Characterizing South American monsoon variability with the moist static energy budget

The physical processes regulating monsoons remain uncertain, undermining rainfall projections for land regions across the tropics. This study utilizes the column-integrated moist static energy (MSE) budget to diagnose the mechanisms of monsoonal precipitation variability in the latest Geophysical Fluid Dynamics Laboratory atmospheric model, AM4. In both a control simulation and a +2K uniform sea surface temperature (SST) perturbation experiment, the ratio of vertical to horizontal MSE advection terms is computed to characterize monsoon systems throughout the seasonal cycle. The uniform warming of SSTs drives a significant drying of the South Amazonian winter and monsoon onset seasons. This has important implications for South American economy, biodiversity, and the global carbon cycle. A comparison of the seasonal cycle over the South American and West African monsoon sectors demonstrates that two systems with similar climatological MSE budget regulation exhibit similar precipitation responses to SST warming.