Southern Hemisphere Summer Monsoon Circulation during the 1978-79 WMONEX

Part I: Monthly Mean Wind Fieldsi1

Abstract

Some of the characteristic features of the Southern Hemisphere summer monsoon were investigated by using twice-daily, objectively analyzed wind data at 850 and 200mb for December 1978 to February 1979, over an expanded WMONEX region (90°E-140°W, 30°N-30°S).
In January, the extent of the Southern Hemisphere monsoon is probably denoted by a zone of strong 850mb equatorial westerlies that extends along about 10°S from the northeastern Indian Ocean (100°E), across the Indonesian Seas and New Guinea, to the western South Pacific (180°). The eastern end of the Southern Hemisphere monsoon trough is characterized by a major low-level (850mb) convergent center and an upper-level (200mb) anticyclonic system associated with pronounced divergence.
In the immediate vicinity of the Southern Hemisphere monsoon trough (15°S), the divergence effect was the main factor in low-level disturbance development. Conversely, between the equator and 10°S, disturbances developed by receiving vorticity from the zonal mean flow via barotropic nonlinear interactions.