Linking the South Atlantic Meridional Overturning Circulation and U.S. heat waves

Heat waves are extreme warm temperature events that are responsible for the most weather-related deaths in the U.S.This study tests the hypothesis whether low frequency decadal variability of the South Atlantic Ocean meridional heat transport (SAMHT) influences decadal variability of heat waves in the U.S. A multi-century run from a state-of-the-art coupled general circulation model is used as basis for the analysis. Our findings indicate that multi-decadal variability of the SAMHT plays a key role in modulating atmospheric circulation via interhemispheric changes in Atlantic Ocean heat content. Specifically, weaker SAMHT produces anomalous ocean heat divergence over the South Atlantic resulting in negative ocean heat content anomaly about 15 years later. This, in turn, forces a thermally direct anomalous interhemispheric Hadley circulation in the atmosphere, transporting heat from the Northern Hemisphere (NH) to the Southern Hemisphere (SH) and moisture from the SH to the NH, thereby intensifying the NH summer monsoon system. The enhanced NH summer monsoons increase the likelihood for atmospheric blocking events and heat waves over the U.S. Overall, SAMHT decadal variability leads its atmospheric response by about 15 years, suggesting that the South Atlantic is a potential predictor of decadal climate variability and extreme events.