Collaborative Research: Understanding Long-Term Variability in the North Atlantic Subtropical High Driven by Evolving Tropical and Subtropical Large-Scale Heating

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This project examines changes in the North Atlantic Subtropical High (NASH, also referred to as the Bermuda High), a large cell of high surface pressure that forms over the subtropical North Atlantic in summer and affects the weather and climate of the southeastern United States (SE US). Recent work by the principal investigators shows that the NASH has intensified in the past 30 years compared to the previous 30-year period, and that the intensification was accompanied by a westward expansion. Similar trends are also found in model simulations of the effect of increased greenhouse gas concentrations on climate. In addition, the western portion of the NASH, which overlaps the SE US, has experienced larger north-south shifts during the past 30 years, and these shifts are associated with heightened variation in SE US precipitation during this period. Work under this grant aims to identify and characterize the causes of the changes of the NASH in observations and climate model simulations through data diagnosis and numerical modeling. Previous studies suggest that both local and remote diabatic heating play important roles in the seasonal development and maintenance of the NASH. Work to be conducted here seeks to identify and quantify the changes of these heating on interannual and interdecadal timescales, and assess their relative contributions to the interannual to interdecadal variability in the NASH. In addition to its scientific merit, the work has broader impacts due to the societal impacts of precipitation fluctuations over the SE US, a populous region with a substantial agricultural sector. In addition, the project will support two graduate students, thereby providing for the future scientific workforce in this area.