The record-breaking meiyu in the Yangtze-Huaihe River valley (YHRV) in 2020 was characterized by an early onset, a delayed retreat, a long duration, a wide meridional rainbelt, abundant precipitation, and frequent heavy rainstorm processes. It is noted that the East Asian monsoon circulation system presented a significant quasi-biweekly oscillation (QBWO) during the meiyu season of 2020 that was associated with the onset and retreat of meiyu, a northward shift and stagnation of the rainbelt, and the occurrence and persistence of heavy rainstorm processes. Correspondingly, during the meiyu season, the monsoon circulation subsystems, including the western Pacific subtropical high (WPSH), the upper-level East Asian westerly jet, and the low-level southwesterly jet, experienced periodic oscillations linked with the QBWO. Most notably, the repeated establishment of a large southerly center, with relatively stable latitude, led to moisture convergence and ascent which was observed to develop repeatedly. This was accompanied by a long-term duration of the meiyu rainfall in the YHRV and frequent occurrences of rainstorm processes. Moreover, two blocking highs were present in the middle to high latitudes over Eurasia, and a trough along the East Asian coast was also active, which allowed cold air intrusions to move southward through the northwestern and/or northeastern paths. The cold air frequently merged with the warm and moist air from the low latitudes resulting in low-level convergence over the YHRV. The persistent warming in the tropical Indian Ocean is found to be an important external contributor to an EAP/PJ-like teleconnection pattern over East Asia along with an intensified and southerly displaced WPSH, which was observed to be favorable for excessive rainfall over YHRV.

2020年江淮流域创纪录的梅雨，具有起发早、后退滞后、持续时间长、经向雨带宽、降水充沛、暴雨过程频繁等特点。值得注意的是，2020年梅雨季东亚季风环流系统呈现显着的准双周振荡（QBWO），与梅雨的起退、雨带的北移和停滞、发生和变化有关。大暴雨过程持续存在。相应地，在梅雨季节，季风环流子系统，包括西太平洋副热带高压（WPSH）、高空东亚西风急流和低空西南急流，都经历了与QBWO相关的周期性振荡。最为显着地，一个大的南风中心的反复建立，纬度相对稳定，导致水汽汇聚和上升，被观察到反复发展。伴随着YHRV梅雨雨持续时间较长，暴雨过程频繁发生。此外，欧亚大陆中高纬度地区存在两个阻塞高压，东亚海岸的一个低压槽也很活跃，这使得冷空气侵入通过西北和/或东北路径向南移动。冷空气经常与来自低纬度地区的暖湿空气合并，导致YHRV上空低层辐合。