Attribution of the Increased Intensity of Upper-Level Hadley Circulation Under Climate Change

The upper-level Hadley circulation is critical to the energy transport from tropical toward mid-to-high latitude regions. In this study, an index denoting the intensity of upper-level Hadley circulation in Northern Hemisphere (Southern Hemisphere) is defined as the areal mean zonal mean meridional mass stream function in the upper-level Hadley circulation, which is referred to as UP-NH-HCI (UP-SH-HCI). An increasing (decreasing) trend of UP-NH-HCI (UP-SH-HCI) is observed during 1979-present using five reanalysis data sets, which denotes increased intensity of upper-level Hadley circulation in Northern Hemisphere (Southern Hemisphere). Furthermore, Nine (13) CMIP6 models are selected to perform the detection and attribution analysis for the trends in UP-NH-HCI (UP-SH-HCI). Using the optimal fingerprinting method, the results indicate that the greenhouse gas forcing accounts for 57%–114% and 61%–89% of the observed changes in UP-NH-HCI and UP-SH-HCI, respectively, at an uncertainty range of 10%–90%.