Mid-Season Average Zonal Winds at Sea Level and at 500 mb South of 25 Degrees South, and a Brief Comparison with the Northern Hemisphere

Abstract

Meridional profiles of sea-level and 500-mb average zonal winds at mid-season in both hemispheres are presented and described. Over much of the southern hemisphere the mean zonal westerly flow changes little during the year, and in each season it is always stronger for the hemisphere as a whole in the southern than in the northern hemisphere. The southern hemisphere circulation and its seasonal changes are shown to be closely related to the surface temperature distribution. It is pointed out that despite the seemingly symmetrical distribution of heat and cold sources over the southern hemisphere, regional differences in the strength and distribution of the mean zonal wind do exist, particularly during the colder part of the year. Thus, although on the whole there is a strong control arising from the ocenic dominance of the hemisphere, there are, especially in the Australian sector, large disturbances connected with continental influences on heating and cooling. The strongest zonal westerly mean circulation in the southern hemisphere at the levels dealt with here is found over the Indian Ocean.