In order to expose the radiative-dynamical relationships that govern the SMD-induced instabilities, we develop a theoretical framework that is built on coupled equations for quasigeostrophic potential vorticity, temperature, and SMD mixing ratio. A perturbation analysis yields, for a subcritical, but otherwise arbitrary, zonal-mean background state, analytical expressions for the growth rate and frequency of the AEWs. The expressions are functions of the domain-averaged wave activity, which is generated by the direct radiative effects of the SMD. The wave activity is primarily modulated by the Doppler-shifted phase speed and the background gradients in potential voriticty and SMD.
Using an idealized version of the Weather Research and Forecasting (WRF) model coupled to an interactive dust model, a linear analysis shows, in agreement with the theoretical prediction, that for a subcritical AEJ and background SMD distribution that are consistent with observations, the SMD destabilizes the AEWs and slows their eastward propagation. The SMD-induced growth rates are commensurate with those obtained in previous dust-free studies in which the AEWs grow on AEJs that are supercritical with respect to the threshold for barotropic-baroclinic instability. The clarity of the theoretical framework can serve as a tool for understanding and predicting the effects of SMD aerosols on the linear instability of AEWs in subcritical, zonal-mean AEJs.
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