HR: 0800h
AN: C21A-1053    [Abstracts]
TI: Wind Tunnel Measurements of Saltation Threshold for Snow
AU: * Clifton, A
EM: clifton@slf.ch
AF: WSL, Swiss Federal Institue for Snow and Avalanche Research SLF, Fluelastrasse 11, Davos Dorf, CH-7260 Switzerland
AU: Rüedi, J
EM: ruedi@slf.ch
AF: WSL, Swiss Federal Institue for Snow and Avalanche Research SLF, Fluelastrasse 11, Davos Dorf, CH-7260 Switzerland
AU: Lehning, M
EM: lehning@slf.ch
AF: WSL, Swiss Federal Institue for Snow and Avalanche Research SLF, Fluelastrasse 11, Davos Dorf, CH-7260 Switzerland
AB: A series of 17 wind-tunnel experiments was made to establish the saltation threshold conditions of natural snow. This information is of significant interest for numerical models of snow pack development. We characterised snow visually on site, using a penetrometer and through image processing of digital images. The profile of the velocity boundary layer over the snow was measured and results were fitted using a log-law. Friction velocities and roughness lengths up to and including the drift threshold will be presented. No relationship was seen between the boundary layer roughness length or threshold friction velocity and grain type, size or snow density alone. Aerodynamic roughness length was found to be independent of friction velocity until the drift threshold was reached. The relationship between the roughness length and friction velocity at the threshold was similar to that predicted by Owen in 1964 for flow over saltating particles. The boundary layer roughness length at the threshold was proportional to the snow unit cell length, which is a characteristic length scale of the snow. The snow unit cell length is determined from density and grain size measurements. A positive correlation was observed between aerodynamic threshold shear and snow surface penetration resistance. No obvious difference was observed between the behaviour of fresh snow and snow which had already undergone some metamorphosis.
DE: 0736 Snow (1827, 1863)
DE: 0762 Mass balance (1218, 1223)
DE: 0790 Weathering (1625, 1886)
SC: Cryosphere [C]
MN: Fall Meeting 2005