Moist Baroclinic Instability in the Development of North Pacific and South American Intermediate-Scale Disturbances

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Abstract
The Mak parameterization of latent heat release is discussed using a finite difference version of a quasigeostrophic β-plane model. It is found that his analytical results can be well reproduced with 20-layer vertical resolution. This finite difference version can be used for the study of baroclinic instability of observed (arbitrary) zonal wind and static stability vertical profiles with more realistic heating. This model with Chang profiles of heating is applied to the North Pacific oceanic polar air cyclones studied by Mullen and to an intermediate-scale (inverted) comma cloud system observed over central South America. The principal features of these disturbances are reproduced by the model. Thus, the generation mechanism of polar cyclones and comma cloud disturbances seems to be the baroclinic instability modified by the latent heat release.