An Investigation of Explosively Deepening Oceanic Cyclones

Abstract

The explosively deepening oceanic cyclone or ?bomb,? one which has central pressure falls of 12 mb (12 h)?1 or greater, has been studied using composites constructed from North Atlantic and Pacific weather ship rawinsonde data during the period October 1965 to May 1974, June through September excluded. The composites revealed that the oceanic bomb evolved in a low-level baroclinic environment where the incipient circulation was confined to the lower troposphere. The cyclone subsequently developed into a deep vortex characterized by strong baroclinicity, strong low and midlevel ascent to the north and east of the cyclone, and lower tropospheric conditional instability found near and to the southeast of the cyclone center. A case study of a very intense cyclone that passed near ship 4YP revealed deep layers of conditional instability near the low center. It appears that explosively deepening cyclones are baroclinic phenomena whose development may be enhanced in some cases by the bulk effects of cumulus convention.