bluuebunny/crossref_metadata_2025 huggingface dataset:
Marine ice beneath the Filchner–Ronne Ice Shelf, Antarctica: a comparison of estimated thickness distributions
Authors: Joughin Ian , Vaughan David G.
Published: November 2007

In 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

This 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

Spatial 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

Solar 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

Dry 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

Avalanche 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

Avalanche 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.
Avalanche hazard zoning in Iceland based on individual risk
Authors: Arnalds Þorsteinn , Jónasson Kristján , Sigurðsson Sven
Published: November 2007

Avalanche hazard is a threat to many residential areas in Iceland. In 1995 two avalanche accidents, causing a total of 34 fatalities in areas thought to be safe, prompted research on avalanche hazard assessment. A new method was developed, and in 2000 a new regulation on avalanche hazard zoning was issued. The method and regulation are based on individual risk, or annual probability of death due to avalanches. The major components of the method are the estimation of avalanche frequency, run-out distribution and vulnerability. The frequency is estimated locally for each path under consideration, but the run-out distribution is based on data from many locations, employing the concept of transferring avalanches between slopes. Finally the vulnerability is estimated using data from the 1995 avalanches. Under the new regulation, new hazard maps have been prepared for six of the most vulnerable villages in Iceland. Hazard zones are delineated using risk levels of 0.2×10–4, 0.7×10–4 and 2×10–4 a–1, with risk less than 0.2×10–4 a–1 considered acceptable. When explaining the new zoning to the public, a measure of annual individual risk that allows comparison with other risks in society has proven advantageous.
The temperature- and density-dependent acoustic emission response of snow in monoaxial compression tests
Authors: Scapozza Carlo , Bucher Felix , Amann Peter , Ammann Walter J. , Bartelt Perry
Published: November 2007

Results of acoustic emission tests on cylindrical specimens under compression are reported. Deformation-rate-controlled tests with strain rates ranging from 1.1 × 10-6 s-1 to 2.6 × 10-3 s-1 at temperatures between T = -11.2°Cand T = -1.7°C were performed. The investigated snow was fine-grained, with a density varying between 220 and 380 kgm-3. The acoustic emission was measured with two distinct piezoelectric sensors: a wide-band sensor (frequency 100–1000 kHz) and a resonant sensor (frequency 35–100 kHz). The relationship between the applied strain rate and the measured maximum acoustic-emission rate as a function of temperature and density was found to obey a power law, which is valid for the ductile behaviour range. The quantitative and qualitative effects produced on the acoustic emissions during the transition from ductile to brittle behaviour, occurring at strain rates of approximately 1 × 10-3 s-1, are reported. Finally, the influence of the load history on the acoustic emissions of snow is discussed on the basis of a cyclic test, including deformation-controlled loading steps and relaxation steps, performed at different strain rates and different relaxation times.
On the fracture toughness of snow
Authors: Schweizer Jürg , Michot Gerard , Kirchner Helmut O.K.
Published: November 2007

The release of a dry-snow slab avalanche involves brittle fracture. It is therefore essentially a non-linear fracture mechanics problem. Traditional snow-stability evaluation has mainly focused on snow strength measurements. Fracture toughness describes how well a material can withstand failure. The fracture toughness of snow is therefore a key parameter to assess fracture propagation propensity, and hence snows lope stability. Fracture toughness in tension KIc and shear KIIc was determined with notched cantilever-beam experiments in a cold laboratory. Measurements were performed at different temperatures and with different snow types of density ρ = 100–300 kgm–3, corresponding to typical dry-snow slab properties. The fracture toughness in tension KIc was found to be larger (by about a factor of 1.4) than in shear KIIc. Typical values of the fracture toughness were 500–1000 Pam1/2 for the snow types tested. This suggests that snow is one of the most brittle materials known to man. A power-law relation of toughness KIc on relative density was found with an exponent of about 2. The fracture toughness in tension KIc decreased with increasing temperature following an Arrhenius relation below about –8°C with an apparent activation energy of about 0.16 eV. Above –6°C the fracture toughness increased with increasing temperature towards the melting point, i.e. the Arrhenius relation broke down. The key property in dry-snow slab avalanche release, the critical crack size under shear at failure, was estimated to be about 1 m.
The Monte Carlo simulation of avalanche-type processes
Authors: Bozhinskiy A. N.
Published: November 2007

The statistical modelling of gravitational avalanche-type processes is carried out using the Monte Carlo method. The process of snow avalanche origin is described with the model of stress state and stability of snow cover on a slope. The statistical simulation of the stress state of a snow slab is performed for avalanche site No. 22 (Khibiny, Russia). The strength characteristics of the snow slab are considered as randomvariables.The influence of the first moments of the distributions of the slab-strength parameters on the probability of avalanche release is studied. Using a hydraulic model of a dense flow avalanche, the statistical modelling of avalanche dynamics for the avalanche site “Domestic” (Elbrus region, Russia) is carried out. The coefficients of dry and turbulent friction and snow entrainment are considered as random parameters of the model. The histograms and distribution functions of the run-out distance, thickness and volume of avalanche depositions are obtained. The model and empirical distribution functions of the avalanche run-out distance are compared. Statistical simulation of slushflow dynamics (basin of Bear brook, Khibiny, Russia) is performed. The two-layer deterministic model of slushflow is used. The random parameters of the model assumed are: the water inflow on the “tail”of the flow and the coefficient of dry friction for slush. The histograms and distribution functions of dynamic characteristics of flow are obtained. The model outcomes are compared with field data.
A new in situ sensor for large-scale snow-cover monitoring
Authors: Stähli Manfred , Stacheder Markus , Gustafsson David , Schlaeger Stefan , Schneebeli Martin , Brandelik Alexander
Published: November 2007

A new in situ sensor for the simultaneous measurement of snow water equivalent, snow density and liquid-water content is presented in this paper. The system consists of radio frequency transmission lines of up to 25 m length cast in a flat PVC band, which can be set up either horizontally to monitor single snow-layer properties or sloping from a mast to the soil surface to determine vertical snowpack properties. The dielectric coefficient along the flat-band cable is measured with a time-domain reflectometer at high frequencies, and with a low-frequency impedance analyzer. The performance of the sensor system was tested during two winter seasons (2001–03) at the high-alpine test site Weissfluhjoch, Davos, Switzerland. The cable suspension and set-up of the sloping cable was shown to be critical with regard to stability and the formation of unwanted air gaps along the cable. Overall, the sensing system proved quite robust and produced results in agreement with manual snowpack observations.
Time-variant snow distribution for use in hydrological models
Authors: Skaugen Thomas , Alfnes Eli , Langsholt Elin G. , Udnæs Hans-Christian
Published: November 2007

A model is put forward which focuses on the dynamical evolution of the spatial distribution of snow water equivalent (SWE). We make use of the fact that when the accumulation and ablation process of the snow reservoir is modelled as a summation of a gamma-distributed variable, both skewed distributions, typical of alpine areas, and more normal distributions, typical of forested areas, can be accounted for. A particular problem is to represent fractional snow-covered area (SCA) within the distribution framework. The change in SCA as a response to a melting event is explicitly linked to the shape of the distribution of SWE and is estimated as the probability of non-exceedance of the melted amount from a scaled version of the spatial distribution of SWE. An extensive snow-measuring programme, where several snow courses have been measured repeatedly throughout the melting season, justifies the dynamical aspects of the snow distribution in the modelling approach. The modelling approach has been tested with the Swedish rainfall–runoff model, HBV, and estimated values of SWE and SCA are compared with results obtained using the statistical distribution (log-normal) traditionally used in the model.
Numerical simulations of dense clouds on steep slopes: application to powder-snow avalanches
Authors: Étienne Jocelyn , Saramito Pierre , Hopfinger Emil J.
Published: November 2007

In this paper, two-dimensional direct numerical simulations (DNS) of dense clouds moving down steep slopes are presented for the first time. The results obtained are in good agreement with the overall characteristics, i.e. the spatial growth rate and velocity variations, of clouds studied in the laboratory. In addition to the overall flow structure, DNS provide local density and velocity variations inside the cloud, not easily accessible in experiments. The validity of two-dimensional simulations as a first approach is confirmed by the dynamics of the flow and by comparison with experimental results. The interest of the results for powder-snow avalanches is discussed; it is concluded that two-dimensionality is acceptable and that large density differences need to be taken into account in future simulations.
Slab avalanche release viewed as interface fracture in a random medium
Authors: Zaiser Michael
Published: November 2007

A theoretical model is formulated to investigate the influence of random variations in strength of the weak layer on slab avalanche release. An equation for slab stability is derived which accounts for stress redistribution between strong and weak regions. The model is first used to re-derive results on shear fractures (shear bands) in a homogeneous slab. It is then applied to the case of a slab with randomly varying peak strength of the weak layer. It is demonstrated that such variation may have a dramatic knock-down effect on the failure strength of a slope. The nature of the critical flaw is studied and precursors to failure are investigated.
Seasonal cycle of the snow coverage in the former Soviet Union and its relation with atmospheric circulation
Authors: Rikiishi Kunio , Sakakibara Junko
Published: November 2007

Historical snow-depth observations in the former Soviet Union (FSU) during the period September 1960–August 1984 have been analyzed in order to understand the seasonal cycle of snow coverage in the FSU. Snow cover first appears in September in northeastern regions, and spreads over the entire territory before early January. Snowmelt begins in mid-January in the southern regions and then snow cover retreats rapidly northward until it disappears completely before late June. Northward of 60°N, the land surface is snow-covered for more than half the year. The longest snow-cover duration is observed on the central Siberian plateau (about 9.5 months) and along the Arctic coastal regions (about 8.5 months). One of the most conspicuous features of the snow coverage in the FSU is that the length of the snow-accumulation period differs considerably from region to region (2–7 months), while the length of the snowmelt period is rather short and uniform over almost the entire territory (1–2 months). Although the maximum snow depths are 20–50 cm in most regions of the FSU, they exceed 80 cm in the mountainous regions in central Siberia, Kamchatka peninsula, and along theYenisei river valley. Values for the maximum snow depth are very small along the Lena river valley in spite of the air temperature being extremely low in winter. By calculating correlation coefficients between the snowfall intensities and the sea-level pressures or 500 hPa heights, it is shown that deep snow along the Yenisei river valley is caused by frequent migration of synoptic disturbances from the Arctic Ocean. Snowfalls along the Lena river valley are also caused by traveling disturbances from the Arctic Ocean. Snow accumulation is suppressed after the Arctic Ocean has been frozen.
Possible erosion mechanisms in snow avalanches
Authors: Gauer Peter , Issler Dieter
Published: November 2007

Snow erosion and entrainment processes in avalanches are classified according to their mechanisms, the flow regimes in which they occur, and their spatial position within the avalanche. Simple, but process-specific, models are proposed for erosion by impacts, abrasion, plowing and blasting. On the basis of order-of-magnitude estimates, the first three mechanisms are clearly expected to be important. The fourth mechanism stipulates that the compaction of the snow cover ahead of the avalanche leads to the flow of escaping air just in front of the avalanche that may disrupt the snow cover and support formation of a saltation layer. The effects of this hypothetical mechanism resemble those of the plowing mechanism. All mechanisms depend strongly on the snow properties, but, with plausible parameter values, erosion rates at or above the experimentally found rates are obtained. The entrainment rate of an avalanche is most often limited by the shear stress needed to accelerate the eroded snow to avalanche speed.
A constitutive law for snow taking into account the compressibility
Authors: Mishra Aloke , Mahajan Puneet
Published: November 2007

A constitutive law for snow derived from a complementary power potential is proposed. The total deformation of snow is divided into elastic and creep parts. A hereditary integral using Norton’s power law is employed to describe primary creep. The concept of effective stress, which takes compressibility of snow into account, is used to calculate creep deformation. The hereditary integral is approximated by a non-linear spring–dashpot model. Results from uniaxial compression experiments (stress range 15– 45 kPa) on sieved snow of density range 180–470 kgm-3 were used to determine the constants appearing in the constitutive equation. The response of snow to constant strain rate (7.4×10-6 s-1 to 2.2×10-5 s-1) under bilaterally confined conditions was found with an iterative scheme employing the proposed constitutive law. The simulated results agree well with the measured axial stresses and volumetric changes.
Scales of spatial heterogeneity for perennial and seasonal snow layers
Authors: Sturm Matthew , Benson Carl
Published: November 2007

Local observations of snow layers are used as the basis for spatial extrapolation of snow properties and for establishing a time record of snow deposition, yet significant lateral variations in layer thickness, density and microstructure are well documented. Here we examine the nature of layer heterogeneity over distances of 10– 100 000 m using data from primarily flat locations in Alaska, Antarctica and Greenland. We find that at a scale of 10 m or less, perennial snow layers on glaciers and ice sheets are more uniform and laterally continuous than seasonal layers, which, in addition to heterogeneity introduced by wind and water percolation, are also affected by local topography and vegetation. At a scale of about 100 m, heterogeneity of seasonal and perennial snow layers converges and approaches a peak value. At larger scales (103–105m), local (order 100 m) forcing continues to produce most of the layer heterogeneity, with synoptic-scale variations adding small amounts. Cross-correlation at these larger scales is based on recognizing distinctive layer sequences or matching a few key layers of snow. Many layers cannot be correlated because they pinch out or change at scales (i.e. 100 m) smaller than the spacing between snow pits.
SNOWPACK model simulations for snow in Hokkaido, Japan
Authors: Hirashima Hiroyuki , Nishimura Kouichi , Baba Emiko , Hachikubo Akihiro , Lehning Michael
Published: November 2007

Numerical simulations using SNOWPACK, a snow-cover model, were carried out to confirm the model’s applicability to conditions in Hokkaido, Japan, where temperatures are fairly low and for 3 months the snow surface is usually dry except during occasional periods of rain or above-freezing temperatures. The simulations were conducted for Sapporo, Kitami and Niseko using meteorological data, and the results were compared with the observed snow profiles. In Sapporo, snow-profile observations were carried out every day for two winters. In Niseko, one of the most popular ski resorts in Japan, an avalanche accident occurred on 28 January 1998 and a snow pit was dug through the fracture line the next morning. The simulated snow profiles agreed fairly well with the observed ones. However, near the surface we observed depth hoar, which can be an important factor in avalanche release after successive snowfalls, that the model did not reproduce distinctly. Extending the model’s metamorphism laws with an expression of depth-hoar formation under a large temperature gradient, as formulated from an experiment by Fukuzawa and Akitaya (1993), the model reproduced the depth hoar adequately.
From snow X-ray microtomograph raw volume data to micromechanics modeling: first results
Authors: Pieritz Romeu André , Brzoska Jean-Bruno , Flin Frédéric , Lesaffre Bernard , Coléou Cécile
Published: November 2007

The new approaches in absorption X-ray microtomography allow snow-volume image acquisition in the cm3 range without destroying snow structure, and make it possible to perform micromechanical studies with the real geometry. The main objective of this paper is to introduce the development of a new three-dimensional (3-D) geometry modeling and finite-element analysis simulation package adapted to these scales. These new code modules and procedures are briefly described using an isothermal metamorphism snow experiment (–2°C, 3 months).This sample of aged snow (3.375mm3; 3003 voxels) allows simulation of a simple hypothetical uniaxial compressive stress experiment. The constitutive equations, boundary conditions, basic assumptions and the result showing the stress field over the 3-D data are discussed. The first qualitative results show a maximum stress of 6–9MPa in some small bonds, showing the potential of these codes to simulate the micromechanical behavior of complex materials.
A nearest-neighbour model for forecasting skier-triggered dry-slab avalanches on persistent weak layers in the Columbia Mountains, Canada
Authors: Zeidler Antonia , Jamieson Bruce
Published: November 2007

Nearest-neighbour models for avalanche forecasting have made little use of snowpack properties; however, slab thickness (H), slab load (Load) and a skier stability index (Sk38) have proven useful for regional avalanche forecasting in the Columbia Mountains, western Canada. This study explores 21 meteorological, snowpack and elaborated variables including Sk38, H and Load. A daily skier instability index (DSI) is developed as a response variable using skier-triggered avalanche activity on persistent weak layers and stability ratings at the end of the day. In rank correlation analysis, Sk38, Load, previous avalanche activity, H and some meteorological variables were highly ranked. The physical explanations are discussed. In classification-tree analysis, Sk38 was ranked as the most important variable and used in the development of the tree structure along with Load. Besides Sk38 and Load, snowpack thickness, the number of previously triggered avalanches and H have potential to predict DSI. Further we included once all 21 variables, and once all variables except Sk38, H and Load in nearest-neighbour models. Comparing the performance of these models shows that Sk38 along with Load and H have high potential to forecast the DSI on a regional scale.
Modeling snow instability with the snow-cover model SNOWPACK
Authors: Lehning Michael , Fierz Charles , Brown Bob , Jamieson Bruce
Published: November 2007

SNOWPACK has been in operational use for five consecutive winters on approximately 100 automatic weather stations in the Swiss Alps. It calculates snow precipitation, snowdrift and the layered structure of the snow cover. An analysis routine has been implemented that gives a stability estimation for a model profile. We distinguish between slab instability and direct action or deformation-rate instability. Slab instability relies on a static force balance within the snowpack (stability index) and may be used to assess stability for both natural and skier-triggered slab avalanches. We heuristically improve the slab index by adding a term of overload correction for all grain types and scaling the stability index with the bond size. Deformation-rate instability means that the load of the snow cover increases faster than the snow gains strength. An index is formulated based on the snow deformation rate. It may be associated with large snowfall events and wet-snow situations as they occur in catastrophic situations, or with the effect of a sudden increase in temperature. The results of both stability indices are compared to the fore-casted avalanche danger. The indices are able to recognize cases of avalanching. It is shown that the inclusion of several locations, for which the indices are calculated, improves the correlation between stability indices and avalanche danger. A sufficient number of profiles could bridge the gap between snow-cover characteristics at a point and avalanche danger.
Application of the numerical snowpack model (SNOWPACK) to the wet-snow region in Japan
Authors: Yamaguchi Satoru , Sato Atsushi , Lehning Michael
Published: November 2007

The snow-cover model SNOWPACK was applied to the wet-snow areas of Japan. Simulated variations of snow type, snow depth and weight, profiles of snow density, temperature and liquid-water content were compared with snow-pit measurements. The snow-depth simulation during early winter agreed with the measurements, but the differences between the simulation and the measurements increased during the course of the melt season. These differences were caused by underestimation of the energy balance at the snow surface, mainly that regarding sensible-heat flux during the melt season. The underestimation was caused by the implicit numerical treatment of the heat-transport equation. Consistent with the underestimation of snowmelt, simulated metamorphosis of compacted particles into melt forms was slower than the change shown by the measurements, and faceted snow particles, which constitute a snow type not actually found in the study area, sometimes appeared in the model. The inaccurate melt treatment also influenced simulated densities, which were larger than the measurements at small densities, while they were smaller than the measurements at large densities. Greater accuracy was achieved when an empirical compressive viscosity formulation for wet snows in Japan was introduced. A new version of SNOWPACK, with an accurate treatment of melt processes, is available.
Climatic response of snow depth to recent warmer winter seasons in heavy-snowfall areas in Japan
Authors: Ishizaka Masaaki
Published: November 2007

In heavy-snowfall areas facing the Sea of Japan, winter seasons with lower volumes of snow occurred from 1986/87 to 1999/2000. In this paper, the changes induced by these warmer winters in snowy areas in Japan are investigated using two datasets. One set was normalized for the period 1971–2000 from manned surface meteorological observations by the Japan Meteorological Agency, and the other set was for 1961– 90. Winter climatic monthly values for the first dataset were thought to be affected by the warmer winter seasons since almost half the relevant period coincides with them. By comparing each monthly climatic value in both datasets, the following results were obtained: (1) At each meteorological observation site the bimonthly average temperature fromJanuary to February increased and the amounts of increase were about 0.4°C on average. (2) The bimonthly maximum snow depth for the same period increased at a number of sites, but usually by only a few centimeters, the maximum increase being 0.05 m. (3) In contrast, the decreases in snow depth in heavy-snowfall areas facing the Japan Sea, which belong to a temperate climate zone, were large, ranging from about 0.05 to 0.22 m in climatic bimonthly maximum snow depth during January and February. The last result shows that snow covers in such warm snowy areas are very sensitive to climatic changes. An attempt is also made in this paper to estimate the amounts of decrease in snow depth from the increases in air temperature and the decreases in precipitation amounts.
Numerical simulation of elastic stress in the microstructure of snow
Authors: Schneebeli Martin
Published: November 2007

The mechanical properties of snow depend on its microstructure. The fabric of snow was reconstructed in three dimensions using serial sections or X-ray microtomography. A voxel-based finite-element model, with the elements based on the microstructure and ice as the material, was used to calculate the stress distribution in the snow. A small elastic deformation was simulated and the bulk elastic moduli of these samples were determined. The simulated elastic modulus was 3–10 times or 10–100 times larger than previously published measurements. The deviation is possibly caused by the relatively slow deformation rates of the usual tests. This strain-rate effect is well known for pure ice. Locations of stress concentrations can be extracted and compared to the micro-structural location of bonds. By this method we are able to determine mechanical properties of thin or extremely brittle snow layers which are otherwise difficult or impossible to measure.
Verified combination of numerical weather- and avalanche-prediction models at Kootenay Pass, British Columbia, Canada
Authors: Roeger Claudia , McClung David M. , Stull Roland
Published: November 2007

The combination of numerical weather prediction (NWP) and snow avalanche forecasting has been performed using the output of two weather models run at the University of British Columbia, Canada, and a local numerical avalanche-forecasting model developed for Kootenay Pass (McClung and Tweedy, 1994). The main motivations for this work are. (1) to extend the lead time of avalanche forecasts by using NWP forecasts of meteorological variables as input to statistical avalanche-threat models (instead of the traditional method of using current/past observed meteorological variables as input); and (2) to create another tool to help avalanche forecasters in their daily decision-making by making true forecasts instead of “nowcasts”. Therefore, verified weather-forecast model output was used as input for the local avalanche-forecasting model at Kootenay Pass. The resulting 24 hour avalanche forecast was compared to observed avalanche occurrences and to the 12 hour avalanche forecast with current weather observations. As a result, the avalanche-model output for the test runs with numerically predicted weather data is comparable in accuracy to the runs with observed weather data. The results also suggest that avalanches may be predicted statistically for 24 hours into the future when high-resolution NWP is used as input, weather- and avalanche-forecast errors taken into account during operational use.
Temporal variability in snow distribution
Authors: Alfnes Eli , Andreassen Liss M. , Engeset Rune V. , Skaugen Thomas , Udnæs Hans-Christian
Published: November 2007

Snow-courses data have been collected in order to investigate the temporal variability of snow distribution in two catchments in southern Norway during the 2002 melt season. The profiles represent different elevations, aspects and terrain types. At snow maximum the spatial distribution of snow above the tree line was positively skewed (long tail in the positive direction), whereas the spatial distribution below the tree line followed a more normal distribution. During the snowmelt season the spatial distribution of snow became increasingly skewed. By separating the datasets into two terrain classes, alpine and forest, the snow distribution could be described by a time-variant gamma distribution function, one for each terrain class. The results of the study will be used to formulate a new snow routine in the Swedish rainfall–runoff model HBV, which is used for flood forecasting in Norway.
The splash function for snow from wind-tunnel measurements
Authors: McElwaine James N. , Maeno Norikazu , Sugiura Konosuke
Published: November 2007

In wind transport of snow, horizontal momentum is extracted from the mean wind flow and transferred to the snow grains. Upon colliding with the surface the grains can bounce and eject further grains in a process known as splashing. How efficiently the horizontal momentum is converted to vertical momentum in the splash process is the determining factor for mass-transport rates. This paper discusses wind-tunnel experiments performed to calculate the splash function for snow particles. The data are used to develop a new splash function. Particular care is taken to include correlations in the data such as between ejection velocity and ejection angle. The new splash function includes these correlations, and its parameters are related to physical properties of the bed and snow.
The duration of the Bølling-Allerød period (Greenland Interstadial 1) in the GRIP ice core
Authors: Seierstad Inger K. , Johnsen Sigfús J. , Vinther Bo M. , Olsen Jesper
Published: November 2007

A new dating of the Bølling-Allerød period (Greenland Interstadial event 1) in the GRIP ice core is presented. Newly measured profiles of δD and δ18O, as well as existing profiles of Ca2+, NH4+, dust and NO3–, have been used for the dating. As seasonal variations can be observed in all six components, it was possible to simultaneously count annual layers in the profiles in order to obtain a multi-parameter dating. The new data presented in this study include a total of 36.85 m of stable-isotope profiles of 1 cm resolution from five sections of the Bølling-Allerød period in the GRIP ice core. The annual-layer counting suggests a duration of the complete Bølling-Allerød period, as revealed in the GRIP ice core, of 1627 ± 52 years. This estimate contrasts with an earlier finding from the same GRIP ice core, where the Bølling-Allerød was found to span 2168 years (Hammer, in press). This estimate was based on layer counting, using dust concentrations only.
Investigations on intra-annual elevation changes using multi-temporal airborne laser scanning data: case study Engabreen, Norway
Authors: Geist Thomas , Elvehøy Hallgeir , Jackson Miriam , Stötter Johann
Published: November 2007

Key issues of glacier monitoring are changes in glacier geometry and glacier mass. As accurate direct measurements are costly and time-consuming, the use of various remote-sensing data for glacier monitoring is explored. One technology used and described here is airborne laser scanning. The method enables the derivation of high-quality digital elevation models (DEMs) with a vertical and horizontal accuracy in the sub-metre range. Between September 2001 and August 2002, three laser scanner data acquisition flights were carried out, covering the whole area of Engabreen, Norway, and corresponding well to the measurement dates for the mass-balance year 2001/02. The data quality of the DEMs is assessed (e.g. by comparing the values with a control area which has been surveyed independently or GPS ground profiles measured during the flights). For the whole glacier, surface elevation change and consequently volume change is calculated, quantified and compared with traditional mass-balance data for the same time interval. For the winter term, emergence/submergence velocity is determined from laser scanner data and snow-depth data and is compared with velocity measurements at stakes. The investigations reveal the high potential of airborne laser scanning for measuring the extent and the topography of glaciers as well as changes in geometry (Δarea, Δvolume).
Response of the Nordenskiöld Land (Spitsbergen) glaciers Grumantbreen, Håbergbreen and Dryadbreen to the climate warming after the Little Ice Age
Authors: Ziaja Wieslaw
Published: November 2007

Three receding glaciers on Spitsbergen were examined on the basis of a 1936 topographic map and field investigations during the summers of 1995 and 2001. Håbergbreen, the largest glacier, has undergone the most intensive recession due to its relatively low altitude. There are two important manifestations of glacial recession: (1) the retreating glaciers leave rocky outcrops in the upper or steeper mountain slopes, and (2) the edges of moving glacier tongues are being transformed into motionless ice-cored moraines in valleys. The glaciers under study have not been transformed into rock glaciers. The recession rate has been increasing since 1995, which can be interpreted as a result both of positive feedback initiated by 20th-century climate warming and of slight warming in the 1990s. The glaciers have not thawed enough in relation to the warming and rise of the equilibrium-line altitude (by at least 250–300 m since the beginning of the 20th century). Håbergbreen, already split up into four ice patches, will disappear without a sustained temperature decrease during the next few decades. Grumantbreen and Dryadbreen will survive as small mountain glaciers if winter snow precipitation does not increase.
Estimating the contribution of Arctic glaciers to sea-level change in the next 100 years
Authors: Oerlemans J. , Bassford R.P. , Chapman W. , Dowdeswell J.A. , Glazovsky A.F. , Hagen J.-O. , Melvold K. , De Ruyter de Wildt M. , van de Wal R.S.W.
Published: November 2007

In this paper, we report on an approach to estimate the contribution of Arctic glaciers to sea-level change. In our calculation we assume that a static approach is feasible. We only calculate changes in the surface balance from modelled sensitivities. These sensitivities, summarized in the seasonal sensitivity characteristic, can be used to calculate the change in the surface mass budget for given anomalies of monthly temperature and precipitation. We have based our calculations on a subdivision of all Arctic ice into 13 regions: four sectors of the Greenland ice sheet; the Canadian Arctic >74˚N; the Canadian Arctic <74˚N; Alaska, USA; Iceland; Svalbard; Zemlya Frantsa Iosifa, Russia; Novaya Zemlya, Russia; Severnaya Zemlya, Russia; and Norway/Sweden >60˚N. As forcing for the calculations, we have used the output from five climate models, for the period 2000–2100. These models were forced by the same greenhouse-gas scenario (IPCC-B2). The calculated contributions to sea-level rise in the year 2100 vary from almost zero to about 6 cm. The differences among the models stem first of all from differences in the precipitation. The largest contribution to sea-level change comes from the Greenland ice sheet. The glaciers in Alaska also make a large contribution, not because of the area they cover, but because they are more sensitive than other glaciers in the Arctic. The climate models do not agree on regional patterns. The runoff from Svalbard glaciers, for instance, increases for two models and decreases for the three other models. We conclude that the uncertainty due to a simple representation of the glaciological processes is probably smaller than the uncertainty induced by the differences in the climate-change scenarios produced by the models.
A revised chronology of key Vatnajökull (Iceland) outlet glaciers during the Little Ice Age
Authors: McKinzey Krista M. , Orwin John F. , Bradwell Tom
Published: November 2007

Glacier fluctuations from key Vatnajökull outlets have been redated using tephrochronology coupled with two lichenometric techniques to ascertain the timing of the Little Ice Age (LIA) maximum in southeast Iceland. An updated tephrochronology for southeast Iceland (both the number of tephra layers present and their geochemical signatures) indicates a LIA maximum for both glaciers between AD 1755 and 1873. Based on a population gradient approach, lichenometrically dated moraines along the margins of Skálafellsjökull and Heinabergsjökull narrow this window to the early to mid-19th century respectively. These revised chronologies, in addition to emerging evidence from elsewhere in Iceland, support a late 18th- to early 19th-century LIA glacier maximum. In contrast, the Norwegian LIA glacial maximum is strongly centred around AD1750. This implies differing glaciological responses to secular shifts in the North Atlantic Oscillation. Such revisions to the Vatnajökull record are crucial, as accurately identifying the timing and delimiting the spatial extent of the Icelandic LIA glacier maximum will allow further light to be shed on glacier–climate interactions in the North Atlantic.