Energy transformations in the tropical circulation during the FGGE winter

Abstract

FGGE level-IIIb data produced by the European Centre for Medium Range Weather Forecasts (ECMWF) for the DJF 1978-79 is used to analyse the kinetic energy budget over the global tropical belt. A detailed energetics of the mean and transient fluctuations, in particular, the generation, the exchange between the mean flow and the transients and the dissipation of kinetic energy are estimated for the tropics and compared with the earlier studies. It is found that about 60% of the kinetic energy generated in the tropics is dissipated by the frictional mechanisms and remaining 40% is transported to the middle latitudes of both the hemispheres. The subtropical westerly jet stream of the winter hemisphere plays a dominant role in the process of kinetic energy flux transport. It is observed that the inter-hemispheric exchange of kinetic energy is negligible. Further, the study confirms the fact that the tropical circulation is mainly maintained by the mean flow while in the extra tropics (beyond 30° latitude) the transients are quite important.