Topographic Effects on the Mean Tropospheric Flow Patterns around Antarctica

Abstract

Topographically induced flows around Antarctica in a rotating tank experiment with both homogeneous and stratified fluid are analyzed and compared with the mean tropospheric circulation. A circular tank of fluid was brought to a state of near-rigid clockwise rotation, and a topographic model of the Antarctic continent was then rotated counterclockwise to simulate a mean westerly zonal wind. Stratification was chosen to give the same ratios of topographic and dynamical length scales as in the atmosphere, as was the Rossby number based on the ratio of rotation rates. After the onset of the relative rotation of the Antarctic model, cyclonic eddies evolved in the coastal areas with, in the homogeneous case, anticyclonic eddies over the Antarctic dome. After about ten tank rotation periods, a dominant wavenumber 3 structure with cyclonic eddies in the Ross and Weddell seas and Prydz Bay is observed as an approximately steady state. Flow over the topography is relatively stagnant, with weak anticyclonic circulation. Variation of the Rossby number by a factor of 4 about the mean atmospheric value showed that the same general behavior was obtained, although there were differences in detail. These flows show remarkable similarity to the observed mean 700 mb height and 850 rob wind fields around Antarctica. This strongly suggests that the same dynamical factors are operating, namely conservation of potential vorticity and strong coupling in the vertical, so that these motions are virtually baratropic. The large cyclonic eddies am then forced by flow separation around prominent coastal irregularities such as the Antarctic Peninsula.