The Role of Equatorially Forced Waves in Triggering Benguela Niño/Niña as Investigated by an Energy Flux Diagnosis

Abstract

AbstractThe Benguela Niño/Niña events manifest the anomalous signals of sea surface temperature (SST) in the coastal region of the tropical Atlantic Ocean. These events are triggered by the interannual modulation of either equatorial waves or local atmospheric forcing. In the present study, the mechanism that equatorial waves induce the coastal SST anomaly is investigated in terms of the transfer episodes of wave energy. The analysis suggests that most of the coastal events can be reproduced by subseasonal wind forcing with an interannual modulation that excites oceanic waves of the first three baroclinic modes. The transfer routes of wave energy illustrate the role of wave dynamics that explains how the interannual variability of SST in the equatorial Atlantic is connected with that in coastal regions. The linearly superposed sign‐indefinite potential energy flux owing to waves manifests its capability of sufficiently displacing the thermocline so as to trigger the coastal events. The results suggest that the equatorial wave signal is able to provide credible predictions for remotely forced Benguela Niño/Niña events if a proper transection in central equatorial Atlantic with an appropriate threshold is selected for observing.