Meiyu (plume rain) is a distinctive weather phenomenon during boreal early summer, known for its increased precipitation during El Niño decay years bridged through the northwest Pacific anticyclone (NWPAC). It has been widely acknowledged that super El Niño (SEN) events consistently correspond to more Meiyu. This study highlights the instability in the relationship between El Niño and Meiyu, particularly during normal El Niño (NEN) decay years, where the probability of more or less Meiyu is almost equal by statistical analysis. Using the Liang-Kleeman information flow (LIF), our findings confirm that warming in the Maritime Continent (MC) induced by SEN leads to tropical North Atlantic warming in boreal spring. This suppresses northwest Pacific convection via Kevin waves and forms the north-south dipole mode of the NWPAC (EOF2), corresponding to strong Meiyu. Moreover, it is found that subtropical North Pacific cooling induced by NEN leads to the tropical North Atlantic warming in boreal spring via Pacific North American (PNA) pattern, reinforcing the region-wide consistent mode of the NWPAC (EOF1) via Rossby waves and resulting in strong Meiyu. Conversely, warming in the tropical North Atlantic induced by NEN in boreal early summer leads to anticyclonic circulation over the east of Japan (EOF3) and weak Meiyu. The contributions of these three causal structures to the uncertainty of Meiyu are 31 %, 25.7 %, and 28.2 %, respectively. This study sheds new light on the understanding the significance of NEN for Meiyu, emphasizing the importance of its causal relationship with warming in the tropical North Atlantic.

中文翻译：

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厄尔尼诺衰减年份长江中下游流域梅雨降水差异


梅雨（羽流雨）是北方初夏的一种独特天气现象，以在通过西北太平洋反气旋 （NWPAC） 过渡的厄尔尼诺衰减年份降水增加而闻名。人们普遍认为，超级厄尔尼诺 （SEN） 事件始终对应于更多的梅雨。本研究强调了厄尔尼诺和梅雨之间关系的不稳定性，尤其是在正常的厄尔尼诺 （NEN） 衰减年份，通过统计分析，或多或少梅雨的概率几乎相等。使用 Liang-Kleeman 信息流 （LIF），我们的研究结果证实，SEN 诱导的海洋大陆 （MC） 变暖导致北方春季热带北大西洋变暖。这抑制了通过凯文波产生的西北太平洋对流，形成了 NWPAC 的南北偶极子模态 （EOF2），对应于强梅雨。此外，研究发现，NEN 诱导的副热带北太平洋降温通过北美太平洋 （PNA） 模式导致北方春季热带北大西洋变暖，通过罗斯比波加强了 NWPAC （EOF1） 的全区域一致模式，并产生了强烈的梅雨。相反，初夏 NEN 引起的热带北大西洋变暖导致日本东部反气旋环流 （EOF3） 和弱梅雨。这三种因果结构对美雨不确定性的贡献分别为 31 % 、 25.7 % 和 28.2 %。这项研究为理解 NEN 对 Meiyu 的重要性提供了新的思路，强调了它与热带北大西洋变暖的因果关系的重要性。