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The Anomalous Mei-yu Rainfall of Summer 2020 from a Circulation Clustering Perspective: Current and Possible Future Prevalence


Highly unusual amounts of rainfall were seen in the 2020 summer in many parts of China, Japan, and South Korea. At the intercontinental scale, case studies have attributed this exceptional event to a displacement of the climatological western North Pacific subtropical anticyclone, potentially associated Indian Ocean sea surface temperature patterns and a mid-latitude wave train emanating from the North Atlantic. Using clusters of spatial patterns of sea level pressure, we show that an unprecedented 80% of the 2020 summer days in East Asia were dominated by clusters of surface pressure greater than normal over the South China Sea. By examining the rainfall and water vapor fluxes in other years when these clusters were also prevalent, we find that the frequency of these types of clusters was likely to have been largely responsible for the unusual rainfall of 2020. From two ensembles of future climate projections, we show that summers like 2020 in East Asia may become more frequent and considerably wetter in a warmer world with an enhanced moisture supply.


2020 年夏季, 中国、 日本和韩国的诸多地区均出现了创纪录的极端强降水. 该事件的个例研究将这一特殊事件归因于西北太平洋副热带反气旋的位置移动, 可能与印度洋海表面温度异常和自北大西洋发出的中纬度波列有关. 本工作通过对东亚逐日海平面气压 (SLP) 空间场的聚类分析, 发现 2020 年夏季南海地区为正 SLP 异常的天气型出现天数达到整个夏季的 80%, 为 1979 年以来之最. 通过与其他环流型所对应的降水和水汽通量异常对比, 发现这类天气型的频繁出现很可能是造成 2020 年梅雨期降水偏多的主要原因. 该研究进一步分析了两个大样本集合气候模拟预估结果, 发现未来在全球进一步增暖、 水分供应相应增加的情景下, 像 2020 年这样的东亚夏季环流可能会出现得更加频繁, 中国降水也会更强.


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Robin CLARK and Peili WU were supported by the UK-China Research & Innovation Partnership Fund through the Met Office Climate Science for Service Partnership (CSSP) China as part of the Newton Fund. Lixia ZHANG was supported by the National Natural Science Foundation of China under Grant No. 42075037 and the Innovative Team Project of Lanzhou Institute of Arid Meteorology (GHSCXTD-2020-2). Chaofan LI was supported by the National Key Research and Development Program of China (2018YFC1506005).We also acknowledge useful discussions with Gill MARTIN during the manuscript preparation.

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Correspondence to Robin T. Clark.

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Article Highlights

• Summer 2020 was dominated to an unprecedented extent, by clusters of days of surface pressure greater than normal in the South China Sea.

• The prevalence of positive surface pressure anomalies over the South China Sea is a potentially useful proxy of such events in the future.

• According to model projections, summers of circulation clusters in China, similar to those of 2020 may become more frequent in the future.

• Projections also suggest potentially large rainfall increases in China in future years when circulation is similar to that of 2020.

This paper is a contribution to the special issue on Summer 2020: Record Rainfall in Asia—Mechanisms, Predictability and Impacts.

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The Anomalous Mei-yu Rainfall of Summer 2020 from a Circulation Clustering Perspective: Current and Possible Future Prevalence

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Clark, R.T., Wu, P., Zhang, L. et al. The Anomalous Mei-yu Rainfall of Summer 2020 from a Circulation Clustering Perspective: Current and Possible Future Prevalence. Adv. Atmos. Sci. 38, 2010–2022 (2021).

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Key words

  • circulation clustering
  • mei-yu front
  • 2020 summer rainfall
  • climate projections


  • 环流分型
  • 梅雨锋
  • 2020 夏季降水
  • 气候预估