Handout (1.5 MB)
In all models, the MSE difference between the Sahel and Sahara increases with warming, and the resulting increased dry advection into the Sahel drives anomalous subsidence. This yields reduced Sahelian rainfall in 14 of 17 atmospheric GCMs analyzed. The three models in which it does not dry are closely related model variants that share a weakly entraining convective parameterization that is largely insensitive to the increased dry air advection. The enhancement of the Sahel-Sahara MSE difference, and with it the Sahel drying response, depends on the Sahel convective depth in the control simulations, and most of the models that dry the Sahel most severely with warming exhibit ascent profiles that are anomalously top-heavy relative to multiple reanalysis products. We discuss the implications of these results and important caveats that complicate efforts to identify quantitative emergent observational constraints on future Sahel rainfall.
Supplementary URL: http://people.atmos.ucla.edu/shill/