Linear evolution of baroclinic waves in saturated air

A primitive-equation model which includes a moisture parametrization that assumes that ascending air is always saturated, has been used to study the characteristics of moist baroclinic waves, exploring their dependence on the Richardson number, besides zonal and meridional wavelength. Growth rates are shown to increase, in consequence of latent-heat release, in a larger measure for the meridionally structured waves than for the two-dimensional ones. Approximate analytic relationships for the normal-modes growth rates, based on the concept of a weighted average of dry and saturated parameters, compare favourably with the numerical results. Asymmetric horizontal structures, previously obtained in quasi-geostrophic approximation, are shown to be consistent with potential-vorticity generation by diabatic heating in the updraught