Impact of observed sea-ice concentration on the Southern Hemisphere extratropical atmospheric circulation in summer

Abstract

The response of the Southern Hemisphere extratropical, atmospheric circulation to extremes of sea-ice concentration in summer is investigated using a fully coupled climate model. Maximum and minimum sea-ice extremes were obtained from satellite-derived data, and a 12-month climatology for each case was created. Two 10-year simulations for each scenario were completed, and the results for the southern summer are compared. At the surface the sea-ice extremes directly affected the temperatures around Antarctica and through these the latitudinal surface temperature and pressure gradients. The midlatitude surface westerlies are weaker in the maximum scenario, while the polar easterlies expand farther north. In the middle troposphere the zonal jet strengthens slightly and shifts equatorward in the maximum scenario. Comparisons of the sea level pressure field and the 500 hPa geopotential height field for the two scenarios show that the leading mode of circulation variability, the Southern Hemisphere Annular Mode, tends toward positive polarity (lower than normal geopotential heights over Antarctica) in the minimum sea-ice scenario. This tendency is associated with local differences in surface pressure gradient and temperature and large scale dynamic responses to extremes of sea-ice concentration. Copyright 2003 by the American Geophysical Union.