration Process in the Moon's High Latitudes

    Science.gov (United States)

    McClanahan, T. P.; Mitrofanov, I. G.; Boynton, W. V.; Chin, G.; Parsons, A.; Starr, R. D.; Evans, L. G.; Sanin, A.; Litvak, M.; Livengood, T.

    2015-01-01

    We report evidence from epithermal neutron flux observations that show that the Moon's high latitude surfaces are being actively hydrated, dehydrated and rehydrated in a diurnal cycle. The near-surface hydration is indicated by an enhanced suppression of the lunar epithermal neutron leakage flux on the dayside of the dawn terminator on poleward-facing slopes (PFS). At 0600 to 0800 local-time, hydrogen concentrations within the upper 1 meter of PFS are observed to be maximized relative to equivalent equator-facing slopes (EFS). During the lunar day surface hydrogen concentrations diminish towards dusk and then rebuild overnight. Surface hydration is determined by differential comparison of the averaged EFS to PFS epithermal neutron count rates above +/- 75 deg latitude. At dawn the contrast bias towards PFS is consistent with at least 15 to 25 parts-per-million (ppm) hydrogen that dissipates by dusk. We review several lines of evidence derived from temperature and epithermal neutron data by a correlated analysis of observations from the Lunar Reconnaissance Orbiter's (LRO) Lunar Exploration Neutron Detector (LEND) that were mapped as a function of lunar local-time, Lunar Observing Laser Altimeter (LOLA) topography and Diviner (DLRE) surface temperature.

  17. Imaging of structures in the high-latitude ionosphere: model comparisons

    Directory of Open Access Journals (Sweden)

    D. W. Idenden

    Full Text Available The tomographic reconstruction technique generates a two-dimensional latitude versus height electron density distribution from sets of slant total electron content measurements (TEC along ray paths between beacon satellites and ground-based radio receivers. In this note, the technique is applied to TEC values obtained from data simulated by the Sheffield/UCL/SEL Coupled Thermosphere/Ionosphere/Model (CTIM. A comparison of the resulting reconstructed image with the 'input' modelled data allows for verification of the reconstruction technique. All the features of the high-latitude ionosphere in the model data are reproduced well in the tomographic image. Reconstructed vertical TEC values follow closely the modelled values, with the F-layer maximum density (NmF2 agreeing generally within about 10%. The method has also been able successfully to reproduce underlying auroral-E ionisation over a restricted latitudinal range in part of the image. The height of the F2 peak is generally in agreement to within about the vertical image resolution (25 km.

    Key words. Ionosphere (modelling and forecasting; polar ionosphere · Radio Science (instruments and techniques

  18. Studies on wind environment around high buildings in urban areas

    Institute of Scientific and Technical Information of China (English)

    LIU; Huizhi; JIANG; Yujun; LIANG; Bin; ZHU; Fengrong; ZHAN

    2005-01-01

    High buildings or architectural complex in urban areas remarkably distort the urban surface wind fields. As the air flow approaches,local strong wind may appear around the buildings. The strong wind makes the pedestrians on sidewalks, entrances and terrace very uncomfortable and causes the pedestrian level wind environment problem. In this studies, hot-wire wind measurement, wind scouring in wind tunnel and numerical computation were carried out to evaluate the wind environment of tall buildings in the prevailing flow conditions in Beijing areas. The results obtained by three techniques were compared and mutually verified. The conclusions drawn from three approaches agree with each other. Also the advantages and limitations of each method were analyzed. It is suggested that the combination of different techniques may produce better assessment of wind environment around high buildings.

  19. Mudstone sedimentation at high latitudes: Ice as a transport medium for mud and supplier of nutrients

    Science.gov (United States)

    Macquaker, J.H.S.; Keller, M.A.

    2005-01-01

    Controls on mudstone deposition at high latitudes are poorly known relative to low latitudes. In recent sediments deposited in these environments, ice significantly influences sediment transport and primary productivity. The products of ice transport are relatively well known in glacimarine settings, but are less well known from below melting sea ice. This latter setting is significant as today it is associated with high primary organic productivity. The aim of this study is to assess how sea ice might have controlled lithofacies variability and organic-matter distribution and preservation in an ancient marine, siliciclastic mudstone-dominated succession deposited at high latitudes. Combined sedimentary logging, optical and electron optical (back-scatte red electron imagery), geochemical, and isotopic methods were used to determine sample variability in forty-five samples collected from the Lower Cretaceous succession in the Mikkelsen Bay State #1 borehole (North Slope, Alaska). The succession overall fines upward and contains muddy sandstones and sand- and silt-bearing, clay-rich mudstones towards its base in contrast to clay-rich and clay-dominated mudstones towards its top. Some of the mudstone units exhibit thin (pelleted. These mudstones are unusual in that they contain minor but very striking outsize grains, composed of subrounded to rounded sand and granule-size material. In addition, they are good petroleum source rocks, with between 2.8 and 5.9 wt % total organic carbon, of predominantly Type II kerogen. The organic matter has an isotopic signature ranging from -25.4??? ??13C to -28.1??? ??13C. Thin tuffs (pelleted the sediment. Bioturbation, which varies through the succession, indicates that sedimentation probably occurred beneath a predominantly oxic or dysoxic water column. In this setting productivity was fueled by nutrients released from melting sea ice in the marginal ice zone. The good petroleum source potential of these mudstones is attributed to

  20. Correlation of High Latitude Coronal Holes with Solar Wind Streams High Above or Below the Ecliptic,

    Science.gov (United States)

    1980-04-01

    STATEMENT (of the abstract entered In Block 20, it differenit from, Report) IS. SUPPLEMENTARY NOTES 9. K EY * OROS (Cunrinn’e on reverse aide if necesary...the total scintillation peaks. The actual position of this point depends on the density spectrum of the plasma along the line of sight, but for most...line originates, rather than of the corona , where the X-ray emission originates. Therefore, the actual location and perimeter of a coronal hole in the

  1. HF omnidirectional spectral CW auroral radar (HF-OSCAR) at very high latitude. Part 1: Technique

    Science.gov (United States)

    Olesen, J. K.; Jacobsen, K. E.; Stauning, P.; Henriksen, S.

    1983-12-01

    An HF system for studies of very high latitude ionospheric irregularities was described. Radio aurora from field-aligned E-region irregularities of the Slant E Condition type were discussed. The complete system combines an ionosonde, a 12 MHz pulse radar and a 12 MHz bistatic CW Doppler-range set-up. The two latter units use alternately a 360 deg rotating Yagi antenna. High precision oscillators secure the frequency stability of the Doppler system in which the received signal is mixed down to a center frequency of 500 Hz. The Doppler shift range is max + or - 500 Hz. The received signal is recorded in analog form on magnetic tape and may be monitored visually and audibly. Echo range of the CW Doppler signal is obtained by a 150 Hz amplitude modulation of the transmitted signal and phase comparison with the backscattered signal.

  2. Power Thresholds of SPEAR-induced Irregularities at Very High Latitudes

    Science.gov (United States)

    Wright, D. M.; Yeoman, T. K.; Robinson, T. R.; Thomas, E. C.; Baddeley, L. J.; Dhillon, R. S.

    2007-05-01

    SPEAR (Space Plasma Exploration by Active Radar) is a high power facility uniquely located to study the plasma physics and geophysics of the very high latitude magnetosphere and ionosphere. Recently, experiments have been undertaken to investigate the power thresholds required to excite field-aligned irregularities (FAIs). The artificially stimulated FAI act as intense targets in the fields of view of the CUTLASS HF coherent radar pair. Data derived using this artificial backscatter technique demonstrate that SPEAR effective radiated powers (ERPs) of the order of 1 MW or less are capable of initiating the formation of the FAI. This represents only 1/30th of the heating capability of SPEAR. Ionospheric hysteresis was also observed to occur during the experiments. This relates to the nature of the instability which leads to their excitation.

  3. Dependence of Arctic climate on the latitudinal position of stationary waves and to high-latitudes surface warming

    Science.gov (United States)

    Shin, Yechul; Kang, Sarah M.; Watanabe, Masahiro

    2017-02-01

    Previous studies suggest large uncertainties in the stationary wave response under global warming. Here, we investigate how the Arctic climate responds to changes in the latitudinal position of stationary waves, and to high-latitudes surface warming that mimics the effect of Arctic sea ice loss under global warming. To generate stationary waves in an atmospheric model coupled to slab ocean, a series of experiments is performed where the thermal forcing with a zonal wavenumber-2 (with zero zonal-mean) is prescribed at the surface at different latitude bands in the Northern Hemisphere. When the stationary waves are generated in the subtropics, the cooling response dominates over the warming response in the lower troposphere due to cloud radiative effects. Then, the low-level baroclinicity is reduced in the subtropics, which gives rise to a poleward shift of the eddy driven jet, thereby inducing substantial cooling in the northern high latitudes. As the stationary waves are progressively generated at higher latitudes, the zonal-mean climate state gradually becomes more similar to the integration with no stationary waves. These differences in the mean climate affect the Arctic climate response to high-latitudes surface warming. Additional surface heating over the Arctic is imposed to the reference climates in which the stationary waves are located at different latitude bands. When the stationary waves are positioned at lower latitudes, the eddy driven jet is located at higher latitude, closer to the prescribed Arctic heating. As baroclinicity is more effectively perturbed, the jet shifts more equatorward that accompanies a larger reduction in the poleward eddy transport of heat and momentum. A stronger eddy-induced descending motion creates greater warming over the Arctic. Our study calls for a more accurate simulation of the present-day stationary wave pattern to enhance the predictability of the Arctic warming response in a changing climate.

  4. Evaluation of Convective Wind Forecasting Methods During High Wind Events

    Science.gov (United States)

    2006-03-01

    is referred to as a derecho . Derechos are described as long-lived convective systems in the form of long bow-shaped segments of cells. Bow-echoes...within a derecho can cause widespread severe winds causing damage for hundreds of miles during the lifetime of a derecho . The shape of a bow-echo

  5. Role of the Ionosphere in the Generation of Large-Amplitude Ulf Waves at High Latitudes

    Science.gov (United States)

    Tulegenov, B.; Guido, T.; Streltsov, A. V.

    2014-12-01

    We present results from the statistical study of ULF waves detected by the fluxgate magnetometer in Gakona, Alaska during several experimental campaigns conducted at the High Frequency Active Auroral Research Program (HAARP) facility in years 2011-2013. We analyzed frequencies of ULF waves recorded during 26 strongly disturbed geomagnetic events (substorms) and compared them with frequencies of ULF waves detected during magnetically quite times. Our analysis demonstrates that the frequency of the waves carrying most of the power almost in all these events is less than 1 mHz. We also analyzed data from the ACE satellite, measuring parameters of the solar wind in the L1 Lagrangian point between Earth and Sun, and found that in several occasions there is a strong correlation between oscillations of the magnetic field in the solar wind and oscillations detected on the ground. We also found several cases when there is no correlation between signals detected on ACE and on the ground. This finding suggests that these frequencies correspond to the fundamental eigenfrequency of the coupled magnetosphere-ionosphere system. The low frequency of the oscillations is explained by the effect of the ionosphere, where the current is carried by ions through highly collisional media. The amplitude of these waves can reach significant magnitude when the system is driven by the external driver (for example, the solar wind) with this particular frequency. When the frequency of the driver does not match the frequency of the system, the waves still are observed, but their amplitudes are much smaller.

  6. Contrasting vulnerability of drained tropical and high-latitude peatlands to fluvial loss of stored carbon

    Science.gov (United States)

    Evans, Chris D.; Page, Susan E.; Jones, Tim; Moore, Sam; Gauci, Vincent; Laiho, Raija; Hruška, Jakub; Allott, Tim E. H.; Billett, Michael F.; Tipping, Ed; Freeman, Chris; Garnett, Mark H.

    2014-11-01

    Carbon sequestration and storage in peatlands rely on consistently high water tables. Anthropogenic pressures including drainage, burning, land conversion for agriculture, timber, and biofuel production, cause loss of pressures including drainage, burning, land conversion for agriculture, timber, and biofuel production, cause loss of peat-forming vegetation and exposure of previously anaerobic peat to aerobic decomposition. This can shift peatlands from net CO2 sinks to large CO2 sources, releasing carbon held for millennia. Peatlands also export significant quantities of carbon via fluvial pathways, mainly as dissolved organic carbon (DOC). We analyzed radiocarbon (14C) levels of DOC in drainage water from multiple peatlands in Europe and Southeast Asia, to infer differences in the age of carbon lost from intact and drained systems. In most cases, drainage led to increased release of older carbon from the peat profile but with marked differences related to peat type. Very low DOC-14C levels in runoff from drained tropical peatlands indicate loss of very old (centuries to millennia) stored peat carbon. High-latitude peatlands appear more resilient to drainage; 14C measurements from UK blanket bogs suggest that exported DOC remains young (hydraulic conductivity and temperature, as well as the extent of disturbance associated with drainage, notably land use changes in the tropics. Data from the UK Peak District, an area where air pollution and intensive land management have triggered Sphagnum loss and peat erosion, suggest that additional anthropogenic pressures may trigger fluvial loss of much older (>500 year) carbon in high-latitude systems. Rewetting at least partially offsets drainage effects on DOC age.

  7. Long-Term High-Latitude Sea and Ice Surface Temperature Record from AVHRR GAC Data

    Science.gov (United States)

    Luis, C. S.; Dybkjær, G.; Eastwood, S.; Tonboe, R. T.; Høyer, J. L.

    2014-12-01

    Surface temperature is among the most important variables in the surface energy balance equation and it significantly affects the atmospheric boundary layer structure, the turbulent heat exchange and, over ice, the ice growth rate. Here we measure the surface temperature using thermal infrared sensors from 10-12 μm wavelength, a method whose primary limitation over sea ice is the detection of clouds. However, in the Arctic and around Antarctica there are very few conventional observations of surface temperature from buoys, and it is sometimes difficult to determine if the temperature is measured at the surface or within the snowpack, the latter of which often results in a warm bias. To reduce this bias, much interest is being paid to alternative remote sensing methods for monitoring high latitude surface temperature. We used Advanced Very High Resolution Radiometer (AVHRR) global area coverage (GAC) data to produce a high latitude sea surface temperature (SST), ice surface temperature (IST) and ice cap skin temperature dataset spanning 27 years (1982-2009). This long-term climate record is the first of its kind for IST. In this project we used brightness temperatures from the infrared channels of AVHRR sensors aboard NOAA and Metop polar-orbiting satellites. Surface temperatures were calculated using separate split window algorithms for day SST, night SST, and IST. The snow surface emissivity across all angles of the swath were simulated specifically for all sensors using an emission model. Additionally, all algorithms were tuned to the Arctic using simulated brightness temperatures from a radiative transfer model with atmospheric profiles and skin temperatures from European Centre for Medium-Range Forecasts (ECMWF) re-analysis data (ERA-Interim). Here we present the results of product quality as compared to in situ measurements from buoys and infrared radiometers, as well as a preliminary analysis of climate trends revealed by the record.

  8. Multi-year lags between forest browning and soil respiration at high northern latitudes.

    Directory of Open Access Journals (Sweden)

    Ben Bond-Lamberty

    Full Text Available High-latitude northern ecosystems are experiencing rapid climate changes, and represent a large potential climate feedback because of their high soil carbon densities and shifting disturbance regimes. A significant carbon flow from these ecosystems is soil respiration (R(S, the flow of carbon dioxide, generated by plant roots and soil fauna, from the soil surface to atmosphere, and any change in the high-latitude carbon cycle might thus be reflected in R(S observed in the field. This study used two variants of a machine-learning algorithm and least squares regression to examine how remotely-sensed canopy greenness (NDVI, climate, and other variables are coupled to annual R(S based on 105 observations from 64 circumpolar sites in a global database. The addition of NDVI roughly doubled model performance, with the best-performing models explaining ∼62% of observed R(S variability. We show that early-summer NDVI from previous years is generally the best single predictor of R(S, and is better than current-year temperature or moisture. This implies significant temporal lags between these variables, with multi-year carbon pools exerting large-scale effects. Areas of decreasing R(S are spatially correlated with browning boreal forests and warmer temperatures, particularly in western North America. We suggest that total circumpolar R(S may have slowed by ∼5% over the last decade, depressed by forest stress and mortality, which in turn decrease R(S. Arctic tundra may exhibit a significantly different response, but few data are available with which to test this. Combining large-scale remote observations and small-scale field measurements, as done here, has the potential to allow inferences about the temporal and spatial complexity of the large-scale response of northern ecosystems to changing climate.

  9. Design of High Performance Permanent-Magnet Synchronous Wind Generators

    Directory of Open Access Journals (Sweden)

    Chun-Yu Hsiao

    2014-11-01

    Full Text Available This paper is devoted to the analysis and design of high performance permanent-magnet synchronous wind generators (PSWGs. A systematic and sequential methodology for the design of PMSGs is proposed with a high performance wind generator as a design model. Aiming at high induced voltage, low harmonic distortion as well as high generator efficiency, optimal generator parameters such as pole-arc to pole-pitch ratio and stator-slot-shoes dimension, etc. are determined with the proposed technique using Maxwell 2-D, Matlab software and the Taguchi method. The proposed double three-phase and six-phase winding configurations, which consist of six windings in the stator, can provide evenly distributed current for versatile applications regarding the voltage and current demands for practical consideration. Specifically, windings are connected in series to increase the output voltage at low wind speed, and in parallel during high wind speed to generate electricity even when either one winding fails, thereby enhancing the reliability as well. A PMSG is designed and implemented based on the proposed method. When the simulation is performed with a 6 Ω load, the output power for the double three-phase winding and six-phase winding are correspondingly 10.64 and 11.13 kW. In addition, 24 Ω load experiments show that the efficiencies of double three-phase winding and six-phase winding are 96.56% and 98.54%, respectively, verifying the proposed high performance operation.

  10. Verification of high-speed solar wind stream forecasts using operational solar wind models

    OpenAIRE

    Reiss, Martin A.; Temmer, Manuela; Veronig, Astrid M.; Nikolic, Ljubomir; Vennerstrom, Susanne; Schoengassner, Florian; Hofmeister, Stefan J.

    2016-01-01

    High-speed solar wind streams emanating from coronal holes are frequently impinging on the Earth's magnetosphere causing recurrent, medium-level geomagnetic storm activity. Modeling high-speed solar wind streams is thus an essential element of successful space weather forecasting. Here we evaluate high-speed stream forecasts made by the empirical solar wind forecast (ESWF) and the semiempirical Wang-Sheeley-Arge (WSA) model based on the in situ plasma measurements from the ACE spacecraft for ...

  11. Identifying Unidentified Fermi-LAT Objects (UFOs) at High-Latitude

    Science.gov (United States)

    Cheung, Chi Teddy

    2009-09-01

    We propose a Chandra study of 8 high Galactic latitude gamma-ray sources in the Fermi-LAT bright source list. These sources are currently unidentified, i.e., they are not clearly associated with established classes of gamma-ray emitters like blazars and pulsars. The proposed observations will determine the basic properties (fluxes, positions, hardness ratio/spectra) of all X-ray sources down to a 0.3-10 keV flux limit of 1.5e-14 erg/cm2/s within the Fermi-LAT localization circles. This will enable further follow-up at other wavelengths, with the ultimate goal to reveal the nature of these enigmatic gamma-ray sources.

  12. Distance to the High-Latitude Molecular Cloud MBM 37 (LDN 183)

    Science.gov (United States)

    Boyle, Richard P.; Janusz, Robert; Straizys, Vytautas; Corbally, Christopher J.; Munari, Ulisse; Andersson, B.-G.; Zdanavicius, Justas; Maskoliunas, Marius; Kazlauskas, Algirdas

    2017-01-01

    The molecular cloud MBM 37 and the corresponding dust cloud LDN 183 belong to a group of high-latitude clouds near the Serpens Caput and Libra border at b = +36 deg. We determined the distance to this cloud applying the extinction Av vs. distance diagram based on two-dimensional photometric classification of about 800 stars down to V = 15 mag and about 200 stars down to V = 19 mag observed in the Vilnius seven-color system. Additionally, for the stars brighter than V = 12 mag MK types were determined spectroscopically. Distances for part of them, located nearer than 500 pc, were calculated from the Gaia parallaxes. The distance to MBM 37 is found to be at 90 pc placing it among the dust and molecular clouds closest to the Sun.

  13. Persistent retrograde flow structures at high latitudes - extent in depth and time

    Science.gov (United States)

    Baldner, Charles; Bogart, Richard S.

    2017-08-01

    Medium resolution helioseismic studies of the near-surface layers of the Sun have revealed the existence of coherent retrograde flow structures that persist for multiple solar rotations (Bogart et al. 2015). Similar surface features have been detected and suggested to be related to giant cell convection (Hathaway et al. 2013). These structures seem to be confined to high latitudes (greater than 60°N/S) and are have magnitudes (relative to the mean solar flow) of less than 1 m s-1. In this work we extend our earlier analysis of these flow structures by studying their extent and structure in depth and their evolution in time. In particular, we attempt to determine the depth at which the anomalous flow structures are most significant, and to determine their migration relative to the Carrington coordinate frame.

  14. Spline model of the high latitude scintillation based on in situ satellite data

    Science.gov (United States)

    Priyadarshi, S.; Wernik, A. W.

    2013-12-01

    We present a spline model for the high latitude ionospheric scintillation using satellite in situ measurements made by the Dynamic Explorer 2 (DE 2) satellite. DE 2 satellite measurements give observations only along satellite orbit but our interpolation model fills the gaps between the satellite orbits. This analytical model is based on products of cubic B-splines and coefficients determined by least squares fit to the binned data and constrained to make the fit periodic in 24 hours of geomagnetic local time, periodic in 360 degrees of invariant longitude, in geomagnetic indices and solar radio flux. Discussion of our results clearly shows the seasonal and diurnal behavior of ionospheric parameters important in scintillation modeling for different geophysical and solar activity conditions. We also show that results obtained from our analytical model match observations obtained from in situ measurements. Shishir Priyadarshi Space Research Centre, Poland

  15. The structure of the high-latitude molecular cloud toward HD 210121

    Science.gov (United States)

    Gredel, Roland; van Dishoeck, Ewine F.; de Vries, Cor P.; Black, John H.

    1992-04-01

    Optical absorption line observations and millimeter emission of the high-latitude cloud toward the star HD 21021 are reported. The cloud was mapped with the ESO submillimeter telescope. Maps of (C-12)O and (C-13)O emission are presented and the line profiles and velocity structure of the cloud are discussed. The optical absorption line observations allow an independent determination of the H2 column density along the line of sight. The molecular column densities found in this cloud were consistent with those measured in diffuse and translucent clouds. Attention is given to the physical and chemical properties of the cloud with reference to chemical models. Analysis indicates that small fluctuations in H2 column density and other factors can produce large variations of CO abundance and column density in clouds where carbon is just being transformed into CO.

  16. Assessing recent trends in high-latitude Southern Hemisphere surface climate

    Science.gov (United States)

    Jones, Julie M.; Gille, Sarah T.; Goosse, Hugues; Abram, Nerilie J.; Canziani, Pablo O.; Charman, Dan J.; Clem, Kyle R.; Crosta, Xavier; de Lavergne, Casimir; Eisenman, Ian; England, Matthew H.; Fogt, Ryan L.; Frankcombe, Leela M.; Marshall, Gareth J.; Masson-Delmotte, Valérie; Morrison, Adele K.; Orsi, Anaïs J.; Raphael, Marilyn N.; Renwick, James A.; Schneider, David P.; Simpkins, Graham R.; Steig, Eric J.; Stenni, Barbara; Swingedouw, Didier; Vance, Tessa R.

    2016-10-01

    Understanding the causes of recent climatic trends and variability in the high-latitude Southern Hemisphere is hampered by a short instrumental record. Here, we analyse recent atmosphere, surface ocean and sea-ice observations in this region and assess their trends in the context of palaeoclimate records and climate model simulations. Over the 36-year satellite era, significant linear trends in annual mean sea-ice extent, surface temperature and sea-level pressure are superimposed on large interannual to decadal variability. Most observed trends, however, are not unusual when compared with Antarctic palaeoclimate records of the past two centuries. With the exception of the positive trend in the Southern Annular Mode, climate model simulations that include anthropogenic forcing are not compatible with the observed trends. This suggests that natural variability overwhelms the forced response in the observations, but the models may not fully represent this natural variability or may overestimate the magnitude of the forced response.

  17. Existence of a component corotating with the earth in high-latitude disturbance magnetic fields

    Science.gov (United States)

    Suzuki, A.; Kim, J. S.; Sugiura, M.

    1982-01-01

    A study of the data from the high-latitude North American IMS network of magnetic stations suggests that there is a component in substorm perturbations that corotates with the earth. It is as yet not certain whether the existence of this component stems from the corotation of a part of the magnetospheric plasma involved in the substorm mechanism or if it is a 'phase change' resulting from the control of the substorm manifestations by the earth's main magnetic field which is not axially symmetric. There are other geophysical phenomena showing a persistence of longitudinal variations corotating with the earth. These phenomena are of significance for a better understanding of ionosphere-magnetosphere coupling.

  18. Population dynamic of high latitude copepods - with emphasis on Metridia longa

    DEFF Research Database (Denmark)

    Kjellerup, Sanne

    2014-01-01

    High latitude ecosystems are shaped by seasonality in light, ranging from complete darkness in winter to midnight sun in summer, influencing both temperature and primary production. Copepods are important grazers on phytoplankton in marine systems and occupy a central role in the marine food......, sampling only the upper water column during the day-as is a usual procedure-would underestimate this potential key species. Reproduction patterns of the large calanoids suggested lifecycles adapted to the seasonal and episodic food availability, and consequently had a pulsed reproduction. In contrast......, small copepod species were less dependent on the spring phytoplankton bloom, and their reproduction and population dynamics were less pulsed. Likewise, a large proportion of Oithona similis was ovigerous from March to August. Reproduction of Microsetella norvegica, another of the small key species...

  19. Experimental determination of effective recombination rates in the disturbed high latitude lower ionosphere

    Energy Technology Data Exchange (ETDEWEB)

    Collis, P.N.; Hargreaves, J.K.; Brekke, A.; Korth, A.

    1986-06-01

    With a view to investigating properties of the high latitude D-region during disturbed conditions, we have undertaken a coordinated study of partial reflection measurements of electron densities, together with estimated ion-pair production rates from observations of energetic electrons by the satellite GEOS-2, during intervals of auroral radio absorption recorded by riometers. The viability of this approach to the problem is found to be restricted, and limitations on the wider applicability of such intercomparisons are identified. For the weak-to moderately-disturbed events which were able to be examined in detail, the results give better resolution in height than a previously reported profile of effective recombination coefficients during D-region disturbances, and suggest a steeper slope at altitudes of 75-80 km.

  20. Influences of basic flow on unstable excitation of intraseasonal oscillation in mid-high latitudes

    Institute of Scientific and Technical Information of China (English)

    李崇银; 曹文忠; 李桂龙

    1995-01-01

    The influences of basic flow fields on the unstable excitation of the intraseasonal atmosphericoscillation in the mid-high latitudes are studied by using a simple nonlinear dynamical model.The results showthat the westerly profile has an important effect on unstable modes in the atmosphere;the growth rates andspectrum distributions of the excited unstable modes are different for the different profiles.For the usualwesterly profile patterns in the real atmosphere,the most unstable mode is in the intraseasonal(30—60 d)frequency band.The local intensity and meridional gradient of the westerlies also clearly affect unstablemodes.The consistency of the results in observational data analyses with that in dynamical theory proved thecorrectness and rationalization of the above-mentioned results.

  1. Calcium isotopic composition of high-latitude proxy carrier Neogloboquadrina pachyderma (sin.

    Directory of Open Access Journals (Sweden)

    A. Eisenhauer

    2009-01-01

    Full Text Available The accurate reconstruction of sea surface temperature (SST history in climate-sensitive regions (e.g. tropical and polar oceans became a challenging task in palaeoceanographic research. Biogenic shell carbonate SST proxies successfully developed for tropical regions often fail in cool water environments. Their major regional shortcomings and the cryptic diversity now found within the major high latitude proxy carrier Neogloboquadrina pachyderma (sin. highlight an urgent need to explore complementary SST proxies for these cool-water regions. Here we incorporate the genetic component into a calibration study of a new SST proxy for the high latitudes. We found that the calcium isotopic composition (δ44/40Ca of calcite from genotyped net catches and core-top samples of the planktonic foraminifera Neogloboquadrina pachyderma (sin. is related to temperature and unaffected by genetic variations. The temperature sensitivity has been found to be 0.17 (±0.02‰ per 1°C, highlighting its potential for downcore applications in open marine cool-water environments. Our results further indicate that in extreme polar environments, below a critical threshold temperature of 2.0 (±0.5°C associated with salinities below 33.0 (±0.5‰, a prominent shift in biomineralization affects the δ44/40Ca of genotyped and core-top N. pachyderma (sin., becoming insensitive to temperature. These findings highlight the need of more systematic calibration studies on single planktonic foraminiferal species in order to unravel species-specific factors influencing the temperature sensitivity of Ca isotope fractionation and to validate the proxies' applicability.

  2. Design of ecoregional monitoring in conservation areas of high-latitude ecosystems under contemporary climate change

    Science.gov (United States)

    Beever, Erik A.; Woodward, Andrea

    2011-01-01

    Land ownership in Alaska includes a mosaic of federally managed units. Within its agency’s context, each unit has its own management strategy, authority, and resources of conservation concern, many of which are migratory animals. Though some units are geographically isolated, many are nevertheless linked by paths of abiotic and biotic flows, such as rivers, air masses, flyways, and terrestrial and aquatic migration routes. Furthermore, individual land units exist within the context of a larger landscape pattern of shifting conditions, requiring managers to understand at larger spatial scales the status and trends in the synchrony and spatial concurrence of species and associated suitable habitats. Results of these changes will determine the ability of Alaska lands to continue to: provide habitat for local and migratory species; absorb species whose ranges are shifting northward; and experience mitigation or exacerbation of climate change through positive and negative atmospheric feedbacks. We discuss the geographic and statutory contexts that influence development of ecological monitoring; argue for the inclusion of significant amounts of broad-scale monitoring; discuss the importance of defining clear programmatic and monitoring objectives; and draw from lessons learned from existing long-term, broad-scale monitoring programs to apply to the specific contexts relevant to high-latitude protected areas such as those in Alaska. Such areas are distinguished by their: marked seasonality; relatively large magnitudes of contemporary change in climatic parameters; and relative inaccessibility due to broad spatial extent, very low (or zero) road density, and steep and glaciated areas. For ecological monitoring to effectively support management decisions in high-latitude areas such as Alaska, a monitoring program ideally would be structured to address the actual spatial and temporal scales of relevant processes, rather than the artificial boundaries of individual land

  3. A new methodology for the development of high-latitude ionospheric climatologies and empirical models

    Science.gov (United States)

    Chisham, G.

    2017-01-01

    Many empirical models and climatologies of high-latitude ionospheric processes, such as convection, have been developed over the last 40 years. One common feature in the development of these models is that measurements from different times are combined and averaged on fixed coordinate grids. This methodology ignores the reality that high-latitude ionospheric features are organized relative to the location of the ionospheric footprint of the boundary between open and closed geomagnetic field lines (OCB). This boundary is in continual motion, and the polar cap that it encloses is continually expanding and contracting in response to changes in the rates of magnetic reconnection at the Earth's magnetopause and in the magnetotail. As a consequence, models that are developed by combining and averaging data in fixed coordinate grids heavily smooth the variations that occur near the boundary location. Here we propose that the development of future models should consider the location of the OCB in order to more accurately model the variations in this region. We present a methodology which involves identifying the OCB from spacecraft auroral images and then organizing measurements in a grid where the bins are placed relative to the OCB location. We demonstrate the plausibility of this methodology using ionospheric vorticity measurements made by the Super Dual Auroral Radar Network radars and OCB measurements from the IMAGE spacecraft FUV auroral imagers. This demonstration shows that this new methodology results in sharpening and clarifying features of climatological maps near the OCB location. We discuss the potential impact of this methodology on space weather applications.

  4. Tracking Jupiter's Quasi-Quadrennial Oscillation and Mid-Latitude Zonal Waves with High Spectral Resolution Mid-Infrared Observations

    Science.gov (United States)

    Greathouse, Thomas K.; Orton, Glenn S.; Cosentino, Rick; Morales-Juberias, Raul; Fletcher, Leigh N.; Giles, Rohini Sara; Melin, Henrik; Encrenaz, Therese A.; Fouchet, Thierry; DeWitt, Curtis N.

    2016-10-01

    We report on early results of a long term observational study to track the temporal and 3-dimensional evolution of the Quasi-Quadrennial Oscillation (QQO) and the propagation and evolution of mid-latitude zonal waves in Jupiter's stratosphere. These wave-driven phenomena affect variations in Jupiter's vertical and horizontal temperature field, which can be inferred by measuring methane emission in the thermal infrared near 1245 cm-1. Using TEXES, the Texas Echelon cross-dispersed Echelle Spectrograph, mounted on the NASA Infrared Telescope Facility (IRTF) we observed high-spectral resolution (R=75,000) scan maps of Jupiter's equator to mid-latitudes from January 2012 through to the present. We will present the zonally averaged inferred thermal structure within ±30° latitude of the equator and between 10 and 0.01 mbar, showing the QQO's downward progression along with inferred 3-dimensional thermal maps (latitude, longitude, pressure) displaying a multitude of independent waves and eddies at various latitudes and pressures. These results reveal a vast array of wave activity on Jupiter and will serve to: 1) significantly improve the determination of the period and vertical descent velocity of Jupiter's QQO; 2) measure the zonal wavenumbers, vertical wavelengths, zonal group velocities and lifetimes of transient mid-latitude waves; and 3) record the thermal state of Jupiter's stratosphere in detail prior to, during, and after Juno's prime mission.

  5. A geographical information system model for creating bioclimatic maps - examples from a high, mid-latitude city.

    Science.gov (United States)

    Svensson, Marie K; Thorsson, Sofia; Lindqvist, Sven

    2003-03-01

    This paper presents a method for creating large-scale bioclimatic maps with the aid of a geographical information system, GIS. Meteorological data are linked with geographical information about land use, elevation and distance to the coast, in order to generate spatial distributions of physiological equivalent temperature, PET. The model combines an air temperature map and a wind map in order to create different zones for which the thermal component is to be calculated. The advantage of the model presented is that it uses generally available information about land use, altitude and distance to the coast. Further, the model uses a GIS application, which makes it non-static. Compared to most other models, a wide range of observations are used as input. Few biometeorological studies have been performed in high-latitude areas. This paper presents bioclimatic maps for the Göteborg urban area, in Sweden, for the month of July. The results show large variations in PET during a clear, calm day at 1200 hours (Delta T 13.4 degrees C) and during average conditions in July (Delta T 6.8 degrees C), which gives an indication of the magnitude and the spatial variations within high, midlatitude, urban area in summer. The highest PET values were found in the central built-up areas and the lowest PET values in the coastal and green areas. The model generates valuable information for urban planners and decision makers when planning and constructing new areas for outdoor activities etc. This information is also useful in the fields of health and energy.

  6. Ecosystem responses to recent oceanographic variability in high-latitude Northern Hemisphere ecosystems

    Science.gov (United States)

    Mueter, Franz J.; Broms, Cecilie; Drinkwater, Kenneth F.; Friedland, Kevin D.; Hare, Jonathan A.; Hunt, George L., Jr.; Melle, Webjørn; Taylor, Maureen

    2009-04-01

    As part of the international MENU collaboration, we compared and contrasted ecosystem responses to climate-forced oceanographic variability across several high latitude regions of the North Pacific (Eastern Bering Sea (EBS) and Gulf of Alaska (GOA)) and North Atlantic Oceans (Gulf of Maine/Georges Bank (GOM/GB) and the Norwegian/Barents Seas (NOR/BAR)). Differences in the nitrate content of deep source waters and incoming solar radiation largely explain differences in average primary productivity among these ecosystems. We compared trends in productivity and abundance at various trophic levels and their relationships with sea-surface temperature. Annual net primary production generally increases with annual mean sea-surface temperature between systems and within the EBS, BAR, and GOM/GB. Zooplankton biomass appears to be controlled by both top-down (predation by fish) and bottom-up forcing (advection, SST) in the BAR and NOR regions. In contrast, zooplankton in the GOM/GB region showed no evidence of top-down forcing but appeared to control production of major fish populations through bottom-up processes that are independent of temperature variability. Recruitment of several fish stocks is significantly and positively correlated with temperature in the EBS and BAR, but cod and pollock recruitment in the EBS has been negatively correlated with temperature since the 1977 shift to generally warmer conditions. In each of the ecosystems, fish species showed a general poleward movement in response to warming. In addition, the distribution of groundfish in the EBS has shown a more complex, non-linear response to warming resulting from internal community dynamics. Responses to recent warming differ across systems and appear to be more direct and more pronounced in the higher latitude systems where food webs and trophic interactions are simpler and where both zooplankton and fish species are often limited by cold temperatures.

  7. Demonstration of short-range wind lidar in a high-performance wind tunnel

    DEFF Research Database (Denmark)

    Pedersen, Anders Tegtmeier; Montes, Belen Fernández; Pedersen, Jens Engholm;

    A short-range continuous-wave coherent laser radar (lidar) has been tested in a high-performance wind tunnel for possible use as a standard component in wind tunnels. The lidar was tested in a low as well as a high speed regime ranging from 5-35 m/s and 40-75 m/s, respectively. In both low and hi...... future for short range lidars as a complement to LDA and other standard equipment in wind tunnels....

  8. Demonstration of short-range wind lidar in a high-performance wind tunnel

    DEFF Research Database (Denmark)

    Pedersen, Anders Tegtmeier; Montes, Belen Fernández; Pedersen, Jens Engholm;

    2012-01-01

    A short-range continuous-wave coherent laser radar (lidar) has been tested in a high-performance wind tunnel for possible use as a standard component in wind tunnels. The lidar was tested in a low as well as a high speed regime ranging from 5-35 m/s and 40-75 m/s, respectively. In both low and hi...... future for short range lidars as a complement to LDA and other standard equipment in wind tunnels....

  9. Variable responses of benthic communities to anomalously warm sea temperatures on a high-latitude coral reef.

    Science.gov (United States)

    Bridge, Tom C L; Ferrari, Renata; Bryson, Mitch; Hovey, Renae; Figueira, Will F; Williams, Stefan B; Pizarro, Oscar; Harborne, Alastair R; Byrne, Maria

    2014-01-01

    High-latitude reefs support unique ecological communities occurring at the biogeographic boundaries between tropical and temperate marine ecosystems. Due to their lower ambient temperatures, they are regarded as potential refugia for tropical species shifting poleward due to rising sea temperatures. However, acute warming events can cause rapid shifts in the composition of high-latitude reef communities, including range contractions of temperate macroalgae and bleaching-induced mortality in corals. While bleaching has been reported on numerous high-latitude reefs, post-bleaching trajectories of benthic communities are poorly described. Consequently, the longer-term effects of thermal anomalies on high-latitude reefs are difficult to predict. Here, we use an autonomous underwater vehicle to conduct repeated surveys of three 625 m(2) plots on a coral-dominated high-latitude reef in the Houtman Abrolhos Islands, Western Australia, over a four-year period spanning a large-magnitude thermal anomaly. Quantification of benthic communities revealed high coral cover (>70%, comprising three main morphospecies) prior to the bleaching event. Plating Montipora was most susceptible to bleaching, but in the plot where it was most abundant, coral cover did not change significantly because of post-bleaching increases in branching Acropora. In the other two plots, coral cover decreased while macroalgal cover increased markedly. Overall, coral cover declined from 73% to 59% over the course of the study, while macroalgal cover increased from 11% to 24%. The significant differences in impacts and post-bleaching trajectories among plots underline the importance of understanding the underlying causes of such variation to improve predictions of how climate change will affect reefs, especially at high-latitudes.

  10. Variable responses of benthic communities to anomalously warm sea temperatures on a high-latitude coral reef.

    Directory of Open Access Journals (Sweden)

    Tom C L Bridge

    Full Text Available High-latitude reefs support unique ecological communities occurring at the biogeographic boundaries between tropical and temperate marine ecosystems. Due to their lower ambient temperatures, they are regarded as potential refugia for tropical species shifting poleward due to rising sea temperatures. However, acute warming events can cause rapid shifts in the composition of high-latitude reef communities, including range contractions of temperate macroalgae and bleaching-induced mortality in corals. While bleaching has been reported on numerous high-latitude reefs, post-bleaching trajectories of benthic communities are poorly described. Consequently, the longer-term effects of thermal anomalies on high-latitude reefs are difficult to predict. Here, we use an autonomous underwater vehicle to conduct repeated surveys of three 625 m(2 plots on a coral-dominated high-latitude reef in the Houtman Abrolhos Islands, Western Australia, over a four-year period spanning a large-magnitude thermal anomaly. Quantification of benthic communities revealed high coral cover (>70%, comprising three main morphospecies prior to the bleaching event. Plating Montipora was most susceptible to bleaching, but in the plot where it was most abundant, coral cover did not change significantly because of post-bleaching increases in branching Acropora. In the other two plots, coral cover decreased while macroalgal cover increased markedly. Overall, coral cover declined from 73% to 59% over the course of the study, while macroalgal cover increased from 11% to 24%. The significant differences in impacts and post-bleaching trajectories among plots underline the importance of understanding the underlying causes of such variation to improve predictions of how climate change will affect reefs, especially at high-latitudes.

  11. High efficient wind-hydrogen facility

    Energy Technology Data Exchange (ETDEWEB)

    Bolcich, J.C. [Centro Atomico Bariloche, San Carlos de Bariloche, Rio Negro (Argentina); Bolcich, A.; Bolcich, D.; Wandyk, N. [ZVALT S.R.L., San Carlos de Bariloche, Rio Negro (Argentina)

    2001-06-01

    Considered a high efficiency and economical option for the conversion of wind energy, a new concept was developed in Patagonia, Argentina. It is called the Ducted Multirotor-Wind Energy Converter (DM-WEC) and was designed to be used in remote areas. Under study is the first prototype (10-30 Kilowatts), while the second prototype (3-5 Kilowatt) is being installed and is undergoing testing. This second prototype is of the multirotor type with the duct for air canalization as an added alternative. In this presentation, the authors described the technical attributes of the two prototypes and provided an evaluation of the potential for hydrogen production using small electrolysis units. They also included a comparison between the ducted and non-ducted prototypes with regard to maximum power attainable. The results obtained so far indicated that it represents an affordable energy source for remote areas with a higher power per unit cross section swept area. The rotating parts are encapsulated, reducing the noise level and vibrations. figs.

  12. Ulysses breaks latitude record

    Science.gov (United States)

    1993-06-01

    Ulysses is gathering important new information concerning the Sun and its environment. Its prime mission objective is to carry out the first systematic exploration of the inner part of the heliosphere - the region of space carved out of the interstellar medium by the solar wind - at all latitudes from the solar equator to the poles. The spacecraft, launched by the space shuttle Discovery on 6 October 1990 in the framework of an ESA-NASA collaborative venture, underwent a gravity assist manoeuvre at Jupiter in February 1992 and is now in a highly inclined solar orbit that will bring it over the south pole of the Sun in September 1994. At that time, Ulysses will establish a new record as it climbs to its maximum latitude of just over 80 degrees. The spacecraft and its scientific instruments are in excellent condition and the data coverage since launch has been consistently close to 100% thanks to the dedicated efforts of the joint ESA-NASA Mission Operations Team and NASA's Deep Space Network. Although the most exciting phase of the mission - the study of the Sun's polar regions - will only begin in mid-1994, Ulysses has already produced a wealth of new scientific results. These include : * - The first direct detection of neutral helium atoms arriving from interstellar space. * - The measurement of micron-sized dust grains arriving from interstellar space. * - The first measurement of singly-charged H, N, O and Ne ions which entered the heliosphere as interstellar neutral atoms and were then ionised. * - The highest-resolution measurements to date of the isotopic composition of cosmic ray nuclei (e.g. C, N, O, Ne, Si and Mg). In addition to the above, the traversal of Jupiter's magnetosphere at the time of the fly-by enabled the Ulysses investigators to acquire new and highly valuable data concerning this very complex and dynamic plasma environment. Among the more exciting results to emerge are the possible entry into the polar cap of Jupiter's magnetosphere near the

  13. Study of high-latitude ionosphere: One-year campaign over Husafell, Iceland

    Science.gov (United States)

    Bahari, S. A.; Abdullah, M.; Hasbi, A. M.; Yatim, B.; Suparta, W.; Kadokura, A.; Bjornsson, G.

    2016-07-01

    This paper reports on the effects of diurnal, seasonal, geomagnetic and solar activity on GPS Vertical Total Electron Content (VTEC) measurements at a high-latitude station in Husafell, Iceland (64.7°N, 21.0°W) from March 2009 to February 2010. According to the diurnal VTEC pattern, there was generally a build-up region at sunrise (0500-1000 LT), a daytime plateau in the afternoon (1200-1400 LT), and a decay region from evening to pre-dawn (1800-0400 LT). The month-to-month analysis showed high VTEC variability, particularly in February 2010, due to an increase in solar activity. The VTEC showed a high variability during both winter and the equinoxes, with the highest value being 90%, but showed a low variability in summer. Two abnormal peaks appeared at sunrise and sunset in winter and the equinoxes. These peaks were the result of steep density gradients caused by the onset and turnoff of solar radiation. The correlation analysis yielded almost no correlation between the VTEC and geomagnetic activity but showed a high correlation with solar activity for all the seasons, particularly at night-time.

  14. Verification of high-speed solar wind stream forecasts using operational solar wind models

    Science.gov (United States)

    Reiss, Martin A.; Temmer, Manuela; Veronig, Astrid M.; Nikolic, Ljubomir; Vennerstrom, Susanne; Schöngassner, Florian; Hofmeister, Stefan J.

    2016-07-01

    High-speed solar wind streams emanating from coronal holes are frequently impinging on the Earth's magnetosphere causing recurrent, medium-level geomagnetic storm activity. Modeling high-speed solar wind streams is thus an essential element of successful space weather forecasting. Here we evaluate high-speed stream forecasts made by the empirical solar wind forecast (ESWF) and the semiempirical Wang-Sheeley-Arge (WSA) model based on the in situ plasma measurements from the Advanced Composition Explorer (ACE) spacecraft for the years 2011 to 2014. While the ESWF makes use of an empirical relation between the coronal hole area observed in Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) images and solar wind properties at the near-Earth environment, the WSA model establishes a link between properties of the open magnetic field lines extending from the photosphere to the corona and the background solar wind conditions. We found that both solar wind models are capable of predicting the large-scale features of the observed solar wind speed (root-mean-square error, RMSE ≈100 km/s) but tend to either overestimate (ESWF) or underestimate (WSA) the number of high-speed solar wind streams (threat score, TS ≈ 0.37). The predicted high-speed streams show typical uncertainties in the arrival time of about 1 day and uncertainties in the speed of about 100 km/s. General advantages and disadvantages of the investigated solar wind models are diagnosed and outlined.

  15. On the importance of appropriate rain-gauge catch correction for hydrological modelling at mid to high latitudes

    Directory of Open Access Journals (Sweden)

    S. Stisen

    2012-03-01

    Full Text Available An existing rain gauge catch correction method addressing solid and liquid precipitation was applied both as monthly mean correction factors based on a 30 yr climatology (standard correction and as daily correction factors based on daily observations of wind speed and temperature (dynamic correction. The two methods resulted in different winter precipitation rates for the period 1990–2010. The resulting precipitation data sets were evaluated through the comprehensive Danish National Water Resources model (DK-Model revealing major differences in both model performance and optimized model parameter sets. Simulated stream discharge is improved significantly when introducing a dynamic precipitation correction, whereas the simulated hydraulic heads and multi-annual water balances performed similarly due to recalibration adjusting model parameters to compensate for input biases. The resulting optimized model parameters are much more physically plausible for the model based on dynamic correction of precipitation. A proxy-basin test where calibrated DK-Model parameters were transferred to another region without site specific calibration showed better performance for parameter values based on the dynamic correction. Similarly, the performances of the dynamic correction method were superior when considering two single years with a much dryer and a much wetter winter, respectively, as compared to the winters in the calibration period (differential split-sample tests. We conclude that dynamic precipitation correction should be carried out for studies requiring a sound dynamic description of hydrological processes and it is of particular importance when using hydrological models to make predictions for future climates when the snow/rain composition will differ from the past climate. This conclusion is expected to be applicable for mid to high latitudes especially in coastal climates where winter precipitation type (solid/liquid fluctuate significantly

  16. Clumped isotope thermometry of modern and early Cretaceous molluscan carbonate from high-latitude seas (Invited)

    Science.gov (United States)

    Henkes, G. A.; Price, G. D.; Ambrose, W. G.; Carroll, M. L.; Passey, B. H.

    2010-12-01

    The carbonate clumped isotope thermometer is based on the temperature sensitivity of the relative abundance of carbonate ion groups containing 13C-18O bonds. One application of clumped isotope thermometry is to determine the temperature of ancient seawater from the skeletal material of calcium carbonate-secreting marine organisms. The relationship between Δ47, a parameter describing isotopic clumping, and the temperature of carbonate biomineralization has been well-defined for fish otoliths, corals, foraminifera, and coccolithophore tests, but few data have been published for brachiopods and bivalve mollusks. A comprehensive evaluation of the Δ47-temperature relationship for mollusks is required for paleotemperature interpretations from the marine fossil record. Here we present a more comprehensive calibration for modern mollusks, including bivalves, cephalopods, and gastropods. Further, we focus on a subset of cold water, high-latitude species collected in the northern Barents Sea. The observed Δ47-temperature relationship is similar to the theoretical relationship presented by Guo et al. (2009) but deviates at low temperatures from the original Ghosh et al. (2007) calibration curve. This divergence could be related to methodological differences or unaccounted differences in the biomineralization of mollusks versus that of other carbonate-secreting organisms at low temperature. One advantage of clumped isotope thermometry over traditional oxygen isotope thermometry is that it does not require assumptions about the isotopic composition of the water in which the carbonate formed. This may be particularly useful in Mesozoic paleoceanography where the oxygen isotope value of seawater is uncertain. Using clumped isotope thermometry applied to early Cretaceous (Valangian) belemnite carbonate from the Yatria River, sub-polar Urals, Siberia, we find shell growth temperatures of 20-26°C at a paleolatitude of ~60-65°N. Our data imply average seawater δ18O values of 0

  17. Numerical Simulation of Atmosphere-Ocean-Sea Ice Interaction During Interannual Cycle in High Northern Latitudes

    Institute of Scientific and Technical Information of China (English)

    LIU Xiying; LIU Hailong; LI Wei; ZHANG Xuehong; YU Rucong; YU Yongqiang

    2008-01-01

    The interannual atmosphere-ocean-sea ice interaction (AOSI) in high northern latitudes is studied with a global atmosphere-ocean-sea ice coupled model system, in which the model components of atmosphere and land surface are from China National Climate Center and that of ocean and sea ice are from LASG,Institute of Atmospheric Physics, Chinese Academy of Sciences. A daily flux anomaly correction scheme is employed to couple the atmosphere model and the ocean model with the effect of inhomogenity of sea ice in high latitudes is considered. The coupled model system has been run for 50 yr and the results of the last 30 years are analyzed. After the sea level pressure (SLP), surface air temperature (SAT), sea surface temperature (SST), sea ice concentration (SIC), and sea surface sensible heat flux (SHF) are filtered with adigital filter firstly, their normalized anomalies are used to perform the decomposition of combined complex empirical orthogonal function (CCEOF) and then they are reconstructed with the leading mode. The atmosphere-ocean-sea ice interactions in high northern latitudes during a periodical cycle (approximately4 yr) are analyzed. It is shown that: (1) When the North Atlantic Oscillation (NAO) is in its positive phase, the southerly anomaly appears in the Greenland Sea, SAT increases, the sea loses less SHF, SST increases and SIC decreases accordingly; when the NAO is in its negative phase, the northerly anomaly appears in the Greenland Sea, SAT decreases, the sea loses more SHF, SST decreases and SIC increases accordingly. There are similar features in the Barents Sea, but the phase of evolution in the Barents Sea is different from that in the Greenland Sea. (2) For an average of multi-years, there is a cold center in the inner part of the Arctic Ocean near the North Pole. When there is an anomaly of low pressure, which is closer to the Pacific Ocean, in the inner part of the Arctic Ocean, anomalies of warm advection appear in the region near the

  18. Atmospheric teleconnections between the tropics and high southern latitudes during millennial climate change

    Science.gov (United States)

    Markle, Bradley; Steig, Eric; Schoenemann, Spruce; Buizert, Christo; Pedro, Joel; Bitz, Cecilia; Ding, Qinghua; Jones, Tyler; Fudge, Tyler

    2015-04-01

    Rapid climate changes, known as Dansgaard-Oeschger (DO) events, are ubiquitous over the last glacial period. DO climate anomalies are propagated globally through climatic teleconnections that are incompletely understood and insufficiently constrained by paleoclimatic data. Here we use a high-resolution deuterium excess record from West Antarctica to show that changes in the moisture sources for Antarctic precipitation occurred in-phase with the DO shifts in Northern Hemisphere (NH) climate and tropical hydrology. These results support the hypothesis that the Southern Hemisphere (SH) storm tracks migrate northwards during NH warm periods, in parallel with the well-established northward migration of the intertropical convergence zone. Variability in the deuterium excess record also suggests that Southern Ocean sea surface temperatures (SST) followed the pattern of Antarctic surface temperatures -- out of phase with NH climate, as expected from conceptual and numerical models of the ocean bipolar "seesaw" mechanism. Furthermore, using a physically-based definition of the deuterium excess parameter, we show East Antarctic records are highly coherent with the WAIS Divide record, indicating that the SST changes are zonally uniform. Our data demonstrate that both atmospheric and oceanic teleconnections couple climate variations between the NH and SH high latitudes, and constrain the timescales on which they operate.

  19. Forecasts for the WFIRST High Latitude Survey using the BLUETIDES Simulation

    Science.gov (United States)

    Waters, Dacen; Di Matteo, Tiziana; Feng, Yu; Wilkins, Stephen M.; Croft, Rupert A. C.

    2016-08-01

    We use the BLUETIDES simulation to predict the properties of the high-z galaxy and active galactic nuclei (AGN) populations for the planned 2200deg2 Wide-Field Infrared Survey Telescope's (WFIRST) High Latitude Survey (HLS). BLUETIDES is a cosmological hydrodynamic simulation, which incorporates a variety of baryon physics in a (400h-1Mpc)3 volume evolved to z = 8 with 0.7 trillion particles. The galaxy luminosity functions in the simulation show good agreement with all the current observational constraints (up to z = 11) and predicts an enhanced number of UV bright galaxies. At the proposed depth of the HLS (mUV luminosity function. At z = 8, galaxies in the mock HLS have specific star formation rates of ˜10Gyr-1 and ages of ˜80Myr (both evolving linearly with redshift) and a non-evolving mass-metallicity relation. BLUETIDES also predicts ˜104 AGN in WFIRST HLS from z = 8 out to z ˜ 14. These AGN host black holes of M ˜ 106 - 108M⊙ accreting close to their Eddington luminosity. Galaxies and AGN have host halo masses of Mhalo ˜ 1011 - 12M⊙ and a linear bias b ≈ 13 - 20. Given the expected galaxy space densities, their high bias and large volume probed we speculate that it may be feasible for WFIRST HLS detect the Baryon Acoustic Oscillation peak in the galaxy power spectrum out to z = 8 - 9.

  20. Seasonal and diurnal variability of the meteor flux at high latitudes observed using PFISR

    Science.gov (United States)

    Sparks, J. J.; Janches, D.; Nicolls, M. J.; Heinselman, C. J.

    2009-05-01

    We report in this and a companion paper [Fentzke, J.T., Janches, D., Sparks, J.J., 2008. Latitudinal and seasonal variability of the micrometeor input function: A study using model predictions and observations from Arecibo and PFISR. Journal of Atmospheric and Solar-Terrestrial Physics, this issue, doi:10.1016/j.jastp.2008.07.015] a complete seasonal study of the micrometeor input function (MIF) at high latitudes using meteor head-echo radar observations performed with the Poker Flat Incoherent Scatter Radar (PFISR). This flux is responsible for a number of atmospheric phenomena; for example, it could be the source of meteoric smoke that is thought to act as condensation nuclei in the formation of ice particles in the polar mesosphere. The observations presented here were performed for full 24-h periods near the summer and winter solstices and spring and autumn equinoxes, times at which the seasonal variability of the MIF is predicted to be large at high latitudes [Janches, D., Heinselman, C.J., Chau, J.L., Chandran, A., Woodman, R., 2006. Modeling of the micrometeor input function in the upper atmosphere observed by High Power and Large Aperture Radars, JGR, 11, A07317, doi:10.1029/2006JA011628]. Precise altitude and radar instantaneous line-of-sight (radial) Doppler velocity information are obtained for each of the hundreds of events detected every day. We show that meteor rates, altitude, and radial velocity distributions have a large seasonal dependence. This seasonal variability can be explained by a change in the relative location of the meteoroid sources with respect to the observer. Our results show that the meteor flux into the upper atmosphere is strongly anisotropic and its characteristics must be accounted for when including this flux into models attempting to explain related aeronomical phenomena. In addition, the measured acceleration and received signal strength distribution do not seem to depend on season; which may suggest that these observed

  1. Shallow food for deep divers: Dynamic foraging behavior of male sperm whales in a high latitude habitat

    DEFF Research Database (Denmark)

    Teloni, Valeria; Johnson, M.P.; Miller, P.J.O.

    2008-01-01

    Groups of female and immature sperm whales live at low latitudes and show a stereotypical diving and foraging behavior with dives lasting about 45 min to depths of between 400 and 1200 m. In comparison, physically mature male sperm whales migrate to high latitudes where little is known about...... their foraging behavior and ecology. Here we use acoustic recording tags to study the diving and acoustic behavior of male sperm whales foraging off northern Norway. Sixty-five hours of tag data provide detailed information about the movements and sound repertoire of four male sperm whales performing 83 dives...... epipelagic prey, is consistent with the hypothesis that male sperm whales may migrate to high latitudes to access a productive, multi-layered foraging habitat....

  2. Energetic particle fluxes in the exterior cusp and the high-latitude dayside magnetosphere: statistical results from the Cluster/RAPID instrument

    Directory of Open Access Journals (Sweden)

    T. Asikainen

    2005-09-01

    Full Text Available In this paper we study the fluxes of energetic protons (30–4000 keV and electrons (20–400 keV in the exterior cusp and in the adjacent high-latitude dayside plasma sheet (HLPS with the Cluster/RAPID instrument. Using two sample orbits we demonstrate that the Cluster observations at high latitudes can be dramatically different because the satellite orbit traverses different plasma regions for different external conditions. We make a statistical study of energetic particles in the exterior cusp and HLPS by analysing all outbound Cluster dayside passes in February and March, 2002 and 2003. The average particle fluxes in HLPS are roughly three (protons or ten (electrons times larger than in the exterior cusp. This is also true on those Cluster orbits where both regions are visited within a short time interval. Moreover, the total electron fluxes, as well as proton fluxes above some 100 keV, in these two regions correlate with each other. This is true even for fluxes in every energy channel when considered separately. The spectral indices of electron and proton fluxes are the same in the two regions. We also examine the possible dependence of particle fluxes at different energies on the external (solar wind and IMF and internal (geomagnetic conditions. The energetic proton fluxes (but not electron fluxes in the cusp behave differently at low and high energies. At low energies (<70 keV, the fluxes increase strongly with the magnitude of IMF By. Instead, at higher energies the proton fluxes in the cusp depend on substorm/geomagnetic activity. In HLPS proton fluxes, irrespective of energy, depend strongly on the Kp and AE indices. The electron fluxes in HLPS depend both on the <Kp index and the solar wind speed. In the cusp the electron fluxes mainly depend on the solar wind speed, and are higher for northward than southward IMF. These results give strong evidence in favour of the idea that the

  3. Accuracy analysis of continuous deformation monitoring using BeiDou Navigation Satellite System at middle and high latitudes in China

    Science.gov (United States)

    Jiang, Weiping; Xi, Ruijie; Chen, Hua; Xiao, Yugang

    2017-02-01

    As BeiDou Navigation Satellite System (BDS) has been operational in the whole Asia-Pacific region, it means a new GNSS system with a different satellite orbit structure will become available for deformation monitoring in the future. Conversely, GNSS deformation monitoring data are always processed with a regular interval to form displacement time series for deformation analysis, where the interval can neither be too long from the time perspective nor too short from the precision of determined displacements angle. In this paper, two experimental platforms were designed, with one being at mid-latitude and another at higher latitude in China. BDS data processing software was also developed for investigating the accuracy of continuous deformation monitoring using current in-orbit BDS satellites. Data over 20 days at both platforms were obtained and were processed every 2, 4 and 6 h to generate 3 displacement time series for comparison. The results show that with the current in-orbit BDS satellites, in the mid-latitude area it is easy to achieve accuracy of 1 mm in horizontal component and 2-3 mm in vertical component; the accuracy could be further improved to approximately 1 mm in both horizontal and vertical directions when combined BDS/GPS measurements are employed. At higher latitude, however, the results are not as good as expected due to poor satellite geometry, even the 6 h solutions could only achieve accuracy of 4-6 and 6-10 mm in horizontal and vertical components, respectively, which implies that it may not be applicable to very high-precision deformation monitoring at high latitude using the current BDS. With the integration of BDS and GPS observations, however, in 4-h session, the accuracy can achieve 2 mm in horizontal component and 4 mm in vertical component, which would be an optimal choice for high-accuracy structural deformation monitoring at high latitude.

  4. High prevalence and no latitude gradient of multiple sclerosis in Norway.

    Science.gov (United States)

    Berg-Hansen, P; Moen, S M; Harbo, H F; Celius, E G

    2014-11-01

    The prevalence of multiple sclerosis (MS) is increasing, and the presence of a latitude gradient for MS risk is still discussed. We present the first nationwide prevalence estimates for Norway, spanning the latitudes from 58-71 degrees North, in order to identify a possible latitude gradient. Information from the Oslo MS Registry and the Norwegian MS Registry and Biobank was combined with data from the Norwegian Patient Registry, the Norwegian Prescription Database and Statistics Norway. We estimated a crude prevalence of 203/100,000 on 1 January 2012. The prevalence in the Northern and Southern regions were not significantly different. MS prevalence in Norway is among the highest reported worldwide. We found no evidence of a latitude gradient.

  5. Quantifying Black Carbon emissions in high northern latitudes using an Atmospheric Bayesian Inversion

    Science.gov (United States)

    Evangeliou, Nikolaos; Thompson, Rona; Stohl, Andreas; Shevchenko, Vladimir P.

    2016-04-01

    Black carbon (BC) is the main light absorbing aerosol species and it has important impacts on air quality, weather and climate. The major source of BC is incomplete combustion of fossil fuels and the burning of biomass or bio-fuels (soot). Therefore, to understand to what extent BC affects climate change and pollutant dynamics, accurate knowledge of the emissions, distribution and variation of BC is required. Most commonly, BC emission inventory datasets are built by "bottom up" approaches based on activity data and emissions factors, but these methods are considered to have large uncertainty (Cao et al, 2006). In this study, we have used a Bayesian Inversion to estimate spatially resolved BC emissions. Emissions are estimated monthly for 2014 and over the domain from 180°W to 180°E and 50°N to 90°N. Atmospheric transport is modeled using the Lagrangian Particle Dispersion Model, FLEXPART (Stohl et al., 1998; 2005), and the inversion framework, FLEXINVERT, developed by Thompson and Stohl, (2014). The study domain is of particular interest concerning the identification and estimation of BC sources. In contrast to Europe and North America, where BC sources are comparatively well documented as a result of intense monitoring, only one station recording BC concentrations exists in the whole of Siberia. In addition, emissions from gas flaring by the oil industry have been geographically misplaced in most emission inventories and may be an important source of BC at high latitudes since a significant proportion of the total gas flared occurs at these high latitudes (Stohl et al., 2013). Our results show large differences with the existing BC inventories, whereas the estimated fluxes improve modeled BC concentrations with respect to observations. References Cao, G. et al. Atmos. Environ., 40, 6516-6527, 2006. Stohl, A. et al. Atmos. Environ., 32(24), 4245-4264, 1998. Stohl, A. et al. Atmos. Chem. Phys., 5(9), 2461-2474, 2005. Stohl, A. et al. Atmos. Chem. Phys., 13

  6. Ocean acidification at high latitudes: potential effects on functioning of the Antarctic bivalve Laternula elliptica.

    Directory of Open Access Journals (Sweden)

    Vonda Cummings

    Full Text Available Ocean acidification is a well recognised threat to marine ecosystems. High latitude regions are predicted to be particularly affected due to cold waters and naturally low carbonate saturation levels. This is of concern for organisms utilising calcium carbonate (CaCO(3 to generate shells or skeletons. Studies of potential effects of future levels of pCO(2 on high latitude calcifiers are at present limited, and there is little understanding of their potential to acclimate to these changes. We describe a laboratory experiment to compare physiological and metabolic responses of a key benthic bivalve, Laternula elliptica, at pCO(2 levels of their natural environment (430 µatm, pH 7.99; based on field measurements with those predicted for 2100 (735 µatm, pH 7.78 and glacial levels (187 µatm, pH 8.32. Adult L. elliptica basal metabolism (oxygen consumption rates and heat shock protein HSP70 gene expression levels increased in response both to lowering and elevation of pH. Expression of chitin synthase (CHS, a key enzyme involved in synthesis of bivalve shells, was significantly up-regulated in individuals at pH 7.78, indicating L. elliptica were working harder to calcify in seawater undersaturated in aragonite (Ω(Ar = 0.71, the CaCO(3 polymorph of which their shells are comprised. The different response variables were influenced by pH in differing ways, highlighting the importance of assessing a variety of factors to determine the likely impact of pH change. In combination, the results indicate a negative effect of ocean acidification on whole-organism functioning of L. elliptica over relatively short terms (weeks-months that may be energetically difficult to maintain over longer time periods. Importantly, however, the observed changes in L. elliptica CHS gene expression provides evidence for biological control over the shell formation process, which may enable some degree of adaptation or acclimation to future ocean acidification scenarios.

  7. Ionospheric Correction of InSAR for Accurate Ice Motion Mapping at High Latitudes

    Science.gov (United States)

    Liao, H.; Meyer, F. J.

    2016-12-01

    Monitoring the motion of the large ice sheets is of great importance for determining ice mass balance and its contribution to sea level rise. Recently the first comprehensive ice motion of the Greenland and the Antarctica have been generated with InSAR. However, these studies have indicated that the performance of InSAR-based ice motion mapping is limited by the presence of the ionosphere. This is particularly true at high latitudes and for low-frequency SAR data. Filter-based and empirical methods (e.g., removing polynomials), which have often been used to mitigate ionospheric effects, are often ineffective in these areas due to the typically strong spatial variability of ionospheric phase delay in high latitudes and due to the risk of removing true deformation signals from the observations. In this study, we will first present an outline of our split-spectrum InSAR-based ionospheric correction approach and particularly highlight how our method improves upon published techniques, such as the multiple sub-band approach to boost estimation accuracy as well as advanced error correction and filtering algorithms. We applied our work flow to a large number of ionosphere-affected dataset over the large ice sheets to estimate the benefit of ionospheric correction on ice motion mapping accuracy. Appropriate test sites over Greenland and the Antarctic have been chosen through cooperation with authors (UW, Ian Joughin) of previous ice motion studies. To demonstrate the magnitude of ionospheric noise and to showcase the performance of ionospheric correction, we will show examples of ionospheric-affected InSAR data and our ionosphere corrected result for comparison in visual. We also compared the corrected phase data to known ice velocity fields quantitatively for the analyzed areas from experts in ice velocity mapping. From our studies we found that ionospheric correction significantly reduces biases in ice velocity estimates and boosts accuracy by a factor that depends on a

  8. MITHRAS: A Program of Simultaneous Radar Observations of the High-Latitude Auroral Zone.

    Science.gov (United States)

    1982-11-01

    CHATANIKA AND MILL - STONE HILL. The vertical arrow indicates local midnight. 29 electron densities. The nighttime minima are not as well reproduced by the... Nuit de Haute Latitude," Proceedings of GRECO Conference, Grenoble, France (September 1982). Senior, C., P. Bauer, C. Taieb, and Michel Petit, "Le R61e...Alignis, Precipitations Diffuses et Electrojets dans le Secteur Nuit de Haute Latitude," C. Senior, Proceedings of GRECO Conference, Grenoble, 1982. 0"On

  9. Lake trout otolith chronologies as multidecadal indicators of high-latitude freshwater ecosystems

    Science.gov (United States)

    Black, B.A.; Von Biela, V.R.; Zimmerman, C.E.; Brown, Randy J.

    2013-01-01

    High-latitude ecosystems are among the most vulnerable to long-term climate change, yet continuous, multidecadal indicators by which to gauge effects on biology are scarce, especially in freshwater environments. To address this issue, dendrochronology (tree-ring analysis) techniques were applied to growth-increment widths in otoliths from lake trout (Salvelinus namaycush) from the Chandler Lake system, Alaska (68.23°N, 152.70°W). All otoliths were collected in 1987 and exhibited highly synchronous patterns in growth-increment width. Increments were dated, the widths were measured, and age-related growth declines were removed using standard dendrochronology techniques. The detrended time series were averaged to generate an annually resolved chronology, which continuously spanned 1964–1984. The chronology positively and linearly correlated with August air temperature over the 22-year interval (p productivity. Given the broad distribution of lake trout within North America, this study suggests that otolith chronologies could be used to examine responses between freshwater ecosystems and environmental variability across a range of temporal and spatial scales.

  10. An accelerating high-latitude jet in Earth’s core

    Science.gov (United States)

    Livermore, Philip W.; Hollerbach, Rainer; Finlay, Christopher C.

    2017-01-01

    Observations of the change in Earth’s magnetic field--the secular variation--provide information about the motion of liquid metal within the core that is responsible for the magnetic field’s generation. High-resolution observations from the European Space Agency’s Swarm satellite mission show intense field change at high latitude, localized in a distinctive circular daisy-chain configuration centred on the north geographic pole. Here we show that this feature can be explained by a localized, non-axisymmetric, westward jet of 420 km width on the tangent cylinder, the cylinder of fluid within the core that is aligned with the rotation axis and tangent to the solid inner core. We find that the jet has increased in magnitude by a factor of three over the period 2000-2016 to about 40 km yr-1, and is now much stronger than typical large-scale flows inferred for the core. We suggest that the current accelerating phase may be part of a longer-term fluctuation of the jet causing both eastward and westward movement of magnetic features over historical periods, and may contribute to recent changes in torsional-wave activity and the rotation direction of the inner core.

  11. High-latitude HF Doppler observations of ULF waves: 2. Waves with small spatial scale sizes

    Directory of Open Access Journals (Sweden)

    D. M. Wright

    Full Text Available The DOPE (Doppler Pulsation Experiment HF Doppler sounder located near Tromsø, Norway (geographic: 69.6°N 19.2°E; L = 6.3 is deployed to observe signatures, in the high-latitude ionosphere, of magnetospheric ULF waves. A type of wave has been identified which exhibits no simultaneous ground magnetic signature. They can be subdivided into two classes which occur in the dawn and dusk local time sectors respectively. They generally have frequencies greater than the resonance fundamentals of local field lines. It is suggested that these may be the signatures of high-m ULF waves where the ground magnetic signature has been strongly attenuated as a result of the scale size of the waves. The dawn population demonstrate similarities to a type of magnetospheric wave known as giant (Pg pulsations which tend to be resonant at higher harmonics on magnetic field lines. In contrast, the waves occurring in the dusk sector are believed to be related to the storm-time Pc5s previously reported in VHF radar data. Dst measurements support these observations by indicating that the dawn and dusk classes of waves occur respectively during geomagnetically quiet and more active intervals.

    Key words. Ionosphere (auroral ionosphere; ionosphere-magnetosphere interactions · Magnetospheric physics (MHD waves and instabilities

  12. Ultraviolet, optical, and infrared observations of the high-latitude molecular cloud toward HD 210121

    Science.gov (United States)

    Welty, Daniel E.; Fowler, James R.

    1992-01-01

    Low-resolution UV spectra of the B3 V star HD 210121, located behind the high-latitude molecular cloud DBB 80, yield an extinction curve exhibiting a far-UV rise that is among the steepest known. The apparently simple line of sight affords an excellent opportunity for investigating the absorption and emission characteristics of a single, isolated interstellar cloud characterized by extreme UV extinction. The low ratios of the IRAS bands with respect to I(100 microns) suggest that the radiation field incident on the cloud is lower than the average interstellar field, with further attenuation of the field within the cloud. The apparent relative enhancement of I(12 microns) compared with models of dust emission, and the extremely steep far-UV extinction together are consistent with the presence of an enhanced population of very small grains; the normal calcium depletion suggests that there has been little wholesale grain destruction. The steep far-UV extinction may help to explain the relatively high abundances of CO and CN. The disagreement in density for this cloud inferred from C2 absorption versus that inferred from CO emission may be due in part to clumping in the gas sample by the radio beams.

  13. Multiwavelength study of the high-latitude cloud L1642: chain of star formation

    CERN Document Server

    Malinen, J; Zahorecz, S; Rivera-Ingraham, A; Montillaud, J; Arimatsu, K; Bernard, J -Ph; Doi, Y; Haikala, L; Kawabe, R; Marton, G; McGehee, P; Pelkonen, V -M; Ristorcelli, I; Shimajiri, Y; Takita, S; Toth, L V; Tsukagoshi, T; Ysard, N

    2014-01-01

    L1642 is one of the two high galactic latitude (|b| > 30deg) clouds confirmed to have active star formation. We examine the properties of this cloud, especially the large-scale structure, dust properties, and compact sources in different stages of star formation. We present high-resolution far-infrared and submm observations with the Herschel and AKARI satellites and mm observations with the AzTEC/ASTE telescope, which we combined with archive data from near- and mid-infrared (2MASS, WISE) to mm observations (Planck). The Herschel observations, combined with other data, show a sequence of objects from a cold clump to young stellar objects at different evolutionary stages. Source B-3 (2MASS J04351455-1414468) appears to be a YSO forming inside the L1642 cloud, instead of a foreground brown dwarf, as previously classified. Herschel data reveal striation in the diffuse dust emission around L1642. The western region shows striation towards NE and has a steeper column density gradient on its southern side. The den...

  14. Seasonal changes in H/V spectral ratio at high-latitude seismic stations

    Science.gov (United States)

    Lee, R. F.; Abbott, R. E.; Knox, H. A.; Pancha, A.

    2014-12-01

    We present results demonstrating seasonal variations in the Horizontal-to-Vertical Spectral Ratio (HVSR) at high-latitude seismic stations. We analyze data from two sites at Poker Flat Research Range, near Fairbanks, Alaska. From the first site, we analyze 3 stations installed by Sandia National Labs (SNL) in a valley with marshy summer conditions. We also analyze the PASSCAL Instrument Center station PIC2, which is installed on rock approximately 3.2 km from the SNL stations. These stations continuously record data at 125 (SNL) and 200 (PIC2) samples per second. Seasonal changes in HVSR at high frequencies (> 20 Hz) appear to be caused by impedance contrasts between frozen and thawed ground. Thawed active layers are known to have slower shear-wave velocities than frozen layers or bedrock. An estimate of active layer thickness at each station is obtained from the quarter-wavelength approximation. We verify the accuracy of this technique by obtaining ground-truth measurements at the sites for both thickness and shear-wave velocity. We use physical probing for the thickness measurements and active-source Refraction-Microtremor (ReMi) surveys for the shear-wave velocities. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000

  15. An accelerating high-latitude jet in Earth’s core

    DEFF Research Database (Denmark)

    W. Livermore, Philip; Hollerbach, Rainer; Finlay, Chris

    2016-01-01

    Observations of the change in Earth’s magnetic field—the secular variation—provide information about the motion of liquid metal within the core that is responsible for the magnetic field’s generation. High-resolution observations from the European Space Agency’s Swarm satellite mission show intense...... field change at high latitude, localized in a distinctive circular daisy-chain configuration centred on the north geographic pole. Here we show that this feature can be explained by a localized, non-axisymmetric, westward jet of 420 km width on the tangent cylinder, the cylinder of fluid within the core...... that is aligned with the rotation axis and tangent to the solid inner core. We find that the jet has increased in magnitude by a factor of three over the period 2000–2016 to about 40 km yr−1, and is now much stronger than typical large-scale flows inferred for the core. We suggest that the current accelerating...

  16. GPS scintillations and total electron content climatology in the southern low, middle and high latitude regions

    Directory of Open Access Journals (Sweden)

    Luca Spogli

    2013-06-01

    Full Text Available In recent years, several groups have installed high-frequency sampling receivers in the southern middle and high latitude regions, to monitor ionospheric scintillations and the total electron content (TEC changes. Taking advantage of the archive of continuous and systematic observations of the ionosphere on L-band by means of signals from the Global Positioning System (GPS, we present the first attempt at ionospheric scintillation and TEC mapping from Latin America to Antarctica. The climatology of the area considered is derived through Ground-Based Scintillation Climatology, a method that can identify ionospheric sectors in which scintillations are more likely to occur. This study also introduces the novel ionospheric scintillation 'hot-spot' analysis. This analysis first identifies the crucial areas of the ionosphere in terms of enhanced probability of scintillation occurrence, and then it studies the seasonal variation of the main scintillation and TEC-related parameters. The results produced by this sophisticated analysis give significant indications of the spatial/ temporal recurrences of plasma irregularities, which contributes to the extending of current knowledge of the mechanisms that cause scintillations, and consequently to the development of efficient tools to forecast space-weather-related ionospheric events.

  17. Longitudinal Distribution of the Dayside Ionosphere of Mars at High Latitude

    Science.gov (United States)

    Haider, S. A.; Sheel, Varun; Singh, V.; Maguire, W. C.; Molina-Cuberos, G. J.

    2009-03-01

    Accelerometer and radio science data obtained from Mars Global Surveyor have been used to study the longitudinal structure of thermosphere and troposphere of Mars at high latitude region. These datasets represent primary and secondary ionization peaks at altitudes 130 km and 122 km, respectively. These peaks are reproduced by photoionization and photoelectron impact processes. The production rates of different ions are estimated in the thermosphere and troposphere at solar zenith angle 80°, using analytical yield spectrum and energy loss models, respectively. The electron densities are calculated under photochemical equilibrium condition. The impact ionization sources are taken as EUV and galactic cosmic rays. The characteristics of longitudinal distribution of production and density are fitted up to waves 2 and 3 by least square method with 0.95 confidence limits. The peak electron density in the troposphere is obtained at an altitude of 30 km due to high efficiency of electron attachment to Ox molecules, which entails that concentration of negative ions is higher than that of electron below 30 km. Of the 35 ions considered in the model, the densities of electron and nine major ions (H3O+(H2O)n for n = 1,2,3,4, notation="LaTeX">CO^{-}_{4}, notation="LaTeX">CO^{-}_{3}, notation="LaTeX">NO^{-}_{2}H_{2}O, and notation="LaTeX">CO^{-}_{3}(H_{2}O)_{n} for n = 1,2) are discussed.

  18. Ultraviolet, optical, and infrared observations of the high-latitude molecular cloud toward HD 210121

    Science.gov (United States)

    Welty, Daniel E.; Fowler, James R.

    1992-01-01

    Low-resolution UV spectra of the B3 V star HD 210121, located behind the high-latitude molecular cloud DBB 80, yield an extinction curve exhibiting a far-UV rise that is among the steepest known. The apparently simple line of sight affords an excellent opportunity for investigating the absorption and emission characteristics of a single, isolated interstellar cloud characterized by extreme UV extinction. The low ratios of the IRAS bands with respect to I(100 microns) suggest that the radiation field incident on the cloud is lower than the average interstellar field, with further attenuation of the field within the cloud. The apparent relative enhancement of I(12 microns) compared with models of dust emission, and the extremely steep far-UV extinction together are consistent with the presence of an enhanced population of very small grains; the normal calcium depletion suggests that there has been little wholesale grain destruction. The steep far-UV extinction may help to explain the relatively high abundances of CO and CN. The disagreement in density for this cloud inferred from C2 absorption versus that inferred from CO emission may be due in part to clumping in the gas sample by the radio beams.

  19. Non-native and native organisms moving into high elevation and high latitude ecosystems in an era of climate change

    DEFF Research Database (Denmark)

    Pauchard, Aníbal; Milbau, Ann; Albihn, Ann;

    2016-01-01

    Cold environments at high elevation and high latitude are often viewed as resistant to biological invasions. However, climate warming, land use change and associated increased connectivity all increase the risk of biological invasions in these environments. Here we present a summary of the key...... discussions of the workshop ‘Biosecurity in Mountains and Northern Ecosystems: Current Status and Future Challenges’ (Flen, Sweden, 1–3 June 2015). The aims of the workshop were to (1) increase awareness about the growing importance of species expansion—both non-native and native—at high elevation and high......, especially if it is coupled with prioritisation schemes for targeting invaders likely to have greatest impact. Communication and co-operation between cold environment regions will facilitate rapid response, and maximise the use of limited research and management resources....

  20. Using operationally synthesized multiple-Doppler winds for high resolution horizontal wind forecast verification

    Science.gov (United States)

    Bousquet, Olivier; Montmerle, Thibaut; Tabary, Pierre

    2008-05-01

    The potential value of operational Doppler radar networks for high resolution wind forecast verification is investigated through comparing wind outputs of the cloud resolving model AROME against newly available operational multiple-Doppler winds in northern France. Quantitative comparisons of radar and model winds for a 16-h frontal precipitation event show good agreement, with differences in wind speed (resp. direction) generally comprised between +/-2.5 m.s-1 (resp. +/-15°). Power spectra deduced from the scale decomposition of radar and model outputs also show good agreement through all scales. The method is also applied to validate the divergence structures as analyzed by AROME's 3Dvar assimilation system that considers, among a comprehensive set of observation types, the same radial velocities than those considered in the wind retrieval.

  1. The Geographic Distribution of Boulder Halo Craters at Mid-to-High Latitudes on Mars

    Science.gov (United States)

    Rader, L. X.; Fassett, C. I.; Levy, J. S.; King, I. R.; Chaffey, P. M.; Wagoner, C. M.; Hanlon, A. E.; Watters, J. L.; Kreslavsky, M. A.; Holt, J. W.; Dyar, M. D.

    2017-01-01

    Extensive evidence exists for ground ice at mid-to-high latitudes on Mars, including results from neutron spectroscopy [1-3], thermal properties [4-5], geomorphology [e.g., 6-9], and the in situ observations of Mars Phoenix [10]. This ground ice has been hypothesized to be emplaced diffusively and fill pores [11], or to have accumulated by ice and dust deposition that draped or mantled the terrain [7, 12]. These two processes are not mutually exclusive; both potentially have occurred on Mars [5]. One of the landforms found in areas where ground ice is common on Mars are boulder halo craters [e.g., 13-15] (Figure 1), which are topographically muted impact craters that are filled by ice-rich regolith. They are outlined by boulders that trace a circular outline of the original crater rim. Boulder halos generally have distinctly higher boulder densities than the surrounding background plains and have few boulders in their interiors. The mechanism of boulder halo crater formation is somewhat uncertain. Our working model is that an impact event occurs with sufficient size to excavate to a depth greater than the boulder-poor, ice-rich soils. Excavated boulders are deposited around the crater's rim and in its proximal ejecta. Quite rapidly [14], the crater becomes infilled by icy soil. Rather than being buried, boulders in the halo remain at the surface, perhaps be-cause they 'float' relative to finer-grained materials [14, 16]. Regardless of the details of this process, the life-time of boulders at the surface is much greater than the timescale needed to remove most of the craters' topography. Physical weathering of rocks must be greatly out-paced by crater infilling (the opposite of what is typical, e.g., on the Moon [17]). The rapidity of this infilling is easiest to understand if icy mantling material is deposited and accumulates, rather than simply being added by pore filling of soils. If this model is correct, boulder halos only form when they excavate rock

  2. Evidence for a very low-column density hole in the Galactic halo in the direction of the high latitude molecular cloud MBM 16

    CERN Document Server

    Liu, Wenhao; Ursino, Eugenio

    2015-01-01

    Shadow observations are the only way to observe emission from the galactic halo (GH) and/or the circumgalactic medium (CGM) free of any foreground contamination from local hot bubble (LHB) and solar wind charge exchange (SWCX). We analyzed data from a shadow observation in the direction of the high latitude, neutral hydrogen cloud MBM 16 with \\Suzaku. We found that all emission can be accounted for by foreground emission from LHB and SWCX, plus power law emission associated with unresolved point sources. The GH/CGM in the direction of MBM 16 is negligible or inexistent in our observation, with upper limits on the emission measure of 9.5x10^{-4} pc cm^{-6} (90% C.L.), at the lowest end of current estimates.

  3. Evidence for a Very Low-column Density Hole in the Galactic Halo in the Direction of the High Latitude Molecular Cloud MBM 16

    Science.gov (United States)

    Liu, W.; Galeazzi, M.; Ursino, E.

    2016-01-01

    Shadow observations are the only way to observe emission from the galactic halo (GH) and/or the circumgalactic medium (CGM) free of any foreground contamination from local hot bubble (LHB) and solar wind charge exchange (SWCX). We analyzed data from a shadow observation in the direction of the high latitude, neutral hydrogen cloud MBM 16 with Suzaku. We found that all emission can be accounted for by foreground emission from LHB and SWCX, plus power-law emission associated with unresolved point sources. The GH/CGM in the direction of MBM 16 is negligible or inexistent in our observation, with upper limits on the emission measure of 9× {10}-4 pc cm-6 (90% C.L.-solar metallicity), at the lowest end of current estimates.

  4. Coral bleaching on high-latitude marginal reefs at Sodwana Bay, South Africa

    Energy Technology Data Exchange (ETDEWEB)

    Celliers, Louis; Schleyer, Michael H

    2002-12-01

    Coral bleaching, involving the expulsion of symbiotic zooxanthellae from the host cells, poses a major threat to coral reefs throughout their distributional range. The role of temperature in coral bleaching has been extensively investigated and is widely accepted. A bleaching event was observed on the marginal high-latitude reefs of South Africa located at Sodwana Bay during the summer months of 2000. This was associated with increased sea temperatures with high seasonal peaks in summer and increased radiation in exceptionally clear water. The bleaching was limited to Two-mile Reef and Nine-mile Reef at Sodwana Bay and affected <12% of the total living cover on Two-mile Reef. Montipora spp., Alveopora spongiosa and Acropora spp. were bleached, as well as some Alcyoniidae (Sinularia dura, Lobophytum depressum, L. patulum). A cyclical increase in sea temperature (with a period of 5-6 years) was recorded during 1998-2000 in addition to the regional temperature increase caused by the El Nino Southern Oscillation phenomenon. The mean sea temperature increased at a rate of 0.27 deg. C year{sup -1} from May 1994 to April 2000. High maximum temperatures were measured (>29 deg. C). The lowest mean monthly and the mean maximum monthly temperatures at which coral bleaching occurred were 27.5 and 28.8 deg. C, respectively, while the duration for which high temperatures occurred in 2000 was 67 days at {>=}27.5 deg. C (4 days at {>=}28.8 deg. C). Increased water clarity and radiation appeared to be a synergistic cause in the coral bleaching encountered at Sodwana Bay.

  5. Dust in High Latitudes in the Community Earth System Model since the Last Glacial Maximum

    Science.gov (United States)

    Albani, S.; Mahowald, N. M.

    2015-12-01

    Earth System Models are one of the main tools in modern climate research, and they provide the means to produce future climate projections. Modeling experiments of past climates is one of the pillars of the Coupled Modelling Inter-comparison Project (CMIP) / Paleoclimate Modelling Inter-comparison Project (PMIP) general strategy, aimed at understanding the climate sensitivity to varying forcings. Physical models are useful tools for studying dust transport patterns, as they allow representing the full dust cycle from sources to sinks with an internally consistent approach. Combining information from paleodust records and climate models in coherent studies can be a fruitful approach from different points of view. Based on a new quality-controlled, size- and temporally-resolved data compilation, we used the Community Earth System Model to estimate the mass balance of and variability in the global dust cycle since the Last Glacial Maximum and throughout the Holocene. We analyze the variability of the reconstructed global dust cycle at different climate equilibrium conditions since the LGM until the pre-industrial climate, and compare with palodust records, focusing on the high latitudes, and discuss the uncertainties and the implications for dust and iron deposition to the oceans.

  6. Mountain birch – potentially large source of sesquiterpenes into high latitude atmosphere

    Directory of Open Access Journals (Sweden)

    S. Haapanala

    2009-06-01

    Full Text Available Emissions of volatile organic compounds (VOCs from mountain birches were measured in Abisko, northern Sweden. Mountain birches make up majority of the tree biomass in Scandinavian high latitudes, area subject to significant climate warming. The measurements were carried out in two growing seasons. The emissions of a branch from four individual trees were measured in June–August 2006 and one of them again in July 2007. The measurements were conducted using a dynamic flow through chamber covered with Teflon film. The studied mountain birches were found to emit substantial amounts of linalool, monoterpenes and sesquiterpenes. The monoterpene emission was dominated by sabinene. The magnitude and composition of sesquiterpene emission changed dramatically between the years. For example, the average α-farnesene emission in 2006 was almost 2000 ng gdw−1 h−1 while in 2007 the emission of α-farnesene was negligible. Also the emissions of other sesquiterpenes decreased in 2007 to a fraction of that in 2006. One possible explanation for the change in emissions is the herbivory damage that occurred in the area in 2004. Herbivory is known to enhance the emissions of sesquiterpenes, especially those of α-farnesene, and the effect may last several years.

  7. Mountain birch – potentially large source of sesquiterpenes into high latitude atmosphere

    Directory of Open Access Journals (Sweden)

    A. Arneth

    2009-11-01

    Full Text Available Emissions of volatile organic compounds (VOCs from mountain birches were measured in Abisko, northern Sweden. Mountain birches make up the majority of the tree biomass in Scandinavian high latitudes, a region subject to significant climate warming. The measurements were carried out in two growing seasons. The emissions of four branches, each from a different individual tree, were measured in June–August 2006 and one of them again in July 2007. The measurements were conducted using a dynamic flow through chamber covered with Teflon film. The studied mountain birches were found to emit substantial amounts of linalool, monoterpenes and sesquiterpenes. The monoterpene emission was dominated by sabinene. The magnitude and composition of the sesquiterpene emission changed dramatically between the years. For example, the average α-farnesene emission potential in 2006 was almost 2600 ng gdw−1 h−1 (3.5 pmol gdw−1 s−1 while in 2007 α-farnesene was not detected at all. Also the emissions of other sesquiterpenes decreased in 2007 to a fraction of that in 2006. One possible explanation for the change in emissions is the herbivory damage that occurred in the area in 2004. Herbivory is known to enhance the emissions of sesquiterpenes, especially those of α-farnesene, and the effect may last for several years.

  8. Extensive wet episodes in Late Glacial Australia resulting from high-latitude forcings

    Science.gov (United States)

    Bayon, Germain; De Deckker, Patrick; Magee, John W.; Germain, Yoan; Bermell, Sylvain; Tachikawa, Kazuyo; Norman, Marc D.

    2017-01-01

    Millennial-scale cooling events termed Heinrich Stadials punctuated Northern Hemisphere climate during the last glacial period. Latitudinal shifts of the intertropical convergence zone (ITCZ) are thought to have rapidly propagated these abrupt climatic signals southward, influencing the evolution of Southern Hemisphere climates and contributing to major reorganisation of the global ocean-atmosphere system. Here, we use neodymium isotopes from a marine sediment core to reconstruct the hydroclimatic evolution of subtropical Australia between 90 to 20 thousand years ago. We find a strong correlation between our sediment provenance proxy data and records for western Pacific tropical precipitations and Australian palaeolakes, which indicates that Northern Hemisphere cooling phases were accompanied by pronounced excursions of the ITCZ and associated rainfall as far south as about 32°S. Comparatively, however, each of these humid periods lasted substantially longer than the mean duration of Heinrich Stadials, overlapping with subsequent warming phases of the southern high-latitudes recorded in Antarctic ice cores. In addition to ITCZ-driven hydroclimate forcing, we infer that changes in Southern Ocean climate also played an important role in regulating late glacial atmospheric patterns of the Southern Hemisphere subtropical regions.

  9. Ecological legacies of Indigenous fire management in high-latitude coastal temperate rainforests, Canada

    Science.gov (United States)

    Hoffman, K.; Lertzman, K. P.; Starzomski, B. M.

    2016-12-01

    Anthropogenic burning is considered to have little impact on coastal temperate rainforest fire regimes in the Pacific Northwest (PNW) of North America, yet few long-term fire histories have been reconstructed in these forests. We use a multidisciplinary approach to reconstruct the ecological impact, scale, and legacies of historic fire regime variability in high-latitude coastal temperate rainforests located in British Columbia, Canada. We map seven centuries of fire activity with fire scars and records of stand establishment, and examine patterns in the distribution and composition of vegetation to assess whether fire was historically used as a tool for resource management. We conduct a paired study of 20 former Indigenous habitation and control sites across a 100 km2 island group to relate historic fire activity with long-term patterns of human land use and contemporary lightning strike densities. Fires were significantly associated with the locations of former Indigenous habitation sites, low and mixed in severity, and likely intentionally used to influence the composition and structure of vegetation, thus increasing the productivity of culturally important plants such as western redcedar, berry-producing shrubs, and bracken fern. Centuries of repeated anthropogenic burning have resulted in a mosaic of vegetation types in different stages of succession. These data are directly relevant to the management of contemporary forests as they do not support the widespread contention that old growth coastal temperate rainforests in this region are pristine landscapes where fire is rare, but more likely the result of long-term human land use practices.

  10. High latitude temperature evolution across the Last Interglacial: a model-data comparison

    Science.gov (United States)

    Capron, Emilie; Stone, Emma; Govin, Aline; Loutre, Marie-France; Masson-Delmotte, Valerie; Mulitza, Stefan; Otto-Bliesner, Betty; Sime, Louise; Waelbroeck, Claire; Wolff, Eric W.

    2014-05-01

    The Last Interglacial (LIG, 129-116 thousand of years, ka) represents an interesting test bed for climate model feedbacks for warmer-than-present high latitudes. However, mainly because synchronising different paleoclimatic archives from different parts of the world is not trivial, a global picture of LIG temperature changes is difficult to obtain. In the framework of the UK iGlass consortium and the European Past4Future project, we have selected 49 polar ice core and sub-polar marine sediment records and developed a strategy to synchronise them onto the recent AICC2012 ice core chronology. This new synthesis enables us to describe the spatial and temporal climatic patterns over polar ice sheets (surface air temperature) and around the ice margins (sea surface temperatures) at a pluri-centennial to millennial-scale. Major features highlighted are (i) non synchronous maximum temperature change between the two hemispheres with the Southern Ocean and Antarctica records showing an early warming compared to North Atlantic records and (ii) Southern hemisphere records exhibiting warm conditions for a longer time period compared to records from the Northern Hemisphere and smaller temperature amplitude changes. Our compiled records are compared with recent snapshot and transient model experiments performed with three state of the art General Circulation Models (HADCM3, CCSM3, FAMOUS) and an Earth Model of Intermediary Complexity (LOVECLIM). Such an exercise enables us to investigate the climate feedbacks which causes the most apparent model-data differences.

  11. The 20 March 2015 total solar eclipse: effects in the high-latitude lower ionosphere

    Science.gov (United States)

    Cherniakov, Sergey; Tereshchenko, Valentina; Ogloblina, Olga; Vasiliev, Evgeny; Gomonov, Alexander

    2016-07-01

    The medium-wave facility of partial reflections of the Polar Geophysical Institute (observatory "Tumanny", 69 N, 35.7 E) has observed behavior of the lower high-latitude ionosphere during the 20 March 2015 total solar eclipse. There were several effects during the eclipse. Generally on the heights of the lower ionosphere the "short night" effect had shown, but at some heights local enhanced electron concentration were revealed and the behavior of the electron concentration had the wave-like form. It had seen also at the behavior of the total electron content of the lower ionosphere. The periods and behavior of the wave are considered. It can be explained by influence of acoustic-gravity waves which originated after cooling of the atmosphere by the lunar shadow during its supersonic movement along the earth surface. The periods and behavior of waves during the eclipse were also received using riometer data at the observatory "Tumanny" and the magnetometer at the observatory "Loparskaya" (68.63 N, 33.38 E).

  12. Early Eocene hyperthermals record orbitally controlled changes in high latitude climates

    Science.gov (United States)

    Galeotti, S.; DeConto, R. M.; Lanci, L.; Pagani, M.; Rohl, U.; Westerhold, T.; Zachos, J. C.

    2012-04-01

    The Late Paleocene to Early Eocene records a succession of short-term (104 yr) negative carbon isotope excursions (CIEs) in marine carbonates and organic carbon. Available data indicate that at least three of these episodes, including the Paleocene Eocene Thermal Maximum (PETM) at ca. 55.5, the Eocene Thermal Maximum (ETM)2 at ca. 53.5 Ma and the ETM3 at ca. 52 Ma, were associated with rapid warming, and widespread marine carbonate dissolution forced by shoaling of the carbonate lysocline and lowering of the carbonate saturation state. Large temperature raises associated with decreased δ13C values in both terrestrial and oceanic records and concomitant acidification of oceanic waters implies that hyperthermals were caused by the addition of massive amounts of 13C-depleted greenhouse gases (CH4 and/or CO-2) into the atmosphere and subsequent sequestration by oceanic waters. Cyclostratigraphic analyses of marine sequences provided evidence that CIEs and associated carbonate dissolution episodes were linked to orbital changes in insolation. Here we show grounds that Early Eocene hyperthermals are part of a continuum of δ13C anomaly and carbonate dissolution episodes and are triggered by long-term orbitally-controlled changes in local climates at high latitudes.

  13. Ionosphere data assimilation capabilities for representing the high-latitude geomagnetic storm event in September 2011

    Science.gov (United States)

    Solomentsev, Dmitry; Jacobsen, Knut Stanley; Khattatov, Boris; Khattatov, Vyacheslav; Cherniak, Yakov; Titov, Anton

    2014-12-01

    Severe geomagnetic storms have a strong impact on space communication and satellite navigation systems. Forecasting the appearance of geomagnetically induced disturbances in the ionosphere is one of the urgent goals of the space weather community. The challenge is that the processes governing the distribution of the crucial ionospheric parameters have a rather poor quantitative description, and the models, built using the empirical parameterizations, have limited capabilities for operational purposes. On the other hand, data assimilation techniques are becoming more and more popular for nowcasting the state of the large-scale geophysical systems. We present an example of an ionospheric data assimilation system performance assessment during a strong geomagnetic event, which took place on 26 September 2011. The first-principle model has assimilated slant total electron content measurements from a dense network of ground stations, provided by the Norwegian Mapping Authority. The results have shown satisfactory agreement with independent data and demonstrate that the assimilation model is accurate to about 2-4 total electron content units and can be used for operational purposes in high-latitude regions. The operational system performance assessment is the subject of future work.

  14. Some aspects of modelling the high-latitude ionospheric convection from Cluster/Edi data

    Science.gov (United States)

    Förster, M.; Feldstein, Y. I.; Gromova, L. I.; Dremukhina, L. A.; Levitin, A. E.; Haaland, S. E.

    2013-01-01

    Measurements onboard Cluster satellites are briefly described, which form the base for determining the intensity and direction of the electric field in the magnetosphere. The aim of this paper is to describe (1) the methodology of calculating the potential distribution at the ionospheric level and the results of constructing spatiotemporal convection patterns for different orientations of the IMF vector in the GSM YZ plane; (2) derivation of basic convection patterns (BCPs), which allow to deduce the statistical ionospheric convection pattern at high latitudes for any IMF Bz and By values (statistical convection model) using different sets of independent data; (3) the consequences of enlarging the amount of data used for analysis; (4) the results of potential calculations with various orders of the spherical harmonics describing them; (5) determination of the cross-polar cap potential with different IMF sector widths (α from 45° down to 10°); (6) the results of our trials to determine the contribution of the IMF Bx component to the convection pattern.

  15. Structuring of full plasma patches in the high latitude with realistic drives-continued.

    Science.gov (United States)

    Guzdar, P. N.; Gondarenko, N. A.; Sojka, J. J.; David, M.

    2002-12-01

    The robustness of plasma patches, in spite of structuring by a combination of gradient drift and secondary Kelvin-Helmholtz (KH) instabilities, has been attributed to the strong stabilizing influence of dynamics of electrons along the field line and the break-up of the gradient drift instability driven fingers by secondary KH instabilities. Another physical effect that contributes significantly to the robustness of the patch is the variability of the convection of the patch over the polar cap region. Recently we have developed a parallel version of our 3D code, which can run on the IBM SP. We will present results of a set of runs with realistic convective drives obtained from MHD simulations of real event studies of substorms. The goal is to develop a database to provide statistical information on the nature of structuring in high latitude plasma patches. We are also developing diagnostic capabilities to compare with reconstructed images of the 3D transverse as well as parallel structure of the irregularities.

  16. Monitoring Atmospheric Dust Spring Activity at High Southern Latitudes on Mars using OMEGA

    CERN Document Server

    Douté, S

    2013-01-01

    This article presents a monitoring of the atmospheric dust in the south polar region during spring of martian year 27. Our goal is to contribute to identifying the source regions and to understanding lifting as well as transport mechanisms in relation with the seasonal ice regression and the dynamics of the atmosphere. This is of paramount importance since local dust storms generated in this region sometimes grow to global proportions. The imaging spectrometer OMEGA on board Mars Express has acquired the most comprehensive set of observations to date in the near-infrared (0.93-5.1 microns) of the southern high latitudes of Mars from mid-winter solstice (Ls=110, December 2004) to the end of the recession at Ls=320 (November 2005) . We use an original method presented in the companion paper in order to retrieve the optical depth of the atmospheric dust above mineral surfaces at a reference wavelength of one micron. The method is applied on a time series of OMEGA images acquired between Ls=220 and Ls=280 in conj...

  17. Diffuse Galactic Gamma Rays at intermediate and high latitudes. I. Constraints on the ISM properties

    CERN Document Server

    Cholis, I; Evoli, C; Maccione, L; Ullio, P

    2011-01-01

    We study the high latitude (|b|>10) diffuse gamma-ray emission in the Galaxy in light of the recently published data from the Fermi collaboration at energies between 100 MeV and 100 GeV. The unprecedented accuracy in these measurements allows to probe and constrain the properties of sources and propagation of cosmic rays (CRs) in the Galaxy, as well as confirming conventional assumptions made on the interstellar medium (ISM). Using the publicly available DRAGON code, that has been shown to reproduce local measurements of CRs, we study assumptions made in the literature on HI and H2 gas distributions in the ISM, and non spatially uniform models of diffusion in the Galaxy. By performing a combined analysis of CR and gamma-ray spectra, we derive constraints on the properties of the ISM gas distribution and the vertical scale height of galactic CR diffusion, which may have implications also on indirect Dark Matter detection. We also discuss some of the possible interpretations of the break at ~230 GV in CR proton...

  18. Diffuse galactic gamma rays at intermediate and high latitudes. Pt. 1. Constraints on the ISM properties

    Energy Technology Data Exchange (ETDEWEB)

    Cholis, Ilias; Tavakoli, Maryam; Ullio, Piero [SISSA, Trieste (Italy); INFN, Trieste (Italy); Evoli, Carmelo [SISSA, Trieste (Italy); Chinese Academy of Sciences, Beijing (China). National Astronomical Observatories; Maccione, Luca [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)

    2011-06-15

    We study the high latitude (vertical stroke b vertical stroke >10 ) diffuse {gamma}-ray emission in the Galaxy in light of the recently published data from the Fermi collaboration at energies between 100 MeV and 100 GeV. The unprecedented accuracy in these measurements allows to probe and constrain the properties of sources and propagation of cosmic rays (CRs) in the Galaxy, as well as confirming conventional assumptions made on the interstellar medium (ISM). Using the publicly available DRAGON code, that has been shown to reproduce local measurements of CRs, we study assumptions made in the literature on HI and H2 gas distributions in the ISM, and non spatially uniform models of diffusion in the Galaxy. By performing a combined analysis of CR and {gamma}-ray spectra, we derive constraints on the properties of the ISM gas distribution and the vertical scale height of galactic CR diffusion, which may have implications also on indirect Dark Matter detection. We also discuss some of the possible interpretations of the break at {proportional_to}230 GeV in CR protons and helium spectra, recently observed by PAMELA and their impact on {gamma}-rays. (orig.)

  19. A Scan with the EUVE DS Telescope across the High-latitude Molecular Cloud MBM12

    Science.gov (United States)

    Berghoefer, Thomas W.

    We propose to scan across the nearby high-latitude molecular cloud MBM12 and its vicinity with the EUVE Deep Survey (DS) telescope. A distance of 65 pc and an EUV mean free path of ~100 pc in the vicinity of MBM12 makes this an ideal target to apply a newly developed method, based on a differential cloud technique, to measure physical conditions of the hot gas in the local ISM by means of EUVE observations. Snowden, McCammon & Verter (1993) reported the detection of an X-ray shadow in the 3/4 keV diffuse background at the position of MBM12. However, a shadow in the 1/4 keV band, which would surely be present as a consequence of the higher optical depth at lower energies, cannot be seen in the data. This is quite suprising! Stellar reddening measurements of stars in the direction of MBM12 indicate an HI column density that is too low to reveal a shadow at soft X-ray wavelength. However, in the EUV range MBM12 is opaque and the proposed observations shall be used to derive the density and the pressure of the hot gas in the direction of MBM12 and hopefully to provide an explanation for the contradictory results given by Snowden et al.

  20. The contribution of CHONS particles to the diffuse high Galactic latitude IR emission

    CERN Document Server

    Papoular, Renaud

    2014-01-01

    This work purports to model the far infrared gray-body emission in the spectra of high-Galactic-latitude clouds. Several carbonaceous laboratory materials are tested for their fitness as carriers of this modified-black-body emission which, according to data delivered by the Planck satellite, and others before, is best fit with temperature 17.9 K and spectral index beta=1.78. Some of these materials were discarded for insufficient emissivity, others for inadequate beta. By contrast, CHONS clusters (beta=1.4, T=19 K) combine nicely with magnesium silicate (beta=2, T=18.7 K) to give a spectrum which falls well within the observational error bars (total emission cross-section at 250 mum: 8.6 10^{-26} cm^{2} per H atom). Only 15 % of all Galactic carbon atoms are needed for this purpose. The CHONS particles that were considered and described have a disordered (amorphous) structure but include a sizable fraction of aromatic rings, although they are much less graphitized than a-C:H/HAC. They can be seen as one embod...

  1. High-latitude cooling associated with landscape changes from North American boreal forest fires

    Directory of Open Access Journals (Sweden)

    B. M. Rogers

    2013-02-01

    Full Text Available Fires in the boreal forests of North America are generally stand-replacing, killing the majority of trees and initiating succession that may last over a century. Functional variation during succession can affect local surface energy budgets and, potentially, regional climate. Burn area across Alaska and Canada has increased in the last few decades and is projected to be substantially higher by the end of the 21st century because of a warmer climate with longer growing seasons. Here we simulated changes in forest composition due to altered burn area using a stochastic model of fire occurrence, historical fire data from national inventories, and succession trajectories derived from remote sensing. When coupled to an Earth system model, younger vegetation from increased burning cooled the high-latitude atmosphere, primarily in the winter and spring, with noticeable feedbacks from the ocean and sea ice. Results from multiple scenarios suggest that a doubling of burn area would cool the surface by 0.23 ± 0.09 °C across boreal North America during winter and spring months (December through May. This could provide a negative feedback to winter warming on the order of 3–5% for a doubling, and 14–23% for a quadrupling, of burn area. Maximum cooling occurs in the areas of greatest burning, and between February and April when albedo changes are largest and solar insolation is moderate. Further work is needed to integrate all the climate drivers from boreal forest fires, including aerosols and greenhouse gasses.

  2. Spatial distribution of spectral parameters of high latitude geomagnetic disturbances in the Pc5/Pi3 frequency range

    Directory of Open Access Journals (Sweden)

    V. A. Pilipenko

    2010-09-01

    Full Text Available We analyze spectral parameters of the geomagnetic disturbances within the 1–4 mHz (Pc5/Pi3 frequency range for 29 observatories from polar to auroral latitudes. The main object of this study is the broadband (noise background under quiet and moderately disturbed conditions. To obtain a quantitative description of background high-latitude long period ULF activity the log-log dependence of the spectral power on frequency is expanded over Legendre polynomials, and the coefficients of this expansion (spectral moments are used to describe the most common features of these spectra. Not only the spectral power, but also the spectral slope and higher spectral moments, averaged over relatively long time intervals, demonstrate a systematic dependence on corrected geomagnetic (CGM latitude, Φ, and magnetic local time, MLT. The 2-D distributions of the spectral moments in Φ-MLT coordinates are characterized by existence of structures, narrow in latitude and extended in MLT, which can be attributed to the projections of different magnetospheric domains. Spatio-temporal distributions of spectral power of elliptically (P-component and randomly (N-component polarized signal are similar, but not identical. The N-component contribution to the total signal becomes non-negligible in regions with a high local activity, such as the auroral oval and dayside polar cusp. The spectral slope indicates a larger relative contribution of higher frequencies upon the latitude decrease, probably, as a result of the resonant effects in the ULF noise. The higher spectral moments are also controlled mostly by CGM latitude and MLT and are fundamentally different for the polarized and non-polarized components. This study is a step towards the construction of an empirical model of the ULF wave power in Earth's magnetosphere.

  3. Using data assimilation to investigate the causes of Southern Hemisphere high latitude cooling from 10 to 8 ka BP

    NARCIS (Netherlands)

    P. Mathiot; H. Goosse; X. Crosta; B. Stenni; M. Braida; A. Mairesse; S. Dubinkina (Svetlana)

    2013-01-01

    htmlabstractFrom 10 to 8 ka BP (thousand years before present), paleoclimate records show an atmospheric and oceanic cooling in the high latitudes of the Southern Hemisphere. During this interval, temperatures estimated from proxy data decrease by 0.8 °C over Antarctica and 1.2 °C over the Southern

  4. What do model results tell us regarding Climate Intervention (Geoengineering) strategies to counter high latitude climate change.

    Science.gov (United States)

    Rasch, P. J.

    2015-12-01

    A number of modeling studies at various levels of complexity have taken place to explore consequences of climate intervention in countering climate change. I will review results from some of those studies, cover some new analysis, and identify areas where more study is needed, with a focus on high latitude climate.

  5. Ions from Different Sources in the near-Earth High-Latitude Magnetotail

    Science.gov (United States)

    Koleva, R.; Semkova, J.; Fedorov, A.; Smirnov, V.

    2003-04-01

    We investigate the characteristics of the ion population in the near-Earth (distances from 5 Re to 10 Re) magnetotail region poleward of the exterior cusp and the auroral field lines. The study presented is based on data from the Low Energy Plasma Composition Experiment (AMEI-2) aboard the high-apogee INTERBALL-1 satellite. Characteristic features of the region are the low plasma density and the low electron energy. We discuss several cases of ion spectral and composition measurements, using He++ as a tracer of SW plasma and O+ as a tracer of ionospheric plasma. Ion fluxes exhibit complex structure bearing the history of ions origin and consecutive acceleration. Both Solar wind and ionospheric ions are present in this region. O+ beams are regularly observed, as expected, going away or towards the Earth, with energies up to about 2 keV/q. A small amount of isotropic, high-temperature plasma sheet ions is always present. But dominating is a He++ population with energies in the interval 1 - 2.5 keV/q, either isotropic in pitch angle or consisting of counter-flowing ions with wide pitch-angular distribution. We discuss the possible relation of these populations with the ion populations observed downtail in the lobes, the PSBL, the 'mixed region' at the dusk flunk as identified by Fuselier et al. on base of ISEE-1 and ISEE-2 (J. Geophys. Res., 1999) and the lobe-plasma transition layer, defined by WIND data by Wilbert et al, (J. Geophys. Res., 2001).

  6. SuperDARN CUTLASS Finland radar observations of high-latitude magnetic reconnections under northward interplanetary magnetic field (IMF) conditions

    Institute of Scientific and Technical Information of China (English)

    ZHANG QingHe; LIU RuiYuan; YANG HuiGen; HU HongQiao; ZHANG BeiChen; DUNLOP Malcolm; LESTER Mark; BOGDANOVA Yulia; WALSH Andrew

    2012-01-01

    A number of backscatter power enhancement events with “equatorward-moving radar auroral forms” in the high-latitude ionosphere were observed by SuperDARN CUTLASS Finland radar when the IMF was northward during 09:00 -10:00 UT on 26 March 2004.These events were also associated with sunward flow enhancements at each location in the Northern Hemisphere which were shown in ionospheric convections measured by the SuperDARN radars.These are typical features of high-latitude (lobe) magnetic reconnections.The durations of the velocity enhancements imply that the evolution time of the lobe reconnections is about 8-16 min from their origin at the reconnection site to their addition to the magnetotail lobe again.In additional,the Double Star TC-1 spacecraft was moving from magnetosheath into magnetosphere,and crossing the magnetopause near the subsolar region during this interval,and observed typical low-latitude magnetic reconnection signatures.This infers that the dayside high- and low-latitude reconnections may occur simultaneously.

  7. DSCOVR High Time Resolution Solar Wind Measurements

    Science.gov (United States)

    Szabo, Adam

    2012-01-01

    The Deep Space Climate Observatory (DSCOVR), previously known as Triana, spacecraft is expected to be launched in late 2014. It will carry a fluxgate magnetometer, Faraday Cup solar wind detector and a top-hat electron electrostatic analyzer. The Faraday Cup will provide an unprecedented 10 vectors/sec time resolution measurement of the solar wind proton and alpha reduced distribution functions. Coupled with the 40 vector/sec vector magnetometer measurements, the identification of specific wave modes in the solar wind will be possible for the first time. The science objectives and data products of the mission will be discussed.

  8. Coordinated Frequency Control of Wind Turbines in Power Systems with High Wind Power Penetration

    DEFF Research Database (Denmark)

    Tarnowski, Germán Claudio

    particular views. These models were developed and verified during this work, basedaround a particular manufacturer’s wind turbine and on said isolated power system withwind power. The capability of variable speed wind turbines for providing Inertial Response is analysed. To perform this assessment, a control...... and the dynamic stability of the grid frequency under large disturbances would be compromised. The aim of this study is to investigate the integration of large scale wind power generation in power systems and its active power control.Novel methods and solutions dealing specifically with the electric frequency...... stability and high wind power penetration or in islanding situations are addressed. The review of relevant theoretical concepts is supported by measurements carried out on an isolated power system characterized by high wind power penetration. Different mathematical and simulation models are used in several...

  9. Solar activity variability in the IRI at high latitudes: Comparisons with GPS total electron content

    Science.gov (United States)

    Themens, David R.; Jayachandran, P. T.

    2016-04-01

    Total electron content (TEC) measurements from 10 dual-frequency GPS receivers in the Canadian High Arctic Ionospheric Network (CHAIN) are used to evaluate the performance of International Reference Ionosphere (IRI)-2007 within the Canadian sector. Throughout the region, we see systematic underestimation of daytime TEC, particularly at solar maximum, where summer and equinox root-mean-square errors reach as high as 14 total electron content units, 1 TECU = 1016 el m-2 (TECU). It is also shown that the use of a monthly IG index, in place of the IRI's standard IG12 index, leads to an improvement in TEC specification by up to 3 TECU in the polar cap and up to 6 TECU in the subauroral region during periods of short-term, large amplitude changes in solar activity. On diurnal timescales, variability in TEC is found to be underestimated by the IRI, during equinox periods, by up to 40% at subauroral latitudes and up to 70% in the polar cap region. During the winter, diurnal variations are overestimated by up to 40% in the subauroral region and are underestimated within the polar cap by up to 80%. Using collocated ionosonde data, we find IRI bottomside TEC to be within 1 TECU of observation with errors largest during the equinoxes. For the topside we find good agreement during the winter but significant underestimation of topside TEC by the IRI during summer and equinox periods, exceeding 6 TECU at times. By ingesting measured NmF2 into the IRI, we show that the topside thickness parameterization is the source of the bulk of the observed TEC errors.

  10. High Latitude Scintillation Monitoring at UHF with the COMMX Experiment on TACSat4

    Science.gov (United States)

    Bernhardt, P. A.; Siefring, C. L.; Akins, K.; Nurnberger, M.

    2013-12-01

    UHF Beacon Transmissions at 253 MHz have provided high latitude scintillation monitoring from Gakona Alaska using the COMMX instrument on TACSat4. TACSat4 was constructed by the Naval Research Laboratory and was launched in September 2011 as an experimental communications satellite. Ground UHF transmissions are uplinked to TACSat4 using the 4 meter diameter antenna deployed to view the earth. These signals are coherently translated to other UHF frequency to be rebroadcast to the ground. Scintillation monitoring is achieved by taking the 401.25 MHz signals from ground DORIS beacons located in Cold Bay, Alaska; Yellowknife, Canada; Kauai, Hawaii; and Soccoro Island, Mexico. These signals are translated to 253 MHz and broadcast with the 4 meter antenna pointed to the UHF receiver located at Gakona, Alaska. The satellite antenna gain is 18 dB in this UHF band and the transmitter power is 2 Watts. The satellite is in an elliptical orbit with an inclination of 63 degrees and a perigee of 12,000 km. Doppler frequency shifts allow separation of each uplink from the ground DORIS beacons. This new scintillation monitoring system has been used to detect natural and artificial field aligned irregularity effects on the amplitude and phase of UHF carriers where typical scintillation amplitudes are 2dB or less. Using the HAARP transmitter in Alaska, TACSat4 was used to discover the artificial ionization clouds produce scintillation with as much as 16 dB and amplitude indices S4 greater than unity. This is the first demonstration of significant effects on radio scintillations using high power HF radio waves to disturb the ionosphere.

  11. An overview of high-latitude hf induced aurora from EISCAT

    Science.gov (United States)

    Kosch, M.; Gustavsson, B.; Rietveld, M.

    The EISCAT HF facility is capable of transmitting over 200 MW into the ionosphere below 5.423 MHz using the low-gain antenna array. Over 1000 MW above 5.423 MHz is available using the high-gain antenna array. During O-mode pumping in the hours after sunset, F-region electrons can be accelerated sufficiently to excite the oxygen atoms and nitrogen molecules, resulting in observable optical emissions at 844.6 (O), 630 (O1D), 557.7 (O1S) and 427.8 (N2) nm above EISCAT. Initial success came in February 1999 with optical recordings by ALIS (Auroral Large Imaging System) from various Swedish locations south of EISCAT and DASI (Digital All-Sky Imager) from Skibotn, Norway, 50 km south-east of EISCAT. Several observations have features unique to high latitudes. Novel discoveries include: (1) Very large electron temperature enhancements of a few 1000 K, which maximise along the magnetic field line direction (2) Ion temperature enhancements of a few 100 K accompanied by large ion outflows, (3) The optical emission usually appears near the magnetic field line direction regardless of the HF transmitter beam pointing direction, (4) The optical emission appears below the HF pump reflection altitude as well as the upper-hybrid resonance height, (5) The optical emission and HF coherent radar backscatter disappears when pumping on the 3rd, 4th or 5th gyro-harmonic frequency, (6) The first artificial optical observations at 844.6 (O) and 427.8 (N2) nm and (7) Annular optical structures, which subsequently collapse into blobs.

  12. Application of a land surface model for simulating river streamflow in high latitudes

    Science.gov (United States)

    Gusev, Yeugeniy; Nasonova, Olga; Dzhogan, Larissa

    2010-05-01

    Nowadays modelling runoff from the pan-Arctic river basins, which represents nearly 50% of water flow to the Arctic Ocean, is of great interest among hydrological modelling community because these regions are very sensitive to natural and anthropogenic impacts. This motivates the necessity of increase of the accuracy of hydrological estimations, runoff predictions, and water resources assessments in high latitudes. However, in these regions, observations required for model simulations (to specify model parameters and forcing inputs) are very scarce or even absent (especially this concerns land surface parameters). At the same time river discharge measurements are usually available that makes it possible to estimate model parameters by their calibration against measured discharge. Such a situation is typical of most of the northern basins of Russia. The major goal of the work is to reveal whether a physically-based land surface model (LSM) Soil Water - Atmosphere - Plants (SWAP) is able to reproduce snowmelt and rain driven daily streamflow in high latitudes (using poor input information) with the accuracy acceptable for hydrologic applications. Three river basins, located on the north of the European part of Russia, were chosen for investigation. They are the Mezen River basin (area: area: 78 000 km2), the Pechora River basin (area: 312 000 km2) and the Severnaya Dvina River basin (area: 348 000 km2). For modeling purposes the basins were presented, respectively, by 10, 57 and 62 one-degree computational grid boxes connected by river network. A priori estimation of the land surface parameters for each grid box was based on the global one-degree datasets prepared within the framework of the International Satellite Land-Surface Climatology Project Initiative II (ISLSCP) / the Second Global Soil Wetness Project (GSWP-2). Three versions of atmospheric forcing data prepared for the basins were based on: (1) NCEP/DOE reanalysis dataset; (2) NCEP/DOE reanalysis product

  13. OCCURRENCE OF HIGH-SPEED SOLAR WIND STREAMS OVER THE GRAND MODERN MAXIMUM

    Energy Technology Data Exchange (ETDEWEB)

    Mursula, K.; Holappa, L. [ReSoLVE Centre of Excellence, Department of Physics, University of Oulu (Finland); Lukianova, R., E-mail: kalevi.mursula@oulu.fi [Geophysical Center of Russian Academy of Science, Moscow (Russian Federation)

    2015-03-01

    In the declining phase of the solar cycle (SC), when the new-polarity fields of the solar poles are strengthened by the transport of same-signed magnetic flux from lower latitudes, the polar coronal holes expand and form non-axisymmetric extensions toward the solar equator. These extensions enhance the occurrence of high-speed solar wind (SW) streams (HSS) and related co-rotating interaction regions in the low-latitude heliosphere, and cause moderate, recurrent geomagnetic activity (GA) in the near-Earth space. Here, using a novel definition of GA at high (polar cap) latitudes and the longest record of magnetic observations at a polar cap station, we calculate the annually averaged SW speeds as proxies for the effective annual occurrence of HSS over the whole Grand Modern Maximum (GMM) from 1920s onward. We find that a period of high annual speeds (frequent occurrence of HSS) occurs in the declining phase of each of SCs 16-23. For most cycles the HSS activity clearly reaches a maximum in one year, suggesting that typically only one strong activation leading to a coronal hole extension is responsible for the HSS maximum. We find that the most persistent HSS activity occurred in the declining phase of SC 18. This suggests that cycle 19, which marks the sunspot maximum period of the GMM, was preceded by exceptionally strong polar fields during the previous sunspot minimum. This gives interesting support for the validity of solar dynamo theory during this dramatic period of solar magnetism.

  14. Multi-Year Radar Observations of Planetary Waves at High Conjugate Latitudes (Invited)

    Science.gov (United States)

    Fritts, D. C.; Iimura, H.; Janches, D.; Mitchell, N. J.; Singer, W.

    2013-12-01

    Meteor radars at nearly conjugate latitudes from ~54o to 68o S and N are enabling multi-year studies of planetary wave (PW) structure and seasonal, interannual, and inter-hemispheric variability. The various PWs exhibit dramatically different seasonal and inter-hemispheric variability, strongly variable amplitude and phase structures with altitude, latitude, and time, and episodic maxima in E-P flux components. This talk will review these features defined with meteor radars at Rothera Station and Ferraz Base (62 and 68 S), on Tierra del Fuego (54 S), and at Juliusruh, Germany and Esrange, Sweden (55 and 68 N).

  15. Statistical properties of Joule heating rate, electric field and conductances at high latitudes

    Directory of Open Access Journals (Sweden)

    A. T. Aikio

    2009-07-01

    Full Text Available Statistical properties of Joule heating rate, electric field and conductances in the high latitude ionosphere are studied by a unique one-month measurement made by the EISCAT incoherent scatter radar in Tromsø (66.6 cgmlat from 6 March to 6 April 2006. The data are from the same season (close to vernal equinox and from similar sunspot conditions (about 1.5 years before the sunspot minimum providing an excellent set of data to study the MLT and Kp dependence of parameters with high temporal and spatial resolution.

    All the parameters show a clear MLT variation, which is different for low and high Kp conditions. Our results indicate that the response of morning sector conductances and conductance ratios to increased magnetic activity is stronger than that of the evening sector. The co-location of Pedersen conductance maximum and electric field maximum in the morning sector produces the largest Joule heating rates 03–05 MLT for Kp≥3. In the evening sector, a smaller maximum occurs at 18 MLT. Minimum Joule heating rates in the nightside are statistically observed at 23 MLT, which is the location of the electric Harang discontinuity.

    An important outcome of the paper are the fitted functions for the Joule heating rate as a function of electric field magnitude, separately for four MLT sectors and two activity levels (Kp<3 and Kp≥3. In addition to the squared electric field, the fit includes a linear term to study the possible anticorrelation or correlation between electric field and conductance. In the midday sector, positive correlation is found as well as in the morning sector for the high activity case. In the midnight and evening sectors, anticorrelation between electric field and conductance is obtained, i.e. high electric fields are associated with low conductances. This is expected to occur in the return current regions adjacent to

  16. High-latitude regions of Siberia and Northeast Russia in the Paleogene: Stratigraphy, flora, climate, coal accumulation

    Science.gov (United States)

    Akhmetiev, M. A.

    2015-07-01

    The geological structure and development history of superposed depressions on the Arctic coast of East Siberia and Bering Sea region (Chukotka, Koryakiya, northern Kamchatka) in the Early Paleogene are considered with the analysis of their flora and climatic parameters. The paleofloral analysis revealed thermophilic assemblages that reflect phases of maximum warming at the Paleocene-Eocene transition and in the Early Eocene. The appearance of thermophilic plants (Magnoliaceae, Myrtaceae, Lauraceae, Araliaceae, Loranthaceae, and others) in the Siberian segment of the Arctic region is explained by the stable atmospheric heat transfer from the Tethys to higher latitudes and absence of the latitudinal orographic barrier (Alpine-Himalayan belt). The plants migrated to high latitudes also along the meridional seaway that connected the Tethys with the Arctic Ocean via marine basins of the Eastern Paratethys, Turgai Strait, and West Siberia. The migration from the American continent was realized along the southern coast of Beringia under influence of a warm current flowing from low latitudes along the western coast of North America. The palm genus Sabal migrated to northern Kamchatka and Koryakiya precisely in this way via southern Alaska. In the Oligocene, shallow-water marine sediments in high-latitude regions were replaced by terrestrial facies. The Late Oligocene was marked by maximum cooling. Coal accumulation in Northeast Russia through the Paleogene is reviewed.

  17. Primary reserve studies for high wind power penetrated systems

    DEFF Research Database (Denmark)

    Das, Kaushik; Altin, Müfit; Hansen, Anca Daniela;

    2015-01-01

    With high penetration of non-synchronous wind generations replacing conventional generators, the inertia of power system will reduce. A large disturbance in such a power system can cause faster frequency change in this power system and might invoke emergency defence strategies like underfrequency....... This paper further explores the capabilities of wind turbines to provide support during underfrequency to prevent load shedding. Maximum wind penetration possible without causing load shedding following a large disturbance is also investigated....

  18. Southern high-latitude terrestrial climate change during the Palaeocene–Eocene derived from a marine pollen record (ODP Site 1172, East Tasman Plateau)

    NARCIS (Netherlands)

    Contreras, L.; Pross, J.; Bijl, P.K.; O'Hara, R.B.; Raine, J.I.; Sluijs, A.; Brinkhuis, H.

    2014-01-01

    Reconstructing the early Palaeogene climate dynamicsof terrestrial settings in the high southern latitudes isimportant to assess the role of high-latitude physical and biogeochemicalprocesses in the global climate system. However,whereas a number of high-quality Palaeogene climaterecords has become

  19. Past perspectives on Northern High-Latitude sensitivity to a 400ppm+ world (Invited)

    Science.gov (United States)

    Jansen, E.; Risebrobakken, B.; Drange, H.

    2013-12-01

    The Cenozoic record of climate change displays clear relationships between global temperatures as well as the development of glaciation in both hemispheres and past atmospheric CO2-levels. A recent update is provided in IPCC AR5 and will be reviewed here. Extensive periods of the past were characterized by CO2-levels in excess of 400ppmv. Analyses of the relationship between carbon emissions and global temperature in 15 Earth System Models used in the CMIP5 experiments underpinning IPCC AR5, show that carbon emissions of about 1000 Pg produces a global warming of about 2 degrees, regardless of emission scenario, indicating that changes in carbon fluxes of this magnitude produces at least 2oC global warming (probably more due to the adjustment of the slower components of the climate system). CO2-levels at the time of 2oC warming are on the order of 400-500ppmv with regional land temperatures at high Northern Latitudes being twice the global average or more, but without major changes in the style and pattern of North Atlantic meridional overturning circulation. Periods with CO2-levels at 400-500ppmv apparently occurred both in the Oligocene and the Pliocene, indicating that these periods may offer insight and perspective into a future climate in equilibrium with CO2-levels between 400 and 500ppmv. Carbonate preservation data from the Nordic Seas indicate that ocean overturning and ventilation was vigourous in the Nordic Seas in the Oligocene, which stands out a colder period, compared to the Eocene and the early Miocene. Isotope data from Oligocene shelf sediments indicate Nordic seas temperatures similar to modern levels or colder, hence implying the possibility of an existing cryosphere in the surrounding region at the time. The timing of this period inside the Oligocene and comparing to the paleo-CO2 record of the Oligocene is difficult, however, in parts because the paleo pCO2-record of the Olgocene shows a declining values also to below 400ppmv in the later part

  20. Global High-Latitude Conductivity Modeling: New Data and Improved Methods

    Science.gov (United States)

    McGranaghan, R. M.; Knipp, D. J.; Matsuo, T.; Godinez, H. C.

    2014-12-01

    The ionospheric conductivity distribution is essential for understanding the coupling in the magnetosphere-ionosphere-thermosphere (MIT) system. Hall conductivities, which regulate ionospheric current flow in the direction perpendicular to both the background magnetic field and the electric field, exert control over magnetospheric configuration, including transport within the plasmasphere and reconnection in the magnetotail [Lotko et al., 2014]. Pedersen conductivities control electric field variability and, in turn, determine the distribution and intensity of Joule heating, a prominent source of upper atmospheric temperature and neutral density enhancement. Contemporary conductivity modeling techniques rely on limiting assumptions and are 2-dimensional by design. Typically these models assume Maxwellian incoming particle energy distributions and simplistic current closure paths within an ionospheric 'shell' located at 110 km. We have developed a method to: 1) eliminate these assumptions and 2) allow 3-dimensional conductivity analysis using particle energy spectra provided by Defense Meteorological Satellite Program (DMSP) satellites. A sequential non-linear procedure then regresses the conductivities derived from DMSP data on the same basis functions used in the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure to obtain a realistic form of the covariance model, with the goal to integrate 3-dimensional conductivity analysis into the AMIE procedure. This addresses one of the primary sources of uncertainty within AMIE, and will ultimately allow more accurate characterization of high-latitude ionospheric electrodynamics. We present 3-dimensional conductivity distributions derived from satellite observations and global maps of these conductivities for the year 2010. References:Lotko, W., et al. (2014), Ionospheric control of magnetotail reconnection, Science, 345(6193), 184-187, doi:10.1126/science.1252907.

  1. Landscape influences on climate-related lake shrinkage at high latitudes

    Science.gov (United States)

    Roach, Jennifer K.; Griffith, Brad; Verbyla, David

    2013-01-01

    Climate-related declines in lake area have been identified across circumpolar regions and have been characterized by substantial spatial heterogeneity. An improved understanding of the mechanisms underlying lake area trends is necessary to predict where change is most likely to occur and to identify implications for high latitude reservoirs of carbon. Here, using a population of ca. 2300 lakes with statistically significant increasing and decreasing lake area trends spanning longitudinal and latitudinal gradients of ca. 1000 km in Alaska, we present evidence for a mechanism of lake area decline that involves the loss of surface water to groundwater systems. We show that lakes with significant declines in lake area were more likely to be located: (1) in burned areas; (2) on coarser, well-drained soils; and (3) farther from rivers compared to lakes that were increasing. These results indicate that postfire processes such as permafrost degradation, which also results from a warming climate, may promote lake drainage, particularly in coarse-textured soils and farther from rivers where overland flooding is less likely and downslope flow paths and negative hydraulic gradients between surface water and groundwater systems are more common. Movement of surface water to groundwater systems may lead to a deepening of subsurface flow paths and longer hydraulic residence time which has been linked to increased soil respiration and CO2 release to the atmosphere. By quantifying relationships between statewide coarse resolution maps of landscape characteristics and spatially heterogeneous responses of lakes to environmental change, we provide a means to identify at-risk lakes and landscapes and plan for a changing climate.

  2. Characteristic features of topside ionograms in the high-latitude ionosphere.

    Science.gov (United States)

    Panshin, Evgeniy; Danilkin, Nick; Tsybulya, Konstantin; Zhuravliov, Sergey

    Topside ionograms display a multitude of specific features in the high-latitude regions. In this report we present an analysis of these features based upon topside ionograms of the Kosmos-1809 satellite taken in May-June 1987. These ionograms were received onboard icebreaker Sibir during a polar expedition in this time. Since the ionograms were downlinked directly in the time of sounding, they were not strongly curtailed to fit the limited onboard memory and thus were much more informative. Acquiring the data in such way allowed us to see little-studied and even unknown ionogram features. Among them we note traces of a characteristic form which were interpreted earlier as signal reflections from almost vertical walls with increased electron density. Such structures are typical for the auroral oval ionosphere. To interpret this features we used a technique of ray trajectory synthesis. We present a sequence of ionograms with all phases of closing to, flying through and away from a higher-density wall. Quite often one find on the polar ionograms broad-band noise signals in different frequency ranges. On the ionograms they are seen as frequency-limited vertical columns from the very top of the ionogram to its bottom. Low-frequency noise (0.3-0.8 MHz) appear during auroral oval fly-throughs and are interpreted as a result of auroral kilometric radiation (AKR). Narrow bands on the magnetic gyrofrequency and upper hybrid frequency could be understood as an ionospheric plasma resonance response near the radiating antenna. Also, there are strong noises in the 3-5 MHz which we were not able to interpret. During some sounding sessions the transmitter was turned off so it was possible to record only natural and artificial noises and separate them from the ionospheric sounding responses.

  3. GNSS ionospheric scintillation and TEC at high latitudes: INGV monitoring and studies

    Science.gov (United States)

    Alfonsi, L.; de Franceschi, G.; Spogli, L.; Romano, V.

    2009-12-01

    The Istituto Nazionale di Geofisica e Vulcanologia (INGV) is monitoring the high latitude ionospheric irregularities causing GNSS signals corruption since 2003 when a GISTM receiver (GPS Ionospheric Scintillation and TEC Monitor) was deployed in Ny Alesund (Svalbard). Currently, INGV manages three GISTMs at Svalbard (two in Ny Alesund, another one in Longyearbyen) and two receivers in Antarctica at Concordia and Mario Zucchelli Stations. The GISTM receivers consist of NovAtel OEM4 dual-frequency receivers with special firmware specifically able to compute in near real time the amplitude and the phase scintillation from the GPS L1 frequency signals, and the ionospheric TEC (Total Electron Content) from the GPS L1 and L2 carrier phase signals. From this ground-based network, we are able to capture the dynamics of ionospheric plasma in a wide latitudinal range, from auroral to cusp/cap regions, considering the contribution of both hemispheres, in a bi-polar framework. The data collected are structured and archived in a dedicated database: www.eswua.ingv.it. The INGV activities in the field of the observation and the investigation of the ionospheric irregularities are included in several international collaborations addressing scientific issues as well as technological applications. This paper would like to give an overview of our recent activities about polar ionospheric imaging, scintillation climatology and scintillation mitigation matured also under the umbrella of the SCAR ICESTAR community and, currently, part of the initiatives of the SCAR Action Group “GPS Weather and Space Weather Forecast”chaired by INGV.

  4. Seasonal patterns in the nocturnal distributionand behavior of the mesopelagic fish Maurolicus muelleri at high latitudes

    KAUST Repository

    Prihartato, Perdana

    2015-02-17

    Acoustic scattering layers (SL) ascribed to pearlside Maurolicus muelleri were studied in Masfjorden, Norway, using upward-looking echo sounders cabled to shore for continuous long-term measurements. The acoustic studies were accompanied by continuous measurements of surface light and supplemented with intermittent field campaigns. From autumn to spring, young M. muelleri formed an SL in the upper ∼75 to 150 m in the daytime, characterized by migration to near-surface water near dusk, subsequent \\'midnight sinking\\', followed by a dawn ascent before a return to the daytime habitat. Light levels were ∼1 order of magnitude lower during the dawn ascent than for ascent in the afternoon, with the latter terminating before fish reached upper layers on ∼1/3 of the nights from late November to mid-April. Adults showed less tendency of migration during autumn and winter, until the SLs of young and adults merged in late spring, and thereafter displayed coherent migration behavior. The midnight sinking became progressively deeper from autumn to winter but was strongly reduced from mid-May when the darkest nocturnal light intensity (PAR) at the surface was above 10-3 μmol m-2 s-1. The pearlside took on schooling in upper waters during the even lighter nights in early June, with minimum light of ∼5 × 10-3 to 10-1 μmol m-2 s-1 at the surface. Nocturnal schooling ceased in early July, and midnight sinking reappeared in mid-August. We suggest that the strong variation in nocturnal light intensity at high latitudes provides changing trade-offs between visual foraging and avoiding predators and hence varying time budgets for feeding in the upper, productive layers.

  5. Fall vortex ozone as a predictor of springtime total ozone at high northern latitudes

    Directory of Open Access Journals (Sweden)

    S. R. Kawa

    2005-01-01

    Full Text Available Understanding the impact of atmospheric dynamical variability on observed changes in stratospheric O3 is a key to understanding how O3 will change with future climate dynamics and trace gas abundances. In this paper we examine the linkage between interannual variability in total column O3 at northern high latitudes in March and lower-to-mid stratospheric vortex O3 in the prior November. We find that these two quantities are significantly correlated in the years available from TOMS, SBUV, and POAM data (1978–2004. Additionally, we find that the apparent decadal shift in March O3 variability from the 1980s to years post-1990 is also seen in the November vortex O3, so that interannual variability in both quantities is largely driven by the later years. The cause of this correlation is not clear, however. Interannual variations in March total O3 are known to correspond closely with variations in winter stratospheric wave driving consistent with the effects of varying residual circulation, temperature, and chemical loss. Variation in November vortex O3 may also depend on dynamical wave activity, however, the dynamics in fall are less variable than in winter and spring. We do not find significant correlations of dynamic indicators for November such as temperature, heat flux, or polar average total O3 with the November vortex O3, nor with dynamical indicators later in winter and spring that might lead to a connection to March. We discuss several potential hypotheses for the observed correlation but do not find strong evidence for any considered mechanism. We present the observations as a phenomenon whose understanding may improve our ability to predict the dependence of O3 on changing dynamics and chemistry.

  6. Fall vortex ozone as a predictor of springtime total ozone at high northern latitudes

    Directory of Open Access Journals (Sweden)

    S. R. Kawa

    2005-01-01

    Full Text Available Understanding the impact of atmospheric dynamical variability on observed changes in stratospheric O3 is a key to understanding how O3 will change with future climate dynamics and trace gas abundances. In this paper we examine the linkage between interannual variability in total column O3 at northern high latitudes in March and lower-to-mid stratospheric vortex O3 in the prior November. We find that these two quantities are significantly correlated in the years available from TOMS, SBUV, and POAM data (1978-2004. Additionally, we find that the increase in March O3 variability from the 1980s to years post-1990 is also seen in the November vortex O3, i.e., interannual variability in both quantities is much larger in the later years. The cause of this correlation is not clear, however. Interannual variations in March total O3 are known to correspond closely with variations in winter stratospheric wave driving consistent with the effects of varying residual circulation, temperature, and chemical loss. Variation in November vortex O3 may also depend on dynamical wave activity, but the dynamics in fall are less variable than in winter and spring. We do not find significant correlations of dynamic indicators for November such as temperature, heat flux, or polar average total O3 with the November vortex O3, nor with dynamical indicators later in winter and spring that might lead to a connection to March. We discuss several potential hypotheses for the observed correlation but do not find strong evidence for any considered mechanism. We present the observations as a phenomenon whose understanding may improve our ability to predict the dependence of O3 on changing dynamics and chemistry.

  7. Remote Sensing of Open Water in Northern High Latitudes for use in Hydrologic Modeling

    Science.gov (United States)

    Podest, E.; McDonald, K. C.; Kimball, J.; Maumenee, N.; Bohn, T.; Lettenmaier, D.; Bowling, L.

    2007-12-01

    In the northern high latitudes open water bodies are common landscape features, having a large influence on hydrologic processes as well as surface-atmosphere carbon exchange and associated impacts on global climate. It is therefore of great importance to assess their spatial extent and temporal character in order to improve hydrologic and ecosystem process modeling. Spaceborne synthetic aperture radar (SAR) is an effective tool for this purpose since it is particularly sensitive to surface water and it can monitor large inaccessible areas on a temporal basis regardless of atmospheric conditions or solar illumination. We employ multi-temporal L-band SAR data from the Japanese Earth Remote Sensing Satellite (JERS-1) and ALOS PALSAR to map open water bodies across Alaska and Eurasia. A supervised decision tree-based classification approach was used to generate open water maps. For Alaska, we assembled regional-scale monthly JERS-1 SAR mosaics from data acquired during 1998. Digital elevation model (DEM) terrain and slope information were also employed in the decision tree classifier. These supplementary data aided significantly in improving classification performance in topographically complex regions where radar shadowing was prevalent. For study regions in Eurasia, PALSAR data was used in conjunction with JERS-1 imagery to map spatial patterns and seasonal variability in open water characteristics over selected study basins. These results were examined in relation to regional topographic and land cover characteristics. Classification results were also evaluated relative to other open water and land cover classification maps derived from Landsat, AVHRR, MODIS and SRTM. This work was carried out at the Jet Propulsion Laboratory, California Institute of Technology; at the University of Montana; at the University of Washington; and at Purdue University under contract with the National Aeronautics and Space Administration.

  8. Frequency control in power systems with high wind power penetration

    Energy Technology Data Exchange (ETDEWEB)

    Tarnowski, German Claudio [Technical Univ. of Denmark (Denmark). Centre for Electric Technology; Vestas Wind Systems A/S, Alsve (Denmark); Kjaer, Philip Carne [Vestas Wind Systems A/S, Alsve (Denmark); Oestergaard, Jacob [Technical Univ. of Denmark (Denmark). Centre for Electric Technology; Soerensen, Poul E. [Risoe National Laboratory for Sustainable Energy, Roskilde (Denmark). Wind Energy Dept.

    2010-07-01

    The fluctuating nature of wind power introduces several challenges to reliable operation of power system. With high wind power penetration, conventional power plants are displaced and wind speed fluctuations introduce large power imbalances which lead to power system frequency control and operational problems. This paper analysis the impact of wind power in the frequency control of power systems for different amount of controllable variable speed wind turbines. Real measurements from short term wind power penetration tests in a power system are shown and used to study the amount of total regulating power needed from conventional power plants. Dynamic simulations with validated model of the power system support the studies. The paper also presents control concepts for wind power plants necessary to achieve characteristic of frequency response and active power balancing similarly to conventional power plants, therefore allowing higher wind power penetration. As the power system dependency on wind power increases, wind power generation has to contribute with dynamic response and control actions similarly to conventional power plants. (orig.)

  9. Space Weather Impact on the European Interconnected Power Transmission System at High Latitudes

    Science.gov (United States)

    Piccinelli, Roberta; Krausmann, Elisabeth

    2016-04-01

    High voltage power transmission grids can suffer outages or blackouts during geomagnetic storms (GMS). More specifically, GMS can inject geomagnetically induced currents (GICs) into the power network. Transformers were identified as the most vulnerable components of the power networks: GICs cause transformers to work in saturation regions generating voltage instabilities and eventually driving the system to collapse. Since GMS are expected to cause more pronounced disturbances at high latitudes, we addressed the effects of extreme GMS on the Scandinavian 400 kV interconnected power transmission grid, including Finland, Sweden and Norway. By applying extreme 100-year-benchmark scenarios, we analyzed potential space-weather triggered voltage instabilities in the power grid considering mono-phase transformers, which are known to be more vulnerable to GIC injection, and three-phase transformers, which are more resistant. We assumed that every node of the grid included either transformers of the mono-phase type, or three-phase transformers.Our simulations indicate that the three-phase configuration of the network is significantly more robust than the mono-phase one. Our study indicates that for a system with only three-phase transformers the likelihood of grid collapse is very low, and collapse only occurs for the worst-case scenario with extremely high geoelectric field intensities. In such a case, the increase in reactive power demand caused by transformer saturation is too high for the system to continue to provide power. Our results indicate that lines that experience higher reactive power losses during normal operation are more likely to increase losses during a GMS event. According to our study, the portion of the Scandinavian interconnected power transmission grid most vulnerable to extreme space weather is the part where the highest reactive losses in transmission lines and in voltage magnitudes are observed. This corresponds to the southern parts of Sweden and

  10. The Energetic Constraints on the Zonal Mean Atmospheric Circulations in the Tropics, Midlatitudes, and High Latitudes

    Science.gov (United States)

    Hwang, Yen-Ting

    In this doctoral thesis, I have studied the processes that affect the atmospheric energy budget and their coupling relationships with atmospheric circulations. The equator-to-pole radiation gradient at the top of the atmosphere is the fundamental driver of atmospheric and oceanic circulations. Any anomaly in the energy budget due to variations in different climate components (such as clouds, aerosols, atmospheric properties, and land surfaces) will have an effect on the atmospheric and oceanic circulations and energy transport. Variations in the energy budget of extratropical regions have a non-local effect on tropical climate and vice versa. We first investigated climate components that affect the atmospheric energy budget and their coupled relationships with the atmospheric energy transport, using CMIP multi-model ensembles. We studied how individual components affect energy transport in three latitude bands: (1) at 70 degrees, where increasing poleward energy transport may cause polar amplification, (2) at 40 degrees, where eddies are the strongest, and (3) in the deep tropics, where global climate models (GCMs) do not agree on the changes in transport in global warming scenarios. In high latitudes, positive radiative effects from melting sea ice decrease the equator-to-pole temperature gradient and prevent poleward fluxes from increasing. Models that have more melting ice tend to predict a smaller increase in the energy transport, which is counterintuitive based on the argument that increasing poleward transport can lead to melting sea ice. The cooling effect of increasing low clouds over newly open ocean along the ice edge sharpens the temperature gradient and increases the energy transport in midlatitudes. Clouds and sea ice in the extratropics can also influence energy transport at the equator. We then shifted our focus to the tropical rain belt, built on the first part that demonstrated a directly linkage from hemispheric asymmetry of the atmospheric energy

  11. A link between high-speed solar wind streams and explosive extratropical cyclones

    Science.gov (United States)

    Prikryl, Paul; Iwao, Koki; Muldrew, Donald B.; Rušin, Vojto; Rybanský, Milan; Bruntz, Robert

    2016-11-01

    A link between solar wind magnetic sector boundary (heliospheric current sheet) crossings by the Earth and the upper-level tropospheric vorticity was discovered in the 1970s. These results have been later confirmed but the proposed mechanisms remain controversial. Extratropical-cyclone tracks obtained from two meteorological reanalysis datasets are used in superposed epoch analysis of time series of solar wind plasma parameters and green coronal emission line intensity. The time series are keyed to times of maximum growth of explosively developing extratropical cyclones in the winter season. The new statistical evidence corroborates the previously published results (Prikryl et al., 2009). This evidence shows that explosive extratropical cyclones tend to occur after arrivals of solar wind disturbances such as high-speed solar wind streams from coronal holes when large amplitude magneto-hydrodynamic waves couple to the magnetosphere-ionosphere system. These MHD waves modulate Joule heating and/or Lorentz forcing of the high-latitude thermosphere generating medium-scale atmospheric gravity waves that propagate energy upward and downward from auroral zone through the atmosphere. At the tropospheric level, in spite of significantly reduced amplitudes, these gravity waves can provide a lift of unstable air to release the moist symmetric instability thus initiating slantwise convection and forming cloud/precipitation bands. The release of latent heat is known to provide energy for rapid development and intensification of extratropical cyclones.

  12. An Automated Approach for Mapping Persistent Ice and Snow Cover over High Latitude Regions

    Directory of Open Access Journals (Sweden)

    David J. Selkowitz

    2015-12-01

    Full Text Available We developed an automated approach for mapping persistent ice and snow cover (glaciers and perennial snowfields from Landsat TM and ETM+ data across a variety of topography, glacier types, and climatic conditions at high latitudes (above ~65°N. Our approach exploits all available Landsat scenes acquired during the late summer (1 August–15 September over a multi-year period and employs an automated cloud masking algorithm optimized for snow and ice covered mountainous environments. Pixels from individual Landsat scenes were classified as snow/ice covered or snow/ice free based on the Normalized Difference Snow Index (NDSI, and pixels consistently identified as snow/ice covered over a five-year period were classified as persistent ice and snow cover. The same NDSI and ratio of snow/ice-covered days to total days thresholds applied consistently across eight study regions resulted in persistent ice and snow cover maps that agreed closely in most areas with glacier area mapped for the Randolph Glacier Inventory (RGI, with a mean accuracy (agreement with the RGI of 0.96, a mean precision (user’s accuracy of the snow/ice cover class of 0.92, a mean recall (producer’s accuracy of the snow/ice cover class of 0.86, and a mean F-score (a measure that considers both precision and recall of 0.88. We also compared results from our approach to glacier area mapped from high spatial resolution imagery at four study regions and found similar results. Accuracy was lowest in regions with substantial areas of debris-covered glacier ice, suggesting that manual editing would still be required in these regions to achieve reasonable results. The similarity of our results to those from the RGI as well as glacier area mapped from high spatial resolution imagery suggests it should be possible to apply this approach across large regions to produce updated 30-m resolution maps of persistent ice and snow cover. In the short term, automated PISC maps can be used to

  13. An automated approach for mapping persistent ice and snow cover over high latitude regions

    Science.gov (United States)

    Selkowitz, David J.; Forster, Richard R.

    2016-01-01

    We developed an automated approach for mapping persistent ice and snow cover (glaciers and perennial snowfields) from Landsat TM and ETM+ data across a variety of topography, glacier types, and climatic conditions at high latitudes (above ~65°N). Our approach exploits all available Landsat scenes acquired during the late summer (1 August–15 September) over a multi-year period and employs an automated cloud masking algorithm optimized for snow and ice covered mountainous environments. Pixels from individual Landsat scenes were classified as snow/ice covered or snow/ice free based on the Normalized Difference Snow Index (NDSI), and pixels consistently identified as snow/ice covered over a five-year period were classified as persistent ice and snow cover. The same NDSI and ratio of snow/ice-covered days to total days thresholds applied consistently across eight study regions resulted in persistent ice and snow cover maps that agreed closely in most areas with glacier area mapped for the Randolph Glacier Inventory (RGI), with a mean accuracy (agreement with the RGI) of 0.96, a mean precision (user’s accuracy of the snow/ice cover class) of 0.92, a mean recall (producer’s accuracy of the snow/ice cover class) of 0.86, and a mean F-score (a measure that considers both precision and recall) of 0.88. We also compared results from our approach to glacier area mapped from high spatial resolution imagery at four study regions and found similar results. Accuracy was lowest in regions with substantial areas of debris-covered glacier ice, suggesting that manual editing would still be required in these regions to achieve reasonable results. The similarity of our results to those from the RGI as well as glacier area mapped from high spatial resolution imagery suggests it should be possible to apply this approach across large regions to produce updated 30-m resolution maps of persistent ice and snow cover. In the short term, automated PISC maps can be used to rapidly

  14. High-resolution HI and CO observations of high-latitude intermediate-velocity clouds

    CERN Document Server

    Röhser, T; Bekhti, N Ben; Winkel, B

    2016-01-01

    Intermediate-velocity clouds (IVCs) are HI halo clouds that are likely related to a Galactic fountain process. In-falling IVCs are candidates for the re-accretion of matter onto the Milky Way. We study the evolution of IVCs at the disk-halo interface, focussing on the transition from atomic to molecular IVCs. We compare an atomic IVC to a molecular IVC and characterise their structural differences in order to investigate how molecular IVCs form high above the Galactic plane. With high-resolution HI observations of the Westerbork Synthesis Radio Telescope and 12CO(1-0) and 13CO(1-0) observations with the IRAM 30m telescope, we analyse the small-scale structures within the two clouds. By correlating HI and far-infrared (FIR) dust continuum emission from the Planck satellite, the distribution of molecular hydrogen (H2) is estimated. We conduct a detailed comparison of the HI, FIR, and CO data and study variations of the $X_\\rm{CO}$ conversion factor. The atomic IVC does not disclose detectable CO emission. The a...

  15. On the importance of appropriate precipitation gauge catch correction for hydrological modelling at mid to high latitudes

    Directory of Open Access Journals (Sweden)

    S. Stisen

    2012-11-01

    . We conclude that TSV precipitation correction should be carried out for studies requiring a sound dynamic description of hydrological processes, and it is of particular importance when using hydrological models to make predictions for future climates when the snow/rain composition will differ from the past climate. This conclusion is expected to be applicable for mid to high latitudes, especially in coastal climates where winter precipitation types (solid/liquid fluctuate significantly, causing climatological mean correction factors to be inadequate.

  16. High-latitude E and F region coupling signature: A case study results from rapid-run ionosonde

    Science.gov (United States)

    Shalimov, S.; Kozlovsky, A.

    2015-04-01

    Rapid-run ionosonde installed in the high-latitude Sodankylä Geophysical Observatory enables us to observe for the first time extraordinary details of E-F region coupling process in high-latitude ionosphere during geomagnetically quiet period. We present an example on 15 August 2009 when a dense, patchy sporadic E layer was detected. Associated with this unstable sporadic E layer, exhibiting in addition an unusual enhancement with a vertical extent of about 10 km, the highly structured F layer plasma was observed with apparent plasma depletions. We examine this event taking into account the presence of mesoscale traveling ionospheric disturbances which can initiate coupling between these two regions and compare the data with current theories.

  17. High-altitude wind resources in the Middle East

    KAUST Repository

    Yip, Chak Man Andrew

    2017-08-23

    In the Middle East, near-surface wind resources are intermittent. However, high-altitude wind resources are abundant, persistent, and readily available and may provide alternative energy resources in this fossil-fuel-dependent region. Using wind field data from the Modern-Era Retrospective Analysis for Research and Applications Version 2 (MERRA-2), this study identifies areas favorable to the deployment of airborne wind energy (AWE) systems in the Middle East and computes the optimal heights at which such systems would best operate. AWE potential is estimated using realistic AWE system specifications and assumptions about deployment scenarios and is compared with the near-surface wind generation potential with respect to diurnal and seasonal variability. The results show the potential utility of AWE in areas in the Middle East where the energy demand is high. In particular, Oman and Saudi Arabia have a high level of the potential power generation with low annual variability.

  18. High-altitude wind resources in the Middle East.

    Science.gov (United States)

    Yip, Chak Man Andrew; Gunturu, Udaya Bhaskar; Stenchikov, Georgiy L

    2017-08-29

    In the Middle East, near-surface wind resources are intermittent. However, high-altitude wind resources are abundant, persistent, and readily available and may provide alternative energy resources in this fossil-fuel-dependent region. Using wind field data from the Modern-Era Retrospective Analysis for Research and Applications Version 2 (MERRA-2), this study identifies areas favorable to the deployment of airborne wind energy (AWE) systems in the Middle East and computes the optimal heights at which such systems would best operate. AWE potential is estimated using realistic AWE system specifications and assumptions about deployment scenarios and is compared with the near-surface wind generation potential with respect to diurnal and seasonal variability. The results show the potential utility of AWE in areas in the Middle East where the energy demand is high. In particular, Oman and Saudi Arabia have a high level of the potential power generation with low annual variability.

  19. Verification of high-speed solar wind stream forecasts using operational solar wind models

    DEFF Research Database (Denmark)

    Reiss, Martin A.; Temmer, Manuela; Veronig, Astrid M.

    2016-01-01

    High-speed solar wind streams emanating from coronal holes are frequently impinging on the Earth's magnetosphere causing recurrent, medium-level geomagnetic storm activity. Modeling high-speed solar wind streams is thus an essential element of successful space weather forecasting. Here we evaluate...... high-speed stream forecasts made by the empirical solar wind forecast (ESWF) and the semiempirical Wang-Sheeley-Arge (WSA) model based on the in situ plasma measurements from the Advanced Composition Explorer (ACE) spacecraft for the years 2011 to 2014. While the ESWF makes use of an empirical relation...... between the coronal hole area observed in Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) images and solar wind properties at the near-Earth environment, the WSA model establishes a link between properties of the open magnetic field lines extending from the photosphere to the corona...

  20. Scientific Studies of the High-Latitude Ionosphere with the Ionosphere Dynamics and ElectroDynamics - Data Assimilation (IDED-DA) Model

    Science.gov (United States)

    2014-09-23

    titlelScientific Studies of the High-Latitude Ionosphere with the Ionosphere Dynamics and Electrodynamics-Data Assimilation (IDED-DA) Model...awardnumberl]N00014-13-l-0267 [awardnumber2] [awardnumbermore] [keywords]Ionosphere, Assimilation , Simulations [specialcat] [pillRobert W...totalminoritypostdocs] [bestaccomplishment] With only ground magnetometer measurements, our high-latitude data assimilation model can track the

  1. Persistence of biological nitrogen fixation in high latitude grass-clover grasslands under different management practices

    Science.gov (United States)

    Tzanakakis, Vasileios; Sturite, Ievina; Dörsch, Peter

    2016-04-01

    Biological nitrogen fixation (BNF) can substantially contribute to N supply in permanent grasslands, improving N yield and forage quality, while reducing inorganic N inputs. Among the factors critical to the performance of BNF in grass-legume mixtures are selected grass and legume species, proportion of legumes, the soil-climatic conditions, in particular winter conditions, and management practices (e.g. fertilization and compaction). In high latitude grasslands, low temperatures can reduce the performance of BNF by hampering the legumés growth and by suppressing N2 fixation. Estimation of BNF in field experiments is not straightforward. Different methods have been developed providing different results. In the present study, we evaluated the performance of BNF, in a newly established field experiment in North Norway over four years. The grassland consisted of white clover (Trifolium repens L.) and red clover (Trifolium pretense L.) sawn in three proportions (0, 15 and 30% in total) together with timothy (Pheum pretense L.) and meadow fescue (Festuca pratensis L.). Three levels of compaction were applied each year (no tractor, light tractor, heavy tractor) together with two different N rates (110 kg N/ha as cattle slurry or 170 kg N/ha as cattle slurry and inorganic N fertilizer). We applied two different methods, the 15N natural abundance and the difference method, to estimate BNF in the first harvest of each year. Overall, the difference method overestimated BNF relative to the 15N natural abundance method. BNF in the first harvest was compared to winter survival of red and white clover plants, which decreased with increasing age of the grassland. However, winter conditions did not seem to affect the grassland's ability to fix N in spring. The fraction of N derived from the atmosphere (NdfA) in white and red clover was close to 100% in each spring, indicating no suppression of BNF. BNF increased the total N yield of the grasslands by up to 75%, mainly due to high

  2. Land Cover Mapping in Northern High Latitude Permafrost Regions with Satellite Data: Achievements and Remaining Challenges

    Directory of Open Access Journals (Sweden)

    Annett Bartsch

    2016-11-01

    resolution around 30 m has been shown to be suitable for a range of applications. This implies that the current Landsat-8, as well as Sentinel-2 missions would be adequate as input data. Recent studies have exemplified the value of Synthetic Aperture Radar (SAR in tundra regions. SAR missions may be therefore of added value for large-scale high latitude land cover mapping.

  3. Ion-neutral coupling in the high-latitude F-layer from incoherent scatter and Fabry-Perot interferometer measurements

    Directory of Open Access Journals (Sweden)

    K. Cierpka

    Full Text Available Since the auroral ionosphere provides an important energy sink for the magnetosphere, ionosphere-thermosphere coupling must be investigated when considering the energy budget of the ionosphere-magnetosphere coupling. We present the first Scandinavian ground-based study of high-latitude F-region ion-neutral frictional heating where ion velocity and temperature are measured by the EISCAT incoherent scatter radar as well as neutral wind and temperature being measured simultaneously by a Fabry-Perot interferometer. A geomagnetically active period (Kp = 7 – 5 and quiet period (Kp = 0+ – 0 were studied. Neglecting the neutral wind can result in errors of frictional heating estimates of 60% or more in the F-layer. About 96% of the local ion temperature enhancement over the neutral temperature is accounted for by ion-neutral frictional heating.

    Key words: Ionosphere (auroral ionosphere; ionosphere-atmosphere interactions

  4. The role of midlatitude mixing barriers in creating the annual variation of total ozone in high northern latitudes

    Science.gov (United States)

    Gille, John; Karol, Svetlana; Kinnison, Douglas; Lamarque, Jean-Francois; Yudin, Valery

    2014-08-01

    Data from the HIgh Resolution Dynamics Limb Sounder (HIRDLS), the Microwave Limb Sounder (MLS), and the Whole Atmosphere Community Climate Model (WACCM) are used to investigate the annual variation of total column ozone in high northern latitudes. Downward transport of ozone-rich air by the residual mean circulation during autumn and winter bends ozone isopleths down and increases the high-latitude ozone amounts, leading to an ozone maximum at the end of the winter. During the summer months eddy mixing acts to restore pre-fall distributions of ozone. In this study the large-scale mixing in the lower stratosphere is analyzed using Nakamura's (1996) equivalent length formulation with observed and simulated ozone. The analysis of ozone mixing is performed in the tracer equivalent latitude-potential temperature coordinate system. Steep latitudinal gradients of ozone isopleths below about 500 K occur during the winter, where there are minima in the equivalent length, indicating barriers to mixing at 30°N-40°N. This transport barrier allows large ozone maxima to develop poleward of it. The barrier disappears over the summer, permitting latitudinal mixing of the high ozone air. Above 500 K mixing is more effective during the winter, so a large winter maximum does not occur. In both midlatitude and high latitude the lower stratospheric layer from 330 to 500 K doubles its ozone content from autumn to spring, compared with much smaller changes in the layer from 500 to 650 K. Our results confirm that the presence of the winter transport barrier in the lower stratosphere controls the seasonal variation of total ozone.

  5. Wp index: A new substorm index derived from high-resolution geomagnetic field data at low latitude

    DEFF Research Database (Denmark)

    Nose, M.; Iyemori, T.; Wang, L.

    2012-01-01

    Geomagnetic field data with high time resolution (typically 1 s) have recently become more commonly acquired by ground stations. Such high time resolution data enable identifying Pi2 pulsations which have periods of 40-150 s and irregular (damped) waveforms. It is well-known that pulsations...... of this type are clearly observed at mid-and low-latitude ground stations on the nightside at substorm onset. Therefore, with 1-s data from multiple stations distributed in longitude around the Earth's circumference, substorm onset can be regularly monitored. In the present study we propose a new substorm...... index, the Wp index (Wave and planetary), which reflects Pi2 wave power at low-latitude, using geomagnetic field data from 11 ground stations. We compare the Wp index with the AE and ASY indices as well as the electron flux and magnetic field data at geosynchronous altitudes for 11 March 2010. We find...

  6. Quantifying the trade-off between carbon sequestration and albedo in midlatitude and high-latitude North American forests

    Science.gov (United States)

    Mykleby, P. M.; Snyder, P. K.; Twine, T. E.

    2017-03-01

    Afforestation is a viable and widely practiced method of sequestering carbon dioxide from the atmosphere. However, because of a change in surface albedo, placement of less reflective forests can cause an increase in net-absorbed radiation and localized surface warming. This effect is enhanced in northern high latitudes where the presence of snow cover exacerbates the albedo difference. Regions where afforestation could provide a climate benefit are determined by comparing net ecosystem production and net radiation differences from afforestation in midlatitude and high latitude of North America. Using the dynamic vegetation model Integrated Biosphere Simulator, agricultural version (Agro-IBIS), we find a boundary through North America where afforestation results in a positive equivalent carbon balance (cooling) to the south, and a negative equivalent carbon balance (warming) to the north. Including the effects of stand age and fraction cover affect whether a site contributes to mitigating global warming.

  7. Modeling of nitrobenzene in the river with ice process in high-latitude regions

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    To deal with the accidental release of pollutants into frozen rivers, those rivers in high-latitude regions should be treated differently. Pollutants could be stored up in the ice and released when the ice melts in spring, perhaps resulting in secondary pollution in the river. A water quality model of nitrobenzene has been developed in this paper to assess the influence on river water quality due to the freezing process. The model is made up of three modules: thermodynamic module, hydrodynamic module and water quality module. The thermodynamic module considers the complex heat exchange processes between the water body and the atmosphere, the water body and the river bed, the water body and the ice cover, and so on. The growth of the ice cover is simulated in a simplified form whilst taking consideration of heat balance. The hydrodynamic model uses the Saint-Venant equations in non-constant flow and the influence of the ice cover is measured. The degradation, diffusion, absorption and desorption, and the influence of the freezing process are incorporated in the water quality module and the concept of Con- tinuously Stirred Tanked Reactors (CSTRs) model is applied in the model construction. The model has been applied to supporting the management of accidental pollution in the Songhua River. The model was calibrated and validated with monitored data. Regional sensitivity analysis based on a task-based Hornberger-Spear-Young (HSY) algorithm was carried out to examine the model structure and the re- sult showed that the model could describe the system very well. Then the conditioned model was ap- plied to predicting the concentration of nitrobenzene in the water when the ice melted in spring. The predictive result showed that the release of pollutants in the ice could lead to an increase in the con- centration of pollutants in the water, but the increase would be very small because there was only a small amount of pollutants stored in the ice. A secondary pollution

  8. The Neogene Redbeds of Iceland - a High-Latitude Terrestrial Paleoclimate Monitor Driven by Chemical Weathering

    Science.gov (United States)

    Riishuus, M. S.; Bird, D. K.

    2012-12-01

    Chemical weathering of tephra and aeolian dust of basaltic composition produces clays and iron oxide/hydroxide minerals preserved in reddened layers referred to as redbeds, boles or paleosols. We propose that the extent of weathering of Neogene redbeds in Iceland and the isotopic composition of structurally bound water in associated weathering clay preserve records of high-latitude paleoclimatic and hydrologic conditions. In support we present whole-rock geochemistry and smectite D/H compositions of redbed horizons from Iceland for comparative analysis with global paleoclimate trends and local independent proxy data. Smectite δD values of 35 basaltic tephras in Iceland (~15-2 Ma) display a general decrease in δD compositions from -110 to -105 ‰ at ~15-13 Ma to -115 to -118 ‰ at ~3-2 Ma which correlates well with the global cooling trend from the Middle Miocene Climatic Optimum (17-15 Ma) to present day. Furthermore, the extent of weathering expressed by the Chemical Index of Weathering increases from 40-50 at 2-3 Ma to 80-90 at 15-16 Ma suggesting enhanced chemical weathering rates during the warmer climate conditions. The weathering extent of modern andosols in Iceland is temperature-dependant and allows construction of a paleo-climate proxy [1]. Application of this proxy suggests that mean annual temperatures (MATs) increased from ~0°C at ~2 Ma to ~9°C at 15-16 Ma in general agreement with independent local proxy data. The δD values of paleo meteoric waters in Iceland, estimated using a smectite-water fractionation factor and model MATs, decrease from -41 ‰ at 15-16 Ma (9°C) to -45 ‰ at 2 Ma (0°C). The paleo meteoric water compositions are increasingly enriched in deuterium relative to present day meteoric water in Iceland (δD ≤ -50 ‰). This is in agreement with global cooling since Middle Miocene toward ice-dominated conditions with greater equator-to-pole temperature contrasts, affecting the distillation process between ocean, atmosphere and

  9. System-level view of geospace dynamics: Challenges for high-latitude ground-based observations

    Science.gov (United States)

    Donovan, E.

    2014-12-01

    high latitude ground based observations can address these challenges.

  10. Absorption properties of high-latitude Norwegian coastal water: The impact of CDOM and particulate matter

    Science.gov (United States)

    Nima, Ciren; Frette, Øyvind; Hamre, Børge; Erga, Svein Rune; Chen, Yi-Chun; Zhao, Lu; Sørensen, Kai; Norli, Marit; Stamnes, Knut; Stamnes, Jakob J.

    2016-09-01

    We present data from measurements and analyses of the spectral absorption due to colored dissolved organic matter (CDOM), total suspended matter (TSM), phytoplankton, and non-algal particles (NAP) in high-latitude northern Norwegian coastal water based on samples taken in spring, summer, and autumn. The Chlorophyll-a (Chl-a) concentration was found to vary significantly with season, whereas regardless of season CDOM was found to be the dominant absorber for wavelengths shorter than 600 nm. The absorption spectral slope S350-500 for CDOM varied between 0.011 and 0.022 nm-1 with mean value and standard deviation given by (0.015 ± 0.002) nm-1. The absorption spectral slope was found to be strongly dependent on the wavelength interval used for fitting. On average, S280-500 was found to be 43% higher than S350-500. A linear relationship was found between the base 10 logarithm of the absorption coefficient at 440 nm [log(ag(440))] and S350-500. Regardless of season, phytoplankton were the dominant component of the TSM absorption indicating little influence from land drainage. The mean values of the Chl-a specific absorption coefficient of phytoplankton aph*(λ) at 440 nm and 676 nm were 0.052 m2 mg-1 and 0.023 m2 mg-1, respectively, and aph*(λ) was found to vary with season, being higher in summer and autumn than in spring. The absorption spectral slope SNAP, which is the spectral slope of absorption spectrum for non-algal particles, was lower than that for European coastal water in general. It varied between 0.0048 and 0.022 nm-1 with mean value and standard deviation given by (0.0083-1 ± 0.003) nm-1. Comparisons of absorption coefficients measured in situ using an ac-9 instrument with those measured in the laboratory from water samples show a good agreement.

  11. Modeling of nitrobenzene in the river with ice process in high-latitude regions

    Institute of Scientific and Technical Information of China (English)

    SUN PengCheng; ZENG SiYu; CHEN JiNing

    2009-01-01

    To deal with the accidental release of pollutants into frozen rivers,those rivers in high-latitude regions should be treated differently.Pollutants could be stored up in the ice and released when the ice melts in spring,perhaps resulting in secondary pollution in the river.A water quality model of nitrobenzene has been developed in this paper to assess the influence on river water quality due to the freezing process.The model is made up of three modules:thermodynamic module,hydrodynamic module and water quality module.The thermodynamic module considers the complex heat exchange processes between the water body and the atmosphere,the water body and the river bed,the water body and the ice cover,and so on.The growth of the ice cover is simulated in a simplified form whilst taking consideration of heat balance.The hydrodynamic model uses the Saint-Venant equations in non-constant flow and the influence of the ice cover is measured.The degradation,diffusion,absorption and desorption,and the influence of the freezing process are incorporated in the water quality module and the concept of Continuously Stirred Tanked Reactors (CSTRs) model is applied in the model construction.The model has been applied to supporting the management of accidental pollution in the Songhua River.The model was calibrated and validated with monitored data.Regional sensitivity analysis based on a task-based Hornberger-Spear-Young (HSY) algorithm was carried out to examine the model structure and the result showed that the model could describe the system very well.Then the conditioned model was applied to predicting the concentration of nitrobenzene in the water when the ice melted in spring.The predictive result showed that the release of pollutants in the ice could lead to an increase in the concentration of pollutants in the water,but the increase would be very small because there was only a small amount of pollutants stored in the ice.A secondary pollution could therefore be avoided

  12. The high-latitude cloud MBM 7. I. H I and CO observations

    Science.gov (United States)

    Minh, Y. C.; Park, Y. S.; Kim, K. T.; Irvine, W. M.; Brewer, M. K.; Turner, B. E.

    1996-01-01

    The high-latitude cloud (HLC) MBM 7 has been observed in the 21 cm H I line and the 12CO(1-0) and 13CO(1-0) lines with similar spatial resolutions. The data reveal a total mass approximately 30 M solar for MBM 7 and a complex morphology. The cloud consists of a cold dense core of 5 M solar surrounded by atomic and molecular gas with about 25 M solar, which is embedded in hotter and more diffuse H I gas. We derive a total column density N(H I + 2H2) of 1 x 10(21) cm-2 toward the center and 1 x 10(20) cm-3 toward the envelope of MBM 7. The CO line indicates the existence of dense cores [n(H2) > or = 2000 cm-3] of size (FWHM) approximately 0.5 pc. The morphology suggests shock compression from the southwest direction, which can form molecular cores along the direction perpendicular to the H I distribution. The H I cloud extends to the northeast, and the velocity gradient appears to be about 2.8 km s-1 pc-1 in this direction, which indicates a systematic outward motion which will disrupt the cloud in approximately 10(6) yr. The observed large line widths of approximately 2 km s-1 for CO suggest that turbulent motions exist in the cloud, and hydrodynamical turbulence may dominate the line broadening. Considering the energy and pressure of MBM 7, the dense cores appear not to be bound by gravity, and the whole cloud including the dense cores seem to be expanding. The distance to HLCs suggest that they belong to the galactic plane, since the scale height of the cloud is < or approximately equal to 100 pc. Compared to the more familiar dense dark clouds, HLCs may differ only in their small mass and low density, with their proximity reducing the filling factor and enhancing the contrast of the core and envelope structure.

  13. A High Efficiency Wind Energy System

    DEFF Research Database (Denmark)

    Khan, M. Z.; Hussain, M. M.; Naveed, M. M.;

    2012-01-01

    In this paper, a wind generator system that employs a Fourphase Interleaved Bi-directional DC / DC Converter, a Selective Harmonic Elimination Sinusoidal Pulse Width Modulation (SHE SPWM) based Inverter and a PermanentMagnet Synchronous Generator (PMSG) is studied. The merits of using the topolog...

  14. A Comparison of High-Latitude Ionosphere Propagation Predictions from AMBCOM with Measured Data

    Science.gov (United States)

    1991-03-01

    radar . The point-to-point mode performs raytracing from a transmitter to a receiver and was used for this thesis. RIAYTRA co,-,putes grokil times... RADAR C and AMBCOM....... 9 3. Thc Naval Postgraduate School Studies ......................... 9 II. THE AMBIENT COMMUNICATIONS MO0DEL (AMBCOM...the transpolar path such as the a communications blackout on 12 November 1986. [Ref. 11] 2. Hi2h-Latitude HF Predictions From RADAR C and AMBCOM

  15. Parallel electron streaming in the high-latitude E region and its effect on the incoherent scatter spectrum

    Science.gov (United States)

    Bahcivan, H.; Cosgrove, R. B.; Tsunoda, R. T.

    2006-07-01

    This article investigates the combined electron heating and streaming effects of low-frequency parallel electric fields on the incoherent scatter measurements of the high-latitude E region. The electric fields distort the electron distribution function, inducing changes on the amplitude and frequency of the ion-acoustic line in the measured incoherent scatter spectrum. If one assumes Maxwellian electrons, the measurements of electron and ion temperatures and electron density are subject to significant percentage errors during geomagnetically active conditions.

  16. A Balloon-borne Measurement of High Latitude Atmospheric Neutrons Using a LiCAF Neutron Detector

    CERN Document Server

    Kole, Merlin; Fukuda, Kentaro; Ishizu, Sumito; Jackson, Miranda; Kamae, Tune; Kawaguchi, Noriaki; Kawano, Takafumi; Kiss, Mózsi; Moretti, Elena; Salinas, Maria Fernanda Muñoz; Pearce, Mark; Rydström, Stefan; Takahashi, Hiromitsu; Yanagida, Takayuki

    2013-01-01

    PoGOLino is a scintillator-based neutron detector. Its main purpose is to provide data on the neutron flux in the upper stratosphere at high latitudes at thermal and nonthermal energies for the PoGOLite instrument. PoGOLite is a balloon borne hard X-ray polarimeter for which the main source of background stems from high energy neutrons. No measurements of the neutron environment for the planned flight latitude and altitude exist. Furthermore this neutron environment changes with altitude, latitude and solar activity, three variables that will vary throughout the PoGOLite flight. PoGOLino was developed to study the neutron environment and the influences from these three variables upon it. PoGOLino consists of two Europium doped Lithium Calcium Aluminium Fluoride (Eu:LiCAF) scintillators, each of which is sandwiched between 2 Bismuth Germanium Oxide (BGO) scintillating crystals, which serve to veto signals produced by gamma-rays and charged particles. This allows the neutron flux to be measured even in high rad...

  17. PFISR GPS tracking mode for researching high-latitude ionospheric electron density gradients associated with GPS scintillation

    Science.gov (United States)

    Loucks, D. C.; Palo, S. E.; Pilinski, M.; Crowley, G.; Azeem, S. I.; Hampton, D. L.

    2016-12-01

    Ionospheric behavior in the high-latitudes can significantly impact Ultra High Frequency (UHF) signals in the 300 MHz to 3 GHz band, resulting in degradation of Global Positioning System (GPS) position solutions and satellite communications interruptions. To address these operational concerns, a need arises to identify and understand the ionospheric structure that leads to disturbed conditions in the Arctic. Structures in the high-latitude ionosphere are known to change on the order of seconds or less, can be decameters to kilometers in scale, and elongate across magnetic field lines at auroral latitudes. Nominal operations at Poker Flat Incoherent Scatter Radar (PFISR) give temporal resolution on the order of minutes, and range resolution on the order of tens of kilometers, while specialized GPS receivers available for ionospheric sensing have a 100Hz observation sampling rate. One of these, ASTRA's Connected Autonomous Space Environment Sensor (CASES) is used for this study. We have developed a new GPS scintillation tracking mode for PFISR to address open scientific questions regarding temporal and spatial electron density gradients. The mode will be described, a number of experimental campaigns will be analyzed, and results and lessons learned will be presented.

  18. Large-scale traveling ionospheric disturbances observed using GPS receivers over high-latitude and equatorial regions

    Science.gov (United States)

    Idrus, Intan Izafina; Abdullah, Mardina; Hasbi, Alina Marie; Husin, Asnawi; Yatim, Baharuddin

    2013-09-01

    This paper presents the first results of large-scale traveling ionospheric disturbances (LSTIDs) observation during two moderate magnetic storm events on 28 May 2011 (SYM-H∼ -94 nT and Dst∼-80 nT) and 6 August 2011 (SYM-H∼-126 nT and Dst∼-113 nT) over the high-latitude region in Russia, Sweden, Norway, Iceland and Greenland and equatorial region in the Peninsular Malaysia using vertical total electron content (VTEC) from the Global Positioning System (GPS) observations measurement. The propagation of the LSTID signatures in the GPS TEC measurements over Peninsular Malaysia was also investigated using VTEC map. The LSTIDs were found to propagate both equatorward and poleward directions during these two events. The results showed that the LSTIDs propagated faster at high-latitude region with an average phase velocity of 1074.91 m/s than Peninsular Malaysia with an average phase velocity of 604.84 m/s. The LSTIDs at the high-latitude region have average periods of 150 min whereas the ones observed over Peninsular Malaysia have average periods of 115 min. The occurrences of these LSTIDs were also found to be the subsequent effects of substorm activities in the auroral region. To our knowledge, this is the first result of observation of LSTIDs over Peninsular Malaysia during the 24th solar cycle.

  19. Mean Climatic Characteristics in High Northern Latitudes in an Ocean-Sea Ice-Atmosphere Coupled Model

    Institute of Scientific and Technical Information of China (English)

    刘喜迎; 张学洪; 俞永强; 宇如聪

    2004-01-01

    Emphasizing the model's ability in mean climate reproduction in high northern latitudes, results from an ocean-sea ice-atmosphere coupled model are analyzed. It is shown that the coupled model can simulate the main characteristics of annual mean global sea surface temperature and sea level pressure well, but the extent of ice coverage produced in the Southern Hemisphere is not large enough. The main distribution characteristics of simulated sea level pressure and temperature at 850 hPa in high northern latitudes agree well with their counterparts in the NCEP reanalysis dataset, and the model can reproduce the Arctic Oscillation (AO) mode successfully. The simulated seasonal variation of sea ice in the Northern Hemisphere is rational and its main distribution features in winter agree well with those from observations.But the ice concentration in the sea ice edge area close to the Eurasian continent in the inner Arctic Ocean is much larger than the observation. There are significant interannual variation signals in the simulated sea ice concentration in winter in high northern latitudes and the most significant area lies in the Greenland Sea, followed by the Barents Sea. All of these features agree well with the results from observations.

  20. Verification of high-speed solar wind stream forecasts using operational solar wind models

    CERN Document Server

    Reiss, Martin A; Veronig, Astrid M; Nikolic, Ljubomir; Vennerstrom, Susanne; Schoengassner, Florian; Hofmeister, Stefan J

    2016-01-01

    High-speed solar wind streams emanating from coronal holes are frequently impinging on the Earth's magnetosphere causing recurrent, medium-level geomagnetic storm activity. Modeling high-speed solar wind streams is thus an essential element of successful space weather forecasting. Here we evaluate high-speed stream forecasts made by the empirical solar wind forecast (ESWF) and the semiempirical Wang-Sheeley-Arge (WSA) model based on the in situ plasma measurements from the ACE spacecraft for the years 2011 to 2014. While the ESWF makes use of an empirical relation between the coronal hole area observed in Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) images and solar wind properties at the near-Earth environment, the WSA model establishes a link between properties of the open magnetic field lines extending from the photosphere to the corona and the background solar wind conditions. We found that both solar wind models are capable of predicting the large-scale features of the observed sol...

  1. In Situ Balloon-Borne Ice Particle Imaging in High-Latitude Cirrus

    Science.gov (United States)

    Kuhn, Thomas; Heymsfield, Andrew J.

    2016-09-01

    Cirrus clouds reflect incoming solar radiation, creating a cooling effect. At the same time, these clouds absorb the infrared radiation from the Earth, creating a greenhouse effect. The net effect, crucial for radiative transfer, depends on the cirrus microphysical properties, such as particle size distributions and particle shapes. Knowledge of these cloud properties is also needed for calibrating and validating passive and active remote sensors. Ice particles of sizes below 100 µm are inherently difficult to measure with aircraft-mounted probes due to issues with resolution, sizing, and size-dependent sampling volume. Furthermore, artefacts are produced by shattering of particles on the leading surfaces of the aircraft probes when particles several hundred microns or larger are present. Here, we report on a series of balloon-borne in situ measurements that were carried out at a high-latitude location, Kiruna in northern Sweden (68N 21E). The method used here avoids these issues experienced with the aircraft probes. Furthermore, with a balloon-borne instrument, data are collected as vertical profiles, more useful for calibrating or evaluating remote sensing measurements than data collected along horizontal traverses. Particles are collected on an oil-coated film at a sampling speed given directly by the ascending rate of the balloon, 4 m s-1. The collecting film is advanced uniformly inside the instrument so that an always unused section of the film is exposed to ice particles, which are measured by imaging shortly after sampling. The high optical resolution of about 4 µm together with a pixel resolution of 1.65 µm allows particle detection at sizes of 10 µm and larger. For particles that are 20 µm (12 pixel) in size or larger, the shape can be recognized. The sampling volume, 130 cm3 s-1, is well defined and independent of particle size. With the encountered number concentrations of between 4 and 400 L-1, this required about 90- to 4-s sampling times to

  2. Can bioenergy cropping compensate high carbon emissions from large-scale deforestation of mid to high latitudes?

    Directory of Open Access Journals (Sweden)

    P. Dass

    2013-02-01

    Full Text Available Numerous studies have concluded that deforestation of mid to high latitudes result in a global cooling. This is mainly because of the increased albedo of deforested land which dominates over other biogeophysical and biogeochemical mechanisms in the energy balance. This dominance however may be due to an underestimation of the biogeochemical response, as carbon emissions are typically at or below the lower end of estimates. Here, we use the dynamic global vegetation model LPJmL for a better estimate of the carbon cycle under such large-scale deforestation. These studies are purely academic to understand the role of vegetation in the energy balance and the earth system. They must not be mistaken as possible mitigation options, because of the devastating effects on pristine ecosystems. We show that even optimistic assumptions on the manageability of these areas and its utilization for bioenergy crops could not make up for the strong carbon losses in connection with the losses of vegetation carbon and the long-term decline of soil carbon stocks. We find that the global biophysical bioenergy potential is 78.9 ± 7.9 EJ yr−1 of primary energy at the end of the 21st century for the most plausible scenario. Due to avoided usage of fossil fuels over the time frame of this experiment, the cooling due to the biogeophysical feedback could be supplemented by an avoided warming of approximately 0.1 to 0.3 °C. However, the extensive deforestation simulated in this study causes an immediate emission of 182.3 ± 0.7 GtC followed by long term emissions. In the most plausible scenario, this carbon debt is not neutralized even if bioenergy production is assumed to be carbon-neutral other than for the land use emissions so that global temperatures would increase by ~0.2 to 0.6 °C by the end of the 21st century. The carbon dynamics in the high latitudes, especially with respect to permafrost dynamics and long-term carbon losses, require additional attention in

  3. High latitude currents in the 0600 to 0900 MLT sector - Observations from Viking and DMSP-F7

    Science.gov (United States)

    Bythrow, P. F.; Potemra, T. A.; Zanetti, L. J.; Erlandson, R. A.; Hardy, D. A.; Rich, F. J.; Acuna, M. H.

    1987-01-01

    High-resolution magnetic field and charged-particle data acquired on March 25, 1986 by the Viking and DMSP-F7 satellites, as they traversed the dawn sector auroral zone on nearly antiparallel trajectories within 40 min of each oher, are analyzed. Magnetic field measurements by Viking at 0850 MLT and by DMSP at 0630 MLT indicate the presence of a large-scale earthward-directed region 1 Birkeland current and an upward-flowing region 2 current. Both satellites also observed a third Birkeland current adjacent to and poleward of the region 1 system with opposite flow. This poleward system is about 0.5 deg invariant latitude wide and has a current density comparable to the region 1 and 2 systems. The highest-latitude current is identified as region 0. Its charged-particle signatures were used to infer field line mapping to the equatorial plane.

  4. Site-level model intercomparison of high latitude and high altitude soil thermal dynamics in tundra and barren landscapes

    Directory of Open Access Journals (Sweden)

    A. Ekici

    2014-09-01

    Full Text Available Modelling soil thermal dynamics at high latitudes and altitudes requires representations of specific physical processes such as snow insulation, soil freezing/thawing, as well as subsurface conditions like soil water/ice content and soil texture type. We have compared six different land models (JSBACH, ORCHIDEE, JULES, COUP, HYBRID8, LPJ-GUESS at four different sites with distinct cold region landscape types (i.e. Schilthorn-Alpine, Bayelva-high Arctic, Samoylov-wet polygonal tundra, Nuuk-non permafrost Arctic to quantify the importance of physical processes in capturing observed temperature dynamics in soils. This work shows how a range of models can represent distinct soil temperature regimes in permafrost and non-permafrost soils. Snow insulation is of major importance for estimating topsoil conditions and must be combined with accurate subsoil temperature dynamics to correctly estimate active layer thicknesses. Analyses show that land models need more realistic surface processes (such as detailed snow dynamics and moss cover with changing thickness/wetness as well as better representations of subsoil thermal dynamics (i.e. soil heat transfer mechanism and correct parameterization of heat conductivity/capacities.

  5. Wake flow characteristics at high wind speed

    DEFF Research Database (Denmark)

    Aagaard Madsen, Helge; Larsen, Torben J.; Larsen, Gunner Chr.

    2016-01-01

    power. In the present study we simulate the wake flow for a row of turbines with the wind aligned with the row using a simplified approach. The velocity deficit, being a function of the thrust coefficient, is simulated based on the BEM solution for wake expansion. An axis-symmetric boundary layer...... equation model (the same as implemented in the DWM model) is subsequently used to develop the deficit down to the next turbine, and then the approach is successively repeated. Simulation results for four different spacing’s in a row with eight turbines show that there are two major flow regimes...... in the intersection region between the two flow regimes a strong variation in power and thrust occur, e.g. going from almost zero power to rated power for a wind speed change of 4m/s. Another result is that the inflow profile to the last turbine in the row at a wind speed of 16m/s for a spacing of 3D shows...

  6. Current state and prospects of carbon management in high latitudes of Northern Eurasia

    Science.gov (United States)

    Schepaschenko, Dmitry; Shvidenko, Anatoly

    2010-05-01

    The current state and trajectories of future development of natural landscapes in high latitudes of Northern Eurasia are defined inter alia by (1) current unsatisfactory social and economic situation in boreal Northern Eurasia; (2) the dramatic magnitude of on-going and expected climatic change (warming up to 10-12oC under global warming at 4oC); (3) increasing anthropogenic pressure, particularly in regions of intensive oil and gas exploration and extraction; (4) large areas of sparsely populated and practically unmanaged land; (5) vulnerability of northern ecosystems which historically developed under cold climates and buffering capacity of which is not well known; (6) risk of catastrophic natural disturbances (fire, insect outbreaks) whose frequency and severity have accelerated during recent decades; and (7) high probability of irreversible changes of vegetation cover. These specifics are overlapped with insufficient governance of natural renewable resources (e.g., forests) and destructed practice of industrial development of new territories (oil and gas extraction and exploration, metallurgy etc.). Based on a full carbon account for terrestrial vegetation ecosystems of Northern Eurasia, we analyze the relative impacts of major drivers on magnitude and uncertainty of the Net Ecosystem Carbon Balance (NECB) under current and expected climate and environment. Dynamic trends and interannual variability of NECB are mostly dependent on weather conditions during growth seasons of individual years, regimes of natural disturbances, and anthropogenic impacts on ecosystems. In a short term, disturbances and human impacts cause a theoretically 'manageable' part of the full carbon account, which on average is estimated to be of about 20% of annual net primary production. In a long term, thawing of permafrost and change of hydrological regimes of vast territories may result in a catastrophic decline of the forested area and wide distribution of 'green desertification'. The

  7. The structure of mid- and high-latitude ionosphere during September 1999 storm event obtained from GPS observations

    Directory of Open Access Journals (Sweden)

    I. I. Shagimuratov

    Full Text Available TEC data, obtained from over 60 GPS stations, were used to study the ionospheric effects of the 12–16 September 1999 magnetic storm over Europe. The spatial and temporal changes of the ionosphere were analysed as a time series of TEC maps, which present 15 min averages of TEC. The data set consisting of GPS observations, collected by a dense network of European stations, with sampling rate of 30 s, enable the creation of TEC maps with high spatial and temporal resolution. The storm included the positive as well as the negative phase. The positive phase took place during the first storm day of 12 September 1999. The short-lived daytime TEC enhancement was observed at all latitudes. The maximal enhancement reached a factor of 1.3–1.5. On the second and third days, the negative phase of the storm developed. The TEC decrease was registered regardless of time of the day. The TEC depression exceeded 70% relative to quiet days. On the following days (15 and 16 September, a significant daytime enhancement of TEC was observed once again. The complex occurrence of the ionospheric storm was probably related to the features of development of the magnetic storm. We found out that during the storm the large and medium-scale irregularities developed in the high-latitude ionosphere. The multi-stations technique, employed to create TEC maps, was particularly successful while studying the mid-latitude ionospheric trough. We found out that the essential changes of TEC during the storm, which were registered at the auroral and sub-auroral ionosphere, were connected with the effect of the trough and its dynamics, which depends on geomagnetic activity.

    Key words. Ionosphere (ionospheric disturbances; auroral ionosphere; mid-latitude ionosphere

  8. A vertical axis tracking method - theoretical consideration for photovoltaic systems at high latitude sites

    Energy Technology Data Exchange (ETDEWEB)

    Gupta, G. R. K; Narasimba Rao, A. V; Subramanyam S [Department of Mechanical Engineering, Warangal (India)

    2000-07-01

    In photovoltaic power generation the photovoltaic array is the most cost intensive unit. In order to make the photovoltaic power competitive the array is to be loaded to its maximum capacity for the longer periods of time. One of the strategies to minimize the cosine effect is by tracking the device. In this paper a novel method of Vertical Axis tracking system with optimum tilt is described. Optimum tilt is obtained by weighting the beam radiation with the altitude of the sun over day. Oslo is chosen for the study because the system is better suited for places having higher latitudes. It is observed that the energy collected in the vertical axis tracking is almost equivalent to that of two-axis tracking mode at latitudes 66.7latitudes. Se observa que la energia recolectada en el seguidor de eje vertical es casi equivalente al modo de rastreo de dos ejes a latitudes de 6.7< {phi}< 23.45. Este metodo ofrece una construccion mecanica mas simple, el cambio del angulo de rastreo en un ano es de 32 grados Celsius que es inferior si se compara con los 47grados Celsius

  9. Review of Power System Stability with High Wind Power Penetration

    DEFF Research Database (Denmark)

    Hu, Rui; Hu, Weihao; Chen, Zhe

    2015-01-01

    analyzing methods and stability improvement approaches. With increasing wind power penetration, system balancing and the reduced inertia may cause a big threaten for stable operation of power systems. To mitigate or eliminate the wind impacts for high wind penetration systems, although the practical......This paper presents an overview of researches on power system stability with high wind power penetration including analyzing methods and improvement approaches. Power system stability issues can be classified diversely according to different considerations. Each classified issue has special...... and reliable choices currently are the strong outside connections or sufficient reserve capacity constructions, many novel theories and approaches are invented to investigate the stability issues, looking forward to an extra-high penetration or totally renewable resource based power systems. These analyzing...

  10. Variability in eastern equatorial Pacific intermediate water circulation during the last glacial termination: the impact of high latitude climate on equatorial stratification

    Science.gov (United States)

    Bova, S. C.; Herbert, T.; Mojarro, A.

    2013-12-01

    The eastern equatorial Pacific (EEP) is linked directly to the Southern High latitudes through an oceanic tunneling system that transports Antarctic Intermediate Water (AAIW) and Subantarctic Mode Water (SAMW) directly into the equatorial and Peru Margin upwelling systems (Toggweiler et al. 1991). These intermediate water masses form within the subantarctic zone and flow north, propagating signals of high latitude climate to the low latitude ocean (Kessler 2006). Their heat and salinity content are transported conservatively along their flow path and the high nutrient content of these waters support up to three-fourths of all biological production north of 30°S (Fiedler and Talley 2006, Sarmiento et al. 2004). Thus, variations in the physio-chemical properties and/or transport of these water masses into the low latitude thermocline have vast implications for oceanic heat transport, primary production, and global nutrient cycles (e.g CO2 and N). Here we assess the physio-chemical response of these Southern Ocean intermediate waters to high latitude forcing during the last glacial termination and the impact of these changes on EEP subsurface structure. Alkenone sea surface temperature reconstructions and benthic foraminiferal stable isotopic records from four rapidly accumulating sediment cores from the EEP cold tongue document variation in temperature and salinity gradients at three intermediate water depths (370, 600, and 1000 m). Our records provide evidence for substantial change in water column structure during the last glacial termination. Regional stratification decreased significantly during the deglacial (11-18 ka) relative to the last glacial period and the Holocene due to asynchronous warming of the EEP water column. Deglacial warming began first at 1000 m depth at ~18.2 ka, in phase with southern hemisphere temperatures, while surface warming experienced a 1-2 kyr delay. Additionally, we observe a convergence of oxygen and carbon isotopes across

  11. Simultaneous in-situ observations of the signatures of dayside reconnection at the high- and low-latitude magnetopause

    Directory of Open Access Journals (Sweden)

    J. A. Wild

    2005-02-01

    Full Text Available We present magnetic field and particle data recorded by the Cluster and Geotail satellites in the vicinity of the high- and low-latitude dayside magnetopause, respectively, on 17 February 2003. A favourable conjunction of these spacecraft culminated in the observation of a series of flux transfer events (FTEs, characterised by bipolar perturbations in the component of the magnetic field normal to the magnetopause, an enhancement in the overall magnetic field strength, and field tilting effects in the plane of the magnetopause whilst the satellites were located on the magnetosheath side of the boundary. Whilst a subset of the FTE signatures observed could be identified as being either normal or reverse polarity, the rapid succession of events observed made it difficult to classify some of the signatures unambiguously. Nevertheless, by considering the source region and motion of flux tubes opened by magnetic reconnection at low latitudes (i.e. between Cluster and Geotail, we demonstrate that the observations are consistent with the motion of northward (southward and tailward moving flux tubes anchored in the Northern (Southern Hemisphere passing in close proximity to the Cluster (Geotail satellites. We are able to demonstrate that a multi-spacecraft approach, coupled with a realistic model of flux tube motion in the magnetosheath, enables us to infer the approximate position of the reconnection site, which in this case was located at near-equatorial latitudes.

  12. 622 Mbps High-speed satellite communication system for WINDS

    Science.gov (United States)

    Ogawa, Yasuo; Hashimoto, Yukio; Yoshimura, Naoko; Suzuki, Ryutaro; Gedney, Richard T.; Dollard, Mike

    2006-07-01

    WINDS is the experimental communications satellite currently under joint development by Japanese Aerospace Exploration Agency (JAXA) and the National Institute of Information and Communications Technology (NICT). The high-speed satellite communication system is very effective for quick deployment of high-speed networks economically. The WINDS will realize ultra high-speed networking and demonstrate operability of satellite communication systems in high-speed internet. NICT is now developing high-speed satellite communication system for WINDS. High-speed TDMA burst modem with high performance TPC error correction is underdevelopment. Up to the DAC on the transmitter and from the ADC on the receiver, all modem functions are performed in the digital processing technology. Burst modem has been designed for a user data rate up to 1244 Mbps. NICT is developing the digital terminal as a user interface and a network controller for this earth station. High compatibility with the Internet will be provided.

  13. LCA of electricity systems with high wind power penetration

    DEFF Research Database (Denmark)

    Turconi, Roberto; O' Dwyer, C. O.; Flynn, D.

    Electricity systems are shifting from being based on fossil fuels towards renewable sources to enhance energy security and mitigate climate change. However, by introducing high shares of variable renewables - such as wind and solar - dispatchable power plants are required to vary their output...... to fulfill the remaining electrical demand, potentially increasing their environmental impacts [1,2]. In this study the environmental impacts of potential short-term future electricity systems in Ireland with high shares of wind power (35-50% of total installed capacity) were evaluated using life cycle...... considered: while not outweighing the benefits from increasing wind energy, cycling emissions are not negligible and should thus be systematically included (i.e. by using emission factors per unit of fuel input rather than per unit of power generated). Cycling emissions increased with the installed wind...

  14. High Power Wind Generator Designs with Less or No PMs

    DEFF Research Database (Denmark)

    Boldea, Ion; Tutelea, Lucian; Blaabjerg, Frede

    2014-01-01

    wind generator systems with less or no PMs: from classifications based in principle and on gear ratio, through topologies, modeling, design and performance issues, with results from literature and also from authors findings. It is hoped that such a study, focused on the wind generator itself (though......The recent steep increase in high energy permanent magnet (PM) price (above 130$/kg and more) triggered already strong R&D efforts to develop wind generators with less PMs (less weight in NdFeB magnets/kW or the use of ferrite PMs) or fully without PMs. All these by optimizing existing dc excited...... synchronous generators, by doubly-fed (wound rotor) induction and cage induction generators and by introducing new topologies with pertinent costs for high power (MW range) wind energy conversion units. The present overview attempts, based on recent grid specifications, an evaluation of commercial and novel...

  15. Assessment of high latitude variability and extreme events in the Bering Sea as simulated by a global climate model

    Science.gov (United States)

    Walston, Joshua M.

    Atmospheric and Oceanic observations of the Arctic and Subarctic are relatively sparse and hinder our ability to analyze short term variability and long-duration anomalies of physical and biological variables over decadal time scales. Earth System Models (ESM's), such as the Community Earth System Model (CESM1), represent a useful tool to advance the understanding and the predictive potential of large-scale shifts in the climate and climate related impacts. This thesis initially focuses on assessing the skill of the Community Climate System Model (CCSM4), to capture natural variability of the climate system. Subsequently, I examine the impacts of variability and seasonal-scale extremes of the physical environment on the marine ecosystem of the eastern Bering Sea as simulated by an earth system model, the CESM1, which includes the CCSM4 and earth system elements. A performance assessment of key atmospheric components (air temperature, sea level pressure, wind speed and direction) simulated by the CCSM4 over the Bering Sea and Arctic domains suggests a general improvement in model predictions at high latitudes relative to the model's predecessor, the CCSM3. However, several shortcomings, with possible implications for marine ecosystem modeling, still remain in this version of the CCSM. The most important of which includes an under-simulated Siberian High and a large northwest displacement of the Aleutian Low resulting in a negative bias of up to 8 hPa over the Bering Sea. The simulated inter-annual variability of surface air temperature and sea level pressure over the Bering Sea was found to exceed observed variability by ˜1.5 to 2 times. The displaced pressure systems and increased variability could have important ramifications for modeling efforts that use CCSM atmospheric output as drivers for marine ecosystem studies. When the CCSM was combined with other earth system elements to form the CESM, the coupled model was found to simulate strong linear relationships

  16. Upper-Thermospheric Observations and Neutral-Gas Dynamics at High Latitudes During Solar Maximum.

    Science.gov (United States)

    1987-01-01

    aeasFPIgure 6.5, ecep orB> oniios -40 TO~ -- 12 p . p’ T5 .ww i - IO RFS 5 183 maximum antisunward neutral winds located in the center of the polar cap. The...Solar flux variability in the *- Schumann-Runge continuum as a function of solar cycle 21. J. Geophys. Res., 85, 6063 - 6068, 1980c. Torr, M. R., P. G

  17. Microgrid optimal scheduling considering impact of high penetration wind generation

    Science.gov (United States)

    Alanazi, Abdulaziz

    The objective of this thesis is to study the impact of high penetration wind energy in economic and reliable operation of microgrids. Wind power is variable, i.e., constantly changing, and nondispatchable, i.e., cannot be controlled by the microgrid controller. Thus an accurate forecasting of wind power is an essential task in order to study its impacts in microgrid operation. Two commonly used forecasting methods including Autoregressive Integrated Moving Average (ARIMA) and Artificial Neural Network (ANN) have been used in this thesis to improve the wind power forecasting. The forecasting error is calculated using a Mean Absolute Percentage Error (MAPE) and is improved using the ANN. The wind forecast is further used in the microgrid optimal scheduling problem. The microgrid optimal scheduling is performed by developing a viable model for security-constrained unit commitment (SCUC) based on mixed-integer linear programing (MILP) method. The proposed SCUC is solved for various wind penetration levels and the relationship between the total cost and the wind power penetration is found. In order to reduce microgrid power transfer fluctuations, an additional constraint is proposed and added to the SCUC formulation. The new constraint would control the time-based fluctuations. The impact of the constraint on microgrid SCUC results is tested and validated with numerical analysis. Finally, the applicability of proposed models is demonstrated through numerical simulations.

  18. A high wind geophysical model fuction for QuikSCAT wind retrievals and application to Typhoon IOKE

    Institute of Scientific and Technical Information of China (English)

    ZOU Juhong; ZENG Tao; CUI Songxue

    2015-01-01

    The geophysical model function (GMF) describes the relationship between a backscattering and a sea surface wind, and enables a wind vector retrieval from backscattering measurements. It is clear that the GMF plays an important role in an ocean wind vector retrieval. The performance of the existing Ku-band model function QSCAT-1 is considered to be effective at low and moderate wind speed ranges. However, in the conditions of higher wind speeds, the existing algorithms diverge alarmingly. owing to the lack ofin situ data required for developing the GMF for the high wind conditions, the QSCAT-1 appears to overestimate thes0, which results in underestimating the wind speeds. Several match-up QuikSCAT and special sensor microwave/imager (SSM/I) wind speed measurements of the typhoons occurring in the west Pacific Ocean are analyzed. The results show that the SSM/I wind exhibits better agreement with the “best track” analysis wind speed than the QuikSCAT wind retrieved using QSCAT-1. On the basis of this evaluation, a correction of the QSCAT-1 model function for wind speed above 16 m/s is proposed, which uses the collocated SSM/I and QuikSCAT measurements as a training set, and a neural network approach as a multiple nonlinear regression technologytechnology.In order to validate the revised GMF for high winds, the modified GMF was applied to the QuikSCAT observations of Hurricane IOKE. The wind estimated by the QuikSCAT for Typhoon IOKE in 2006 was improved with the maximum wind speed reaching 55 m/s. An error analysis was performed using the wind fields from the Holland model as the surface truth. The results show an improved agreement with the Holland model wind when compared with the wind estimated using the QSCAT-1. However, large bias still existed, indicating that the effects of rain must be considered for further improvement.

  19. Cluster observations of the high-latitude magnetopause and cusp: initial results from the CIS ion instruments

    Directory of Open Access Journals (Sweden)

    J. M. Bosqued

    Full Text Available Launched on an elliptical high inclination orbit (apogee: 19.6 RE since January 2001 the Cluster satellites have been conducting the first detailed three-dimensional studies of the high-latitude dayside magnetosphere, including the exterior cusp, neighbouring boundary layers and magnetopause regions. Cluster satellites carry the CIS ion spectrometers that provide high-precision, 3D distributions of low-energy (<35 keV/e ions every 4 s. This paper presents the first two observations of the cusp and/or magnetopause behaviour made under different interplanetary magnetic field (IMF conditions. Flow directions, 3D distribution functions, density profiles and ion composition profiles are analyzed to demonstrate the high variability of high-latitude regions. In the first crossing analyzed (26 January 2001, dusk side, IMF-BZ < 0, multiple, isolated boundary layer, magnetopause and magnetosheath encounters clearly occurred on a quasi-steady basis for ~ 2 hours. CIS ion instruments show systematic accelerated flows in the current layer and adjacent boundary layers on the Earthward side of the magnetopause. Multi-point analysis of the magnetopause, combining magnetic and plasma data from the four Cluster spacecraft, demonstrates that oscillatory outward-inward motions occur with a normal speed of the order of ± 40 km/s; the thickness of the high-latitude current layer is evaluated to be of the order of 900–1000 km. Alfvénic accelerated flows and D-shaped distributions are convincing signatures of a magnetic reconnection occurring equatorward of the Cluster satellites. Moreover, the internal magnetic and plasma structure of a flux transfer event (FTE is analyzed in detail; its size along the magnetopause surface is ~ 12 000 km and it convects with a velocity of ~ 200 km/s. The second event analyzed (2 February 2001 corresponds to the first Cluster pass within the cusp when the IMF-BZ component was northward directed. The analysis of

  20. A high-altitude balloon experiment to probe stratospheric electric fields from low latitudes

    Science.gov (United States)

    Gurubaran, Subramanian; Shanmugam, Manu; Jawahar, Kaliappan; Emperumal, Kaliappan; Mahavarkar, Prasanna; Buduru, Suneel Kumar

    2017-02-01

    The Earth's electrical environment hosts a giant electrical circuit, often referred to as the global electric circuit (GEC), linking the various sources of electrical generators located in the lower atmosphere, the ionosphere and the magnetosphere. The middle atmosphere (stratosphere and mesosphere) has been traditionally believed to be passively transmitting electric fields generated elsewhere. Some observations have reported anomalously large electric fields at these altitudes, and the scientific community has had to revisit the earlier hypothesis time and again. At stratospheric altitudes and especially at low latitudes, horizontal electric fields are believed to be of ionospheric origin. Though measurements of these fields from a balloon platform are challenging because of their small magnitudes (around a few mV m-1), a suitably designed long-duration balloon experiment capable of detecting such small fields can provide useful information on the time evolution of ionospheric electric fields, which is otherwise possible only using radar or satellite in situ measurements. We present herein details of one such experiment, BEENS (Balloon Experiment on the Electrodynamics of Near Space), carried out from a low-latitude site in India. The instrument package for this experiment is comprised of four deployable booms for measurements of horizontal electric fields and one inclined boom for vertical electric field measurements, all equipped with conducting spheres at the tip. The experiment was conducted from Hyderabad (17.5° N, 78.6° E) during the post-midnight hours on 14 December 2013. In spite of a few shortcomings we report herein, a noticeable feature of the observations has been the detection of horizontal electric fields of ˜ 5 mV m-1 at the stratospheric altitudes of ˜ 35 km.

  1. Towards an Improved Algorithm for Estimating Freeze-Thaw Dates of a High Latitude Lake Using Texture Analysis of SAR Images

    Science.gov (United States)

    Uppuluri, A. V.; Jost, R. J.; Luecke, C.; White, M. A.

    2008-12-01

    Analyzing the freeze-thaw dates of high latitude lakes is an important part of climate change studies. Due to the various advantages provided by the use of SAR images, with respect to remote monitoring of small lakes, SAR image analysis is an obvious choice to estimate lake freeze-thaw dates. An important property of SAR images is its texture. The problem of estimating freeze-thaw dates can be restated as a problem of classifying an annual time series of SAR images based on the presence or absence of ice. We analyzed a few algorithms based on texture to improve the estimation of freeze-thaw dates for small lakes using SAR images. We computed the Gray Level Co-occurrence Matrix (GLCM) for each image and extracted ten different texture features from the GLCM. We used these texture features (namely, Energy, Contrast, Correlation, Homogeneity, Entropy, Autocorrelation, Dissimilarity, Cluster Shade, Cluster Prominence and Maximum Probability as previously used in studies related to the texture analysis of SAR sea ice imagery) as input to a group of classification algorithms to find the most accurate classifier and set of texture features that can help to decide the presence or absence of ice on the lake. The accuracy of the estimated freeze-thaw dates is dependent on the accuracy of the classifier. It is considered highly difficult to differentiate between open water (without wind) and the first day of ice formed on the lake (due to the similar mean backscatter values) causing inaccuracy in calculating the freeze date. Similar inaccuracy in calculating the thaw date arise due to the close backscatter values of water (with wind) and later stages of ice on the lake. Our method is promising but requires further research in improving the accuracy of the classifiers and selecting the input features.

  2. High energy neutrinos from pulsar wind nebulae

    Science.gov (United States)

    Di Palma, Irene

    2017-09-01

    Several Pulsar Wind Nebulae have been detected in the TeV band in the last decade.The TeV emission is typically interpreted in a purely leptonic scenario, but this usually requires that the magnetic field in the Nebula be much lower than the equipartition value and the assumption of an enhanced target radiation at IR frequencies. In this work we consider the possibility that, in addition to the relativistic electrons, also relativistic hadrons are present in these nebulae. Assuming that part of the emitted TeV photons are of hadronic origin, we compute the associated flux of ∼ 1 ‑ 100 TeV neutrinos. We use the IceCube non detection to put constraints on the fraction of TeV photons that might be contributed by hadrons and estimate the number of neutrino events that can be expected from these sources in IceCube, ANTARES and in KM3Net.

  3. Adequacy of Frequency Reserves for High Wind Power Generation

    DEFF Research Database (Denmark)

    Das, Kaushik; Litong-Palima, Marisciel; Maule, Petr

    2016-01-01

    In this article, a new methodology is developed to assess the adequacy of frequency reserves to handle power imbalances caused by wind power forecast errors. The goal of this methodology is to estimate the adequate volume and speed of activation of frequency reserves required to handle power...... imbalances caused due to high penetration of wind power. An algorithm is proposed and developed to estimate the power imbalances due to wind power forecast error following activation of different operating reserves. Frequency containment reserve requirements for mitigating these power imbalances...... are developed through this methodology. Furthermore, the probability of reducing this frequency containment reserve requirement is investigated through this methodology with activation of different volumes and speed of frequency restoration reserve. Wind power generation for 2020 and 2030 scenarios...

  4. Variability of the nighttime OH layer and mesospheric ozone at high latitudes during northern winter: influence of meteorology

    OpenAIRE

    Damiani, A.; M. Storini; Santee, M.L.; Wang, S

    2010-01-01

    Analyses of OH zonal means, recorded at boreal high latitudes by the Aura Microwave Limb Sounder (MLS) in winters of 2005–2009, have shown medium- (weeks) and short- (days) term variability of the nighttime OH layer.

    Because of the exceptional descent of air from the mesosphere-lower thermosphere (MLT) region, medium-term variability occurred during February 2006 and February/March 2009. The layer normally situated at about 82 km descended by about 5–7 km, and its density...

  5. Variability of the nighttime OH layer and mesospheric ozone at high latitudes during northern winter: influence of meteorology

    OpenAIRE

    Damiani, A.; M. Storini; Santee, M.L.; Wang, S

    2010-01-01

    Analyses of OH zonal means, recorded at boreal high latitudes by the Aura Microwave Limb Sounder (MLS), have shown medium- (weeks) and short-term (days) variability of the nighttime OH layer.

    Because of the exceptional descent of air from the mesosphere-lower thermosphere region, medium-term variability occurred during February 2006 and February/March 2009. The layer normally situated at about 82 km descended by about 5–7 km, and its density increased to more than twice J...

  6. The role of sexual and asexual reproduction in structuring high latitude populations of the reef coral Pocillopora damicornis.

    Science.gov (United States)

    Miller, K J; Ayre, D J

    2004-06-01

    The genotypic composition of populations of the asexually viviparous coral Pocillopora damicornis varies in a manner that challenges classical models of the roles of sexual and asexual reproduction. On the geographically isolated Hawaiian reefs and high latitude reefs in Western Australia, P. damicornis populations are highly clonal although it has been argued that sexual reproduction via broadcast spawning generates widely dispersed colonists. In contrast, on eastern Australia's tropical Great Barrier Reef populations show little evidence of clonality. Here, we compare the genotypic diversity of adult and juvenile colonies of P. damicornis at seven sites on eastern Australia's high latitude Lord Howe Island reefs to determine if levels of clonality vary with habitat heterogeneity and age of colonies (as predicted by theory) or alternatively if clonality is again always high as for other isolated reef systems. We found 55-100% of the genotypic diversity expected for random mating at all seven sites and little evidence of asexual recruitment irrespective of habitat heterogeneity (sheltered versus wave exposed) or colony age. We found reduced levels of genetic diversity compared with tropical reefs (2.75 versus 4 alleles/locus), which supports earlier findings that Lord Howe Island is an isolated reef system. Furthermore, heterozygote deficits coupled with significant genetic subdivision among sites (FST=0.102+/-0.03) is typical of populations that have limited larval connections and are inbred. We conclude that the genetic structure of P. damicornis at Lord Howe Island reflects populations that are maintained through localised recruitment of sexually produced larvae.

  7. The large-scale energetic ion layer in the high latitude Jovian magnetosphere as revealed by Ulysses/HI-SCALE cross-field intensity-gradient measurements

    CERN Document Server

    Anagnostopoulos, G C; Marhavilas, P K; Sarris, E T

    2012-01-01

    Ulysses investigated the high latitude Jovian magnetosphere for a second time after Pioneer 11 mission and gave us the opportunity to search the structure and the dynamics of this giant magnetosphere above the magnetodisc. Kivelson(1976) and Kennel & Coroniti(1979) reported that Pioneer 11 observed energetic particle intensities at high latitudes at the same level with those measured in the plasma sheet and inferred that they were not consistent with the magnetodisc model. Ulysses observations supported the idea about a large-scale layer of energetic ions and electrons in the outer high latitude Jovian magnetosphere (Cowley et al.1996; Anagnostopoulos et al. 2001). This study perform a number of further tests for the existence of the large scale layer of energetic ions in the outer high latitude Jovian magnetosphere by studying appropriate cross-B field anisotropies in order to monitor the ion northward/southward intensity gradients. In particular, we examined Ulysses/HI-SCALE observations of energetic io...

  8. Stable isotope ecology of land snails from a high-latitude site near Fairbanks, interior Alaska, USA

    Science.gov (United States)

    Yanes, Yurena

    2015-05-01

    Land snails have been investigated isotopically in tropical islands and mid-latitude continental settings, while high-latitude locales, where snails grow only during the summer, have been overlooked. This study presents the first isotopic baseline of live snails from Fairbanks, Alaska (64°51‧N), a proxy calibration necessary prior to paleoenvironmental inferences using fossils. δ13C values of the shell (- 10.4 ± 0.4‰) and the body (- 25.5 ± 1.0‰) indicate that snails consumed fresh and decayed C3-plants and fungi. A flux-balance mixing model suggests that specimens differed in metabolic rates, which may complicate paleovegetation inferences. Shell δ18O values (- 10.8 ± 0.4‰) were 4‰ higher than local summer rain δ18O. If calcification occurred during summer, a flux-balance mixing model suggests that snails grew at temperatures of 13°C, rainwater δ18O values of - 15‰ and relative humidity of 93%. Results from Fairbanks were compared to shells from San Salvador (Bahamas), at 24°51‧N. Average (annual) δ18O values of shells and rainwater samples from The Bahamas were both 10‰ 18O-enriched with respect to seasonal (summer) Alaskan samples. At a coarse latitudinal scale, shell δ18O values overwhelmingly record the signature of the rainfall during snail active periods. While tropical snails record annual average environmental information, high-latitude specimens only trace summer season climatic data.

  9. Comparing Herschel dust emission structures, magnetic fields observed by Planck, and dynamics: high-latitude star forming cloud L1642

    Science.gov (United States)

    Malinen, Johanna

    2016-01-01

    The nearby high-latitude cloud L1642 is one of only two known very high latitude (|b| > 30 deg) clouds actively forming stars. This cloud is a rare example of star formation in isolated conditions, and can reveal important details of star formation in general, e.g., of the effect of magnetic fields. We compare Herschel dust emission structures and magnetic field orientation revealed by Planck polarization maps in L1642, and also combine these with dynamic information from molecular line observations. The high-resolution Herschel data reveal a complex structure including a dense, compressed central blob with elongated extensions, low density striations, "fishbone" like structures with a spine and perpendicular striations, and a spiraling "tail". The Planck polarization data reveal an ordered magnetic field that pervades the cloud and is aligned with the surrounding low density striations. We show that there is a complex interplay between the cloud structure and large scale magnetic fields revealed by Planck polarization data at 10' resolution. This suggests that the magnetic field is closely linked to the formation and evolution of the cloud. We see a clear transition from aligned to perpendicular structures approximately at a column density of NH = 2x10^21 cm-2. We conclude that Planck polarization data revealing the large scale magnetic field orientation can be very useful even when comparing to the finest structures in higher resolution data, e.g. Herschel at ~18" resolution.

  10. Discovery of two embedded clusters with WISE in the high Galactic latitude cloud HRK 81.4-77.8

    CERN Document Server

    Camargo, Denilso; Bonatto, Charles; Salerno, Gustavo

    2015-01-01

    Molecular clouds at very high latitude ($b>60^{\\circ}$) away from the Galactic plane are rare and in general are expected to be non-star-forming. However, we report the discovery of two embedded clusters (Camargo 438 and Camargo 439) within the high-latitude molecular cloud HRK 81.4-77.8 using WISE. Camargo 439 with Galactic coordinates $\\ell=81.11^{\\circ}$ and $b=-77.84^{\\circ}$ is an $\\sim2$ Myr embedded cluster (EC) located at a distance from the Sun of $d_{\\odot}=5.09\\pm0.47$ kpc. Adopting the distance of the Sun to the Galactic centre $R_{\\odot}=7.2$ kpc we derive for Camargo 439 a Galactocentric distance of $R_{GC}=8.70\\pm0.26$ kpc and a vertical distance from the plane of $-4.97\\pm0.46$ kpc. Camargo 438 at $\\ell=79.66^{\\circ}$ and $b=-78.86^{\\circ}$ presents similar values. The derived parameters for these two ECs put HRK 81.4-77.8 in the halo at a distance from the Galactic centre of $\\sim8.7$ kpc and $\\sim5.0$ kpc from the disc. Star clusters provide the only direct means to determine the high latitu...

  11. Evidence of wintertime CO2 emission from snow-covered grounds in high latitudes

    Institute of Scientific and Technical Information of China (English)

    方精云; 唐艳鸿KOIZUMI; Hiroshi(Division; of; Plant; Ecology; National; Institute; of; Agro-Environmental; Sciences; Tsukuba; 305; Japan)BEKKU; Yukiko(National; Polar; Institute; Tokyo; 192; Japan)

    1999-01-01

    In order to measure CO2 flux in wintertime arctic ecosystems, CO2 gas was sampled from various snow-covered grounds by using a closed chamber method during the First China Arctic Scientific Expedition from March to May in 1995. The CO2 gas samples were measured by using an infra-red analyzer (IRGA). The results showed that (ⅰ) CO2 emission was detected from all kinds of the snow-covered grounds, which provides direct evidence that the arctic tundra is functioning as a source of atmospheric CO2; (ⅱ) CO2 release was also detected from the permanent ice profile and icecap, and (ⅲ) CO2 evolution from terrestrial ecosystems in higher latitudes increased with an increase of surface temperature in accordance with the exponential function. This indicates a close coincidence with that under normal temperature conditions, and provides a useful method for predicting change in CO2 flux in the arctic ecosystems with the global climate change.

  12. All-sky census of Galactic high-latitude molecular intermediate-velocity clouds

    Science.gov (United States)

    Röhser, T.; Kerp, J.; Lenz, D.; Winkel, B.

    2016-12-01

    Context. The H i halo clouds of the Milky Way, and in particular the intermediate-velocity clouds (IVCs), are thought to be connected to Galactic fountain processes. Observations of fountain clouds are important for understanding the role of matter recycling and accretion onto the Galactic disk and subsequent star formation. Aims: Here, we quantify the amount of molecular gas in the Galactic halo. We focus on the rare class of molecular IVCs (MIVCs) and search for new objects. Methods: The H i-FIR correlation was studied across the entire northern and southern Galactic hemispheres at Galactic latitudes | b | > 20° to determine the amount and distribution of molecular gas in IVCs. We used the most recent large-scale H i and FIR data, the Effelsberg Bonn-H i Survey, the Parkes Galactic All-Sky Survey, and the Planck FIR surveys. Results: We present a catalogue of 239 MIVC candidates on the northern and southern Galactic hemispheres. Among these candidates, all previously known MIVCs are recovered except for one single source. The frequency of candidates differs significantly between the northern and southern Galactic hemispheres and between negative and positive LSR velocities as well. Conclusions: In our approach we analyse the local Galactic environment. Extrapolating our results to the entire Galaxy, the global inflow of atomic and molecular IVC gas onto the Milky Way may account for the major fraction of the gaseous mass that is required to sustain the current Galactic star formation rate.

  13. An all-sky census of Galactic high-latitude molecular intermediate-velocity clouds

    CERN Document Server

    Röhser, T; Lenz, D; Winkel, B

    2016-01-01

    The HI halo clouds of the Milky Way and in particular the intermediate-velocity clouds (IVCs) are thought to be connected to Galactic fountain processes. Observations of fountain clouds are important for understanding the role of matter recycling and accretion onto the Galactic disk and subsequent star formation. Here, we quantify the amount of molecular gas in the Galactic halo. We focus on the rare class of molecular IVCs (MIVCs) and search for new objects. The HI-FIR correlation is studied across the entire northern and southern Galactic hemispheres at Galactic latitudes $|b|>20^\\circ$ in order to determine the amount and distribution of molecular gas in IVCs. We use the most recent large-scale HI and FIR data, the Effelsberg Bonn-HI Survey, the Parkes Galactic All-Sky Survey, and the Planck FIR surveys. We present a catalogue of 239 MIVC candidates on the northern and southern Galactic hemispheres. Among these candidates all previously known MIVCs are recovered except for a single one only. The frequency ...

  14. Observations of IMF and seasonal effects in high-latitude convection

    Science.gov (United States)

    Ruohoniemi, J. M.; Greenwald, R. A.

    1995-01-01

    Strong interplanetary magnetic field (IMF) and seasonal effects in the convection of nightside ionospheric plasma are described. The findings are based on a statistical analysis of observations made with the Johns Hopkins University/ Applied Physics Lab (JHU/APL) HF radar located at Goose Bay, Labrador. For positive sign of the IMF dusk-dawn component, By greater than 0 the dawn cell is more crescent shaped and the dusk cell more round while for BY less than 0 these pairings of size and shape are reversed. The more extreme crescent /round cell dichotomy is obtained for BY greater than 0. The return flows associated with the crescent-shaped cell dominate at midnight MLT (magnetic local time); the reversal in the zonal velocity in the 67 deg-69 deg lambda (magnetic latitude) interval occurs 2.5 hr earlier in summer than in winter. The maximum effects are obtained on the nightside for the pairings By greater than 0, summer and BY less than 0, winter; the first produces the more structured cell in the morning, the second in the evening, and this cell dominates the return flow at midnight. The difference in the zonal flow reversals for these pairings exceeds 4 hr in MLT.

  15. Phase fluctuations of GPS signals and irregularities in the high latitude ionosphere during geomagnetic storm

    Science.gov (United States)

    Shagimuratov, I.; Chernouss, S.; Cherniak, Iu.; Efishov, I.; Filatov, M.; Tepenitsyna, N.

    2016-05-01

    In this report we analysed latitudinal occurrence of TEC fluctuations over Europe during October 2, 2013 geomagnetic storm. The data of GPS stations spaced in latitudinal range 68°-54° N over longitude of 20°E were involved in this investigation. The magnetograms of the IMAGE network and geomagnetic pulsations at Lovozero (68°02'N 35°00'W) and Sodankyla (67°22'N 26°38'W) observatories were used as indicator of auroral activity. During October 2, 2013 the strong geomagnetic field variations took place near 05 UT at auroral IMAGE network. We found good similarities between time development of substorm and fluctuations of GPS signals. The bay-like geomagnetic variations were followed by intensive phase fluctuations at auroral and subauroral stations. The strong short-term phase fluctuations were also found at mid-latitude Kaliningrad station near 05 UT that correspond to the maximal intense geomagnetic bay variations. This date confirms the equatorward expansion of the auroral oval. It brings in evidence also the storm time behavior of the irregularities oval obtained from multi-site GPS observations.

  16. The high latitude convection response to an interval of substorm activity

    Directory of Open Access Journals (Sweden)

    T. K. Yeoman

    Full Text Available On 17 March 1991, five clear substorm onsets/intensifications took place within a three hour interval. During this interval ground-based data from the EISCAT incoherent scatter radar, a digital CCD all sky camera, and an extensive array of magnetometers were available, in addition to data from the CRRES and DMSP spacecraft, whose footprints passed over Scandinavia very close to most of the ground-based instrumentation. This interval of substorm activity has been interpreted as being in support of a near-Earth current disruption model of substorm onset. In the present study the ionospheric convection response, observed some four hours to the west in MLT by the Halley HF radar in Antarctica, is related to the growth, expansion and recovery phases of two of the substorm onsets/expansions observed in the Northern Hemisphere. Bursts of ionospheric flow and motion of the convection reversal boundary (CRB are observed at Halley in response to the substorm activity and changes in the IMF. The delay between the substorm expansion phase onset and the response in the CRB location is dependent on the local time separation from, and latitude of, the initial substorm onset region. These results are interpreted in terms of a synthesis of the very near-Earth current disruption model and the near-Earth neutral line model of substorm onset.

  17. Generation Expansion Planning with High Penetration of Wind Power

    Science.gov (United States)

    Sharan, Ishan; Balasubramanian, R.

    2016-08-01

    Worldwide thrust is being provided in generation of electricity from wind. Planning for the developmental needs of wind based power has to be consistent with the objective and basic framework of overall resource planning. The operational issues associated with the integration of wind power must be addressed at the planning stage. Lack of co-ordinated planning of wind turbine generators, conventional generating units and expansion of the transmission system may lead to curtailment of wind power due to transmission inadequacy or operational constraints. This paper presents a generation expansion planning model taking into account fuel transportation and power transmission constraints, while addressing the operational issues associated with the high penetration of wind power. For analyzing the operational issues, security constrained unit commitment algorithm is embedded in the integrated generation and transmission expansion planning model. The integrated generation and transmission expansion planning problem has been formulated as a mixed integer linear problem involving both binary and continuous variables in GAMS. The model has been applied to the expansion planning of a real system to illustrate the proposed approach.

  18. Laboratory Measurement of Enthalpy Flux in High Winds

    Science.gov (United States)

    Jeong, D.; Haus, B. K.; Donelan, M. A.; Zhang, J.

    2006-12-01

    The intensity of tropical cyclones is sensitive to the rates at which enthalpy and momentum are transferred between sea and air in the high-wind core of the storm. Present models of the wind dependence of these transfer rates, does not allow for storms of greater than marginal hurricane intensity. Recent studies have shown that there is a saturation of the bulk drag coefficient in high winds, however more information on the enthalpy flux is required. In particular the role that sea spray plays in enhancing the enthalpy transfer at very high wind speeds is not known. The coefficients for sensible and latent heat transfer (Stanton and Dalton numbers) were measured in the 15-m wind-wave facility at the University of Miami's Air-Sea Interaction Saltwater Tank (ASIST). The wind speed (referred to 10m) was explored over a range of 0 to 45 m/s, covering a full range of aerodynamic conditions from smooth to fully rough. Experiments were designed with water temperatures set between 2 and 5° C above/below the air temperature, with precision thermistors (± 0.002° C) to monitor temperature and Li-Cor infra-red absorption devices to monitor specific humidity changes at upstream and downstream ends of the wave tank during the experiment. The calorimetric use of a wind-wave tank gave precise flux estimates, and experiments were repeated at different Bowen ratios to allow the separation of the heat and moisture parts of the transfer. The effect of spray on the moisture flux was reflected in the drop in temperature along the air path from upstream to downstream and this made it possible to estimate the total spray evaporated in the air column.

  19. Ion escape from the high latitude magnetopause: analysis of oxygen and proton dynamics in the presence of magnetic turbulence

    Directory of Open Access Journals (Sweden)

    A. Taktakishvili

    2007-08-01

    Full Text Available Recent Cluster observations of the vicinity of the high latitude magnetopause indicate the presence of beams of singly charged oxygen ions, which are of ionospheric origin. In this paper we examine the role of magnetic turbulence combined with a dc electric field across the magnetopause in causing the cross field transport of protons and of singly charged oxygen ions, by means of a kinetic test particle simulation. We find that the observed values of magnetosheath turbulence and electric fields can produce a substantial escape of the oxygen ions relative to protons. By varying the magnetic turbulence level in the simulation, we find that the number of O+ crossing the magnetopause grows with δB/B0, and that very few ions can cross the magnetopause for δB/B0=0. The ion temperature also grows with δB/B0, showing that magnetic turbulence is effective in thermalizing the kinetic energy gain due to the cross-magnetopause potential drop. We suggest that this mechanism can help to explain Cluster observations of energetic oxygen ions during a high-latitude magnetopause crossing.

  20. Evidence of meso-scale structure in the high-latitude thermosphere

    Directory of Open Access Journals (Sweden)

    A. L. Aruliah

    Full Text Available There is a widely held assumption that the thermospheric neutral gas is slow to respond to magnetospheric forcing owing to its large inertia and therefore, may be treated as a steady state background medium for the more dynamic ionosphere. This is shown to be over simplistic. The data presented here compare direct measurements of the thermospheric neutral winds made in Northern Scandinavia by Fabry-Perot Interferometers (FPIs with direct measurements of the ionosphere made by the EISCAT radar and with model simulations. These comparisons will show that the neutral atmosphere is capable of responding to ionospheric changes on mesoscale levels, i.e., spatial and temporal scale sizes of less than a few hundred kilometres and tens of minutes, respectively.

    Key words. Atmospheric composition and structure (air-glow and aurora; instruments and techniques – Ionosphere (ionosphere-atmosphere interactions

  1. GPS phase scintillation at high latitudes during the geomagnetic storm of 17-18 March 2015

    DEFF Research Database (Denmark)

    Prikryl, P.; Ghoddousi-Fard, R.; Weygand, J. M.

    2016-01-01

    , and magnetometers. The phase scintillation index is computed for signals sampled at a rate of up to 100 Hz by specialized GPS scintillation receivers supplemented by the phase scintillation proxy index obtained from geodetic-quality GPS data sampled at 1 Hz. In the context of solar wind coupling...... the scintillation and auroral electrojet currents observed by arrays of ground-based magnetometers as well as energetic particle precipitation observed by the DMSP satellites. Equivalent ionospheric currents are obtained from ground magnetometer data using the spherical elementary currents systems technique...... of energetic electron precipitation observed by DMSP satellites with the exception of a period of pulsating aurora when only very weak currents were observed....

  2. Changes in opal fluxes along the northwest African margin during the last glacial period; linking high and low latitude patterns of productivity

    Science.gov (United States)

    Bradtmiller, L. I.; Galgay, M.; McGee, D.; Kinsley, C. W.; Anderson, R. F.

    2014-12-01

    Recent studies have proposed competing hypotheses to explain increased opal fluxes in high and low latitudes during the most recent deglaciation. Anderson et al. (2009) rely on increased wind-driven upwelling in the Southern Ocean to explain the increased availability of Si in both the Southern Ocean and tropical thermoclines, leading to increased opal fluxes in both regions coincident with the deglacial rise in CO2. Meckler et al. (2013) suggest that a decrease in the presence of North Atlantic intermediate water (GNAIW) during the deglaciation allowed Si-rich southern-sourced waters to fill the tropical Atlantic leading to increased opal burial. We attempt to distinguish between these two mechanisms by reconstructing opal fluxes and fluxes of windblown dust over the past ~65ka at four sites along the northwest African margin. The records include the deglaciation, including Heinrich Event 1 (H1) and the Younger Dryas (YD), as well as several earlier Heinrich events. We find that opal and dust fluxes increase simultaneously during the deglaciation, and more highly resolved cores record H1 and the YD as distinct peaks within the deglaciation. Furthermore, opal and dust fluxes scale approximately linearly with one another during these events. We observe opal peaks associated with most Heinrich Events through H6. Finally, we observe a strong similarity between patterns of opal flux in the Southern Ocean and along the African Margin. This suggests that the pattern of diatom productivity and opal flux along the African Margin reflects a combination of changes in wind strength due to shifting temperature gradients, and changes in the export of silica-rich water from the Southern Ocean, both as a result of the global scale climate changes associated with Heinrich Events. Anderson, R. F., S. Ali, L. I. Bradtmiller, S. H. H. Nielsen, M. Q. Fleisher, B. E. Anderson and L. H. Burckle. Wind-Driven Upwelling in the Southern Ocean and the Deglacial Rise in Atmospheric CO2

  3. A possible origin of dayside Pc1 magnetic pulsations observed at high latitudes

    Directory of Open Access Journals (Sweden)

    V. Safargaleev

    2004-09-01

    Full Text Available Induction magnetometer observations of dayside Pc1 activity at Barentsburg (BAB, Spitsbergen archipelago, 78.05°N, 14.12°E are combined with data from two magnetometers located in Scandinavia and the Kola peninsula. Seven events with very large negative IMF Bz components were considered. For all of the events, the cusp location was expected to be significantly shifted equatorward from the statistical position such that the BAB magnetometer was located well inside the polar cap. The DMSP particle data indicated that the BAB magnetometer was indeed inside the polar cap, whereas other magnetometers were collocated with the ionospheric projections of the cusp, the low-latitude boundary layer or the boundary plasma sheet. Pc1 magnetic pulsations were observed only at BAB. In three cases, for which SuperDARN convection data were available, the Pc1 activity correlated with intervals of large-scale convection reconfiguration, such that the plasma flow crossing the BAB location was associated with newly-reconnected magnetic flux tubes drifting tailward. The convection reconfigurations were in response to a decrease in the IMF By component. We argue that the source of the observed Pc1 pulsations is anisotropic plasma of the depletion layer within the magnetosheath. The plasma anisotropy supports the excitation of electromagnetic ion cyclotron waves that are detectable with a ground-based magnetometer when the flux tubes containing the unstable plasma become connected to the Earth's ionosphere in the course of the dayside reconnection processes.

  4. Ozone depletion in the high latitude lower stratosphere - 1979-1990

    Science.gov (United States)

    Callis, Linwood B.; Boughner, Robert E.; Natarajan, Murali; Lambeth, James D.; Baker, Daniel N.

    1991-01-01

    Archived Stratospheric Aerosol and Gas Experiment (SAGE, SAGE II) and Solar and Backscattered Ultraviolet (SBUV) data are used to examine lower stratospheric O3 variations at 50 deg latitude in both hemispheres. These data indicate that from 1979 to 1985, 73-90 percent of the total O3 changes have occurred below approximately 25 km in altitude. Significant O3 depletions (up to 15 percent) have occurred in the partial column (127-15.8 mbar) in both hemispheres with indications of a recovery after 1985. Two-dimensional model simulations of O3 changes from 1979 to 1990 have been carried out. Comparisons with O3 data are presented. Model results suggest that by 1985, significant declines in global O3 were caused by destruction by odd nitrogen associated with long-term variations in the flux of precipitating relativistic electrons (2.6 percent); solar UV flux changes (1.8 percent); the dilution effect associated with the Antarctic O3 hole (1.2 percent); and atmospheric increases in CH4, N2O, and chlorofluorocarbons (0.4 percent). Analyses of drift-corrected SBUV and Total Ozone Mapping Spectrometer data and model calculations indicate that between 1979 and 1985, reductions of 4.3 to 4.8 percent in total column O3 averaged between 65 deg S and 65 deg N have occurred. Calculations indicate a full global O3 decline of 5.2 percent (peak-to-peak) or 6 percent (annual average) between 1979 and 1985 with a partial recovery between 1985 and 1989.

  5. Natural disturbance shapes benthic intertidal macroinvertebrate communities of high latitude river deltas

    Science.gov (United States)

    Churchwell, Roy T.; Kendall, Steve J.; Blanchard, Amy L.; Dunton, Kenneth H.; Powell, Abby N.

    2016-01-01

    Unlike lower latitude coastlines, the estuarine nearshore zones of the Alaskan Beaufort Sea are icebound and frozen up to 9 months annually. This annual freezing event represents a dramatic physical disturbance to fauna living within intertidal sediments. The main objectives of this study were to describe the benthic communities of Beaufort Sea deltas, including temporal changes and trophic structure. Understanding benthic invertebrate communities provided a baseline for concurrent research on shorebird foraging ecology at these sites. We found that despite continuous year-to-year episodes of annual freezing, these estuarine deltas are populated by a range of invertebrates that represent both marine and freshwater assemblages. Freshwater organisms like Diptera and Oligochaeta not only survive this extreme event, but a marine invasion of infaunal organisms such as Amphipoda and Polychaeta rapidly recolonizes the delta mudflats following ice ablation. These delta sediments of sand, silt, and clay are fine in structure compared to sediments of other Beaufort Sea coastal intertidal habitats. The relatively depauperate invertebrate community that ultimately develops is composed of marine and freshwater benthic invertebrates. The composition of the infauna also reflects two strategies that make life on Beaufort Sea deltas possible: a migration of marine organisms from deeper lagoons to the intertidal and freshwater biota that survive the 9-month ice-covered period in frozen sediments. Stable isotopic analyses reveal that both infaunal assemblages assimilate marine and terrestrial sources of organic carbon. These results provide some of the first quantitative information on the infaunal food resources of shallow arctic estuarine systems and the long-term persistence of these invertebrate assemblages. Our data help explain the presence of large numbers of shorebirds in these habitats during the brief summer open-water period and their trophic importance to migrating

  6. First Evaluation of the Climatological Calibration Algorithm in the Real-time TMPA Precipitation Estimates over Two Basins at High and Low Latitudes

    Science.gov (United States)

    Yong, Bin; Ren, Liliang; Hong, Yang; Gourley, Jonathan; Tian, Yudong; Huffman, George J.; Chen, Xi; Wang, Weiguang; Wen, Yixin

    2013-01-01

    The TRMM Multi-satellite Precipitation Analysis (TMPA) system underwent a crucial upgrade in early 2009 to include a climatological calibration algorithm (CCA) to its realtime product 3B42RT, and this algorithm will continue to be applied in the future Global Precipitation Measurement era constellation precipitation products. In this study, efforts are focused on the comparison and validation of the Version 6 3B42RT estimates before and after the climatological calibration is applied. The evaluation is accomplished using independent rain gauge networks located within the high-latitude Laohahe basin and the low-latitude Mishui basin, both in China. The analyses indicate the CCA can effectively reduce the systematic errors over the low-latitude Mishui basin but misrepresent the intensity distribution pattern of medium-high rain rates. This behavior could adversely affect TMPA's hydrological applications, especially for extreme events (e.g., floods and landslides). Results also show that the CCA tends to perform slightly worse, in particular, during summer and winter, over the high-latitude Laohahe basin. This is possibly due to the simplified calibration-processing scheme in the CCA that directly applies the climatological calibrators developed within 40 degrees latitude to the latitude belts of 40 degrees N-50 degrees N. Caution should therefore be exercised when using the calibrated 3B42RT for heavy rainfall-related flood forecasting (or landslide warning) over high-latitude regions, as the employment of the smooth-fill scheme in the CCA bias correction could homogenize the varying rainstorm characteristics. Finally, this study highlights that accurate detection and estimation of snow at high latitudes is still a challenging task for the future development of satellite precipitation retrievals.

  7. Inconclusive Predictions and Contradictions: A Lack of Consensus on Seed Germination Response to Climate Change at High Altitude and High Latitude

    OpenAIRE

    Jaganathan, GK; Dalrymple, SE

    2016-01-01

    Climate change directly affects arctic-alpine plants and acute responses to increased temperatures may be seen in their reproductive fitness and germination ability. However, uncertainties prevail in predicting whether a future warmer climate favors or hampers seed germination in high latitude and high altitude soils and seed germination research in such systems has not been able to provide generalizable patterns of response. The available literature on this subject has been conducted at vari...

  8. Features of the EAP events on the medium-range evolution process and the mid- and high-latitude Rossby wave activities during the Meiyu period

    Institute of Scientific and Technical Information of China (English)

    BUEH Cholaw; SHI Ning; JI LiRen; WEI Jie; TAO ShiYan

    2008-01-01

    In this paper, features for the evolution of the East Asia/Pacific (EAP) events and their association with high-and mid-latitude Rossby waves during the Meiyu period are analyzed on the medium-range time scale. It is shown that life cycles of the positive and negative EAP events cannot be simply regarded as "mirror" each other, in the upper troposphere, downward propagations of Rossby wave packets both over high- and mid-latitude regions of Eurasian continent and over the Asian jet region are responsible for generating basic patterns of high- and mid-latitude anomaly centers of the events. In this layer, Rossby wave packets also propagate from the mid-latitude anomaly center to the high-latitude one. In the middle and lower troposphere, the formation of the subtropical anomaly center of the event is mainly attributed to the anomalous convective activity in the tropical Pacific warm pool. The northward Rossby wave energy dispersion from this center is favorable to the enhancement and maintenance of the mid-latitude anomaly center in the same layer. Finally, it might be hypothesized that typical features of the positive and negative EAP events in their mature phase result from the interaction between (or phase-locking of) respective anomalous circulations induced both by quasi-zonal Rossby wave packets embedded in upper troposphere westerly and by quasi-meridional Rossby wave packets in the background flow of the East Asian summer monsoon in the middle and lower troposphere.

  9. Changes in Sea-Level Pressure over South Korea Associated with High-Speed Solar Wind Events

    CERN Document Server

    Cho, Il-Hyun; Marubashi, Katsuhide; Kim, Yeon-Han; Park, Young-Deuk; Chang, Heon-Young

    2011-01-01

    We explore a possibility that the daily sea-level pressure (SLP) over South Korea responds to the high-speed solar wind event. This is of interest in two aspects: First, if there is a statistical association this can be another piece of evidence showing that various meteorological observables indeed respond to variations in the interplanetary environment. Second, this can be a very crucial observational constraint since most models proposed so far are expected to preferentially work in higher latitude regions than the low latitude region studied here. We have examined daily solar wind speed ${\\rm V}$, daily SLP difference ${\\rm \\Delta SLP}$, and daily ${\\rm \\log(BV^{2})}$ using the superposed epoch analysis in which the key date is set such that the daily solar wind speed exceeds 800 ${\\rm kms^{-1}}$. We find that the daily ${\\rm \\Delta SLP}$ averaged out of 12 events reaches its peak at day +1 and gradually decreases back to its normal level. The amount of positive deviation of ${\\rm \\Delta SLP}$ is +2.5 hPa...

  10. Modeling the high-latitude ground response to the excitation of the ionospheric MHD modes by atmospheric electric discharge

    Science.gov (United States)

    Fedorov, E.; Mazur, N.; Pilipenko, V.; Baddeley, L.

    2016-11-01

    The ionospheric Alfvén resonator (IAR) and fast magnetosonic (FMS) waveguide, which can trap the electromagnetic wave energy in the range from fractions of Hz to several Hz, are characteristic features of the upper ionosphere. Their role in the electromagnetic impulsive coupling between atmospheric discharge processes and the ionosphere can be elucidated with a proper model. The presented model is based on numerical solution of coupled wave equations for electromagnetic modes in the ionosphere and atmosphere in a realistic ionosphere modeled with the use of IRI (International Reference Ionosphere) vertical profiles. The geomagnetic field is supposed to be nearly vertical, so the model can be formally applied to high latitudes, though the main features of ground ULF structure will be qualitatively similar at middle latitudes as well. The modeling shows that during the lightning discharge a coupled wave system comprising IAR and MHD waveguide is excited. Using the model, the spatial structure, frequency spectra, and polarization parameters have been calculated at various distances from a vertical dipole. In the lightning proximity (about several hundred kilometer) only the lowest IAR harmonics are revealed in the radial magnetic component spectra. At distances >800 km the multiband spectral structure is formed predominantly by harmonics of FMS waveguide modes. The model predictions do not contradict the results of search coil magnetometer observations on Svalbard; however, the model validation demands more dedicated experimental studies.

  11. Eocene high-latitude temperature gradients over time and space based on d18O values of fossil shark teeth

    Science.gov (United States)

    Zeichner, S. S.; Kim, S.; Colman, A. S.

    2015-12-01

    Early-Mid Eocene (56.0-33.9Mya) is characterized by a temperate Antarctic climate and shallower latitudinal temperature gradients than those in present day. The warmer waters off the coast of the Antarctic Peninsula provided suitable habitats for taxa (i.e., sharks) that live today at lower latitudes. Stable isotope analysis of Eocene shark teeth provides a proxy to understand high latitude temperature gradients. However, shark ecology, in particular migration and occupation of tidal versus pelagic habitats, must be considered in the interpretation of stable isotope data. In this study, we analyze d18OPO4 values from the enameloid of Striatolamia (synonymized with Carcharias) shark teeth from the La Meseta formation (Seymour Island, Antarctica) to estimate paleotemperature in Early-Mid Eocene Antarctica, and assess the impact of ecology versus environmental signals on d18OPO4 values. We compare the ranges and offsets between our measured shark tooth d18OPO4 and published bivalve d18OCO3 values to test whether shark teeth record signals of migration across latitudinal temperature gradients, or instead reflect seasonal and long-term temporal variation across La Meseta stratigraphic units.

  12. Dawn-dusk asymmetries and sub-Alfvénic flow in the high and low latitude magnetosheath

    Directory of Open Access Journals (Sweden)

    M. Longmore

    2005-11-01

    Full Text Available We present the results of a statistical survey of the magnetosheath using four years of Cluster orbital coverage. Moments of the plasma distribution obtained from the electron and ion instruments together with magnetic field data are used to characterise the flow and density in the magnetosheath. We note two important differences between our survey and the gasdynamic model predictions: a deceleration of the flow at higher latitudes close to the magnetopause, resulting in sub-Alfvénic flow near the cusp, and a dawn-dusk asymmetry with higher velocity magnitudes and lower densities measured on the dusk side of the magnetosheath in the Northern Hemisphere. The latter observation is in agreement with studies carried out by Paularena et al. (2001, Němeček et al. (2000, and Šafránková et al. (2004. In equations of hydrodynamics for a single-component additon to this we observe a reverse of this asymmetry for the Southern Hemisphere. High-latitude sub-Alfvénic flow is thought to be a necessary condition for steady state reconnection pole-ward of the cusp.

  13. High Galactic latitude polarized emission at 1.4 GHz and implications for cosmic microwave background observations

    CERN Document Server

    Carretti, E; Sault, R J; Cortiglioni, S; Poppi, S

    2005-01-01

    We analyse the polarized emission at 1.4 GHz in a 3x3 deg^2 area at high Galactic latitude (b ~ -40deg). The region, centred in (RA=5h, Dec=-49deg), was observed with the Australia Telescope Compact Array radio-interferometer, whose 3-30 arcmin angular sensitivity range allows the study of scales appropriate for CMB Polarization (CMBP) investigations. The angular behavior of the diffuse emission is analysed through the E- and B-mode power spectra. These follow a power law $C^X_l \\propto l^{\\beta_X}$ with slopes \\beta_E = -1.97 \\pm 0.08 and \\beta_B = -1.98 \\pm 0.07. The emission is found to be about a factor 25 fainter than in Galactic plane regions. The comparison of the power spectra with other surveys indicates that this area is intermediate between strong and negligible Faraday rotation effects. A similar conclusion can be reached by analysing both the frequency and Galactic latitude behaviors of the diffuse Galactic emission of the 408-1411 MHz Leiden survey data. We present an analysis of the Faraday rot...

  14. Reconnection electric field estimates and dynamics of high-latitude boundaries during a substorm

    Directory of Open Access Journals (Sweden)

    T. Pitkänen

    2009-05-01

    Full Text Available The dynamics of the polar cap and the auroral oval are examined in the evening sector during a substorm period on 25 November 2000 by using measurements of the EISCAT incoherent scatter radars, the north-south chain of the MIRACLE magnetometer network, and the Polar UV Imager.

    The location of the polar cap boundary (PCB is estimated from electron temperature measurements by the mainland low-elevation EISCAT VHF radar and the 42 m antenna of the EISCAT Svalbard radar. A comparison to the poleward auroral emission (PAE boundary by the Polar UV Imager shows that in this event the PAE boundary is typically located 0.7° of magnetic latitude poleward of the PCB by EISCAT. The convection reversal boundary (CRB is determined from the 2-D plasma drift velocity extracted from the dual-beam VHF data. The CRB is located 0.5–1° equatorward of the PCB indicating the existence of viscous-driven antisunward convection on closed field lines.

    East-west equivalent electrojets are calculated from the MIRACLE magnetometer data by the 1-D upward continuation method. In the substorm growth phase, electrojets together with the polar cap boundary move gradually equatorwards. During the substorm expansion phase, the Harang discontinuity (HD region expands to the MLT sector of EISCAT. In the recovery phase the PCB follows the poleward edge of the westward electrojet.

    The local ionospheric reconnection electric field is calculated by using the measured plasma velocities in the vicinity of the polar cap boundary. During the substorm growth phase, values between 0 and 10 mV/m are found. During the late expansion and recovery phase, the reconnection electric field has temporal variations with periods of 7–27 min and values from 0 to 40 mV/m. It is shown quantitatively, for the first time to our knowledge, that intensifications in the local reconnection electric field correlate with appearance of auroral poleward boundary intensifications (PBIs

  15. Matching dust emission structures and magnetic field in high-latitude cloud L1642: comparing Herschel and Planck maps

    CERN Document Server

    Malinen, J; Montillaud, J; Juvela, M; Ristorcelli, I; Clark, S E; Berné, O; Bernard, J -Ph; Pelkonen, V -M; Collins, D C

    2015-01-01

    The nearby cloud L1642 is one of only two known very high latitude (|b| > 30 deg) clouds actively forming stars. It is a rare example of star formation in isolated conditions, and can reveal important details of star formation in general, e.g., of the effect of magnetic fields. We compare Herschel dust emission structures and magnetic field orientation revealed by Planck polarization maps in L1642. The high-resolution (~18-40") Herschel data reveal a complex structure including a dense, compressed central blob with elongated extensions, low density striations, "fishbone" like structures with a spine and perpendicular striations, and a spiraling "tail". The Planck polarization data (at 10' resolution) reveal an ordered magnetic field pervading the cloud and aligned with the surrounding striations. There is a complex interplay between the cloud structure and large scale magnetic field. This suggests that magnetic field is closely linked to the formation and evolution of the cloud. CO rotational emission confirm...

  16. Distances to the high galactic latitude molecular clouds G192-67 and MBM 23-24

    CERN Document Server

    Grant, C E; Grant, Catherine E.; Burrows, David N.

    1999-01-01

    We report on distance determinations for two high Galactic latitude cloud complexes, G192-67 and MBM 23-24. No distance determination exists in the literature for either cloud. Thirty-four early type stars were observed towards the two clouds, more than half of which have parallaxes measured by the Hipparcos satellite. For the remaining stars we have made spectroscopic distance estimates. The data consist of high resolution echelle spectra centered on the Na I D lines, and were obtained over six nights at the Coude Feed telescope at Kitt Peak National Observatory. Interstellar absorption lines were detected towards some of the stars, enabling estimates of the distances to the clouds of 109 +/- 14 pc for G192-67, and of 139 +/- 33 pc for MBM 23-24. We discuss the relationship of these clouds to other ISM features such as the Local Hot Bubble and the local cavity in neutral hydrogen.

  17. Operation of Power Grids with High Penetration of Wind Power

    Science.gov (United States)

    Al-Awami, Ali Taleb

    The integration of wind power into the power grid poses many challenges due to its highly uncertain nature. This dissertation involves two main components related to the operation of power grids with high penetration of wind energy: wind-thermal stochastic dispatch and wind-thermal coordinated bidding in short-term electricity markets. In the first part, a stochastic dispatch (SD) algorithm is proposed that takes into account the stochastic nature of the wind power output. The uncertainty associated with wind power output given the forecast is characterized using conditional probability density functions (CPDF). Several functions are examined to characterize wind uncertainty including Beta, Weibull, Extreme Value, Generalized Extreme Value, and Mixed Gaussian distributions. The unique characteristics of the Mixed Gaussian distribution are then utilized to facilitate the speed of convergence of the SD algorithm. A case study is carried out to evaluate the effectiveness of the proposed algorithm. Then, the SD algorithm is extended to simultaneously optimize the system operating costs and emissions. A modified multi-objective particle swarm optimization algorithm is suggested to identify the Pareto-optimal solutions defined by the two conflicting objectives. A sensitivity analysis is carried out to study the effect of changing load level and imbalance cost factors on the Pareto front. In the second part of this dissertation, coordinated trading of wind and thermal energy is proposed to mitigate risks due to those uncertainties. The problem of wind-thermal coordinated trading is formulated as a mixed-integer stochastic linear program. The objective is to obtain the optimal tradeoff bidding strategy that maximizes the total expected profits while controlling trading risks. For risk control, a weighted term of the conditional value at risk (CVaR) is included in the objective function. The CVaR aims to maximize the expected profits of the least profitable scenarios, thus

  18. Possible crater-based pingos, paleolakes and periglacial landscapes at the high latitudes of Utopia Planitia, Mars

    Science.gov (United States)

    Soare, R. J.; Conway, S. J.; Pearce, G. D.; Dohm, J. M.; Grindrod, P. M.

    2013-08-01

    Closed-system pingos (CSPs) are perennial ice-cored mounds that evolve in relatively deep and continuous permafrost. They occur where thermokarst lakes either have lost or are losing their water by drainage or evaporation and by means of freeze-thaw cycling, permafrost aggradation and pore-water migration. The presence of CSPs on Mars, particularly on late-Amazonian Epoch terrain at near-polar latitudes, would indicate: (1) the antecedent occurrence of ponded water at the mound-formation sites; (2) freeze-thaw cycling of this water; and (3) boundary-conditions of pressure and temperature at or above the triple point of water much more recently and further to the north than has been thought possible. In 2005 we studied two crater-floor landscapes in northern Utopia Planitia and used MOC narrow-angle images to describe mounds within these landscapes that shared a suite of geological characteristics with CSPs on Earth. Here, we show the results of a circum-global search for similar crater-floor landscapes at latitudes >˜55°N. The search incorporates all relevant MOC and HiRISE images released since 2005. In addition to the two periglacially suggestive crater-floor landscapes observed by us earlier, we have identified three other crater floors with similar landscapes. Interestingly, each of the five mound-bearing craters occur within a tight latitudinal-band (˜64-69°N); this could be a marker of periglacial landscape-modification on a regional scale. Just to the north of the crater-based pingo-like mounds Conway et al. have identified large (km-scale) crater-based perennial ice-domes. They propose that the ice domes develop when regional polar-winds transport and precipitate icy material onto the floor of their host craters. Under a slightly different obliquity-solution ice domes could have accumulated at the lower latitudes where the putative CSPs have been observed. Subsequently, were temperatures to have migrated close to or at 0 °C the ice domes could have

  19. Observation of Neon at mid and high latitudes in the sunlit lunar exosphere: Results from CHACE aboard MIP/Chandrayaan-1

    Science.gov (United States)

    Das, Tirtha Pratim; Thampi, Smitha V.; Bhardwaj, Anil; Ahmed, S. M.; Sridharan, R.

    2016-07-01

    The distribution of neutral Neon at the mid and high latitudes in the sunlit lunar exosphere observed by CHandra's Altitudinal Composition Explorer (CHACE) aboard the Moon Impact Probe (MIP) of the Chandrayaan-1 is reported. The CHACE observation was made when Moon was in the Earth's magnetotail. The upper limits of the surface number density are found to vary from (7-22) × 103 cm-3 at the pole, to (3-5) × 103 cm-3 in mid (50°S) latitudes and to (0.5-1.1) × 103 cm-3 in lower (20°S) latitudes. The surface number densities estimated at lower latitudes from CHACE observations are consistent with the LADEE Neutral Mass Spectrometer (NMS) observations.

  20. Wind Erosion and Dune Formation on High Frozen Bluffs

    Science.gov (United States)

    Marsh, W. M.; Marsh, B. D.

    1984-01-01

    Frost penetration increases upslope on barren, windswept bluffs in cold environments. Along the south shore of Lake Superior, near the brow of 100 m high bluffs it typically exceeds 5 m. Frost increases the shear strength of damp sand to a level comparable to that of concrete, making winter slopes highly stable despite undercutting by waves and ground-water sapping along the footslope. Sublimation of interparticle ice in the slope face increases with wind speed and lower vapor pressures. The cold and dry winter winds of Lake Superior ablate these slopes through loss of binding ice. Wind erosion rates, based on measurements of sand accumulation on the forest floor downwind of the brow, show most airborne sand falls out within several meters of the brow, forming a berm 1 to 3 m high after many years. The spatial pattern of sand deposition, however, varies considerably over distances of several hundred meters along the top bluffs in response to frost conditions and the build-up of gravel lag on the slope face, sand exposure from mass movements, and local aerodynamics of the crest slope. The formation of perched sand dunes in the Great Lakes region is clearly related to wind erosion of sand from high bluffs in winter. Broadly similar processes may operate on Mars.

  1. High-Energy 2-Micrometers Doppler Lidar for Wind Measurements

    Science.gov (United States)

    Koch, Grady J.; Beyon, Jeffrey Y.; Barnes, Bruce W.; Petros, Mulugeta; Yu, Jirong; Amzajerdian, Farzin; Kavaya, Michael J.; Singh, Upendra N.

    2006-01-01

    High-energy 2-micrometer wavelength lasers have been incorporated in a prototype coherent Doppler lidar to test component technologies and explore applications for remote sensing of the atmosphere. Design of the lidar is presented including aspects in the laser transmitter, receiver, photodetector, and signal processing. Calibration tests and sample atmospheric data are presented on wind and aerosol profiling.

  2. High Power Density Power Electronic Converters for Large Wind Turbines

    DEFF Research Database (Denmark)

    Senturk, Osman Selcuk

    In large wind turbines (in MW and multi-MW ranges), which are extensively utilized in wind power plants, full-scale medium voltage (MV) multi-level (ML) voltage source converters (VSCs) are being more preferably employed nowadays for interfacing these wind turbines with electricity grids...... assessments of these specific VSCs so that their power densities and reliabilities are quantitatively determined, which requires extensive utilization of the electro-thermal models of the VSCs under investigation. In this thesis, the three-level neutral-point-clamped VSCs (3L-NPC-VSCs), which are classified......-HB-VSCs). As the switch technology for realizing these 3L-VSCs, press-pack IGBTs are chosen to ensure high power density and reliability. Based on the selected 3L-VSCs and switch technology, the converter electro-thermal models are developed comprehensively, implemented practically, and validated via a full-scale 3L...

  3. The effects of divergent and nondivergent winds on the kinetic energy budget of a mid-latitude cyclone - A case study

    Science.gov (United States)

    Chen, T.-C.; Alpert, J. C.; Schlatter, T. W.

    1978-01-01

    The magnitude of the divergent component of the wind is relatively small compared to that of the nondivergent component in large-scale atmospheric flows; nevertheless, it plays an important role in the case of explosive cyclogenesis examined here. The kinetic energy budget for the life cycle of an intense, developing cyclone over North America is calculated. The principal kinetic energy source is the net horizontal transport across the boundaries of the region enclosing the cyclone. By investigating the relative importance of the divergent and nondivergent wind components in the kinetic energy budget, it was found, as expected, that neglecting the divergent wind component in calculating the magnitude of the kinetic energy is of little consequence, but that the horizontal flux convergence and generation of kinetic energy depend crucially upon the divergent component. Modification of the divergent wind component can result in significant changes in the kinetic energy budget of the synoptic system.

  4. Comparison of high latitude electron density profiles obtained with the GPS radio occultation technique and EISCAT measurements

    Directory of Open Access Journals (Sweden)

    C. Stolle

    2004-06-01

    Full Text Available To obtain a comprehensive view on high latitude processes by applying different observation techniques, the SIRCUS campaign was initiated in 2001/2002. This paper compares electron density profiles derived from CHAMP radio occultation data and those measured with the EISCAT facility. Since ionospheric profiling with the help of space-based received GPS is a relatively new technique, validations with established independent instruments are of crucial need. We present 28 profiling events for quasi-statistical analyses, which occurred during the SIRCUS campaigns and describe some of them in more detail. We found out that the majority of profile comparisons in electron density peak value and height, as well as in TEC, lie within the error ranges of the two methods. Differences in the ionospheric quantities do not necessarily occur when the locations of the occultation and of the radar site show considerable distances. Differences are more pronounced when the ionosphere is remarkably structured.

  5. A High Galactic Latitude HI 21 cm-line Absorption Survey using the GMRT: I. Observations and Spectra

    Indian Academy of Sciences (India)

    Rekhesh Mohan; K. S. Dwarakanath; G. Srinivasan

    2004-09-01

    We have used the Giant Meterwave Radio Telescope (GMRT) to measure the Galactic HI 21-cm line absorption towards 102 extragalactic radio continuum sources, located at high (|| > 15°) Galactic latitudes. The Declination coverage of the present survey is ≳ -45°. With a mean rms optical depth of ∼ 0.003, this is the most sensitive Galactic HI 21-cm line absorption survey to date. To supplement the absorption data, we have extracted the HI 21-cm line emission profiles towards these 102 lines of sight from the Leiden Dwingeloo Survey of Galactic neutral hydrogen. We have carried out a Gaussian fitting analysis to identify the discrete absorption and emission components in these profiles. In this paper, we present the spectra and the components. A subsequent paper will discuss the interpretation of these results.

  6. Detection of wetland dynamics with ENVISAT ASAR in support of methane modelling at high latitudes

    Directory of Open Access Journals (Sweden)

    A. Bartsch

    2011-08-01

    Full Text Available Spatial information on inundation dynamics is expected to improve greenhouse gas estimates in climate models. Satellite data can provide land cover information from local to global scale. The detection capability for dynamics is however limited. Cloud cover and daylight independent methods are required for frequent updates. Suitable are therefore sensors which make use of microwaves. The purpose of the present study is to assess such data for determination of wetland dynamics from the viewpoint of use in climate models of the boreal and tundra environments. The focus is on synthetic aperture radar (SAR operating in C-band due to, among microwave systems, comparably good spatial resolution and data availability. Continuity is also expected for such systems. Simple classification algorithms can be applied to detect open water in an automatised way allowing the processing of time series. Such approaches are robust when the water surface is smooth. C-band data from ENVISAT ASAR (Advanced SAR operating in wide swath mode (150 m resolution have been investigated for implementation of an automated detection procedure of open water fraction. More than 4000 samples (single acquisitions tiled into 0.5 degree grid cells have been analysed for July/August 2007 and 2008. Modification of input parameters results in differences below 1 % open water fraction. The actual challenge is the frequent occurrence of waves due to wind and precipitation. This reduces the separability of the water class from other land cover. The possible update intervals for surface water extent are therefore decreased considerably. Statistical measures of the backscatter distribution can be applied in order to retrieve the for classification suitable data. The Pearson correlation between each sample dataset and a location specific representation of the bimodal distribution has been used for assessment. On average only 40 % of acquisitions allow a separation of the open water class

  7. Northern high-latitude climate change between the mid and late Holocene – Part 2: Model-data comparisons

    Directory of Open Access Journals (Sweden)

    J. Nilsson

    2009-06-01

    Full Text Available The solar orbital forcing induced changes in insolation at the mid-Holocene compared to the late Holocene, which causes an amplification of the seasonal cycle in the Northern Hemisphere in the earlier period. The climate response over northern high latitudes, to this change in forcing has been investigated in three types of PMIP (Paleoclimate Modelling Intercomparison Project simulations with different complexity of the climate system. The model results have also been compared with available reconstructions from temperature proxy data. Both the reconstructions and the PMIP2 models show a warm response in annual mean temperature, as well as in summer and winter temperature. The model-model comparisons indicate the importance of including the different physical feedbacks (ocean, sea-ice, vegetation in the climate model. An objective selection method is applied in the model-data comparison to evaluate the capability of the climate model in reproducing the spatial response pattern. The comparisons between the reconstructions and the best-fit selected simulations show that over the northern high latitudes, summer temperature change follows closely to the insolation and shows a common feature with strong warming over land and relatively weak warming over ocean. A pronounced warming centre is found over Barents Sea in winter in model simulations, which is also supported by the nearby northern Eurasian continental reconstructions. The warming over Barents Sea corresponds to a positive North Atlantic Oscillation (NAO. The strengthened sea level pressure gradient may have caused a northward shift of the Atlantic storm track. It results in enhanced westerlies towards the northern Eurasia, which may be responsible for the winter warming over northern Fennoscandia and northern Siberia.

  8. Meta-analysis of high-latitude nitrogen-addition and warming studies imply ecological mechanisms overlooked by land models

    Directory of Open Access Journals (Sweden)

    N. J Bouskill

    2014-08-01

    Full Text Available Accurate representation of ecosystem processes in land models is crucial for reducing predictive uncertainty in energy and greenhouse gas feedbacks with the atmosphere. Here we describe an observational and modeling meta-analysis approach to benchmark land models, and apply the method to the land model CLM4.5 with two versions of belowground biogeochemistry. We focused our analysis on the above and belowground high-latitude ecosystem responses to warming and nitrogen addition, and identified mechanisms absent, or poorly parameterized in CLM4.5. While the two model versions predicted similar trajectories for soil carbon stocks following both types of perturbation, other variables (e.g., belowground respiration differed from the observations in both magnitude and direction, indicating the underlying mechanisms are inadequate for representing high-latitude ecosystems. The observational synthesis attribute these differences to missing representations of microbial dynamics, characterization of above and belowground functional processes, and nutrient competition. We use the observational meta-analyses to discuss potential approaches to improving the current models (e.g., the inclusion of dynamic vegetation or different microbial functional guilds, however, we also raise a cautionary note on the selection of data sets and experiments to be included in a meta-analysis. For example, the concentrations of nitrogen applied in the synthesized field experiments (average =72 kg ha−1 yr−1 are many times higher than projected soil nitrogen concentrations (from nitrogen deposition and release during mineralization, which preclude a rigorous evaluation of the model responses to nitrogen perturbation. Overall, we demonstrate here that elucidating ecological mechanisms via meta-analysis can identify deficiencies in both ecosystem models and empirical experiments.

  9. Climate change between the mid and late Holocene in northern high latitudes – Part 2: Model-data comparisons

    Directory of Open Access Journals (Sweden)

    K. Holmgren

    2010-09-01

    Full Text Available The climate response over northern high latitudes to the mid-Holocene orbital forcing has been investigated in three types of PMIP (Paleoclimate Modelling Intercomparison Project simulations with different complexity of the modelled climate system. By first undertaking model-data comparison, an objective selection method has been applied to evaluate the capability of the climate models to reproduce the spatial response pattern seen in proxy data. The possible feedback mechanisms behind the climate response have been explored based on the selected model simulations. Subsequent model-model comparisons indicate the importance of including the different physical feedbacks in the climate models. The comparisons between the proxy-based reconstructions and the best fit selected simulations show that over the northern high latitudes, summer temperature change follows closely the insolation change and shows a common feature with strong warming over land and relatively weak warming over ocean at 6 ka compared to 0 ka. Furthermore, the sea-ice-albedo positive feedback enhances this response. The reconstructions of temperature show a stronger response to enhanced insolation in the annual mean temperature than winter and summer temperature. This is verified in the model simulations and the behaviour is attributed to the larger contribution from the large response in autumn. Despite a smaller insolation during winter at 6 ka, a pronounced warming centre is found over Barents Sea in winter in the simulations, which is also supported by the nearby northern Eurasian continental and Fennoscandian reconstructions. This indicates that in the Arctic region, the response of the ocean and the sea ice to the enhanced summer insolation is more important for the winter temperature than the synchronous decrease of the insolation.

  10. Examining the Role of Aquatic Vegetation in Methane Production: Examples From a Shallow High Latitude Lake in Abisko, Sweden.

    Science.gov (United States)

    Horruitiner, C. D.; Varner, R. K.; Palace, M. W.; Johnson, J. E.; Wik, M.; Lundgren, D. J.; Sinclair, S. N.; Nicastro, A. J. D.; Crawford, M.

    2015-12-01

    High latitude lakes and ponds are a large source of atmospheric methane. Emissions from lakes are thought to be controlled primarily by temperature and secondarily by the availability of labile organic carbon. Aquatic plants provide insitu carbon sources to lake bottoms and therefore can potentially impact rates of methane production. We studied vegetation and lake sediment characteristics across shallow depths in Inre Harrsjön, a lake located within the Stordalen Mire in the discontinuous permafrost zone in subarctic Sweden. Vegetation surveys using a submerged quadrat with camera were performed in transects across IH to characterize bottom vegetation. Carbon and nitrogen elemental analysis was performed on vegetation samples from both the lake and surrounding mire ecosystem. Sediment cores representing each vegetation type were analyzed for CH4, δ13CH4, and elemental CHNS. In all cores but one, total organic carbon (TOC) is greatest near the surface and decreases downcore. Methane concentrations correlated with TOC indicating insitu methane production. C:N ratios in sediment cores are more reflective of aquatic than terrestrial mire vegetation indicating that organic carbon in the lake sediments is dominated by aquatic sources. δ13CH4 is relatively constant downcore, which indicates little to no methane oxidation. The methane produced in sediments is consistently within the range of hydrogenotrophic methanogenesis via CO2 reduction. We suggest the role of aquatic vegetation in the production of methane in high latitude shallow lakes may be important and will likely have a positive feedback in a warming climate with longer ice-free seasons.

  11. Cluster multispacecraft observations at the high-latitude duskside magnetopause: implications for continuous and component magnetic reconnection

    Directory of Open Access Journals (Sweden)

    A. Retinò

    2005-02-01

    Full Text Available We report multispacecraft Cluster observations of magnetic reconnection at the high-latitude magnetopause/magnetospheric boundary layer (MP/BL under mainly northward interplanetary magnetic field (IMF conditions. The event we study is on 3 December 2001 when the Cluster spacecraft were skimming the high-latitude duskside MP/BL during a period of about four hours. The orbit and configuration of the spacecraft were such that at least one satellite was present in the MP/BL during most of that period. We present the evidence of reconnection in the form of tangential stress balance between the magnetosheath and the MP/BL (Walén test and in several cases in the form of transmitted magnetosheath ions in the MP/BL and incident/reflected magnetosheath ions in the magnetosheath boundary layer (MSBL . The observations are consistent with magnetic reconnection occurring tailward of the cusp and going on continuously for a period of about four hours. The observed directions of the reconnection flows are consistent with the IMF orientation, thus indicating that reconnection is globally controlled by the IMF. Observations of a few flow reversals suggest passages of the spacecraft close to the X-line. The observation of low magnetic shear across the magnetopause during a flow reversal is consistent with component merging at least in one case. The observation of reconnection flows on the duskside magnetopause irrespective of the change in the sign of the IMF BY also suggests a better agreement with the component merging model, though antiparallel merging cannot be excluded because the distance from the X-line is not known.

  12. HD 187885 and s-process elements in high galactic latitude supergiants

    NARCIS (Netherlands)

    VanWinckel, H; Waelkens, C; Waters, LBFM

    1996-01-01

    We present an accurate LTE chemical analysis of HD 187885 on the basis of high-resolution, high signal-to-noise spectra. The low iron abundance of [Fe/H] = -0.5 confirms the old, low-mass nature of the supergiant. With [C/Fe] = +0.9, [N/Fe] = +0.7, [O/Fe] = +0.6 and above all the high s-process elem

  13. HD 187885 and s-process elements in high galactic latitude supergiants

    NARCIS (Netherlands)

    VanWinckel, H; Waelkens, C; Waters, LBFM

    We present an accurate LTE chemical analysis of HD 187885 on the basis of high-resolution, high signal-to-noise spectra. The low iron abundance of [Fe/H] = -0.5 confirms the old, low-mass nature of the supergiant. With [C/Fe] = +0.9, [N/Fe] = +0.7, [O/Fe] = +0.6 and above all the high s-process

  14. Analysis of the high Reynolds number 2D tests on a wind turbine airfoil performed at two different wind tunnels

    Science.gov (United States)

    Pires, O.; Munduate, X.; Ceyhan, O.; Jacobs, M.; Madsen, J.; Schepers, J. G.

    2016-09-01

    2D wind tunnel tests at high Reynolds numbers have been done within the EU FP7 AVATAR project (Advanced Aerodynamic Tools of lArge Rotors) on the DU00-W-212 airfoil and at two different test facilities: the DNW High Pressure Wind Tunnel in Gottingen (HDG) and the LM Wind Power in-house wind tunnel. Two conditions of Reynolds numbers have been performed in both tests: 3 and 6 million. The Mach number and turbulence intensity values are similar in both wind tunnels at the 3 million Reynolds number test, while they are significantly different at 6 million Reynolds number. The paper presents a comparison of the data obtained from the two wind tunnels, showing good repeatability at 3 million Reynolds number and differences at 6 million Reynolds number that are consistent with the different Mach number and turbulence intensity values.

  15. Estimated changes in wind speed and wind power density over the western High Plains, 1971-2000

    Science.gov (United States)

    Greene, J. Scott; Chatelain, Matthew; Morrissey, Mark; Stadler, Steve

    2012-08-01

    This manuscript presents the results of research on the temporal patterns in wind speed and wind power density from 1971 to 2000. The study area is across the western High Plains states east of the Rocky Mountains in an area which has a proven wind power resource. Policies and economic analyses involving the rapidly expanding wind power industry have often assumed a constant in the wind resource; however, any temporal pattern or trend in wind speeds can have a meaningful impact on the reliability of wind power as an energy resource. Using data provided by the North American Regional Climate Change Assessment Program (NARCCAP) to analyze decadal and seasonal trends of wind data, this study shows that from 1971 to 2000 there were some notable changes in the NARCCAP simulated wind velocities over the study region. Wind speed trends across the central High Plains of the USA were most notable across the western portion of the study area along the higher terrain near the front range of the Rocky Mountains. The most significant changes occurred during winter and spring when a large portion of the study area experienced the most substantial decrease in wind speed, with a 20% reduction in wind power density during spring across the western portion of the study area. During summer and fall, the trends are less noticeable, with only very small changes in the summer. Fall was the only season that saw widespread increased values of wind power density from the 1970s to 1990s, with increases of nearly 10% in some southern areas of the study area. Based upon the analysis of the data and previous literature, it is theorized that these changes could be the result of changing synoptic patterns across the study region.

  16. A high resolution WRF model for wind energy forecasting

    Science.gov (United States)

    Vincent, Claire Louise; Liu, Yubao

    2010-05-01

    The increasing penetration of wind energy into national electricity markets has increased the demand for accurate surface layer wind forecasts. There has recently been a focus on forecasting the wind at wind farm sites using both statistical models and numerical weather prediction (NWP) models. Recent advances in computing capacity and non-hydrostatic NWP models means that it is possible to nest mesoscale models down to Large Eddy Simulation (LES) scales over the spatial area of a typical wind farm. For example, the WRF model (Skamarock 2008) has been run at a resolution of 123 m over a wind farm site in complex terrain in Colorado (Liu et al. 2009). Although these modelling attempts indicate a great hope for applying such models for detailed wind forecasts over wind farms, one of the obvious challenges of running the model at this resolution is that while some boundary layer structures are expected to be modelled explicitly, boundary layer eddies into the inertial sub-range can only be partly captured. Therefore, the amount and nature of sub-grid-scale mixing that is required is uncertain. Analysis of Liu et al. (2009) modelling results in comparison to wind farm observations indicates that unrealistic wind speed fluctuations with a period of around 1 hour occasionally occurred during the two day modelling period. The problem was addressed by re-running the same modelling system with a) a modified diffusion constant and b) two-way nesting between the high resolution model and its parent domain. The model, which was run with horizontal grid spacing of 370 m, had dimensions of 505 grid points in the east-west direction and 490 points in the north-south direction. It received boundary conditions from a mesoscale model of resolution 1111 m. Both models had 37 levels in the vertical. The mesoscale model was run with a non-local-mixing planetary boundary layer scheme, while the 370 m model was run with no planetary boundary layer scheme. It was found that increasing the

  17. Numerical Investigation of Wind Conditions for Roof-Mounted Wind Turbines: Effects of Wind Direction and Horizontal Aspect Ratio of a High-Rise Cuboid Building

    Directory of Open Access Journals (Sweden)

    Takaaki Kono

    2016-11-01

    Full Text Available From the viewpoint of installing small wind turbines (SWTs on rooftops, this study investigated the effects of wind direction and horizontal aspect ratio (HAR = width/length of a high-rise cuboid building on wind conditions above the roof by conducting large eddy simulations (LESs. The LES results confirmed that as HAR decreases (i.e., as the building width decreases, the variation in wind velocity over the roof tends to decrease. This tendency is more prominent as the angle between the wind direction and the normal vector of the building’s leeward face with longer roof edge increases. Moreover, at windward corners of the roof, wind conditions are generally favorable at relatively low heights. In contrast, at the midpoint of the roof's windward edge, wind conditions are generally not favorable at relatively low heights. At leeward representative locations of the roof, the bottoms of the height range of favorable wind conditions are typically higher than those at the windward representative locations, but the favorable wind conditions are much better at the leeward representative locations. When there is no prevailing wind direction, the center of the roof is more favorable for installing SWTs than the corners or the edge midpoints of the roof.

  18. Tropical and High-latitude Surface Ocean Circulation Across The Mid-Pleistocene Transition: Teleconnections And Impacts For Ice-sheet Growth And Environmental Change Onshore

    Science.gov (United States)

    McClymont, E. L.; Rosell-Mele, A.; Lloyd, J. M.

    2006-12-01

    The Mid-Pleistocene Transition (MPT) is a major event in the Quaternary record, marking the shift to a dominant glacial/interglacial period of 100-kyr and the development of larger northern hemisphere ice-sheets at ca. 0.9 Ma. The significance of the MPT lies in the change of the global climate system response to external insolation forcing, which cannot account for the strength of the 100-kyr cycles. Existing hypotheses link the MPT to falling atmospheric CO2 concentrations, cooler deep-water temperatures, changes in sea-ice distribution and to the basal conditions of the northern hemisphere ice-sheets. We present alkenone-derived records of sea-surface temperature from the tropical Pacific and the south-east Atlantic spanning 1.5-0.5 Ma, coupled with evidence of arctic/polar water mass distributions in the high northern latitudes of the Atlantic and Pacific Oceans. Interaction between the tropics and high-latitudes across the MPT is suggested by the results presented here. At all sites we find evidence for cooling beginning from 1.15 Ma, supporting the hypotheses invoking cooling of both the atmosphere and deep-waters as a driver of the MPT. Sea-ice expansion from 1.15 Ma is suggested by the equatorward migration of arctic/polar water masses in both the Atlantic and Pacific, which reached their maximum extent at 1.0 Ma. The negative impact of more expansive sea-ice cover to the transport of moisture to the ice-sheet source regions may have been critical to the later development of larger northern hemisphere ice-sheets from 0.9 Ma. Significantly, we find that the MPT was not simply a high-latitude phenomenon, but was accompanied by (and perhaps driven by) significant changes to circulation in the tropical Pacific. Between 1.15 0.9 Ma a secular decrease in mean sea-surface temperatures of c.1.5*C in the eastern tropical Pacific marks an intensification of Walker Circulation and a shift towards a `La Niña'-like circulation state. The associated Trade Wind

  19. G181.1+9.5, a new high-latitude low-surface brightness supernova remnant

    Science.gov (United States)

    Kothes, Roland; Reich, Patricia; Foster, Tyler J.; Reich, Wolfgang

    2017-01-01

    Context. More than 90% of the known Milky Way supernova remnants (SNRs) are within 5° of the Galactic plane. The discovery of the new high-latitude SNR G181.1+9.5 will give us the opportunity to learn more about the environment and magnetic field at the interface between disk and halo of our Galaxy. Aims: We present the discovery of SNR G181.1+9.5, a new high-latitude SNR, serendipitously discovered in an ongoing survey of the Galactic anti-centre High-Velocity Cloud complex, observed with the DRAO Synthesis Telescope in the 21 cm radio continuum and H i spectral line. Methods: We use radio continuum observations (including the linearly polarized component) at 1420 MHz (observed with the DRAO ST) and 4850 MHz (observed with the Effelsberg 100-m radio telescope) to map G181.1+9.5 and determine its nature as a SNR. High-resolution 21 cm H i line observations and H i emission and absorption spectra reveal the physical characteristics of its local interstellar environment. Finally, we estimate the basic physical parameters of G181.1+9.5 using models for highly-evolved SNRs. Results: G181.1+9.5 has a circular shell-like morphology with a radius of about 16 pc at a distance of 1.5 kpc some 250 pc above the mid-plane. The radio observations reveal highly linearly polarized emission with a non-thermal spectrum. Archival ROSAT X-ray data reveal high-energy emission from the interior of G181.1+9.5 indicative of the presence of shock-heated ejecta. The SNR is in the advanced radiative phase of SNR evolution, expanding into the HVC inter-cloud medium with a density of nHI ≈ 1 cm-3. Basic physical attributes of G181.1+9.5 calculated with radiative SNR models show an upper-limit age of 16 000 yr, a swept-up mass of more than 300M⊙, and an ambient density in agreement with that estimated from H i observations. Conclusions: G181.1+9.5 shows all characteristics of a typical mature shell-type SNR, but its observed faintness is unusual and requires further study.

  20. The rotation of the plasmapause-like boundary at high latitudes in Saturn's magnetosphere and its relation to the eccentric rotation of the northern and southern auroral ovals

    Science.gov (United States)

    Gurnett, D. A.; Persoon, A. M.; Groene, J. B.; Kurth, W. S.; Morooka, M.; Wahlund, J.-E.; Nichols, J. D.

    2011-11-01

    Here we present a study of the rotation of the plasmapause-like density boundary discovered by the Cassini spacecraft at high latitudes in the Saturnian magnetosphere, and compare the results with previously published studies of high-latitude magnetic field perturbations and the eccentric rotation of the auroral ovals. Near the planet the density boundary is located at dipole L values ranging from about 8 to 15, and separates a region of very low densities at high latitudes from a region of higher densities at lower latitudes. We show that the density boundary rotates at different rates in the northern and southern hemispheres, and that the periods are the same as the modulation periods of Saturn kilometric radiation in those hemispheres. We also show that the phase of rotation in a given hemisphere is closely correlated with the phase of the high-latitude magnetic field perturbations observed by Cassini in that hemisphere, and also with the phase of the eccentric rotation of the auroral oval observed by the Hubble Space Telescope.

  1. Paleoseismology at high latitudes: Seismic disturbance of upper Quaternary deposits along the Castle Mountain fault near Houston, Alaska

    Science.gov (United States)

    Haeussler, P.J.; Best, T.C.; Waythomas, C.F.

    2002-01-01

    Most paleoseismic studies are at low to moderate latitudes. Here we present results from a high-latitude (61??30??? N) trenching study of the Castle Mountain fault in south-central Alaska. This fault is the only one known in the greater Anchorage, Alaska, area with historical seismicity and a Holocene fault scarp. It strikes eastnortheast and cuts glacial and postglacial sediments in an area of boreal spruce-birch forest, shrub tundra, and sphagnum bog. The fault has a prominent vegetation lineament on the upthrown, north side of the fault. Nine trenches were logged across the fault in glacial and postglacial deposits, seven along the main trace, and two along a splay. In addition to thrust and strike-slip faulting, important controls on observed relationships in the trenches are the season in which faulting occurred, the physical properties of the sediments, liquefaction, a shallow water table, soil-forming processes, the strength of the modern root mat, and freeze-thaw processes. Some of these processes and physical properties are unique to northern-latitude areas and result in seismic disturbance effects not observed at lower latitudes. The two trenches across the Castle Mountain fault splay exposed a thrust fault and few liquefaction features. Radiocarbon ages of soil organic matter and charcoal within and overlying the fault indicate movement on the fault at ca. 2735 cal. (calendar) yr B.P. and no subsequent movement. In the remaining seven trenches, surface faulting was accompanied by extensive liquefaction and a zone of disruption 3 m or more wide. The presence of numerous liquefaction features at depths of soil, but did not penetrate the interlocking spruce-birch root mat. The strength of the root mat prohibited development of a nonvegetated scarp face and colluvial wedge. In only one trench did we observe a discrete fault plane with measurable offset. It lay beneath a 2-m-thick carapace of liquefied sand and silt and displayed a total of 0.9-1.85 m of

  2. Tropospheric mixing ratios of NO and NOy obtained during TROPOZ II in the latitude region 67 deg N-56 deg S

    Energy Technology Data Exchange (ETDEWEB)

    Rohrer, F.; Bruening, D.; Ehhalt, D.H. [Forschungszentrum Juelich GmbH (Germany). Inst. fuer Atmosphaerische Chemie

    1997-12-31

    Tropospheric mixing ratios of NO and NOy were measured along the flight track of the TROPOZ II aircraft campaign. These measurements cover regions along the east coast of North America, the Pacific and Atlantic coast of South America and the Atlantic coast of North Africa and Europe. The meteorological conditions are close to the climatological mean: westerly winds at high and mid latitudes, variable and weak winds at low latitudes. (author) 2 refs.

  3. Occurrence of weak, sub-micron, tropospheric aerosol events at high Arctic latitudes

    Science.gov (United States)

    O'Neill, N. T.; Pancrati, O.; Baibakov, K.; Eloranta, E.; Batchelor, R. L.; Freemantle, J.; McArthur, L. J. B.; Strong, K.; Lindenmaier, R.

    2008-07-01

    Numerous fine mode (sub-micron) aerosol optical events were observed during the summer of 2007 at the High Arctic atmospheric observatory (PEARL) located at Eureka, Nunavut, Canada. Half of these events could be traced to forest fires in southern and eastern Russia and the Northwest Territories of Canada. The most notable findings were that (a) a combination of ground-based measurements (passive sunphotometry, high spectral resolution lidar) could be employed to determine that weak (near sub-visual) fine mode events had occurred, and (b) this data combined with remote sensing imagery products (MODIS, OMI-AI, FLAMBE fire sources), Fourier transform spectroscopy and back trajectories could be employed to identify the smoke events.

  4. High troposphere O3 filament at mid-latitude: a BORTAS campaign case study

    Science.gov (United States)

    Aruffo, Eleonora; Peterson, David; Di Carlo, Piero; Biancofiore, Fabio; Busilacchio, Marcella; Dari Salisburgo, Cesare; Giammaria, Franco; Bauguitte, Stephane; Lee, James; Moller, Sarah; Hopkins, James; Punjabi, Shalini; Lewis, Alistair C.; Palmer, Paul; Hyer, Edward

    2016-04-01

    During a flight (B625, 24 July 2011) of the BORTAS campaign (BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites, Nova Scotia, Canada, July-August 2011), an increase in the ozone (O3) concentrations has been observed at high altitude (about 7.5 Km a.s.l.) correlated with a significant growth of total peroxy nitrates (∑PNs), CO, NO2, NOy, black carbon (BC), isoprene and other species. We will illustrate the data analysis, the Hysplit back trajectories calculation and the analysis of the meteorological/physical conditions occurred during this case study in order to demonstrate that the O3 filament measured at high altitude over the Atlantic Ocean (between Nova Scotia and the Gulf of St. Lawrence) is a consequence of boreal biomass burning fires.

  5. Species Richness and Community Structure on a High Latitude Reef: Implications for Conservation and Management

    Directory of Open Access Journals (Sweden)

    Wayne Houston

    2011-07-01

    Full Text Available In spite of the wealth of research on the Great Barrier Reef, few detailed biodiversity assessments of its inshore coral communities have been conducted. Effective conservation and management of marine ecosystems begins with fine-scale biophysical assessments focused on diversity and the architectural species that build the structural framework of the reef. In this study, we investigate key coral diversity and environmental attributes of an inshore reef system surrounding the Keppel Bay Islands near Rockhampton in Central Queensland, Australia, and assess their implications for conservation and management. The Keppels has much higher coral diversity than previously found. The average species richness for the 19 study sites was ~40 with representatives from 68% of the ~244 species previously described for the southern Great Barrier Reef. Using scleractinian coral species richness, taxonomic distinctiveness and coral cover as the main criteria, we found that five out of 19 sites had particularly high conservation value. A further site was also considered to be of relatively high value. Corals at this site were taxonomically distinct from the others (representatives of two families were found here but not at other sites and a wide range of functionally diverse taxa were present. This site was associated with more stressful conditions such as high temperatures and turbidity. Highly diverse coral communities or biodiversity ‘hotspots’ and taxonomically distinct reefs may act as insurance policies for climatic disturbance, much like Noah’s Arks for reefs. While improving water quality and limiting anthropogenic impacts are clearly important management initiatives to improve the long-term outlook for inshore reefs, identifying, mapping and protecting these coastal ‘refugia’ may be the key for ensuring their regeneration against catastrophic climatic disturbance in the meantime.

  6. Multifractal analysis of high resolution solar wind proton density measurements

    Science.gov (United States)

    Sorriso-Valvo, Luca; Carbone, Francesco; Leonardis, Ersilia; Chen, Christopher H. K.; Šafránková, Jana; Němeček, Zdenek

    2017-03-01

    The solar wind is a highly turbulent medium, with a high level of field fluctuations throughout a broad range of scales. These include an inertial range where a turbulent cascade is assumed to be active. The solar wind cascade shows intermittency, which however may depend on the wind conditions. Recent observations have shown that ion-scale magnetic turbulence is almost self-similar, rather than intermittent. A similar result was observed for the high resolution measurements of proton density provided by the spacecraft Spektr-R. Intermittency may be interpreted as the result of the multifractal properties of the turbulent cascade. In this perspective, this paper is devoted to the description of the multifractal properties of the high resolution density measurements. In particular, we have used the standard coarse-graining technique to evaluate the generalized dimensions Dq , and from these the multifractal spectrum f (α) , in two ranges of scale. A fit with the p-model for intermittency provided a quantitative measure of multifractality. Such indicator was then compared with alternative measures: the width of the multifractal spectrum, the peak of the kurtosis, and its scaling exponent. The results indicate that the small-scale fluctuations are multifractal, and suggest that different measures of intermittency are required to fully understand the small scale cascade.

  7. Comparison study on ionospheric spread-F between high and low latitude regions during the storm time

    Science.gov (United States)

    Shi, Jiankui; Tao, Wei; Wang, Guojun; Wang, Xiao; Zherebtsov, Gelii; Pirog, Olga; Romanova, Elena

    We use DPS-4 digisonde measurement data from ionospheric station Hainan (19.4N, 109.0E), China, and Yakutsk (62N, 129E) and Zhigansk (66N, 123E), Russia to study ionospheric Spread-F (SF) properties during the magnetic storm time. The results show that: (1) The SF can take place in any phase (suddenly commencement, main phase and recovery phase). (2) The SF always take place from about 2000LT to around midnight, and the more the latitude is, the earlier the SF takes place. (3) Yakutsk station has a higher occurrence of SF than that both in the higher latitude station (Zhigansk) and lower latitude station (Hainan). (4) The frequency SF, range SF and mixed SF can be observed at any latitude station. The strong range SF can only be observed at Hainan station (low latitude station) and it confirms that the strong range SF concerns the equatorial plasma bubble. Our results indicate that ionospheric disturbance which causes the SF, during the storm time, is original from the higher latitude region and propagate to the lower region. Sometimes it could excite out SF at low latitude region and sometimes it could not.

  8. Comparison of mesospheric winds from a high-altitude meteorological analysis system and meteor radar observations during the boreal winters of 2009-2010 and 2012-2013

    Science.gov (United States)

    McCormack, J.; Hoppel, K.; Kuhl, D.; de Wit, R.; Stober, G.; Espy, P.; Baker, N.; Brown, P.; Fritts, D.; Jacobi, C.; Janches, D.; Mitchell, N.; Ruston, B.; Swadley, S.; Viner, K.; Whitcomb, T.; Hibbins, R.

    2017-02-01

    We present a study of horizontal winds in the mesosphere and lower thermosphere (MLT) during the boreal winters of 2009-2010 and 2012-2013 produced with a new high-altitude numerical weather prediction (NWP) system. This system is based on a modified version of the Navy Global Environmental Model (NAVGEM) with an extended vertical domain up to ∼116 km altitude coupled with a hybrid four-dimensional variational (4DVAR) data assimilation system that assimilates both standard operational meteorological observations in the troposphere and satellite-based observations of temperature, ozone and water vapor in the stratosphere and mesosphere. NAVGEM-based MLT analyzed winds are validated using independent meteor radar wind observations from nine different sites ranging from 69°N-67°S latitude. Time-averaged NAVGEM zonal and meridional wind profiles between 75 and 95 km altitude show good qualitative and quantitative agreement with corresponding meteor radar wind profiles. Wavelet analysis finds that the 3-hourly NAVGEM and 1-hourly radar winds both exhibit semi-diurnal, diurnal, and quasi-diurnal variations whose vertical profiles of amplitude and phase are also in good agreement. Wavelet analysis also reveals common time-frequency behavior in both NAVGEM and radar winds throughout the Northern extratropics around the times of major stratospheric sudden warmings (SSWs) in January 2010 and January 2013, with a reduction in semi-diurnal amplitudes beginning around the time of a mesospheric wind reversal at 60°N that precedes the SSW, followed by an amplification of semi-diurnal amplitudes that peaks 10-14 days following the onset of the mesospheric wind reversal. The initial results presented in this study demonstrate that the wind analyses produced by the high-altitude NAVGEM system accurately capture key features in the observed MLT winds during these two boreal winter periods.

  9. Testing species distribution models across space and time: high latitude butterflies and recent warming

    DEFF Research Database (Denmark)

    Eskildsen, Anne; LeRoux, Peter C.; Heikkinen, Risto K.

    2013-01-01

    changes at expanding range margins can be predicted accurately. Location. Finland. Methods. Using 10-km resolution butterfly atlas data from two periods, 1992–1999 (t1) and 2002–2009 (t2), with a significant between-period temperature increase, we modelled the effects of climatic warming on butterfly...... butterfly distributions under climate change. Model performance was lower with independent compared to non-independent validation and improved when land cover and soil type variables were included, compared to climate-only models. SDMs performed less well for highly mobile species and for species with long...

  10. Observations of E region irregularities generated at auroral latitudes by a high-power radio wave

    Science.gov (United States)

    Djuth, F. T.; Jost, R. J.; Noble, S. T.; Gordon, W. E.; Stubbe, P.

    1985-01-01

    The initial results of a series of observations made with the high-power HF heating facility near Tromso, Norway are reported. During these experiments, attention was focused on the production of artificial geomagnetic field-aligned irregularities (AFAIs) in the auroral E region by HF waves. A mobile 46.9-MHz radar was used to diagnose the formation of AFAIs having spatial scales of 3.2 across geomagnetic field lines. The dynamic characteristics of the AFAIs are discussed within the context of current theoretical work dealing with the natural production of AFAIs in the ionosphere.

  11. Cirrus, contrails, and ice supersaturated regions in high pressure systems at northern mid latitudes

    Science.gov (United States)

    Immler, F.; Treffeisen, R.; Engelbart, D.; Krüger, K.; Schrems, O.

    2008-03-01

    During the European heat wave summer 2003 with predominant high pressure conditions we performed a detailed study of upper tropospheric humidity and ice particles which yielded striking results concerning the occurrence of ice supersaturated regions (ISSR), cirrus, and contrails. Our study is based on lidar observations and meteorological data obtained at Lindenberg/Germany (52.2° N, 14.1° E) as well as the analysis of the European centre for medium range weather forecast (ECMWF). Cirrus clouds were detected in 55% of the lidar profiles and a large fraction of them were subvisible (optical depth <0.03). Thin ice clouds were particularly ubiquitous in high pressure systems. The radiosonde data showed that the upper troposphere was very often supersaturated with respect to ice. Relating the radiosonde profiles to concurrent lidar observations reveals that the ISSRs almost always contained ice particles. Persistent contrails observed with a camera were frequently embedded in these thin or subvisible cirrus clouds. The ECMWF cloud parametrisation reproduces the observed cirrus clouds consistently and a close correlation between the ice water path in the model and the measured optical depth of cirrus is demonstrated.

  12. High Galactic latitude interstellar neutral hydrogen (HI) structure and associated acoustic-scale WMAP hot spots

    CERN Document Server

    Verschuur, Gerrit L

    2007-01-01

    Associations have been found between interstellar neutral hydrogen (HI) emission morphology and small-scale structure observed by the Wilkinson Microwave Anisotropy Probe (WMAP) in a Target Area bounded by l = 60 deg & 180 deg, b = 30 deg & 70 deg. This area is marked by the presence of highly disturbed local HI and a preponderance of intermediate- and high-velocity gas and it remains to be determined whether the claimed associations are a hallmark of the presence of the anomalous velocity gas. The HI distribution toward the 33 brightest WMAP peaks in the Target Area is examined and it is demonstrated that the associations do not appear to be the result of chance coincidence. Furthermore, several important properties of diffuse interstellar neutral hydrogen structure have been identified that might otherwise have been overlooked if it were not for the fact that the continuum data focused attention on certain areas of the HI sky. Some of the most dramatic associations are illustrated. It is suggested t...

  13. Daylight photodynamic therapy - Experience and safety in treatment of actinic keratoses of the face and scalp in low latitude and high brightness region*

    Science.gov (United States)

    Galvão, Luiz Eduardo Garcia; Gonçalves, Heitor de Sá; Botelho, Karine Paschoal; Caldas, Juliana Chagas

    2017-01-01

    Daylight photodynamic therapy has been used in countries with high latitudes during the summer for actinic keratoses treatment with reports of similar efficacy to conventional photodynamic therapy. We evaluate its safety in 20 patients in the city of Fortaleza, a local with low latitude and high brightness. Sixteen patients did not report any discomfort due to the procedure. Daylight photodynamic therapy is an easy application method with great tolerability by the patient and has the possibility of being performed throughout the year in these regions. It can mean a promising tool in the control of skin cancer. PMID:28225978

  14. Determination of stratospheric temperature and density by GOMOS: Verification with respect to high latitude LIDAR profiles from Thule, Greenland

    Science.gov (United States)

    di Sarra, A.; Iannone, R. Q.; Casadio, S.; Di Biagio, C.; Pace, G.; Cacciani, M.; Muscari, G.; Dehn, A.; Bojkov, B.

    2017-02-01

    High resolution temperature profiles (HRTP) have been derived from measurements performed by Global Ozone Monitoring by Occultation of Stars (GOMOS) onboard ENVISAT. HRTP are derived from measurements with two fast photometers whose signal is sampled at 1 kHz, and allows investigating the role of irregularities in the density and temperature profiles, such as those associated with gravity waves. In this study high resolution temperature and density profiles measured at high latitude by GOMOS are compared with observations made with the ground-based aerosol/temperature LIDAR at Thule, Greenland. The LIDAR at Thule contributes to the Network for the Detection of Atmospheric Composition Change. The LIDAR profiles are analyzed in the height interval overlapping with GOMOS data (22-35 km), and the density and temperature profiles are obtained with 250 m vertical resolution. The comparison is focused on data collected during the 2008-2009 and 2009-2010 Arctic winters. Profiles measured within 6 hours and 500 km are selected. The profiles are classified based on spatial and temporal variability of dynamical indicators over Thule and at the GOMOS tangent height position. Several corresponding features can be identified in the GOMOS and LIDAR profiles, suggesting that the GOMOS HRTP could be used to investigate the global distribution of small scale fluctuations. As an example, two cases corresponding to inner and outer vortex conditions during the 2008-2009 winter are discussed, also in relation with the very intense sudden stratospheric warming occurred in this season.

  15. Five new Fast Radio Bursts from the HTRU