Potential vorticity structure and evolution in African Easterly Waves

African easterly waves (AEWs) have been identified as precursors to approximately half of the tropical cyclogenesis events in the Atlantic basin. While many of these waves traverse the Atlantic basin with little or no development, only a subset of them evolves into tropical cyclones. In this study, a composite of the potential vorticity (PV) associated with these waves is constructed to diagnose the following: the salient balanced characteristics of these disturbances, the extent to which AEWs are indeed waves (as opposed to coherent vortical structures), the longevity of AEWs, and the characteristic changes in the larger-scale flow preceding the intensification of AEWs into tropical cyclones.

AEWs are identified and tracked using ECMWF global analyses in conjunction with NHC determined positions. Composites of AEWs are binned according to geography and growth characteristics. For those waves which develop, a composite evolution is constructed.