Mechanisms of ENSO’s cross-seasonal modulation of winter–spring atmospheric river activity over East Asia

In this study, based on MERRA-2 reanalysis data and a multi-algorithm integrated atmospheric river (AR) identification method, the authors reveal the cross-seasonal regulation mechanism of El Niño–Southern Oscillation (ENSO) on winter–spring AR activities in East Asia. The results show that ENSO asymmetrically modulates AR activity through teleconnection and hysteresis effects, and has significant enhancement/inhibition effects on ARs in different regions. At the onset of El Niño, enhanced southwesterly flow at the western edge of the western Pacific subtropical high (WPSH) leads to enhanced AR activity in the western Pacific, and anomalous southerly winds in the Indian Ocean promote northward transport of water vapor in the Arabian Sea and Bay of Bengal. With a three-month lag, the weakening and eastward retreat of the WPSH weakens the low-latitude AR activity, but persistent southerly winds in the Bay of Bengal maintain the AR activity over Southwest China. The mid- to high-latitude AR response exhibits delayed dynamics, initially dominated by the synergistic effect of the southward deviation of the upper-air rapids and the low-level convergence (double-rapid-flow effect) and later modulated by the Pacific–North American teleconnection (PNA)-triggered East Asian ridge, which enhances the precipitation efficiency through prolonged frontal activity and enhanced cold–warm airmass convergence. Overall, El Niño promotes the development of low- and midlatitude AR activity in East Asia, while La Niña promotes (maritime continental) AR activity in the tropics. This study establishes the “ENSO teleconnection → circulation adjustment → East Asian AR response” chain, revealing a cross-seasonal lagged response mechanisms of East Asian AR activity, and provides a theoretical basis for winter and spring climate prediction and extreme precipitation forecasting. 摘要 本研究基于MERRA-2再分析数据及多算法融合的AR识别方法, 揭示ENSO通过遥相关效应对东亚冬春季大气河活动的跨季节调控机制. 厄尔尼诺初期, 西太平洋副高西侧增强的西南风激发西太平洋AR活动, 同时印度洋偏南风异常促进阿拉伯海-孟加拉湾水汽北输; 滞后3个月后, WPSH东退削弱低纬AR, 但孟加拉湾持续南风维持西南地区AR活动. 中高纬AR响应初期受高空急流南偏与低层辐合 (双急流效应) 协同作用, 后期由PNA遥相关触发的东亚脊调制, 通过延长锋面活动及增强冷暖空气辐合提升降水效率. 总体而言, 厄尔尼诺促进东亚中低纬AR发展, 拉尼娜则增强热带海洋性大陆AR活动. "ENSO遥相关-环流调整-东亚AR响应"机制链为冬春季气候预测及极端降水预报提供理论基础.