Necessary conditions for the instability of quasigeostrophic waves induced by trace shortwave radiative absorbers

Abstract

Necessary conditions for the radiative-dynamical instability of quasigeostrophic waves induced by trace shortwave radiative absorbers are derived. The analysis pivots on a pseudomomentum conservation equation that is obtained by combining conservation equations for quasigeostrophic potential vorticity, thermodynamic energy, and trace absorber mixing ratio. Under the assumptions that the absorber-induced diabatic heating rate is small and the zonal-mean basic state is hydrodynamically neutral, a perturbation analysis of the pseudomomentum equation yields the conditions for instability. The conditions, which only require knowledge of the zonally-averaged background distributions of wind and absorber, expose the physical processes involved in the destabilization, processes not exposed in previous analytical and modeling studies of trace absorber-induced instabilities. The simplicity of the instability conditions underscores their utility as a tool that is both interpretive and predictive. The conditions for instability, which have broad application to synoptic-scale waves in Earth's and other planetary atmospheres, are discussed in light of previous instability studies involving stratospheric ozone and Saharan mineral dust aerosols.