HR: 0800h
AN: C21B-0473    [Abstracts]
TI: Surface Hoar Formation in Complex Terrain
AU: * Guala, M
EM: guala@slf.ch
AF: Swiss Federal Institute for Snow and Avalanche Research SLF, Fluelastrasse 11, Davos, 7260, Switzerland
AU: Stoessel, F
EM: stoessel@slf.ch
AF: Swiss Federal Institute for Snow and Avalanche Research SLF, Fluelastrasse 11, Davos, 7260, Switzerland
AU: Fierz, C
EM: fierz@slf.ch
AF: Swiss Federal Institute for Snow and Avalanche Research SLF, Fluelastrasse 11, Davos, 7260, Switzerland
AU: Manes, C
EM: manes@slf.ch
AF: Swiss Federal Institute for Snow and Avalanche Research SLF, Fluelastrasse 11, Davos, 7260, Switzerland
AU: Huwald, H
EM: hendrik.huwald@epfl.ch
AF: Ecole Polytechnique Federale de Lausanne EPFL, Batiment GR, Lausanne, 1015, Switzerland
AU: Parlange, M
EM: marc.parlange@epfl.ch
AF: Ecole Polytechnique Federale de Lausanne EPFL, Batiment GR, Lausanne, 1015, Switzerland
AU: Lehning, M
EM: lehning@slf.ch
AF: Swiss Federal Institute for Snow and Avalanche Research SLF, Fluelastrasse 11, Davos, 7260, Switzerland
AB: Vapor exchange processes between the snow surface and the lower atmosphere lead to mass sublimation or deposition. While the former usually occurs during day, the latter often co-occurs at night with the formation of surface hoars. These crystals, when buried after snow falls, often form failure planes for avalanches. Understanding surface hoar formation and modeling the underlying physics would then substantially improve avalanche warning and reduce hazards in the alpine area. The present experimental study is based on measurements obtained at 2540 m a.s.l. above Davos, Switzerland, during winter 2007 and it focuses on the formation, development and destruction of surface hoar crystals. Mass changes were measured with a box in the field, turbulent fluxes were estimated by means of two sonic anemometers coupled with two fast gas analyzers, snow parameters were collected as well as meteorological parameters in situ and at synoptic scale. Measurements clearly indicate that turbulent vapour fluxes (obtained at three meters above the surface) are entirely responsible for the mass gain in the snow pack and thus of the formation and growth of surface hoars. The analysis of the meteo-data suggest that local katabatic winds from nearby slopes during nights of surface hoar development significantly contribute to the turbulent fluxes measured near the surface and thus to the growing of surface hoars. From the modeling side, the bulk-approach as implemented in the snow cover model SNOW-PACK agrees well with the eddy correlation, and the mass balance measurements, thus resulting in a correct prediction of surface hoar formation, for the cases examined.
DE: 0736 Snow (1827, 1863)
DE: 0742 Avalanches
DE: 0762 Mass balance (1218, 1223)
DE: 3307 Boundary layer processes
DE: 3379 Turbulence (4490)
SC: Cryosphere [C]
MN: 2007 Fall Meeting