Abstract
Abstract. Mountain snow-cover is normally heterogeneously distributed due to wind and precipitation interacting with the snow cover on various scales. The aim of this study was to investigate snow deposition and wind-induced snow-transport processes on different scales and to analyze some major drift events caused by north-west storms during two consecutive accumulation periods. In particular, we distinguish between the individual processes that cause specific drifts using a physically based model approach. Very high resolution wind fields (5 m) were computed with the atmospheric model Advanced Regional Prediction System (ARPS) and used as input for a model of snow-surface processes (Alpine3D) to calculate saltation, suspension and preferential deposition of precipitation. Several flow features during north-west storms were identified with input from a high-density network of permanent and mobile weather stations and indirect estimations of wind directions from snow-surface structures, such as snow dunes and sastrugis. We also used Terrestrial and Airborne Laser Scanning measurements to investigate snow-deposition patterns and to validate the model. The model results suggest that the in-slope deposition patterns, particularly two huge cross-slope cornice-like drifts, developed only when the prevailing wind direction was northwesterly and were formed mainly due to snow redistribution processes (saltation-driven). In contrast, more homogeneous deposition patterns on a ridge scale were formed during the same periods mainly due to preferential deposition of precipitation. The numerical analysis showed that snow-transport processes were sensitive to the changing topography due to the smoothing effect of the snow cover.
Highlights
Snow-transport processes shape the mountain snow-cover during the winter season
This study drew on the findings of Schirmer et al (2010b), who showed that the final snow distribution at the time of www.the-cryosphere.net/4/545/2010/
We have been able to demonstrate that most snow-deposition patterns found at the time of peak accumulation can be explained and modeled with the help of a few mean flow fields calculated by Advanced Regional Prediction System (ARPS)
Summary
Snow-transport processes shape the mountain snow-cover during the winter season. The driving force for these processes is the atmospheric boundary layer flow. The mean air flow is modified by the local topography, especially in highly complex terrain. Local high wind velocities initiate the relocation of snow particles already deposited on the ground, through saltation and suspension processes. The interaction of wind and topography during snowfall promotes enhanced snow loading on leeward slopes due to the preferential deposition of the precipitation (Lehning et al, 2008). These process interactions result in very heterogeneous snow depths and snow-cover properties. The heterogeneity of snow-cover properties arising from particular storm events, on the one hand, is a special challenge for avalanche forecasting The snow distribution at the time of peak accumulation, on the other hand, has a major influence on the timing and the magnitude of snowmelt runoff (Pomeroy et al, 1997; Luce et al, 1998; Liston et al, 2007; Grunewald et al, 2010)
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