A Case Study of Explosive Subsynoptic-Scale Cyclogenesis

Abstract

The continental cyclone of 28?29 March 1984 was noteworthy for its explosive intensification within six hours. Surface and upper-air data are analyzed for this storm throughout its 18-h life cycle of growth and decay over the eastern United States. The short time scale of this low's explosive development motivates us to place particular emphasis upon the hourly surface observations and their relationship to the rapid cyclogenesis. While the synoptic-scale environment of the cyclogenesis consisted of quasi-geostrophic ascent, surface data reveal that the intersection of a heated moist tongue of air and an intensifying cold front was the approximate location of the initial vortex. The surface-based lifted index over the incipient cyclone was about ?8°C. Static stability had decreased steadily prior to the cyclogenesis. Frontogenctic forcing and deep convection followed the surface cyclone for the next four hours of explosive deepening. Filling of the cyclone occurred as the surface frontogenetic forcing eased, and the convection was displaced from the cyclone's center. The second pulse of explosive deepening ensued as an axis of maximum 500-mb cyclonic vorticity advection passed over the surface low. This study shows that several physical processes, of differing scales, combine synergistically to effect this rare case of explosive land cyclogenesis.