SATELLITE-DERIVED INTEGRATED WATER-VAPOR AND RAIN INTENSITY PATTERNS - INDICATORS FOR RAPID CYCLOGENESIS

Rapidly deepening cyclones in midlatitudes are characterized by large cloud shields and abundant condensation qualitatively evident in infra red and visible satellite images. With the availability of passive mic rowave measurements from polar-orbiting satellites, it is now possible to characterize rapidly deepening cyclones quantitatively in terms of integrated water vapor and precipitation intensity. In this study, fi elds of integrated water vapor, integrated water vapor anomaly (define d as the observed water vapor content minus the monthly mean water vap or content at the particular location), and rainfall intensity index d erived from the Special Sensor Microwave Imager (SSM/I) on the F-8 sat ellite of the Defense Meteorological Satellite Program are examined fo r 12 North Atlantic rapidly deepening and 11 North Atlantic non-rapidl y deepening storms that occurred during the 1988 and 1989 winter month s. By correlating concurrent 6-h deepening rates with the satellite-de rived parameters for a region within 550 km of the surface low pressur e center, signatures of rapid cyclogenesis are identified in the SSM/I fields. Maximum water vapor anomaly and average precipitation index h ave correlations with concurrent 6-h deepening rates of 0.56 and 0.55, respectively. The correlations improve dramatically when two outliers are removed, becoming 0.68 and 0.70, respectively. These results indi cate that, although most rapidly deepening cyclones have high water va por anomaly and stronger precipitation index than non-rapidly deepenin g cyclones, there are storms that deepen rapidly in the absense of hig h water vapor anomaly or heavy precipitation. In addition, occasionall y there are storms that have exceptionally high water vapor anomalies yet do not deepen rapidly. In these unusual cases, it is suggested tha t atmospheric water vapor and condensation play a secondary role and t hat dynamical processes are dominant.