Satellite‐derived atmospheric characteristics of spiral and comma‐shaped southern hemisphere mesocyclones

Abstract

Mesoscale cyclones in cold airstreams poleward of major frontal zones are generated frequently over the Southern Ocean. Quantitative information regarding the atmospheric water and wind fields of these systems can be retrieved from satellite‐borne microwave instruments. These instruments include the Special Sensor Microwave Imager (SSM/I), the first European Remote Sensing satellite (ERS‐1) scatterometer and the TIROS‐N operational vertical sounder (TOVS). In this study, we summarize the structures found in the SSM/I‐derived integrated water vapor (IWV), cloud liquid water, wind speed, and liquid and solid precipitation fields for 33 Southern Ocean mesolows. We present the ERS‐1 scatterometer surface wind vector fields for nine of these mesolows, and we analyze the TOVS‐derived geopotential thickness fields for one case. This study confirms earlier results and also examines several features not previously investigated in Southern Ocean mesolows. We find that (1) solid precipitation is more prevalent than liquid precipitation in most mesocyclones; (2) the higher‐latitude, smaller‐scale mesolows with spiral‐shaped cloud systems have lower IWV content than comma‐shaped mesolows; and (3) the surface cyclonic circulation of the mesolows is confirmed by the ERS‐1 winds. Surface fluxes of heat and moisture were estimated from European Centre for Medium‐Range Weather Forecasting (ECMWF) gridded fields for two highlighted cases and found to be moderate during the formation of the mesolow that occurred near the Antarctic ice edge and low for a comma cloud case. In addition, TOVS‐derived thickness patterns show that the Antarctic case lacked strong baroclinic structure, whereas comma cloud cases tend to develop in baroclinic environments.