Convectively Coupled Kelvin Waves and Their Interactions with African Easterly Waves

Despite past research, the interactions between convectively coupled Kelvin waves (CCKWs) and African easterly waves (AEWs) are still poorly understood. Here, AEW-CCKW interactions and their impacts on tropical cyclone (TC) formation are explored in detail. First, a 39-year climatology of AEW-CCKW interactions is investigated using reanalysis and satellite data. These interactions are common, with over 70% of AEWs encountering at least one CCKW in their lifetime. CCKWs are shown to modify the characteristics and behavior of AEWs, and statistics from this climatology reaffirm the relationship between CCKWs and TC genesis. Next, the climatology of AEW-CCKW interactions is evaluated in the context of TC formation (“genesis”) processes. It is argued that convectively active CCKWs encourage TC genesis through the enhancement of column moisture and cloud-radiative feedbacks in AEWs. The magnitude of convective activity is found to be the main discriminator of AEW–CCKW interactions that result in TC genesis. A set of global simulations is then produced for a time period in which several CCKWs coexisted around the globe. In these experiments, the amplitudes of CCKWs are modified at model initialization. This method is effective at robustly changing the strength and structure of simulated CCKWs and can make their convective coupling easier to identify. However, these experiments fail to simulate convective coupling in a strong Atlantic CCKW, only capturing the wave’s upper-level winds. The cause of this failure is unclear and motivates additional work into the predictability of CCKW events. Finally, the AEW-CCKW interaction associated with Tropical Storm Victor’s (2021) genesis is investigated in these MPAS-A simulations. Differences in the vertical wind shear encountered by the pre-Victor AEW, as well as the AEW’s initial strength and moisture, are directly attributable to the Atlantic CCKW. These results demonstrate that a CCKW’s upper-level winds could impact AEW growth and TC genesis through changes to environmental wind shear, convection, and moisture.