Item: Multi-scale spatial variability of a layer of buried surface hoar
Title: Multi-scale spatial variability of a layer of buried surface hoar
Proceedings: Proceedings of the 2004 International Snow Science Workshop, Jackson Hole, Wyoming
Authors: Jerg Schweizer and Kalle Kronholm, Swiss Federal Institute for Snow and Avalanche Research SLF, Davos, Switzerland, Department of Earth Sciences, Montana State University, Bozeman, U.S.A.
Abstract: Spatial variability of the snowpack exists at different scales. Various studies have investigated and quantified snowpack spatial variability at either the slope scale or the regional scale. This study investigates spatial variability at both of these scales simultaneously. Field measurements were made on a buried layer of surface hoar over a wide range of scales from 0.5 m to 5 km near Davos in the eastern Swiss Alps. The surface hoar layer did exist widespread before burial. At each measurement location, the layer thickness, grain size and stability of the buried surface hoar layer was recorded if the layer was present. At the slope scale fine-resolution measurements were made with a micro-penetrometer. These measurements showed that the surface hoar layer was continuously present at the slope scale. In the surrounding terrain, on slopes of similar aspect, the surface hoar layer was found in 83% of the snow profiles (point observation), and independent of aspect in 72%. However, in an adjacent region, about 12 km to the east, only on 25-30% of the slopes the buried layer of surface hoar was observed. Surface hoar distribution in one region showed a distinct pattern in regard to slope aspect. This could be explained by conditions that likely were responsible for surface hoar destruction before burial: wind and solar radiation. Whereas the surface hoar grain size was initially best predicted by the coordinates and elevation, the best predictor changed to the radiation index (a proxy for the slope aspect). Combining the slope scale measurements with the profile observations showed that within a few 100 m the existence of surface hoar could be extrapolated. But beyond about 500 rn extrapolation became merely incidental.
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Keywords: spatial variability, snow stability, avalanche forecasting
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