Linkage of the Decadal Variability of Extreme Summer Heat in North China with the IPOD since 1981

Extreme summer heat can have serious socioeconomic impacts in North China.Here,we explore the decadal variability of the number of extreme heat days in early-to-mid summer(June and July)and a related potential mechanism consistent with the major seasonal occurrence period of extreme heat events in North China(NCSH).Observational analyses show significant decadal variability in NCSH for 1981–2021,potentially linked to the Indo-Pacific warm pool and Northwest Pacific Ocean dipole(IPOD)in early-to-mid summer.Dynamic diagnostic analysis and the linear baroclinic model(LBM)show that the positive IPOD in early-to-mid summer can excite upward vertical wind anomalies in the South China-East China Sea region,shifting the position of the western Pacific subtropical high(WPSH)to the east or weakening the degree of its control of the South China-East China Sea region,thus generating a positive geopotential height quadrupole(EAWPQ)pattern in the East Asia-Northwest Pacific region.Subsequently,the EAWPQ can cause air compression(expansion)over North China by regulating the tropospheric thickness anomalies in North China,thus increasing(decreasing)NCSH.Finally,an empirical model that incorporates the linear trend can better simulate the decadal NCSH compared to an empirical model based solely on the IPOD index,suggesting that the decadal variability of NCSH may be a combined contribution of the decadal IPOD and external linear forcing.

Extreme characteristics and causes of the drought event in the whole Yangtze River Basin in the midsummer of 2022

Due to their huge socio-economic impacts and complex formation causes,extreme and continuous drought events have become the focus and nodus of research in recent years.In the midsummer(July-August)of 2022,a severe drought event occurred in the whole Yangtze River Basin(YRB),China.During that period,the precipitation in the upper,middle and lower reaches of the YRB dropped over 40%less than the 1961-2021 climatic mean,which had never happened previously.Furthermore,the temperature was the highest during 1961-2022.The record-breaking magnitude of less rainfall and high temperature directly led to the continuous development of this extreme drought event.An atmospheric moisture budget analysis revealed that the YRB midsummer rainfall anomaly was dominated by the anomalous powerful vertical moisture advection,which was derived from the strongest descending motion over the whole YRB in the 2022 midsummer during 1981-2022.The western Pacific subtropical high(WPSH)during the midsummer remained stronger,more westward and lasted longer than the climatic mean.As a result,the whole YRB was controlled by a positive geopotential height centre.Further evidence revealed that the anomalous subtropical zonal flow played a crucial role in inducing the extreme descent over the YRB.Moreover,the anomalous upper-tropospheric easterly flow over the YRB in 2022 is the strongest during 1981-2022,modulating the generation of the unprecedented descent anomaly over the YRB.The likelihood that an integrated connection of severe drought in East Asia and flood in West Asia and northwestern South Asia would increase when the extremely strong easterly anomalies in the upper troposphere emerged and induced descending adiabatic flow on the eastern sides of the Tibetan Plateau.The results of this study can provide scientific insights into the predictability of extreme drought events and provide ways to improve predictions.

Changes in Polyphenols and Antioxidant Activities of Yingshan Yunwu Tea during Digestion in Vitro

[Objectives]To explore the change rule of polyphenol content and antioxidant activity of coarse old leaves of Yingshan Yunwu Tea in the process of human digestion.[Methods]The coarse and old leaves of Yunwu tea in Yingshan,Huanggang,Hubei Province were selected as the research object,and their digestion in vitro was simulated.The total polyphenol content was determined by Folin-phenol reagent colorimetric method,and the DPPH radical scavenging activity and total antioxidant activity were determined.[Results]After simulated gastrointestinal digestion in vitro,the polyphenol content and antioxidant activity of coarse old leaf tea soup showed a downward trend.After gastrointestinal digestion,the polyphenol content in tea infusion separately decreased by 31.8%and 8.5%;the scavenging rate of DPPH free radical was 97%before digestion,decreased to 92%after gastric digestion and 65%after intestinal digestion,which decreased by 5%and 27%,respectively;after gastrointestinal digestion,the total antioxidant capacity of tea soup decreased by 4.7%and 3.1%,respectively.[Conclusions]This study provided a reference for the development and application of coarse old leaves of Yingshan Yunwu tea,and provided a reference for the nutritional value evaluation and comprehensive utilization of coarse old leaves,so as to make the best use of coarse tea leaves and reduce the waste of resources.

2018: The Hottest Summer in China and Possible Causes

In 2018,China experienced the hottest summer since 1961.The maximum,mean,and minimum temperatures all reached the highest.Air temperatures in most regions were much higher than normal;in northern China especially,the temperature anomalies were above double of the standard deviations.Consistent variations of temperature anomalies appeared in the national mean and in northern China on different timescales from intraseasonal to annual,indicating that the above normal temperature in northern China contributed significantly to the record-breaking hot summer of entire China.Relationships among the high temperature in summer 2018,the tropospheric circulation,and the global sea surface temperatures(SSTs)are further analyzed.It is found that the intensified and more northward western Pacific subtropical high(WPSH),weakened Northeast China cold vortex(NECV),and positive geopotential height anomaly from northern China to the Sea of Japan resulted in the abnormally high temperature in summer 2018.From late July to mid August,the WPSH was stronger than normal,with its ridge line jumping to north of 40°N;meanwhile,the NECV was much weaker and more northward than normal;both of the two systems led to the persistent high temperature in northern China during this period.In addition,the SSTs in Kuroshio and its extension area(K–KE)in summer 2018 were also the highest since 1961 and the greatest positive SST anomaly in K–KE was favorable for the above normal geopotential height over North China–Northeast China–Japan at 500 hPa,giving rise to the exceptionally high temperature in northern China.

The Record-Breaking Extreme Drought in Yunnan Province, Southwest China during Spring-Early Summer of 2019 and Possible Causes

In spring and early summer of 2019, Yunnan Province experienced the most severe seasonal drought on record,with days of extreme drought area exceeding 10^5 km^2 far more than normal. Consistently, the precipitation in each month from February to June is over 30% less than normal, and about 50% less in the most severe drought period(April–June). The rainy season in Southwest China(SWC) started on the third pentad in June 2019, which is the second latest in history. The rainy season in Yunnan started on 24 June, which is the latest(29 days later than normal). On the contrary, the onset of the South China Sea summer monsoon(SCSSM) is abnormally early. The lag time between the start of the rainy season in SWC and the onset of the SCSSM in 2019 is 7 pentads, which is the largest since 1961, much longer than the climate mean(less than 1 pentad). The present study analyzes the possible reasons why the rainy season came extremely late and the drought disaster persisted and intensified after a much early SCSSM, at both seasonal and subseasonal timescales. The abnormally late onset of the rainy season and the second greatest potential evapotranspiration(PET) since 1981 are the direct reasons for the persistent drought. Statistical results show that the water vapor from southwest of Yunnan in April–June contributes more than that from the east at the seasonal scale. In April–June 2019, however, the southern branch trough(SBT) was abnormally weak, the large and strong anticyclonic wind anomaly prevailed over the Bay of the Bengal(BOB), and the meridional water vapor transport to Yunnan was weak. At the subseasonal scale, the weaker SBT lasted the longest, and the strong convection over the BOB came up late despite of an early onset of the SCSSM, which resulted in reduced low-level moisture convergence in Yunnan and development of drought prior to the SCSSM onset. From the onset of SCSSM to the start of rainy season in SWC, the SBT and meridional water vapor transport from the BOB were still weak, and the water vapor was mainly transported into the coastal area of South and Southeast China rather than Yunnan. After the start of the rainy season in SWC, the SBT was still weak. This led to less moisture transport in the westerlies to the west of Yunnan and the persistent extreme drought. Both the statistical results and case analysis indicate that the stronger Australian high in spring and early summer of 2019 was associated with the abnormally strong anticyclone over the BOB and the always weak SBT. In sum, the anomalous weakness of SBT played a critical role in the extreme drought occurrence and persistence in Yunnan of Southwest China in 2019.

An unprecedented high temperature event in southern China in autumn 2021 and the essential role of the mid-latitude trough

Studies about high temperatures in China rarely touched the period beyond summer.But in September-early October 2021,a record-breaking high temperature event occurred in southern China,and affected agriculture in many provinces.Both the daily maximum temperature and the number of high temperature days were the highest in September since 1951.To better understand the different features and possible causes of the extreme event in autumn from those in summer,the analysis of atmospheric circulation patterns was conducted.The western Pacific subtropical high(WPSH)was quite stronger and extended much more westward in most of the days in September 2021 than its climatology,which directly caused this unprecedented autumn high temperature event.Besides,the mid-latitude trough over the east of Japan may also play an essential role in this high temperature event.Due to the southward extension of the trough,a cyclonic circulation anomaly appeared at 850 hPa,and its northerly wind component prevailed in the west of the trough and blocked the eastward retreat of the WPSH.As a result,southern China was stably controlled by the WPSH,which led to the persistence of this high temperature event.The conclusion is further confirmed by the statistical results from the analysis of the multi-year data and analogue analysis.Compared to the previous studies,this study reveals the essential role of the mid-latitude trough and highlights the joint impacts of the WPSH and the trough in causing the unprecedented autumn high temperature event.

Abrupt Flood–Drought Alternation in Southern China during Summer 2019

We investigated the abrupt alternation from flood to drought in southern China during summer 2019 using multiple datasets.Positive anomalies of precipitation occurred in southern China in the summer of 2019 and the daily precipitation in the south of the middle and lower reaches of the Yangtze River valley showed an abrupt change from flood to drought conditions around mid-July.The highest precipitation in 39 yr was recorded between 1 June and 14 July 2019.The circulation systems affecting this high precipitation included a persistent deepened East Asian trough,the southward location of the western Pacific subtropical high,an intensified East Asian subtropical jet,an anomalous low-level cyclone from southern Japan to southern China,and extremely strong positive vorticity over the Jiangnan area.Completely different atmospheric circulation anomalies from 15 July to 31 August caused continuously high temperatures,below-normal precipitation,and severe drought in Jiangnan area.Further investigations showed that the sudden change in atmospheric circulation around mid-July started in the mid and lower troposphere and was influenced by the northward track of Tropical Cyclone Danas in the northwestern Pacific.

Extreme cold wave in early November 2021 in China and the influences from the meridional pressure gradient over East Asia

In early November 2021,China experienced its second strongest cold wave event during 1981-2021.Although the Siberian high is considered the main factor influencing cold wave events in East Asia,it was not extremely strong from 4 to November 9,2021.The spatial distribution of the correlation coefficients between the sea level pressure and the daily temperature anomalies shows a monopole pattern,with a notable negative centre in the southern part of the Siberian high monitoring domain.However,the correlation between the sea level pressure and temperature drop presents a typical dipole pattern,with a distinct negative centre in the northern monitoring domain and a positive centre in southern East Asia.During the November 2021 super cold wave process,the sea level pressure anomalies display a dipole pattern with a higher centre in the north and a lower centre in the south owing to the northward shift of the Intertropical Convergence Zone.The meridional pressure gradient index clearly reveals the non-negligible effect of subtropical low-pressure on this super cold wave process,indicating its possibly essential supplementary role in enhancing this process.The above findings provide a new understanding of its mechanism and long-range forecasts.