Sigma-coordinate calculation of topographically forced baroclinicity around Antarctica

A two-layer model of baroclinicity on pressure levels is re-formulated on sigma -levels and its ability to predict observed areas of cyclone intensification from observed time-mean fields is evaluated. Because of the high topography of Antarctica, the implementation of the model on a coordinates is particularly useful around and near the continent, and the results presented here focus on this region. The incipient baroclinic instability predicted by the simple two-layer model agrees well with Sinclair's (Sinclair, M.R., 1995. A climatology of cyclogenesis for the Southern Hemisphere. Mon. Wea. Rev., 123 1601-1619.) results. The model is used to diagnose baroclinicity from the output of a GCM in this region. A series of winter GCM experiments in which the height of Antarctica is changed to varying ratios of its actual value is also examined from the standpoint of the influence of changing topography on baroclinicity in the region surrounding Antarctica. It is found that topography has an important influence on baroclinicity in the oceanic areas around the continent. It is also found that some features of the baroclinicity field near Antarctica are independent of topography, while over the continent itself, the presence of topography strongly suppresses baroclinicity. (C) 2000 Elsevier Science B.V. All rights reserved.