ON MOIST QUASI-GEOSTROPHIC BAROCLINIC INSTABILITY IN A GENERAL MODEL

Abstract

This analysis investigates the roles of the beta-effect, the static stability profile, the heating profile and the basic baroclinie shear in the process of moist quasi-geostrophic baroclinic instability. The condensational heating is parameterized in terms of the vorticity field of the baroclinic wave itself on the basis of the postulate that the feedback upon the heating is due to the moisture convergence associated with the baroclinically induced low level vertical velocity. As in the case β=0, the growth rate of the unstable modes, with the β-effect included, first increases rapidly with the heating intensity parameter e. The preferred wavelength is also reduced to that of an intermdeiate scale for representative parametric heating conditions. It is found that the β-effect is a weak stabilizing factor when e is small or moderate. For the case of a basic westerly shear, β becomes a progressively stronger stabilizing factor as e is large. But for the case of a basic easterly shear, β becomes a weakly destabilizing factor when e is large. The effect of the static stability profile and that of the heating profile are found to be interdependent. Moist baroclinically unstable process would be most efficient if the heating is relatively stronger at the lower levels where the static stability in pressure coordinate is typically smaller.