SAHEL DROUGHTS AND ENSO DYNAMICS

Correlations between summer Sahel rainfall and Southern Oscillation In dex has increased during the last thirty years. At high frequency time scale (periods lower than 8 years), an intertropical Atlantic zonal d ivergent circulation anomaly is forced by the difference of sea surfac e temperature (SST) anomalies between the eastern equatorial parts of Pacific and Atlantic. This zonal connection worked well during most of the El Nine/Southern Oscillation (ENSO) events occurring after 1970; positive/negative SST anomalies in the eastern Pacific/Atlantic led to rainfall deficits over the whole West Africa. At low frequency time s cale (periods greater than 8 years), positive SST anomalies in the Ind ian ocean and in equatorial Pacific existing after 1970 have been asso ciated with decreasing rainfall intensity over West Africa through ano ther zonal divergent circulation. These different time scales remote S ST forcings are combined to provide a global zonal divergent circulati on anomaly pattern which could explain the strong association between Sahel drought and ENSO dynamics after 1970.