Aspects of the Year-to-Year Variation of Seasonal and Monthly Mean Station Temperature over the Southern Hemisphere

Abstract

An analysis is made of the geographical variations in the magnitude of, and the relation between, the ranges of monthly and seasonal mean temperatures for longer established stations over the Southern Hemisphere from the beginning of observations in the mid-nineteenth century to 1970. The latitude of maximum variation between the same seasons of different years varies with the region; but over the lower latitude continents it occurs, in general, equatorward of the subtropical anticyclones. An extreme variation exists in winter at islands on the fringe of the pack ice zone of the Weddell Sea. The temporal frequency of occurrence of maximum and minimum seasonal temperatures over the past century displays considerable regional differences and no clear hemispheric trends are apparent; however, some evidence exists of fewer extreme warm seasons after 1950 over Australasia and Africa in summer. Differing circulation patterns associated with extremes of temperature in winter months over the pack ice zone in the southwest Atlantic, over southern Africa and over the Australian region are described primarily using sequences of indices of zonal and meridional flow. Some indication is given of the accuracy that would be required in a numerical prognosis of monthly mean pressure field over the hemisphere to permit inferences to regional anomalies of mean temperature.