Item: A 3d model for snow drift and snow cover development in steep alpine terrain
Title: A 3d model for snow drift and snow cover development in steep alpine terrain
Proceedings: 2002 International Snow Science Workshop, Penticton, British Columbia
Authors: Michael Lehning, Judith Doorschot, Charles Fierz and Norbert Raderschall, VVSL, Swiss Federal Institute for Snow and Avalanche Research, SLF
Abstract: Since blowing and drifting snow is a major factor influencing avalanche danger and the local micro climate, a high resolution, objective and quantitative assessment and forecast of snow transport by wind is of great practical value. Wind transport of snow is governed by three components: the erodability of the snow pack, the current snowfall and the wind field. A snowdrift model has been developed that combines an atmospheric model analysis of the high resolution wind field over steep topography, a novel formulation for snow drift and a snow cover model. For modeling snow drift, the transport modes saltation and suspension are distinguished. This presentation focuses on the model parts describing snow drift and snow cover. The snow cover is represented by the numerical model SNOWPACK. A novel model for snow saltation is presented, which is suitable for steep terrain. Based on a computationally efficient equilibrium approach, the description of saltation uses explicit trajectory calculations to estimate mass fluxes on steep slopes. Emphasis of the presentation is further on the coupling between the snow cover, the drifting and blowing snow and the wind field. For a correct description of the erosion and deposition pattern, the formulation of the coupling functions is of major importance. The model system is applied to predict snow loading in avalanche slopes. Results for the avalanche winter 1998 / 1999 are presented. The evaluation of these results show that major characteristics of snow redistribution are captured by the model. In steep terrain, saltation appears to contribute less to snow redistribution than previously assumed. Preferential deposition during snow fall events appears to be a major factor influencing snow distribution in small scale steep terrain. Remaining uncertainties of the model system concern the formulation of suspension and the accuracy of the flow simulation. Suggestions for improvements are made.
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Keywords: arps, lee slope, avalanches, wind slab, flow simulation, saltation, suspension, erosion, snow preferential deposition
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