南海强夏季风(1994年)和弱夏季风(1998年)建立的机理分析

用NCEP／NCAR的再分析资料和局地纬向平均Hadley环流(反Hadley环流)诊断方程,探讨南海强夏季风年(1994年)建立初期(5月1～5日)和弱夏季风年(1998年)建立初期(5月21～25日)的物理机理。数值诊断结果表明：强南海夏季风年(1994年)建立初期候平均气压梯度力(地转风)作用相对较小,而弱夏季风年(1998年)则相对较大。1994年5月第1候候平均非地转南风比1998年5月第5候候平均非地转南风强的主要原因是1994年南海地区稳定度较小。对1994年5月第1候南海地区近地面候平均最大非地转南风起正贡献的主要因子为：潜热加热,纬向温度平流,垂直温度对流,边界效应;对1998年5月第5候南海地区近地面候平均最大非地转起主要贡献因子为：潜热加热,边界效应,垂直温度对流。     

东亚夏季风降水年代际变异模态及其与太平洋年代际振荡的关系

利用全球陆地月平均降水资料、英国气象局哈德莱中心的月平均海表温度距平(SSTA)资料及NCEP/NCAR再分析大气环流资料,探讨东亚夏季风降水年代际变率及其与太平洋年代际振荡(PDO)的联系。研究指出:东亚夏季风降水年代际变异模态以及PDO均在1976年前后呈现显著的年代际转折,并且东亚夏季风降水与PDO在年代际尺度上具有较好的相关关系。PDO能够在对流层低层激发出与年代际东亚夏季风环流较为相似的大气环流异常特征,表明东亚夏季风环流的年代际变化可能受大气外强迫因子PDO在对流层低层的外源强迫作用影响,最终导致东亚夏季风降水发生年代际变化。     

南海夏季风爆发的数值预报模拟实验

1998年5月21日00时（UTC）,对流层上部200hPa的南亚反气旋中心位于（16oN,94oE）附近,850hPa南海的中南部仍为副热带反气旋控制;到21日12时,200hPa的南亚反气旋中心迅速移到（21oN,94oE）附近,同时850hPa的南海副热带反气旋减弱东撤,南海的中南部由东南风转变为西南风,南海夏季风爆发。本文利用美国国家大气研究中心和宾西法尼亚州大学联合研制的中尺度模式（MM5V2）模拟预报这一过程,同时通过敏感性实验研究了区域边界条件和水平分辨率对季风预报模拟实验的影响。     

1991 年夏暴雨期间Walker 环流和Hadley 环流的特征

该文分析了1991年7月中国江淮暴雨洪水期间赤道太平洋沃克环流及沿115°E哈得莱环流的逐日演变特征。结果发现在暴雨时期赤道东风减弱，西风加强，反哈得莱环流（即季风环流）在中国东部上空加强。在暴雨期间，高低空散度风场的分析指出，在低空出现明显的散度风越赤道气流，而在对流层上部出现散度风的流出。     

冬夏东亚季风环流对太平洋热状况的响应

冬夏隔季韵律关系一直是我国长期天气预报和短期气候预测的一个重要依据,然而迄今为止对它们之间的物理过程及成因机理并不十分清楚。利用NCEP/NCAR全球2.5°×2.5°网格月平均再分析资料,研究1951~2000年冬夏东亚季风环流异常变化与太平洋海面温度(SST)的关系及对关键海温区响应机理。研究指出:冬夏东亚季风环流隔季韵律关系及其年际变化与赤道东太平洋海面温度异常(SSTA)变化密切相关,冬季赤道东太平洋出现La Ni~na(El Ni~no)型的SST分布,有利冬、夏东亚季风环流加强(减弱),其影响过程通过赤道Walker环流强(弱)以及东亚地区Hadley环流强(弱)过程完成。冬季赤道东太平洋海温变化是冬、夏东亚环流季节以及年际变化的一个重要外强迫因子。     

季风指数及其年际变化I·环流强度指数

季风环流可以分解为经向环流和纬向环流。使用NCEP和ECMWF再分析资料,计算亚洲季风区的经向动量环流和纬向动量环流强度的季节内和年际变化,结果表明:对于南亚夏季风和东南亚-西太平洋夏季风,其各自的经向环流和纬向环流的季节内变化和年际变化存在着相当的联系,尤其东南亚-西太平洋夏季风。但南亚夏季风的经向环流和纬向环流的年际变化在不同月份有着不同的关系。对于东亚夏季风,经向环流和纬向环流变化之间的相关在季节内尺度上是线性独立的,而在年际尺度上存在一定的联系。作者指出:这种大尺度上的联系是通过科里奥利力发生作用,并且受热源调节的。同时局地的对流和辐射相互作用则在某种程度上削弱这种联系,导致在不同月份相关程度有所不同。从各季风系统的经向环流之间或纬向环流之间的线性相关看,南亚夏季风,东亚夏季风和东南亚-西太平洋夏季风是相互独立的系统。计算表明,Webster-Yang和Wang-Fan分别提出的南亚夏季风指数在描述纬向环流年际变化上较好,而在经向上勉强令人满意。Wang-Fan提出的描述东南亚-西太平洋夏季风指数,则较好地表示了该区域的经向和纬向环流的年际变化。Goswami提出的季风Hadley环流指数,以及郭其蕴、施能等提出的东亚夏季风指数则较好地描述了相应区域的经向环流圈年际变化,却无法描述相应的纬向环流圈的年际变化。通过计算还表明,NCEP再分析资料和ECMWF再分析资料在1968年以前的南亚季风区和东亚季风区存在着较大的差异。用NCEP再分析资料计算东亚季风区和南亚季风区经向动量环流圈的变率在20世纪60年代较ECMWF的偏大。用NCEP再分析资料计算施能等定义的东亚季风区指数,也较使用ECMWF再分析资料、UCAR的DS010.1及CRU的北半球海平面气压资料计算的偏大。     

东亚夏季风成因的数值试验

本文应用中科院大气所二室设计的二层球谱模式，并引入OSU二层格点模式的物理过程，模拟了5月东亚夏季风的形成。通过四个试验的分析对比，揭示出:5月东亚季风的越赤道气流并不出现在105°E附近，它位于45°—90°E之间，但分析表明来自南半球的影响并不重要；海陆热力差异对低层西南风的形成起了一定的作用，但以地形的作用占主要，地形的动力作用在高原东南侧形成一个低压或槽，热力作用又使得它们加强并移近高原，于是形成了季风低压和季风槽。     

印度夏季风的减弱及其与对流层温度的关系

对43aNCEP/NCAR再分析资料和台站实际观测资料的分析,揭示了对流层温度变化和印度夏季风环流减弱之间的联系。印度夏季风的变化与东亚上空对流层温度具有密切的关系,主要表现为对流层平均温度与整个印度夏季降雨和季风环流强度之间存在显著的正相关。结果表明:印度夏季风环流在近几十年经历了两次减弱过程,第一次减弱约发生在20世纪60年代中期,第二次减弱则发生在20世纪70年代后期;通过改变海陆热力对比,对流层平均温度在印度夏季风减弱过程中可能起着重要作用,东亚地区与东印度洋至西太平洋热带地区之间的对流层温度差异导致了印度夏季风环流的减弱。     

Asian summer monsoon anomalies induced by aerosol direct forcing: the role of the Tibetan Plateau

In this paper we present results of a numerical study using the NASA finite-volume GCM to elucidate a plausible mechanism for aerosol impact on the Asian summer monsoon involving interaction with physical processes over the Tibetan Plateau (TP). During the pre-monsoon season of March–April, dusts from the deserts of western China, Afghanistan/Pakistan, and the Middle East are transported into and stacked up against the northern and southern slopes of the TP. The absorption of solar radiation by dust heats up the elevated surface air over the slopes. On the southern slopes, the atmospheric heating is reinforced by black carbon from local emission. The heated air rises via dry convection, creating a positive temperature anomaly in the mid-to-upper troposphere over the TP relative to the region to the south. In May through early June in a manner akin to an “elevated heat pump”, the rising hot air forced by the increasing heating in the upper troposphere, draws in warm and moist air over the Indian subcontinent, setting the stage for the onset of the South Asia summer monsoon. Our results suggest that increased dust loading coupled with black carbon emission from local sources in northern India during late spring may lead to an advance of the rainy periods and subsequently an intensification of the Indian summer monsoon. The enhanced rainfall over India is associated with the development of an aerosol-induced large-scale sea level pressure anomaly pattern, which causes the East Asia (Mei-yu) rain belt to shift northwestward, suppressing rainfall over East Asia and the adjacent oceanic regions.     

RELATIONSHIP BETWEEN THE SEASONAL TRANSITION OF EAST ASIAN MONSOON CIRCULATION AND ASIAN-PACIFIC THERMAL FIELD AND POSSIBLE MECHANISMS

The NCEP/NCAR reanalysis, CMAP rainfall and Hadley Centre sea surface temperature (SST) datasets are used to investigate the relationship between the seasonal transition of East Asian monsoon and Asian-Pacific thermal contrast, together with the possible causes. Based on the 250 hPa air temperature over two selected key areas, the Asian-Pacific thermal difference (APTD) index is calculated. Results show that the APTD index is highly consistent with the Asian-Pacific Oscillation (APO) index defined by Zhao et al., in terms of different key areas in different seasons. Moreover, the time point of the seasonal transition of the Asian-Pacific thermal contrast can be well determined by the APTD index, indicative of seasonal variation in East Asian atmospheric circulation from winter to summer. The transition characteristic of the circulation can be summarized as follows. The continental cold high at lower tropospheric level moves eastward to the East China Sea and decreases rapidly in intensity, while the low-level northerlies turn to southerlies. At middle tropospheric level, the East Asia major trough is reduced and moves eastward. Furthermore, the subtropical high strengthens and appears near Philippines. The South Asia high shifts from the east of Philippines to the west of Indochina Peninsula, and the prevailing southerlies change into northerlies in upper troposphere. Meanwhile, both the westerly and easterly jets both jump to the north. The seasonal transition of atmospheric circulation is closely related to the thermal contrast, and the possible mechanism can be concluded as follows. Under the background of the APTD seasonal transition, the southerly wind appears firstly at lower troposphere, which triggers the ascending motion via changing vertical shear of meridional winds. The resultant latent heating accelerates the transition of heating pattern from winter to summer. The summer heating pattern can further promote the adjustment of circulation, which favors the formation and strengthening of the low-level southerly and upper-level northerly winds. As a result, the meridional circulation of the East Asian subtropical monsoon is established through a positive feedback between the circulation and thermal fields. Moreover, the time point of this seasonal transition has a significant positive correlation with the SST anomalies over the tropical central-eastern Pacific Ocean, providing a basis for the short-term climate prediction.     

热带太平洋、印度洋海温异常对处于厄尔尼诺事件成熟期的东亚Hadley环流的影响

分析了热带太平洋El Nino事件和热带印度洋海盆一致的暖海温异常事件（记为暖海盆模态）与东亚Hadley环流的关系及海温异常对东亚Hadley环流的影响。结果表明：（1）东亚Hadley环流与El Nino循环的关系密切,El Nino事件从开始到消亡的不同位相期,东亚地区表现为随位相变化的异常经向垂直环流,在El Nino成熟期由异常顺时针经向环流圈转换为异常逆时针经向环流圈,意味着东亚Hadley环流圈的显著减弱。（2）冬季Nino3指数、赤道印度洋海盆一致型模态指数（IOBMI）与东亚Hadley环流指数间呈负相关关系,相关系数分别为-0.42、-0.39,远超过0.01信度的显著性检验,表明当El Nino事件和印度洋暖海盆模事件发生时,东亚Hadley环流减弱。模拟结果与诊断分析结果一致。（3）鉴于印度洋海盆模态和太平洋El Nino事件的密切联系,在考虑冬季东亚Hadley环流变化时,应考虑El Nino事件和印度洋海盆一致型海温异常事件的共同作用。数值试验结果表明两大洋的共同作用会产生更强的东亚异常逆时针经向垂直环流,使得东亚Hadley环流显著减弱。     

影响东亚夏季风降水异常的前期海温信号

采用NCEP/NCAR大气再分析资料、HadISST海温数据以及中国东亚季风区的实测降水资料,探讨前期冬季海温与东亚夏季风之间的关系。研究表明,影响东亚夏季风异常的海温变化存在2个关键区,分别位于南印度洋中部和北太平洋东部,关键区的海温与东亚季风区的降水在长江中游有显著正相关,与东亚夏季风指数有显著负相关。基于此,定义了印-太海温指数。强海温指数年的南亚高压、索马里越赤道气流、西太平洋副高偏强,有利于东亚夏季风北进,中国大部降水偏多;弱海温指数年则相反。      

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.     

1979年东亚夏季风环流建立过程的分析

本文用1979年5—7月低纬地区的格点风资料,对东亚季风地区的逐日平均经圈环流进行了分析,发现东亚夏季风环流的建立过程和印度季风有很大不同。东亚夏季风环流建立时间较早,它是由副热带季风环流和南海热带季风环流组成的。副热带季风环流与源于南亚副热带地区的偏南风,北支高空东风相联系;而南海热带季风环流与源于澳大利亚的跨赤道气流,南支高空东风相联系。印度夏季风环流建立时间较晚,它与索马里低空急流,北支高空东风急流相联系。在季风环流的结构上,两者也是不同的,东亚季风环流是一个准经向环流圈,而印度季风环流则是一个准纬      

印度洋冬季风异常海气环流耦合模态分析

本文对印度洋冬季风异常海气环流耦合主要模态做了分析和讨论,得到以下结果:第一模态海面和低空大气环流的异常主要发生在东印度洋海域上空,而上层大洋环流的异常则主要反映了印度洋冬季风环流的异常,并主要体现在西向赤道暖流和东向赤道逆流上。第二模态的大气环流相应异常主要发生在孟加拉湾、阿拉伯海和赤道印度洋上空,而上层大洋环流异常除与第一模态类似外,还包括索马里暖流的明显异常。第一、二模态分别是印度洋冬季风的偏东、偏西模态,也是其主、次模态;均有约4年的年际变化,还分别有约18、22年的年代际变化;该主、次模态分别在1976年及1976、1986年有突变发生;这样印度洋冬季风有约4年的年际变化,并在1976年出现明显突变。该主、次模态的年代际变化周期也是冬季北太平洋海气联合复EOF分解第二、第一模态的年代际变化周期,这反映两大洋之间有密切联系,这是因冬季蒙古西伯利亚高压是南亚、东亚冬季风的共同源头,对两大洋的大气环流异常都有明显影响。南亚冬季风偏强时印度洋的Hadley环流和赤道辐合带上的对流均偏强,反之亦然;且该冬季风的主、次模态都如此;这也反映了南亚冬季风大气环流异常与冬季热带大气环流异常之间的耦合关系。当该主、次模态发生正、负异常变化时,近表层热带印度洋海温异常分别呈现横贯大洋的南北向跷跷板变化以及大洋东、西向的跷跷板变化;但前者是主要的。印度洋冬季风对印度洋偶极子起着抑制作用,这是该偶极子在冬季最弱的原因。在热带印度洋,大气低空垂直运动下沉、上升区域都分别大致位于该大洋近表层的下沉、上升运动区域之上,这构成了海气相互作用的负反馈机制,并有助于南亚冬季风、Hadley环流、赤道辐合带以及印度洋中冬季风环流的维持和稳定。     

1982—1983年冬季亚澳地区季风环流的低频演变特征

本文应用1982年11月16日—1983年3月15日欧洲中期预报中心的格点资料及向外长波辐射资料(OLR),考察了冬季亚澳季风区季风环流的演变规律。分析了冬季亚澳季风盛期的月平均流场;对澳大利亚季风活跃与中断的几个不同时期流场进行了对比。结果表明,冬季亚澳地区季风环流的演变具有准40天低频振荡特征。主要表现是局地哈得莱环流的准40天强弱变化,澳大利亚季风槽的东西进退,以及北半球副热带高压的东西摆动。      

Progress in the study on the formation of the summertime subtropical anticyclone

The studies in China on the formation of the summertime subtropical anticyclone on the climate timescale are reviewed. New insights in resent studies are introduced. It is stressed that either in the free atmosphere or in the planetary boundary, the descending arm of the Hadley cell cannot be considered as a mechanism for the formation of the subtropical anticyclone. Then the theories of thermal adaptation of the atmosphere to external thermal forcing and the potential vorticity forcing are developed to understand the formation of the subtropical anticyclone in the three-dimensional domain. Numerical experiments are designed to verify these theories. Results show that in the boreal summer, the formation of the strong South Asian High in the upper troposphere and the subtropical anticyclone over the western Pacific in the middle and lower troposphere is, to a great extent, due to the convective latent heating associated with the Asian monsoon, but affected by orography and the surface sensible heating over the continents.On the other hand, the formation of the subtropical anticyclone at the surface over the northern Pacific and in the upper troposphere over North America is mainly due to the strong surface sensible heating over North America, but affected by radiation cooling over the eastern North Pacific. Moreover, in the real atmosphere such individual thermal forcing is well organized. By considering the different diabatic heating in synthesis, a quadruple heating pattern is found over each subtropical continent and its adjacent oceans in summer. A distinct circulation pattern accompanies this heating pattern. The global summer subtropical heating and circulation may be viewed as “mosaics” of such quadruplet heating and circulationpatterns respectively. At last, some important issues for further research in understanding and predicting the variations of the subtropical anticyclone are raised.     

A tripolar pattern as an internal mode of the East Asian summer monsoon

A tripolar anomaly pattern with centers located around the Philippines, China/Japan, and East Siberia dominantly appears in climate variations of the East Asian summer monsoon. In this study, we extracted this pattern as the first mode of a singular value decomposition (SVD1) over East Asia. The squared covariance fraction of SVD1 was 59?%, indicating that this pattern can be considered a dominant pattern of climate variations. Moreover, the results of numerical experiments suggested that the structure is also a dominant pattern of linear responses, even if external forcing is distributed homogeneously over the Northern Hemisphere. Thus, the tripolar pattern can be considered an internal mode that is characterized by the internal atmospheric processes. In this pattern, the moist processes strengthen the circulation anomalies, the dynamical energy conversion supplies energy to the anomalies, and the Rossby waves propagate northward in the lower troposphere and southeastward in the upper troposphere. These processes are favorable for the pattern to have large amplitude and to influence a large area.     

夏季东亚副热带经圈环流特征及其对长江流域降水的影响

利用NCEP/NCAR 1979-2009年月平均风场资料,用质量流函数来定义东亚副热带的经圈环流指数,分析夏季(6-8月)东亚副热带经圈环流特征.结果表明,夏季东亚地区受反Hadlev环流影响,表现出与全球平均经圈环流不同的特征,用指数表征的东亚副热带经圈环流强度存在明显的年际和年代际变化.另外,利用相关性及水汽通量...