Annals qfGlacioLogy 26 1998 © Internationa l Glaciological Society Numerical simulation of drifting snow: erosion and deposition rn.odels

ABSTRACT. Earli er works on numerica l modelling arc analysed. Anderson a nd H a fT (1991) proposed a model using the "splas h " function which was defin ed for cohesionless sand. The Uematsu and others (1989, 1991) and Liston and others (1993, 1994) approaches a re based on fluid-mechanics conservation laws where the snow is transported and di f-fused by the a ir now. These models consider the salta tion layer as a boundary condition. For the now, and for the suspension, we adopt the same model as that ofUemats u a nd Liston. For mass exchange be tween the now a nd snow surface, we have developed an ero-sion- deposition model where mass excha nge is defined in rela tion to fl ow turbul ence, threshold-fri cti on velocity and snow concentration. Our snow-erosion model was cali-brated using Takeuchi 's (1980) fi eld measurements. T he depositi on model was tested by comparing numerical results with wind-tunnel ones, for sawdust-acc umulation windward and leewa rd of a solid snow fence with a bottom gap. The numerical results obtained a rc close to the experimenta l res ul ts. The ma in res ults of the \'ari ous sensitiyity experiments a rc: the leewa rd acc umul a ti on is ve r y sensiti\'e to th e rat io (U. /U. l) ( it ap pea l's for (u./u. t) close to 1 and di sappears for (u. /u.d> 1.2), the global acc umul ation produced by the fence increases as (u. /u. t) dec reases a nd the back reaction of pa rticle ' on turbu-lence extends slightly the windward acc umulation. NOTATION Qs 10 ta l mass-transport rate per uni t of latera l dimen-Us Friction velocity (m s ') u. r Real friction velocity, corresponding to the friction velocity modified by the presence of snow pa rticles (m s ') U. t Threshold friction velocity (m s ') UF Particle-settling velocity (m s ') (u, v) M ean velocity components in the x (m) (hori zonta l) and y (m) (vertical) di rections (m s ') Uj M ean veloci t y component in the O Xj d irection (m s ') Zo Aerodynam ic roughness height (m) D p Pa rticle di ameter (m) Vp Par ticle vo lume (m 3