Topographic Wave Modification and the Angular Momentum Balance of the Antarctic Troposphere

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Abstract
A shallow inversion layer with southeasterly outflow and a cyclonic vortex in the troposphere are the basic characteristics of the Antarctic mean circulation. An attempt is made to model this pattern in a two-layer representation of the atmosphere where all equations are averaged horizontally over the Antarctic domain. Cooling at the slope drives a direct circulation that acts as a source of westerly angular momentum. This momentum is transferred out of Antarctica by topographically modified large-scale waves, enforced at the northern boundary of the model. Two types of steady states are found for fixed frequency and zonal wavenumber: one where the wave is quite effective in performing the required momentum transport so that a qualitatively realistic circulation results and another one with strong upper-level westerlies but virtually no surface easterlies. A model climatology can be derived if stochastic forcing is added to the equations. It turns out that the distribution of the flow states is centered near a “realistic” equilibrium if a wave spectrum is prescribed at the northern boundary according to observations.

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