Modelling snowdrift sublimation and its effect on the moisture budget of the atmospheric boundary layer

Abstract

A one-dimensional atmospheric surface layer model including turbulent diffusion and gravitationalsettling of suspended snow particles is used to simulate vertical profiles of snowdriftsublimation rates and the associated effects on the humidity and temperature profiles in thelowest 10 m. The simulations show that the thermodynamic feedback effects associated withsnowdrift sublimation, i.e., strong increases in humidity and cooling, can significantly reducethe snowdrift sublimation rate, in particular in strong winds when large numbers of particlesare being suspended. This negative feedback occurs because snowdrift sublimation depends onthe undersaturation and temperature. Mechanisms that take away moisture from the surfacelayer, such as entrainment or horizontal advection of dry air, tend to weaken this feedback andenhance modelled snowdrift sublimation as the air generally remains undersaturated. Near thesurface, however, the thermodynamic feedbacks dominate in strong winds, reducing the upwardmoisture flux from the surface. Then, snowdrift sublimation is the main contributor to theupward moisture flux at 10 m. Interestingly, in strong winds, the simulated total upward moistureflux in snowdrifting conditions is less than that in similar non-drifting conditions. Hence, the model results indicate that occurrence of snowdrift sublimation may, counterintuitively, eventually lead to a reduction of the surface-atmosphere moisture transport.