The spring soil moisture and the summer rainfall in eastern China

The relation between the soil moisture in spring and the rainfall in summer in eastern China is investi- gated. Results show that the summer rainfall in eastern China is closely related to the spring soil moisture in the area from North China to the lower reaches of Yangtze River (NCYR). When spring soil moisture anomalies over NCYR are positive, the summer precipitation exhibits positive anomalies in Northeast China and the lower reaches of Yangtze River, and negative anomalies in southern China and North China. The higher soil moisture over NCYR cools land surface and reduces the land-sea tem- perature gradient, which weakens East Asian summer monsoon. The western Pacific Subtropical High (WPSH) is located to the south and shifts westward, resulting in more rainfall in the lower reaches of Yangtze River and less in southern China and North China.     

四川南部秋季降水变化及相应大气环流异常特征

利用1961—2014年全国756站的降水资料和美国NOAA-CIRES的20CR月平均再分析资料,研究了四川南部秋季(9～11月)降水变化及其相应的大气环流异常特征。结果表明,四川南部秋季降水具有显著的年际和年代际变化特征,其年际周期以2～4 a和准6 a为主,年代际周期以9～15 a为主。它与黄淮流域同期降水存在显著的负相关关系,与四川南部秋季降水关系密切的大气环流结构是北大西洋—俄罗斯西部—蒙古西部—东亚(NRMA)遥相关波列,NRMA遥相关波列在东亚地区激发出一个气旋性环流,与此同时,中南半岛西侧存在一个反气旋性环流,以上环流型有利于北方冷空气和来自孟加拉湾的暖湿气流在四川南部地区汇合,从而容易导致该地区降水的产生,反之亦然。     

Characteristics of decadal-centennial-scale changes in East Asian summer monsoon circulation and precipitation during the Medieval Warm Period and Little Ice Age and in the present day

Using meteorological observations, proxies of precipitation and temperature, and climate simulation outputs, we synthetically analyzed the regularities of decadal-centennial-scale changes in the summer thermal contrast between land and ocean and summer precipitation over the East Asian monsoon region during the past millennium; compared the basic characteristics of the East Asian summer monsoon (EASM) circulation and precipitation in the present day, the Little Ice Age (LIA) and the Medieval Warm Period (MWP); and explored their links with solar irradiance and global climate change. The results indicate that over the last 150 years, the EASM circulation and precipitation, indicated by the temperature contrast between the East Asian mainland and adjacent oceans, had a significant decadal perturbation and have been weaker during the period of rapid global warming over the past 50 years. On the centennial time scale, the EASM in the MWP was strongest over the past 1000 years. Over the past 1000 years, the EASM was weakest in 1450?C1570. When the EASM circulation was weaker, the monsoon rain belt over eastern China was generally located more southward, with there being less precipitation in North China and more precipitation in the Yangtze River valley; therefore, there was an anomalous pattern of southern flood/northern drought. From the 1900s to 1920s, precipitation had a pattern opposite to that of the southern flood/northern drought, with there being less precipitation in the Yangtze River valley and more precipitation in North China. Compared with the case for the MWP, there was a longer-time-scale southern flood/northern drought phenomenon in 1400?C1600. Moreover, the EASM circulation and precipitation did not synchronously vary with the trend of global temperature. During the last 150 years, although the annual mean surface temperature around the world and in China has increased, the EASM circulation and precipitation did not have strengthening or weakening trends. Over the past 1000 years, the weakest EASM occurred ahead of the lowest Northern Hemispheric temperature and corresponded to the weakest solar irradiance.     

Tropospheric biennial oscillation of the western Pacific subtropical high and its relationships with the tropical SST and atmospheric circulation anomalies

There is the significant period of tropospheric biennial Oscillation(TBO)over East Asian monsoon region at the interannual timescales,which has the important influences on East China climate.Based on a set of reconstructed indices which describes the western Pacific subtropical high(WPSH)objectively,this paper focuses on the TBO component of WPSH,one of the key members of the East Asian Monsoon system,and its relationships with the tropical SST and atmospheric circulation anomalies.It is found that(1)As an important interannual component of WPSH,the time series of TBO has the obvious transition in the late1970s,and the variability of the WPSH’s TBO component is more significant after the late 1970s.(2)The time-lag correlations between the WPSH’s TBO and the tropical sea surface temperature(SST)anomalies in several key ocean regions are more significant and have longer correlation duration than the raw data.The response of the western boundary index to ENSO is earlier than the intensity index,and the time-lag correlations of them are up to maximum when lagging ENSO by 3–5 months and 5–6months,respectively.(3)In the course of the WPSH’s TBO cycle,the occurrence of the El Ni o-like anomaly in the tropical central-eastern Pacific in winter is always coupled with the weak East Asian winter monsoon,with the most significant enhancing phase of the WPSH’TBO.In contrast,the La Ni a-like anomaly in the central-eastern Pacific in winter is coupled with the strong East Asian winter monsoon,with the most weakening phase of the WPSH’s TBO.(4)The distribution of the tropical SST and atmospheric circulations anomalies are asymmetric in the TBO cycle.The WPSH’s TBO is more significant in the period of the developing El Ni o-like anomaly in central-eastern Pacific than in the period of the developing La Ni a-like anomaly.Therefore,during the period of developing El Ni o-like anomaly,more attention should be paid to the interannual component of TBO signal in the short-term climate prediction.     

南海夏季风活动激发的大气遥相关型

北半球夏季,南海地区是全球大气热状况变化最为激烈的区域之一,而南海夏季风则是该地区最为活跃的天气事件,它的演变必将导致其它地区大气环流的响应．通过相关计算、合成分析等手段,揭示与南海夏季风活动相关联的北半球大气遥相关型的存在．该波列状的遥相关型与东亚地区相连,经北太平洋延伸至北美西岸．最高的相关位于西太平洋副热带高压区域,因而它可能对我国旱涝天气产生重要影响．     

Statistical characteristics of the double ridges of subtropical high in the Northern Hemisphere

The generality and some climatological characteristics of the double ridge systems of subtropical high （SH） are investigated statistically by using the daily NCEP/NCAR reanalysis data from 1958 to 1998. The results show that the SH double-ridge event is a common phenomenon in the Northern Hemisphere, with the distinct seasonal and regional features, that is, the majority of SH double-ridge geneses concentrate over the eastern North India Ocean-western North Pacific as well as the central North Pacific in the period from mid-July to mid-September. Especially over the western North Pacific subtropics, the SH double-ridge events are extremely active. It is found that the life cycle of most double-ridge events of western Pacific subtropical high （WPSH） is shorter but some still last longer. The WPSH double-ridge events occur most frequently from July to September, while there is a paucity of occurrences during November-March. Also, it is shown that the WPSH double-ridge events have a strong interannual variation with a certain periodicity which possesses a remarkably abrupt change in the mid-1970s. Additionally, the relationship between the WPSH double ridges and the meridional movement of WPSH is discussed.     

基于自组织映射的梅雨期西太副高分型及降水特征研究

为了研究梅雨期西太副高的变化特征及其对梅雨降水的影响,本文利用1951-2016年西太副高监测指数,采用自组织映射（self-organizing map,SOM）方法对梅雨期西太副高进行聚类分析,得到9种SOM分型,并利用中国1km分辨率逐月降水量数据集和中国雨季历年信息表进行不同西太副高分型下梅雨降水的特征分析。结果表明,9种梅雨期西太副高分型对应着多种不同的梅雨降水特征：纬向上,当西太副高偏东时,梅雨区降水强度偏低,反之则强度偏高。经向上,在西太副高主体位于我国陆地的前提下,脊线指数高于25°N时,梅雨区大部被副热带高压控制,整体降水偏少且有小幅度南少北多态势;脊线指数偏低时,副高控制梅雨区南部边缘或更南地区,水汽输送导致降水整体偏多。本文得到了不同类型副高与梅雨降水特征的对应关系,也说明SOM方法能较好地对副热带高压等气象要素做出客观分型,并进行气候现象的相关性研究。     

Interdecadal change of summer precipitation over Eastern China around the late-1990s and associated circulation anomalies, internal dynamical causes

Observational study indicated that the summer precipitation over Eastern China experienced a notable interdecadal change around the late-1990s. Accompanying this interdecadal change, the dominant mode of anomalous precipitation switched from a meridional triple pattern to a dipole pattern, showing a "south-flood-north-drought" structure (with the exception of the Yangtze River Valley). This interdecadal change of summer precipitation over Eastern China was associated with circulation anomalies in the middle/upper troposphere over East Asia, such as changes in winds and corresponding divergence, vertical motion and moisture transportation (divergence), which all exhibit remarkable meridional dipole structures. Furthermore, on the internal dynamic and thermodynamic aspects, the present study investigated the influence of the midtroposphere zonal and meridional flow changes over East Asia on the interdecadal change around the late-1990s. Results suggested that, during 1999-2010, the East Asia subtropical westerly jet weakened and shifted poleward, forming a meridional dipole feature in anomalous zonal flow. This anomalous zonal flow, on one hand, induced changes in three teleconnection patterns over the Eurasian continent, namely the "Silk Road" pattern along the subtropical upper troposphere westerly jet, the East Asia/Pacific (EAP) pattern along the East Asian coast, and the Eurasia (EU) pattern along the polar jet; on the other hand, it brought about cold advection over Northern China, and warm advection over Southern China in the mid-troposphere. Through these two ways, the changes in the zonal flow induced descent over Northern China and ascent over Southern China, which resulted in the anomalous "south-flood-north-drought" feature of the summer precipitation over Eastern China during 1999-2010.     

Record-breaking SST over mid-North Atlantic and extreme high temperature over the Jianghuai–Jiangnan region of China in 2013

In July 2013, the Jianghuai–Jiangnan region of China experienced a persistent extreme high temperature,and the surface air temperature(SAT) over many areas of the region set a new record, which had a profound impact on people's lives. This study explored the possible mechanism for this extreme climate phenomenon. The results show that the sea surface temperature(SST) over the midNorth Atlantic in July 2013 was the warmest observed over the past 160 years. The strong anomaly of the SST connects to the East Asian upper level westerly and western Pacific subtropical high(WPSH) via the teleconnection wave train and further contributes to the SAT variability over the Jianghuai–Jiangnan region; this connection could be one possible mechanism for the formation of the recordbreaking extreme hot event(EHE) over the Jianghuai–Jiangnan region in July 2013. In addition, for the EHE over the Jianghuai–Jiangnan region, the role of the WPSH was generally emphasised. This study found that the variability of the upper level westerly over the Jianghuai–Jiangnan region is also an important climate factor impacting the SAT of the region. In particular, the record-breaking weakness of the upper level westerly corresponded to the record-breaking SAT over the Jianghuai–Jiangnan region in July 2013. These results indicate that the role of the upper level westerly should be emphasised in addition to the WPSH, according to both the variability in the summer air temperature and the EHE over the Jianghuai–Jiangnan region.     

2008年1月中国南方地区罕见低温冰雪天气的气候特征及其成因

 利用1951～2008年1月的中国160站气温降水资料和NCEP/NCAR再分析资料,分析了2008年1月中国南方地区罕见低温冰雪天气的气候特征及其成因,结果表明:①中国南方地区持续的低温和降水叠加是形成罕见低温冰雪灾害的直接原因;②2008年1月亚洲地区大气环流异常,出现了4个较异常的环流.乌拉尔山地区阻塞高压环流异常偏强,导致冷空气活动频繁、气流南北交换较强;东亚槽异常偏强,利于强冷空气南下;西太平洋副热带高压异常偏北,对冷空气滞留在中国南方地区和持续水汽输送起重要作用;高原南侧的南支槽异常偏强,这是持续水汽输送的必要条件;③导致中国南方地区罕见低温冰雪天气的主要原因是大气异常环流的异常配置.乌山阻塞经向环流较大,但东亚槽的位置偏北偏东,在加强气流东西交换的同时削弱了冷空气南下的速度;副高较强,一方面阻挡了强冷气团的快速南下,另一方面加强了副高西侧偏南气流的水汽输送;高原南侧的南支槽的强弱对水汽的输送起决定性作用.     

全球地表温度大气遥相关路径研究

基于复杂网络方法,分析不同区域地表温度之间存在的相关关系及其时滞,建立了体现大气遥相关的全球地表温度网络,进而给出地表温度网络遥相关路径．研究表明:网络连接的空间距离在3 500和7 000 km处有1个峰值,这与大气Rossby波的1/2和1倍波长一致．地表温度网络中,影响传播的主导节点在北半球分布在东亚、向西延伸的北太平洋、美国东海岸及邻接的北大西洋地区;在南半球分布在50° S纬度带．遥相关现象在南半球比北半球更显著,典型遥相关路径与不同的环流作用有明确对应:1）北太平洋中部到墨西哥的连接反映了西风带的作用;2）北大西洋传播到非洲北部、格陵兰岛到里海的连接,均属于连接北大西洋到欧亚大陆的跨欧亚波列的一部分;3）俄罗斯喀拉海到北太平洋的连接与北大西洋涛动（NAO）密切关联;4）南半球的连接反映了大气西风带和Rossby波的影响．大气遥相关路径分析有利于深化对地表温度变化的认识,可为减缓气候全球变化提供理论基础．      

冬季西太平洋副热带高压脊线位置异常与热带对流异常的关系

利用NCEP/NCAR再分析资料、射出长波辐射(OLR)资料,国家气候中心提供的1979~2008年1月西太副高脊线指数和逐日降水资料,对1月西太副高脊线位置与热带对流异常的关系进行了分析。结果表明,1月西太副高脊线位置与南海及菲律宾以东地区OLR场存在显著的负相关关系。进一步研究发现,副高脊线的南北位置异常是由于南海及菲律宾以东地区对流偏强(弱)造成这一区域出现异常的上升(下沉)运动;由于对流层高层(低层)南风距平的作用,在我国东南部的下沉运动增强(减弱);同时,在对流层的低(高)层出现了异常北风,从而构成了一个向北(南)的经向环流,有利于副高脊线的北抬(南退)。这种对流异常是造成2008年初我国南方超过1/3区域出现了50年一遇的低温、雨雪、冰冻灾害的间接原因之一。     

Large-scale atmospheric singularities and summer long-cycle droughts-floods abrupt alternation in the middle and lower reaches of the Yangtze River

The summer droughts and floods in the middle and lower reaches of the Yangtze River valley (MLYRV) have often been one of the basic contents of the pre- cipitation forecasting during the flooding period in China. Lots of studies suggest that summer rainfa…     

Simulation of the future change of East Asian monsoon climate using the IPCC SRES A2 and B2 scenarios

In this paper, we applied the newest emission scenarios of the sulfur and greenhouse gases, i.e. Intergovernmental Panel on Climate Change (IPCC) Special Report on Emission Scenarios (SRES) A2 and B2 scenarios, to investigating the change of the East Asian climate in the last three decades of the 21st century with an atmosphere-ocean coupled general circulation model. The global warming enlarges the land-sea thermal contrast and, hence, enhances (reduces) the East Asian summer (winter) monsoon circulation. The precipitation from the Yangtze and Huaihe river valley to North China increases significantly. In particular, the strong rainfall increase over North China implies that the East Asian rainy area would expand northward. In addition, from the southeastern coastal area to North China, the rainfall would increase significantly in September, implying that the rainy period of the East Asian monsoon would be prolonged about one month. In July, August and September, the interannual variability of the precipitation enhances evidently over North China, meaning a risk of flooding in the future.     

Interdecadal variation of tropical cyclone activity in association with summer monsoon, sea surface temperature over the western North Pacific

Based on geographic division over the western North Pacific (WNP), the interdecadal relationships between summer monsoon, sea surface temperature (SST) and tropical cyclones activity (including number, track and intensity) are examined. In the past several decades, the western Pacific subtropical high (WPSH) and tropical westerlies contribute to the interdecadal variation of TC number in the northwest and southeast of WNP respectively. The increased TC occurrence density to the east of Philippines related to TC track appears during the 1990s, in terms of both steer flow induced by WPSH and genesis location. From the interdecadal viewpoint, the tendency of TC intensity, measured by averaged accumulated cyclone energy, does well agree with that of SST, implying that SST plays an important role in TC intensity. Supported by Special Scientific Research Project for Public Interest (Grant No. GYHY200806009) and National Basic Research Program of China (Grant No. 2009CB421505)     

Abrupt variations of the radiolarian fauna at Mid-Pleistocene climate transition in the South China Sea

Based on a detailed study of the radiolarian fauna, the abundance pattern of planktic foraminifera as well as on isotope and sedimentological records, the Mid-Pleistocene climate transition as a multiple transition phenomenon could be recognized at Core 17957-2 from the South China Sea. Distinct changes in the radiolarian/foraminfera ratio, the coarse fraction and the radiolarian assemblages can be related to the global climate cooling observed at the Mid-Pleistocene revolution (MPR) around 900 ka. A pronounced southward shift of the North Equatorial Current that leads to lower sea-surface temperatures in the South China Sea is documented by the shift of tropical to subtropical radiolarian assemblages at 900 ka. Increasing radiolarian abundance after the MPR can be interpreted as a result of stronger upwelling and nutrient supply. These abrupt variations could result from the northern trade wind system and East Asian monsoon circulation.     

南海夏季风建立期间副高带断裂和东撤及其可能机制

使用1998年南海夏季风试验（SCSMEX）资料和日本气象研究所（MRI）所提供的TBB资料，分析了南海夏季风建立期间副高带断裂和东撤过程的主要特征及其可能机制。发现北半球副热带高压带的断裂（低层早于高层）和印缅槽（或孟加拉湾槽）的形成是南海夏季风建立的重要前期征兆之一，也为副高东撤和南海夏季风的建立提供了重要条件。斯里兰卡附近低涡的持续北移是副高断裂和印缅槽建立过程的显特征。分析表明，南海夏季风建立之前，印度半岛的感热加热和中南半岛的潜热加热所激发的气旋性流场在孟加拉湾地区是相互迭加的，这有利于孟加拉湾低涡活动和低槽的形成，这可能是副高断裂和印缅槽活跃的机制。伴随着印缅前西南气流和赤道副高东撤、季风加强和对流加热之间存在一种正反馈作用，这导致了副高的连续东撤和南海夏季风的“爆发性”以及各种要素的突变特征。当南海夏季风对流减弱后，西太平洋副高则会西伸。     

Interdecadal variations of the East Asian winter surface air temperature and possible causes

Using the NCEP/NCAR and JRA-25 monthly analysis data from 1979 to 2011, this paper analyzes the interdecadal variations of winter (Dec.–Feb.) mean surface air temperature (SAT) over East Asia by means of the empirical orthogonal function (EOF) analysis method. Two dominant modes were extracted, with the leading mode basically depicting a sign consistent SAT variation and the second mode describing a meridional dipole structure between the northern and southern parts of East Asia. These two modes can explain more than 60% of the variance. The leading mode is closely related to the intensity of Siberian high and the East Asian winter monsoon. The second mode exhibits a notable interdecadal shift in the late 1990s, with a turning point around 1996/1997. Winter SAT in the northern (southern) part of East Asia tends to be cooler (warmer) since the late 1990. Winter sea level pressure (SLP) differences between 1997–2011 and 1979–1996 show negative (positive) anomalies over southern (northern) Eurasia. At 500-hPa, an anomalous blocking high occurs over northern Eurasia, while a cyclone anomaly appears over northern East Asia. In addition, the upper-level East Asian jet stream tends to shift northward and become stronger after the late 1990. Indeed, the interdecadal shift of winter SAT over East Asia is dynamical consistent with changes of the large-scale atmospheric circulation in the late 1990s. The result indicates that previous autumn sea surface temperature (SST) in the North Atlantic Ocean, the Northern Indian Ocean and the western North Pacific Ocean, as well as sea ice concentration (SIC) in the northern Eurasia marginal seas and the Beaufort Sea also experienced obvious changes in the late 1990s. In particular, the interdecadal shifts of both SST in the North Atlantic Ocean and SIC in the Arctic Ocean and its marginal seas are well coherent with that of the winter SAT over East Asia. The results indicate that the interdecadal shift of East Asian winter SAT may be related to changes in the North Atlantic SST and the Arctic SIC in the late 1990s.     

Transition of the annual cycle of precipitation from double-peak mode to single-peak mode in South China

Previous studies revealed the double-peak mode (DPM) in South China precipitation, corresponding to the two stages in the rainy season, i.e. the first rainy stage (FRS) and the second rainy stage (SRS). But observations in recent two decades show that the DPM has changed to a single-peak mode (SPM). Both the precipitation amount and the heavy rainfall event frequency enhanced significantly in the gap between the FRS and the SRS in 1991–2010, compared to those in 1961-1990. This change can be linked to the effects of the global warming. During the warmer period, the July sea surface temperature over the western Pacific has greater increases than that over the central and eastern Pacific, especially west of 140°E. It may generate more tropical cyclones (TCs) in the inshore areas and then more typhoon rainfall over South China. On the other hand, the increments of the air temperature over the East Asian continent are greater than those of the SST over the western Pacific under the global warming, which enlarges the land-ocean temperature/pressure contrast and leads to a trend of the earlier onset dates of the Asian summer monsoon (ASM) in recent two decades. Then, the earlier ASM will facilitate the western Pacific subtropical high (WPSH) to retreat earlier from the South China Sea and enhance the convective precipitation in South China between the FRS and the SRS. Also, due to the warmer ocean, the WPSH locates more westward in July, and more moisture will be transported to South China from the southwest side to the WPSTH. All these influences favor a remarkably increasing precipitation in the gap in the warmer period and changes the seasonal cycle from double-peak mode to single-peak mode.     

东亚夏季风异常的研究

本文运用经验正交函数分析方法,对10～65°N,90°E～175°W范围内近30年逐年7月和8月平均海平面气压场进行了分析研究.结果表明,第一、第三特征向量与东亚季风异常有关,第二特征向量与西风环流异常有关.讨论了东亚季风异常与大气环流的关系,以及季风异常对华北东部地区降水时空分布的影响.