Drought-Induced Warming in the Continental United States under Different SST Regimes

The U.S. Climate Variability and Predictability (U.S. CLIVAR) Drought Working Group (DWG) recently performed a series of experiments in which a number of AGCMs were forced with different leading patterns of global SST variability. These experiments provide a unique opportunity to examine how different SST regimes affect temperature over the continental United States. Herein, the focus is on a particular aspect of June-August (JJA) near-surface air temperature: the temperature during relatively dry years for a given SST regime. For most of the models participating in the DWG experiments, a cold Pacific produces greater warming in the central United States during relatively dry years than a warm Pacific does for the following two separate reasons: (i) the cold Pacific leads on average, across all years, to drier conditions, and (ii) the particular evaporation regime induced by the cold Pacific enhances the impact of evaporation feedback on temperature, that is, the sensitivity of temperature to within-climate variations in moisture availability. These results are supported, to a large extent, by the observational record.