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Sea Surface Temperature Fields Associated with West African Rainfall Anomaly Types

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  • 1 CNRS, Centre de Recherches do Climatologie de I'Université de Bourgogne, Sciences Gabriel, Dijon, France
  • | 2 Météo-France, Laboratoire de Météorologie Dynamique du CNRS, Ecole Polytechnique, Palaiseau, France
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Abstract

Four West African rainfall anomaly types are defined in relation to the northern summer rainfall departure signs in the Sahel and in the Guinean region in order to investigate the statistical links between interannual variability of West African rainfall and sea surface temperature (SST) through the period 1950–90. Composite analysis depicts the setup of four different mean SST anomaly fields. Drought over all of West Africa is associated with the growth of positive SST anomalies in the eastern Pacific and in the Indian Ocean, and negative SST anomalies in the northern Atlantic and in the Gulf of Guinea. In contrast, drought limited to the Sahel corresponds mostly to a northward expansion of positive SST anomalies in the southern Atlantic, and negative SST anomalies in the northern Atlantic. Northward expansion of negative SST anomalies in the southern Atlantic, positive SST departures in the northern Atlantic, and development of negative SST anomalies in the eastern Pacific appear to be synchronous of flood limited to the Sahel. Flooding over all of West Africa is mainly associated with positive SST anomalies in the northern Atlantic. This approach complements previous papers dealing with rainfall anomalies located in the Sahel alone. In particular, it points out different associations between Atlantic/Pacific SST anomalies and Sahel rainfall variability. Individual cases are also discussed, especially the case of 1972 when a West African rainfall deficit was concomitant to a southward location of the intertropical convergence zone over the tropical Atlantic.

Abstract

Four West African rainfall anomaly types are defined in relation to the northern summer rainfall departure signs in the Sahel and in the Guinean region in order to investigate the statistical links between interannual variability of West African rainfall and sea surface temperature (SST) through the period 1950–90. Composite analysis depicts the setup of four different mean SST anomaly fields. Drought over all of West Africa is associated with the growth of positive SST anomalies in the eastern Pacific and in the Indian Ocean, and negative SST anomalies in the northern Atlantic and in the Gulf of Guinea. In contrast, drought limited to the Sahel corresponds mostly to a northward expansion of positive SST anomalies in the southern Atlantic, and negative SST anomalies in the northern Atlantic. Northward expansion of negative SST anomalies in the southern Atlantic, positive SST departures in the northern Atlantic, and development of negative SST anomalies in the eastern Pacific appear to be synchronous of flood limited to the Sahel. Flooding over all of West Africa is mainly associated with positive SST anomalies in the northern Atlantic. This approach complements previous papers dealing with rainfall anomalies located in the Sahel alone. In particular, it points out different associations between Atlantic/Pacific SST anomalies and Sahel rainfall variability. Individual cases are also discussed, especially the case of 1972 when a West African rainfall deficit was concomitant to a southward location of the intertropical convergence zone over the tropical Atlantic.

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