Response of Planetary Waves to Stationary Tropical Heating in a Global Atmosphere with Meridional and Vertical Shear

Abstract

The response of planetary waves to stationary tropical heating in a stratified global atmosphere linearized with respect to a basic zonal mean flow is investigated. The basic zonal wind has meridional and vertical shear. The basic equations are solved by using the method of three-dimensional normal-mode expansion. Forced solutions to a prescribed tropospheric equatorial heating distribution with a specific wavenumber in longitude are examined. Without the basic zonal flow, the internal vertical modes whose equivalent depths are on the order of a few hundred meters are favorably excited, but the response of the external mode (?barotropic? mode) is relatively small. With the inclusion of a zonal flow, the vertical shear of the zonal wind permits the coupling of the external mode with the internal vertical modes. As a result of the coupling, a significant response occurs in the external mode due to the excitation of the ?baroclinic? internal modes by tropical heating. The meridional structures of internal vertical modes are equatorially trapped and their intensities are less affected by the basic zonal flow. Since the meridional structures of the external mode is global, a significant response of the external mode to tropospheric tropical heating is no longer confined to the tropics. The direction of the basic zonal flow and its meridional shear have a profound influence on the intensity of planetary waves in the mid- to higher latitudes generated by stationary tropical heating. The present findings may fill in a missing link in the dynamical theory of atmospheric teleconnections.