Northern poleward edge of regional Hadley cell over western Pacific during boreal winter: year-to-year variability,influence factors and associated winter climate anomalies

Compared to the zonal-mean Hadley cell (HC), our knowledge of the characteristics, influence factors and associated climate anomalies of the regional HC remains quite limited. Here, we examine interannual variability of the northern poleward HC edge over western Pacific (WPHCE) during boreal winter. Results suggest that interannual variability of the WPHCE is impacted by the El Niño-Southern Oscillation (ENSO) Modoki, North Pacific Oscillation (NPO) and North Atlantic Oscillation (NAO). The WPHCE tends to shift poleward during negative phase of the ENSO Modoki, and positive phases of the NPO and NAO, which highlights not merely the tropical forcing but also the extratropical signals that modulate the WPHCE. ENSO modoki, NPO and NAO modulate the WPHCE via inducing atmospheric anomalies over the western North Pacific. We further investigate the climatic impacts of the WPHCE on East Asia. The poleward shift of the northern descending branch of the WPHC results in anomalous upward (downward) motions and upper-level divergence (convergence) anomalies over south-central China (northern East-Asia), leading to increased (decreased) rainfall there. Moreover, pronounced cold surface air temperature anomalies appear over south-central China when the sinking branch of the WPHC moves poleward. Based on the temperature diagnostic analysis, negative surface temperature tendency anomalies over central China are mostly attributable to the cold zonal temperature advection and ascent-induced adiabatic cooling, while the negative anomalies over South China are largely due to the cold meridional temperature advection. These findings could improve our knowledge of the WPHCE variability and enrich the knowledge of forcing factors for East Asian winter climate.

     

The seasonal footprinting mechanism in CFSv2: simulation and impact on ENSO prediction

The seasonal footprinting mechanism (SFM) is thought to be a pre-cursor to the El Nino Southern Oscillation (ENSO). Fluctuations in the North Pacific Oscillation (NPO) impact the ocean via surface heat fluxes during winter, leaving a sea-surface temperature (SST) “footprint” in the subtropics. This footprint persists through the spring, impacting the tropical Pacific atmosphere–ocean circulation throughout the following year. The simulation of the SFM in the National Centers for Environmental Prediction (NCEP)/Climate Forecast System, version 2 (CFSv2) is likely to have an impact on operational predictions of ENSO and potentially seasonal predictions in the United States associated with ENSO teleconnection patterns. The ability of the CFSv2 to simulate the SFM and the relationship between the SFM and ENSO prediction skill in the NCEP/CFSv2 are investigated. Results indicate that the CFSv2 is able to simulate the basic characteristics of the SFM and its relationship with ENSO, including extratropical sea level pressure anomalies associated with the NPO in the winter, corresponding wind and SST anomalies that impact the tropics, and the development of ENSO-related SST anomalies the following winter. Although the model is able to predict the correct sign of ENSO associated with the SFM in a composite sense, probabilistic predictions of ENSO following a positive or negative NPO event are generally less reliable than when the NPO is not active.     

Interdecadal Modulation of AMO on the Winter North Pacific Oscillation-Following Winter ENSO Relationship

It is known that the wintertime North Pacific Oscillation (NPO) is an important extratropical forcing for the occurrence of an El Ni?o?Southern Oscillation (ENSO) event in the subsequent winter via the “seasonal footprinting mechanism” (SFM). This study reveals that the Atlantic Multidecadal Oscillation (AMO) can notably modulate the relationship between the winter NPO and the following winter ENSO. During the negative AMO phase, the winter NPO has significant impacts on the following winter ENSO via the SFM. In contrast, the influence of the winter NPO on ENSO is not robust at all during the positive AMO phase. Winter NPO-generated westerly wind anomalies over the equatorial western Pacific during the following spring are much stronger during negative than positive AMO phases. It is suggested that the AMO impacts the winter NPO-induced equatorial westerly winds over the western Pacific via modulating the precipitation climatology over the tropical central Pacific and via modulating the connection of the winter NPO with spring sea surface temperature in the tropical North Atlantic.     

冬季北太平洋海温主模态在1990年前后调整及其成因初探?

太平洋年代际振荡(PDO)和北太平洋涡旋振荡(NPGO)是北太平洋(20°~60°N,120°E~120°W)海温(SST)的EOF前两个模态,本文通过比较1990年前后北太平洋冬季SST EOF前两个模态,揭示了PDO和NPGO在1990年前后特征,并从关键区海温变化、北太平洋涛动(NPO)、赤道太平洋中部变暖(CPW)和北极涛动(AO)的影响,揭示了北太平洋主模态在1990年之后调整的成因。我们发现,1990年之前,北太平洋SST场的EOF前两个模态与PDO和NPGO的空间结构类似,但是在1990年之后,SST的EOF第一模态的最大荷载中心向日界线移动,40°N以北的太平洋被正的SST异常控制,表现出与NPGO模态的负位相相似的空间分布特征,而EOF第二模态由偶极子演变成了三极子结构。北太平洋中部(28°~36°N,152°~178°W)和北太平洋北部(44°~49°N,151°~177°W)海温距平在1990年之后呈显著的负相关变化,是导致在1990年之后冬季NPGO成为主模态的内部原因,而NPO在1990年之后的显著增强则是重要的外部原因。分析显示,NPO在1980年开始表现出增强趋势,通过风生流机制,NPO可以增强北太平洋45°N附近的气压梯度和西风异常幅度,从而导致了1990年之后NPGO海温模态的加强。虽然CPW和AO对NPO的南支(夏威夷)和北支(阿拉斯加)的海平面气压异常中心加强有贡献,但是上述两个因子与NPGO之间的关系在1990年之前并不明显。因此,CPW和AO与NPGO之间并不存在稳定的物理联系。     

Joint Propagating Patterns of SST and SLP Anomalies in the North Pacific on Bidecadal and Pentadecadal Timescales

Wavelet analyses are applied to the Pacific Decadal Oscillation index and North Pacific index for the period 1900-2000, which identifies two dominant interdecadal components, the bidecadal (15-25-yr) and pentadecadal (50-70-yr) modes. Joint propagating patterns of sea surface temperature (SST) and sea level pressure (SLP) anomalies in the North Pacific for the two modes are revealed by using the techniques of multi-channel singular spectrum analysis (MSSA) and linear regression analysis with the global sea surface temperature (GISST) data and the northern hemispheric SLP data for the common period 1903-1998. Significant differences in spatio-temporal structures are found between the two modes.For the bidecadal mode, SST anomalies originating from the Gulf of Alaska appear to slowly spread southwestward, inducing a reversal of early SST anomalies in the central North Pacific. Due to further westward spreading, the SST variation of the central North Pacific leads that of the Kuroshio-Oyashio Extension (KOE) region by approximately 4 to 5 years. Concomitantly, SLP anomalies spread over most parts of the North Pacific during the mature phase and then change into an NPO(North Pacific Oscillation)-like pattern during the transition phase. For the pentadecadal mode, SST anomalies develop in the southeast tropical Pacific and propagate along the North American coast to the mid-latitudes; meanwhile,SST anomalies with the same polarity in the western tropical Pacific expand northward to Kuroshio and its extension region; both merge into the central North Pacific reversing the sign of early SST anomalies there.Accompanying SLP anomalies are characterized by an NPO-like pattern during the mature phase while they are dominant over the North Pacific during the transitional phase. The bidecadal and pentadecadal modes have different propagating Patterns, suggesting that the two interdecadal modes may arise from different physical mechanisms.     

北方涛动同北半球温带大气环流的遥相关(一)——基本结构

本文利用1951—1980年逐季的平均值资料(共120个季)讨论了北方涛动和与其相联系的北太平洋海温与北半球海平面气压场、500hPa位势高度场遥相关的基本结构,并与南方涛动和赤道东太平洋海温的结果进行了对比分析.发现北太平洋Namias海区和加利福尼亚海流区海温的变化与北方涛动具有很密切的联系;北方涛动和这两个海区的海温同北半球中高纬度大气环流特别是PNA型和NAO型环流异常存在明显的遥相关关系;南方涛动和赤道太平洋海温同WP型或NPO型环流异常关系比较密切,而与PNA型和NAO型的关系不如北方涛动和Namias海区及加利福尼亚海流区海温的显著.     

北太平洋海平面气压场变化与海温的关系

利用SVD（singular value decomposition）方法分析了1948年1月—2002年12月北太平洋海平面气压场与海温的关系。结果表明,SVD第1对异类相关分布型反映出,当东北太平洋副热带高压加强（减弱）时,Namias海区海温升高（降低）,而加利福尼亚海流区海温降低（升高）。SVD第2对异类相关分布型表明,当阿留申低压加深、北太平洋副热带地区气压升高时,黑潮暖流区海温升高,而北太平洋高、低纬海温降低;反之亦然。时滞相关表明,北太平洋大气环流异常超前海温1个月的相关最好,海温变化对大气环流异常分布型具有维持作用。NCAR CCSM3模拟结果很好地验证了上述结论,即在海气相互作用过程中,东北太平洋副热带高压和NPO（North Pacific Oscillation）与北太平洋海温存在密切联系。     

北太平洋冬季海-气耦合的主模态及其与瞬变扰动异常的联系

利用45年的ECMWF再分析资料,使用SVD方法研究了冬季北太平洋地区表层海温(SST)异常与大气环流异常间的主要耦合模态,探讨了大尺度海-气耦合型与天气尺度瞬变扰动的相互关系。分析结果表明,中纬度北太平洋地区冬季存在两种主要的海-气耦合型,第1种耦合型反映了与ENSO紧密相关的中纬度北太平洋冬季海温异常分布型以及大气的PNA型,第2种耦合型SST异常集中在东亚沿海以及中纬度北太平洋海流区,相应的大气场则为暖(冷)SSTA上空东西向带状区域内位势高度偏高(低),明显独立于ENSO型。进一步的合成分析表明,在第1种耦合型SST正(负)异常年里,冬季阿留申低压主体位置偏西南(东北),从东北亚到北美西海岸的西北—东南向带状区域内是低层大气温度正(负)异常区和高层西风负(正)异常区,西风负(正)异常中心位于西风急流出口处的北太平洋中东部,而西风急流主体区的风速变化很小。在第2种耦合型东亚沿海至中纬度北太平洋海流区SST偏暖(冷)时,阿留申低压整体偏弱(强),SST暖(冷)异常上空的大气温度偏暖(冷),高层西风急流区西风偏弱(强)。两种耦合型均显示出在北太平洋中纬度地区大气和海洋的异常相关中心有很好的空间对应性。在两种耦合型下,中纬度北太平洋冬季的大气斜压性也发生截然不同的改变,引起中纬度天气尺度瞬变扰动活动异常。瞬变扰动异常的动力强迫作用对北太平洋西风异常的形成存在正反馈作用,而其热力作用则试图破坏与两种海-气耦合模态相关的大气温度异常型。     

Impact of the Winter North Pacific Oscillation on the Surface Air Temperature over Eurasia and North America: Sensitivity to the Index Definition

This study analyzes the impact of the winter North Pacific Oscillation(NPO) on the surface air temperature(SAT)variations over Eurasia and North America based on six different NPO indices. Results show that the influences of the winter NPO on the SAT over Eurasia and North America are sensitive to the definition of the NPO index. The impact of the winter NPO on the SAT variations over Eurasia(North America) is significant(insignificant) when the anticyclonic anomaly associated with the NPO index over the North Pacific midlatitudes shifts westward and pronounced northerly wind anomalies appear around Lake Baikal. By contrast, the impact of the winter NPO on the SAT variations over Eurasia(North America)is insignificant(significant) when the anticyclonic anomaly over the North Pacific related to the NPO index shifts eastward and the associated northerly wind anomalies to its eastern flank extend to North America. The present study suggests that the NPO definition should be taken into account when analyzing the impact of the winter NPO on Eurasian and North American SAT variations.     

Temporal Characteristics of Pacific Decadal Oscillation (PDO) and ENSO and Their Relationship Analyzed with Method of Empirical Mode Decomposition (EMD)

1. IntroductionPacific Decadal Oscillation (PDO) is a long-termENSO-like variability of the North Pacific. It can becharacterized by the first principal component of EOFof the North Pacific SST (Zhu and Yang, 2003; Tren-berth, 1990; Yang and Zhang, 2003). ENSO is thestrongest signal of annular change of global climatesystem (Trenberth, 1997). The spatial pattern of PDOis a wedge similar to El Nino. In the cool (warm)phases of PDO, the central and northwest Pacific is ofwarm (co…     

Phase‐locked and asymmetric correlations of the wintertime atmospheric patterns with the ENSO

Abstract

Teleconnections between sea surface temperature (SST) anomalies over the Pacific and the dominant patterns of wintertime Northern Hemisphere 500‐hPa height are examined by applying statistical techniques such as rotated principal component analysis and composite analysis. It is shown that the Pacific/North American (PNA) patterns in December through March are correlated most significantly with the ENSO‐related SST anomalies in the previous October, while the western Pacific (WP) patterns in December through February are most closely linked to the ENSO‐related SST anomalies in the same season. In addition, the PNA response to the ENSO signal during La Niña events is more significant than that during El Niño events, while the WP response is stronger during El Niño events than during La Niña events. A composite analysis shows that in the El Niño winters the North Pacific centre of the PNA pattern is located about 10 degrees east of its normal position, leading to a less significant correlation between the ENSO signal and the PNA pattern in these winters.

The ENSO‐related SST anomalies include a large centre of action over the tropical Pacific and an oppositely signed anomaly centre over the North Pacific. The North Pacific centre appears to the west of the dateline in September and October. This ENSO‐related seed of SST anomalies slowly moves eastward in the following months, gradually cutting off its connection with SST anomalies over the tropical Pacific and being coupled with the PNA pattern. It is pointed out that, although the wintertime SST anomaly over the North Pacific may appear as a mode linearly independent of the ENSO signal in the same season, it is partially related to the ENSO signal in the preceding autumn.

Possible dynamical explanations of the above results are discussed. It is suggested that the WP pattern can be linked to the tropical Pacific heat source via advection of vorticity by the upper‐tropospheric divergent/convergent flow, and the intensification of vorticity gradients associated with a stronger east Asian jet is likely to be responsible for a more significant WP pattern response to the ENSO signal in the El Niño winters. On the other hand, the ENSO‐related PNA pattern could be considered a manifestation of the eastward extension (El Niño) or westward withdrawal (La Niña) of the east Asian jet stream due to the local Hadley cell over the Pacific. In addition, the ENSO‐related seed of extratropical SST anomaly over the western Pacific in autumn may also play an important role in the development of the PNA pattern in the following winter.     

华北夏季降水异常与南太平洋夏季海表温度变化主要模态的可能联系

利用1951—2006年NCEP/NCAR再分析资料,采用EOF（empirical orthogonal function,经验正交函数）展开方法提取了南太平洋12—2月海表温度变化的主要模态,其第一模态反映了ENSO（El Nino-Southern Oscillation）的信号,周期为3～5a;第二模态与南半球环状模（Southern-Hemi-sphere annual mode,SAM）相联系,周期为准两年。结果表明,南太平洋EOF1时间序列处于正（负）相位时华北地区后期5月多（少）雨,同时注意到南、北太平洋EOF1对中国5月降水的影响区域基本一致。南太平洋EOF2时间序列处于正（负）相位时江南地区的夏季平均降水减少（增多）。去掉EOF1和EOF2的线性趋势后,这种显著相关仍然存在,只是显著相关区域有所缩小。利用南、北太平洋EOF1时间序列作为预报因子,建立回归预报方程,可为预测中国华北地区5月降水提供依据     

气候系统模式FGOALS_gl模拟的赤道太平洋年际变率

本文分析了中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室 (LASG/IAP) 发展的气候系统模式FGOALS_gl对赤道太平洋年际变率的模拟能力。结果表明, FGOALS_gl可以较好地模拟出赤道太平洋SST异常年际变率的主要特征, 但模拟的ENSO事件振幅偏大, 且变率周期过于规则。耦合模式模拟的气候平均风应力在热带地区比ERA40再分析资料的风应力强度偏弱30%左右, 由此引起的海洋平均态的变化, 是造成模拟的ENSO振幅偏强的主要原因。FGOALS_gl模拟的ENSO峰值多出现在春季或夏季, 原因可归之于模式模拟的SST季节循环偏差。耦合模式可以合理再现ENSO演变过程, 但观测中SST异常的东传特征在模式中没有得到再现, 这与模拟的ENSO发展模态表现为单一的 “SST模态” 有关。模拟的ENSO位相转换机制与 “充电—放电” 概念模型相符合, 赤道太平洋热含量的变化是维持ENSO振荡的机制。在ENSO暖位相时期, 赤道中东太平洋与印度洋—西太平洋暖池区的海平面气压距平型表现为南方涛动型 (SO型), 200 hPa位势高度分布表现为太平洋—北美遥相关型 (PNA型)。     

中纬度北太平洋依赖于ENSO事件及独立于ENSO事件的变率特征:观测事实与海气耦合模式模拟

观测事实显示,在E1 Ni(?)o发生期间,伴随着赤道中东太平洋的增暖,中纬度北大平洋中部表层海温（SST）常出现冷距平,而北美大陆西海岸SST则出现暖距平。借助观测资料分析和海气耦合模式模拟两种手段,检验了北太平洋对ENSO事件的上述响应。观测证据和数值模拟都支持有关学者提出的“大气桥”概念,即大气对赤道中东太平洋SST异常增暖的响应,随后强迫中纬度北太平洋,并导致那里SST的变冷,从而起到了连接热带和热带外特别是中纬度北太平洋的“桥梁”的作用。关于其机制,本文认为主要是海洋对大气强迫的动力响应导致那里的SST变冷,尽管潜热通量的贡献也很显著。至少模式结果证明短波辐射、长波辐射和感热通量的贡献都是次要的。进一步的分析揭示,北太平洋存在着线性独立于ENSO事件的所谓“北太平洋模态”,在空间型上,它和线性地依赖于ENSO事件的模态非常相近,即它们的纬向结构都呈现出扁平的“双极”型,只是彼此间SST距平极大值的中心位置不同。模拟结果表明,北太平洋模态与大气的耦合作用,主要是通过海气热通量交换实现的,其中短波辐射和长波辐射的作用居主导地位,而潜热通量的贡献则基本可以忽略。     

加利福尼亚附近的海温强迫及其与北太平洋年代际振荡的可能联系

本文利用1958～2018年期间海表面温度（SST）异常和湍流热通量异常变化的关系,探讨了其与北太平洋年代际振荡（PDO）相关的年际和年代际时间尺度上在不同海域的海气相互作用特征。结果表明:在年际尺度上,黑潮—亲潮延伸区（KOE）表现为显著大气强迫海洋,赤道中东太平洋表现为显著海洋强迫大气;在年代际尺度上,PDO北中心表现为大气强迫海洋,加利福尼亚附近则表现为显著海洋强迫大气。进一步分析表明:加利福尼亚附近区域是北太平洋准12年振荡的关键区域之一,与PDO准十年的周期类似,加利福尼亚附近的冷（暖）海温对应其上有反气旋（气旋）型环流,赤道中太平洋海水上翻和北太平洋东部副热带区域经向风应力的变化是北太平洋准12年振荡的另外两个重要环节。     

1月份两类ENSO的海气环流模态分析

本文对1950～2001年1月份的大气风场和大洋流场做了联合复EOF（Empirical Orthogonal Function）分解,用以探讨1月份两类ENSO（El Ni?o-Southern Oscillation）的海气环流及耦合情况,所得结果主要有:该分解第1、2模态空间场分别相应于东部型、中部型ENSO,前者在赤道太平洋东部和中部都有海温动力异常,并以东部异常最强,后者仅在中部存在此异常,两模态的时间系数都与ENSO有很好相关,为此第1、2模态可分别称为东部型、中部型ENSO的风场流场（异常）模态。东部型ENSO模态具有3～6年的年际变化和13～14年的年代际变化,中部型则有明显的7年年际变化和12、17年的年代际变化,两者中约13年的周期与冬季北太平洋NPGO（North Pacific Gyre Oscillation）的周期相同。东、中部型El Ni?o期间,沃克环流上升支分别从印尼东移至赤道西、中太平洋,并有所减弱;南、北支哈得莱环流则分别位于日界线以东及该线附近,且均有所加强,从而使南、北太平洋副热带高压偏强;而在5°S的南美沿岸则分别有垂直运动上升和下沉异常。在海气耦合上,两类ENSO模态在赤道中太平洋均存在西风异常与海洋赤道Kelvin波和Rossby波的波包解耦合,而海温动力异常对大气的影响则都起到负反馈作用,从而有利于ENSO的维持和稳定。     

The influence of tropical Pacific forcing on the Arctic Oscillation

The potential role of tropical Pacific forcing in driving the seasonal variability of the Arctic Oscillation (AO) is explored using both observational data and a simple general circulation model (SGCM). A lead–lag regression technique is first applied to the monthly averaged sea surface temperature (SST) and the AO index. The AO maximum is found to be related to a negative SST anomaly over the tropical Pacific three months earlier. A singular value decomposition (SVD) analysis is then performed on the tropical Pacific SST and the sea level pressure (SLP) over the Northern Hemisphere. An AO-like atmospheric pattern and its associated SST appear as the second pair of SVD modes. Ensemble integrations are carried out with the SGCM to test the atmospheric response to different tropical Pacific forcings. The atmospheric response to the linear fit of the model’s empirical forcing associated with the SST variability in the second SVD modes strongly projects onto the AO. Idealized thermal forcings are then designed based on the regression of the seasonally averaged tropical Pacific precipitation against the AO index. Results indicate that forcing anomalies over the western tropical Pacific are more effective in generating an AO-like response while those over the eastern tropical Pacific tend to produce a Pacific-North American (PNA)-like response. The physical mechanisms responsible for the energy transport from the tropical Pacific to the extratropical North Atlantic are investigated using wave activity flux and vorticity forcing formalisms. The energy from the western tropical Pacific forcing tends to propagate zonally to the North Atlantic because of the jet stream waveguide effect while the transport of the energy from the eastern tropical Pacific forcing mostly concentrates over the PNA area. The linearized SGCM results show that nonlinear processes are involved in the generation of the forced AO-like pattern.     

Year-to-Year and interdecadal variability in the activity of intraseasonal fluctuations in the Northern Hemisphere wintertime circulation

Summary Interannual variability in the activity of fluctuations with subseasonal time scales is investigated based upon observed data of the extratropical Northern Hemisphere circulation over the recent 38 winters. Their activity is represented in the root mean square (RMS) field of filtered geopotential height in which the fluctuations with time scales between 10 days and a season are retained. The singular value decomposition (SVD) was applied to the covariance matrix between the seasonal mean and RMS fields for the 500-hPa height.The leading SVD mode for the north Pacific represents the strong relationship between the polarity of the Pacific/North American (PNA) pattern in the seasonal-mean anomalies and the amplitude of a meridionally-oriented dipole-like oscillation within the season. It tends to be more active when the seasonal-mean jet stream is strongly diffluent over the central Pacific than when the jet is extended zonally across the Pacific. The leading SVD mode for the north Atlantic is indicative of stronger intraseasonal fluctuations near Greenland in the presence of anticyclonic seasonal-mean anomalies associated with the North Atlantic Oscillation (NAO).The intraseasonal variability in the extratropics is strongly correlated with the underlying sea surface temperature (SST) anomalies, and that in the north Pacific also exhibits significant but rather weak correlation with SST anomalies in the equatorial Pacific. The activity of the atmospheric intraseasonal fluctuations is found to be modulated in accordance with interdecadal variability in the seasonal-mean circulation and SST.On leave from Department of Earth & Planetary Physics, University of Tokyo.With 12 Figures     

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。     

The Southern Oscillation / Northern Oscillation Cycle Associated with Sea Surface Temperature in the Equatorial Pacific

This paper analyzed the time evolution of the global 1000 hPa height anomalies related to the sea surface temperature (SST) in the eastern equatorial Pacific by using ECMWF data in the period 1979-1988, in which two Pacific warm events, 1982/83 and 1986/787, are included. It is found that there are distinct evidences of eastward propagation of alternate positive / negative height anomalies not only in the tropical South Pacific but also in the tropical North Pacific. The former is associated with the Southern Oscillation (SO) and the latter is associated with the so-called Northern Oscillation (NO).It is noteworthy that the alternate positive / negative anomaly centers associated with SO and NO can be traced back to the middle and higher latitudes of the South Indian Ocean and the East Asian continent respectively, which may be significant for the understanding of the causes and mechanism of SO and NO and for the monitoring of ENSO.Furthermore, these evolution processes have a strong symmetry about the