Satellite-Derived Integrated Water Vapor and Rain Intensity Patterns: Indicators for Rapid Cyclogenesis

Abstract

Rapidly deepening cyclones in midlatitudes are characterized by large cloud shields and abundant condensation qualitatively evident in infrared and visible satellite images. With the availability of passive microwave 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, fields of integrated water vapor, integrated water vapor anomaly (defined as the observed water vapor content minus the monthly mean water vapor content at the particular location), and rainfall intensity index derived from the Special Sensor Microwave Imager (SSM/I) on the F-8 satellite of the Defense Meteorological Satellite Program are examined for 12 North Atlantic rapidly deepening and 11 North Atlantic non-rapidly deepening storms that occurred during the 1988 and 1989 winter months. By correlating concurrent 6-h deepening rates with the satellite-derived parameters for a region within 550 km of the surface low pressure center, signatures of rapid cyclogenesis are identified in the SSM/I fields. Maximum water vapor anomaly and average precipitation index have 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 indicate that, although most rapidly deepening cyclones have high water vapor anomaly and stronger precipitation index than non-rapidly deepening cyclones, there are storms that deepen rapidly in the absence of high water vapor anomaly or heavy precipitation. In addition, occasionally there are storms that have exceptionally high water vapor anomalies yet do not deepen rapidly. In these unusual cases, it is suggested that atmospheric water vapor and condensation play a secondary role and that dynamical processes are dominant.