On the theory of the steady perturbations in the troposphere



The linear steady-state response of a hemispheric two-level primitive equation model to forcing by heat sources and by topography is studied. Realistic forcing is considered for January where the zonal variation of the release of latent heat and of the sensible heating dominates the radiational heating. The response to each of these heat sources is discussed and an attempt is made to understand the computed patterns by aid of a simple quasigeostrophic theory. The combined topographical and thermal forcing induces standing waves which verify favourably against observations. At 400 mb, the ridge on the windward side of the Himalayas and the trough over north-eastern Asia appear to be induced by the orography whereas the heat sources play an almost dominant role over North America and determine the position of the ridge over the Atlantic. At 800 mb, the linear model fails to simulate the Aleutean low but is rather satisfactory elsewhere. The northward transport of heat and momentum by the standing waves is discussed.