On Multi-Timescale Variability of Temperature in China in Modulated Annual Cycle Reference Frame

The traditional anomaly (TA) reference frame and its corresponding anomaly for a given data span changes with the extension of data length. In this study, the modulated annual cycle (MAC), instead of the widely used climatological mean annual cycle, is used as an alternative reference frame for computing climate anomalies to study the multi-timescale variability of surface air temperature (SAT) in China based on homogenized daily data from 1952 to 2004. The Ensemble Empirical Mode Decomposition (EEMD) method is used to separate daily SAT into a high frequency component, a MAC component, an interannual component, and a decadal-to-trend component. The results show that the EEMD method can reflect historical events reasonably well, indicating its adaptive and temporally local characteristics. It is shown that MAC is a temporally local reference frame and will not be altered over a particular time span by an extension of data length, thereby making it easier for physical interpretation. In the MAC reference frame, the low frequency component is found more suitable for studying the interannual to longer timescale variability (ILV) than a 13-month window running mean, which does not exclude the annual cycle. It is also better than other traditional versions (annual or summer or winter mean) of ILV, which contains a portion of the annual cycle. The analysis reveals that the variability of the annual cycle could be as large as the magnitude of interannual variability. The possible physical causes of different timescale variability of SAT in China are further discussed.     

传统距平与变年循环参照系下的中国气温变率比较

用功率谱分析、小波分析和经验正交函数(EOF)分析三种方法,对比分析了1953～2002年北京单站以及中国区域地表气温的传统距平与以集合经验模分解(EEMD)的频-幅调制年循环(MAC)为参照的"距平",同时还比较了用传统距平描述的"年际及更长尺度变率"和以MAC为参照的年以上尺度低频分量。通过对比分析,发现传统距平和用传统距平所描述的"年际及更长尺度变率"仍然包含有年周期,而且还包含有小于年尺度的波动;而去除MAC的距平则更好地去除了准年周期,而且以MAC为参照的年以上尺度低频分量只包含有1年以上尺度的波动,因而更适合用来描述"年际及更长尺度变率"。     

Low Frequency Characteristics of Tropical Pacific Wind Stress Anomalies in Observations and Simulations from a Simple and a Comprehensive Models

Low frequency characteristics of tropical Pacific wind stress anomalies in observation and simulations; from the CZ simple atmospheric model and COLA R15 AGCM are analyzed. The results show that ENSO event may be a multi-scale process, that is, ENSO time scale has the period longer than three yean; biennial oscillation and annual variability Dynamical characteristics are involved in the evolution process of wind stress anomaly with ENSO time scale: 1) the development and eastward movement of a cyclonic anomaly circulation in subtropical northwestern Pacific and weakening of Southern Oscillation result in the eastward propagation of westerly anomaly along the equator, there?fore, interactions between flows in subtropics and in tropics play an important role in the evolution of wind stress anomaly with ENSO time scale; 2) easterly and westerly anomalies with ENSO time scale are one kind of propagating wave, which differs from Barnett’s (1991). It is interesting that the evolution of observed and simulated wind stress anomalies with biennial time scale bears a strong resemble to that with ENSO time scale although their period it dif?ferent. Observed annual variability it weak during 1979-1981 and intensified after 1981, especially it reaches to max?imum during 1982-1984, and the spatial structure of the first mode is the ENSO-like pattern.     

A Hybrid Coupled Ocean–Atmosphere Model and Its Simulation of ENSO and Atmospheric Responses

A new hybrid coupled model(HCM) is presented in this study, which consists of an intermediate tropical Pacific Ocean model and a global atmospheric general circulation model. The ocean component is the intermediate ocean model(IOM)of the intermediate coupled model(ICM) used at the Institute of Oceanology, Chinese Academy of Sciences(IOCAS). The atmospheric component is ECHAM5, the fifth version of the Max Planck Institute for Meteorology atmospheric general circulation model. The HCM integrates its atmospheric and oceanic components by using an anomaly coupling strategy. A100-year simulation has been made with the HCM and its simulation skills are evaluated, including the interannual variability of SST over the tropical Pacific and the ENSO-related responses of the global atmosphere. The model shows irregular occurrence of ENSO events with a spectral range between two and five years. The amplitude and lifetime of ENSO events and the annual phase-locking of SST anomalies are also reproduced realistically. Despite the slightly stronger variance of SST anomalies over the central Pacific than observed in the HCM, the patterns of atmospheric anomalies related to ENSO,such as sea level pressure, temperature and precipitation, are in broad agreement with observations. Therefore, this model can not only simulate the ENSO variability, but also reproduce the global atmospheric variability associated with ENSO, thereby providing a useful modeling tool for ENSO studies. Further model applications of ENSO modulations by ocean–atmosphere processes, and of ENSO-related climate prediction, are also discussed.     

The impact of combined ENSO and PDO on the PNA climate: a 1,000-year climate modeling study

This study analyzes the atmospheric response to the combined Pacific interannual ENSO and decadal–interdecadal PDO variability, with a focus on the Pacific-North American (PNA) sector, using a 1,000-year long integration of the Canadian Center for Climate Modelling and Analysis (CCCma) coupled climate model. Both the tropospheric circulation and the North American temperature suggest an enhanced PNA-like climate response and impacts on North America when ENSO and PDO variability are in phase. The anomalies of the centers of action for the PNA-like pattern are significantly different from zero and the anomaly pattern is field significant. In association with the stationary wave anomalies, large stationary wave activity fluxes appear in the mid-high latitudes originating from the North Pacific and flowing downstream toward North America. There are significant Rossby wave source anomalies in the extratropical North Pacific and in the subtropical North Pacific. In addition, the axis of the Pacific storm track shifts southward with the positive PNA. Atmospheric heating anomalies associated with ENSO variability are confined primarily to the tropics. There is an anomalous heating center over the northeast Pacific, together with anomalies with the same polarity in the tropical Pacific, for the PDO variability. The in-phase combination of ENSO and PDO would in turn provide anomalous atmospheric energy transports towards North America from both the Tropical Pacific and the North Pacific, which tends to favor the occurrence of stationary wave anomalies and would lead to a PNA-like wave anomaly structure. The modeling results also confirm our analysis based on the observational record in the twentieth century.     

Variability and trends of sub-continental scale surface climate in the twentieth century. Part I: observations

An analysis is presented of observed temperature and precipitation variability and trends throughout the twentieth century over 22 land regions of sub-continental scale. Summer, winter and annual data are examined using a range of variability measures. Statistically significant warming trends are found over the majority of regions. The trends have a magnitude of up to 2 K per century and are maximum over cold climate regions. Only a few precipitation trends are statistically significant. Regional temperature and precipitation show pronounced variability at scales from interannual to multidecadal, with maximum over cold climate regions. The interannual variability shows significant variations and trends throughout the century, the latter being mostly negative for precipitation and both positive and negative for temperature. Temperature and precipitation anomalies show a chaotic-type behavior in which the regional conditions oscillate around the long term mean trend and occasionally fall into long-lasting (up to 10 years or more) anomaly regimes. A generally modest temporal correlation is found between anomalies of different regions and between temperature and precipitation anomalies for the same region. This correlation is mostly positive for temperature in cases of adjacent regions or regions in the same latitude belts. Several cases of negative inter-regional precipitation anomaly correlation are found. The ENSO significantly affects the anomaly variability patterns over a number of regions, primarily in tropical areas, while the NAO significantly affects the variability over northern mid- and high-latitude regions of Europe and Asia.     

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)。     

ENSO and seasonal sea-level variability – A diagnostic discussion for the U.S.-Affiliated Pacific Islands

Summary The El Ni?o-Southern Oscillation (ENSO) climate cycle is the basis for this paper, aimed at providing a diagnostic outlook on seasonal sea-level variability (i.e. anomalies with respect to the Climatology) for the U.S.-Affiliated Pacific Islands (USAPI). Results revealed that the sea-level variations in the northwestern tropical Pacific islands (e.g. Guam and Marshall Islands) have been found to be sensitive to ENSO-cycle, with low sea-level during El Ni?o and high sea-level during La Ni?a events. The annual cycle (first harmonic) of sea-level variability in these north Pacific islands has also been found to be very strong. The composites of SST and circulation diagnostic show that strong El Ni?o years feature stronger surface westerly winds in the equatorial western/central Pacific, which causes north Pacific islands to experience lower sea-level from July to December, while the sea-level in south Pacific islands (e.g. American Samoa) remains unchanged. As the season advances, the band of westerly winds propagates towards the south central tropical Pacific and moves eastward, which causes American Samoa to experience a lower sea-level from January to June, but with six months time lag as compared to Guam and the Marshalls. U.S.-Affiliated Pacific Islands are among the most vulnerable communities to climate variability and change. This study has identified the year-to-year ENSO climate cycle to have significant impact on the sea-level variability of these islands. Therefore, regular monitoring of the ENSO climate cycle features that affect seasonal sea-level variability would provide substantial opportunities to develop advance planning and decision options regarding hazard management in these islands.     

ENSO循环对福建省近地层臭氧浓度变化的影响

ENSO(El Ni?o-Southern Oscillation)循环被认为是年际气候变化的最强信号,是由东亚季风异常造成的赤道西太平洋异常纬向风驱动的热带太平洋次表海温距平的循环.利用NOAA提供的ONI(Oceanic Ni?o Index)指数资料与福建省近地层质量臭氧浓度(ρ(O3))资料,经数理统计、标准化...     

Impacts of large-scale teleconnections on climate variability over Southwest Asia

The atmospheric low frequency variability at a regional or global scale is represented by teleconnection. Using monthly dataset of the Climatic Research Unit (CRU) for the period 1971–2016, the impacts of four large-scale teleconnection patterns on the climate variability over Southwest Asia are investigated. The large-scale features include the El Niño-Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO) and the East Atlantic (EA) teleconnection patterns, as well as western tropical Indian Ocean (WTIO) sea surface temperature anomaly index. Results indicate that ENSO and EA are the first leading modes that explain variation of Southwest Asian precipitation, with positive (negative) anomalies during El Niño (La Niña) and the negative (positive) phase of EA. Variation of Southwest Asian near-surface temperature is most strongly related to WTIO index, with above-average (below-average) temperature during the positive (negative) phase of WTIO index, although the negative (positive) phase of NAO also favours the above-average (below-average) temperature. On the other hand, temperature (precipitation) over Southwest Asia shows the least response to ENSO (WTIO). ENSO and EA individually explain 13 percent annual variance of precipitation, while WTIO index explains 36 percent annual variance of near-surface temperature over Southwest Asia. Analysis of the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis Interim (ERA-Interim) data indicated establishments of negative (positive) geopotential height anomalies in the middle troposphere over Southwest Asia during El Niño (La Niña) or the negative (positive) phase of NAO, EA and WTIO. The response of precipitation variability over Southwest Asia to NAO is opposite to that expected from the geopotential height anomalies, but the correlation between precipitation and NAO is not statistically significant. Due to predictability of large-scale teleconnections, results of this study are encouraging for improvement of the state-of-the-art seasonal prediction of the climate over Southwest Asia.     

The influence of systematic errors in the Southeast Pacific on ENSO variability and prediction in a coupled GCM

The impact of the warm SST bias in the Southeast Pacific (SEP) on the quality of seasonal and interannual variability and ENSO prediction in a coupled GCM is investigated. The reduction of this bias is achieved by means of empirical heat flux correction that is constant in time. It leads to a wide range of changes in the tropical Pacific climate including enhanced southeast trades, well-defined dry zone in the SEP, better simulation of the South Pacific Convergence Zone and stronger cross-equatorial asymmetry of the mean state in the eastern Pacific. As a result of the mean climate correction, significant improvements in the simulation of the seasonal cycle of the oceanic and atmospheric states are also observed both at the equator and basin-wide. Due to more realistic simulation of the seasonal evolution of the cold tongue, tropical convection and surface winds in the corrected version of the model, phase-lock of ENSO to the annual cycle looses its strong semi-annual component and becomes quite similar to the observed, although the amplitude of ENSO is reduced. Zonal wind stress response to the SST anomalies in the central-eastern Pacific also becomes more realistic. ENSO retrospective forecast experiments conducted with the directly coupled and the flux-corrected versions of the model demonstrate that deficiencies in the seasonal evolution of the cold tongue/Inter-Tropical Convergence Zone complex (that were largely due to the SEP bias in this model) and the related errors in the ENSO phase-lock to the annual cycle can seriously degrade ENSO prediction. By reducing these errors, ENSO predictive skill in the coupled model was substantially enhanced.     

ENSO循环的数值模拟(Ⅱ)──变化性及时间尺度选择机制

利用热带太平洋海气耦合异常模式的３０ａ模拟结果，对模式ＥＮＳＯ的变化性及多重时间尺度过程进行了细致分析，建立了一ＥＮＳＯ循环多重时间尺度过程相互作用的非线性相似（Ａｎａｌｏｇ）模型，并提出了ＥＮＳＯ循环主周期形成的一种可能机制。指出：和观测事实类似，模式ＥＮＳＯ过程确实涉及到三种时间尺度，即３—４ａ主周期振荡（ＬＦ）、准两年振荡（ＱＢ）和年循环（ＡＣ）；其中，ＱＢ过程是线性海气耦合系统的本征模态，年循环（ＡＣ）对其形成没有本质的影响；３—４ａ主周期振荡（ＬＦ）是一非线性系统的自激振荡现象，其形成是线性系统的本征模即ＱＢ过程通过非线性机制尤其是通过大气辐合反馈加热的“单向性”过程在ＱＢ的暖态产生的减频增幅所致；平均年循环（ＡＣ）虽然不能对ＥＮＳＯ循环形成有本质影响，但它可明显影响ＥＮＳＯ循环的具体振幅和位相，使得ＥＮＳＯ循环具有明显的不规则性并对季节循环具有明显的“锁相”特征；ＥＮＳＯ变化性确是ＬＦ、ＱＢ以及ＡＣ多重时间尺度相互作用形成的。本文提出的ＥＮＳＯ循环时间尺度选择机制不仅解释了主周期振荡的形成过程，而且也较好地解释了ＥＮＳＯ变化的谱，因此，这一机制更接近于观测事实。     

Interannual variability of summer monsoon precipitation over the Indochina Peninsula in association with ENSO

The interannual variability of summer monsoon precipitation (1979–2011) over the Indochina Peninsula (ICP) is characterized using the first empirical orthogonal function of 5-month total precipitation (May to September). The leading mode, with a monopole pattern, accounts for 30.6 % of the total variance. Dynamic composites and linear regression analysis indicate that the rainy season precipitation over the ICP is linked to El Niño–Southern Oscillation (ENSO) on interannual scales. The preceding winter [D(?1)JF(0)] negative sea surface temperature (SST) over the Niño-3.4 region is predominantly correlated with the rainy season precipitation over the ICP. Notably, the simultaneous correlation between remote SST anomalies in the Niño-3.4 region and the rainy season precipitation over the ICP is weak. The interannual variation of tropical cyclones modulated by ENSO is a significant contributing factor to the rainy season precipitation over the ICP. However, this relationship is not homogeneous over the ICP if ENSO is considered. Before removing the ENSO signal, enhanced precipitation is present over the northeastern part of the ICP and reduced precipitation appears in the western ICP, especially in coastal areas. In contrast, after removing ENSO, only a minor significant positive precipitation anomaly occurs over the northeastern part of the ICP and the negative anomaly appears particularly in the western and eastern coastal regions. The results obtained through the present study are useful for our understanding of circulation mechanisms and provide information for assessing the ability of regional and global climate models in simulating the climate of Southeast Asia.     

海-气耦合系统的非线性不稳定行为与年际气候变率

文中从理论上论述了气候系统的基本态—季节循环的非线性不稳定特征 ,研究了年际气候变率特别是ENSO与季节循环间非线性相互作用 ,并通过Oxford海 气耦合模式数值实验具体展示了上述理论分析。理论与数值实验表明 ,海 气耦合系统可经过年周期态失稳→新周期产生→与季节循环锁相→混沌这一系列分岔过程产生类似ENSO的无规则运动。这一规律为正确认识ENSO的动力机制及客观确定简化海 气耦合模式中的参数提供了理论依据     

ENSO variability and atmospheric response in a global coupled atmosphere-ocean GCM

The interannual variability associated with the El Ni?o/Southern Oscillation (ENSO) cycle is investigated using a relatively high-resolution (T42) coupled general circulation model (CGCM) of the atmosphere and ocean. Although the flux correction is restricted to annual means of heat and freshwater, the annual as well as the seasonal climate of the CGCM is in good agreement with that of the atmospheric model component forced with observed sea surface temperatures (SSTs). During a 100-year simulation of the present-day climate, the model is able to capture many features of the observed interannual SST variability in the tropical Pacific. This includes amplitude, lifetime and frequency of occurrence of El Ni?o events and also the phase locking of the SST anomalies to the annual cycle. Although the SST warming during the evolution of El Ni?os is too confined spatially, and the warming along the Peruvian coast is much too weak, the patterns and magnitudes of key atmospheric anomalies such as westerly wind stress and precipitation, and also their eastward migration from the western to the central equatorial Pacific is in accord with observations. There is also a qualitative agreement with the results obtained from the atmospheric model forced with observed SSTs from 1979 through 1994. The large-scale dynamic response during the mature phase of ENSO (December through February) is characterized by an eastward displacement and weakening of the Walker cell in the Pacific while the Hadley cell intensifies and moves equatorward. Similar to the observations, there is a positive correlation between tropical Pacific SST and the winter circulation in the North Pacific. The deepening of the Aleutian low during the ENSO winters is well captured by the model as well as the cooling in the central North Pacific and the warming over Canada and Alaska. However, there are indications that the anomalies of both SST and atmospheric circulation are overemphasized in the North Pacific. Finally, there is evidence of a coherent downstream effect over the North Atlantic as indicated by negative correlations between the PNA index and the NAO index, for example. The weakening of the westerlies across the North Atlantic in ENSO winters which is related to a weakening and southwestward displacement of the Icelandic low, is in broad agreement with the observations, as well as the weak tendency for colder than normal winters in Europe. Received: 31 October 1995 / Accepted: 29 May 1996     

利用混合海气耦合模式的气候异常预报试验

用混合海气耦合模式长期积分的模拟结果, 分析了模式大气的年际变化性; 用1979~1994年间的“回报”个例, 探讨了该模式对ENSO引起的全球气候异常的预报。结果表明:模式能较好地再现与ENSO相关的全球大气环流的年际变化特征; 对预报而言, 模式较高的预报技巧主要分布在热带地区, 全球热带大气具有较稳定的1年左右的可预报时效; 基本上可预报中、高纬地区由ENSO引起的冬、夏季大气环流异常 (包括气温和降水), 超前时间可达9个月至1年。     

近期气候预测系统IAP-DecPreS对印度洋偶极子的回报技巧:全场同化和异常场同化的比较

印度洋偶极子（IOD）是热带印度洋年际变率主导模态之一,对于区域乃至全球气候有重要影响。准确预报IOD对于短期气候预测具有重要意义。中国科学院大气物理研究所最近建立了近期气候预测系统IAP-DecPreS,其初始化方案采用“集合最优插值—分析增量更新”（EnOI-IAU）方案,能够同化观测的海洋次表层温度廓线资料。本文分析了IAP-DecPreS季节回报试验对IOD的回报技巧,重点比较了全场同化和异常场同化两种初始化策略下预测系统对IOD的回报技巧。分析表明,8月起报秋季IOD,无论从确定性预报还是概率性预报的角度,基于全场同化的回报试验技巧均高于异常场同化的回报试验。对于5月起报的秋季IOD,基于两种初始化策略的回报试验技巧相当。研究发现,全场同化策略相对于异常场的优势主要源于它提高了对伴随ENSO发生的IOD的预报技巧。ENSO遥强迫触发的热带东印度洋“风—蒸发—SST”正反馈过程是IOD发展和维持的关键。采用全场同化策略的回报结果能够更好地模拟出IOD发展过程中ENSO遥强迫产生的异常降水场和异常风场的空间分布特征;而采用异常场同化策略,模拟的异常降水场和风场偏差较大。导致两种初始化策略预测结果技巧差异的主要原因是,全场同化能够减小模式对热带印度洋气候平均态降水固有的模拟偏差,从而提升了热带印度洋对ENSO遥强迫响应的模拟能力。而异常场同化由于在同化过程中保持了模式固有的气候平均态,因此模拟的热带印度洋对ENSO遥强迫的响应存在与模式自由积分类似的模拟偏差。     

ENSO及其组合模态对中国东部各季节降水的影响

近期的研究发现,热带太平洋低层大气存在两种主要模态,即经向对称ENSO模态和ENSO与海表温度(SST)年循环相互作用产生的经向反对称组合模态。主要探讨了这两种不同ENSO模态对中国东部各季节降水的影响。结果表明,厄尔尼诺年秋季,中国西南、长江及华南大部分区域呈现显著正降水异常;冬季,正降水异常范围扩大,覆盖华南、华东及华北东南部地区。这两个季节的异常降水都主要受ENSO模态的影响。与ENSO模态相关的正异常海温局地强迫导致120°E以西出现反气旋性环流,其西北侧增强的西南暖湿气流使得中国东部地区降水增多。次年春季,从中国华南延伸到东北出现正的异常降水,主要是ENSO组合模态的贡献。因为次年春季热带太平洋地区ENSO模态信号只局限于赤道地区,并没有对中国东部降水有显著的影响,而ENSO与海温年循环相互作用的组合模态使得与ENSO相关的赤道大气异常可以扩展到赤道以外地区。ENSO组合模态对中国降水异常有重要影响,在今后的研究和短期预测中需引起重视。      

A global analysis of austral summer ocean wave variability during SAM–ENSO phase combinations

Anticipating and mitigating wave-related hazards rely heavily on understanding wave variability drivers. Here, we describe wave conditions related to concurrent Southern Annular Mode (SAM) and El Niño–Southern Oscillation (ENSO) phases during the austral summer. To identify such conditions, significant wave height (Hs) and peak wave period (Tp) daily anomalies were composited during different SAM–ENSO phase combinations over the last four decades (1979–2018). Surface wind anomalies were also composited to assist in the interpretation of wave conditions. The composites show significant wave variability across all ocean basins and in several semi-enclosed seas throughout the different SAM–ENSO phase combinations. The Southern, Indian, and Pacific Oceans generally experience the strongest Tp anomalies during combinations of SAM phases with El Niño, and the weakest Tp anomalies during combinations of SAM phases with La Niña. The anomalously large waves observed in the south-western Pacific, Tasman Sea, and the Southern Ocean, previously ascribed to ENSO conditions, seem to be instead associated with the SAM variability. SAM-related atmospheric conditions are found to be able to modulate the intensity of ENSO-related winds over the South China Sea, which, in turn, alter the magnitude of waves in that region. These and other wave anomaly structures described here, especially those contrasting the behaviour expected for a given ENSO phase, such as the one found along the California coast, stress the importance of understanding relationships between wave parameters and climate patterns interactions.     

THE INFLUENCE OF PERSISTENT ANOMALY OF MJO ON ENSO

In this study, two possible persistent anomalies of the Madden-Julian Oscillation mode (MJO) are found in the summer season (persistently Pacific active and Indian Ocean active), and an index is set to define the intensity of the two modes. They are proved to have high statistical correlations to the later ENSO events in the autumn and winter seasons: When persistent anomaly of MJO happens in the Pacific Ocean in summer, El Ni?o events are often induced during the autumn and winter seasons of that year. However, during the other MJO mode when the summer persistent anomaly of MJO occurs in the Indian Ocean, La Ni?a events often follow instead. The analysis of the atmospheric circulation field indicates that persistent anomaly of MJO can probably affect the entire Equatorial Pacific circulation, and results in wind stress anomalies. The wind stress anomalies could excite warm or cold water masses which propagate eastwards at the subsurface ocean. The accumulation of warm or cold subsurface water in the Equatorial Eastern Pacific Ocean may eventually lead to the formation of an ENSO.