Effects of Saharan Dust Aerosols and West African Precipitation on the Energetics of African Easterly Waves

Abstract

Abstract The effects of Saharan dust aerosols and West African precipitation on the seasonally averaged energetics of African easterly waves (AEWs) are examined using the Weather Research and Forecasting Model coupled to an interactive dust model. Four experiments are conducted: a control for the period July–September 2008, and three other experiments in which the dust emissions and precipitation are reduced separately and in combination. An analysis of the total energy shows the relative importance of the dust and precipitation to the seasonally averaged AEW strength and AEW tracks, which straddle the African easterly jet (AEJ). Changes in the dust amount have a larger effect on the strength of the AEWs than changes in the precipitation amount. The north AEW track is more strongly affected by changes in dust, while the south AEW track is more strongly affected by changes in precipitation. An analysis of the energy conversions aids in identifying the relative importance of the wave–mean flow interaction pathways that connect the dust and precipitation fields to the AEJ–AEW system. The analysis shows that the variability of the AEWs is primarily coupled to the dust- and precipitation-modified variability of the AEJ through wave–mean flow interaction. These results are discussed in light of tropical cyclone development over the eastern Atlantic Ocean.