Historical Rankings and Vortices' Activities of the Extreme Mei‐yu Seasons: Contrast 2020 to Previous Mei‐yu Seasons.

The Mei‐yu season (MYS) is one of the most important components of the East Asian rainy season. As the MYS rainfall is significantly uneven, determining its notable features is crucial to understanding/predicting the MYS precipitation. This study provided the first report on the historical rankings of the accumulated precipitation within different regions during extreme MYSs. It was shown that, in the extreme 2020 MYS, the area‐averaged precipitation within/around the Sichuan Basin ranked first during a 70‐year period. For the first time, quantitative contributions of mesoscale vortices to the total precipitation of extreme MYSs were shown. It was found that, during the 2020 MYS, vortices accounted for up to 50% of the MYS's duration within/around Sichuan Basin, and induced up to 90% of the total precipitation there. The abnormally active vortices in the 2020 MYS were the direct reason for the highest precipitation in the past 70 years within/around the Sichuan Basin. Plain Language Summary: The Mei‐yu season (MYS) is a climatic phenomenon of continuous overcast and rainy weather (typically appears in June and July), that occurs in the Yangtze River Basin, Taiwan, Japan and Southern Korea. As the MYS rainfall was uneven, to determine its notable features is crucial to understanding and predicting the MYS precipitation. We provided the first report on the historical rankings of the accumulated precipitation within different regions during the extreme MYSs of 1954, 1998 and 2020. It is shown that, during the 2020 MYS, the area‐averaged precipitation within/around Sichuan Basin was the highest in the past 70 years. By calculating the quantitative contributions of mesoscale vortices to the total MYS precipitation (this study provided the first report), we attributed the abnormally high precipitation within/around Sichuan Basin of the 2020 MYS to the abnormally active mesoscale vortices in this region. Results show that, during the 2020 MYS, vortices accounted for up to 50% of the MYS's whole duration within/around Sichuan Basin, and induced up to 90% of the total precipitation there. Therefore, improving the forecast of mesoscale vortices is of great importance to improve the MYS‐rainfall prediction. Key Points: Historical rankings of the precipitation within different regions during extreme Mei‐yu seasons were determined for the first timeQuantitative contributions of mesoscale vortices to the total precipitation of the extreme Mei‐yu seasons were shown for the first timeAbnormally active vortices in the 2020 Mei‐yu season were the direct reason for its abnormally high rainfall within/around Sichuan Basin [ABSTRACT FROM AUTHOR]