On a steady state theory of global monsoons

Abstract

Steady-state solutions of the quasi-geostrophic perturbation equations are obtained for the forced response of the atmosphere to a parameterized form of heating which is proportional to the difference between the mean lowlevel air temperature and the prescribed ground surface temperature. The solutions, obtained as a sum of spherical harmonic components, are shown to be sensitive to the form of the vertical variation of the heating, as well as to the horizontal scale. This is due to the possibility for a “matching” of the vertical variation of the internal forcing with the vertical variation of the solution for the “quasi-resonant” horizontal mode. For a particular vertical variation of the heating which is removed from this point of magnified quasi-resonance, the composite solutions up to the 15th degree, for January and July conditions in the Northern Hemisphere, show a fair amount of agreement with observed normal maps. The main errors are a tendency for the computed features to be displaced to the east of the observations at both upper and lower levels, and an overly weak response over Asia and the Pacific. Some possibilities for improving the model are discussed.