A New Look to Interactions of Saharan Dust with Waves in the Tropical Atlantic Storm Track

Abstract:

This study addresses mechanisms of the interactions between light-absorbing aerosols and transient atmospheric waves, including their feedback onto the mean-circulation in one of the most meteorologically sensitive areas of the world: the tropical western African/eastern Atlantic Ocean. Evidence of these interactions are presented based on analyses of an ensemble of NASA satellite data sets, including aerosol optical thickness (AOT) observations from the Moderate Resolution Imaging Spectro-radiometer (MODIS) and the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS), as well as an atmospheric reanalysis from the Modern-Era Retrospective Analysis for Research and Applications (MERRA) and a simulation of The Goddard Chemistry Aerosol Radiation and Transport (GOCART) model. We analyzed the components of the rate of change of eddy kinetic energy (EKE) to explore the possible role of dust aerosol radiative forcing on reinforcing energetic terms associated with the African easterly waves (AEWs) during boreal summer seasons when the activity of AEWs peaks. This study shows that the anomalous perturbations in concentration of dust in the oceanic Saharan Air Layer (OSAL) precede amplified growth and decay of the subsequent waves compared to waves occurring prior to dust outbreaks. The amplified EKE associated with dust outbreaks are followed by seeding of new wave packets through enhanced divergence and convergence of ageostrophic geopotential height fluxes in the tropical Atlantic storm track. Meanwhile, the enhanced forcing of the mean-circulation associated with the increased momentum fluxes of the high frequency eddies at the northern track of AEWs occurs with a time-lag after the peak of dust concentration in the OSAL. We suggest that dust radiative heating in the OSAL may act as an additional energy source to amplify the thermal/mechanical activity of eddies in the northern track of the AEWs.