Browsing by Author "Hansingo, Kabumbwe"

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    An investigation into the impacts of the Benguela Niño on rainfall over southern Africa
    (2008) Hansingo, Kabumbwe; Reason, Chris
    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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    Sea surface temperature anomalies in the South Indian ocean : observations and atmospheric modelling
    (2003) Hansingo, Kabumbwe; Reason, Chris
    Sea surface temperature (SSTs) variations in the South Indian Ocean have been found to influence rainfall over Southern Africa. As one of the modes of South Indian Ocean SST variability, the subtropical South Indian Ocean dipole is observed to be associated with dry and wet summer conditions over Southern Africa. The positive phase of the subtropical South Indian Ocean dipole is characterized by warm SST anomalies in the southwest South Indian Ocean and cool SST anomalies in the southeast. This phase is associated with above average summer rainfall over the subcontinent. The negative phase is associated with dry conditions over Southern Africa and is characterized by cool SST anomalies in the southwest and warm anomalies in the southeast South Indian Ocean. In order to investigate the atmospheric response over Southern Africa to this phenomenon, this study uses the MM5 regional climate model in which the model is forced with a warm pole SST anomaly south of Madagascar.