Indices of the mean monthly surface circulation over the southern hemisphere during FGGE

Monthly indices of the southern hemisphere surface circulation are derived from the operational analyses of the Australian Bureau of Meteorology during FGGE, and are compared with similarly derived data for the period 1972-1977. The FGGE period exhibits an annual average zonal westerly circulation between 40°5 and 60°5 some 18 per cent higher than that of the five-year period. Although this may reflect in part the greater number of pressure observations from the buoy network, it is also found that the winter westerly maximum results in an anomalous annual cycle in comparison to long-term independent station data. The FGGE winter was marked by a substantial southward movement of the axis of subtropical high pressure and an expansion of the area of the subtropical highs particularly at eastern longitudes. In June some anomalies in the longitudes of high pressure centres were evident over the Atlantic and Indian Oceans. Longitudes of relatively high and low pressure on the Antarctic trough also differed from the five-year period over the southeast Pacific and Weddell Sea areas but these differences may be related to poorer analyses in the earlier years.