Anomalous Midsummer Rainfall in Yangtze River-Huaihe River Valleys and Its Association with the East Asia Westerly Jet

In this study, the interannual and interdecadal relationship between midsummer Yangtze River-Huaihe River valley （YHRV） rainfall and the position of the East Asia westerly jet （EAWJ） were investigated. The midsummer YHRV rainfall was found to significantly increase after the 1980s. Moreover, the location of the EAWJ was found abnormally south of the climatic mean during 1980–2008 （ID2） compared to 1951–1979 （ID1）. During ID2, associated with the southward movement of the EAWJ, an anomalous upper-level conver-gence occurred over middle-high latitudes （35° –55° N） and divergence occurred over lower latitudes （～30°N） of East Asia. Correspondingly, anomalous descending and ascending motion was observed in middle-high and lower latitudes along 90°–130° E, respectively, favoring more precipitation over YHRV. On an interan-nual time scale, the EAWJ and YHRV rainfall exhibited similar relationships during the two periods. When the EAWJ was centered abnormally southward, rainfall over YHRV tended to increase. However, EAWJ-related circulations were significantly different during the two periods. During ID1, the circulation of the southward-moving EAWJ exhibited alternating positive–negative–positive distributions from low to middle– high latitudes along the East Asian coast; the most significant anomaly appeared west of the Okhotsk Sea. However, during ID2 the EAWJ was more closely correlated with the tropical and subtropical circulations. Significant differences between ID1 and ID2 were also recorded sea surface temperatures （SSTs）. During ID1, the EAWJ was influenced by the extratropical SST over the northern Pacific; however, the EAWJ was more significantly affected by the SST of the tropical western Pacific during ID2.

The Westerly Anomalies over the Tropical Pacific and Their Dynamical Effect on the ENSO Cycles during 1980～1994

In this paper, the zonal wind anomalies in the lower troposphere over the tropical Pacific during 1980-1994 are analyzed by using the observed data. The results show that during the formation of the 1982/83, 1986/87 and 1991/92 ENSO events, there were the larger westerly anomalies in the lower troposphere over the equatorial Pacific. Moreover, it is explained by using the correlation analyses that the westerly anomalies over the equatorial Pacific could cause the warm episodes of the equatorial central and eastern Pacific. A simple air-sea coupled model is used to discuss theoretically the dynamical effect of the observed westerly anomalies of wind stress near the sea surface of the equatorial Pacific on the ENSO cycle occurred in the period of 1981-1983. It is shown by using the theoretical calculations of the equatorial oceanic Kelvin wave and Rossby waves responding to the forcing of the observed anomalies of zonal wind stress near the sea surface of the equatorial Pacific that the westerly anomalies of wind stress near the sea surface of the equatorial Pacific make significant dynamical effect on the ENSO cycles occurred in the period of 1982-1983.

STUDY OF ANOMALOUS SST FIELD IN TROPICAL PACIFIC IN PRECEDING YEARS OF TWO PATTERNS OF ENSO EVENTS

Analyzing the anomalous field of SST over the tropical Pacific for two kinds of ENSO events after 1956. we find that in the preceding year before the eastern pattern of El Nino event there is the La Nina event and large negative anomalies of SST in the tropical central and eastern Pacific; the preceding year before the eastern pattern of La Nina event witnesses the prevalence of the El Nino event and large positive anomalies of SST in the same waters: the preceding year before the central patterns of the El Nino (La Nina) events are generally marked by significant positive (negative) SST anomalies in central/western (eastern) tropical Pacific. The fields are just the opposite for two patterns of ENSO events. For waters in the warm pool in the western tropical Pacific, the central (eastern) pattern of El Nino event is with a warm (cool) preceding year of the pool. The warmer conditions in the western Pacific warm pool are a necessity for the occurrence of the central pattern of El Nino event.

ANALYSIS OF THE RELATIONSHIP BETWEEN THE CHINA ANOMALOUS CLIMATE VARIATION AND ENSO CYCLE ON THE QUASI-FOUR-YEAR SCALE

The relationship between the ENSO and abnormal variation of precipitation and temperature in China is investigated based on the monthly data. Firstly, interannual variability of precipitation and temperature are discussed in different sub-areas using Rotational EOF (REOF). Then, the variation of precipitation and temperature in different phases of ENSO cycle is each investigated with Complex Singular Value Decomposition (CSVD). Results show that, during the period of El Nio, precipitation in the eastern China, especially in the northeastern China and Yangtze River valley, is much more than normal and is apt to flood. Precipitation in northern China and Huanghe River valley, especially in the middle reach of Huanghe River, is less than normal and is apt to be less. Precipitation in the Yangtze River valley is closely related to the SSTA in the central and eastern tropical Pacific on the QFO scale, and the precipitation variation lags behind SSTA by about 3 months. For the variation of surface temperature, during the period of El Nio, it is usually colder than normal in northeastern China, and in other regions, especially in the region of Great Bend of the Yellow River and southwestern China, is warmer than normal. The temperature in northeast China is closely associated with SSTA in eastern Pacific on the QFO scale and the surface temperature variation in the northeast China lags behind that of SSTA about 2 months.

西太平洋暖池次表层海温异常与ENSO循环的相互作用

利用 1 964～ 1 993年的太平洋次表层海温资料 ,进一步分析研究了西太平洋暖池次表层海温异常与ENSO循环的关系。合成及相关分析的结果进一步表明 ,西太平洋暖池次表层海温的暖 (冷 )异常及其东传对ENSO的发生起着十分重要、且更直接的作用。然而 ,赤道西太平洋异常纬向风是造成次表层海温异常东传的重要原因 ,而纬向风的异常又是由于东亚冬季风异常活动所引起的 ,这间接地说明了异常东亚冬季风对西太平洋暖池次表层海温距平东传的重要作用。通过研究还发现 ,ENSO发生后 ,北半球副热带地区将有次表层暖 (冷 )海温距平沿着 1 0～ 2 0 oN纬带西传 ,这是导致西太平洋暖池次表层海温发生异常的重要原因之一。也就是说 ,西太平洋暖池次表层海温异常与ENSO循环之间是相互影响、相互作用的。

两类ENSO背景下中国东部夏季降水的环流特征及关键系统

利用全国160站逐月降水资料、74项环流指数、HadISST月平均海温资料以及NCEP/NCAR月平均再分析资料,对比分析了两类ENSO事件衰减阶段中国东部夏季降水及相应大气环流的差异,并探讨其可能成因。结果表明:1)EP型ElNio(LaNia)事件次年夏季,中国东部降水由北至南呈正负正(负正负)的三极型反相分布;CP型ElNio(LaNia)事件次年夏季,中国东部降水由北至南呈正负(负正)的偶极型反相分布;2)ElNio事件次年夏季,西北太平洋副热带高压(以下简称西太副高)及南亚高压均偏强,EP型西太副高偏西、南亚高压偏东,CP型西太副高范围更大、强度更强;LaNia事件次年夏季,西太副高及南亚高压强度偏弱,CP型强于EP型但弱于气候平均;3)ElNio事件期间西北太平洋上存在异常反气旋,EP型位置偏南,强度更强,持续时间更长,CP型位置偏北,范围更大;LaNia事件期间,西北太平洋区域至中国东南部存在异常气旋,EP型异常气旋的强度及范围均不及CP型;4)两类ElNio事件期间异常反气旋的差异可能与印度洋海盆增暖及太平洋海温持续性偏冷有关;两类LaNia事件期间异常气旋的差异可能由赤道西太平洋海温持续偏暖造成。

ENSO循环过程对南极海冰的影响

应用 1 951— 2 0 0 2年NINO特征指数 (NINO1 +2 ,NINO3 ,NINO4 ,NINO3 .4)和 1 973—1 998年南极海冰北界范围以及 1 950— 2 0 0 1年SODA海洋温度资料。首先分析探讨了在ElNi no期间 ,堆积于赤道东太平洋的异常暖水在南半球的传播途径 ,进而研究了ENSO以及东南太平洋异常海温场与南极海冰之间的关系。结果表明 ,在ElNino期间 ,堆积于赤道东太平洋的异常暖水 ,是沿秘鲁和智利沿岸向极传播。其传播过程持续大约 1年的时间 ,但未发现沿南赤道流的西传现象。ENSO循环过程与南极海冰变化存在一定联系 ,特别是Amundsen Belling shausen海和南极半岛海冰的变化与ENSO暖事件 (ElNino)较为密切。当ElNino事件发生后 ,时滞 2年左右的时间 ,Amundsen Bellingshausen海和南极半岛的海冰将出现明显的减少现象 ,特别是南极半岛的海冰减少最为明显。ElNino事件对南极海冰的影响过程是 ,堆积于赤道东太平洋的大量异常暖水 ,沿南美 (秘鲁和智利 )沿岸近海向极地传播 ,异常暖水的这种向极传播过程将引起近极的海温场出现异常升高 ,最终导致Amundsen Bellingshausen海和南极半岛地区的海冰减少。自 2 0世纪 80年代以来 ,Amundsen Bellingshausen海和南极半岛的海冰出现明显减少的趋势 ,与这一时期的ElNino事件的频繁发生?

中国气候异常变化与ENSO准四年循环的联系分析

从月资料分析入手,分析了中国大陆地区的降水和气温异常与ENSO的联系。首先用REOF方法对降水和气温的变化进行分区分析,并讨论其年际变化特点。然后对降水和海温场、气温和海温场分别进行CSVD分析,讨论了在ENSO准四年循环的不同位相上,气温和降水的异常变化情况。结果表明:(1)在El Nino期间,我国东部地区,尤其是东北、长江中下游的江南地区降水偏多,容易发生洪涝,华北地区、黄河流域尤其是中部降水偏少,可能发生干旱。其中长江中下游的南部降水与赤道中东太平洋海温在准四年变化上关系密切,当中东太平洋海温达到最高值后约3个月,长江中下游的南部降水出现最大正距平。(2)在El Nino期间,东北容易出现低温天气,而其它地区尤其是河套地区及西南南部易出现高温天气。其中东北地区气温变化与赤道中东太平洋海温在准四年变化上关系密切,当中东太平洋海温达到最高值后约2个月,东北气温的负距平出现最低。La Nina阶段,情况与前述相反。

热带印度洋海温异常与ENSO关系的进一步研究

用1955年1月—2001年12月美国Scripps海洋研究所的海温再分析资料、美国NCEP再分析资料和美国气候预测中心(CPC)资料,讨论了热带太平洋ENSO与热带印度洋海温距平以及与印度洋偶极子(Dipole)的关系,研究结果发现:在垂直最大温度距平曲面(MTAL)上,热带印度洋海温距平分布存在着与热带太平洋ENSO密切相关的Dipole现象,其中最大的相关在太平洋ENSO超前印度洋Dipole一个月。但是,热带印度洋Dipole的分布与Saij定义的位置略有不同,为东北西南向,它们分别在6°—10°S、65°—75°E(西印度洋)和2°—6°N、85°—95°E(东印度洋),它是赤道印度洋的一个主要海温距平系统。另外,在热带印度洋东北部与ENSO相关的海温距平是一个上下不一致的系统,该海温距平并没有伸展到海面,从海面到20—50m的浅薄水层,则为与赤道西南印度洋相同符号的海温距平分布。因此在海面,海温距平不存在与ENSO有关的Dipole现象,赤道印度洋Dipole只存在于次表层以下,这是赤道印度洋Dipole与ENSO不同之处。这种赤道东北印度洋表层与赤道西南印度洋表层同符号的海温距平现象,有可能是海气热力过程如感热过程造成的。热带印度洋Dipole的周期要小于ElNin^o,一般为1—6a。

热带太平洋年代际平均气候态变化与ENSO循环

文中用观测的热带太平洋海表温度资料、风应力资料和 OLR资料 ,通过多时间尺度分析 ,将与 ENSO有关的变化分为 3个主要的分量 ,一是 2～ 7a的 ENSO循环尺度 ,二是 8～2 0 a的年代际尺度 ,三是 2 0 a以上的平均气候态变化。讨论了热带太平洋这种平均气候态变化的主要特征以及与 ENSO循环的关系 ,并用耦合模式的数值试验来研究平均气候态的变化对 ENSO循环的影响。结果表明 :热带太平洋的平均气候态在 2 0世纪 70年代后期发生了一次由冷态向暖态的变化 ,主要增暖区是沿赤道以及热带东太平洋的 ,海表温度变化最大中心可以达到 0 .6℃。伴随着海表温度的变化 ,赤道西太平洋的西风距平加强 ,赤道东太平洋的东风距平也加强 ,在赤道中太平洋形成了一个加强的辐合中心。年代际平均气候冷暖态的变化对 ENSO最直接的线性影响是使 El Nino位相增加 ,而形成 ENSO冷位相和暖位相的不对称。另一方面较暖的平均气候态可能引起海洋和大气之间的耦合加强 ,导致 ENSO循环振荡有所加强。

1991—1992年ENSO事件的特征

根据美国国家海洋大气局气候分析中心(CAC)和中国气象局气候监测公报所提供的海—气资料,综合分析了1991—1992年ENSO事件的形成、发展过程。这次ENSO事件的主要特点是:(1)在ENSO事件爆发前一年内热带太平洋海气特性频频呈现异常,暖水堆积在赤道中太平洋(5°N—5°S,160°E—160°W)约12个月,然后自西向东传输,爆发1991—1992年ENSO事件。(2)对ENSO事件作出响应的西太平洋副高在这次ENSO事件爆发前12个月出现异常,其明显增强,且在爆发期位置较正常偏西、偏北,导致ENSO事件前异常的气象变化.(3)在这次ENSO事件中,海-气参数发生二次异常的变化,第二次是ENSO事件延长及增强的主要原因。

过去60年中3—5年时间尺度的强ENSO过程与平流层环流异常的滞后耦合及其机理

基于1950—2009年60a月平均Nino3指数和NCEP/NCAR第一套等压面再分析资料,关注3—5a时间尺度的强ENSO过程与平流层环流年际异常的时空联系及其机理,通过对此期间出现在3次持续强ENSO阶段中的11次3—5a时间尺度的强ENSO过程的诊断表明,平流层环流的年际尺度异常与3—5a时间尺度的强ENSO循环过程密切耦合。极夜急流强度趋于在ENSO暖/冷峰值之后减弱/加强,最大异常值多滞后ENSO峰值约1/4周期(接近1a),出现在ENSO峰值之后的下一年冬季;且3—5a时间尺度的ENSO峰值愈强,滞后约1/4周期出现的热带外平流层纬向风的年际异常也愈强;平均而言,这种年际时间尺度的耦合关系,也对实际的季节尺度平流层极涡振荡的强度和性质有显著的调制作用。进一步研究这种滞后耦合关系与年际时间尺度的行星波活动异常的联系发现,在暖ENSO峰值所在的当年冬季,对流层高层被强迫出年际时间尺度的太平洋-北美(PNA)型异常环流,而与冷ENSO峰值相对应的是相反的太平洋-北美异常型;这种太平洋-北美型与平流层热带外地区的行星波1波的发展相联系;在ENSO峰值之后的下一年冬季,太平洋-北美型环流减弱但对流层高层的主要异常分布在中高纬度,多对应着平流层行星波2波的显著增强,与平流层极区最强的高度异常相联系。行星波活动所引起的经向动量通量和经向热量通量的辐合、辐散异常对平流层滞后异常响应的贡献,存在显著的阶段性差异,在不同的阶段两者可以共同起作用,也可以分别起作用。

ENSO事件次表层海温的两个模态及其对大气环流的影响

利用SODA海洋同化资料和NCEP再分析大气资料,分析了热带太平洋次表层海温异常(subsurfaceoceantemperatureanomaly,SOTA)与厄尔尼诺与南方涛动(ElNi?o-SouthernOscillation,ENSO)循环的联系,及SOTA对大气环流的影响。回顾传统ENSO研究,指出存在的问题,提出了ENSO影响大气研究的新思路,得到以下结果:(1)以SOTA为基本资料的研究发现, ENSO事件有两个模态,主要出现在冬季的第一模态对冬季及夏季亚洲-北太平洋-北美地区上空中高纬大气环流有重要影响,主要出现在夏季的第二模态对该地区上空夏季热带和副热带大气系统有重要作用。(2)ENSO事件通过与ENSO相联系的热带太平洋海面温度异常(ENSO-relatedseasurface temperatureanomaly,RSSTA)对大气的异常热通量输送,强迫Walker环流和Hadley环流变化,导致热带和北太平洋及周边地区上空大气环流异常,进而影响相关地区冬季和夏季的气候。(3)海表面温度异常(seasurfacetemperatureanomaly,SSTA)包含RSSTA和大气异常导致的海温变化(sea temperature anomaly caused by atmospheric anomaly, STA)两部分, RSSTA是ENSO事件过程中海洋内部热动力结构调整导致的海面温度变化,在海洋对大气的热输送过程中,它随ENSO事件演变不断更新;STA是大气受RSSTA海洋异常加热后导致的大气环流异常对海面温度的影响,在海洋浅表层STA对RSSTA有重大影响。本文最后讨论了ENSO事件期间热带海洋对大气热输送过程,指出ENSO事件通过海洋内部热动力结构调整产生RSSTA,它直接对大气异常加热,导致大气环流和气候异常,局地海气之间负反馈过程产生STA,反过来抑制RSSTA。结果还指出,人们常用的SSTA变率实际上主要由秋冬季节RSSTA主导,丢失了春夏季ENSO信息,用SSTA研究ENSO事件存在局限性,这也可能是ENSO事件春季预报障碍的原因之一。

南海夏季风爆发与前期东亚冬季风异常的关系以及ENSO的作用

基于ERA-interim再分析资料采用相关分析研究了东亚冬季风和南海夏季风爆发的关系,并探讨了ENSO在其中的作用。结果表明,弱冬季风之后的南海地区5月有异常东风、降水偏少,对应于夏季风爆发偏晚;强冬季风之后则相反;但上述关系并不十分显著。进一步利用线性回归将东亚冬季风分为与ENSO有关和无关的部分,对于与ENSO有关的冬季风,上述冬季风—夏季风爆发的关系的显著性有明显提高;但与ENSO无关的冬季风和夏季风爆发并无显著联系。这说明冬季风—南海夏季风爆发的关系主要是由与ENSO有关的冬季风造成的。这一关系可以用ENSO激发的菲律宾异常反气旋或气旋来解释,以弱冬季风之后夏季风爆发偏晚为例:El Ni?o事件一方面激发出菲律宾异常反气旋,使得冬季风偏弱;另一方面又引起热带印度洋增暖,由于局地海气相互作用正反馈和印度洋电容器效应,菲律宾异常反气旋得以维持到晚春。该异常反气旋及其南侧的异常东风不利于南海夏季风的爆发,从而导致夏季风爆发偏晚。

ENSO Indices and Analyses

New ENSO indices were developed and the spatial variability and temporal evolution of ENSO were analyzed based on the new indices and modeling experiments, as well as multiple data resources. The new indices, after being defined, were validated with their good diagnostic characteristics and correlation with wind and SST. In the analysis after the definition and validation of the new indices, ENSO feedbacks from wind, heat fluxes, and precipitation were spatially and temporally examined in order to understand ENSO variability and evolution with some emphasized points such as the interaction among the feedbacks, the role of westerly wind bursts and the transformation between zonal and meridional circulations in an ENSO cycle, and the typical pattern of modern ENSO.

CONNECTION OF THE SOUTH CHINA SEA SUMMER MONSOON TO MARITIME CONTINENT CONVECTION AND ENSO

The relationship between the intensity of the South China Sea summer monsoon (SCSSM) and the Nino3.4 index and anomalous atmospheric circulation patterns associated with a strong and weak SCSSM are investigated using the NCEP/NCAR reanalysis data, Extended Reconstructed Sea Surface Temperature (ERSST) data and Climate Prediction Center Merged Analysis of Precipitation (CMAP) data. The SCSSM is significantly positively correlated with the Nino3.4 index in the succeeding northern autumn and winter. In the strong minus weak SCSSM composite, a positive East Asia-Pacific teleconnection (EAP) pattern and a negative Europe-Asian-Pacific teleconnection (EUP) pattern appear in the 500 hPa height difference field; low-level cross-equatorial flows are strengthened over the Maritime Continent (MC) region; positive (negative) precipitation anomalies occur in the South China Sea and western north Pacific (MC). A possible mechanism through which SCSSM affects ENSO is proposed. A strong (weak) SCSSM strengthens (weakens) cross-equatorial flows over the MC. The anomalous cross-equatorial flows cool (warm) the SST around the MC through enhanced (reduced) surface latent heat fluxes. The cooling (warming) further leads to suppressed (enhanced) convection over the MC, and causes the anomalous westerly (easterly) in the equatorial western Pacific, which favors the onset of El Nio (La Nia) through modulating the positive air-sea feedback process.

TBO的原因─异常东亚冬季风与ENSO循环的相互作用(英文)

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。

THE CONTRASTS BETWEEN STRONG AND WEAK MJO ACTIVITY OVER THE EQUATORIAL WESTERN PACIFIC IN WINTER

This paper investigates the contrasts between strong and weak Madden-Julian Oscillation(MJO) activity over the equatorial western Pacific during winter using the NCEP reanalysis data. It is shown that the MJO over the equatorial western Pacific in winter shows significant interannual and interdecadal variabilities. During the winters with strong MJO activity, an anomalous cyclonic circulation lies east of the Philippines, strong anomalous easterlies control the equatorial eastern Pacific, and anomalous westerlies extend from the Indian Ocean to the western Pacific in the lower troposphere, which strengthens the convergence and convection over the equatorial western Pacific. The moisture convergence in the lower troposphere is also enhanced over the western Pacific, which is favorable to the activity of MJO. Eastward propagation is a significant feature of the MJO, though there is some westward propagation. The space-time spectral power and center period of the MJO are higher during strong MJO activity winters. The anomalous activity of MJO is closely related to the sea surface temperature(SST) and East Asian winter monsoon(EAWM).During strong MJO activity winters, there are positive/negative anomalies at high/low latitudes in both sea level pressure and 500 h Pa geopotential height, and the temperature is lower over the central part of the Chinese mainland, which indicates a strong EAWM. China experiences more rainfall between the Yellow and Yangtze Rivers, but less rainfall south of the Yangtze River. The SSTA is negative near the Taiwan Island due to the impact of strong EAWM and shows a La Nina pattern anomaly over the eastern Pacific. During the weak MJO activity winters, the situation is reversed.

Important role of the ENSO combination mode in the maintenance of the anomalous anticyclone over the western North Pacific in boreal summer

This study demonstrates the main physical mechanism for the maintenance of the western North Pacific(WNP)anomalous anticyclone(WNPAC)during the El Niño decaying summer by analyzing the respective effects of the cold sea surface temperature(SST)anomalies in the WNP,the warm SST anomalies in the Indian Ocean(IO),and the El Niño and Southern Oscillation(ENSO)combination mode.We find that the WNPAC is usually accompanied by significant cold WNP SST anomalies in the El Niño mature winter and following spring,which almost disappear in the decaying summer and cannot explain the maintenance of the WNPAC in summer.The influence of the IO warm SST anomalies on the WNPAC exhibits conspicuous decadal differences.Before the 2000 s,the IO warm SST anomalies played a role in the WNPAC maintenance through the response of the baroclinic atmospheric Kelvin wave;however,this effect cannot be evidently detected after the 2000 s.This decadal difference may be related to changes in the decaying speed of ENSO events.In contrast to El Niño events before the 2000 s,El Niño events after the 2000 s decay more rapidly,and the associated tropical central-eastern Pacific SST features a La Ni?a-like condition in the El Niño decaying summer.Concomitantly,no significant warm SST anomalies appear over the tropical Indian Ocean,exerting a weak influence on the WNPAC.Relative to the cold WNP SSTanomalies and warm IO SST anomalies,the ENSO combination mode,originating from the nonlinear interaction between ENSO and the annual cycle,has a relatively stable relationship with the WNPAC during the El Niño decaying summer,which exhibits a crucial role in the maintenance of the WNPAC.Considering the persistence of the ENSO combination mode,the WNPAC and associated climate variability during the El Niño decaying summer can be skillfully predicted at least one season in advance based on the ENSO combination mode.

Theories on Formation of an Anomalous Anticyclone in Western North Pacific during El Nino:A Review

The western Noah Pacific anomalous anticyclone （WNPAC） is an important atmospheric circulation system that conveys El Nifio impact on East Asian climate. In this review paper, various theories on the formation and maintenance of the WNPAC, including warm pool atmosphere-ocean interaction, Indian Ocean capacitor, a combination mode that emphasizes nonlinear interaction between ENSO and annual cycle, moist enthalpy advecfion/Rossby wave modulation, and central Pacific SST forcing, are discussed. It is concluded that local atmosphere-ocean interaction and moist enthalpy advection/Rossby wave modulation mechanisms are essential for the initial development and maintenance of the WNPAC during El Nifio mature winter and subsequent spring. The Indian Ocean capacitor mechanism does not contribute to the earlier development but helps maintain the WNPAC in El Nifio decaying summer. The cold SST anomaly in the western North Pacific, although damped in the summer, also plays a role. An inter- basin atmosphere-ocean interaction across the Indo-Pacific warm pool emerges as a new mechanism in summer. In addition, the central Pacific cold SST anomaly may induce the WNPAC during rapid El Nifio decaying/La Nina developing or La Nifia persisting summer. The near-annual periods predicted by the combination mode theory are hardly detected from observations and thus do not contribute to the formation of the WNPAC. The tropical Atlantic may have a capacitor effect similar to the tropical Indian Ocean.