Sigma-coordinate calculation of topographically forced baroclinicity around Antarctica

A two-layer model of baroclinicity on pressure levels is re-formulated on s igma -levels and its ability to predict observed areas of cyclone intensifi cation from observed time-mean fields is evaluated. Because of the high top ography of Antarctica, the implementation of the model on a coordinates is particularly useful around and near the continent, and the results presente d 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 cha nged to varying ratios of its actual value is also examined from the standp oint of the influence of changing topography on baroclinicity in the region surrounding Antarctica. It is found that topography has an important influ ence on baroclinicity in the oceanic areas around the continent. It is also found that some features of the baroclinicity field near Antarctica are in dependent of topography, while over the continent itself, the presence of t opography strongly suppresses baroclinicity. (C) 2000 Elsevier Science B.V. All rights reserved.