An investigation into the impacts of the Benguela Niño on rainfall over southern Africa
The impacts of the Benguela Niño on southern African rainfall and circulation are investigated using an atmospheric general circulation model. The model used is the United Kingdom Met Office Hadley Centre Atmospheric General Circulation Model version 3 and experiments using idealizations of observed regional and remote SST anomalies during various Benguela Niño events were performed. It is found that SST forcing in tropical South East Atlantic induces a regional baroclinic response and that a Benguela Niño is capable of forcing anomalous wet conditions over western Angola on its own, via changes to uplift and evaporation over the SST forcing. It is also capable of forcing anomalous rainfall much further inland when the intensity is increased. An experiment with the tropical South East Atlantic SST anomaly shifted slightly further north produced a larger circulation and rainfall response in the model. Additional experiments with various SST anomalies in the South West Indian Ocean/central equatorial Pacific combined with those in the South East Atlantic were performed. These experiments are motivated by the fact that equatorial Pacific/South Indian Ocean SST anomalies of varying signs often occur at the same time as the Benguela Niño Events. The results suggest that depending on its sign, magnitude and location, SST forcing from the South West Indian Ocean may augment or oppose the southern African rainfall anomalies occurring during a Benguela Niño event to varying degree.
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