Interdecadal changes in the leading ocean forcing of Sahelian rainfall interannual variability: Atmospheric dynamics and role of multidecadal SST background.



Roberto Suárez-Moreno

Additional authors:

Belén Rodríguez-Fonseca, Jesús A. Barroso, and Andreas H. Fink


The atmospheric response to global sea surface temperatures is the leading cause of rainfall variability in the West African Sahel. On interannual periodicities, the El Niño-Southern Oscillation, the Atlantic equatorial mode and Mediterranean warm/cold events primarily drive variations of summer rainfall over the Sahel. Nevertheless, the rainfall response to these modes of interannual SSTs variability has been suggested to be unstable throughout the observational record. This study explores changes in the leading patterns of co-variability between Sahel rainfall and SSTs, analyzing the dynamical mechanisms at work to explain the non-stationary relationship between anomalies in these two fields. A new network of rain-gauge stations across West Africa is used for the first time to investigate these instabilities during the period 1921-2010. A hypothesis is raised that the underlying SSTs background seems to favor some interannual teleconnections and inhibit others in terms of the cross-equatorial SSTs gradients and associated impacts on the location of the Inter-tropical Convergence Zone. Results of this study are relevant for improving the seasonal predictability of summer rainfall in the Sahel.