SATELLITE-DERIVED ATMOSPHERIC CHARACTERISTICS OF SPIRAL AND COMMA-SHAPED SOUTHERN-HEMISPHERE MESOCYCLONES

Mesoscale cyclones in cold airstreams poleward of major frontal zones are generated frequently over the Southern Ocean. Quantitative informa tion regarding the atmospheric water and wind fields of these systems can be retrieved from satellite-borne microwave instruments. These ins truments include the Special Sensor Microwave Imager (SSM/I), the firs t European Remote Sensing satellite (ERS-1) scatterometer and the TIRO S-N operational vertical sounder (TOVS). In this study, we summarize t he structures found in the SSM/I-derived integrated water vapor (IWV), cloud liquid water, wind speed, and liquid and solid precipitation fi elds for 33 Southern Ocean mesolows. We present the ERS-1 scatteromete r surface wind vector fields for nine of these mesolows, and we analyz e the TOVS-derived geopotential thickness fields for one case. This st udy confirms earlier results and also examines several features not pr eviously investigated in Southern Ocean mesolows. We find that (1) sol id precipitation is more prevalent than liquid precipitation in most m esocyclones; (2) the higher-latitude, smaller-scale mesolows with spir al-shaped cloud systems have lower IWV content than comma-shaped mesol ows; and (3) the surface cyclonic circulation of the mesolows is confi rmed by the ERS-1 winds. Surface fluxes of heat and moisture were esti mated from European Centre for Medium-Range Weather Forecasting (ECMWF ) gridded fields for two highlighted cases and found to be moderate du ring the formation of the mesolow that occurred near the Antarctic ice edge and low for a comma cloud case. fn addition, TOVS-derived thickn ess patterns show that the Antarctic case lacked strong baroclinic str ucture, whereas comma cloud cases tend to develop in baroclinic enviro nments.