17 January 2018

The Response of Atlantic Tropical Cyclones to Suppression of African Easterly Waves

Understanding the physical mechanisms that drive variability and change in Atlantic hurricanes


We discovered that Atlantic tropical cyclones (TCs) are not limited by their typical precursor, African easterly waves (AEWs), on seasonal-climate time scales. TCs will generate by other mechanisms in the absence of AEWs.


This research suggests that AEW activity is not a reliable predictor of variability and change in basin-wide Atlantic TC frequency. This work paves the way to investigate how AEWs influence the spatial statistics of TC landfall.


Atlantic tropical cyclone (TC) genesis is strongly linked with African easterly waves (AEWs) on the weather time scale. However, the TC-AEW relationship is unclear on interannual to climate time scales, and it is unknown whether AEWs are necessary to maintain climatological TC frequency, that is, whether TCs are limited by AEWs. We investigated the impact of AEW suppression on seasonal Atlantic TC activity using a 10-member ensemble of regional climate model simulations in which AEWs were either prescribed or removed through the lateral boundary condition. The climate model experiments produced no significant change in seasonal Atlantic TC number, indicating that AEWs are not necessary to maintain climatological basin-wide TC frequency even though TCs readily originate from these types of disturbances. This suggests that the specific type of “seedling” disturbance is unimportant for determining basin-wide seasonal Atlantic TC number, and that in the absence of AEWs, TCs will generate by other mechanisms. The results imply that changes in the presence of AEWs may not be reliable predictors of seasonal variability and future change in Atlantic TC frequency.

William D. Collins
Lawrence Berkeley National Laboratory
Chang, P. "The Response of Atlantic Tropical Cyclones to Suppression of African Easterly Waves." Geophysical Research Letters (2017). [10.1002/2017gl076081].