Aerosol Radiative Forcing and Interactions with Atmospheric Wave Activity

Aerosols induce significant modifications to atmospheric circulation patterns, the hydrological cycle, cloud properties, and the climate system in general. However, many of the physical and dynamical processes involved in these multi-scale interactions are still poorly understood and not well represented in global climate models. This study provides more insight into mechanisms involved in aerosol-climate interactions. Roughly 70% of the baroclinic instability over the eastern tropical Atlantic Ocean and western African monsoon (WAM) region is related to ultra-high to high-pass filtered African easterly waves (AEWs). The amplitude of these waves, which exhibit 2 to 7 day and 5 to 11 day variability and are present along the southern and northern sides of the African easterly jet (AEJ) respectively, are increased during Saharan dust outbreak events. Evidence of this relationship is presented based on analysis 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 global aerosol distributions made with the Goddard Earth Observing System Model version 5 (GEOS-5) Earth system model with meteorology constrained by MERRA and an assimilation of MODIS AOT (MERRAero). We propose that aerosol radiative forcing may act as an additional energy source to fuel the thermal/mechanical activity of eddies in the AEJ-AEW system.