Numerical studies with a regional atmospheric climate model based on changes in the roughness length for momentum and heat over Antarctica

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 lower 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 (1) 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(-3) m; and (2) a lowering of z0h from a value equal to z(0m) to a constant value of 10(-3) m 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 in the depth of the layer in which southeasterly near-surface winds prevail, and in a decrease in the 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 modelled best by using the z0h based on the surface renewal method.