Assessment of the 1998-99 southern Africa summer rains

ed.NCEP/NCAR reanalysis data and OI SST data are used to study the atmospheric characteristics associated with southern Africa summer rainfall and its relationship with global SSTs. Results show an evident influence of ENSO on southern Africa summer rains. In particular, southern Africa summer rainfall tends to be abundant during a La Niña episode and drier than normal during a warm episode. However, and perhaps more importantly, the atmospheric response to ENSO over the Indian Ocean and the Atlantic has a much greater impact on southern Africa summer rains. For example, it is shown that during a warm ENSO event, an anomalous low level cyclonic circulation over Madagascar and the Mozambique channel tends to keep convection away from southern Africa. However, during January 1998, extremely warm conditions over the Indian ocean associated with an anomalous northeast-southwest extension of the central Indian Ocean low level wind anomalies, resulted in above normal rains in parts of southern Africa, especially in January 1998. The period 1997-99 was characterized by a major warm phase of ENSO followed by a moderate cold episode. Their influence on southern Africa summer rains is assessed. Predictions for the southern Africa rainfall at one month lead based on Canonical Correlation Analysis (CCA) and using global SSTs as predictor field were also made and evaluat