A Generalization of Gill's Heat-Induced Tropical Circulation

Abstract

In this note, the local solution of Gill for the symmetric and the antisymmetric heat sources and sinks is extended to the entire global tropical belt by the authors. The symmetric and antisymmetric heating forced solutions of the motion field derived from the linearized shallow-water equations describe many aspects of the winter and the summer monsoon circulations. The extension, provided here, describes the response of tropical circulation to the global tropical heat sources and sinks retrieved from a satellite-based field of the outgoing longwave radiation through regression algorithms. Such a prescribed field is expanded into a low-order set of trigonometric functions in the zonal direction and parabolic cylinder functions along the meridional coordinate. Upon sequential substitution of these modes into the linearized shallow-water equations on a beta plane, it is possible to solve for the heating forced solutions in a closed analytical form for the entire Tropics. The solutions exhibit most of the climatological features of the wintertime and the summertime circulations of the lower troposphere, such as the trades of the two hemispheres and the Asian monsoon with its elements; for example, monsoon trough, cross-equatorial flows, southwest monsoon current, Mascarene high, and the subtropical anti-cyclones. Furthermore, the solutions also describe features such as the heat lows over Arabia, the Sahara, and Mexico. Overall, these solutions confirm the importance of diabatic heat sources and sinks in the shaping of the tropical climate.