An energetic perspective on the impact of the Atlantic Multidecadal Variability on the West African Monsoon

Abstract. This study explores mechanisms by which the Atlantic Multidecadal Variability (AMV) drives multidecadal changes in the West African Monsoon (WAM), with a focus on Sahel rainfall. We investigate this connection through an energetic perspective using atmosphere-ocean coupled models forced by an idealized AMV sea surface temperature (SST) pattern. Results show that a positive AMV phase (warmer North Atlantic) increases net energy input to the atmosphere via enhanced surface latent heat flux. The atmospheric circulation adjusts by exporting this excess energy from the North Atlantic. In the Tropical Atlantic and Africa, this is accomplished by anomalous southward cross-equatorial energy transport and a northward shift of the Intertropical Convergence Zone (ITCZ). Over West Africa, this ITCZ shift leads to increased and northward displaced Sahel rainfall. The monsoon intensification is dynamically consistent with enhanced low-level convergence and high-level divergence in the main ascent region and a decrease in mid-level dry-air intrusion, linked to a weakening of the shallow meridional circulation over the Sahara.