Cause of Extreme Heavy and Persistent Rainfall over Yangtze River in Summer 2020
Cause of Extreme Heavy and Persistent Rainfall over Yangtze River in Summer 2020
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DOI：
10.1007/s00376-021-0433-3
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发表时间：
2021-06-30
影响因子：
5.8
通讯作者：
Zhu, Zhiwei
中科院分区：
文献类型：
--
作者：
Pan, Xiao;Li, Tim;Zhu, Zhiwei
2020年6-7月，长江流域出现了创纪录的强降水和持续性降水。观测资料分析表明，这次强持续降水是南风异常与西北太平洋极强反气旋(WNPAC)和北上东北风异常与东北亚高压异常的汇合。进一步的观测和模拟研究表明，极强的WNPAC是赤道太平洋类拉尼娜海温异常(SSTA)强迫和热带印度洋(IO)暖SSTA强迫共同作用的结果。与传统的中太平洋厄尔尼诺(CP)厄尔尼诺现象衰减缓慢不同，2020年初的CP厄尔尼诺现象衰减迅速，到初夏变成了拉尼娜现象。这一快速过渡对WNPAC产生了关键影响。同时，热带IO出现了异常大范围的SST增暖，这是因为与CP El Nino有关的IO上的中等年际SSTA被年代际/长期趋势分量所叠加。数值敏感性试验表明，IO的加热异常和热带太平洋的加热异常对WNPAC的形成和维持都有贡献。持续的东北亚高压异常是中纬度地区静止Rossby波列的一部分，由印度、热带东太平洋和热带大西洋上空的综合加热异常驱动。
Record-breaking heavy and persistent precipitation occurred over the Yangtze River Valley (YRV) in June-July (JJ) 2020. An observational data analysis has indicated that the strong and persistent rainfall arose from the confluence of southerly wind anomalies to the south associated with an extremely strong anomalous anticyclone over the western North Pacific (WNPAC) and northeasterly anomalies to the north associated with a high-pressure anomaly over Northeast Asia. A further observational and modeling study has shown that the extremely strong WNPAC was caused by both La Nina-like SST anomaly (SSTA) forcing in the equatorial Pacific and warm SSTA forcing in the tropical Indian Ocean (IO). Different from conventional central Pacific (CP) El Ninos that decay slowly, a CP El Nino in early 2020 decayed quickly and became a La Nina by early summer. This quick transition had a critical impact on the WNPAC. Meanwhile, an unusually large area of SST warming occurred in the tropical IO because a moderate interannual SSTA over the IO associated with the CP El Nino was superposed by an interdecadal/long-term trend component. Numerical sensitivity experiments have demonstrated that both the heating anomaly in the IO and the heating anomaly in the tropical Pacific contributed to the formation and maintenance of the WNPAC. The persistent high-pressure anomaly in Northeast Asia was part of a stationary Rossby wave train in the midlatitudes, driven by combined heating anomalies over India, the tropical eastern Pacific, and the tropical Atlantic.