On the 60-month cycle of multivariate ENSO index

Many point indices have been developed to describe El Niño/Southern Oscillation, but the multivariate El Niño Southern Oscillation (ENSO) index (MEI) is considered the most representative since it links six different meteorological parameters measured over the tropical Pacific. Spectral analysis with appropriate data reduction techniques of monthly values of MEI (1950–2008) has allowed the identification of a large 60-month cycle, statistically confident at a level larger than 99%. The highest values of MEI (typical of El Niño events) and the lowest values of MEI (typical of La Niña events) are concordant with respective maxima and minima values of the identified 60-month cycle.     

Global warming,low-frequency variability,and biennial oscillation: an attempt to understand the physical mechanisms driving major ENSO events

Three primary global modes of sea surface temperature (SST) variability during the period of 1871–2010 are identified through cyclostationary empirical orthogonal function analysis. The first mode exhibits a clear trend and represents global SST warming with an ‘El Niño-like’ SST pattern in the tropical Pacific. The second mode is characterized by considerable low-frequency variability in both the tropical Pacific and the North Pacific regions, indicating that there is a close connection between the two regions on interannual and decadal time scales. The third mode shows a seesaw pattern between El Niño and La Niña within a two-year period; this mode is derived by the oscillatory tendency of the tropical Pacific ocean–atmosphere coupled system. A SST reconstruction based on these three modes captures a significant portion of the SST variability in the raw data, which is primarily associated with El Niño-Southern Oscillation (ENSO) events in the tropical Pacific. Additionally, this study attempts to interpret the major ENSO events that have occurred since the 1970s in terms of the interplay originating from these three modes of variability. In particular, two key points are derived from this analysis: (1) the most extreme El Niño events occurred in 1982/1983 and 1997/1998 are attributed to the positive contributions of all three modes; and (2) the central Pacific (CP) El Niño events in the 1990s and 2000s have different physical mechanisms, that is, the CP El Niño events in the early 1990s originated mainly from the low-frequency mode, while those in the early 2000s derived mainly from the global warming mode.     

What happened to surface temperature with sunspot activity in the past 130 years?

Based on composite analysis using categories of solar inactivity and activity, the responses of surface temperature to different categorized solar activity and a plausible mechanism have been discussed. The results show the increasing solar sunspot activity during solar cycles 13 to 24 (1880–2010) and it seemed to make a positive contribution to rising global temperature. However, the sunspots were fewer in number, if we focused on the most recent 60 years (1950–2010), and the decreasing solar activity did not contribute to a cooler Earth. This result indicates that the connection between sunspots and the Earth’s climate is sensitive to the study period. An extreme analysis was performed in an attempt to gain a better understanding of solar impacts. The extreme top 10 composite analysis demonstrated that the surface temperature response to solar activity is spatially different and is highly sensitive to El Niño–Southern Oscillation (ENSO) events. The most sensitive areas in the Pacific sector revealed a significant difference between including and excluding ENSO years. During the solar inactive years, the tropical eastern Pacific was observed as a weak El Niño-like (strong La Niña-like) pattern in the composite including (excluding) ENSO events. Another interesting feature is the strong similarity in the composites which include or exclude ENSO events during the sunspot active years, but it differs from the La Niña-like pattern observed in previous studies. The bottom-up mechanism associated with the response of the surface dynamical circulation and the heat balance when compared to the total solar irradiance forcing partially explains the connection.     

Modulation of El Nino-Southern Oscillation by Freshwater Flux and Salinity Variability in the Tropical Pacific

The El Nin o-Southern Oscillation (ENSO) is modulated by many factors; most previous studies have emphasized the roles of wind stress and heat flux in the tropical Pacific. Freshwater flux (FWF) is another environmental forcing to the ocean; its effect and the related ocean salinity variability in the ENSO region have been of increased interest recently. Currently, accurate quantifications of the FWF roles in the climate remain challenging; the related observations and coupled ocean-atmosphere modeling involve large elements of uncertainty. In this study, we utilized satellite-based data to represent FWF-induced feedback in the tropical Pacific climate system; we then incorporated these data into a hybrid coupled ocean-atmosphere model (HCM) to quantify its effects on ENSO. A new mechanism was revealed by which interannual FWF forcing modulates ENSO in a significant way. As a direct forcing, FWF exerts a significant influence on the ocean through sea surface salinity (SSS) and buoyancy flux (Q B ) in the western-central tropical Pacific. The SSS perturbations directly induced by ENSO-related interannual FWF variability affect the stability and mixing in the upper ocean. At the same time, the ENSO-induced FWF has a compensating effect on heat flux, acting to reduce interannual Q B variability during ENSO cycles. These FWF-induced processes in the ocean tend to modulate the vertical mixing and entrainment in the upper ocean, enhancing cooling during La Nin a and enhancing warming during El Nin o, respectively. The interannual FWF forcing-induced positive feedback acts to enhance ENSO amplitude and lengthen its time scales in the tropical Pacific coupled climate system.     

Changes in mixed layer depth under climate change projections in two CGCMs

Two coupled general circulation models, i.e., the Meteorological Research Institute (MRI) and Geophysical Fluid Dynamics Laboratory (GFDL) models, were chosen to examine changes in mixed layer depth (MLD) in the equatorial tropical Pacific and its relationship with ENSO under climate change projections. The control experiment used pre-industrial greenhouse gas concentrations whereas the 2 × CO₂ experiment used doubled CO₂ levels. In the control experiment, the MLD simulated in the MRI model was shallower than that in the GFDL model. This resulted in the tropical Pacific’s mean sea surface temperature (SST) increasing at different rates under global warming in the two models. The deeper the mean MLD simulated in the control simulation, the lesser the warming rate of the mean SST simulated in the 2 × CO₂ experiment. This demonstrates that the MLD is a key parameter for regulating the response of tropical mean SST to global warming. In particular, in the MRI model, increased stratification associated with global warming amplified wind-driven advection within the mixed layer, leading to greater ENSO variability. On the other hand, in the GFDL model, wind-driven currents were weak, which resulted in mixed-layer dynamics being less sensitive to global warming. The relationship between MLD and ENSO was also examined. Results indicated that the non-linearity between the MLD and ENSO is enhanced from the control run to the 2 × CO₂ run in the MRI model, in contrast, the linear relationship between the MLD index and ENSO is unchanged despite an increase in CO₂ concentrations in the GFDL model.     

一个新的ENSO监测指标的研究

利用1982～1996年逐月平均SST和OLR资料,首先通过奇异值分解（SVD）技术研究了热带太平洋大气对流活动和海温场的时间和空间结构及其相互关系。结果表明,第一模态都明显地反映出ENSO信息,两场间具有很高的相关。分析了80年代以来的E1 Ni?o/La Ni?a盛期的热带太平洋对流活动场以及NINO 3指数与OLR场的点相关,结果指出,中东太平洋和西太平洋上存在类似偶极子型的两个符号相反的相关区,与SVD第一模态空间分布型十分相似。由此建立了反映ENSO期间热带中东太平洋和西太平洋反向变化的对流涛动     

Interdecadal modulation of Australian rainfall

Interdecadal variability is investigated in a 300 year run of the Parallel Climate Model, a global coupled atmosphere-land-ocean-sea ice model. The model simulates El Niño variability of realistic magnitude and is found to produce interdecadal characteristics similar to those observed, both in frequency, spatial patterns and amplitude. Modulation of Australian rainfall on interdecadal time scales is similar to observed and is found to have contributions from both the modulation of ENSO, changes in the position of the Walker circulation and variations in western Pacific SSTs. A slackening of the equatorial Pacific thermocline slope is associated with diminished ENSO variability during interdecadal periods of positive tropical Pacific SSTs. These interdecadal changes to ENSO and shifts in the position of the Walker circulation are physical mechanisms that contribute to the weakened correlations between the SOI and Australian climate during interdecadal periods of positive tropical Pacific SSTs. Warm anomalies in the western Pacific also contribute to a decrease in Australian rainfall in the model on interdecadal time scales.     

印度洋偶极子与热带太平洋海洋表面温度异常多时间尺度相互作用初析

本文利用交叉谱方法, 将印度洋偶极子 (简称IOD) 与ENSO的相关关系分解到不同的时间尺度上来分析, 进而通过对海气耦合过程的初步分析, 讨论了不同时间尺度上IOD与ENSO的相互作用。结果表明, IOD与ENSO在准1～2年、 准3年、 准4年等三个时间尺度上存在显著相关, 同时, IOD还存在一个独立于ENSO的模态, 主要表现在准8个月时间尺度上。从海气相互作用的角度看, 在与ENSO相关的三个特征时间尺度上, IOD年际变率主要通过引发热带印度洋纬向风异常并且东传到太平洋, 从而引起热带中东太平洋海温的年际变率。与ENSO相对独立的IOD模态则没有类似的纬向风异常东传过程。此外, 在上述四个不同时间尺度上, 产生IOD变率的印度洋海气耦合过程不尽相同, 各具特点。     

Interannual and interdecadal variabilities in the Pacific in an MRI coupled GCM

Interannual and interdecadal variabilities in the Pacific are investigated with a coupled atmosphere-ocean GCM developed at MRI, Japan. The model is run for 70 years with flux adjustments. The model shows interannual variability in the tropical Pacific which has several typical characteristics shared with the observed ENSO. A basin-scale feature of the principal SST variation for the ENSO time scale shows negative correlation in the central North Pacific with the tropical SST, similar to that of the observed one. Associated variation of the model atmosphere indicates an intensification of the Aleutian Low and a PNA-like teleconnection pattern as a response to the tropical warm SST anomaly. The ENSO time scale variability in the midlatitude ocean consists of the westward propagation of the subsurface temperature signal and the temperature variation within the shallow mixed layer forced by the anomalous atmospheric heat fluxes. For the interdecadal time scale, variation of the SST is simulated realistically with a geographical pattern similar to that for the ENSO time scale, but it has a larger relative amplitude in the northern Pacific. For the atmosphere, spatial structure of the variation in the interdecadal time scale is also similar to that in the ENSO time scale, but has smaller amplitude in the northern Pacific. Long oceanic spin-up time (>∼10 y) in the mid-high latitude, however, makes oceanic response in the interdecadal time scale larger than that in the ENSO time scale. The lagged-regression analysis for the ocean temperature variation relative to the wind stress variation indicates that interdecadal variation of the ocean subsurface at the mid-high latitudes is considered as enhanced ocean gyre spin-up process in response to the atmospheric circulation change at the mid-high latitudes, remotely forced by the interdecadal variation of the tropical SST. Received: 6 November 1995 / Accepted: 19 April 1996     

高低层纬向风切变的年际变率及气候学意义

用1959～1998共40年全球格点风场资料计算了200 hPa与850 hPa的纬向风速差, 即对流层纬向风切变(简称TZWS),并在此基础上得到其距平值。为了全面考察对流层中环流异常的年际变率特征, 根据TZWS的标准差分布, 文中选出了7个TZWS标准差数值大于5 m/s的代表性区域。这7个区域分别位于赤道中太平洋、赤道东太平洋、北太平洋亚热带地区、南太平洋亚热带地区、赤道大西洋、亚洲西南部以及东北部。前5个分别位于赤道、亚热带太平洋和大西洋的区域TZWS指数, 其年际变率与ENSO循环有密切联系, 反映了热带海洋温度异常对低纬度地区对流层环流的影响; 后2个区域的TZWS指数反映的是亚洲西南部和东北部的气候统变率, 在年际时间尺度上与ENSO循环有着明显的区别。通过对全球陆地降水和温度场的分析, 比较了热带、副热带的TZWS指数以及北极涛动指数的异同, 发现后2个区域TZWS指数能很好且能独立反映出北半球中高纬度地区陆地降水及陆地温度的异常模态。     

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8～20a的年代际尺度，三是20a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20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ElNio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。     

ENVIRONMENTAL INFLUENCES ON NORTHWEST PACIFIC TROPICAL CYCLONE NUMBERS

In this study,the relationship between tropical cyclone numbers in the Northwest Pacific,Southern Oscillation (SO) and some environmental variables observed over the global oceans has been examined.The major results indicate that the pattern of correlations between the tropical cyclone numbers and the environmental variables is in a sense analogous to that between the SO and the same environmental variables,but the correlation is weak.The study indicates that the relationship between tropical cyclone numbers and environmental variables is more complex,and the factors affecting the variation in tropical cyclone numbers in the Northwest Pacific should include not only ENSO events but also a long-term effect which is not related to ENSO.     

Role of the upper ocean structure in the response of ENSO-like SST variability to global warming

The response of El Niño and Southern Oscillation (ENSO)-like variability to global warming varies comparatively between the two different climate system models, i.e., the Meteorological Research Institute (MRI) and Geophysical Fluid Dynamics Laboratory (GFDL) Coupled General Circulation Models (CGCMs). Here, we examine the role of the simulated upper ocean temperature structure in the different sensitivities of the simulated ENSO variability in the models based on the different level of CO₂ concentrations. In the MRI model, the sea surface temperature (SST) undergoes a rather drastic modification, namely a tendency toward a permanent El Niño-like state. This is associated with an enhanced stratification which results in greater ENSO amplitude for the MRI model. On the other hand, the ENSO simulated by GFDL model is hardly modified although the mean temperature in the near surface layer increases. In order to understand the associated mechanisms we carry out a vertical mode decomposition of the mean equatorial stratification and a simplified heat balance analysis using an intermediate tropical Pacific model tuned from the CGCM outputs. It is found that in the MRI model the increased stratification is associated with an enhancement of the zonal advective feedback and the non-linear advection. In the GFDL model, on the other hand, the thermocline variability and associated anomalous vertical advection are reduced in the eastern equatorial Pacific under global warming, which erodes the thermocline feedback and explains why the ENSO amplitude is reduced in a warmer climate in this model. It is suggested that change in stratification associated with global warming impacts the equatorial wave dynamics in a way that enhances the second baroclinic mode over the gravest one, which leads to the change in feedback processes in the CGCMs. Our results illustrate that the upper ocean vertical structure simulated in the CGCMs is a key parameter of the sensitivity of ENSO-like SST variability to global warming.     

A comparison of regional monsoon variability using monsoon indices

The present study aims to (a) examine meteorological basis for construction of regional monsoon indices and (b) explore the commonality and differences among tropical regional monsoons, especially the teleconnection and monsoon–ENSO relationship. We show that the area-averaged summer precipitation intensity is generally a meaningful precipitation index for tropical monsoons because it represents very well both the amplitude of annual cycle and the leading mode of year-to-year rainfall variability with a nearly uniform spatial pattern. The regional monsoon circulation indices can be defined in a unified way (measuring monsoon trough vorticity) for seven tropical monsoon regions, viz.: Indian, Australian, western North Pacific, North and South American, and Northern and Southern African monsoons. The structures of the tropical monsoons are commonly characterized by a pair of upper-level double anticyclones residing in the subtropics of both hemispheres; notably the winter hemispheric anticyclone has a barotropic structure and is a passive response. Two types of upper-level teleconnection patterns are identified. One is a zonal wave train emanating from the double anticyclones downstream along the westerly jets in both hemispheres, including Indian, Northern African and Australian monsoons; the other is a meridional wave train emanating from the double anticyclones polewards, such as the South American and western North Pacific monsoons. Over the past 55 years all regional summer monsoons have non-stationary relationship with ENSO except the Australian monsoon. The regional monsoon–ENSO relationship is found to have common changing points in 1970s. The relationships were enhanced for the western North Pacific, Northern African, North American and South American summer monsoons, but weakened for the Indian summer monsoon (with a recovery in late 1990s). Regardless the large regional differences, the monsoon precipitations over land areas of all tropical monsoon regions are significantly correlated with the ENSO, suggesting that ENSO drives global tropical monsoon rainfall variability. These results provide useful guidance for monitoring sub-seasonal to seasonal variations of the regional monsoons currently done at NCEP and for assessment of the climate models’ performances in representing regional and global monsoon variability.     

全球增暖对ENSO影响的数值模拟研究

利用日本东京大学气候系统研究所、日本环境研究所和日本地球环境研究中心联合开发的海气耦合模式MIROC3.2，研究了全球变暖对ENSO年际变率的影响。该模式较好地模拟了ENSO循环的不同阶段表层和次表层海水温度变化，海表温度最大振幅出现在120°W以东，与观测一致，表明模式可以较好反映热带地区大气、海洋的动力、热力特征。研究还比较了控制试验和CO2浓度年增长1%的瞬时试验，结果表明，在全球变暖的大环境下ENSO事件发生频率没有显著变化，但ENSO事件强度增大，年际变率变大；热带太平洋呈现整体增暖趋势，表层温度尤其是热带中太平洋地区温度升高显著。敏感性分析表明，年际ENSO变率的振幅增大的主要贡献来自于海洋。海水增温导致热带太平洋海温垂直梯度增大，在热带西太平洋海温垂直温度梯度变化最为明显；次表层海温对单位大气风应力变化的响应大于表层海温响应。当这种响应与热带太平洋赤道地区径向温度梯度变化的共同作用导致温室效应下ENSO振幅增大。     

Global and regional variability in a coupled AOGCM

 The variability of near surface temperature on global and regional spatial scales and interannual time scales from a 1000 year control integration of the Hadley Centre coupled model (HADCM2-CTL) are compared with the observational record of surface temperature. The model succeeds in reproducing the observed patterns of natural variability, with high variability over the northern continents and low variability over much of the tropics. The model global mean variability has similar strength to observed global mean variability on time scales less than 20 years. The warming seen in the historical record is outside the range of natural variability as simulated in HADCM2-CTL. The model has El-Ni?o/Southern Oscillation (ENSO)-like behaviour with a central Pacific, peak to peak, strength of approximately 3 K. Changes in near surface temperature in the central Pacific are strongly correlated with changes in near surface temperature over most of the tropics, large regions of the extra-tropics and changes in tropical ocean upper 250 m heat content. Tropospheric temperature changes and tropical surface pressure changes are also strongly correlated with changes in the central Pacific surface temperature. Oceanic regions show significant departures from an AR1 or first order Markov behaviour in the Northwest Atlantic, Northwest Pacific and Arctic oceans. The Northwest Atlantic region has large amounts of variability over periods greater than 50 years. This variability is associated with a jump in the strength of North Atlantic meridional stream function. The spectra of the Western European and Continental US land regions are not significantly different from an AR1 process. The flow through the Drake Passage has an interannual standard deviation of approximately 2.5 Sv with significant departures from an AR1 process at time scales greater than 40 years. Winter northern hemispheric 500 hPa geopotential height shows some evidence of multiple regimes but no year to year persistence of these regimes. Received: 31 January 1996/Accepted: 22 July 1996     

Interannual and interdecadal variability of ocean temperature along the equatorial Pacific in conjunction with ENSO

In this paper, the leading modes of ocean temperature anomalies (OTA) along the equatorial Pacific Ocean are analyzed and their connection with El Niño-Southern Oscillation (ENSO) and interdecadal variation is investigated. The first two leading modes of OTA are connected with the different phases of the canonical ENSO and display asymmetric features of ENSO evolution. The third leading mode depicts a tripole pattern with opposite variation of OTA above the thermocline in the central Pacific to that along the thermocline in the eastern and western Pacific. This mode is found to be associated with so-called ENSO-Modoki. Insignificant correlations of this mode with the first two leading modes suggest that ENSO-Modoki may be a mode that is independent to the canonical ENSO and also has longer time scales compared with the canonical ENSO. The fourth mode reflects a warming (cooling) tendency above (below) the thermocline since 2000. Both the first and second modes have a large contribution to the interdecadal change in thermocline during 1979–2012. Also, the analysis also documents that both ENSO and OTA shifted into higher frequency since 2000 compared with that during 1979–1999. Interestingly, the ENSO-Modoki related OTA mode does not have any trend or significant interdecadal shift during 1979–2012. In addition, it is shown that first four EOF modes seem robust before and after 1999/2000, suggesting that the interdecadal shift of the climate system in the tropical Pacific is mainly a frequency shift and the changes in spatial pattern are relatively small, although the mean states over two periods experienced some significant changes.     

海洋对ENSO和其他时间尺度上风应力振荡的响应

利用带通滤波方法，将FSU风应力资料分离成ENSO时间尺度上的分量及其剩余部分，将这两部分分别作用于模式海洋（2层热带太平洋区域模式），研究海洋对不同时间尺度大气变化的响应。结果表明：尺管ENSO时间尺度上的风应力分量只占风应力扰动总方差的30％左右，它却能激发出全部异常风应力强迫海洋时所产生的El Nino/La Nina现象和十分相近的SSTA变化周期与振幅。而其余占总异常风应力方差60％以上的部分强迫海洋仅能产生振幅较小的海表温度异常，在非ENSO和ENSO时间尺度上的风应力强迫下，海洋中可产生相近振幅的Kelvin波，但SSTA振幅却存在显著差别，表明海洋对大气扰动信号的频率非常敏感，这里从理论上对该现象作了解释和说明。     

Predictable patterns and predictive skills of monsoon precipitation in Northern Hemisphere summer in NCEP CFSv2 reforecasts

The predictable patterns and predictive skills of monsoon precipitation in the Northern Hemisphere summer (June–July–August) are examined using reforecasts (1983–2010) from the National Center for Environmental Prediction Climate Forecast System version 2 (CFSv2). The possible connections of these predictable patterns with global sea surface temperature (SST) are investigated. The empirical orthogonal function analysis with maximized signal-to-noise ratio is used to isolate the predictable patterns of the precipitation for three regional monsoons: the Asian and Indo-Pacific monsoon (AIPM), the Africa monsoon (AFM), and the North America monsoon (NAM). Overall, the CFSv2 well predicts the monsoon precipitation patterns associated with El Niño-South Oscillation (ENSO) due to its good prediction skill for ENSO. For AIPM, two identified predictable patterns are an equatorial dipole pattern characterized by opposite variations between the equatorial western Pacific and eastern Indian Ocean, and a tropical western Pacific pattern characterized by opposite variations over the tropical northwestern Pacific and the Philippines and over the regions to its west, north, and southeast. For NAM, the predictable patterns are a tropical eastern Pacific pattern with opposite variations in the tropical eastern Pacific and in Mexico, the Guyana Plateau and the equatorial Atlantic, and a Central American pattern with opposite variations in the eastern Pacific and the North Atlantic and in the Amazon Plains. The CFSv2 can predict these patterns at least 5 months in advance. However, compared with the good skill in predicting AIPM and NAM precipitation patterns, the CFSv2 exhibits little predictive skill for AFM precipitation, probably because the variability of the tropical Atlantic SST plays a more important than ENSO in the AFM precipitation variation and the prediction skill is lower for the tropical Atlantic SST than the tropical Pacific SST.     

The extratropical sensitivity to the meridional extent of tropical ENSO forcing

The extratropical response to tropical remote forcing has been examined with so-called tropical ocean-global atmosphere experiments, which use prescribed sea surface temperature (SST) in the tropical Pacific and a slab mixed-layer ocean model elsewhere. In this study we have revisited this experimental design and found that the extratropical response is quite sensitive to the meridional extent of tropical prescribed SST domain. Even in the case of a prescribed annual cycle only (i.e., no ENSO), the differences in the prescribed SST regions lead to different atmospheric motions in the adjacent extratropics. When the tropical forcing includes ENSO, the sensitivity to the meridional domain is more prominent, especially during La Niña events. In La Niña, the prescribed SST is warmer than the simulated SST in the northern subtropics, and the warmer SST differences continue to 30°N. This broad SST differences accompany enhanced atmospheric meridional circulation that directly connects the tropics and extratropics within the Pacific basin. Moreover, the Rossby wave excitation also increases, so the effect of prescribed region difference is felt beyond the Pacific basin. On the other hand, the effect of ENSO sea surface temperature anomalie (i.e., ENSO experiment composite minus control experiment annual cycle, both of which have the same prescribed SST domain) is stronger in the broad tropical forcing experiment. However, the ENSO anomaly composite from own annual cycle is similar regardless of the meridional extent of forcing region, and commonly mimics the Northern Hemisphere El Niño composite of nature in the boreal winter season.