How low-frequency Equatorial Kelvin Wave activity and local coastal winds modulate the south-eastern interannual Atlantic variability?

Several studies suggest that the mean atmospheric and oceanic features in south-eastern Atlantic have experienced changes over the last few decades with, in particular, a shift in the mean position of the Saint Helena Hight Anticyclone and an increase in the mean ocean stratification. Modification of the wind forcing and the mean state at the equator and along the south-western coast of Africa will most likely impact the characteristics of the eastward propagating interannual Equatorial Kelvin Waves (EKW) and subsequent Coastal Trapped Waves (CTW) in the south-eastern Atlantic. These changes will also affect the interannual variability in the Benguela Upwelling System, especially since the remote equatorial ocean dynamics is instrumental in the development of extreme warm and cold Benguela Niño/Niña events. The objective of this study is to document the low-frequency change in the characteristics (amplitude, duration and timing) of the interannual Benguela Niño/Niña events. Using model solutions and sensitivity experiments, we investigate the mechanisms that control the low-frequency modulation of the coastal interannual variability off the coasts of Angola/Namibia. Our results reveal that the decadal modulation of the interannual variability off the Angolan coast is controlled by change in the EKW activity. In the Southern Benguela, the modulation of the interannual is dominated by the influence of the local alongshore winds. However, periods during which the equatorial forcing is intensified, EKW propagate and imprint the oceanic variability off the coast of Namibia.