The African Easterly Jet: Structure and Effect on Easterly Wave Development

The African Easterly Jet (AEJ) and African Eastern Waves (AEWs) within the Sahel region of Africa are major features driving atmospheric circulation and play a major role in the development of the West African Monsoon. On a regional scale, instability associated with the AEJ determines AEW development. Most tropical cyclones originate as AEWs in August and September. It has been observed in a previous study that in the month of August, the AEJ possesses two distinct cores (double core), different from the general picture of the AEJ, which may affect how AEWs develop. The goal of this study is to determine if the presence of a double AEJ core structure has an effect on AEWs. Comparisons between zonal wind structures and the corresponding wave activity for different cases can provide valuable insight into the relationship between the AEJ, easterly waves and rainfall variability over the Sahel as well as tropical cyclogenesis at the West African coast. Zonal and meridional wind data measured at 600 hPa was obtained from NCEP-NCAR reanalysis during the month of August when the AEJ has a peak intensity. The years where the double core structure was apparent were counted. Additionally, Hovmoller diagrams of the meridional wind were constructed for the years where the double core structure was apparent to determine AEW track and lifespan. Preliminary results showed that out of 69 years in the dataset, 34 years showed the double core structure. Comparison of years with one core and years with two cores indicate stronger AEW activity off the West African coast when a double core structure is present. The differences in AEW activity with the AEJ changes provide a better understanding of the link between them and how rainfall and storm development are affected.