The existence of an intensifying shift in the East Asian summer monsoon(EASM)since~2000 years ago that differs from the decreasing trend of Northern Hemisphere summer insolation remains controversial.Therefore,we comp...The existence of an intensifying shift in the East Asian summer monsoon(EASM)since~2000 years ago that differs from the decreasing trend of Northern Hemisphere summer insolation remains controversial.Therefore,we compared and synthesized stalagmiteδ^(18)O records from eastern China to clarify the EASM trend during this period.A total of 30 caveδ^(18)O records that did not consistently indicate a depleted trend during 2-0 ka.Rather,they included increasing(14 caves),decreasing(8 caves),and non-significant(8 caves)trends.The spatially interpolated trends of caveδ^(18)O suggested spatial differences among three subregions:North China(NC),decreasing trend(5 caves);Central-East China/Yangtze River Valley(CEC),increasing trend(17 caves);South China(SC),decreasing trend(8 caves).The caveδ^(18)O evidence supports spatial differences in precipitation in eastern China that have been substantially demonstrated by observations and model simulations.The decreasingδ^(18)O anomaly from NC and SC was associated with the decreasing sea surface temperature over Pacific Decadal Oscillation region and increasing South Oscillation Index.The increasing CECδ^(18)O anomaly was linked to southward Intertropical Convergence Zone shift and decreasing solar irradiance.Consequently,EASM circulation is jointly forced by external and internal factors at various timescales.展开更多
A strong （weak） East Asian summer monsoon （EASM） is usually concurrent with the tripole pattern of North Atlantic SST anomalies on the interannual timescale during summer, which has positive （negative） SST anoma...A strong （weak） East Asian summer monsoon （EASM） is usually concurrent with the tripole pattern of North Atlantic SST anomalies on the interannual timescale during summer, which has positive （negative） SST anomalies in the northwestern North Atlantic and negative （positive） SST anomalies in the subpolar and tropical ocean. The mechanisms responsible for this linkage are diagnosed in the present study. It is shown that a barotropie wave-train pattern occurring over the Atlantic-Eurasia region likely acts as a link between the EASM and the SST tripole during summer. This wave-train pattern is concurrent with geopotential height anomalies over the Ural Mountains, which has a substantial effect on the EASM. Diagnosis based on observations and linear dynamical model results reveals that the mechanism for maintaining the wave-train pattern involves both the anomalous diabatic heating and synoptic eddy-vorticity forcing. Since the North Atlantic SST tripole is closely coupled with the North Atlantic Oscillation （NAO）, the relationships between these two factors and the EASM are also examined. It is found that the connection of the EASM with the summer SST tripole is sensitive to the meridional location of the tripole, which is characterized by large seasonal variations due to the north-south movement of the activity centers of the NAO. The SST tripole that has a strong relationship with the EASM appears to be closely coupled with the NAO in the previous spring rather than in the simultaneous summer.展开更多
An unusually warm East Asia in spring 2018,when exceptionally high surface air temperatures were recorded in large areas of Asia,such as northern China,southern China,and Japan,was investigated based on the ERA-Interi...An unusually warm East Asia in spring 2018,when exceptionally high surface air temperatures were recorded in large areas of Asia,such as northern China,southern China,and Japan,was investigated based on the ERA-Interim reanalysis.The East Asian warming anomalies were primarily attributed to a tripole mode of North Atlantic SST anomalies,which could have triggered anomalous Rossby wave trains over the North Atlantic and Eurasia through modulating the North Atlantic baroclinic instability.Atlantic-forced Rossby waves tend to propagate eastward and induce anomalously high pressure and anticyclonic activity over East Asia,leading to a northward displacement of the Pacific subtropical high.As a result,descending motion,reduced precipitation,and increased surface solar radiation due to less cloud cover appear over East Asia,accompanied by remarkably warm advection from the ocean to southern China,northern China,and Japan.The transportation of anomalously warm advection and the feedbacks between soil moisture and surface temperature were both favorable for the recordbreaking warmth in East Asia during spring 2018.The seasonal‘memory’of the North Atlantic tripole SST mode from the previous winter to the following spring may provide useful implications for the seasonal prediction of East Asian weather and climate.展开更多
Monthly precipitation over north China in August(NCAP)is the second highest in the year,and it is important to understand its driving mechanisms to facilitate reliable forecasting.The NCAP displays a significant decad...Monthly precipitation over north China in August(NCAP)is the second highest in the year,and it is important to understand its driving mechanisms to facilitate reliable forecasting.The NCAP displays a significant decadal variability of a cycle about 10-year and negatively correlates with the July north-east North Atlantic Tripole(NAT)over the decadal timescales.This study shows that the Eurasian decadal teleconnection(EAT)acts as a bridge that links the July NAT with NCAP decadal variability.This coupled ocean–atmosphere bridge(COAB)mechanism,through which the July NAT influences the decadal variability of NCAP,can be summarized as follows.The cumulative effect of the NAT drives the EAT to adjust atmospheric circulation over north China and the surrounding regions,and so regulates precipitation in north China by influencing local water vapor transport.When the July NAT is in a negative(positive)phase,the EAT pattern has a positive(negative)pattern,which promotes(weakens)the transmission of water vapor from the sea in the south-east to north China,thus increasing(decreasing)NCAP over decadal timescales.The decadal NCAP model established based on the July NAT can effectively predict the NCAP decadal variability,illustrating that the July NAT can be implicated as a predictor of the NCAP decadal variability.展开更多
与现有交流输电线路扩容改造方案相比,将交流输电线路改造成直流输电线路(输电线路交改直)的方式能够最大程度地发挥原有线路的输电能力使其输电功率最大化,因而具有较好的应用前景。为此,从架空线路改造、电缆线路改造和多条线路改造3...与现有交流输电线路扩容改造方案相比,将交流输电线路改造成直流输电线路(输电线路交改直)的方式能够最大程度地发挥原有线路的输电能力使其输电功率最大化,因而具有较好的应用前景。为此,从架空线路改造、电缆线路改造和多条线路改造3种交改直方式入手,对输电线路交改直技术进行论述。针对架空线路改造,概括阐述了基于三极结构的直流输电(tripole structure based HVDC,TPS-HVDC)技术和基于三线双极结构的直流输电(three-wire bipole structure based HVDC,TWBS-HVDC)技术在运行特性、拓扑结构、传输容量等方面的相关特性。针对电缆线路改造,鉴于国内外研究文献较少,提出了对称和不对称两种调制方式,同时还提出了两种拓扑结构:三极式方波交流(tripole type square wave AC,TPT-SWAC)和三相双极式方波交流(three-phase bipole type SWAC,TPBT-SWAC)输电结构。针对TPBT-SWAC内用于调节支路电流的可变电阻器,对其阻值分配方案进行了研究,得到了计算阻值的通用公式。针对多条线路改造,描述了基于TPS和TPT-SWAC或TWBS和TBPT-SWAC构建的多端直流结构,分析表明TWBS和TPBT-SWAC相较于TPS和TPT-SWAC在多端直流应用上更具优越性。多角度、多层次地分析了输电线路交改直的关键技术,能够为输电线路交改直提供更加开阔的技术思路,进而促进该领域的创新发展。展开更多
基于美国国家大气研究中心的CCSM3(community climate system model version 3)模式,对淡水扰动试验下不同平均强度热盐环流(thermohline circulation,THC)的年代际波动特征及北大西洋气候响应特征进行研究。结果表明,百年以上尺度的TH...基于美国国家大气研究中心的CCSM3(community climate system model version 3)模式,对淡水扰动试验下不同平均强度热盐环流(thermohline circulation,THC)的年代际波动特征及北大西洋气候响应特征进行研究。结果表明,百年以上尺度的THC变化对其年代际尺度波动产生显著影响,高平均强度下THC的年代际波动周期更长、更显著。对不同平均强度下北大西洋海、气要素与THC在年代际尺度上的相关分布进行分析,发现在高平均强度下,THC与海表温度(sea surface temperature,SST)的相关呈现为经向三核型分布,与海平面气压(sea lever pressure,SLP)的相关呈现为类NAO(North Atlantic oscillation)分布,而在低平均强度下,则不存在这2种模态分布;同时,在不同平均强度下,THC与各要素间的相关程度也不同,高平均强度下相关程度更高。展开更多
In contrast to previous studies that have tended to focus on the influence of the total Arctic sea-ice cover on the East Asian summer tripole rainfall pattern, the present study identifies the Barents Sea as the key r...In contrast to previous studies that have tended to focus on the influence of the total Arctic sea-ice cover on the East Asian summer tripole rainfall pattern, the present study identifies the Barents Sea as the key region where the June sea-ice variability exerts the most significant impacts on the East Asian August tripole rainfall pattern, and explores the teleconnection mechanisms involved. The results reveal that a reduction in June sea ice excites anomalous upward air motion due to strong near-surface thermal forcing, which further triggers a meridional overturning wave-like pattern extending to midlatitudes.Anomalous downward motion therefore forms over the Caspian Sea, which in turn induces zonally oriented overturning circulation along the subtropical jet stream, exhibiting the east–west Rossby wave train known as the Silk Road pattern. It is suggested that the Bonin high, a subtropical anticyclone predominant near South Korea, shows a significant anomaly due to the eastward extension of the Silk Road pattern to East Asia. As a possible descending branch of the Hadley cell, the Bonin high anomaly ultimately triggers a meridional overturning, establishing the Pacific–Japan pattern. This in turn induces an anomalous anticyclone and cyclone pair over East Asia, and a tripole vertical convection anomaly meridionally oriented over East Asia. Consequently, a tripole rainfall anomaly pattern is observed over East Asia. Results from numerical experiments using version 5 of the Community Atmosphere Model support the interpretation of this chain of events.展开更多
基金National Natural Science Foundation of China,No.42225105National Natural Science Foundation of China,No.42471177,No.42201175,No.41901099+1 种基金The Open Foundation of MOE Key Laboratory of Western China's Environmental System,Lanzhou Universitythe Fundamental Research Funds for the Central Universities,No.lzujbky-2022-kb04。
文摘The existence of an intensifying shift in the East Asian summer monsoon(EASM)since~2000 years ago that differs from the decreasing trend of Northern Hemisphere summer insolation remains controversial.Therefore,we compared and synthesized stalagmiteδ^(18)O records from eastern China to clarify the EASM trend during this period.A total of 30 caveδ^(18)O records that did not consistently indicate a depleted trend during 2-0 ka.Rather,they included increasing(14 caves),decreasing(8 caves),and non-significant(8 caves)trends.The spatially interpolated trends of caveδ^(18)O suggested spatial differences among three subregions:North China(NC),decreasing trend(5 caves);Central-East China/Yangtze River Valley(CEC),increasing trend(17 caves);South China(SC),decreasing trend(8 caves).The caveδ^(18)O evidence supports spatial differences in precipitation in eastern China that have been substantially demonstrated by observations and model simulations.The decreasingδ^(18)O anomaly from NC and SC was associated with the decreasing sea surface temperature over Pacific Decadal Oscillation region and increasing South Oscillation Index.The increasing CECδ^(18)O anomaly was linked to southward Intertropical Convergence Zone shift and decreasing solar irradiance.Consequently,EASM circulation is jointly forced by external and internal factors at various timescales.
基金jointly supported by the National Basic Research Program of China (Grant Nos. 2010CB950404, 2013CB430203, 2010CB950501 and 2012CB955901)the National Natural Science Foundation of China (Grant No. 41205058)+1 种基金the China Postdoctoral Science Foundation (Grant No. 2012M510634)the National Science and Technology Support Program of China (Grant No. 2009BAC51B05)
文摘A strong （weak） East Asian summer monsoon （EASM） is usually concurrent with the tripole pattern of North Atlantic SST anomalies on the interannual timescale during summer, which has positive （negative） SST anomalies in the northwestern North Atlantic and negative （positive） SST anomalies in the subpolar and tropical ocean. The mechanisms responsible for this linkage are diagnosed in the present study. It is shown that a barotropie wave-train pattern occurring over the Atlantic-Eurasia region likely acts as a link between the EASM and the SST tripole during summer. This wave-train pattern is concurrent with geopotential height anomalies over the Ural Mountains, which has a substantial effect on the EASM. Diagnosis based on observations and linear dynamical model results reveals that the mechanism for maintaining the wave-train pattern involves both the anomalous diabatic heating and synoptic eddy-vorticity forcing. Since the North Atlantic SST tripole is closely coupled with the North Atlantic Oscillation （NAO）, the relationships between these two factors and the EASM are also examined. It is found that the connection of the EASM with the summer SST tripole is sensitive to the meridional location of the tripole, which is characterized by large seasonal variations due to the north-south movement of the activity centers of the NAO. The SST tripole that has a strong relationship with the EASM appears to be closely coupled with the NAO in the previous spring rather than in the simultaneous summer.
基金supported by the National Key Research and Development Program of China [grant number2016YFA0602703]the National Natural Science Foundation of China [grant numbers 41661144019,41690123,41690120,and91637208]+1 种基金the CMA Guangzhou Joint Research Center for Atmospheric Sciencesthe Jiangsu Collaborative Innovation Center for Climate Change
文摘An unusually warm East Asia in spring 2018,when exceptionally high surface air temperatures were recorded in large areas of Asia,such as northern China,southern China,and Japan,was investigated based on the ERA-Interim reanalysis.The East Asian warming anomalies were primarily attributed to a tripole mode of North Atlantic SST anomalies,which could have triggered anomalous Rossby wave trains over the North Atlantic and Eurasia through modulating the North Atlantic baroclinic instability.Atlantic-forced Rossby waves tend to propagate eastward and induce anomalously high pressure and anticyclonic activity over East Asia,leading to a northward displacement of the Pacific subtropical high.As a result,descending motion,reduced precipitation,and increased surface solar radiation due to less cloud cover appear over East Asia,accompanied by remarkably warm advection from the ocean to southern China,northern China,and Japan.The transportation of anomalously warm advection and the feedbacks between soil moisture and surface temperature were both favorable for the recordbreaking warmth in East Asia during spring 2018.The seasonal‘memory’of the North Atlantic tripole SST mode from the previous winter to the following spring may provide useful implications for the seasonal prediction of East Asian weather and climate.
基金supported by the Innovation and development project of China Meteorological Administration(No.CXFZ2021J030).
文摘Monthly precipitation over north China in August(NCAP)is the second highest in the year,and it is important to understand its driving mechanisms to facilitate reliable forecasting.The NCAP displays a significant decadal variability of a cycle about 10-year and negatively correlates with the July north-east North Atlantic Tripole(NAT)over the decadal timescales.This study shows that the Eurasian decadal teleconnection(EAT)acts as a bridge that links the July NAT with NCAP decadal variability.This coupled ocean–atmosphere bridge(COAB)mechanism,through which the July NAT influences the decadal variability of NCAP,can be summarized as follows.The cumulative effect of the NAT drives the EAT to adjust atmospheric circulation over north China and the surrounding regions,and so regulates precipitation in north China by influencing local water vapor transport.When the July NAT is in a negative(positive)phase,the EAT pattern has a positive(negative)pattern,which promotes(weakens)the transmission of water vapor from the sea in the south-east to north China,thus increasing(decreasing)NCAP over decadal timescales.The decadal NCAP model established based on the July NAT can effectively predict the NCAP decadal variability,illustrating that the July NAT can be implicated as a predictor of the NCAP decadal variability.
文摘与现有交流输电线路扩容改造方案相比,将交流输电线路改造成直流输电线路(输电线路交改直)的方式能够最大程度地发挥原有线路的输电能力使其输电功率最大化,因而具有较好的应用前景。为此,从架空线路改造、电缆线路改造和多条线路改造3种交改直方式入手,对输电线路交改直技术进行论述。针对架空线路改造,概括阐述了基于三极结构的直流输电(tripole structure based HVDC,TPS-HVDC)技术和基于三线双极结构的直流输电(three-wire bipole structure based HVDC,TWBS-HVDC)技术在运行特性、拓扑结构、传输容量等方面的相关特性。针对电缆线路改造,鉴于国内外研究文献较少,提出了对称和不对称两种调制方式,同时还提出了两种拓扑结构:三极式方波交流(tripole type square wave AC,TPT-SWAC)和三相双极式方波交流(three-phase bipole type SWAC,TPBT-SWAC)输电结构。针对TPBT-SWAC内用于调节支路电流的可变电阻器,对其阻值分配方案进行了研究,得到了计算阻值的通用公式。针对多条线路改造,描述了基于TPS和TPT-SWAC或TWBS和TBPT-SWAC构建的多端直流结构,分析表明TWBS和TPBT-SWAC相较于TPS和TPT-SWAC在多端直流应用上更具优越性。多角度、多层次地分析了输电线路交改直的关键技术,能够为输电线路交改直提供更加开阔的技术思路,进而促进该领域的创新发展。
文摘基于美国国家大气研究中心的CCSM3(community climate system model version 3)模式,对淡水扰动试验下不同平均强度热盐环流(thermohline circulation,THC)的年代际波动特征及北大西洋气候响应特征进行研究。结果表明,百年以上尺度的THC变化对其年代际尺度波动产生显著影响,高平均强度下THC的年代际波动周期更长、更显著。对不同平均强度下北大西洋海、气要素与THC在年代际尺度上的相关分布进行分析,发现在高平均强度下,THC与海表温度(sea surface temperature,SST)的相关呈现为经向三核型分布,与海平面气压(sea lever pressure,SLP)的相关呈现为类NAO(North Atlantic oscillation)分布,而在低平均强度下,则不存在这2种模态分布;同时,在不同平均强度下,THC与各要素间的相关程度也不同,高平均强度下相关程度更高。
基金supported by the National Key R&D Program of China(Grant No.2016YFA0600703)the National Natural Science Foundation of China(Grant Nos.41605059,41505073 and 41375083)+1 种基金the Young Talent Support Program of the China Association for Science and Technology(Grant No.2016QNRC001)the Research Council of Norway SNOWGLACE(244166/E10)project
文摘In contrast to previous studies that have tended to focus on the influence of the total Arctic sea-ice cover on the East Asian summer tripole rainfall pattern, the present study identifies the Barents Sea as the key region where the June sea-ice variability exerts the most significant impacts on the East Asian August tripole rainfall pattern, and explores the teleconnection mechanisms involved. The results reveal that a reduction in June sea ice excites anomalous upward air motion due to strong near-surface thermal forcing, which further triggers a meridional overturning wave-like pattern extending to midlatitudes.Anomalous downward motion therefore forms over the Caspian Sea, which in turn induces zonally oriented overturning circulation along the subtropical jet stream, exhibiting the east–west Rossby wave train known as the Silk Road pattern. It is suggested that the Bonin high, a subtropical anticyclone predominant near South Korea, shows a significant anomaly due to the eastward extension of the Silk Road pattern to East Asia. As a possible descending branch of the Hadley cell, the Bonin high anomaly ultimately triggers a meridional overturning, establishing the Pacific–Japan pattern. This in turn induces an anomalous anticyclone and cyclone pair over East Asia, and a tripole vertical convection anomaly meridionally oriented over East Asia. Consequently, a tripole rainfall anomaly pattern is observed over East Asia. Results from numerical experiments using version 5 of the Community Atmosphere Model support the interpretation of this chain of events.
