A moist static energy budget–based analysis of the Sahel rainfall response to uniform oceanic warming

This study compares the Sahel's wet season response to uniform 2-K SST warming in AM2.1 using either its default convective parameterization, relaxed Arakawa–Schubert (RAS), or an alternate, the University of Washington (UW) parameterization, using the moist static energy (MSE) budget to diagnose the relevant mechanisms.

UW generates a drier, cooler control Sahel climate than does RAS and a modest rainfall increase with SST warming rather than a sharp decrease. Horizontal advection of dry, low-MSE air from the Sahara Desert—a leading-order term in the control MSE budget with either parameterization—is enhanced with oceanic warming, driven by enhanced meridional MSE and moisture gradients spanning the Sahel. With RAS, this occurs throughout the free troposphere and is balanced by anomalous MSE import through anomalous subsidence, which must be especially large in the midtroposphere where the moist static stability is small.