Impact of El Niño–Southern Oscillation on the Benguela Upwelling

Abstract

The impact of El Niño–Southern Oscillation (ENSO) on the southern African climate is well documented and provides skill in the seasonal forecast of rainfall, but less is known about the impact of ENSO on the Benguela Current west of southern Africa. There is a significant weak correlation between ENSO and the Benguela Current upwelling sea surface temperature (SST) in austral summer. Correlation is positive for southern Benguela and negative for northern Benguela. A significant correlation exists with up to 8 months lag when ENSO leads. The impact of ENSO is due to weaker-than-normal upwelling favorable southeasterly winds during El Niño in southern Benguela, leading to warmer-than-normal coastal SST. In contrast, during La Niña, stronger-than-normal southeasterly winds lead to cooler-than-normal SST. The opposite effect applies to northern Benguela. The coastal wind change is part of an ENSO large-scale basinwide perturbation in the tropical and South Atlantic. However, non-ENSO-related SST variation in the Benguela upwelling can be as important as ENSO-related SST perturbation, and some ENSO events do not lead to the expected changes. Changes in the Benguela upwelling are linked to changes in the intensity of the trade winds associated with a change of the South Atlantic anticyclone intensity and position. In southern Benguela, changes are also associated with variations in midlatitude low pressure systems and associated upwelling unfavorable westerly winds. La Niñas favor the development of Benguela Niños in Angola and Namibia. This study shows the potential for SST seasonal predictability in the Benguela upwelling due to the leading lag correlation between ENSO and the Benguela upwelling SST.