Climatology of the “Instant Occlusion” Phenomenon for the Southern Hemisphere Winter

Abstract

A five-winter satellite study of the ?instant occlusion" mode of extratropical cyclogenesis has been undertaken for the Southern Hemisphere oceans. The phenomenon shows a maximum frequency of occurrence over latitudes 30?55°S, where it is closely associated with the locations of the winter ?climatic fronts? The longitudes of Australasia and the eastern Indian Ocean are particularly favored for "instant occlusion? developments. Month-to-month variations in the frequency of their occurrence are relatedtothebemispheric-scale changes in total cyclonic vortex activity observed during the winter season.