Simulating the effect of natural convection in a tundra snow cover

Abstract. As a direct solution to improve the one-dimensional physics-based multi-layer snow model SNOWPACK, a C++ interface is implemented for a tight coupling between SNOWPACK and OpenFOAM with the aim to investigate natural convection in real snow covers. OpenFOAM simulates convection in two dimensions based on SNOWPACK snow profiles and feeds the convective vapor fluxes back to SNOWPACK. Among different snow covers and conditions, significant convection events that are well synchronized with cold events are numerically simulated by the SNOWPACK-OpenFOAM coupler for a herb tundra permafrost at Bylot Island only if we neglect wind slab formation for surface layers. We find significant sublimation in downward flow regions and that convection generates a low-density path extending vertically almost through the whole snow column. The strong footprint of convection on snow density and temperature with significant lateral variations up to 90 kg m−3 and 5 K respectively makes a consistent representation in the SNOWPACK one-dimensional profile difficult. But the most prominent effect of convection on the snow density profile, namely a low density foot and high density top, corresponds qualitatively to observations. Further work is required to achieve the full magnitude of observed density differences and to adapt physical parameterizations in conventional snow models to represent this effect in particular for snow settling and metamorphism.