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

本项目研究北大西洋副热带高压（NASH，也被称为百慕大高压）的变化，它是夏季在北大西洋副热带上空形成的一个大的高地面气压单元，影响美国东南部（东南US）的天气和气候。主要研究者最近的工作表明，与前30年相比，NASH在过去30年里有所加剧，而且这种加剧伴随着向西扩张。在温室气体浓度增加对气候影响的模式模拟中也发现了类似的趋势。此外，与东南US重叠的NASH西部在过去30年中经历了更大的南北移动，这些移动与东南US降水在此期间的增加变化有关。这项拨款的目的是通过数据诊断和数值模拟，在观测和气候模式模拟中确定和描述NASH变化的原因。以往的研究表明，局地和远地非绝热供暖在NASH的季节性发展和维持中都起着重要作用。这里进行的工作旨在确定和量化这些加热在年际和年代际时间尺度上的变化，并评估它们对NASH年际至年代际变率的相对贡献。除了其科学价值之外，这项工作还具有更广泛的影响，因为东南美国是一个拥有大量农业部门的人口稠密地区，降水波动对社会产生了影响。此外，该项目将支持两名研究生，从而为该领域未来的科学劳动力提供支持。

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.