The Effect of Saharan Mineral Dust Aerosols on the Inter-Annual Variability of the Strength of African Easterly Waves

African easterly waves (AEWs) are a signature feature of the summertime circulation over North Africa. AEWs not only affect regional meteorology, but they can also serve as seed disturbances for the development of tropical cyclones over the Eastern Atlantic Ocean. In this study, we examine the radiative effects of Saharan mineral dust (SMD) aerosols on the strength of AEWs. To do so, we use the Weather Research and Forecasting model coupled to an interactive dust model. Two experiments are conducted for each of ten summers, which span 2006-2015. One class of experiments includes dust-radiative effects and the other does not. ECMWF reanalysis data is used to initialize each experiment; the model is then integrated forward in time for three months, July-September. Seasonal averages are calculated and compared, which yields information on the effects of SMD on the inter-annual variability of the strength of AEWs. We measure the AEW strength via two complementary approaches. The first approach involves an energetics analysis, whereas the second approach involves analysis of the mean potential vorticity (PV). For the latter analysis, we introduce a strength parameter that corresponds to an upper bound on the AEW growth rate. The strength parameter is a function two background flow features: (1) the meridional gradient of the mean PV and (2) the mean wind along the African easterly jet axis. Our calculations show that the strength parameter increases with SMD, which is indicative of stronger AEWs. We compare these results across the ten summers and discuss how the inter-annual variability of SMD affects the inter-annual variability of AEW strength.