A Decadal Shift of Summer Surface Air Temperature over Northeast Asia around the Mid-1990s

This study identifies a decadal shift of summer surface air temperature （SAT） over Northeast Asia,including southeastern parts of Russia,Mongolia and northern China,around the mid-1990s.The results suggest that the SAT over the Northeast Asia experienced a significant warming after 1994 relative to that before 1993.This decadal shift also extends to northern China,and leads to a warmer summer over Northeast China and North China after the mid-1990s.The decadal warming over Northeast Asia is found to concur with the enhancement of South China rainfall around the mid-1990s.On the one hand,both the Northeast Asian SAT and South China rainfall exhibit this mid-1990s decadal shift only in summer,but not in other seasons.On the other hand,both the Northeast Asian SAT and South China rainfall exhibit this mid-1990s decadal shift not only in the summer seasonal mean,but also in each month of summer （June,July and August）.Furthermore,the decadal warming is found to result from an anticyclonic anomaly over Northeast Asia,which can be interpreted as the response to the increased precipitation over South China,according to previous numerical results.Thus,we conclude that the warming shift of summer Northeast Asian SAT around the mid-1990s was a remote response to the increased precipitation over South China.

THE INTERDECADAL VARIABILITY OF EAST ASIA MONSOON AND ITS EFFECT ON THE RAINFALL OVER CHINA

The interdecadal variability of the East Asia summer monsoon during 1951～1999 is analyzed by using two different East Asia monsoon indices. The results agree on the point that the East Asia monsoon has undergone an interdecadal variability in the mid-1970s. The intensity of the East Asia monsoon is weaker after this transition. Moreover the intensity and location of subtropical high that is an important component in East Asia monsoon system also shows interdecadal variation obviously. It is the interdecadal variation in atmospheric circulation that causes the drought over North China and flooding along the middle and lower reaches of the Yangtze River after the mid-1970s.

EAST ASIA SUMMER MONSOON ONSET DATE CALCULATED FROM OBSERVED, REANALYZED AND COMBINED DAILY RAINFALL

In this paper, the East Asia summer monsoon onset date lines in East China are calculated by the definition similar to the traditional one, with the ECMWF reanalyzed 850 hPa daily wind and observed, reana-lyzed and combined daily rainfall during 1980 ~ 1993. To make the onset date line as close as possible to the previous work, the earliest onset date limits have to be applied for the regions with different latitude and the daily mean datasets have to be smoothed by space before calculation, therefore their space-resolution is reduced to about 3 longitude ×1 latitude. The results show that the multiyear mean summer monsoon onset date lines are quite similar to each other. Compared with the one from the reanalysis, the 14-year average onset date line form combination is obviously improved in the southern Sichuan Basin and the correlation between observed and combined onset date is also slightly higher over the Huaihe valley and Northeast China. Since daily rainfall combination also improved the long term daily mean and standard deviation through the pentad CMAP, if no better daily dataset is available, such a kind of daily rainfall combination can be used to get reasonable result in the Indian monsoon region without sufficient observatories or over the North Pacific without any ground obser-vation at all in future study.

Impact of European Black Carbon on East Asian Summer Climate

The remote response of the East Asian summer monsoon （EASM） to European black carbon （EUBC） aerosols was studied by using an ensemble of sensitivity experiments with the Geophysical Fluid Dynamics Laboratory （GFDL） atmospheric general circulation model （AGCM） Atmospheric Model version 2.1 （AM2.1）.The results show that EUBC causes an enhanced EASM.The resulted enhanced southwesterly brings more moisture supply from the Bay of Bengal,which causes an increase in precipitation over the Yangtze River valley,northeastem China,the eastern part of the Yellow River valley,and the Tibetan Plateau.Diagnostic examination suggests that EUBC induces enhanced tropospheric heating over most of the Eurasian Continent through a propagating wave train and horizontal air temperature advection.This phenomenon results in intensified thermal contrast between land and ocean,which accounts for the enhanced EASM.Moreover,reductions in EUBC emission in 1992 may have contributed to decadal weakening of the EASM in the early 1990s.

A STUDY ON THE RELATIONSHIP BETWEEN SPRING SOIL MOISTURE OVER CHINA AND EAST ASIA SUMMER MONSOON

The correlation analysis has been used to study the relationship between spring soil moisture over China and East Asian summer monsoon (EASM). It is shown that EASM has a strong positive correlation with spring soil moisture over southwest China and the Great Bend region of the Yellow River. A standard soil moisture index (SMI) has been defined using the observed soil moisture of the two regions. The results show that SMI has a strong correlation with EASM. The years of strong (weak) SMI are associated with stronger (weaker) summer monsoon circulation. In the years of strong SMI, the west Pacific subtropical high is much northward in position and weaker in intensity;the westerlies zone is also more to the north. All of these make EASM circulation move northward and cause the rainfall belt to relocate to North China and Northeast China. SMI can reflect the variation of the summer rainfall anomaly over eastern China. In the years of strong SMI, the rainfall belt is mainly located over the northern part of China. However, during the weak years, the summer rainfall belt is largely located over the mid-and lower-reaches of the Yangtze River. Additionally, the SMI has obvious oscillations of quasi 4-6 years and quasi 2 years. Moreover, negative SMI predicts EASM better than positive SMI.

Precipitation Regime Shift Associated with the Pacific Decadal Oscillation in the Maritime Continent

Recent changes in precipitation regime in South-East Asia are a subject of ongoing discussion. In this article, for the first time, evidence of a precipitation regime shift during the mid-1970s in the Northern Hemispheric part of South-East Asia is demonstrated. The detection of regime shifts is made possible by using a new comprehensive dataset of daily precipitation records (South-East Asian Climate Assessment and Dataset) and applying a novel Bayesian approach for regime shift detection. After the detected regime shift event in the mid-1970s, significant changes in precipitation distribution occurred in the Northern Hemispheric regions—Indochina Peninsula and the Philippines. More specifically, dry days became up to 10% more frequent in some regions. However, no precipitation regime shift is detected in Southern Hemisphere regions—Java and Northern Australia, were the number of observed dry days increased gradually.

Synergistic Impacts of the Atlantic and Pacific Oceans on Interdecadal Variations of Summer Rainfall in Northeast Asia

This study presents a comprehensive analysis of the synergistic impacts of the Atlantic multidecadal oscillation(AMO)and Pacific decadal oscillation(PDO)on the interdecadal variations of summer rainfall in Northeast Asia.Following the construction of four probable scenarios under various combinations of the AMO and PDO phases,it is found that when the AMO and PDO are out of phase,both of them induce a strong or weak East Asian summer monsoon and a low or high pressure system over Northeast Asia through atmospheric teleconnection,which results in significant wet or dry conditions over the whole of Northeast Asia through the effects of superimposition.In contrast,when the AMO and PDO are in-phase,they induce moderate and regional wet or dry conditions in Northeast Asia,and only a slightly strong or weak East Asian summer monsoon through the effects of cancellation.During the mid-1960 s-1990 s,a period of drought first began in Northeast Asia under a negative AMO and negative PDO in the mid-1960 s,which then increased in severity under a negative AMO and positive PDO in the 1980 s,before finally coming to an end under a positive AMO and negative PDO in the late 1990 s.The interdecadal predictability of summer rainfall in Northeast Asia may reside in the interdecadal behavior of the North Atlantic and Pacific Oceans.

Water Vapor Transport Related to the Interdecadal Shift of Summer Precipitation over Northern East Asia in the Late 1990s

In this study, an interdecadal shift of summer precipitation over northern East Asia （NEA） was identified, demon-strating that summer precipitation decreased abruptly after 1998/99. The synchronous shift in summer moisture budget and water vapor transport over NEA was further investigated by using the NCEP/NCAR reanalysis data. The results indicate that water vapor transported northward into NEA from three low-latitude paths was limited because most water vapor was transported eastward. Water vapor transported from the westerly path in mid-high （WMH） lat-itudes exhibited significant correlations with summer precipitation in NEA and experienced a significant adjustment in the late 1990s. Regarding the spatial distributions of water vapor transport, less input was found through the west-ern boundary while more output occurred through the eastern boundary of NEA, and zonal water vapor transport fluxes mainly concentrated at the low to middle levels, which led to the summer precipitation shift in NEA around the late 1990s. Furthermore, it is also confirmed that the wind anomalies （rather than the moisture disturbance） as the dominant internal dynamic factor and Pacific Decadal Oscillation/Atlantic Multidecadal Oscillation （PDO/AMO） as possible external force played important roles in influencing the water vapor transport and causing the summer pre-cipitation shift over NEA in the late 1990s.

The Enhancement of the East Asian Summer Monsoon over Northeast Asia over the Most Recent Two Decades

The East Asian summer monsoon in Northeast Asia(NEA)has experienced an increase in summer rainfall and a delayed end to the rainy season after 2000,suggesting a trend of enhancement.Based on the data analyses spanning 1979-2022,our results show that the increased rainfall amounts are associated with a more pronounced Mongolian cyclone(MC)in July−August,a manifestation of a portion of the Eurasian barotropic Rossby wave train.Sea surface temperature(SST)anomalies in the North Atlantic(NA)regulate this wave train,with SST increases leading to its amplification.Somewhat independently,a delayed end to the rainy season in September is related to an enhanced anticyclone over the Kuril Islands(ACKI)in the Russian Far East.This anticyclone originates in the Arctic region,possibly induced by the loss of sea ice in the East Siberian Sea,a condition that can be detected two months in advance.The stronger MC and ACKI jointly contribute to the observed enhancement in the East Asian summer monsoon in NEA since 2000 by facilitating ascending motion and moisture transport.Therefore,the SST anomaly in the NA,which is responsible for the intensified rainfall in the rainy season in NEA,coupled with the sea ice conditions in the East Siberian Sea,provides a potential prediction source for the retreat of the rainy season.

Interannual variability of Mascarene high and Australian high and their influences on summer rainfall over East Asia

Based on the reanalysis data fromNCEP/NCAR and other observational data, interannualvariability of Mascarene high (MH) and Australian high (AH) from 1970 to 1999 is examined. It is shown that interannual variability of MH is dominated by the Antarctic oscillation (AAO), when the circumpolar low in the high southern lati-tudes deepens, the intensity of MH will be intensified. On the other hand, AH is correlated by AAO as well as El Nio and South Oscillation (ENSO), the intensity of AH will be inten-sified when El Nio occurs. Both correlation analysis andcase study demonstrate that summer rainfall over East Asia is closely related to MH and AH. When MH intensifies from boreal spring to summer (i.e. from austral autumn to winter)there is more rainfall over regions from the Yangtze Rivervalley to Japan, in contrast, less rainfall is found over south-ern China and western Pacific to the east of Taiwan, andmost of regions in mid-latitudes of East Asia. Compared with MH, the effect of AH on summer rainfall in East Asia is lim-ited to localized regions, there is more rainfall over southern China with the intensification of AH. The results in this study show that AAO is a strong signal on interannual time-scale, which plays an important role in summer rainfall over East Asia. This discovery is of real importance to revealing the physical mechanism of interannual variability of EastAsian summer monsoon and prediction of summer precipi-tation in China.

Dynamic-statistics combined forecast scheme based on the abrupt decadal change component of summer precipitation in East Asia

Based on the 1983~2011 CMAP data,the precipitation anomaly in East Asia and its nearby sea regions（hereafter called East Asia for short） demonstrates the ＂＋-＋＂ pattern before 1999 and the ＂-＋-＂ pattern afterwards; this decadal change is contained principally in the corresponding EOF3 component.However,the NCC_CGCM forecast results are quite different,which reveal the ＂＋-＋-＂ pattern before 1999 and the ＂-＋-＋＂ pattern afterwards.Meanwhile,the probability of improving NCC_CGCM＇s forecast accuracy based on these key SST areas is discussed,and the dynamic-statistics combined forecast scheme is constructed for increasing the information of decadal change contained in the summer precipitation in East Asia.The independent sample forecast results indicate that this forecasting scheme can effectively modify the NCC_CGCM＇s decadal change information contained in the summer precipitation in East Asia（especially in the area of 30°N–55°N）.The ACC is 0.25 and ACR is 61% for the forecasting result based on the V SST area,and the mean ACC is 0.03 and ACR is 51% for the seven key areas,which are better than NCC_CGCM＇s system error correction results（ACC is -0.01 and ACR is 49%）.Besides,the modified forecast results also provide the information that the precipitation anomaly in East Asia mainly shows the ＂＋-＋＂ pattern before 1999 and the ＂-＋-＂ pattern afterwards.

Global and China temperature changes associated with the inter-decadal variations of East Asian summer monsoon advances

The modern atmospheric observation and literatural historical drought-flood records were used to extract the inter-decadal signals of dry-wet modes in eastern China and reveal the possible relationship of global and China temperature changes associated with the East Asian summer monsoon advances.A climate pattern of "wet-north and dry-south" in eastern China and cool period in China and globe are associated with the strong summer monsoon that can advance further to the northernmost part in the East Asian monsoon region.On the contrary,a climate pattern of "dry-north and wet-south" in eastern China and a warm period in China and globe are associated with the weaker summer monsoon that only reaches the southern part in the region.An interdecadal oscillation with the timescale about 60 years was found dominating in both the dry-wet mode index series of the East Asian summer monsoon and the global temperature series after the secular climate states and long-term trend over inter-centennial timescales have been removed.

An East Asian Subtropical Summer Monsoon Index and Its Relationship to Summer Rainfall in China

Using the monthly mean NCEP/NCAR reanalysis data and the monthly rainfall observations at 160 rain gauge stations of China during 1961 1999, and based on major characteristics of the atmospheric circulation over East Asia and the western Pacific, a simple index for the East Asian subtropical summer monsoon （EASSM） is defined. The relationship between this index and summer rainfall in China and associated circulation features are examined. A comparison is made between this index and other monsoon indices. The results indicate that the index defined herein is reflective of variations of both the thermal low pressure centered in Siberia and the subtropical ridge over the western Pacific. It epitomizes the intensity of the EASSM and the variability of summer rainfall along the Yangtze River. Analysis shows that the Siberian low has a greater effect on the rainfall than the subtropical ridge, suggesting that the summer rainfall variability over the eastern parts of China is to a large extent affected by anomalies of the atmospheric circulation and cold air development in the midlatitudes. Taking into account of the effects of both the Siberian low and the subtropical ridge can better capture the summer rainfall anomalies of China. The index exhibits interannual and decadal variabilities, with high-index values occurring mainly in the 1960s and 1970s and low-index values in the 1980s and 1990s. When the EASSM index is low, the Siberian low and the subtropical ridge are weaker, and northerly wind anomalies appear at low levels over the midlatitudes and subtropics of East Asia, whereas southwesterly wind anomalies dominate in the upper troposphere over the tropics and subtropics of Asia and the western Pacific. The northerly wind anomalies bring about frequent cold air disturbances from the midlatitudes of East Asia, strengthening the convergence and ascending motions along the Meiyu front, and result in an increase of summer rainfall over the Yangtze River.

Numerical simulation and cause analysis of persistent summer drought during the 1920s in eastern China

In the late 1920’s,a mega-drought in China resulted in widespread crop failure and famine.Sufficient evidence suggests that this drought belonged to a dry period ranging from approximately 1922 to 1932.To understand the characteristics and the cause of this persistent drought period,we combined various data,including observations,tree ring proxy data,reanalysis data,simulation results of the Fifth Phase of the Coupled Model Intercomparison Project and numerical downscaling simulations.The results show that during 1922-1932,most regions in eastern China suffered from a persistent drought that lasted for six years,and the maximum negative precipitation anomaly reached−1.5 times the standard deviation.Given its spatial coverage,duration,and strength,the 1920s drought was unique for the 20th century.The 1920s drought was primarily caused by internal variability.Strong easterlies in lower latitudes,strong monsoon circulation,and abnormally high geopotential heights at middle and upper levels were responsible for the 1920s drought conditions in eastern China;these drought conditions could be further attributed to the joint impact of the Atlantic Multidecadal Oscillation,Pacific Decadal Oscillation and Indian Ocean Basin Mode.

中亚副热带西风急流的年代际变化及其与环流和降水的联系

基于1961~2016年美国国家环境预测中心(NCEP)/美国国家大气研究中心(NCAR)提供的大气环流再分析数据和全球降水气候中心(GPCC)提供的逐月降水数据,研究了副热带西风急流与中亚夏季降水的年代际关系。结果表明,副热带西风急流经向位置在1997/1998年发生年代际突变。急流经向位置突变前,当急流偏南时,中亚上空受异常气旋控制,印度半岛上空受异常反气旋控制,在印度半岛和中亚上空反气旋和气旋的共同作用下,将热带印度洋的水汽接力输送至中亚上空,中亚夏季降水偏多;急流经向位置突变后,副热带西风急流位置与中亚夏季降水的关系减弱,当急流偏南时,中亚上空的异常气旋减弱中心西移,印度半岛上的异常反气旋加强并西移,导致热带印度洋到中亚上空的经向输送减弱,水汽不再深入至中亚东部和北部地区。东大西洋—西俄罗斯型遥相关(EA-WR)和中亚副热带西风急流经向位置存在不同的年代际联系,且对其体现为间接影响。中亚副热带急流经向位置突变前,EA-WR负位相对应乌拉尔山脉地区的异常反气旋,反气旋东侧的异常偏北风将高纬冷空气向南输送,导致中亚对流层中上层气温降低,形成异常气旋,对应副热带西风急流位置偏南;副热带急流经向位置突变后,原乌拉尔山附近上空的异常反气旋东移,不再导致中亚上空对流层中高层气温降低,EA-WR和中亚副热带西风急流经向位置的联系也减弱。中亚副热带西风急流经向位置突变前后,太平洋—北美型遥相关(PNA)正位相均能导致中亚上空受异常气旋控制,对应急流位置偏南。

塔里木盆地夏季降水的年代际变化及其影响环流

基于1961-2020年夏季塔里木盆地33站逐日降水数据和NCEP/NCAR大气环流再分析数据,分析了塔里木盆地夏季降水的年代际变化特征及影响环流。结果表明:塔里木盆地夏季降水在1986/1987年发生了由少到多的年代际突变,降水显著增加的区域集中在盆地的西部和北部,主要由降水日数的增加贡献。不同年代际背景下,塔里木盆地夏季降水的影响环流配置存在差异。1961-1986年,影响盆地夏季降水的中亚副热带西风急流位置显著南移,中亚上空的异常气旋位于40°N附近,水汽主要源于阿拉伯海;1987-2020年,中亚上空的异常气旋位置移至40°N以南,水汽主要源于孟加拉湾和西北太平洋。东大西洋-西俄罗斯大气遥相关型在塔里木盆地夏季降水的年代际变化中扮演了重要角色。

东亚夏季风推进过程的气候特征及其年代际变化

利用1951￣2001年NECP的逐日再分析资料及中国东部366站1957￣2000年逐日降水资料,提出东亚夏季风推进过程的定量指标,分析东亚夏季风推进过程的年代际变化。结果表明:标准降水指数为1.5的等值线较好反映了中国东部夏季雨带的南北移动,以及雨带推进过程中呈现的阶段性与突变性特征。东亚夏季风的推进过程具有显著年代际变化,与夏季风前沿位置有关的指标在20世纪60年代中期前后发生显著变化,与夏季风推进强度有关的指标则在70年代末出现突变。60年代中期前,南海夏季风的建立时间较迟,但北推较快,夏季风前沿到达华北地区时间较早,在华北地区维持时间长,夏季风的北界位置偏北,华北雨季、淮河梅雨明显。70年代末以后南海夏季风的建立时间较早,夏季风前沿附近南风强度明显偏弱,降水主要集中在长江流域及其以南地区,华北雨季不明显。

2012年我国夏季降水预测与异常成因分析

本文对2012年我国夏季降水的实况和预测进行简要回顾,发现2012年夏季降水大体呈北方涝、长江旱的分布,主雨带位于黄河流域及其以北,降水异常偏多的区域主要位于西北大部、内蒙古和环渤海湾,黄淮与江淮地区降水偏少,江汉至淮河上游一带干旱严重;预测的主雨带位于华北南部至淮河,较实况偏南。对我国北方降水异常偏多的成因分析表明:2012年夏季欧亚中高纬地区阻塞高压(简称阻高)强盛,同时东北冷涡活动频繁,中高纬500 hPa高度场从西至东呈"+-+"的分布,这种环流形势没有造成长江洪涝是因为东亚夏季风异常偏强,同时西太平洋副热带高压(副高)偏北,冷暖空气对峙于我国北方地区,导致北方降水异常偏多。分析还表明阻高、东北冷涡、东亚夏季风和副高这四个系统的不同配置影响着冷暖气流的对峙位置,进而形成我国夏季的主雨带。最后通过定量和定性判断相结合的方法,选取了2012年夏季降水的最佳相似年和最佳相反年,对比分析了2012年夏季降水与其最佳相似年和最佳相反年的海温演变与东亚夏季风环流系统主要成员的差异:1959年夏季降水作为2012年夏季降水的最佳相似年,虽然海温及东亚夏季风系统关键成员异常不明显,但是和2012年也呈近似相反的特征;而1980年夏季降水作为2012年夏季降水的最佳相反年,海温及东亚夏季风环流系统关键成员和2012年呈显著的反向特征,这些观测事实反映了我国夏季降水与海温及东亚夏季风环流系统关键成员这些主要影响因子之间关系的年代际变化。

东亚夏季风指数的年际变化与东亚大气环流

文中从夏季东亚热带、副热带环流系统特点出发 ,定义了能较好表征东亚夏季风环流年际变化的特征指数 ,并分析了东亚夏季风指数的年际变化与东亚大气环流及夏季中国东部降水的关系。文中定义的东亚夏季风指数既反映了夏季东亚大气环流风场的变化特征 ,也较好地反映了夏季中国东部降水的年际变化特征。此外 。

2015年汛期气候预测先兆信号的综合分析

文章全面回顾了发布2015年汛期预测时考虑的先兆信号及其应用情况。2015年春夏季厄尔尼诺事件进一步发展,并由中部型向东部型转变,热带印度洋为一致偏暖模态发展;冬、春季北大西洋三极子为正位相;冬、春季北极海冰较常年略偏少,南极海冰偏多;冬季欧亚积雪增量略少,青藏高原积雪略多但气温偏高。通过诊断分析,认为2015年汛期预测的主导外强迫信号是太平洋厄尔尼诺事件和印度洋海温一致偏暖模态。同时参考动力气候模式的预测,在4月初的预报中,重点考虑了厄尔尼诺事件的强度和空间型变化对东亚夏季风环流的影响,有利于东亚夏季风偏弱,西太平洋副热带高压偏强偏西,季风季节内进程偏晚,我国降水呈南多北少型。在5月底的订正预报中,进一步考虑热带印度洋偏暖模态对副热带高压偏强偏西偏南的影响,以及南半球越赤道气流强度偏弱特征及对夏季风季节进程和强度的影响。经过综合分析,准确地预测了2015年东亚夏季风偏弱、我国夏季降水南多北少的布局,以及季节内主要气候事件的演变。最后对汛期气候预测存在的不足进行了初步分析和讨论。