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Atlantic warm and cold water events and impact on African west coast precipitation

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ABSTRACT

Variability of sea surface temperatures (SSTs) in the tropical southeast Atlantic Ocean has previously been shown to significantly contribute to changes in summer rainfall along the West African as well as the Angolan coast. This study examines links between southeast Atlantic SST and African west coast precipitation variability for an extended 60-year period from 1951 to 2010. In contrast to earlier studies, our analyses cover the whole Atlantic coast from Guinea to South Africa and are not limited to specific seasons. In addition to the analyses of the total variability, pronounced anomalies in terms of warm and cold water events and their impact on African west coast precipitation are analyzed. By using for the first time a new comprehensive classification of Atlantic Niño and Niña events, consistent results are achieved for a larger region of Africa, also considering Atlantic cold water events which have rather been neglected so far.

Results show that, depending on the particular region, southeast Atlantic SSTs play an important role for coastal rainfall variability throughout the year. Furthermore, the rainfall response to Atlantic cold and warm water events appears to be asymmetric in season and magnitude. Atlantic cold events can cause a stronger decrease in rainfall along the West African and Gabon coast than the increase is in warm events. In addition, not all seasons show a significant rainfall response to both warm and cold water events.

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