Steady and Transient Waves Excited by Diabatic Heat Sources During the Summer Monsoon

Abstract

In the present study a steady heat source is prescribed to be maximum at 28N and 100E, while a transient heat source specified at 20N oscillates in time with a period of 16 days and zonal wavenumbers 1 to 3. The basic equations for excited wave perturbations are the primitive equations in spherical coordinates with a log-pressure system in the vertical. We apply them over a region extending from 48S to 64N. The basic nonlinear equations are separated into two parts, one for 16-day time mean motions and another for transient wave perturbations. The numerical integration is done as a marching problem with respect to time for the period from 0 to 48 days, at which time the 16-day mean motions are almost independent of time (steady) and transient waves change nearly periodically in time. The steady wave perturbations are characterized by a pronounced anticyclonic circulation centering at about 15 km near 80E and 32N, accompanied by strong easterlies prevailing to its south. They transport wave energy southward across the equator, but carry westerly momentum from the winter to the summer hemispheres. The transient wave perturbations exhibit a great similarity in their structural features to the 16-day filtered wind fluctuations observed in the monsoon region.