The antarctic winter; simulations with climatological and reduced sea‐ice extents

Abstract The southern hemisphere climatology of a recent version of the Meteorological Office 11‐layer general circulation model is presented. The simulated climate is compared with observational data, including Meteorological Office operational analyses for the period 1983‐1987. The surface temperatures and depth and position of the antarctic circumpolar trough are substantially more realistic than found in earlier climate models, but the high latitude upper troposphere is still colder than observed giving an excessively strong westerly jet. The sensitivity of the model to changes in the distribution of sea‐ice is investigated and compared with that found in other models. In a first experiment, all southern hemisphere sea‐ice equatorward of 67.5°S was replaced by sea at 271.2 K, and the surface roughness length was reduced from 10 −1 m to 10 −4 m. In a second experiment only the roughness length was changed. It is found that the change in surface roughness contributes substantially to the response to reduced sea‐ice extents. The specification of surface roughness over sea‐ice in numerical models is discussed.