Significance of the South Pacific Convergence Zone (SPCZ) in the Energy Budget of the Southern Hemisphere Tropics

Abstract

A modified set of FGGE Level III-b gridpoint analyses, originally produced by ECMWF, is used to diagnose the eddy energy budgets of four equal-area regions within the tropical Southern Hemisphere (0–30°S) during the SOP-1 period of 10–27 January 1979. Each region is approximately centered on a wave axis of maximum warm, rising air. Three of the four wave axes are tied to the continents of Africa, Australia, and South America, while the fourth coincides extremely well with the South Pacific Convergence Zone (SPCZ). Daily variations of the energy conversions are examined. In addition, time-averaged results of energy contents, conversions and boundary transports are compiled for a 15–day period, 10–24 January, when the, SPCZ was most active. Results show that the eddy kinetic energy (KE) exceeds the eddy available potential energy (AE) in all four regions, with that in the SPCZ being the largest. Of the conversion and boundary flux terms, only the conversion of AE to KE is significant. Again, the region containing the largest value is the SPCZ. The main flow of energy in each region appears to consist of a generation of AE by diabatic heating, a conversion of AE to KE by thermally-direct eddy circulations, and a dissipation of KE. The relationships among the four subareas are investigated, primarily through evaluations of the boundary fluxes of KE. Results indicate that the only significant transport between regions is a flow of KE from the SPCZ region into the South American region. Thus, it appears likely that some of the KE from the SPCZ is helping to maintain the KE of the South American region and, in particular, the South Atlantic Convergence Zone (SACZ). These results seem to be in good agreement with the modeling results produced by the NASA Goddard Laboratory for Atmospheres (GLA) General Circulation Model.