Shanghai experienced the longest rainy days in 2018/2019 winter since 1988. The physical cause of such an unusual climate condition was investigated through the diagnosis of observational data. From a seasonal perspective, a long persistent rainy winter was often associated with an El Niño condition in the equatorial Pacific. This abnormal oceanic condition induces a remote teleconnection pattern with pronounced low-level southerly anomalies over East China. The wind anomalies transported moisture from tropical oceans and caused persistent rainfall in East Asia. Meanwhile, the local rainfall time series exhibited a strong quasi-biweekly oscillation (QBWO). Three persistent rainy events were identified in the 2018/2019 winter and they all occurred during the active phase of the QBWO. The first two events were associated with a low pressure anomaly west of Shanghai. Southerly anomalies associated with the low pressure system advected high mean moisture into central eastern China, leading to the persistent rainfall there. The third event was associated with a high pressure anomaly in lower troposphere to the east of Shanghai, which induced anomalous southerlies to its west, favoring the occurrence of rainfall in Shanghai. The result suggests the importance of high-frequency variability in affecting seasonal rainfall anomalies.

中文翻译：

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2018/2019年冬季上海持续降雨相关的季节性和亚季节循环异常

上海自1988年以来是2018/2019年冬季最长的雨天。通过观测数据的诊断研究了这种异常气候条件的物理原因。从季节的角度来看，赤道太平洋的一个长期持续多雨的冬天常常与厄尔尼诺现象有关。这种异常的海洋状况导致了遥远的遥相关型，并在华东地区出现了明显的低水平南风异常。异常的风将热带海洋的水分运走，并导致东亚持续降雨。同时，当地降雨时间序列表现出强烈的准双周振荡（QBWO）。在2018/2019年冬季确定了三场持续的降雨事件，这些都发生在QBWO的活动阶段。前两个事件与上海以西的低压异常有关。与低压系统有关的南风异常使华东中部平均水汽含量较高，导致该地区持续降雨。第三次事件与上海东部对流层下部高压异常有关，导致其西南偏南方向异常，有利于上海降雨。结果表明，高频变化在影响季节性降雨异常中的重要性。导致西南偏南，有利于上海降雨的发生。结果表明，高频变化在影响季节性降雨异常中的重要性。导致西南偏南，有利于上海降雨。结果表明，高频变化在影响季节性降雨异常中的重要性。