A surface energy and mass balance model for simulations over multiple glacial cycles
Abstract. A comprehensive understanding of the state and dynamics of the land cryosphere and associated sea level rise is not possible without taking into consideration the intrinsic time scales of the continental ice sheets. At the same time, the ice sheet mass balance is the result of seasonal variations in the meteorological conditions. Simulations of the coupled climate-ice sheet system thus face the dilemma of skillfully resolving short-lived phenomena, while also being computationally fast enough to run over tens of thousands of years. Further complications arise from the fact that the mass balance is a small residual of various contributions that individually are much larger, and that even a marginal bias will develop into an erroneous solution over the long integration time and when amplified by strong positive feedback mechanisms. As a possible solution, we present the BErgen Snow SImulator (BESSI), a surface energy and mass balance model that achieves computational efficiency while simulating all surface and internal fluxes of heat and mass explicitly and based on physical first principles. In its current configuration it covers most land areas of the Northern Hemisphere. Two large ensembles of simulations are investigated, one to calibrate the model and another one to assess its sensitivity to variations in air temperature.