An Externally Forced Decadal Rainfall Seesaw Pattern Over the Sahel and Southeast Amazon

By analyzing observations and model simulations, here we show that there exists a significant anticorrelation on interannual to multidecadal time scales between the Sahel and southeast Amazon rainfall during July-August-September. This rainfall seesaw, which is strongest on decadal to multidecadal scales, is due to an anomalous meridional gradient of sea surface temperatures across the tropical Atlantic that pushes the Intertropical Convergence Zone and its associated rain belt toward the anomalously warm hemisphere. Large ensemble model simulations suggest that the seesaw pattern is likely caused by decadal changes in anthropogenic and volcanic aerosols, rather than internal climate variability. Our results suggest that the recent decadal to multidecadal climate variations in and around the North Atlantic basin are largely externally forced and that projected large North Atlantic warming could lead to a wetter Sahel but drier Amazon in the future.