Multidecadal variations in Hadley circulation (HC) strength have been observed during the historical period, which have significant implications for global and regional climate. However, the relationship between HC intensities in the two hemispheres remains unclear. In this study, we identify an interhemispheric seesaw in the annual HC strength at multidecadal timescales. This seesaw pattern physically corresponds to the meridional movement of the ascending branch of annual HC, leading to strengthened HC in one hemisphere and weakened HC in the other. The HC strength seesaw strongly correlates with the tropical land surface precipitation at multidecadal timescales, particularly for the monsoonal land regions. Further analyses link the HC strength seesaw to the Atlantic multidecadal variability (AMV). A suite of Atlantic Pacemaker experiments successfully reproduces the multidecadal HC strength seesaw and its relation to the AMV. The Northern Hemisphere SST warming associated with the positive AMV phase induces a northward shift of the upward branch of HC, and the Southern Hemispheric HC is strengthened in contrast to the weakened Northern Hemispheric HC. Comparisons of the North Atlantic SST forced HC changes between the coupled air–sea model and stand-alone atmospheric model suggest an important and non-negligible role of the SST footprint of AMV over the Indo-Pacific basins. The AMV and its Indo-Pacific SST footprint make a comparable contribution to the SST changes in the Northern Hemisphere, which control the movement of the HC ascending branch and thereby the interhemispheric seesaw in HC strength.

在历史时期内，人们已经观察到哈德利环流（HC）强度发生了数十年的变化，这对全球和区域气候都有重要影响。但是，两个半球中HC强度之间的关系仍不清楚。在这项研究中，我们确定了在多年代际尺度上年际HC强度的半球跷跷板。这种跷跷板模式在物理上与年度HC上升分支的子午运动相对应，从而导致一个半球的HC增强而另一个半球的HC减弱。HC强度​​跷跷板在数十年尺度上与热带土地表面降水密切相关，特别是在季风性土地区域。进一步的分析将HC强度跷跷板与大西洋多年代际变率（AMV）联系起来。一组大西洋起搏器实验成功地再现了多年代HC强度跷跷板及其与AMV的关系。与AMV正相相关的北半球SST变暖引起HC向上分支向北移动，与减弱的北半球HC相反，南半球HC增强。对北海海温强迫HC变化的耦合海气模型和独立大气模式之间的比较表明，AMV在印度洋-太平洋海盆上的海温覆盖足迹具有重要且不可忽略的作用。AMV及其印度洋-太平洋SST足迹对北半球的SST变化做出了可比的贡献，它控制了HC上升分支的运动，从而控制了HC强度的半球跷跷板。