A composite study of African Easterly Waves and tropical cyclogenesis: Do African Easterly Waves matter?

Tropical cyclone activity over the tropical North Atlantic has often been related to changes in the large-scale environment such as variation in North Atlantic SSTs, various phases of ENSO and tropospheric deep wind shear. In such studies the timescales usually considered range from seasonal to multi-decadal. While the focus for numerous earlier studies has been the variability of tropical storms, hurricanes and/or the large scale environment, the variability of the precursor disturbances for these storms has not been discussed as much.

The high-resolution ERA40 dataset has been analyzed for July, August, and September from 1979 through 2001 to generate a climatology of African Easterly Waves (AEWs) leaving the West African coast. By identifying all AEWs that were associated with named tropical cyclones over the main development region (MDR), we obtain a composite view of the structure and characteristics of these AEWs and their large-scale environment. This is compared to the composite of all disturbances that ultimately failed to develop into named tropical storms. It will be shown that there exist substantial differences in structure and characteristics for AEWs that become associated with named tropical cyclones and the ones that aren't associated with any further downstream development.