Numerical experiments of wind transport over a mountainous instrumented site:: I.: Regional scale

For about ten winter seasons, the Centre d'Etudes de la Neige and CEMAGREF have performed intensive field measurement campaigns concerning various snow and weather parameters during blowing-snow events. The observation sites are located near the ski resort, Alpe d'Huez, Col du Lac Blanc, France (2700-2800 m a.s.l.). Our first objective is to include the main effects of the wind in the operational avalanche-hazard forecast at the massif scale ' taking into account the effects of local winds on our snow-cover estimation without simulating the phenomena exactly. Only the effects on snow accumulation or erosion and snow characteristics are measured, without any direct link with a precise field location except for the validation. The underlying numerical simulations have been tested on the instrumented site and include an assessment of the, appropriate shear velocity, an evaluation of the occurrence of transport related to the snow characteristics provided by the software PROTEON and an estimation of the transport rates. These different computations are embedded in the new software, SYTRON, which is inserted in the SAFRAN/Crocus/MEPRA operational chain. Different validations of this new application are presented in terms of shear velocities, observed transport periods and snow depths. The encouraging results augur well for an operational implementation next winter.