Unstable Radiative-Dynamical Interactions. Part II: Expanded Theory

Abstract

The basic theory of unstable radiative-dynamical interactions developed in a companion paid is extended to account for several complicating effects. Treating the effect of absorber perturbations on the shortwave radiative heating rate at all levels, rather than simply locally, is shown to either enhance or suppress the radiative-dynamical instability, depending on the perturbation vertical wavelength. Dissipative processes generally reduce or eliminate the instability, although in one case mechanical dissipation can actually enhance the instability. Vertical shear generally suppresses the instability for radiative-dynamical feedback rates greater than the adiabatic growth rate associated with baroclinic instability, and enhances the instability for feedback rates less than the adiabatic growth rate. The radiative-dynamical interaction generally increases the growth ate beyond that associated with baroclinic instability, but the growth rate never exceeds the sum of the feedback rate and the adiabatic growth rate. Scattering of sunlight by the radiative constituent can either suppress or enhance the instability, depending particularly on the solar zenith angle. The effect of vertical variations in the radiative-dynamical feedback parameter is also assessed.