Snowdrift suspension and atmospheric turbulence. Part I: Theoretical background and model description

Snowdrift is one of the many manifestations of two-phase flow, in which the interaction between suspended particles and the ambient fluid brings about some interesting features. Specifically, the drag required to keep particles in suspension against the downward gravitational pull requires expenditure of turbulent kinetic energy (TKE). Other effects include the increased density of the air-snow mixture and the stable thermal stratification caused by the snowdrift sublimation-induced cooling. An atmospheric surface-layer model that includes snowdrift suspension is described that includes the effects of upward diffusion, gravitational settling and sublimation of snow particles in 48 size classes, the effects of snowdrift sublimation on the heat and moisture budget of the surface layer and the damping of turbulence in the presence of suspended particles. The well-known E-epsilon closure model is applied to evaluate the eddy exchange coefficient, with a new term representing buoyancy reduction induced by the stably stratified suspended particle profile included in the prognostic equation for TKE.