A CLIMATOLOGY OF SOUTHERN-HEMISPHERE ANTICYCLONES

A climatology of anticyclones generated by an objective automatic sche me applied to 15 years of once-daily Australian Bureau of Meteorology hemispheric analyses is presented. Contour maps of the anticyclone sys tem density, positions of formation and dissipation together with othe r statistics are shown. The distribution of anticyclones through the h emisphere was found to be dominated by a mid latitude belt of high den sity, located in the band 25-42-degrees-S, typically 2-4-degrees south of the time-mean subtropical ridge. Within this band the anticyclone density displays considerable structure with greater system numbers ov er the eastern parts of the three subtropical ocean basins in the vici nity of the three subtropical ocean time-mean anticyclones. During win ter the system density displays a bifurcation in the New Zealand secto r, with the highest density along the 30 and 45-degrees-S latitude ban ds. The movement of systems in the subtropical ocean basins was found to be in a general easterly direction with a weak equatorwards compone nt, the transport of systems closely following the orientation of the belt of highest system density. In the vicinity of the African and Sou th American continents, movement was more complex with east-south-east motion upstream, and east-north-east movement downstream, the net tra nsport being such as to encourage a general steering of systems around the continental land masses more particularly during the warmer seaso ns. To highlight the dynamic role played by these systems and their cy clonic counterparts, we present a limited investigation of the respons e of Southern Hemisphere synoptic systems to variations of the broader atmospheric system and compare these findings to those obtained by mo re traditional analysis techniques.