bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the role of grain growth, recrystallization and polygonization in a continuum theory for anisotropic ice sheets
Authors: Placidi Luca , Faria Sérgio H. , Hutter Kolumban 
Published: November 2007

AbstractWe outline how to incorporate microscale effects of polycrystalline ice into a continuum description. Actually, analyses of ice cores in Antarctica show that different microstructures generally produce different responses, i.e. a non-uniform distribution of c axes gives rise to anisotropic behaviour. It has been recognized that, to describe certain microstructural processes, like recrystallization or polygonization, we need a parameter able to switch them on (e.g. dislocation density or its associated lattice distortion energy). With this in mind, balance equations for a continuum theory of an anisotropic ice sheet undergoing recrystallization have been recently proposed. In this work, we examine relations for some constitutive quantities, in order to take into account the effects of grain-boundary migration, nucleation and polygonization. We check our assumptions by explicit comparison with the first 1200 m of the Byrd (Antarctica) ice core. Current literature usually gives a relation between normal grain growth and grain boundary migration rate. Here, an equation for normal grain growth which also incorporates the influence of polygonization is suggested. It is based on experimental data from the same core in Antarctica. Polygonization is a microscopic process, but here we present a continuum description of the bending stresses which promote the fragmentation of crystallites in terms of the theory of mixtures with continuous diversity.
Climate variability in West Antarctica derived from annual accumulation-rate records from ITASE firn/ice cores
Authors: Kaspari Susan , Mayewski Paul A. , Dixon Daniel A. , Spikes Vandy Blue , Sneed Sharon B. , Handley Michael J. , Hamilton Gordon S. 
Published: November 2007

AbstractThirteen annually resolved accumulation-rate records covering the last ~200 years from the Pine Island–Thwaites and Ross drainage systems and the South Pole are used to examine climate variability over West Antarctica. Accumulation is controlled spatially by the topography of the ice sheet, and temporally by changes in moisture transport and cyclonic activity. A comparison of mean accumulation since 1970 at each site to the long-term mean indicates an increase in accumulation for sites located in the western sector of the Pine Island–Thwaites drainage system. Accumulation is negatively associated with the Southern Oscillation Index (SOI) for sites near the ice divide, and periods of sustained negative SOI (1940–42, 1991–95) correspond to above-mean accumulation at most sites. Correlations of the accumulation-rate records with sea-level pressure (SLP) and the SOI suggest that accumulation near the ice divide and in the Ross drainage system may be associated with the mid-latitudes. The post-1970 increase in accumulation coupled with strong SLP–accumulation-rate correlations near the coast suggests recent intensification of cyclonic activity in the Pine Island– Thwaites drainage system.
Atmosphere–snow interaction by a comparison between aerosol and uppermost snow-layers composition at Dome C, East Antarctica
Authors: Udisti Roberto , Becagli Silvia , Benassai Silvia , Castellano Emiliano , Fattori Ilaria , Innocenti Massimo , Migliori Alessio , Traversi Rita 
Published: November 2007

AbstractThe study of aerosol composition and air–snow exchange processes is relevant to the reconstruction of past atmosphere composition from ice cores. For this purpose, aerosol samples, superficial snow layers and firn samples from snow pits were collected at Dome Concordia station, East Antarctica, during the 2000/01 summer field season. The aerosol was collected in a ‘coarse’ and a ‘fine’ fraction, roughly separated from each other by a stacked filter system (5.0 and 0.4 μm). Atomic Force Microscopy (AFM) direct measurements on the fine fraction showed that 72% of surface size distribution ranges from 1.0 x 105 to 1.2 x 106 nm2. Assuming a spherical model, the volume size distribution of particles smaller than 5.0 μm shows a mode in the radius range 0.2–0.6 μm. Ion chromatographic (IC) measurements of selected chemical components allowed calculation of the ionic balance of the two size fractions. The fine fraction is dominant, representing 86% of the total ionic budget, and it is characterized by high content of sulphate and acidity. Principal component analysis (PCA) identified sea-spray and biogenic aerosol sources and showed some particulars of the transport and depositional processes of some chemical components (Ca2+, MSA, nssSO42–). Comparative analysis of aerosol, surface hoar and superficial snow showed differences in chemical composition: nitrate and chloride exhibit very high concentrations in the uppermost snow layers and in the surface hoar, and low values in the aerosol. This evidence demonstrates that nitrate and chloride are mainly in gas phase at Dome C and they can be caught on the snow and hoar surface through dry deposition and adsorption processes.
Meteorological and glaciological evidence for different climatic variations on the east and west sides of the Lambert Glacier basin, Antarctica
Authors: Cunde Xiao , Allison Ian , Jiawen Ren , Dahe Qin , Mingjun Zhang , Zhongqin Li 
Published: November 2007

AbstractSurface mass-balance studies and climatic records from firn cores show remarkable differences between the east and west sides of the Lambert Glacier basin (LGB). The spatial distribution of the surface accumulation is influenced by the atmospheric moisture flux, and by the surface wind field, which is largely determined by topography. Atmospheric water-vapor budget data for the ice-sheet sector covering the basin (45–90˚ E) show that on the east side of the LGB the moisture flux is poleward, averaging 18 kgm–1 s–1 in 1988, while for the west side it is Equatorward, averaging 5 kgm–1 s–1. A similar pattern, but with much lower transport of vapor flux, is seen across 70˚ S. Two firn cores from the east side of the basin and two from the west side were analyzed to determine accumulation-rate and temperature-proxy variations for the past 50 years. The trends were opposite on the different sides of the basin. Similar opposing trends are seen in meteorological records from Davis and Mawson coastal stations, situated on the east and west sides of the LGB respectively. There is a good correlation between the accumulation/18O record in ice cores from the eastern LGB and the sea-level pressure (obtained from the US National Centers for Environmental Prediction/US National Center for Atmospheric Research (NCEP/NCAR) re-analyses) of a Southern Indian Ocean low (SIOL), but not between the SIOL and the records from the western LGB. This study reveals that variations in local circulation could alter at least the annual to decadal time-scale climate records, and may result in completely different climate histories between adjacent areas.
Elevation change and ice flow at Horseshoe Valley, Patriot Hills, West Antarctica
Authors: Casassa Gino , Rivera Andrés , Acuña César , Brecher Henry , Lange Heiner 
Published: November 2007

AbstractPatriot Hills is located at 80˚18’ S, 81˚22’W, at the southernmost end of the Heritage Range, Ellsworth Mountains, West Antarctica. A comparison of glacier elevation data and ice velocities obtained by the differential global positioning system in the period 1996–97 is presented. Ablation/accumulation rates measured at a network of stakes in Horseshoe Valley show average accumulation of 70 kg m–2a–1in the central part of the valley, and a maximum ablation of ∼170 kg m–2a–1at the edge of the blue-ice area, close to Patriot Hills. Changes in the surface elevation of the glacier measured at 81 stakes in the period 1995–97 show a mean thickening of +0.43±0.42ma–1, which, considering the uncertainties, indicates that the ice sheet around Patriot Hills is in near steady state. Surface velocities, in combination with ice thicknesses obtained by ground-based radio-echo sounding, are used to compute the ice flux across the Horseshoe Valley transect. A total outflow of 0.44 ±0.08km3a–1is obtained. Considering a catchment area for Horseshoe Valley of 1087 km2upstream from the flow transect, and a net accumulation rate of 100 kg m–2a–1, a total input of 0.11 ±0.04km3a–1by snow accumulation is obtained. Accepting a near-equilibrium condition for the ice sheet, the flux difference, i.e. 0.33 km3a–1, must be supplied by flow from the inland ice sheet through ice cliffs located in mountain gaps in the Heritage Range. If Horseshoe Valley is not in steady state but is thickening, the positive mass balance could be due to increased snow accumulation or enhanced ice flow from the interior of the ice sheet. New data are needed to elucidate this.
The European Space Agency’s Earth Explorer Mission CryoSat: measuring variability in the cryosphere
Authors: Drinkwater Mark R. , Francis Richard , Ratier Guy , Wingham Duncan J. 
Published: November 2007

AbstractCryoSat is currently being prepared for a 2005 launch as the first European Space Agency Earth Explorer Opportunity mission. It is a dedicated cryospheric mission equipped with a Ku-band SIRAL (SAR/Interferometric Radar ALtimeter), whose primary objectives are to measure the variability and trends in the mass of the Arctic sea-ice cover and large terrestrial ice sheets. In this paper, an overview is provided of the mission and of the measurement characteristics of the new SIRAL instrument. Examples of data acquired on recent preparatory campaigns are presented, illustrating the operating characteristics of the key SIRAL modes. Preparatory plans for calibration and validation of CryoSat data are described.
A reinterpretation of sea-salt records in Greenland and Antarctic ice cores?
Authors: Rankin Andrew M. , Wolff Eric W. , Mulvaney Robert 
Published: November 2007

AbstractIt has recently been shown that much sea-salt aerosol around the coast of Antarctica is generated not from open water, but from the surface of newly formed sea ice. Previous interpretations of ice-core records have disregarded the sea-ice surface as a source of sea salt. The majority of sea-salt aerosol at Halley research station originates from frost flowers rather than open water, and the seasonal cycle of sea salt in aerosol at Halley appears to be controlled by ice production in the Weddell Sea, as well as variations in wind speed. Frost flowers are also an important source of aerosol at Siple Dome, suggesting that variations in sea-salt concentrations in the core, and other cores drilled in similar locations, may be reflecting changes in sea-ice production rather than changes in transportation patterns. For Greenland cores, and those from low-accumulation inland sites in Antarctica, it is not simple to calculate the proportion of sea salt originating from frost flowers rather than open water. However, modelling studies suggest that a sea-ice surface source contributed much of the flux of sea salt to these sites in glacial periods, suggesting that interpretations of ice-core records from these locations should also be revisited.
Accumulation variability, density profiles and crystal growth trends in ITASE firn and ice cores from West Antarctica
Authors: Gow Anthony J. , Meese Debra A. , Bialas Robert W. 
Published: November 2007

AbstractResults of analyses of snow annual accumulation variability, density and crystal growth measurements in firn and ice cores recovered from the upper layers of the West Antarctic ice sheet during the US component of the International Trans-Antarctic Scientific Expedition (ITASE) are presented. Annual-layer structure was analyzed on the basis of the visible stratigraphy and electrical conductivity measurement record in each core. Annual accumulation varied appreciably between core sites and within cores at individual sites where undulating surface topography appears to be exerting a significant impact on the magnitude of snow deposition. All density profiles except one exhibited densification that was normal with respect to snow annual accumulation and 10 m firn temperatures. Snow annual accumulation was determined stratigraphically, and 10m firn temperatures were either measured in the holes drilled for cores or inferred using elevation changes relative to Byrd Station, the 10m temperature at Byrd Station and an assumed lapse rate. Measurements at the one exceptional location indicated that the firn had undergone extremely rapid densification to ice, with the transition to ice occurring at 35–36m depth. Furthermore, thin-section measurements of grain-size show that the growth of crystals accelerated below the firn–ice transition. The behavior at this one site is attributed to localized deformation in the upper layers of firn and ice. Enhanced crystal growth was also observed at another site. At all other locations where grain-sizes were measured, the rates of crystal growth were in accord with age–temperature relationships observed by other researchers in Antarctica and Greenland. Profiles illustrating pore–crystal structure changes with increasing depth of burial are also presented.
Marine ice beneath the Filchner–Ronne Ice Shelf, Antarctica: a comparison of estimated thickness distributions
Authors: Joughin Ian , Vaughan David G. 
Published: November 2007

AbstractIn an earlier study, melt/freeze rates beneath most of the Filchner–Ronne Ice Shelf, Antarctica, were estimated using an assumption of a steady-state ice shelf applied to a velocity field derived from RADARSAT and ERS-1 interferometric synthetic aperture radar (InSAR) data and an ice-thickness map inferred from ERS-1 satellite radar altimeter data. Here, we use these basal accumulation rates and the InSAR velocity data to estimate the distribution and thickness of marine ice beneath the Filchner–Ronne Ice Shelf. These estimates are compared with a marine-ice thickness map derived from radio-echo sounding (RES) data and airborne radar altimetry. In general, we find close agreement between these estimates. In the few locations where there are significant differences, the discrepancies are largely attributable to artifacts in the radar-altimeter thickness map. With improvements such as a much smaller footprint, the next generation of altimeters should overcome many of these limitations, leading to improved marine-ice accumulation estimates. Overall, the good agreement with the RES data validates the InSAR-based estimates over much of the Ronne Ice Shelf.
Ground ice in the Northern Foothills, northern Victoria Land, Antarctica
Authors: Guglielmin Mauro , French Hugh M. 
Published: November 2007

AbstractThis progress report classifies the different types of ground-ice bodies that occur in the Northern Foothills, northern Victoria Land, Antarctica. Oxygen isotope variations are presented, but interpretation is kept to a minimum pending further investigations. Surface ice, as distinct from moving glacier ice, occurs in the form of widespread buried (‘dead’) glacier ice lying beneath ablation (sublimation) till, together with perennial lake ice, snow banks and icing-blister ice.’Dry’ permafrost is uncommon, and interstitial ice is usually present at the base of the active layer and in the near-surface permafrost. This probably reflects the supply of moisture from the Ross Sea and limited sublimation under today’s climate. Intrusive ice occurs as layers within perennial lake-ice covers and gives rise to small icing blisters. Small ice wedges found beneath the furrows of high-centered polygons appear to agree with the model of sublimation-till development proposed by Marchant and others (2002).
Implications of spatial distributions of snow mass and melt rate for snow-cover depletion: observations in a subarctic mountain catchment
Authors: Pomeroy John , Essery Richard , Toth Brenda 
Published: November 2007

AbstractSpatial statistics of snow water equivalent (SWE) and melt rate were measured using spatially distributed, sequential ground surveys of depth and density in forested, shrub and alpine tundra environments over several seasons within a 185 km2 mountain catchment inYukonTerritory, Canada.When stratified by slope/aspect sub-units within landscape classes, SWE frequency distributions matched the log-normal, but multiclass surveys showed a more bimodal distribution. Within-class variability of winter SWE could be grouped into (i) windswept tundra and (ii) sheltered tund ra/forest regimes. During melt, there was little association between the standard deviation and mean of SWE. At small scales, a negative correlation developed between spatial distributions of pre-melt SWE and melt rate where shrubs were exposed above the snow. This was not evident in dense-forest, alpine-tundra or deep-snowdrift landscape classes. At medium scales, negative SWE and melt-rate correlations were also found between mean values from adjacent slope sub-units of the tundra landscape class. Themedium-scale correlation was likely due to slope effects on insolation and blowing-snow redistribution. At the catchment scale, the correlation between mean SWE and melt rate from various landscape classes reversed to a positive one, likely influenced by intercepted and blowing regimes, shrub exposure during melt and adiabatic cooling with elevation rise. Covariance at the catchment scale resulted in a 40% acceleration of snow depletion. These results suggest that the spatial variability and covariability of both SWE and melt rate are scale- and landscape-class-specific and need to be considered in a landscape-stratified manner at the appropriate scale when snow depletion is described and the snowmelt duration predicted.
Measurements and model calculations of the solar shortwave fluxes in snow on Summit, Greenland
Authors: Meirold-Mautner Ingo , Lehning Michael 
Published: November 2007

AbstractSolar shortwave (SW) radiation is a primary energy source for the snow cover. Accurate measurements of the radiation energy balance in snow are not yet available over a broad spectral band. For accurate measurements in snow, sources of errors have to be eliminated such as the temperature dependence of some sensors, investigating a disturbed snow cover or neglecting the variation of the incoming radiation. The objective of our investigation is to measure the spectral SW energy balance in and above snow and to validate a radiation transfer model against the data. In July 2002 up- and down-welling fluxes at several heights in snow were measured on Summit, Greenland, with a spectrometer sensitive in the 340–1050 nm spectral band. Changing incoming solar radiation was accounted for by using two sensor heads. The resulting data are compared to the δ–Eddington model of radiative transfer in combination with Mie single-scattering calculations. Using as input the snow data obtained by weekly snow profiles, a good agreement between measured and modelled radiative fluxes was obtained when increasing the absorption in the snow grains which is justified by snow impurities. In the near-infrared a disagreement between model and measurements is obvious. This is most likely caused by non-sphericity of the snow grains.
Avalanche simulation with SAMOS
Authors: Sampl Peter , Zwinger Thomas 
Published: November 2007

AbstractDry snow avalanches consist of two distinct layers. A dense-flow layer is superposed by a powder-snow layer, a cloud of relatively small ice particles suspended in air. The density of this suspension is one order of magnitude smaller than that of the dense flow. A simulation model for dry avalanches has been developed, based on separate sub-models for the two layers. The sub-models are coupled by an additional transition model, describing the exchange of mass and momentum between the layers. The fundamentals of the two-dimensional granular flow model for the dense flow and of the three-dimensional turbulent mixture model for the powder flow are presented. Results of the complete coupled model, SAMOS (Snow Avalanche MOdelling and Simulation), applied to observed catastrophic avalanche events, are discussed, and the prediction of powder-snow pressures acting on a tunnel bridge is briefly described. SAMOS is used routinely for hazard zoning at the Austrian Federal Service for Torrent and Avalanche Control.
Wind-tunnel study of snowdrift around avalanche defence structures
Authors: Jaedicke Christian , Naaim-Bouvet Florence , Granig Matthias 
Published: November 2007

AbstractAvalanche defence structures such as retarding dams and breaking mounds are widely used to protect residential areas and other kinds of infrastructure. The effect of the defence structures depends largely on their effective height relative to the velocity, volume and flow depth of the avalanche. Snow depositions from earlier avalanches as well as from drifting snow can significantly alter the effective height of defence structures. Different designs of avalanche-breaking mounds and retarding dams were tested in the Cemagref (Grenoble, France) wind tunnel for their effect on drifting snow. Examples included dams and mounds of different sizes and heights. The models were tested in a wind tunnel with sand particles subjected to different wind directions. The resulting depositions were scanned with a laser system to obtain a three-dimensional picture of the accumulation pattern. The results show that the accumulated snow varies widely with the design of the structure for a given wind direction. Most snow is accumulated around narrow mounds, with least accumulation observed around mounds covering a smaller relative area of the avalanche path. The data obtained can be used to study the effect of the depositions on the retarding effect of the avalanche defence structures. However, because the similarity criteria for studying the interaction between structures and saltating particles in a wind tunnel cannot be met, the transfer of the results to reality must be performed with caution.
Using vegetation to characterize the avalanche of Canal del Roc Roig, Vall de Núria, eastern Pyrenees, Spain
Authors: Molina Ricard , Muntán Elena , Andreu Laia , Furdada Glòria , Oller Pere , Gutiérrez Emilia , Martínez Pere , Vilaplana Joan Manue 
Published: November 2007

AbstractAvalanche hazard maps of high accuracy are difficult to produce. For land-use planning and management purposes, a good knowledge of extreme run-out zones and frequencies of avalanches is required. In the present work, vegetation recognition (especially focused onPinus uncinatatrees) and dendrochronological techniques are used to characterize avalanches that have occurred in historical times, helping to determine both the extent of large or extreme avalanches and their occurrence in time. Vegetation was studied at the Canal del Roc Roig (eastern Pyrenees, Spain) avalanche path. The avalanches descending this path affect the railway that reaches the Vall de Núria resort and the run-up to the opposite slope. During winter 1996, two important avalanches affecting this path were well documented. These are compared with the results of the vegetation study, consisting of an inventory of flora, the recording of vegetation damages along eight transverse profiles at different altitudes on the path and a dendrochronological sampling campaign. The data obtained contributed to a characterization of the predominant snow accumulation in the starting zone, the 1996 avalanches and the range of frequencies of large avalanches. Also, traces of avalanches that increase the path mapped in the avalanche paths map published by the Institut Cartogràfic de Catalunya in 2000 were identified, improving the initial existing information.