SYNOPTIC ASPECTS OF ANTARCTIC MESOCYCLONES

The characteristic regimes (formation and dissipation areas, tracks) and synoptic environments of cold air mesocyclones over Antarctic and Subantarctic latitudes are determined for the contrasting winters (June, July, and August) of 1988 and 1989. Defense Meteorological Satellite Program (DMSP) thermal infrared (IR) imagery is used in conjunction with southern hemisphere pressure/height analyses. Outbreaks of mesocyclones (''active periods'') are frequent in the Ross Sea sector in 1988. They are associated most often with areas of maximum horizontal gradient of the 1000- to 500-mbar thickness. Over higher latitudes of the Southeast Pacific in 1989, mesocyclones develop in association with a ''cold pool'' that migrates equatorward. The between-winter differences in mesocyclone frequencies are examined for associations with sea ice conditions and the continental katabatic winds using correlation and ''superposed epoch'' analysis of temperature data from selected automatic weather stations (AWSs). The results support a katabatic wind-sea ice extent-mesocyclone link for key sectors of the Antarctic.