Radiative Effects of Saharan Mineral Dust on the Linear Dynamics of African Easterly Waves in the Weather Research and Forecasting Tracer Model

The Weather Research and Forecasting Tracer (WRFT) model is used to examine the radiative effects of Saharan mineral dust aerosols on the linear dynamics of African easterly waves (AEWs). The WRFT model is governed by the Advanced Research WRF (ARW) dynamical core, and continuity equations for twelve dust particle sizes that represent the spectrum of mineral dust aerosols observed in the atmosphere. Choosing idealized zonal-mean distributions of zonal wind and dust that are consistent with observations, linear simulations are carried out that show the effects of dust-radiative feedbacks on the intrinsic properties of AEWs. These properties, which include growth rate, group velocity, and instantaneous fluxes of heat, momentum, and dust, are examined in light of different concentrations, locations and spatial distributions of the dust field. Among the questions to be addressed are the following: To what extent are the intrinsic properties of the AEWs modified by dust? What is the relative importance of meridional versus vertical dust transport on the dust-radiative heating and its feedback on the AEWs? Can dust-radiative feedbacks affect the formation and location of critical latitudes? Are there certain dust distributions that foster AEW development? And how do the dust-modified AEW fluxes feedback on the AEJ to affect its structure? Answers to these questions will aid in the understanding and forecasting of AEWs and their possible subsequent development into tropical storms.