Contrasting impacts of Atlantic and Pacific decadal SST variability on regional Sahel precipitation

We investigate the impacts of the Atlantic Multidecadal Variability (AMV) and Interdecadal Pacific Variability (IPV) on Sahel precipitation during June–September (JJAS) using 45-member ensemble simulations with the atmospheric model OpenIFS for 1950–2013. Sahel precipitation is enhanced during the positive phase of the AMV (AMV +) and the negative phase of the IPV (IPV−), and reduced during the negative phase of the AMV (AMV−) and the positive phase of the IPV (IPV +). The Sahel precipitation response to the AMV weakens from west to east, whereas the response to the IPV is stronger in the eastern Sahel. The east–west contrast of Sahel precipitation responses is due to the distinct pathways through which the AMV and IPV influence the Sahel. AMV+ enhances Sahel precipitation through a Walker-like circulation with ascent over the tropical Atlantic, which is associated with a northward shift of the meridional temperature gradient between the Sahara and Guinea coast. The associated northward shift of monsoon circulation is consistent with a stronger precipitation response over the western Sahel. However, the IPV− induces a similar thermodynamic change through ascent over the Arabian Sea, leading to a stronger impact over the eastern Sahel. These results are robust across earlier and recent decades, suggesting the potential value of the AMV and IPV for decadal prediction of Sahel precipitation.