TBO的原因－异常东亚冬季风与ENSO循环的相互作用

基于对 ＮＣＥＰ／ ＮＣＡＲ再分析资料以及其他资料（ＯＬＲ，降水和气温等）的分析研究，结果表明东亚和西北太平洋地区的对流层环流和气候变化都有明显的准两年振荡（ＴＢＯ）特征。同时，异常东亚冬季风可以影响次年夏季的大气环流和气候变化，特别是在东亚地区；而异常东亚冬季风和ＥＮＳＯ循环间又有明显相互作用：持续的强（弱）东亚冬季风通过海─气相互作用可以激发 Ｅｌ Ｎｉ　ｏ（Ｌａ Ｎｉ　ａ）， Ｅｌ Ｎｉ　ｏ（Ｌａ Ｎｉ　ａ）反过来又可通过遥相关或遥响应而导致东亚冬季风偏弱（强）。强或弱的冬季风和ＥＮＳＯ循环是相互衔接在一起的，因此可以认为异常东亚冬季风与ＥＮＳＯ循环的相互作用是ＴＢＯ对流层准两年振荡）的基本原因。     

NUMERICAL SIMULATION OF LAG INFLUENCE OF ENSO ON EAST-ASIAN MONSOON

By prescribing sea surface temperature anomalies(SSTAs)over eastern equatorial Pacific inJanuary—March,the lag influence of ENSO(El Nino and La Nina)on monsoon over East Asiahas been studied.The results suggest that,due to the excitation of atmospheric low-frequencyoscillation by the SSTA,ENSO has significant lag influence on the monsoon over East Asia.During the summer after E1 Nino,the subtropical high over western Pacific is intensified andshows the northward and westward displacement,meanwhile,the rainfall over East China isbelow normal,especially in North China:during the winter after E1 Nino,both the Asian troughand the winter monsoon over East Asia are strengthened.During the summer after La Nina,theanomalous subtropical high prevails over the lower reaches of Yangtze(Changjiang)River,therainfall between Yangtze and Huaihe Rivers is below normal:during the winter after La Nina,both the Asian trough and the winter monsoon over East Asia are weaker.Compared with LaNina,the effect of El Nino is stronger,but it is not always opposite to the one of La Nina.     

AIR-SEA COUPLING FEATURES FROM THE WARM PHASE TO THE COLD PHASE OF ENSO CYCLES IN THE SEVENTIES TO THE EIGHTIES*

Using the sea surface temperature and wind anomalies(SSTA and SSWA for short) of the tropical Pacific from January 1970 to December 1989,main spatial patterns of tropical Pacific SSTA and SSWA coupling features in the transform course from the warm phase to the cold phase of El Nino-southern Oscillation(ENSO) cycles are discussed.The main conclusions are as follows:(1)air-sea coupling patterns at the mature stage of El Nino(La Nina) are main spatial ones of tropical Pacific SSWA and SSTA coupling:(2)at the mature stage of El Nino,the interaction of the anticyclonic anomaly wind,generated by the forcing of distinct meridional SSTA gradient in the Northern Hemisphere tropical central Pacific.with the California cold current and SSTA is mainly responsible for weakening of El Nino;(3)the second sea temperature increase along the South American coast in the decaying course of El Nino results from the eastward movement of the weakened positive SSTA in the tropical central-eastern Pacific forced by anomalous west wind stress:(4)La Nina results from the joint effect of Walker circulation,Ekman drift and negative SSTA in the tropical central-eastern Pacific.     

AIR-SEA COUPLING FEATURES FROM THE WARM PHASE TO THE COLD PHASE OF ENSO CYCLES IN THE SEVENTIES TO THE EIGHTIES

Using the sea surface temperature and wind anomalies(SSTA and SSWA for short)of thetropical Pacific from January 1970 to December 1989,main spatial patterns of tropical PacificSSTA and SSWA coupling features in the transform course from the warm phase to the cold phaseof El Nino-southern Oscillation(ENSO)cycles are discussed.The main conclusions are as follows:(1)air-sea coupling patterns at the mature stage of ElNino(La Nina)are main spatial ones of tropical Pacific SSWA and SSTA coupling:(2)at themature stage of El Nino,the interaction of the anticyclonic anomaly wind,generated by the forcingof distinct meridional SSTA gradient in the Northern Hemisphere tropical central Pacific.with theCalifornia cold current and SSTA is mainly responsible for weakening of El Nino;(3)the secondsea temperature increase along the South American coast in the decaying course of El Nino resultsfrom the eastward movement of the weakened positive SSTA in the tropical central-eastern Pacificforced by anomalous west wind stress:(4)La Nina results from the joint effect of Walkercirculation,Ekman drift and negative SSTA in the tropical central-eastern Pacific.     

亚澳季风异常与ENSO准四年变化的联系分析

分析了赤道地区纬向风的年际变化特征，以及亚澳季风与ENSO在各个位相的联系。结果表明：赤道纬向风变化与中东太平洋海温变化在准四年周期上是强烈耦合的；在El Eino期间东亚冬季风弱，夏季风强，而南亚夏季风弱，反之，在La Nina期间东亚冬季风强，夏季风弱，而南亚夏季风强；东亚地区的异常北风有利于西太平洋西风异常爆发，使得东太平洋海温升高，但只有随后在中东太平洋出现持续性西风异常，El Nino才能发展，其中来自太平洋中部的异常北风（并不是来自东亚大陆地区）和南太平洋中部的异常南风的辐合对中东太平洋出现持续性西风异常起重要的作用，尤其是澳大利亚东北部的季风异常的影响更为显。     

厄尔尼诺和反厄尔尼诺事件与西北太平洋台风活动

用统计相关和典型年合成方法分析了厄尔尼诺和反厄尔尼诺事件与西北太平洋台风活动的关系,指出厄尔尼诺年台风活动减少,反厄尔尼诺年台风活动增加,而且台风活动与厄尔尼诺、反厄尔尼诺事件起始和终止时间、强度、台风生成区域有关。利用厄尔尼诺和反厄尔尼诺年台风活动频数的统计特征,及台风频数与海温等要素的时滞相关关系,为台风频数的预测提供了有益的信息。还应用奇异值分解方法,分析了高度场和海温场的相关关系。结果表明,厄尔尼诺年海气耦合作用将造成不利于台风发展的环流条件,因此台风偏少,反厄尔尼诺年则出现相反的情况。     

ENSO发展和衰减阶段的陕西夏季降水异常特征

利用1961—2008年陕西78个气象站夏季 (6—8月) 降水资料、NCEP/NCAR位势高度场和风场月平均再分析资料,采用合成及相关分析方法探讨ENSO发展和衰减阶段对陕西夏季降水异常的影响,以期为陕西夏季降水的气候预测提供线索和依据。结果表明:陕西夏季降水异常对ENSO发展和衰减阶段的响应存在显著差异,El Ni?o发展阶段和La Ni?a衰减阶段,陕西夏季降水偏少; El Ni?o衰减阶段和La Ni?a发展阶段,陕西夏季降水偏多; ENSO不同阶段对陕西7月降水影响最为显著。比较而言,El Ni?o事件对陕西夏季降水的影响更加显著。在El Ni?o衰减、La Ni?a发展阶段,西太平洋副热带高压偏强、偏西,东亚夏季风偏弱,而在El Ni?o发展、La Ni?a衰减阶段,西太平洋副热带高压偏弱、偏东,东亚夏季风偏强,El Ni?o过程对东亚夏季风强弱的影响更加显著。ENSO发展和衰减阶段通过影响大气环流变化和东亚夏季风的强弱,进而影响陕西夏季降水。     

The Role of the Asian/Australian Monsoons and the Southern/Northern Oscillation in the ENSO Cycle

Summary  In this paper, we first examine the relationship of El Nino and La Nina events with the westerly wind anomalies over the western Pacific warm pool. On this basis, the roles of the Asian and Australian winter monsoons in the formation and progress of the westerly wind anomalies are studied. Finally, we analyze the associations of the Asian and Australian winter monsoons, the westerly wind anomalies and the El Nino and La Nina alternations with the propagating anomalies of the Southern and Northern Oscillation. The results show that the westerly wind bursts are frequent over the Maritime Continent and western Pacific, only those which can further intensify and propagate eastward are accompanied by an El Nino event. It is identified that the establishment and eastward propagation of westerly wind bursts are related to enhanced East Asian and Australian winter monsoon, respectively. The activities of the East Asian and Australian winter monsoon, the variation of the Pacific westerly and trade winds and the alternate appearance of El Nino and La Nina events should be internally connected. The main agents of this relationship are the eastward propagation of alternate positive and negative height anomalies associated with the Southern and Northern Oscillation on a 3–5 year time scale over the south and north tropical Pacific. Received January 4, 1998/Revised January 19, 1999     

Sea surface temperature associations with the late Indian summer monsoon

Recent gridded and historical data are used in order to assess the relationships between interannual variability of the Indian summer monsoon (ISM) and sea surface temperature (SST) anomaly patterns over the Indian and Pacific oceans. Interannual variability of ISM rainfall and dynamical indices for the traditional summer monsoon season (June–September) are strongly influenced by rainfall and circulation anomalies observed during August and September, or the late Indian summer monsoon (LISM). Anomalous monsoons are linked to well-defined LISM rainfall and large-scale circulation anomalies. The east-west Walker and local Hadley circulations fluctuate during the LISM of anomalous ISM years. LISM circulation is weakened and shifted eastward during weak ISM years. Therefore, we focus on the predictability of the LISM. Strong (weak) (L)ISMs are preceded by significant positive (negative) SST anomalies in the southeastern subtropical Indian Ocean, off Australia, during boreal winter. These SST anomalies are mainly linked to south Indian Ocean dipole events, studied by Besera and Yamagata (2001) and to the El Niño-Southern Oscillation (ENSO) phenomenon. These SST anomalies are highly persistent and affect the northwestward translation of the Mascarene High from austral to boreal summer. The southeastward (northwestward) shift of this subtropical high associated with cold (warm) SST anomalies off Australia causes a weakening (strengthening) of the whole monsoon circulation through a modulation of the local Hadley cell during the LISM. Furthermore, it is suggested that the Mascarene High interacts with the underlying SST anomalies through a positive dynamical feedback mechanism, maintaining its anomalous position during the LISM. Our results also explain why a strong ISM is preceded by a transition in boreal spring from an El Niño to a La Niña state in the Pacific and vice versa. An El Niño event and the associated warm SST anomalies over the southeastern Indian Ocean during boreal winter may play a key role in the development of a strong ISM by strengthening the local Hadley circulation during the LISM. On the other hand, a developing La Niña event in boreal spring and summer may also enhance the east–west Walker circulation and the monsoon as demonstrated in many previous studies.     

ENSO对其后东亚季风活动影响的GCM模拟研究

将１～３月赤道东太平洋海表水温距平（ＳＳＴＡ）引入大气环流模式,模拟研究了ＥＮＳＯ（厄尔尼诺和拉尼娜）对其后东亚季风活动的影响。结果表明,由于ＳＳＴＡ在大气中强迫激发出了大气低频振荡,使得ＥＮＳＯ对其后的东亚季风活动仍有明显影响。厄尔尼诺之后的夏季,西太平洋副热带高压偏强偏北且西伸明显,中国东部降水偏少,尤其是华北地区;厄尔尼诺之后的冬季,东亚大槽偏深,冬季风偏强。拉尼娜之后的夏季,中国长江下游为异常副热带高压单体控制,江淮流域雨量偏少;拉尼娜之后的冬季,东亚大槽偏弱,东亚冬季风偏弱。厄尔尼诺的影响比拉尼娜的影响略强,两者的影响并非完全反相。     

INFLUENCE OF TIBETAN PLATEAU ON AIR-SEA INTERACTION OVER TROPICAL PACIFIC IN OCEAN-ATMOSPHERIC COUPLED SYSTEM

A hybrid coupled ocean-atmosphere model is designed,which consists of a global atmosphericgeneral circulation model(L9R15 AGCM)and a simple ocean model(ZC ocean model over tropicalPacific).Using the model,experimental predictions are performed for the 1986/87 El Nino eventand the 1988/89 La Nina event with and without the Tibetan Plateau respectively(called TPFORC and NTP FORC hereinafter).It is found as follows:(1)The coupled system cansuccessfully predict the El Nino or La Nina event even if the Tibetan Plateau orography is notincluded in the model.The patterns of SSTA and wind anomalies in the model without the TibetanPlateau are similar to those with the Tibetan Plateau,which further verifies the fact that ENSOprocess is mainly caused by the air-sea interaction in tropical Pacific.(2)However.the existenceof the Tibetan Plateau exerts its influences on the intensity and duration of El Nino(or La Nina).It is unfavorable to the development and maintenance of westerly anomalies,so to some extent,restrains the development of El Nino,but favors the development of La Nina.(3)Effects of theTibetan Plateau orography on the wind anomalies in the coupled system are different from those inuncoupled AGCM simulation.     

华南登陆台风频数的变化及其与ENSO事件的关系

利用 18 90～ 1999年登陆于我国的台风资料 (指热带风暴、强热带风暴及台风 ) ,主要采用小波分析方法研究华南登陆台风多时间尺度特征 ,并探讨台风与 ENSO事件的关系。结果表明 ,华南登陆台风占全国的 6 3%,平均每年 5个 (最多 10个、最少 1个 ) ,主要周期有 15、5、80年 ,在 2 0世纪 6 0年代以前 15年周期显著 ,6 0年代及以后5年周期明显。台风频数与 ENSO事件的类型及其季节有密切的关系 ,华南台风在拉尼娜年始于夏季的当年明显偏多 (比厄尔尼诺年平均多 1.8个 ) ,台风偏多年 (年频数≥ 7) ,也是拉尼娜年数多于厄尔尼诺年数。影响台风活动的因素非常复杂 ,对拉尼娜年一般可考虑当年台风可能偏多 ,但厄尔尼诺年台风偏多的可能性亦不容忽视。     

El Nino事件当年和次年夏季低纬环流特征的初步分析

分析1950年以来中等强度以上的ElNiño和LaNina当年和次年夏季(7月)低纬度风场和500hPa高度距平场,发现有不同的特征。其中中-西太平洋近赤道地区850、200hPa上风场异常变化十分明显,这种异常变化与南北半球大气相互作用有密切关系。在500hPa高度距平场上,北半球中、高和低纬地区表现出不同的正、负距平分布型式。上述特点对气候短期预测有一定参考意义。     

INFLUENCE OF TIBETAN PLATEAU ON AIR-SEA INTERACTION OVER TROPICAL PACIFIC IN OCEAN-ATMOSPHERIC COUPLED SYSTEM*

A hybrid coupled ocean-atmosphere model is designed,which consists of a global atmospheric general circulation model(L9R15 AGCM)and a simple ocean model(ZC ocean model over tropical Pacific).Using the model,experimental predictions are performed for the 1986/87 El Nino event and the 1988/89 La Nina event with and without the Tibetan Plateau respectively(called TP FORC and NTP FORC hereinafter).It is found as follows:(1)The coupled system can successfully predict the El Nino or La Nina event even if the Tibetan Plateau orography is not included in the model.The patterns of SSTA and wind anomalies in the model without the Tibetan Plateau are similar to those with the Tibetan Plateau,which further verifies the fact that ENSO process is mainly caused by the air-sea interaction in tropical Pacific.(2)However.the existence of the Tibetan Plateau exerts its influences on the intensity and duration of El Nino(or La Nina).It is unfavorable to the development and maintenance of westerly anomalies,so to some extent,restrains the development of El Nino,but favors the development of La Nina.(3)Effects of the Tibetan Plateau orography on the wind anomalies in the coupled system are different from those inuncoupled AGCM simulation.     

ElNino事件当年和次年夏季低纬环流特征的初步分析

分析１９５０年以来中等强度以上的ＥｌＮｉｎｏ和ＬａＮｉｎａ当年和次年夏季低纬度风场和５００ｈＰａ高度距平场发现有不同特征。其中中－西太平洋近赤道地区８５０、２００ｈＰａ上风场异常变化十分明显,这种异常变化与南北半球大气相互作用有密切关系。     

南极海冰涛动与ENSO的关系

对近30年南极海冰密集度资料的EOF和SVD分析，发现南极地区在罗斯海外围和别林斯高晋海的海冰密集度场存在着“翘翘板”的变化特征，并与ENSO有密切联系。由此定义两个海冰关键区的差值为南极海冰涛动指数（ASOI），ASOI超前SOI和Nino3指数2个月时，其正、负相关系数达到最大，并通过α=0.001的信度检验。ASOI高、低指数阶段对应的南半球海平面气温、气压场和风场的合成分析表明，海冰关键区的异常变化可能引起温度、气压、风场的响应而影响南太平洋的洋流，进而对ENSO的发生、发展产生影响。     

Influence of the Eastern Pacific and Central Pacific Types of ENSO on the South Asian Summer Monsoon

Based on observational and reanalysis data,the relationships between the eastern Pacific(EP)and central Pacific(CP)types of El Ni?o?Southern Oscillation(ENSO)during the developing summer and the South Asian summer monsoon(SASM)are examined.The roles of these two types of ENSO on the SASM experienced notable multidecadal modulation in the late 1970s.While the inverse relationship between the EP type of ENSO and the SASM has weakened dramatically,the CP type of ENSO plays a far more prominent role in producing anomalous Indian monsoon rainfall after the late 1970s.The drought-producing El Ni?o warming of both the EP and CP types can excite anomalous rising motion of the Walker circulation concentrated in the equatorial central Pacific around 160°W to the date line.Accordingly,compensatory subsidence anomalies are evident from the Maritime Continent to the Indian subcontinent,leading to suppressed convection and decreased precipitation over these regions.Moreover,anomalously less moisture flux into South Asia associated with developing EP El Ni?o and significant northwesterly anomalies dominating over southern India accompanied by developing CP El Ni?o,may also have been responsible for the Indian monsoon droughts during the pre-1979 and post-1979 sub-periods,respectively.El Ni?o events with the same“flavor”may not necessarily produce consistent Indian monsoon rainfall anomalies,while similar Indian monsoon droughts may be induced by different types of El Ni?o,implying high sensitivity of monsoonal precipitation to the detailed configuration of ENSO forcing imposed on the tropical Pacific.     

ENSO循环与亚、澳季风和南、北方涛动的关系

文中从研究 ENSO循环的成因出发 ,分析了厄尔尼诺 ( El Nino)和拉尼娜 ( La Nina)的产生与西太平洋暖池地区西风异常的关系 ;在此基础上 ,探讨了西太平洋西风异常的形成和变化与亚洲和澳大利亚冬季风的关系 ;最后 ,分析了亚、澳冬季风的活动 ,西太平洋西风异常的形成和东传 ,以及厄尔尼诺和拉尼娜的交替出现等现象与南方涛动和北方涛动传播波的联系。     

ENSO对亚洲夏季风环流和中国夏季降水影响的诊断研究

文中以ＳＶＤ分析技术为基础,发展了一种用以提取一个矢量场和一个标量场耦合信号的统计诊断方法——联合ＳＶＤ方法（简记为ＣＳＶＤ）,并运用ＣＳＶＤ分析了ＥＮＳＯ对亚洲季风环流系统及中国夏季降水的年际变化的影响。结果表明,在ＥｌＮｉｎｏ年,印度夏季风减弱,东亚夏季风增强;而在ＬａＮｉｎａ年,印度夏季风增强,东亚夏季风减弱。且ＥＮＳＯ对亚洲夏季风环流影响显著的区域主要在长江流域南北气流交汇区和索马里急流区,而对中国夏季降水影响最显著的区域则在江淮流域。     

STUDY ON THE QUASI-FOUR YEAR OSCILLATION OF AIR-SEA INTERACTION

Complex Singular Value Decomposition(CSVD)analysis technique was applied to study theQuasi Four year Oscillation(QFO)of air sea interaction and its coupled pattern evolution duringdifferent phases.Results show that:(1)CSVD method can better reveal phase relation betweentwo physical fields:(2)Not only northerly anomalies from Northern Hemisphere but alsosoutherly anomalies from Southern Hemisphere contribute to EI Nino.They converge in westernequatorial Pacific,leading to outburst of strong equatorial westerly anomalies,and result in strongEl Nino event onset:(3)An abnormal subtropical anticyclone circulation appears overnorthwestern Pacific while El Nino developing.It favors transitions from the warm SST(EINino)to the cold SST(La Nina),just as the tropical westerly anomalies produced by abnormalcyclone during a decaying La Nina.which encourage the development of El Nino:(4)Thewesterly anomalies in equatorial Pacific are mainly induced by eastward abnormal subtropicalcyclone pairs,which are located in north and south Pacific respectively,and are not the eastwardwesterly anomalies from equatorial Indian Ocean.