东亚夏季风与澳洲冬季风强弱互补变化联系及其异常环流特征

利用NCEP/NCAR再分析资料、Hadley中心海温资料及CMAP降水资料等,通过亚澳季风联合指数挑选异常年份,对东亚夏季风和澳洲冬季风强度反相变化特征进行研究。结果表明,当东亚夏季风偏强、澳洲冬季风偏弱时,南北半球中低纬地区都出现了复杂的异常环流系统。在热带地区对流层低层,西北太平洋为异常反气旋式环流系统所控制,与南太平洋赤道辐合带的异常反气旋环流在赤道地区发生耦合,形成赤道异常东风,而在南北印度洋上则存在两个异常气旋式环流系统。在这两对异常环流之间的海洋性大陆地区,出现赤道以南为反气旋环流而赤道以北为气旋式环流。在东亚季风区,东南沿海的东侧海洋上存在反气旋异常,中国东南地区受异常反气旋西南侧的东南风影响。此外,澳洲北部受异常西风影响。这就形成了东亚夏季风偏强、澳洲冬季风偏弱的情形,从而东亚夏季风和澳洲冬季风活动出现了强弱互补的变化特征。当东亚夏季风偏弱、澳洲冬季风偏强时,南北半球的环流特征则出现与上述相反的环流特征。总体而言,当东亚夏季风偏强、澳洲冬季风偏弱时,东亚—澳洲季风区在南北半球呈现出不同的气候异常分布特征,即北半球降水北少南多、气温北高南低,南半球降水西多东少、气温西高东低。     

The intensified impact of El Niño on late-summer precipitation over East Asia since the early 1990s

Climate Dynamics - This study reveals a pronounced enhancement of the relationship between the winter El Niño and the following late-summer precipitation over East Asia since the early 1990s....     

华南夏季降水20世纪90年代初的年代际变化及其与南亚高压关系

在全球变暖背景下,干旱事件发生的频率和强度不断增大、影响不断加重,干旱发生规律的异常性和机制的复杂性也更为突出,对干旱形成机制、预测理论方法及灾害风险变化规律等方面都提出了新的挑战,也制约了当前干旱预测、预警及其灾害防控能力的提高。近年来,在国家重点基础研究发展计划（973计划）课题等多个国家级项目支持下,已在干旱灾害形成机制与预测理论方法及其风险特征方面取得了一系列新成果。通过动力诊断、数值模拟和田间试验等方法,开展了干旱形成的多因子协同作用和多尺度叠加机制、干旱致灾过程的逐阶递进特征,以及干旱灾害风险分布演化的主控因素等方面的研究。对如下几方面的新进展进行了系统总结归纳：（1）厘清了全球变暖背景下青藏高原热力、海温、夏季风、遥相关等多因子对干旱形成的作用机制。（2）发现了降水亏缺时间尺度和农作物不同生长阶段的干旱敏感性规律。（3）揭示了变暖背景下典型区域干旱灾害风险分布及其变异的新特征;构建了干旱灾害风险新概念模型。（4）研发了东亚季风区的季节和次季节干旱集成预测系统。在总结归纳已取得研究成果的基础上,对未来干旱形成机制及其灾害风险科学研究进行了展望,提出了5个重点研究方向：（1）多因子联动及其多尺度叠加效应对干旱形成的影响;（2）系统整合人类活动和决策以及相关反馈的气候模式研究;（3）揭示陆-气耦合和大气环流协同作用对干旱的影响;（4）认识干旱灾害对粮食安全和生态安全影响的关键过程;（5）提高不同气候情景下干旱预估的准确度。

     

华南夏季降水20世纪90年代初的年代际变化及其与南亚高压关系

分析资料,应用1978—2008年全球逐月观测海表温度驱动NCAR CAM5.1全球大气环流模式进行数值模拟,探讨了华南夏季降水的年代际变化特征及其与南亚高压的关系。结果表明,华南夏季降水与南亚高压的东伸脊点关系密切,均在20世纪90年代初存在年代际转变。在1993—2008（1979—1992）年期间,南亚高压位置偏西（东）,西北太平洋副热带高压位置偏东（西）,华南地区则低层辐合（辐散）异常、高层辐散（辐合）异常,产生异常上升（下沉）运动,华南地区降水年代际偏多（少）,这也被数值试验结果所验证。     

江淮夏季降水异常与西印度洋地区大气环流异常的关系

运用NCEP/NCAR再分析资料和中国气候中心整编的160站月平均降水资料应用经验正交函数、线性相关分析等,分析了江淮地区夏季降水异常特征及其与西印度洋区域大气环流年际异常关系的变化及其可能的机理。结果表明:当500 hPa中纬度低槽活动偏多(少),西太平洋副热带高压偏强(弱),东亚夏季风偏强(弱)时,江淮地区降水偏多(少)。进一步分析还发现西印度洋上空的垂直环流与江淮夏季降水存在较好的关系,但这种年际异常之间的联系受到背景场的影响明显:1979—1993年西印度洋垂直上升运动与江淮夏季降水的变化趋势基本相反,两者线性相关系数为-0.43;1994—2010年两者的变化趋势基本一致,相关系数达0.71。即当西印度洋地区存在环流异常下沉(上升)时,西太平洋副热带高压通常异常减弱东退(增强西伸),副热带季风减弱(增强),有利于雨带偏南(北)。因此,在西太平洋副热带高压和副热带季风年代际偏强(弱)阶段,西印度洋环流与江淮夏季降水呈负(正)相关。     

热带太平洋低层环流主模态与东亚大气环流的可能联系

利用1958—2001年NCEP/NCAR再分析资料,探讨了热带太平洋(100°E~60°W,10°S~10°N)10 m风场的时空变化特征及其与东亚大气环流的可能联系。结果表明:1)热带太平洋风场异常存在两种主模态,第一模态对应中西太平洋一致的西(东)风异常,关于赤道呈准对称分布,与ENSO(El Nio-Southern Oscillation)暖(冷)位相时风场的分布对应;第二模态则关于赤道呈反对称分布,西北太平洋存在显著的反气旋(气旋)式环流,中太平洋异常西风不再位于赤道上,而是南移到了10°S左右,对应ENSO暖(冷)位相向相反位相转换时的风场分布特征。2)两模态时间系数的主振荡周期不同,与ENSO循环的位相关系也不同。研究发现,当两模态呈正(负)位相分布时,贝加尔湖南侧(South to Lake Baikal,SLB)容易发生持续的高压(低压)异常环流。3)两模态与SLB异常环流的联系途径不同。第一模态正位相对应热带中东太平洋大范围暖海温引起的二极型Walker环流异常,SLB异常高压不仅能通过东亚沿岸北风和南海低槽的作用促进第一模态的前期发展,还对其后期维持起重要作用。负位相时,情况相反。该环流系统既与热带中东太平洋大范围垂直运动有关,还与邻近的中国东南沿海低层异常辐合有关;第二模态则对应热带西太平洋及东印度洋为主、大西洋为辅的暖海温引起的热带四极型Walker环流异常。此时热带西太平洋到东印度洋局地偏强的经圈Hadley环流可能是SLB异常环流维持的主要原因。     

Causes of mid-Pliocene strengthened summer and weakened winter monsoons over East Asia

The mid-Pliocene warm period was the most recent geological period in Earth's history that featured long-term warming.Both geological evidence and model results indicate that East Asian summer winds(EASWs) strengthened in monsoonal China, and that East Asian winter winds(EAWWs) weakened in northern monsoonal China during this period, as compared to the pre-industrial period. However, the corresponding mechanisms are still unclear. In this paper, the results of a set of numerical simulations are reported to analyze the effects of changed boundary conditions on the mid-Pliocene East Asian monsoon climate, based on PRISM3(Pliocene Research Interpretation and Synoptic Mapping) palaeoenvironmental reconstruction. The model results showed that the combined changes of sea surface temperatures, atmospheric CO2 concentration,and ice sheet extent were necessary to generate an overall warm climate on a large scale, and that these factors exerted the greatest effects on the strengthening of EASWs in monsoonal China. The orographic change produced significant local warming and had the greatest effect on the weakening of EAWWs in northern monsoonal China in the mid-Pliocene. Thus,these two factors both had important but different effects on the monsoon change. In comparison, the effects of vegetational change on the strengthened EASWs and weakened EAWWs were relatively weak. The changed monsoon winds can be explained by a reorganization of the meridional temperature gradient and zonal thermal contrast. Moreover, the effect of orbital parameters cannot be ignored. Results showed that changes in orbital parameters could have markedly affected the EASWs and EAWWs, and caused significant short-term oscillations in the mid-Pliocene monsoon climate in East Asia.     

青藏高原地区地表热力异常与夏季东亚环流和江淮降水的关系

利用NCEP/NCAR再分析月平均资料和中国160个站降水资料,以及由国家气候中心提供的西太平洋副高脊线指数资料,分析了青藏高原地区多年平均地表温度季节转换(3-6月)的空间特征,结合均方差分析,确定高原主体(28°-38°N,75°-100°E)、高原东部以北区域(38°-48°N,90°-105°E)和高原西部以北区域(38°-45°N,75°-90°E)为关键区,分析了1951-2002年5月不同关键Ⅸ地表温度的空间变化与夏季东亚季风环流和江淮降水的关系.结果发现,这3个区域地表温度异常均对夏季东哑850 hPa环流有显著的影响.5月高原和其以北区域地表温度异常存在较大尺度的热力对比,由此,将高原主体和其以北区域的温度异常之差定义为一个指数,反映这种热力差异.相关分析发现:当5月这一热力差异增大(减小)时,夏季东亚中高纬的中高层(500-200 hPa平均)西风加强(减弱),且两风中心轴线位簧南移(北抬);造成西太平洋副热带高压脊线位置偏南(偏北),致使夏季东亚季风环流偏弱(偏强),江淮流域降水增多(减少).     

On the relationship between the winter Eurasian teleconnection pattern and the following summer precipitation over China

The Eurasian teleconnection pattern(EU) is an important low-frequency pattern with well-known impacts on climate anomalies in Eurasia. The difference of low-level v-winds in several regions in the Eurasian mid–high latitudes is defined as the EU index(EUIV). In this study, the relationship between the winter EUIVand precipitation in the following summer over China is investigated. Results show that there is a significant positive(negative) correlation between the winter EUIVand the following summer precipitation over North China(the Yangtze River–Huaihe River basins). Meanwhile, an interdecadal variability exists in the interannual relationship, and the correlation has become significantly enhanced since the early 1980 s.Thus, the proposed EUIVmay have implications for the prediction of summer precipitation anomalies over China. In positive winter EUIVyears, three cyclonic circulation anomalies are observed—over the Ural Mountains, the Okhotsk Sea, and the subtropical western North Pacific. That is, the Ural blocking and Okhotsk blocking are inactive, zonal circulation prevails in the mid–high latitudes, and the western Pacific subtropical high tends to be weaker and locates to the north of its normal position in the following summer. This leads to above-normal moisture penetrating into the northern part of East China, and significant positive(negative) precipitation anomalies over North China(the Yangtze River–Huaihe River basins), and vice versa. Further examination shows that the SST anomalies over the Northwest Pacific and subtropical central North Pacific may both contribute to the formation of EUIV-related circulation anomalies over the western North Pacific.     

Variation in summer surface air temperature over Northeast Asia and its associated circulation anomalies

This study investigates the interannual variation of summer surface air temperature over Northeast Asia(NEA) and its associated circulation anomalies.Two leading modes for the temperature variability over NEA are obtained by EOF analysis.The first EOF mode is characterized by a homogeneous temperature anomaly over NEA and therefore is called the NEA mode.This anomaly extends from southeast of Lake Baikal to Japan,with a central area in Northeast China.The second EOF mode is characterized by a seesaw pattern,showing a contrasting distribution between East Asia(specifically including the Changbai Mountains in Northeast China,Korea,and Japan) and north of this region.This mode is named the East Asia(EA) mode.Both modes contribute equivalently to the temperature variability in EA.The two leading modes are associated with different circulation anomalies.A warm NEA mode is associated with a positive geopotential height anomaly over NEA and thus a weakened upper-tropospheric westerly jet.On the other hand,a warm EA mode is related to a positive height anomaly over EA and a northward displaced jet.In addition,the NEA mode tends to be related to the Eurasian teleconnection pattern,while the EA mode is associated with the East Asia-Pacific/PacificJapan pattern.     

ENSO和北极涛动对东亚冬季气候异常的综合影响

基于1901-2000年多种海-气资料,分析了厄尔尼诺成熟年冬季-初夏西北太平洋异常反气旋（WNPAC）的年际变化特征及其对东亚气候的影响。结果表明,无论是厄尔尼诺事件成熟期的冬季还是次年的春季和初夏,WNPAC的年际变化主要存在两个空间变化型,即反映其强度变化的经验正交函数分解第1模态和反映其位置变化的第2模态。厄尔尼诺成熟年冬季WNPAC强度不仅与赤道中东太平洋海温异常有关,而且与太平洋西部（WP）型遥相关的强度有关,而其位置的变化则主要与西北太平洋局地海温异常以及北极涛动（AO）有关;次年春季,WNPAC的强度除了与赤道中东太平洋海温异常和太平洋西部型遥相关存在显著相关外,还与赤道大西洋海温异常有关,而其位置的变化则主要与西北太平洋局地海温异常和太平洋西部型遥相关有关;次年初夏,WNPAC强度主要与西北印度洋和西南印度洋的海温异常以及东亚-太平洋（EAP）型遥相关的强度有关。进一步分析表明,成熟年冬季-初夏WNPAC的强度和位置的变化均可对东亚地区降水异常分布产生影响,这对预测厄尔尼诺事件发生后冬季及后期春、夏季节东亚地区降水异常分布具有一定的指示意义。此外,次年初夏,WNPAC强度变化与西北太平洋台风发生频数存在显著负相关,即WNPAC越强,台风发生的频数越少,反之亦然。     

Abrupt summer warming and changes in temperature extremes over Northeast Asia since the mid-1990s: Drivers and physical processes

This study investigated the drivers and physical processes for the abrupt decadal summer surface warming and increases in hot temperature extremes that occurred over Northeast Asia in the mid-1990 s. Observations indicate an abrupt increase in summer mean surface air temperature(SAT) over Northeast Asia since the mid-1990 s. Accompanying this abrupt surface warming, significant changes in some temperature extremes, characterized by increases in summer mean daily maximum temperature(Tmax), daily minimum temperature(Tmin), annual hottest day temperature(TXx), and annual warmest night temperature(TNx) were observed. There were also increases in the frequency of summer days(SU) and tropical nights(TR).Atmospheric general circulation model experiments forced by changes in sea surface temperature(SST)/ sea ice extent(SIE),anthropogenic greenhouse gas(GHG) concentrations, and anthropogenic aerosol(AA) forcing, relative to the period 1964–93, reproduced the general patterns of observed summer mean SAT changes and associated changes in temperature extremes,although the abrupt decrease in precipitation since the mid-1990 s was not simulated. Additional model experiments with different forcings indicated that changes in SST/SIE explained 76% of the area-averaged summer mean surface warming signal over Northeast Asia, while the direct impact of changes in GHG and AA explained the remaining 24% of the surface warming signal. Analysis of physical processes indicated that the direct impact of the changes in AA(through aerosol–radiation and aerosol–cloud interactions), mainly related to the reduction of AA precursor emissions over Europe, played a dominant role in the increase in TXx and a similarly important role as SST/SIE changes in the increase in the frequency of SU over Northeast Asia via AA-induced coupled atmosphere–land surface and cloud feedbacks, rather than through a direct impact of AA changes on cloud condensation nuclei. The modelling results also imply that the abrupt summer surface warming and increases in hot temperature extremes over Northeast Asia since the mid-1990 s will probably sustain in the next few decades as GHG concentrations continue to increase and AA precursor emissions over both North America and Europe continue to decrease.     

东亚冬夏季风关系在1970s末的年代际转变

利用NCEP/NCAR和Hadley中心的大气与海洋再分析资料,选取具有代表性的东亚冬、夏季风指数,采用滑动相关和线性回归等方法,主要讨论了受ENSO影响的东亚冬季风分量和后期夏季风之间关系的年代际变化,并分析了二者关系发生变化的原因。结果表明:在1965—1979年,受ENSO影响的冬季风与后期夏季风强度的对应关系并不明显。在1980—2004年,受ENSO影响的冬季风强,对应后期的夏季风偏弱,弱冬季风对应的后期夏季风偏强。当受ENSO影响的冬季风较强时,冬季在对流层低层西北太平洋出现了异常气旋并可以维持到次年夏季,低纬地区位势高度偏低,削弱了西太平洋副热带高压,异常气旋西部的偏北气流阻碍了西南风的北进,导致夏季风偏弱。海表温度异常在1980年前后春、夏季不同的分布型可以解释环流在不同时段内的差异。     

冬季北太平洋涛动和我国夏季降水

本文分析了冬季北太平洋涛动与我国夏季降水的关系。结果表明,当冬季北太平洋涛动偏强时,我国夏季主要多雨带位于黄河流域及其以北地区(即1类雨型);当冬季北太平洋涛动偏弱时,夏季主要多雨带位于黄河与长江之间,中心在淮河流域一带(即2类雨型)。据此建立了我国夏季1、2类雨型的预报判据。并进一步分析了北太平洋涛动遥相关型从冬到夏的演变过程及其对北太平洋地区海温异常的响应。     

Interdecadal change in the connection between Hadley circulation and winter temperature in East Asia

Based on NCEP/NCAR reanalysis data, the interdecadal variability of Hadley circulation （HC） and its association with East Asian temperature in winter are investigated. Results indicate that the Northern Hemisphere winter HC underwent apparent change in the 1970s, with transition occurring around 1976/77. Along with interdecadal variability of HC, its linkage to surface air temperature （SAT） in East Asia also varied decadally, from weak relations to strong relations. Such a change may be related to the interaction between HC and the atmospheric circulation system over the Philippines, which is associated with the East Asian winter monsoon （EAWM）. Before the 1970s, the connection between HC and the anticyclonic circulation around the Philippines was insignificant, but after the late 1970s their linkage entered a strong regime. The intensification of this connection may therefore be responsible for the strong relations between HC and East Asian winter temperatures after the late 1970s.     

ENSO与北半球冬季大气环流异常年代际关系的数值模拟

利用NCAR/CCM3大气环流模式,模拟不同海温背景场强迫下,北半球冬季大气环流对ENSO事件的响应。结果表明,模式能够模拟出不同海温背景场下,北半球冬季大气环流对ENSO事件的不同响应,模拟结果与诊断结果基本一致。在20世纪70年代末之后的平均海温背景场强迫下,El Nio对阿留申低压的加强作用比70年代末之前更明显,而ENSO暖位相对蒙古高压的作用则由70年代末之前的轻微减弱变为明显加强。虽然70年代末以后ENSO事件的强度比70年代末之前有所增大,但ENSO对东亚大槽和东亚冬季风的减弱作用反而不再那么明显;同时在高空风场中,由ENSO激发出的PNA型异常环流在70年代末以后明显加强。     

The impact of boreal autumn SST anomalies over the South Pacific on boreal winter precipitation over East Asia

The possible mechanism behind the variability in the dipole pattern of boreal winter precipitation over East Asia is analyzed in this study. The results show that the SST anomalies(SSTAs) over the South Pacific Ocean(SPO) in boreal autumn are closely related to the variability in the dipole pattern of boreal winter precipitation over East Asia. The physical link between the boreal autumn SPO SSTAs and the boreal winter East Asian precipitation dipole pattern is shown to mainly be the seasonal persistence of the SPO SSTAs themselves. The seasonal persistence of the SPO SSTAs can memorize and transport the signal of the boreal autumn SSTAs to the following winter, and then stimulates a meridional teleconnection pattern from the SH to the NH, resulting in a meridional dipole pattern of atmospheric circulation over East Asia in boreal winter. As a major influencing factor, this dipole pattern of the atmospheric circulation can finally lead to the anomalous precipitation dipole pattern over East Asia in boreal winter. These observed physical processes are further confirmed in this study through numerical simulation. The evidence from this study, showing the impact of the SPO SSTAs in boreal autumn,not only deepens our understanding of the variability in East Asian boreal winter precipitation, but also provides a potentially useful predictor for precipitation in the region.     

三类厄尔尼诺事件对东亚大气环流及中国东部次年夏季降水的影响

利用全球海表温度(SST)资料、ONI(Oceanic Nino Index)序列以及中国160站逐月降水资料,研究了不同类型El Nino事件的主要特征及其对东亚大气环流及中国东部次年夏季逐月及季节降水的影响。结果表明:1)据El Nino事件期间SST最大正异常所在区域,将El Nino事件分为Nino3、Nino4和Nino3.4型。2)El Nino事件次年6月,Nino3型时降水显著正异常区主要位于鄱阳湖和洞庭湖流域,Nino4型时位于鄱阳湖流域、桂粤湘三省交界及广西西部,Nino3.4型时位于洞庭湖流域。7月Nino3型降水显著正异常区北移至长江流域,8月则呈西多东少反相分布。从次年6月至8月,Nino4型降水显著正异常区逐渐北移,Nino3.4型降水显著正异常区则从南到北再移向东北。3)在整个次年夏季,Nino3、Nino4和Nino3.4型降水显著正异常区在中国东部呈自南向北分布。无论逐月或季节降水,均是Nino4型降水正异常最强、Nino3.4型最弱。4)不同类型事件次年夏季和各月环流特征存在一定差异,总体而言,对于南亚高压,Nino3型、Nino4型事件后呈偏强、东伸和北抬的特点,且后者较前者时更强;Nino3.4型事件后主要呈减弱、西退特征。对于西太平洋副热带高压,Nino3型、Nino4型事件后主要呈偏强、西伸、北抬特征,后者较前者更强,西伸、北抬也更明显;Nino3.4型后,副高以东撤、北抬特征为主。     

The upper-level circulation anomaly over Central Asia and its relationship to the Asian monsoon and mid-latitude wave train in early summer

A large intraseasonal variation in geopotential height over the Central Asia region, where the Asian subtropical jet is located, occurs between May and June, and the most dominant variation has a wave-like distribution. This variation in geopotential height influences precipitation across South and Southeast Asia. In this paper, we use composite analysis to determine the causes of this intraseasonal variation over Central Asia. The wave train propagates from the northern Atlantic Ocean to Central Asia over a period of a week, and generates an anomaly in geopotential height over the region. The tropical disturbance, which is similar to the Madden–Julian oscillation, appears a few days before the maximum of the anticyclonic anomaly over Central Asia, and is accompanied by active convection over the Indian Ocean and suppressed convection over Central America. Results of numerical experiments using a linear baroclinic model show that the active convection over the northern Indian Ocean causes the anticyclonic anomaly over Central Asia. The wave train that extends from the northern Atlantic Ocean to Central Asia is generated by negative thermal forcing over Central America, and the phase distribution of this wave train is similar to that observed in the composite analysis. Central Asia is the region where the effects of the tropics and middle latitudes overlap, and it is an important connection point between the Asian monsoon and middle latitudes.