Modelling the precipitation response over southern Africa to the 2009–2010 El Niño using a stretched grid global atmospheric model
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The 2009–2010 El Niño event was a moderately strong Central Pacific type ENSO and, as such, expected to lead to a substantial drought over southern Africa during austral summer. However, many parts of the region experienced average to well above average rainfall during this season. Given that seasonal forecasting skill tends only to be good during ENSO seasons and many parts of the sub-continent rely on rain-fed agriculture, understanding why the rainfall was so anomalous during this El Niño event is important. To this end, a global stretched grid atmospheric general circulation model with relatively high horizontal resolution of 0.5° × 0.5° is applied over the region with observed and idealised SST forcing. In the latter experiments, SSTs are kept as observed over one ocean basin (e.g. Pacific) and as climatology over the other two basins (e.g. Atlantic, Indian), or as climatology over one basin and as observed over the other two basins in order to help understand which of these three basins may have contributed most to the observed rainfall anomalies in summer 2009–2010. It is found that Pacific Ocean forcing contributed to the summer rainfall anomalies over most regions of southern Africa with the Atlantic acting to oppose the effects of the Pacific. However, over Mozambique, and to some extent Zimbabwe, the Indian Ocean was more important with the Atlantic again acting in opposition. The increased rainfall over most of southern Africa appears mainly due to a stronger Angola Low circulation system and to anomalously strong moisture flux from the tropical western Indian Ocean and, to lesser extent, the tropical South East Atlantic Ocean.
The first author gratefully acknowledges PhD scholarship funding from the South African National Research Foundation ACCESS programme, and the University of Cape Town. J. Prusa gave invaluable technical help to the first author in implementing the CEU model. The authors declare that they have no conflict of interest.
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