Roughness length for momentum and heat over Antarctica in a regional atmospheric climate model

A regional atmospheric climate model is used to examine the effect of changes in the roughness lengths of momentum (z_0m) and heat (z_0h) on the structure of the atmosphere and on the surface energy fluxes over Antarctica. Four experiments were carried out in which z_0m and/or z_0h were altered with respect to a control experiment. The changes consisted of a lowering of z_0m from a field aggregated from a vegetation map with an orographic correction based on the European Centre for Medium-Range Weather Forecasts z_0m-field, to a constant value of 10^-3m and a lowering of z_0h from a value equal to z_0m to a constant value of 10^-3m or a value dependent on the wind speed via a surface renewal model. A reduction of z_0m results in the expected increase in near surface wind speed. It also results in an increase of the depth of the katabatic wind layer, but unexpectedly, in a decrease in strength of the large-scale flow over the continent, in particular in summer. In the escarpment region a decrease of z_0m is found to result in too high wind speeds. Surface temperatures on average decrease while atmospheric temperatures increase, resulting in an increase of near surface static stability. Changes in roughness lengths do not significantly change the temperature profiles. The surface fluxes, on average found reduced, are modeled best by using the z_0h based on the surface renewal method.