bluuebunny/crossref_metadata_2025_split huggingface dataset:
Changes in Antarctic temperature, wind and precipitation in response to the Antarctic Oscillation
Authors: van den Broeke Michiel R. , van Lipzig Nicole P. M. 
Published: November 2007

AbstractOutput of a 14 year integration with a high-resolution (55 km ×55 km) regional atmospheric climate model is used to study the response of Antarctic near-surface climate to the Antarctic Oscillation (AAO), the periodical strengthening and weakening of the circumpolar vortex in the Southern Hemisphere. In spite of the relatively short record, wind, temperature and precipitation show widespread and significant AAO-related signals. When the vortex is strong (high AAO index), northwesterly flow anomalies cause warming over the Antarctic Peninsula (AP) and adjacent regions in West Antarctica and the Weddell Sea. In contrast, cooling occurs in East Antarctica, the eastern Ross Ice Shelf and parts of Marie Byrd Land. Most of the annual temperature signal stems from the months March–August. The spatial distribution of the precipitation response to changes in the AAO does not mirror temperature changes but is in first order determined by the direction of flow anomalies with respect to the Antarctic topography. When the vortex is strong (high AAO index), the western AP becomes wetter, while the Ross Ice Shelf, parts of West Antarctica and the Lambert Glacier basin, East Antarctica, become drier.
Heat flow from wet to dry snowpack layers and associated faceting
Authors: Jamieson Bruce , Fierz Charles 
Published: November 2007

AbstractLayers of faceted crystals adjacent to crusts form the failure layers for some unexpected dry-slab avalanches. This paper focuses on the case of facets that form when dry snow overlies wet snow. From a basic equation for heat flow in solids, the approximate freezing time of the wet layer is derived. Seven experiments are described in which a wet layer was placed between two dry-snowlayers in a cold laboratory. Measured freezing times are comparable to the freezing times from the approximate solution assuming that latent heat from the irreducible water content flowed up. In four of the experiments, evidence of faceting was observed at the base of the upper dry snow layer within 5 hours and before the wet layer froze. In all seven experiments faceting was observed in the upper dry layer after the wet layer froze. Simulations performed with the snow-cover model SNOWPACK yield freezing times that agree reasonably with the approximate solution and allow the influence of various parameters on the results to be explored. In addition, simulated temperatures and grain evolution are compared with observations, showing good agreement.
Hazard scenarios for avalanche actions on bridges
Authors: Margreth Stefan , Ammann Walter J. 
Published: November 2007

AbstractEngineers require impact scenarios when developing hazard mitigation strategies to protect structures against snow avalanches. Since direct measurements of avalanche impacts on large obstacles are rare, the documentation and post-event analysis of avalanche damages is essential to understand the interaction of avalanches with obstacles. The objective of this paper is to develop hazard scenarios for avalanche actions on bridges, based on a case study of a well-documented avalanche event. The 40 m long pre-stressed road bridge Ri di Rialp in the Swiss Alps collapsed after being struck by a dense-flow avalanche in 1998. The post-event analysis shows that the controlling hazard scenario was an inclined avalanche impact, not a horizontal impact as one would assume given the topographical situation. Using a failure analysis, an impact angle of 40° and a minimal impact pressure of 172 kN m−2 were found. Finally the insights are summarized so that engineers can apply the results when designing a bridge at risk from avalanches.
Modeling the density variation in the shallow firn layer
Authors: Li Jun , Zwally H. Jay 
Published: November 2007

AbstractVapor-transfer theory is incorporated into a previous firn-densification model to investigate the effect of vapor-transfer processes on densification in firn within 10 m of the surface. The densification rate in the model is governed by the change of overburden pressure (determined by the accumulation rate), the firn temperature, and the temperature gradient. The time of exposure to temperature gradients at shallow depths is a critical factor determining the importance of vapor-transfer processes. In high-accumulation and high-temperature conditions such as for the Greenland ice sheet, the temperature gradient and vapor transfer are less important due to the shorter exposure times. The high summer temperatures dominate the rate of densification and annual variations in density. In low-accumulation and low-temperature conditions, such as for inland Antarctica, the vapor transfer driven by the temperature gradient has a stronger effect on the densification rate, and temperature-driven processes are less important. These factors determine both the rate of density increase with depth and the amplitudes of annual variations in density with depth.
Regular packing of grains as a model of snow structure
Authors: Golubev Vladimir N. , Sokratov Sergey A. 
Published: November 2007

AbstractThis paper presents a model of snow structure (model of regular grain packing) that is based on experimental determination of various geometrical characteristics of fine-, medium- and large-grained granular snow. Data analysis supports the possibility of approximating the ice-matrix configuration as a regular lattice of nearly spherical ice grains connected by rigid ice bonds. The model was successfully used for relating microstructural parameters of snow to snow density, compaction behavior and evolution of mechanical properties.
Mechanical vibration responses of snow samples near the melting temperature
Authors: Takei Iwao , Maeno Norikazu 
Published: November 2007

AbstractMechanical properties of snow were investigated by means of a vibration response technique in a frequency range from 10Hz to 1MHz and a temperature range from –15° to –0.1°C with heating and cooling processes. The response signals were divided into two kinds of propagation, transverse and longitudinal waves through the snow sample. The temperature dependence of elastic-wave velocities showed a large decrease above –0.6°C. Poisson’s ratio and Young’s modulus of snow samples were derived from the longitudinal and transverse wave velocities. Poisson’s ratio of snow samples showed a value of 0.35 ± 0.01 below –0.6°C, and dropped to 0.29 or less at –0.1°C. Young’s modulus of snow samples at –0.1°C showed values seven-tenths as large as (25–34%less than) those below –0.6°C. These phenomena suggest weakening and slipping of boundaries between ice particles in snow samples near the melting temperature. The elastic-wave velocities and Young’s modulus change with the density of samples and with time and temperature cycling. These changes are related to the number and state of bonds between ice particles in snow samples.
Shear strength and angle of repose of snow layers including graupel
Authors: Abe Osamu 
Published: November 2007

AbstractSnow avalanches with failure layers including graupel are sometimes observed in Japan. A snow layer including graupel may be formed close to the melting point (0°C) after passage of a cold front with cumulus clouds. Graupel particles have a large diameter and a spherical shape, so they have a relatively small contact area per unit volume and may form weak layers within the snowpack. In this paper, characteristics of snow layers that include graupel are described by angle of repose, shear frame index (SFI), grain-size distribution, density and temperature. The mean value of the angle of repose was found to be 45°, independent of the grain-size. This suggests that a graupel layer near 0°C will not be formed on a slope exceeding 45°. SFI data for three different graupel layers were measured over 1–3 days for each layer, and were correlated with density. An exponential relationship between shear strength and density was found. The results indicate that the SFI of graupel layers is approximately one-third that of dry new snow with the same density.
Dense and powder avalanches: momentumreduction generated by a dam
Authors: Naaim-Bouvet Florence , Naaim Mohamed , Faug Thierry 
Published: November 2007

AbstractPassive protection structures reduce avalanche run-out distance and hence the potential damages brought about by an avalanche, by reducing its velocity and mass. This paper starts with a summary of the main existing results on interactions between snow avalanches and dams. In the case of dense avalanches, the effects of dams are re-examined and previous results are theoretically justified. For a powder-snow avalanche a dam has two primary effects. The momentum is reduced by the retarding force upstream of the dam and when the jet collides with the ground after the dam. Entrainment of air during the jet reduces its velocity since the mass increases. For a dense avalanche, there is a retarding force upstream of the dam and when the jet collides with the ground, but there is no significant effect of air entrainment. There is, however, deposition of snow which reduces the momentum of the avalanche without affecting the velocity. The reduction of the volume due to deposition reduces the spreading length and therefore the run-out distance of the avalanche. Downstream of the obstacle, the avalanche flow is regarded as an airborne jet. A comparative study shows that density and ambient-fluid entrainment effects are significant for gravity currents, powder and dense snow avalanches whereas they are negligible in granular flows.
A system for prediction of avalanche hazard in the windy climate of Iceland
Authors: Haraldsdóttir Svanbjörg H. , Ólafsson Haraldur , Durand Yves , Giraud Gerald , Mérindol Laurent 
Published: November 2007

AbstractA system for predicting avalanche hazard in the windy climate of Vestfirðir, northwest Iceland, is presented. The system is based on (a) numerical simulations of the snowpack and evaluation of avalanche hazard due to overloading by the snow models SAFRAN–Crocus and MÉPRA, and (b) observations of wind speed in the mountains used as a proxy for snowdrift. The system was tested during two winter seasons and correctly predicts 30 out of 35 avalanche days. The 5 missing days feature either large spatial gradients in precipitation or very strong winds a few days before the avalanches, indicating much snowdrift. A comparison of the simulated avalanche hazard and observations of avalanches confirms that snowdrift is of primary importance not only for large avalanches, as already established, but also for small and medium-size avalanches in Vestfirðir. The system is a first step towards an objective evaluation of avalanche hazard in Iceland.
Linear trends of the length of snow-cover season in the Northern Hemisphere as observed by the satellites in the period 1972–2000
Authors: Rikiishi Kunio , Hashiya Eisuke , Imai Masafumi 
Published: November 2007

AbstractThe dataset of Northern Hemisphere EASE-Grid weekly snow cover and sea-ice extent (U.S. National Snow and Ice Data Center) for the period September 1972–August 2000 is analyzed to examine the possible influence of recent global warming on the seasonal change of snow cover in the Northern Hemisphere. It is found that the total snow-cover area in the 1980s and 1990s is diminished by 36106 km2, and the length of snow-cover season is reduced by 2 –3 weeks, as compared with the 1970s. In general, the contribution from earlier snowmelt is greater than that from delayed snow accumulation. In addition, the maximum snow-cover area during January–February has gradually decreased by about 36106 km2 within the two decades. Geographically, the rate of decrease of snow-cover duration is 50.1 week per year (wpy) in the high-latitude regions such as the Siberian Plains and Northwest Territories of Canada and 40.2 wpy in the high-elevation regions such as the Scandinavian Peninsula, Tibetan Plateau and Rocky Mountains. The earlier snowmelt in the high-elevation regions suggests that the snowfall amounts there are decreasing owing to global warming.
Dynamics of avalanches along general mountain slopes
Authors: Pudasaini Shiva Prasad , Wang Yongqi , Hutter Kolumban 
Published: November 2007

AbstractA continuum dynamical hydraulic model for the flow of a finite mass of cohesionless shallow granular material down an inclined plane was proposed by Savage and Hutter (SH) in 1989. This model consists of depth-averaged equations for the time and space evolution of the velocity profile and the avalanche depth. Their model was generalized to incorporate more complicated topography in which the coordinate lines in the downhill direction are curved but not twisted. We present recently developed model equations by Pudasaini and Hutter for free-surface geophysical gravity-driven flows (e.g. avalanches, debris and pyroclastic flows) down complicated realistic mountain terrain generated by arbitrary space curves with slowly varying curvature and torsion. These are very important extensions to the successful SH theory, which incorporate curvature and torsion effects of the sliding surface. Shock-capturing numerical schemes are used to integrate the hyperbolic conservation system of equations. The physical significance of the numerical solutions is discussed.
Surface mass-balance observations and automatic weather station data along a transect near Kangerlussuaq, West Greenland
Authors: van de Wal R.S.W. , Greuell W. , van den Broeke M.R. , Reijmer C.H. , Oerlemans J. 
Published: November 2007

AbstractSurface mass-balance data from the Kangerlussuaq transect (K-transect) located on the western part of the Greenland ice sheet near 67° N are presented. The series covers the period 1990-2003 and is the longest series of surface mass-balance measurements in Greenland. The surface mass-balance measurements cover an altitude range of 390-1850 m and show a linear increase of the specific mass balance, with a mass-balance gradient of 3.7 × 10–3 m m–1 and a mean equilibrium-line altitude of 1535 ma.s.l. Interannual variability shows a weak 4 yearly periodicity. In addition to the surface mass-balance data, automatic weather station data at an elevation of approximately 1010m are available for the period 1997-2002. These data are used to explain observed surface mass-balance anomalies over the same 5 years. It is shown that variations in shortwave radiation dominate interannual variability. The mean annual cycle of temperature is characterized by a maximum in summer around the melting point, leading to a mean summer outgoing longwave radiation of approximately 314 W–2. The mean annual cycle in wind speed shows a maximum in winter (on average around 8 m s–1) and a minimum in summer (on average around around 5 m s–1), which is characteristic for a katabatic forcing. During summer the net radiation is on average about 61 Wm–2, which is used for ice melting at a rate of typically 2 cm w.e.d-1. Net radiation contributes 84% of the total energy used for summer melting averaged over the 5 years.
The methanesulfonic acid (MSA) record in a Svalbard ice core
Authors: Isaksson Elisabeth , Kekonen Teija , Moore John , Mulvaney Robert 
Published: November 2007

AbstractSvalbard ice cores have not yet been fully exploited for studies of climate and environmental conditions. In one recently drilled ice core from Lomonosovfonna, we have studied the methanesulfonic acid (MSA) records in relation to temperature and sea ice. Under the present climatic conditions, MSA appears to be negatively correlated with the sea-ice conditions in the Barents Sea, and positively correlated with the instrumental temperature record from Svalbard. However, prior to about 1920 the MSA concentrations were about twice as high, despite the more extensive sea-ice coverage. After exploring different possibilities, we suggest that MSA concentrations were higher in the 19th century than in the 20th century due to increased primary production, in response to increased vertical stability of the sea surface layers, caused by increased meltwater production from the more extensive sea-ice cover. Thus, the MSA record from Lomonosovfonna probably both is a measure of the regional sea-ice variability on the multi-decadal scale and reflects locally favorable conditions for marine biogenic dimethyl sulfide (DMS) production on the sub-decadal scale.
Velocity measurements on Engabreen, Norway
Authors: Jackson Miriam , Brown Ian A. , Elvehøy Hallgeir 
Published: November 2007

AbstractHorizontal velocity measurements on the lower part of Engabreen, Norway, were made from repeat aerial photography. IMCORR software, which has been widely used to measure velocities from satellite images, was used to make the measurements. This is the first known successful use of IMCORR on aerial photographs. Supplementary horizontal velocity measurements were made from repeat measurements of stakes, giving velocities over different periods and also in areas that are too slow-moving to register a measurable velocity after only a few days.
Problems with the retrieval of glacier net surface balance from SAR imagery
Authors: Brown Ian A. , Klingbjer Per , Dean Andy 
Published: November 2007

AbstractThere are relatively few comparisons between synthetic aperture radar (SAR) observations and glacier mass-balance measurements. More typically, SAR has been deployed to identify changes in the end-of-summer snowline and other facies boundaries. In this paper, we analyze the geophysical processes affecting SAR amplitude data over two Arctic glacier systems in northern Scandinavia to assess the potential of SAR observations for the retrieval of surface balance parameters. Using a backscatter model and in situ data, we identify the controls on SAR imagery in terms of mass-balance measurement and discuss the glaciological parameters which can reasonably be derived from multi-temporal SAR data. Our results show that amplitude SAR imagery, in the absence of in situ measurements, is not capable of providing meaningful mass-balance data. We show that backscatter from temperate glaciers is affected primarily by snow grain-size and density, and therefore processes such as firnification or depth-hoar formation can complicate the analysis of imagery. We conclude that SAR imagery over temperate glaciers can provide valuable proxy information but not direct mass-balance terms.
Temporal changes in the radiophysical properties of a polythermal glacier in Spitsbergen
Authors: Jania J. , Macheret Yu.Ya. , Navarro F.J. , Glazovsky A.F. , Vasilenko E.V. , Lapazaran J. , Glowacki P. , Migala K. , Balut A. , Piwowar B.A. 
Published: November 2007

AbstractIn order to study the seasonal and inter-seasonal variations in radio-wave velocity (RWV), radiophysical investigations were made at Hansbreen, a polythermal glacier in Spitsbergen, in July– August 2003 and April 2004. These investigations included repeated radar profiling (20 and 25 MHz) along a transverse profile, repeated common-midpoint measurements, continuous radar measurements during 8 days at a fixed site, meteorological observations, and continuous ice surface velocity monitoring by differential GPS. Seasonal and inter-seasonal RWV changes in the temperate ice layer are attributed, respectively, to rapid water redistribution within it during the summer, and to variations in water content from 2.1% in summer to 0.4% in spring. The reflection properties of the temperate ice layer correlate well with the air temperature, with a nearly semi-diurnal time lag. The temporal variability of the reflection properties of the internal horizon suggests enlargement of water inclusions or water drainage from the horizon. Repeated profiling shows a stable spatial pattern in bed reflection power interpreted as changes in water content controlled by bedrock topography. The spatial variations of internal reflection energy along the repeated profile correlate with the thickness of the cold ice layer and the occurrence of drainage and crevasse systems.
Greenland ice sheet surface mass-balance variability: 1991–2003
Authors: Box J.E. 
Published: November 2007

AbstractThe Polar MM5 mesoscale atmospheric model was run for 13 years (1991–2003) over Greenland at 24 km horizontal resolution (Box and others, 2004). The model physics were driven by satellite, station and weather-balloon observational data assimilation, i.e. European Centre for Medium-Range Weather Forecasts (ECMWF) operational analysis. The analysis in this study focuses on the response of the surface mass balance to its primary controls: temperature and precipitation. The results indicate coherent spatial patterns of variability and statistically significant links with temperature and precipitation and the North Atlantic Oscillation. Precipitation trends have the same spatial pattern and sign as temperature, suggesting an association of precipitation and temperature variability. Increasing temperatures contribute to an increasing ablation trend and expansion of the ablation zone despite increasing accumulation trends. The Pinatubo (Philippines) volcanic cooling in the early 1990s enhances this apparent warming trend. Only in the northeast does precipitation appear to dominate the surface mass balance, where both temperature and precipitation have decreased. There is little evidence for a total ice-sheet surface mass-balance trend, although the meltwater runoff has a positive trend and, combined with iceberg discharge and basal melting estimates, suggests the ice sheet as a whole is in a state of net mass loss over this period.
Microstructural characterization of ice cores
Authors: Baker Ian , Iliescu Daniel , Obbard Rachel , Chang Hui , Bostick Benjamin , Daghlian Charles P. 
Published: November 2007

AbstractIn this paper, we outline the use of Raman spectroscopy coupled with scanning confocal optical microscopy for determining the microstructural location of impurities in ice-core specimens. We also demonstrate how the orientations of grains and the misorientations across grain boundaries can be determined to high precision for ice polycrystals using either selected area channeling patterns or electron backscatter patterns in a scanning electron microscope.
Assessing the future evolution of meltwater intrusions into a mine below Gruvefonna, Svalbard
Authors: Schuler T.V. , Melvold K. , Hagen J.O. , Hock R. 
Published: November 2007

AbstractMeltwater intrusions of glacial origin complicate the operation of a coalmine situated approximately 200 m below the bed of Gruvefonna ice cap, Svalbard. The magnitude of this water input is expected to increase with the intended enlargement of the mine. The current praxis, evacuation of the water by pumping, is an expensive undertaking and prompts the investigation of alternative solutions. The evaluation of different options requires reliable values of the total volume and the input rate of the water to be drained. To quantify the melt rate at the glacier surface, we applied a distributed temperature-index model. The model parameters were calibrated using mass-balance measurements performed at Gruvefonna during the 2003 ablation season. The water discharge in the mine during the same period was derived from records of the pump rate. Comparing the records of modelled melt and measured discharge reveals an efficient hydraulic connection between the glacier surface and the mine. The total discharge volume in the mine over the 2003 melt season was about 2.8 × 106m3, exceeding significantly the total melt- and rainwater production on the glacier surface directly above the mine (1.2 × 106m3). This implies that the mine discharge receives contributions from a larger surface area. Based on the distribution of hydraulic potential at the glacier bed, we estimate this contributing area. In a number of scenarios, we calculate the amount of meltwater intrusions for several steps of the planned mine enlargement.