The South Asian summer monsoon (SASM) is a significant monsoon system that exerts a profound impact on climate and human livelihoods. According to 38 models from the Coupled Model Intercomparison Project Phase 6, the SASM circulation is projected to weaken significantly under global warming as seen in the weakened low-level westerly wind over the northern tropical Indian Ocean; however, the associated climate dynamics is still under debate. Here, we identify that the weakened low-level westerly wind is closely related to the enhanced latent heating over the Tibetan Plateau (TP), which corresponds with increased summer precipitation in the future. The intensified TP latent heating triggers an anomalous meridional circulation with ascending motions over the plateau and descending motions to the south, leading to an anomalous low-level anticyclone over the northern tropical Indian Ocean. This anticyclone greatly weakens the prevailing low-level westerlies of the SASM through easterly anomalies at the anticyclone’s southern flank. Moisture budget analysis further reveals that increased atmospheric water vapor, rather than the vertical dynamic component, makes the largest contribution to the increased precipitation over the TP. This result confirms that the enhanced TP latent heating is a driver of atmospheric circulation change and contributes to weakening the SASM circulation.

南亚夏季风（SASM）是一个重要的季风系统，对气候和人类生计产生深远影响。根据耦合模式比对项目第六阶段的38个模式，预计在全球变暖的情况下，SASM环流将显着减弱，如热带印度洋北部低层西风减弱所示；然而，相关的气候动态仍在争论中。在这里，我们发现低层西风的减弱与青藏高原（TP）潜热的增强密切相关，这与未来夏季降水的增加相对应。青藏高原潜热加热的增强引发了异常的经向环流，高原上空上升，南部下降，导致热带印度洋北部出现异常低层反气旋。该反气旋通过反气旋南翼的东风异常极大地削弱了SASM盛行的低层西风。水分收支分析进一步表明，大气水汽的增加，而不是垂直动力分量，对青藏高原降水增加的贡献最大。这一结果证实了TP潜热增强是大气环流变化的驱动因素，并有助于减弱SASM环流。