Sensitivity of African Easterly Waves to Dust Forcing

There is a lack of consensus regarding the sign and magnitude of the effect of dust-radiative forcing on African easterly waves (AEWs) among past studies. The uncertainty in the dust-radiative forcing associated with the estimation of shortwave absorption is a leading cause of disagreement in the literature. The inability of models to represent various dust-AEW interaction pathways also leads to uncertainty among modeling studies. The present study investigates the sensitivity of AEWs to the observed variability in dust shortwave absorption using a high-resolution atmospheric general circulation model. Global simulations are conducted at a spatial resolution of about 25 km to simulate AEWs and associated circulation features adequately well. The results reveal that AEWs are highly sensitive to dust shortwave absorption. In addition, the AEW activity intensifies and broadens the wave track with a southward shift in response to dust shortwave absorption. Eddy kinetic energy (EKE) associated with AEWs changes by approximately +/- 25% for the range of dust shortwave absorption used. The 6-9 days waves are more sensitive to dust shortwave absorption than the 3-5 days waves, with the response in the former exhibiting a stark land-sea contrast. The sensitivity of AEWs to dust heating stems from a combination of the responses from various energy conversions. Although baroclinic energy conversion is the dominant term in the energy cycle, the responses to dust shortwave heating in barotropic and generation terms are comparable to those in baroclinic conversion.