Relationship between Tropical Heating and Subtropical Westerly Maxima in the Southern Hemisphere during SOP-1, FGGE

Abstract

FGGE Level III-b analyses, produced by the Goddard Laboratory for Atmospheres, NASA, are used to investigate the relationship between tropical heating and subtropical westerly maxima in the Southern Hemisphere during SOP-1 (5 January-4 March 1979). The mean state of two 15-day periods is examined, as well as day-to-day variations for the entire 59-day period. In Period 1 (6?20 January), the central South Pacific was extremely active convectively, while in Period 2 (3?17 February), convective activity over the western Indian Ocean was enhanced. Episodes of strong outflow in the tropics, as measured by the upper tropospheric velocity potential, were found to be well correlated with the strengthening and propagation of westerly wind maxima in the subtropics. The average location of the westerly maximum over the South Pacific and Indian oceans oceans about 16° latitude south, and slightly east, of its corresponding heat source. For a cyclone case study which is presented, however, this distance was considerably less. The response time between the upper level tropical outflow and subtropical westerly enhancement appears to be less than 12 hours; however, an exact temporal scale was difficult to identify.