Thermally Forced Stationary Waves in a Quasigeostrophic System

Abstract

Analytical solutions of thermally forced stationary waves in a linear quasigeostrophic model are obtained. It is found that the zonal flow has a profound impact on the structure of the responses. The inviscid solutions on a resting basic state are the Sverdrup solutions that are confined to the heating region. The solutions on a westerly zonal flow are composed of a local and a vertically propagating part. The local response exists only in the heating region. The vertically propagating response exists in the far field as well as in the heating region. The thermally forced vertically propagating response can be conceptualized as a response to an ?equivalent topography,? the height of which is proportional to the intensity and zonal scale of the heating, and inversely proportional to the strength of the zonal flow. Particular solutions forced by realistic summer heating fields reveal that, for weak westerlies, the height of the equivalent topography is much larger than that of the real topography, suggesting that heating is more important than topography in forcing the summer stationary waves in the subtropics. It is also found that Newtonian cooling has a significant effect on the structure of the thermally forced stationary waves.