冬季亚洲—太平洋涛动年际变率与东亚气候异常

利用1948—2011年NCEP/NCAR月平均再分析资料和1951—2010年我国160站降水量资料,研究了冬季亚洲—太平洋区域的大气遥相关及其与东亚冬季风和降水的关系。结果表明:冬季在亚洲—西太平洋与中、东太平洋中低纬度对流层上层扰动温度之间存在类似于夏季的亚洲—太平洋涛动 (APO) 现象,即当东亚中低纬度对流层中、上层偏暖时,中东太平洋中低纬度对流层中上层温度偏冷,反之亦然。冬季APO可以反映冬季亚洲—太平洋东西向热力差异强度变化,与夏季相比,冬季APO遥相关在亚洲的中心位置略偏南、偏东,且冬季APO与大气环流关系与夏季也有所不同;当冬季APO指数偏高时,对流层上层东亚大槽位置偏西,而东亚热带地区的高压向北伸展,导致我国南方对流层为深厚的异常反气旋系统所控制,此时南方地区对流层低层盛行异常的偏东北气流,并伴随水汽辐散和异常下沉运动,南方降水偏少;冬季APO指数与ENSO有紧密联系。     

Boreal summer continental monsoon rainfall and hydroclimate anomalies associated with the Asian-Pacific Oscillation

With the twentieth century analysis data (1901–2002) for atmospheric circulation, precipitation, Palmer drought severity index, and sea surface temperature (SST), we show that the Asian-Pacific Oscillation (APO) during boreal summer is a major mode of the earth climate variation linking to global atmospheric circulation and hydroclimate anomalies, especially the Northern Hemisphere (NH) summer land monsoon. Associated with a positive APO phase are the warm troposphere over the Eurasian land and the relatively cool troposphere over the North Pacific, the North Atlantic, and the Indian Ocean. Such an amplified land–ocean thermal contrast between the Eurasian land and its adjacent oceans signifies a stronger than normal NH summer monsoon, with the strengthened southerly or southwesterly monsoon prevailing over tropical Africa, South Asia, and East Asia. A positive APO implies an enhanced summer monsoon rainfall over all major NH land monsoon regions: West Africa, South Asia, East Asia, and Mexico. Thus, APO is a sensible measure of the NH land monsoon rainfall intensity. Meanwhile, reduced precipitation appears over the arid and semiarid regions of northern Africa, the Middle East, and West Asia, manifesting the monsoon-desert coupling. On the other hand, surrounded by the cool troposphere over the North Pacific and North Atlantic, the extratropical North America has weakened low-level continental low and upper-level ridge, hence a deficient summer rainfall. Corresponding to a high APO index, the African and South Asian monsoon regions are wet and cool, the East Asian monsoon region is wet and hot, and the extratropical North America is dry and hot. Wet and dry climates correspond to wet and dry soil conditions, respectively. The APO is also associated with significant variations of SST in the entire Pacific and the extratropical North Atlantic during boreal summer, which resembles the Interdecadal Pacific Oscillation in SST. Of note is that the Pacific SST anomalies are not present throughout the year, rather, mainly occur in late spring, peak at late summer, and are nearly absent during boreal winter. The season-dependent APO–SST relationship and the origin of the APO remain elusive.     

夏季亚洲—太平洋涛动与大气环流和季风降水

利用ERA-40再分析资料和数值模拟,分析了在亚洲-太平洋区域的大气遥相关以及与亚洲季风降水和西北太平洋热带气旋活动气候特征的关系,探讨了青藏高原加热和太平洋海表温度(SST)对遥相关的影响,结果表明:亚洲-太平洋涛动(Asian-Pacific Oscillation,APO)是夏季对流层扰动温度在亚洲与太平洋中纬度之间的一种"跷跷板"现象,当亚洲大陆中纬度对流层偏冷时,中、东太平洋中纬度对流层偏暖,反之亦然;这种遥相关也出现在平流层中,只是其位相与对流层的相反.APO为研究亚洲与太平洋大气环流相互作用提供了一个途径.APO指数也是亚洲-太平洋对流层热力差异指数,它具有年际和年代际的多时间尺度变化特征,在1958-2001年亚洲与太平洋之间的对流层热力差异呈现出减弱趋势,同时也有显著的5.5 a周期.APO形成可能与太阳辐射在亚洲陆地和太平洋的加热差异所造成的纬向垂直环流有关,数值模拟进一步表明:夏季青藏高原加热可以造成高原附近对流层温度升高、上升运动加强,太平洋下沉运动加强、温度下降,从而形成APO现象;而太平洋年代际涛动和赤道东太平洋的厄尔尼若现象对APO的影响可能较小.当夏季APO异常时,南亚高压、欧亚中纬度西风急流、南亚热带东风急流以及太平洋上空的副热带高压都出现显著变化,并伴随着亚洲季风降水及西北太平洋热带气旋活动异常.过去40多年来的长江中上游地区夏季变冷与APO有关,可能是全球大气环流年代际变化在该区域的一种反映.APO异常信号可以传播到南、北两极.此外,亚洲-太平洋之间的这种遥相关型也出现在其他季节.     

Characteristics of the Asian–Pacific Oscillation in Boreal Summer Simulated by BCC_CSM with Different Horizontal Resolutions

The summer Asian–Pacific Oscillation(APO) is a major teleconnection pattern that reflects the zonal thermal contrast between East Asia and the North Pacific in the upper troposphere. The performance of Beijing Climate Center Climate System Models(BCC CSMs) with different horizontal resolutions, i.e., BCC CSM1.1 and BCC CSM1.1(m), in reproducing APO interannual variability, APO-related precipitation anomalies, and associated atmospheric circulation anomalies, is evaluated.The results show that BCC CSM1.1(m) can successfully capture the interannual variability of the summer APO index. It is also more capable in reproducing the APO's spatial pattern, compared to BCC CSM1.1, due to its higher horizontal resolution. Associated with a positive APO index, the northward-shifted and intensified South Asian high, strengthened extratropical westerly jet, and tropical easterly jet in the upper troposphere, as well as the southwesterly monsoonal flow over North Africa and the Indian Ocean in the lower troposphere, are realistically represented by BCC CSM1.1(m), leading to an improvement in reproducing the increased precipitation over tropical North Africa, South Asia, and East Asia, as well as the decreased precipitation over subtropical North Africa, Japan, and North America. In contrast, these features are less consistent with observations when simulated by BCC CSM1.1. Regression analysis further indicates that surface temperature anomalies over the North Pacific and the southern and western flanks of the Tibetan Plateau are reasonably reproduced by BCC CSM1.1(m), which contributes to the substantial improvement in the simulation of the characteristics of summer APO compared to that of BCC CSM1.1.     

南极海冰涛动对北半球夏季大气环流的影响

南极海冰首要模态呈现偶极子型异常,正负异常中心分别位于别林斯高晋海/阿蒙森海和威德尔海。过去研究表明冬春季节南极海冰涛动异常对后期南极涛动（Antarctic Oscillation,AAO）型大气环流有显著影响,而AAO可以通过经向遥相关等机制影响北半球大气环流和东亚气候。本文中我们利用观测分析发现南极海冰涛动从5～7月（May–July,MJJ）到8～10月（August–October, ASO）有很好的持续性,并进一步分析其对北半球夏季大气环流的可能影响及其物理过程。结果表明,MJJ南极海冰涛动首先通过冰气相互作用在南半球激发持续性的AAO型大气环流异常,使得南半球中纬度和极地及热带之间的气压梯度加大,在MJJ至JAS,纬向平均纬向风呈现显著的正负相间的从南极到北极的经向遥相关型分布。对流层中层位势高度场上,在澳大利亚北部到海洋性大陆区域,出现显著的负异常,在东亚沿岸从低纬到高纬呈现南北走向的“? + ?”太平洋—日本（Pacific–Japan,PJ）遥相关波列,其对应赤道中部太平洋及赤道印度洋存在显著的降水和海温负异常,西北太平洋至我国东部沿海地区存在显著降水正异常和温度负异常;低纬度北美洲到大西洋一带存在的负位势高度异常和北大西洋附近存在的正位势高度异常中心,构成一个类似于西大西洋型遥相关（Western Atlantic,WA）的结构,对应赤道南大西洋降水增加和南撒哈拉地区降水减少。从物理过程来看,南极海冰涛动首先通过局地效应影响Ferrel环流,进而通过经圈环流调整使得海洋性大陆区域和热带大西洋上方的Hadley环流上升支得到增强,海洋性大陆区域特别是菲律宾附近的热带对流活动偏强,激发类似于负位相的PJ波列,影响东亚北太平洋地区的大气环流,而热带大西洋对流增强和北传特征,则通过激发WA遥相关影响大西洋和欧洲地区的大气环流。以上两种通道将持续性MJJ至ASO南极海冰涛动强迫的大气环流信号从南半球中高纬度经热带地区传递到北半球中高纬地区,从而对热带和北半球夏季大气环流产生显著影响。     

中国北方季风区盛夏典型雨型的大气环流背景和海表温度演变特征

利用中国北方季风区46站盛夏降水观测资料,采用经验正交函数分解（EOF）、合成分析和相关分析等方法,将盛夏北方季风区划分为4类雨型:A型全区一致偏多、B型全区一致偏少、C型华北偏多东北偏少和D型华北偏少东北偏多,并对比分析了四类雨型同期大气环流和前期至同期海温演变特征的差异,以探讨其形成机制及前期预测信号。结果表明:四类雨型对应的东亚大气环流和海温演变具有明显的差异。A型年:东亚副热带西风急流（西风急流）和西太平洋副热带高压（西太副高）位置偏北,东亚夏季风偏强,欧亚中高纬以纬向环流为主,北方季风区低层辐合、高层辐散,冷暖空气在北方季风区辐合;从前冬至夏季,赤道中东太平洋类似于东部型La Ni?a发展年的海温异常分布,北大西洋海温三极子模态（NAT）负位相逐渐形成;B型年则基本相反。C（D）型年:西风急流异常偏北（略偏南）,西太副高偏西（东）偏北,华北盛行西南（西北）风,东北盛行东北（东南）风,华北地区对流层低层辐合（辐散）高层辐散（辐合）,东北地区对流层低层辐散（辐合）高层辐合（辐散）,东北冷涡较弱（活跃）;从前冬至夏季,赤道中东太平洋和印度洋逐渐由暖海温向冷海温转变（El Ni?o分布形态逐渐形成）。     

2015/2016年超强El Nio事件背景下我国月预测技巧差异分析

利用中国站点观测降水资料、国家气候中心第2代月动力延伸预报模式(BCC_DERF2.0)的回报和预报数据、NCEP/NACR再分析资料和国家气候中心实时发布的月尺度降水预测评分数据,通过评估和诊断分析发现,在2015/2016年超强El Nio事件背景下,这两年内业务发布的月降水预报能力有明显不同,BCC_DERF2.0对月环流的预测技巧也存在差异:在2015年(El Nio发展位相),降水预报和环流预测技巧较高且稳定,而在2016年(El Nio衰减位相)的预报技巧总体偏低。进一步的研究显示,亚洲—太平洋涛动(Asia-Pacific Oscillation,APO)可能是导致2015年和2016年夏季预测技巧高低的重要影响因素。2015(2016)年夏季为APO低(高)指数年,且2016年具有高指数年的典型环流特征。而APO高指数对应的环流特征与El Nio衰减位相对西北太平洋环流的影响不同,在El Nio和APO的物理影响途径不一致时,将直接影响东亚环流可预报性的高低及动力气候模式的预报技巧,即El Nio在发展和衰减位相与APO型不同组合的影响是2015和2016年月预测技巧有差异的重要原因。     

南半球环流异常与我国夏季旱涝分布关系及其影响机制

利用1951—2000年NCEP/NCAR风场和高度场再分析资料及全国160站降水量资料, 采用奇异值分解、相关和合成分析方法, 研究6—8月南半球500 hPa高度、高低层纬向风距平差异常 (Δu₈₅₀-Δu₂₀₀) 与我国夏季旱涝分布的关系及其影响机制。结果表明:当500 hPa澳大利亚高压脊偏强及西南太平洋热带地区高低层纬向风距平差为负值时, 来自南半球冷空气活动偏弱, 有利于西北太平洋副热带高压位置偏南, 热带季风偏弱, 我国夏季雨带偏南。反之, 当澳大利亚高压脊偏弱及西南太平洋热带地区高低层纬向风距平差为正值时, 我国北方降水偏多。同时, 定义了澳大利亚冬季风指数, 指出澳大利亚冬季风强年和弱年影响我国夏季旱涝分布异常的水汽输送型式不同。     

春季热带南大西洋海表温度异常与夏季亚澳季风区降水异常的联系

利用1979—2019年Hadley中心的海表温度资料、GPCP的降水资料以及NCEP-DOE的再分析资料等,分析了北半球春季热带南大西洋海表温度异常与北半球夏季亚澳季风区降水异常的联系。研究表明,北半球春季热带南大西洋海表温度异常与随后夏季热带西太平洋到南海（澳大利亚东侧海域到热带东印度洋）地区的降水异常为显著负相关（正相关）关系。北半球春季热带南大西洋的海表温度正异常可以引起热带大西洋和热带太平洋间的异常垂直环流,其中异常上升支（下沉支）位于热带大西洋（热带中太平洋）。热带中太平洋的异常下沉气流和低层辐散气流引起热带中西太平洋低层的异常东风,后者有利于热带中东太平洋海表温度出现负异常。通过Bjerknes正反馈机制,热带中东太平洋海表温度异常从北半球春季到夏季得到发展。热带中东太平洋海表温度负异常激发的Rossby波使得北半球夏季热带西太平洋低层出现一对异常反气旋。此时,850 hPa上热带西太平洋到海洋性大陆地区为显著的异常东风,有利于热带西太平洋到南海（澳大利亚东侧海域到热带东印度洋）地区出现异常的水汽辐散（辐合）,导致该地区降水减少（增加）。     

2015年夏季东亚和南亚降水异常与热带太平洋海温异常的联系及机理

2015年我国东部夏季降水呈现南北反位相的空间分布,河套地区降水异常偏少、长江中下游地区降水异常偏多,同期印度中部地区降水负异常,上述三个区域2015年夏季降水距平百分率绝对值极大值均超过55%。东亚和南亚地区2015年夏季降水异常的形成机理主要是由于该年夏季处于El Niňo事件的发展位相,菲律宾群岛及邻近区域反气旋环流异常,江淮地区至日本列岛气旋式环流异常,对流层低层位势高度异常场和整层水汽异常输送场亦存在相一致的空间分布,表现为负位相的EAP(East Asian-Pacific)/PJ(Pacific-Japan)型遥相关,有利于河套地区降水偏少和长江流域降水偏多。热带太平洋海温异常引起热带地区Walker环流负异常,热带西太平洋地区上空受异常下沉气流控制,热带印度洋区域对流层盛行东风异常,减弱了印度夏季风,并造成了印度中部地区夏季降水偏少。另一方面,印度上空对流层低层受异常反气旋控制,该异常反气旋北侧的西风异常沿着青藏高原南麓向东运动,增强了与EAP/PJ型遥相关相联系的异常水汽输送,有利于维持和增强河套地区降水负异常和长江中下游地区降水正异常。     

Effects of atmosphere-ocean interaction on the interannual variability of winter temperature in Taiwan and East Asia

 This study investigated the ocean-atmosphere interaction effect on the winter surface air temperature in Taiwan. Temperature fluctuations in Taiwan and marine East Asia correlated better with a SST dipole in the western North Pacific than the SST in the central/eastern equatorial Pacific. During the warm (cold) winters, a positive (negative) SST anomaly appears in marine East Asia and a negative (positive) SST anomaly appears in the Philippine Sea. The corresponding low-level atmospheric circulation is a cyclonic (anticyclonic) anomaly over the East Asian continent and an anticyclonic (cyclonic) circulation in the Philippine Sea during the warm (cold) winters. Based on the results of both numerical and empirical studies, it is proposed that a vigorous ocean-atmosphere interaction occurring in the western North Pacific modulates the strength of the East Asian winter monsoon and the winter temperature in marine East Asia. The mechanism is described as follows. The near-surface circulation anomalies, which are forced by the local SST anomaly, strengthen (weaken) the northeasterly trade winds in the Philippine Sea and weaken (strengthen) the northeasterly winter monsoon in East Asia during warm (cold) winters. The anomalous circulation causes the SST to fluctuate by modulating the heat flux at the ocean surface. The SST anomaly in turn enhances the anomalous circulation. Such an ocean-atmosphere interaction results in the rapid development of the anomalous circulation in the western North Pacific and the anomalous winter temperature in marine East Asia. This interaction is phase-locked with the seasonal cycle and occurs most efficiently in the boreal winters. Received: 22 October 1999 / Accepted: 5 June 2000     

How the “best” CMIP5 models project relations of Asian–Pacific Oscillation to circulation backgrounds favorable for tropical cyclone genesis over the western North Pacific

Based on the simulations of 32 models from the Coupled Model Intercomparison Project Phase 5 (CMIP5), the present study assesses their capacity to simulate the relationship of the summer Asian–Pacific Oscillation (APO) with the vertical zonal wind shear, low-level atmospheric vorticity, mid-level humidity, atmospheric divergence in the lower and upper troposphere, and western Pacific subtropical high (WPSH) that are closely associated with the genesis of tropical cyclones over the western North Pacific. The results indicate that five models can simultaneously reproduce the observed pattern with the positive APO phase accompanied by weak vertical zonal wind shear, strengthened vorticity in the lower troposphere, increased mid-level humidity, intensified low-level convergence and high-level divergence, and a northward-located WPSH over the western North Pacific. These five models are further used to project their potential relationship under the RCP8.5 scenario during 2050–2099. Compared to 1950–1999, the relationship between the APO and the vertical zonal wind shear is projected to weaken by both the multi-model ensemble and the individual models. Its linkage to the low-level vorticity, mid-level humidity, atmospheric divergence in the lower and upper troposphere, and the northward–southward movement of the WPSH would also reduce slightly but still be significant. However, the individual models show relatively large differences in projecting the linkage between the APO and the mid-level humidity and low-level divergence.     

APO异常对我国西北地区东部秋季干湿变化影响

利用1961—2010年NCEP/NCAR的月平均和逐日再分析资料、中国区域589个站月降水量和气温月平均资料,研究夏季亚洲—太平洋涛动 (APO) 异常与我国西北地区东部秋季干湿变化的关系。结果表明:夏季亚洲—太平洋涛动指数 (APOI) 的异常变化与我国西北地区东部干湿指数 (DROI) 呈显著正相关。夏季APOI正异常年对应的秋季中高纬度地区500 hPa高度场乌拉尔山以西高压脊加强、巴尔喀什湖至贝加尔湖之间的低压槽加深、鄂霍次克海东部高压脊加强;东亚西风急流轴偏北;经阿拉伯海、印度半岛—孟加拉湾的西风水汽以及北太平洋反气旋底部的偏东水汽输送均为加强趋势,并结合中纬度西风水汽输送使研究区秋季偏湿,反之亦然。进一步研究表明,夏季APO为正异常时,秋季西北地区东部上升运动加强、暖湿气流加强 (均在第54—56候最为明显)。     

A 150-year reconstructed summer Asian�CPacific Oscillation index and its association with precipitation over eastern China

Reconstructing the long-term series of the East Asian summer monsoon (EASM) indices may help understand long-term variability of EASM and its associations with precipitation. In this study, the summer middle?Cupper tropospheric temperature over the Asian?CNorth Pacific sector is reconstructed from sea level pressure during the past 150?years, and then an atmospheric thermal contrast between Asia and the North Pacific, called the Asian?CPacific Oscillation (APO) index, is calculated from the reconstructed temperature. The results show that the APO phenomenon may occur in the reconstructed temperature fields, and its index has a significant positive/negative correlation with SST over the extratropical North Pacific/the tropical central?Ceastern Pacific in the past 150?years. The reconstructed summer APO index shows inter-decadal variability, with a positive phase in the 1870?C1890s, the 1920s, and the 1940?C1970s, indicating a stronger thermal contrast between Asia and the North Pacific, and with a negative phase in the 1860s, the 1900?C1910s, and the 1980?C1990s, indicating a weaker thermal contrast. Corresponding to a higher APO index in earlier decades of the twentieth century, there are more rainfall to the south of the Yangtze River and over North China and less rainfall over the Huaihe River valley. In the recent decades, however, more- and less-rain belts shifted southwards when the APO index is higher. During 1850?C1900, the reconstructed APO index also showed a significant positive correlation with precipitation in some regions of North China.     

我国华南3月份降水年代际变化的特征

利用1951～2005年华南3月份降水资料、太平洋年代际振荡(PDO)指数以及NCEP再分析资料,对华南3月份降水年代际变化特征、及其对应的大尺度环流以及与PDO的关系进行了分析。结果表明,华南3月份降水存在显著的年代际变化特征,并且Mann-Kendal突变检验表明华南3月份降水在1978年左右发生年代际突变,从之前的降水偏少转变为降水偏多。我国华南3月份降水与PDO有着显著的相关。进一步研究表明,在年代际降水偏少时期,PDO处于负位相(北太平洋海温偏高,中东太平洋海温偏低),北太平洋海平面气压场和高度场偏高,亚洲大陆海平面气压场和高度场偏低,赤道西太平洋到赤道东印度洋附近的海平面气压场偏低,赤道辐合带附近地区的高度场偏低,东亚对流层大气偏暖,西太平洋副热带高压偏东,东亚高空急流偏北,东亚Hadley环流偏弱。在年代际降水偏多时期,PDO处于正位相,情况则与降水偏少时期相反。     

我国华南3月份降水异常的可能影响因子分析

利用1951～2005年华南地区3月份的降水资料、NOAA海温资料、Ni?o3.4指数和NCEP再分析资料,分析了华南3月份降水异常与同期环流场、全球海温场的关系,从环流和海温的角度揭示了华南3月份降水异常的可能原因。结果表明,当华南3月份降水偏多(少)时,在对流层中低层,北太平洋海区存在气旋(反气旋)性环流异常,西太平洋及南海海面上存在反气旋(气旋)性环流异常,这样的环流异常有利(不利)于东南暖湿气流与北方东部异常冷空气在华南地区形成水汽辐合,导致降水显著增多(减少)。进一步的分析表明,ENSO和北印度洋及南海附近海温是影响华南3月份降水异常的重要外强迫因子,ENSO对华南3月降水异常的影响是通过影响春季西太平洋副热带高压和低层风场异常实现的,而北印度洋及南海附近海温对华南3月降水异常的影响则是通过垂直环流场异常和低层风场以及西太平洋副热带高压异常来实现的。     

EFFECTS OF PACIFIC SSTA ON SUMMER PRECIPITATION OVER EASTERN CHINA, PART Ⅰ: OBSERVATIONAL ANALYSIS

With the methods of REOF (Rotated Empirical Orthogonal Function), the summer precipitation from 43 stations over eastern China for the 1901 - 2000 period was examined. The results show that South China and Southwest China, the middle and lower reaches of Changjiang River, North China and the southwestern of Northeast China are the three main areas of summer rainfall anomaly. Furthermore, correlation analysis is used in three time series of three mostly summer rainfall modes and four seasonal Pacific SSTA (Sea Surface Temperature Anomaly), and the results suggest that the Pacific SSTA which notably causes the summer rainfall anomaly over eastern China are the SSTA of the preceding winter over Kuroshio region of Northwest Pacific, SSTA of the preceding spring in the eastern and central equatorial Pacific, and SSTA of the current summer in the central region of middle latitude. The relationship between summer precipitation over eastern China and SSTA of Pacific key regions was further verified by SVD (Singular Value Decomposition) analysis.The composite analysis was used to analyze the features of atmospheric general circulation in the years of positive and negative precipitation anomaly. Its results were used to serve as the base of numerical simulation analysis.     

EFFECTS OF PACIFIC SSTA ON SUMMER PRECIPITATION OVER EASTERN CHINA, PART Ⅰ: OBSERVATIONAL ANALYSIS

With the methods of REOF (Rotated Empirical Orthogonal Function), the summer precipitation from 43 stations over eastern China for the 1901 - 2000 period was examined. The results show that South China and Southwest China, the middle and lower reaches of Changjiang River, North China and the southwestern of Northeast China are the three main areas of summer rainfall anomaly. Furthermore, correlation analysis is used in three time series of three mostly summer rainfall modes and four seasonal Pacific SSTA (Sea Surface Temperature Anomaly), and the results suggest that the Pacific SSTA which notably causes the summer rainfall anomaly over eastern China are the SSTA of the preceding winter over Kuroshio region of Northwest Pacific, SSTA of the preceding spring in the eastern and central equatorial Pacific, and SSTA of the current summer in the central region of middle latitude. The relationship between summer precipitation over eastern China and SSTA of Pacific key regions was further verified by SVD (Singular Value Decomposition) analysis.The composite analysis was used to analyze the features of atmospheric general circulation in the years of positive and negative precipitation anomaly. Its results were used to serve as the base of numerical simulation analysis.     

1880—2010年中国东部夏季降水年代际变化特征

利用1880—2010年中国东部66站夏季降水数据,开展夏季长序列降水的年代际变化特征研究。结果表明,中国东部夏季降水年代际变化特征显著,华北、江淮和华南地区存在明显的差异。经验正交分解结果表明,偶极型("-+"和"+-")和三极型("+-+"和"-+-")分布是中国东部夏季的两种主要降水模态。夏季500 h Pa高度场年代际分量与同期太平洋SST典型相关分析(BP-CCA)得出,太平洋年代际振荡(PDO,Pacific Decadal Oscillation)正位相可以激发出负的PJ型遥相关波列,导致长江中下游地区降水偏多,华北降水偏少;反之亦然。同时,通过滑动相关分析发现,中国东部不同区域的夏季降水对PDO不同位相的响应特征存在差异。     

NUMERICAL SIMULATION OF THE IMPACT OF LATENT HEAT FLUX ANOMALY IN THE TROPICAL WESTERN PACIFIC ON PRECIPITATION OVER SOUTH CHINA IN JUNES

Based on composite analysis and numerical simulations using a regional climate model （RegCM3）, this paper analyzed the impact of the LHF anomaly in the tropical western Pacific on the precipitation over the south of China in June. The results are as follows. （1） Correlation analysis shows that the SC precipitation in June is negatively correlated with the LHF of the tropical western Pacific in May and June, especially in May. The SC precipitation in June appears to negatively correlate with low-level relative vorticity in the abnormal area of LHF in the tropical western Pacific. （2） The LHF anomaly in the tropical western Pacific is a vital factor affecting the flood and drought of SC in June. A conceptual model goes like this： When the LHF in the tropical western Pacific is abnormally increased （decreased）, an anomalous cyclone （anticyclone） circulation is formed at the low-level troposphere to its northwest. As a result, an anomalous northeast （southwest） air flow affects the south of China, being disadvantageous （advantageous） to the transportation of water vapor to the region. Meanwhile, there is an anomalous anticyclone （cyclone） at the low-level troposphere and an anomalous cyclone （anticyclone） circulation at the high-level troposphere in the region, which is advantageous for downdraft （updraft） there. Therefore a virtual circulation forms updraft （downdraft） in the anomalous area of LHF and downdraft （updraft） in the south of China, which finally leads to the drought （flood） in the region.