Ice-ocean-atmosphere interactions at high southern latitudes in winter from satellite observation

Abstract

A satellite-derived index of cyclonic activity is used to evaluate the relationship between the middle and higher latitude atmospheric circulation and the Antarctic sea ice regime in winter. The mean month-to-month variations in the latitude band of maximum depression frequency reflect the semi-annual oscillation of surface pressures, and show little dependence on the seasonal expansion of the pack ice zone. However, marked interannual variations in cyclonic activity reveal close ice-ocean-atmosphere feedbacks operating at the synoptic scale for certain high latitude regions. Increases between winters in the frequencies of cyclones entering the cireumpolar trough serve to promote ice advances in some longitudes, mainly through enhancement of ice advection processes, while retarding expansion in other sectors. Important surface-atmosphere feedbacks are evident for ice-extent variations in the Weddell Sea sector, as given by the frequencies of cyclones occurring at the ice edge. The interannual variation in the position of the ice margin for the South Pacificinfluences the dominant latitude zone for cyclogenesis. Similarly, a large open-water polynya in the Weddell Sea is found to increase substantially theincidence of high-latitude cyclogenesis for those winters in which it is present. It is implied that the occurrence and persistence of such areas of low ice concentration are crucial for estimates of the tetal energy budget within the seasonal sea ice zone and the possibly marked effects of interannual variations in ice extent and concentration upon those estimates.