Representation of Antarctic Katabatic Winds in a High-Resolution GCM and a Note on Their Climate Sensitivity

Abstract

A high-resolution GCM (ECHAM-3 T106, resolution 1.1° ? 1.1°) is found to simulate many characteristic features of the Antarctic climate. The position and depth of the circumpolar storm belt, the semiannual cycle of the midlatitude westerlies, and the temperature and wind field over the higher parts of the ice sheet are well simulated. However, the strength of the westerlies is overestimated, the annual latitudinal shift of the storm belt is suppressed, and the wintertime temperature and wind speed in the coastal areas are underestimated. These errors are caused by the imperfect simulation of the position of the subtropical ridge, the prescribed sea ice characteristics, and the smoothened model topography in the coastal regions. Ice shelves in the model are erroneously treated as sea ice, which leads to a serious overestimation of the wintertime surface temperature in these areas. In spite of these deficiencies, the model results show much improvement over earlier simulations. In a climate run, the model was forced to a new equilibrium state under enhanced greenhouse conditions (IPCC scenario A, doubled CO2), which enables us to cast a preliminary look at the climate sensitivity of Antarctic katabatic winds. Summertime katabatic winds show a decrease of up to 15% in the lower parts of the ice sheet, as a result of the destruction of the surface inversion by increased absorption of solar radiation (temperature?albedo feedback). On the other hand, wintertime near-surface winds increase by up to 10% owing to a deepening of the circumpolar trough. As a result, the model predicts that the annual mean wind speed remains within 10% of its present value in a doubled CO2 climate, but with an increased amplitude of the annual cycle.