An unexpected super mei-yu struck in 2020 in the Yangtze-Huaihe River basin,southern Korea,and southern Japan(hereafter referred to as the mei-yu regions),causing many casualties and huge economic losses.The super mei...An unexpected super mei-yu struck in 2020 in the Yangtze-Huaihe River basin,southern Korea,and southern Japan(hereafter referred to as the mei-yu regions),causing many casualties and huge economic losses.The super mei-yu was characterized by a remarkably early onset(around 1 June),late withdrawal(around 1 August),and intense rainfalI during the mei-yu season.The precipitation in the early onset and late withdrawal stages contributed more than half of the total mei-yu-period precipitation over the mei-yu regions in 2020.In this study,the authors explored the dominant remote forcing of the mei-yu early onset and late withdrawal to understand the mechanisms of this super mei-yu.The early onset can mainly be attributed to an early northward-shifted East Asian jet stream(EAJS).The late withdrawal mainly resulted from the stagnant EAJS and the western North Pacific subtropical high(WPSH) during 10 July to 1 August.Specifically,North Atlantic sea surface temperature anomalies(SSTAs) excited a Rossby wave,which was steered by atmospheric anomalies related to the western North Pacific SSTAs,causing the early northward-shifted EAJS and generating an early onset.The record-breaking warm SSTAs over the North Indian Ocean to South China Sea and the reduced sea-ice concentration(SIC) over the Laptev-East Siberian Sea played important roles in causing the stagnant WPSH and EAJS during July,which led to the late withdrawal.Meanwhile,the SIC anomalies may have caused the inhomogeneous rainfall distribution in the mei-yu regions.Furthermore,projection results suggest that the probability of a late mei-yu withdrawal similar to the 2020 case will increase in the future.Finally,potential predictors of an extreme mei-yu are discussed.展开更多
This study examined the rainfall around the middle and lower reaches of the Yangtze River and related atmospheric circulation by using NCEP reanalysis data. The purpose of this study is to analyze their decadal variat...This study examined the rainfall around the middle and lower reaches of the Yangtze River and related atmospheric circulation by using NCEP reanalysis data. The purpose of this study is to analyze their decadal variation and the relationship among rainfall, atmospheric circulation around East Asia and the ENSO episodes. Current results are presented as follows: (1) Very clear increasing trend of the rainfall around the middle and low reaches of the Yangtze River during the Meiyu period and June to July is found in the recent 15 years. Meanwhile, the geopotential height at 500 hPa around the Okhotsk Sea also holds similar increasing trend. It is noticeable that ENSO episodes tend to occur more frequently in the recent 15 years. (2) An index describing East Asian summer monsoon is well correlated with the SST in the Nino-3 region in preceding autumn in the recent 20 years but is not prior to the period. This means that the El Nino phenomenon exerts more impacts on East Asian summer monsoon recently. (3) The warm phase of PDO in the recent 20 years basically coincides with the increasing trend of the atmospheric circulation in East Asia.展开更多
基金supported by the National Natural Science Foundation of China [grant number 42088101]the Major Program of the National Natural Science Foundation of China [grant number 41991283]。
文摘An unexpected super mei-yu struck in 2020 in the Yangtze-Huaihe River basin,southern Korea,and southern Japan(hereafter referred to as the mei-yu regions),causing many casualties and huge economic losses.The super mei-yu was characterized by a remarkably early onset(around 1 June),late withdrawal(around 1 August),and intense rainfalI during the mei-yu season.The precipitation in the early onset and late withdrawal stages contributed more than half of the total mei-yu-period precipitation over the mei-yu regions in 2020.In this study,the authors explored the dominant remote forcing of the mei-yu early onset and late withdrawal to understand the mechanisms of this super mei-yu.The early onset can mainly be attributed to an early northward-shifted East Asian jet stream(EAJS).The late withdrawal mainly resulted from the stagnant EAJS and the western North Pacific subtropical high(WPSH) during 10 July to 1 August.Specifically,North Atlantic sea surface temperature anomalies(SSTAs) excited a Rossby wave,which was steered by atmospheric anomalies related to the western North Pacific SSTAs,causing the early northward-shifted EAJS and generating an early onset.The record-breaking warm SSTAs over the North Indian Ocean to South China Sea and the reduced sea-ice concentration(SIC) over the Laptev-East Siberian Sea played important roles in causing the stagnant WPSH and EAJS during July,which led to the late withdrawal.Meanwhile,the SIC anomalies may have caused the inhomogeneous rainfall distribution in the mei-yu regions.Furthermore,projection results suggest that the probability of a late mei-yu withdrawal similar to the 2020 case will increase in the future.Finally,potential predictors of an extreme mei-yu are discussed.
基金Research Fund for Tropical Oceans Project 973 of the Ministry of Science and Technology(2004CB418300) No. 2002DIB20067 from the Ministry of Science and Technology.
文摘This study examined the rainfall around the middle and lower reaches of the Yangtze River and related atmospheric circulation by using NCEP reanalysis data. The purpose of this study is to analyze their decadal variation and the relationship among rainfall, atmospheric circulation around East Asia and the ENSO episodes. Current results are presented as follows: (1) Very clear increasing trend of the rainfall around the middle and low reaches of the Yangtze River during the Meiyu period and June to July is found in the recent 15 years. Meanwhile, the geopotential height at 500 hPa around the Okhotsk Sea also holds similar increasing trend. It is noticeable that ENSO episodes tend to occur more frequently in the recent 15 years. (2) An index describing East Asian summer monsoon is well correlated with the SST in the Nino-3 region in preceding autumn in the recent 20 years but is not prior to the period. This means that the El Nino phenomenon exerts more impacts on East Asian summer monsoon recently. (3) The warm phase of PDO in the recent 20 years basically coincides with the increasing trend of the atmospheric circulation in East Asia.
