Improvement of a numerical snow drift model and field validation

For about 10 years, Météo-France has developed and operated a real time operational suite aimed at snowpack simulation and avalanche risk forecasting: the numerical model chain Safran-Crocus-Mepra (SCM). It presently includes only a crude formulation of snowdrift effects at large spatial scales (massif). This paper presents the improvements to a snow drift module suited to the SCM chain. The new version called SYTRON3 which aims at an improved simulation of snow drift effects at smaller spatial scales. It is coupled with the SCM environment, which provides hourly meteorological conditions and snow forcing. The main modifications concern the new parameterisation schemes, which are more realistic and more physically based. The increased number of vertical layers allows now to represent explicitly the three modes of movement during snow drift: creep, saltation and diffusion. The validation of this new version as well as comparisons with the previous version are performed at the Col du Lac Blanc test site (2700 m a.s.l., French Alps) by the use of digital photographs and field observations.