The effect on southern hemisphere circulation and Antarctic coastal climate of changing baroclinicity

Long time-series of station surface observations at a number of Antarctic coastal sites have been analysed. These series indicate changes in the mean climate and in frequencies of extreme weather that suggest that these are responses to large-scale circulation changes. Alterations to the numbers and intensities of extra-tropical cyclones may explain these climate changes and the different influences on local weather at sites depending on local topography. We propose that changes to the tropospheric meridional temperature gradient between Antarctica and the oceans to the north may be responsible.

To investigate, we have performed sensitivity experiments with the Arpege 1 general circulation model. The temperature at 500 hPa and 50 degrees south has been nudged so as to increase and decrease the meridional temperature gradient in two different experiments so as to examine the response of the atmospheric circulation. The resulting changes in the behaviour of extra-tropical cyclones have been investigated through the use of a sophisticated cyclone-tracking scheme, and are seen to be different for the two scenarios. The most significant differences in the circulation changes are seen in the Ross Sea and the Antarctic peninsula regions. These circulation changes and their relation to the observed climate changes on the Antarctic coast are discussed.