Extended Abstract (680K)12.5
Boundary layer wind field over steep, snow covered, high alpine topography
Norbert Raderschall, Swiss Federal Institue for Snow and Avalanche Research, Davos, Switzerland; and M. Lehning and J. Doorschot
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 numerical snow drift model has been developed that combines an atmospheric model analysis of the high resolution wind field, a novel snow drift formulation and a snow cover model. This presentation focuses on the part of the research project dealing with the realistic estimation of the high resolution wind field over steep alpine terrain. Adapting the non hydrostatic and compressible atmospheric prediction model ARPS (Advanced Regional Prediction System) to high alpine topography, wind fields have been calculated and evaluated against measurements. A high resolution grid with horizontal spacing up to 25 m and vertical spacing up to 1 m has been used to calculate realistic wind fields. With such a high resolution we are able to simulate the general structure of the atmospheric flow as well as the boundary layer flow for limited areas of approx. 2 x 2 km. As an example results of computations for the Gaudergrat, our experimental site in the Weissfluh area near Davos will be shown. The Gaudergrat is a quasi 2 dimensional mountain ridge with slopes up to 38 degrees and a rather sharp crest. The prevailing wind direction during strong precipitation events is north west and thus perpendicular to the crest line. The Gaudergrat site is equipped with 6 masts carrying instruments measuring wind profiles and meteorological parameters with a temporal resolution up to 1 Hz at different heigths. It will be shown how ARPS handles the problems of the terrain following coordinate system in such steep terrain. In addition, the performance of the model calculating typical flow pattern like separation and recirculation and turbulence characteristics of the flow field such as the turbulent kinetic energy (TKE) has been analyzed.
Session 12, Numerical Modeling and Data Assimilation
Wednesday, 19 June 2002, 3:30 PM-5:00 PM
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