bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical modelling of sublimation on snow and comparison with field measurements
Authors: Hachikubo Akihiro 
Published: November 2007

AbstractVarious field observations of surface-hoar formation were carried out with measurements of vapor sublimation rate and meteorological conditions from 1994 to 1996 in a mountainous area of northern Hokkaido,Japan. The sublimation rate seemed to increase with wind speed when the relative humidity was high, whereas the sublimation rate changed from positive to negative as the wind speed increased when the relative humidity was low (60–70%RH). These results were explained with a numerical model (called the Simple model) for the heat balance at the snow surface; the results of the model showed that there is a specific wind speed which maximizes the sublimation rate when the relative humidity is low, and indicated that the sublimation rate becomes large under humid conditions (>90%RH) and if wind speeds are increasing in the range 0.5–3.5 m s–1. The heat balance at the snow surface reproduced by another snow model, Crocus, agreed well with the observation results. However, Crocus overestimated the sublimation rate by about 1.3 × 10–6 kg m–2 s–1 when surface hoar formed, and underestimated snow surface temperature by several degrees.
Application of statistical simulation for avalanche-risk evaluation
Authors: Chernouss P. A. , Fedorenko Yu. 
Published: November 2007

AbstractAvalanche risk is considered as the probability of an avalanche event that could cause certain losses. A unified approach for avalanche-risk evaluation by statistical simulation is suggested. A chain of models, describing snow deposition, transformation, stability, avalanche dynamics and interaction with an obstacle, is used within such an approach. Each of the models evaluates a given situation in a deterministic manner, yielding a unique result value. Output data of each model can be the input for the next model in the chain. Uncertainty of input data is described in a probabilistic manner. Using the chain of the deterministic models and simulating the input data according to appropriate probability distributions with the Monte Carlo method, risk evaluations are obtained as the ratio of a number of certain types of outcome to the total number of tests. All kinds of information on weather, snow and avalanches can be used within this scheme. The simulation process can be started at any stage of the modelling. In this study it was started from the snow-cover stability simulation. Application of the statistical simulation in such a way gives an opportunity to reflect uncertainty of the initial data in the results obtained. The suggested scheme was used for producing a computer-assisted workplace for avalanche forecasting, “LAVINA”, which has been exploited at the Centre of Avalanche Safety of “Apatit”, Kirovsk, Russia, since the early 1990s. It is an integrated system that permits spatial and temporal estimations of snow stability and avalanche dynamics to be made. Assessments of the validity of the risk estimation made with LAVINA are presented.
Snow-cover depth, distribution and duration data from northeast Greenland obtained by continuous automatic digital photography
Authors: Christiansen Hanne H. 
Published: November 2007

AbstractDetailed data on autumn, winter and spring snow-cover conditions from remote areas are often difficult or very expensive to obtain. Therefore, an inexpensive method of digital photography was tested in high-Arctic Greenland. Automatic digital photography has provided daily data on snow distribution and snow depth for > 1 year from the Zackenberg area (74°30’ N) in northeast Greenland. A standard digital hand-held camera (Kodak Digital Science DC50) was equipped to become automatic; it is supplied with an “automatic finger” and an external power supply and built into a protecting box with additional solar panels on top, in order to secure continuous operation throughout the year. The daily photograph covers a 100 m transect through a seasonal snowpatch, and thus on an annual basis also yields information on snow-cover duration in the different vegetation zones of the snowpatch. The camera was installed in mid-August 1998. Photographs from the period mid-August 1998 to early September 1999 were collected and analyzed. All photos are taken at astronomic noon in order to use the daylight as long as possible into the winter season before the 24 h winter darkness begins in mid-November.The digital photographs yielded the following information for the year 1998/99: The first winter snowfall occurred on 18 October; small-scale snow redistribution by snow-drifting started when the winter snow cover was about 5 cm thick. The continuous winter snow cover lasted for a minimum of 170 days in the most snow-deprived areas downwind of the snowpatch, whereas snow in the centre of the snowpatch stayed on the ground for > 325 days, turning the snowpatch perennial in summer 1999.Meteorological data obtained close to the photographed snowpatch site, in combination with the snow-cover depth and distribution data derived from the photographs, show that at wind speeds (at 2 m height) of up to around 6 m s−1, only small-scale snow-drifting took place, when the snow cover was thin. Intense snowdrifting, however, took place at wind speeds of 8–13 m s−1, particularly when enough snow was available in the upwind area. The automatic continuous photography technique demonstrated here could be particularly useful in remote areas at high risk of avalanches during winter. It is an alternative to traditional snow monitoring achieved mainly by sonic sensors, snow pillows or manual measurements of snow depths Likewise, it can provide better areal information than most standard methods, which give only point measurements.
Estimate of uncertainties in avalanche hazard mapping
Authors: Barbolini M. , Savi F. 
Published: November 2007

AbstractThe present work addresses the urgent demand for methods of quantifying the uncertainties inherent in the current procedures for avalanche hazard assessment. A Monte Carlo approach to hazard mapping is proposed for this purpose. This statistical sampling-analysis method allows us to evaluate the probability distributions of the relevant variables for avalanche hazard assessment –– essentially runout distance and impact pressure-once the release variables and the model parameters are expressed in terms of suitable probability distributions. In this way it is possible to explicitly account for uncertainties both in the input-data definition of the dynamic models and in the mapping results. The overall methodology is presented in detail and applied to a real-world avalanche mapping problem. The one-dimensional version of the VARA models is used for avalanche dynamics simulations.
On the characterization of seismic signals generated by snow avalanches for monitoring purposes
Authors: Suriñach E. , Furdada G. , Sabot F. , Biesca B. , Vilaplana J. M. 
Published: November 2007

AbstractSeismic signals from artificially released avalanches were studied in an attempt to characterize them for avalanche-monitoring purposes. The seismic signals generated by different sizes and types of avalanches were recorded and analyzed in the time and frequency domains. Synchronized recordings of the corresponding seismic signals and the video images of the evolution of the avalanches were obtained together with a detailed cartography. Characteristic signatures in the frequency and time domains were found to depend on the characteristics of the avalanche path and measuring location, but to be mostly independent of avalanche size. The source of the different parts of the recorded seismic signals was determined. A relationship was observed between the avalanche size and the amplitude of the signals. Given the presence of local site effects, a prior seismic characterization of the avalanche path in relation to the recording sites is necessary for monitoring purposes. Moreover” it was found that sliding slabs in the early phase of acceleration produce little seismic energy, resulting in a time lapse between the observable start of the avalanche and the arrival of the detectable seismic waves at the receiving station.
Stable-isotope records from Dronning Maud Land, Antarctica
Authors: Graf Wolfgang , Oerter Hans , Reinwarth Oskar , Stichler Willibald , Wilhelms Frank , Miller Heinz , Mulvaney Robert 
Published: November 2007

AbstractThe European Project for Ice Coring in Antarctica (EPICA) includes a comprehensive pre-site survey on the inland ice plateau of Dronning Maud Land. This paper focuses on the investigation of the 18O content of shallow firn and ice cores. These cores were dated by profiles derived from dielectric-profiling and continuous flow analysis measurements. the individual records were stacked in order to obtain composite chronologies of 18O contents and accumulation rates with enhanced signal-to-noise variance ratios. These chronologies document variations in the last 200 and 1000 years. The18O contents and accumulation rates decreased in the 19th century and increased during the 20th century. Using the empirical relationships between stable isotopes, accumulation rates and the 10 m firn temperature, the variation of both parameters can be explained by the same temperature history. But other causes for these variations, such as the build-up of the snow cover, cannot be excluded. A marked feature of the 1000 year chronology occurs during the period AD 1180–1530 when the 18Ocontents remains below the long-term mean. Cross-correlation analyses between five cores from the Weddell Sea region and Dronning Maud Land show that 18O records can in some periods be positively correlated and in others negatively correlated, indicating a complex climatic history in time and space.
The irregular pattern of isotopic and ionic signals in the typical monsoon temperate-glacier area, Yulong mountain, China
Authors: Yuanqing He , Theakstone Wilfred H. , Tandong Yao , Tuo Chen , Zhang David D. 
Published: November 2007

AbstractSampling was carried out at Baishui glacier No. 1, the largest glacier on Yulong mountain, China, during the summers of 1999 and 2000, to investigate the spatial variations of oxygen isotopes in the atmosphere–glacier–river system. the results confirm that there is an apparent inverse relation between the oxygen isotopic composition of precipitation and air-temperature/precipitation amount in this region, with lower δ18O values when the amount of precipitation and air temperature in summer is higher, due to the influence of intense monsoon climate on the study area. There are marked differences in the δ18O values of winter-accumulated snow, glacial meltwater, summer precipitation and the glacier-fed river water. Spatial and temporal variations of isotopic composition are controlled by varied weather conditions at different altitudes. Isotopic depletion or fractionation occurs during phase changes, snow-to-ice and ice-to-meltwater transformations and runoff processes.Variations of stable isotopes in glacier runoff can indicate variations of sources of supply. Ionic changes occur as a result of meltwater contact with glacier bed materials.
Seasonal changes in snow surface roughness characteristics at Summit, Greenland: implications for snow and firn ventilation
Authors: Albert Mary R. , Hawley Robert L. 
Published: November 2007

AbstractAir–snow transfer processes impact both ice-core interpretation and exchange affecting atmospheric chemistry. An understanding of seasonal differences in the character of the surface snow will facilitate evaluation of possible preferential seasonal exchange of reactive chemical species. Both diffusive processes and advective (ventilation) processes can serve to alter the physical, chemical and isotopic character of snow and firn. In this paper, we examine measurements of surface roughness over the course of a year at Summit, Greenland, and the implications for snow and firn ventilation. At Summit, during the winter-over experiment, summer and fall sastrugi amplitudes were approximately 5 cm and had smoothly curved profiles. the average amplitudes experienced mild increases in January, but by the end of February through March the amplitude increased to approximately 20 cm, and the profiles exhibited more abrupt geometries. Calculations are performed to show the potential impact of the changing roughness on interstitial ventilation rates in the snow, assuming that the permeability profile does not change in time. Under high winds, ventilation velocities in the near-surface snow can be up to 3 cms–1 in the winter, compared to 1 cms–1 in the summer. the frequency of 12 ms–1 winds in the summer, however, is less than in the winter. Under low-wind conditions, the summer roughness causes ventilation rates that are comparable to diffusion rates. However, in winter even 5 ms–1 wind conditions can cause the interstitial airflow due to ventilation to exceed the diffusion rates.
Mass balance and accumulation rate across Siple Dome, West Antarctica
Authors: Hamilton Gordon S. 
Published: November 2007

AbstractSnow-accumulation rates and rates of ice-thickness change (mass balance) are studied at several sites on Siple Dome,West Antarctica. Accumulation rates are derived from analyses of gross beta radioactivity in shallow firn cores located along a 60 km transect spanning both flanks and the crest of the dome. There is a north–south gradient in snow-accumulation rate across the dome that is consistent with earlier radar mapping of internal stratigraphy. Orographic processes probably control this distribution. Mass balance is inferred from the difference between global positioning system (GPS)-derived vertical velocities and snow-accumulation rates for sites close to the firn-core locations. Results indicate that there is virtually no net thickness change at four of the five sites. the exception is at the northernmost site where a small amount of thinning is detected, that appears to be inconsistent with other studies. A possible cause of this anomalous thinning is recent retreat of the grounding line of Ice Stream D.
Potential for climate variability reconstruction from Andean glaciochemical records
Authors: Ginot Patrick , Schwikowski Margit , Schotterer Ulrich , Stichler Willibald , Gäggeler Heinz W. , Francou Bernard , Gallaire Robert , Pouyaud Bernard 
Published: November 2007

AbstractIn order to select glacier sites suitable for the reconstruction of short-term climate variability, chemical constituents of shallow cores from Chimborazo, Ecuador, Illimani, Bolivia, and Cerro Tapado, Chile, were analyzed to determine if they represent the climate and atmospheric conditions of the particular area. Pronounced variations were observed in the Chimborazo core, which were attributed to the seasonal occurrence of wet and dry periods. Using chemical tracers, the Pacific and the Amazon basin were identified as the two principal sources of atmospheric moisture. In the Illimani record, seasonality is obvious but is less regular than in the Chimborazo core. Chemical tracers point to the Amazon basin as a moisture source. Post-depositional sublimation masks a possible atmospheric signal in the glaciochemical records from Cerro Tapado. the arid conditions and a prevailing high condensation level also cause little variability in the stable-isotope content. Irregular, more negative δ18O values occur during the humid phases of El Niño events. Despite alterations due to sublimation, chemical tracers indicate the Pacific Ocean as a main moisture source for precipitation preserved on Glaciar CerroTapado.
Folding in strongly anisotropic layers near ice-sheet centers
Authors: Thorsteinsson Throstur , Waddington Edwin D. 
Published: November 2007

AbstractConditions for passive folding near ice-sheet centers are derived treating the ice as an anisotropic viscous medium. Vertical uniaxial compression at a dome, or pure shear stress near a ridge divide, both tend to stretch and flatten folds, while horizontal simple shear deformation tends to overturn folds. Overturned folding is likely in a given vicinity in a steady-state flow field, if the initial slope of a layer disturbance exceeds the ratio of compressive/extensive deformation to shear deformation. Analytical equations for particle tracks in steady state allow us to model the evolution of layers with initial slope disturbances (``wrinkles’’). the effects of anisotropy are explored using an analytical solution for the strain rate as a function of a vertically symmetric c-axis orientation distribution, called a cone fabric. Stronger anisotropy (small cone angle) makes the material softer in horizontal shear, and facilitates folding, i.e. elements with smaller slopes can be overturned for the same stress. the relation between anisotropy and folding is complicated by the fact that, for a range of cone angles, the material is also softer in compression, which opposes folding. Simulating a layer with spatially variable tilt of cone symmetry axes, and accounting for fabric development, demonstrates that variations in the fabric cause localized flow variations that could create the initial perturbations.
Changes in chemical and isotopic properties near infiltrated cracks in an ice core from Ürümqi glacier No. 1, Tien Shan, China
Authors: Xinqing Lee , Dahe Qin , Shugui Hou , Jiawen Ren , Keqin Duan , Hui Zhou 
Published: November 2007

AbstractIce cores recovered for paleoclimatic and/or paleoenvironmental reconstructions in the Tien Shan and Qinghai–Tibetan Plateau often encounter cracks. Although we expect that cracks opened to surface meltwater will inevitably change ice-core records, we do not know how and to what extent records are influenced. An ice core retrieved from glacier No. 1 at Ürümqi river head, Tien Shan, China, exhibits a crack nearly 2.5 m long that has admitted meltwater, forming secondary ice within the fracture. A small inclusion of the infiltrated ice in sampling is shown to reduce δ18O by an extent of Holocene vs Last Glacial Maximum while enhancing significantly the pH, conductivity and the following ionic species: CH3COO–, and CO(COO)22–. of the parameters increased, and HCOO– are the most affected, being enhanced nearly six-fold in the fractured section compared to the non-fractured sections, followed by CO(COO)22– and electrical conductivity measurement (ECM). Despite the alteration, primary fluctuations of some parameters are still recognizable. This suggests that if the infiltrated ice can be avoided in the sampling operation, ice cores with cracks may still provide authentic records. This shows the need to pay close attention to physical characteristics of ice cores in order to identify such secondary ice.
Shallow firn cores from Neumayer, Ekströmisen, Antarctica: a comparison of accumulation rates and stable-isotope ratios
Authors: Schlosser Elisabeth , Oerter Hans 
Published: November 2007

AbstractSince 1979/80, glaciological studies have been carried out at Ekströmisen, Antarctica, including accumulation-stake measurements, snow-pit and shallow-firn-core studies. Snow stratigraphy, chemical properties and stable-isotope ratios (δ18O) were investigated. This study focuses on three cores taken between 1982 and 1998. the 1998 core was dated using dielectric profiling, δ18O profiles and stake measurements. Accumulation rates show high interannual and spatial variability due to the extreme wind influence. No significant trend was found for the last 50 years; during the first half of the 20th century, accumulation decreased. the high spatial and interannual variability, however, means that trends must be interpreted with care. In spite of the highly irregular accumulation distribution, stable-isotope ratios show little spatial variability. the mean annual δ18O values of cores B04 and FB0198 agree fairly well for the time period 1955–82 covered by both cores. δ18O values have increased during most of the 20th century; since the late 1980s a decrease is observed. This change is not related to air temperature, since mean annual air temperatures at Neumayer show no significant trend over the last two decades.
Comparison of analytical methods used for measuring major ions in the EPICA Dome C (Antarctica) ice core
Authors: Littot Geneviève C. , Mulvaney Robert , Röthlisberger Regine , Udisti Roberto , Wolff Eric W. , Castellano Emiliano , De Angelis Martine , Hansson Margareta E. , Sommer Stefan , Steffensen Jørgen P. 
Published: November 2007

AbstractIn the past, ionic analyses of deep ice cores tended to consist of a few widely spaced measurements that indicated general trends in concentration. the ion-chromatographic methods widely used provide well-validated individual data, but are time-consuming. the development of continuous flow analysis (CFA) methods has allowed very rapid, high-resolution data to be collected in the field for a wide range of ions. In the European Project for Ice Coring in Antarctica (EPICA) deep ice-core drilling at Dome C, many ions have been measured at high resolution, and several have been analyzed by more than one method. the full range of ions has been measured in five different laboratories by ion chromatography (IC), at resolutions of 2.5–10 cm. In the field, CFA was used to measure the ions Na+, Ca2+, nitrate and ammonium. Additionally, a new semi-continuous in situ IC method, fast ion chromatography (FIC), was used to analyze sulphate, nitrate and chloride. Some data are now available to 788 m depth. In this paper we compare the data obtained by the three methods, and show that the rapid methods (CFA and FIC) give an excellent indication of trends in ionic data. Differences between the data from the different methods do occur, and in some cases these are genuine, being due to differences in speciation in the methods. We conclude that the best system for most deep ice-core analysis is a rapid system of CFA and FIC, along with in situ meltwater collection for analysis of other ions by IC, but that material should be kept aside for a regular check on analytical quality and for more detailed analysis of some sections.
Bidirectional permeability measurements of polar firn
Authors: Luciano Gina L. , Albert Mary R. 
Published: November 2007

AbstractIce cores provide a valuable archive of climate history. for a complete understanding of this archive, it is important to understand air–snow exchange processes through the snow and firn in order to fully decode the ice-core record. Transport processes through the snow and firn are dependent upon their physical properties. In this paper, bidirectional permeabilities from selected sections of a 13 mcore from Summit, Greenland, are presented. Differences between lateral and vertical permeabilities are evident throughout the core in permeameter data and in microstructure statistics. Both lateral and vertical permeabilities are consistent with overall patterns of previous polar permeability data with depth. the differences between lateral and vertical permeability measurements for some samples can be attributed to equivalent sphere radius. Further studies examining mean free-path length may be helpful in chemical modeling and in deriving an equation relating permeability to microstructure.
The Comninou–Dundurs effect and position stability of subglacial lakes
Authors: Weertman Johannes 
Published: November 2007

AbstractThe Comninou–Dundurs effect (C-D effect) has yet to be considered in slip processes at the base of ice sheets and glaciers. This effect exists whenever slip occurs between two solids of differing mechanical properties and at least one of the solids is compressible. It gives rise to an additional normal traction stress across a non-uniformly slipping interface, a stress which otherwise would not exist if the two solids had identical properties. the C-D effect should exist to some degree, therefore, wherever ice slips over glacial till. It will be enhanced where large slip gradients exist, such as at boundaries of subglacial lakes. In this paper it is shown that, because of the C-D effect, subglacial lakes that lie at a basal till/ice interface may migrate in the direction of increasing ice thickness.