The Longest 2020 Meiyu Season Over the Past 60 Years: Subseasonal Perspective and Its Predictions
The Longest 2020 Meiyu Season Over the Past 60 Years: Subseasonal Perspective and Its Predictions
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60年来最长的2020梅雨季节：次季节视角及其预测
DOI：
10.1029/2021gl093596
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发表时间：
2021-05-16
影响因子：
5.2
通讯作者：
Dong, Wenjie
中科院分区：
文献类型：
--
作者：
Qiao, Shaobo;Chen, Dong;Dong, Wenjie
自1961年以来，创纪录的2020年梅雨季节导致长江和淮河流域（YHRV）发生严重洪水。为什么梅雨的持续时间在2020年翻了一番仍然是个谜。我们发现，长期梅雨可分为三个阶段：早发期、强持续期和延迟戒断期。早发与极负相东大西洋/西俄罗斯远程连接有关。此次强持续与拉尼娜快速发展所维持的正相位太平洋-日本（PJ）模式有关。这次延迟的撤退与正PJ型和对流层中“两脊一槽”型在亚洲上空的共同作用有关。两个亚季节预报系统均预报了前两阶段的正降水异常，而第三阶段的正降水异常则未出现，这可能与两脊一槽模式预报较差有关。这些结果突出了亚季节演化在极端气候事件中的作用。在东亚夏季风向北推进的过程中，东亚副热带地区通常在6月中旬至7月中旬出现一个准静止的雨带，中国称其为梅雨，日本称其为白雨。2020年“梅雨”的持续时间和累计降雨量均创1961年以来的最高记录，给中国中东部的长江和淮河流域造成了严重的洪灾和巨大的经济损失。我们研究了这种长期洪水的机制和预测。创纪录的2020年“梅雨”可以分为三个阶段：先发阶段、强持续阶段和延迟退出阶段。早发期主要由东大西洋/西俄罗斯遥相关的温带气候异常引起。相反，强持续阶段是由于热带强迫的增强，触发了太平洋-日本型。撤退阶段的延迟是由热带强迫和中纬度遥相关的共同作用引起的。目前先进的预报系统可以预测前两阶段的正降水异常，但不能预测第三阶段的正降水异常。这些发现促进了我们对2020年极端洪水的理解，并有助于改善未来极端季风的预测。短句来源2020年梅雨季节持续时间较长，呈现出提前开始、强持续和延迟退出三个阶段的特征，其中中纬度遥相关对2020年梅雨的开始和退出起关键作用，后两个阶段热带强迫的作用增强，由于中纬度遥相关预测失败，高级预报系统无法预测延迟退出
The record-long 2020 Meiyu season since 1961 caused severe floods over the Yangtze and Huaihe River valleys (YHRV). Why the Meiyu duration doubled in 2020 remains a puzzle. We show that the long-lasting Meiyu can be divided into three stages: advanced-onset, strong-persisting, and delayed-withdrawal. The advanced-onset was associated with an extremely negative-phase East Atlantic/West Russia teleconnection. The strong-persisting was attributed to a positive-phase Pacific-Japan (PJ) pattern sustained by La Nina's rapid development. The delayed withdrawal was related to the combined effect of a positive PJ pattern and a mid-troposphere "two ridge-one trough" pattern over Asia. Two subseasonal forecasting systems predicted the positive rainfall anomalies over the YHRV in the first two stages, but not the third stage, which may be associated with poor prediction of the two ridge-one trough pattern. These results highlight the role of subseasonal evolution in extreme climate events.Plain Language Summary During the northward advance of the East Asian summer monsoon, the East Asian subtropical region is normally characterized by a quasi-stationary rainband that persists from mid-June to mid-July, which is known as Meiyu in China and Baiu in Japan. Both the duration and the accumulated rainfall of the 2020 Meiyu set the highest record since 1961, which caused a severe flood and an enormous economic loss in the Yangtze and Huaihe River valleys (YHRV), central-eastern China. We investigated the mechanism and predictions of this long-lasting flood. The record-long 2020 Meiyu can be divided into three stages: advanced-onset, strong-persisting, and delayed withdrawal. The advanced-onset stage was mainly induced by the extratropical climate anomalies associated with the East Atlantic/West Russia teleconnection. In contrast, the strong-persisting stage was due to the enhanced tropical forcing via triggering the Pacific-Japan pattern. The delayed withdrawal stage arises from the combined effect of tropical forcing and mid-latitude teleconnection. The current advanced forecasting systems can predict the positive rainfall anomalies over the YHRV in the first two stages, but not the third stage. These findings advance our understanding of the extreme 2020 flood and help improve future extreme monsoon prediction.Key PointsThe long-lasting 2020 Meiyu season was characterized by three stages: advanced-onset, strong-persisting, and delayed withdrawalThe mid-latitude teleconnection played a crucial role in the 2020 Meiyu onset and withdrawal, while tropical forcing's role is enhanced in the last two stagesAdvanced forecasting systems cannot predict the delayed withdrawal due to the failure in predicting the mid-latitude teleconnection