Inaugural address. Stationary aspects of the tropical general circulation.

Abstract

At first, the mean summer circulation is surveyed for three meteorological regimes near the surface and at 200 mb: the Atlantic trade, the Pacific trade and the Asiatic monsoon. There is a complete inversion of atmospheric structure comparing the trades with the monsoon. In the trades the lower winds are steady and diverging; at 200-mb high cyclonic vorticity along narrow shearlines with convergence is found. The air is cold relative to the surroundings in these shearlines. Frequently the flow is quite unsteady, with large or small cyclonic vortices travelling west along the shear line. The monsoon has the same structure, inverted. Here the steady easterlies with divergent anticyclonic flow are found in the high troposphere above the well known monsoon or equatorial low pressure trough with strong cyclonic shear and moving disturbances. Temperatures in the trough are very high, especially in the upper troposphere. Computations are performed to determine whether the stationary part of trade and monsoon regimes can provide for balance of heat, moisture and kinetic energy. It is found that this is the case and that unsteady flow features or forcing from extra tropical latitude~ need not be invoked to maintain the tropical summer circulation systems. In particular, the efficiency of conversion of latent heat release to production of kinetic energy by the mean circulation is found to be 2.5 per cent, about the same as computed for conversion of potential to kinetic energy in extratropical disturbances.