Barotropic Scale Interactions in the Tropical Upper Troposphere During the Northern Summer

Abstract

A semi-spectral numerical model is used to investigate the nonlinear interactions between quasi-stationary long waves and transient synoptic waves in the tropical upper troposphere. Results from a long-term integration of this model show that nonlinear barotropic energy exchange between large-scale quasi-stationary forced waves and transient synoptic-scale waves is important in producing several features of the tropical upper tropospheric general circulation. In particular, the development of the small-scale waves and vortices often present in the mid-oceanic troughs and the disturbances observed by Krishnamurti which form along the easterly jet over the Indian Ocean is shown to be due to scale interactions involving short-term nonlinear barotropic instability. This nonlinear transfer of energy to smaller scales of motion acts as a damping mechanism to the large-scale forced circulation.