Reorganization of moisture transport underpins the leading modes of East Asian summer precipitation

East Asian summer precipitation (EASP) alternates interannually mainly between a meridional tripole mode (with a wet Yangtze River basin and dry north/south) and a dipole mode (with a wet south and dry north). How associated moisture pathways reorganize remains poorly quantified from a Lagrangian perspective. The authors analyze moisture transport to East Asia during July–August 1961–2022 using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model to trace backward air-parcel trajectories, categorizing pathways into four quadrants (SW, SE, NW, NE). Climatologically, the SW pathway dominates, supplying 48% of the total moisture. The positive tripole mode, driven by a southwestward-shifted western Pacific subtropical high (WPSH), reduces SE moisture by 25% while the other three paths strengthen. In the positive dipole mode, an eastward-retreating WPSH and prevalent northerlies boost NE moisture by 42% but reduce SE and NW by 14% and 7%. This pathway-resolved budget links circulation regimes to rainfall anomalies, advances understanding of EASP variability, and also provides an analogue for interpreting moisture‑sensitive paleoclimate records. 摘要 东亚夏季降水年际变率主要呈现两种典型模态: 经向三极模态 (长江流域偏湿, 而其南北两侧偏干) 和偶极模态 (南方偏湿,北方偏干) . 然而, 与降水模态相关的水汽输送格局的变化仍缺乏定量认识. 本研究利用HYSPLIT模式, 对1961–2022年7–8月输送至东亚的水汽进行后向轨迹追踪, 并将水汽输送路径划分为四类 (西南,东南,西北和东北) . 三极模态正位相期间, 受西太平洋副热带高压向西南偏移的影响, 东南路径的水汽贡献减少约25%, 而其余三条路径均有所增强. 偶极模态正位相期间, 东亚盛行异常偏北风, 东北路径的水汽贡献增加约42%, 而东南和西北路径分别减少约14%和7%. 本研究建立了大尺度环流, 水汽输送与降水异常之间的联系, 深化了对东亚夏季降水变率的认识, 并为解释对水汽敏感的古气候记录提供了类比框架.