On the Interaction Between the Zonal Mean Flow and Equatorial Waves Excited by Diabatic Beat Sources at 20° Latitude

Abstract

In the present study a stationary heat source is prescribed to be maximum at 20° latitude, oscillating in time with a period of 15 days and zonal wavenumber 1. The basic equations for excited perturbation waves are the linearized primitive equations in spherical coordinates with a log-pressure system in the vertical. The zonal mean primitive equations are used to predict the time evolution of the mean fields. The numerical integration is done as a marching problem with respect to time for the period from 0 to 30 days. The prescribed heat source excites eastward and downward propagating Kelvin waves in the equatorial stratosphere. The Kelvin mode is a maximum neat 25 km and damps out rapidly above that level. This, in turn, leads to the decay of the upward westerly momentum flux with height, and to a consequent acceleration of the zonal mean westerly wind near 25 km above the equator. The westerly acceleration amounts to about 2 m sec−1 per month.