A CLIMATOLOGY OF SOUTHERN-HEMISPHERE EXTRATROPICAL CYCLONES

A climatology of extratropical cyclones determined by an objective automatic scheme applied to 15 years (1975-89) of once-daily Australian Bureau of Meteorology hemispheric analyses is presented. Contour maps of the positions of formation (cyclogenesis), dissipation (cyclolysis) together with other cyclone statistics are presented. The distribution of cyclones through the hemisphere was found to be dominated by a permanent high latitude core coincident with the circumpolar trough. During the winter and intermediate seasons, two mid latitude branches are evident in the cyclone density originating in the Tasman Sea and South American sectors, both spiraling poleward and merging with the circumpolar core in the Southern Oceans. Systems were observed to move in an east-south-east direction, away from their location of formation, exhibiting peak speeds of migration in the mid latitudes. Little seasonality was evident in the density distribution of cyclones through the Southern Oceans, but a considerable amount was found in their central pressure.