On the triggering of Benguela Niños: Remote equatorial versus local influences

The relative importance of remote and local influences in the development of Benguela Nios is examined using observations and a coupled general circulation model capable of simulating interannual variability in the tropical Atlantic. While previous studies have emphasized the role of equatorially excited Kelvin waves, the present study finds that meridional wind anomalies along the southwest African coast contribute substantially. Both observations and model output indicate that sea-surface temperatures along the southwest African coast respond rapidly to changes in meridional wind stress. These wind anomalies form part of a basin-scale weakening of the subtropical anticyclone that extends to the equator. As the weakening begins three months before the peak of the event it might have some predictive potential. Results also indicate that the close correlation between Benguela and Atlantic Nios in observations might result from the large spatially coherent wind stress anomalies associated with the weakened anticyclone.