Modelling the surface energetics of patchy arctic tundra snowcover

Abstract

A combination of field observations and measurements were used to study the energy-balance of a patchy arctic tundra snow-cover during the winter of 2003/2004 at a mountain tundra site in Northern Sweden. To quantify the effect of patchy snow-cover on surface energetic, the Met. Office Surface Exchange Scheme (MOSES 2) was employed to simulate surface snow dynamics. Surface snow patchiness was controlled by the interaction of blowing snow with surface topography and vegetation, with deep drifts forming in topographic hollows and tall shrub beds. Some exposed ridge tops remained exposed for the majority of the winter. The surface patchiness was found to significantly alter the surface energetics, and the interaction between snow and snow-free surfaces was critical to accurately numerically simulating snow-cover ablation. The assumption of uniform snow- covers in large-scale atmospheric models may lead to significant errors in model simulations. It was found that for large-scale models, heterogeneous snow-covers can be adequately represented by the use of separate energy-balances for snow and snow-free surfaces respectively with a single underlying soil layer. The proportions of each surface can be represented using a snow covered fraction which is a parameterisation of the distribution of snow depths. Simulated surface fluxes, particularly surface runoff and heat and water vapour, were found to be highly sensitive to the exact form of this parameterisation. No field evidence was found for the advection of turbulent energy between snow and snow-free surfaces