Abstract
Numerous budget studies of organized persistent systems of convective clouds outside the tropics suggest that circulations of mesoscale proportions are important in supplying moisture to the convective clouds, though the dynamical nature of mesoscale flows remains poorly defined. In Part I (Emanuel, 1979, hereafter referred to as Part I) it is demonstrated that circulations resulting from symmetric instability of shear flows in rotating fluids have a fundamentally mesoscale character in that both ambient rotation and ageostrophic advection are necessary for instability. The results of Part I are here extended to include the effects of latent heat release in a conditionally unstable atmosphere, using the formalism of the CISK approach. It is found that the presence of shear parallel to the wave fronts introduces new wave-CISK modes which are not strongly dependent on the specified vertical structure of the cumulus heating. The new baroclinic modes are of mesoscale dimensions, have growth rates proportional to the vertical shear of the ambient flow and propagate toward the warm air. These modes compare favorably with observations of squall lines within baroclinic flows.
