Tropical Pacific Decadal Oscillation in Subsurface Ocean Temperature

This study utilizes a new monthly-assimilated sea temperature and analyzes trend and decadal oscillations in tropical Pacific 100-200 m subsurface ocean temperature (SOT) from 1945 to 2005 on the basis of the harmonic analysis and Empirical Orthogonal Function (EOF) methods. Significant cooling trends in the SOT in the tropical western Pacific were found over this 60-year period. The first EOF of the SOT in tropical Pacific displays an ENSO-like zonal dipole pattern on decadal time scale, and we considered this pattern in subsurface ocean temperature the tropical Pacific decadal oscillation (TPDO). Our analysis suggests that TPDO is closely correlated with the Pacific decadal oscillation (PDO) in the surface sea temperature (SST). The correlation coefficient between the indices of TPDO and PDO is +0.81 and reaches a maximum of +0.84 when TPDO lags behind PDO by 2 months. Therefore, a change of TPDO is likely related to the variation of PDO. The long-term change in TPDO best explains decadal warming in the tropical eastern Pacific SST and implies potential impact on the weakening of East Asian summer monsoons after the late 1970s.     

Decadal Indian Ocean Dipolar Variability and Its Relationship with the Tropical Pacific

A robust decadal Indian Ocean dipolar variability(DIOD) is identified in observations and found to be related to tropical Pacific decadal variability(TPDV).A Pacific Ocean–global atmosphere(POGA) experiment,with fixed radiative forcing,is conducted to evaluate the DIOD variability and its relationship with the TPDV.In this experiment,the sea surface temperature anomalies are restored to observations over the tropical Pacific,but left as interactive with the atmosphere elsewhere.The TPDV-forced DIOD,represented as the ensemble mean of 10 simulations in POGA,accounts for one third of the total variance.The forced DIOD is triggered by anomalous Walker circulation in response to the TPDV and develops following Bjerknes feedback.Thermocline anomalies do not exhibit a propagating signal,indicating an absence of oceanic planetary wave adjustment in the subtropical Indian Ocean.The DIOD–TPDV correlation differs among the 10 simulations,with a low correlation corresponding to a strong internal DIOD independent of the TPDV.The variance of this internal DIOD depends on the background state in the Indian Ocean,modulated by the thermocline depth off Sumatra/Java.     

太平洋年代际振荡研究进展(英)

近10年来,太平洋年代际振荡(PDO)因其对全球气候系统的深远影响而得到广泛的研究。PDO指的足在太平洋的气候变率中具有类似ENSO空间结构但周期为10-30年的一种振荡,当北太平洋中部海面温度异常增暖(冷却)时,热带太平洋中部和东部以及北美沿岸常同时伴随有同等幅度的异常冷却(增暖)。总体而言,有两类观点分别认为PDO起源于确定的海气耦合过程或起源于大气的随机强迫。确定性起源论强调,一个海气耦合系统内部的物理过程可以提供一个正反馈机制以增强一初始扰动,及一个负反馈机制以促使振荡位相发生逆转;海洋环流的动力演变过程决定了振荡的时间尺度。随机性起源论则强调,因为大气活动没有一个特定的时间尺度,其时间尺度谱实际上对应于白噪音谱,所以大气对海洋的强迫是随机的;而海洋常在低频谱段有最大的响应振幅,其对应的周期约为十几年或几十年。作者试图系统性地理解PDO在观测、理论和数值方面的研究现状,从而为当前研究提供一个有用的背景性参考。     

太平洋年代际振荡研究进展

近10年来，太平洋年代际振荡(PDo)因其对全球气候系统的深远影响而得到广泛的研究。PDo指的是在太平洋的气候变率中具有类似ENSo空间结构但周期为10-30年的一种振荡，当北太平洋中部海面温度异常增暖(冲却)时，热带太平洋中部和东部以及北美沿岸常同时伴随有同等幅度的异常冷却(增暖)。总体而言，有两类观点分别认为PDO起源于确定的海气耦合过程或起源于大气的随机强迫。确定性起源论强调，一个海气耦合系统内部的物理过程可以提供一个正反馈机制以增强一初始扰动，及一个负反馈机制以促使振荡位相发生逆转；海洋环流的动力演变过程决定了振荡的时间尺度。随机性起源论则强调，因为大气活动没有一个特定的时间尺度，其时间尺度谱实际上对应于白噪音谱，所以大气对海洋的强迫是随机的；而海洋常在低频谱段有最大的响应振幅，其对应的周期约为十几年或几十年。作试图系统性地理解PDO在观测、理论和数值方面的研究现状，从而为当前研究提供一个有用的背景性参考。     

太平洋次表层海温年代际变率及其突变特征

利用经验正交函数展开和滑动t检验等方法研究了太平洋次表层海温的年代际变率特征。研究表明，太平洋次表层海温在19800年前后从上至下，先后经历了一次显著的年代际突变，而且随深度不同存在着四种不同的空间突变模态，这四种模态的形成与北太平洋海温异常的西南潜沉路径有着密切的联系。从北太平洋窗口区潜沉的年代际信号沿西南路径传播到副热带地区，在温跃层160m上下与西太平洋向东北传播的异常信号汇合。因此，北太平洋沿西南潜沉路径传播的年代际信号对ENSO的影响可能是间接的，而热带西南太平洋则可能扮演更为重要的角色。     

Possible Origins of the Western Pacific Warm Pool Decadal Variability

In this study,the impacts of the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO) on the western Pacific warm pool (WPWP) were investigated.Our results show that the WPWP is linked with the PDO and the AMO at multiple time scales.On the seasonal time scales,the WPWP and the PDO/AMO reinforce each other,while at decadal time scales the forcing roles of the PDO and the AMO dominate.Notably,a positive PDO tends to enlarge the WPWP at both seasonal and decadal time scales,while a positive AMO tends to reduce the WPWP at decadal time scales.Furthermore,the decadal variability of the WPWP can be well predicted based on the PDO and AMO.     

Decadal and interannual variability of the Indian Ocean Dipole

This study investigates the decadal and interannual variability of the Indian Ocean Dipole （IOD）. It is found that the long-term IOD index displays a decadal phase variation. Prior to 1920 negative phase dominates but after 1960 positive phase prevails. Under the warming background of the tropical ocean, a larger warming trend in the western Indian Ocean is responsible for the decadal phase variation of the IOD mode. Due to reduced latent heat loss from the local ocean, the western Indian Ocean warming may be caused by the weakened Indian Ocean westerly summer monsoon. The interannual air-sea coupled IOD mode varies on the background of its decadal variability. During the earlier period （1948-1969）, IOD events are characterized by opposing SST anomaly （SSTA） in the western and eastern Indian Ocean, with a single vertical circulation above the equatorial Indian Ocean. But in the later period （1980-2003）, with positive IOD dominating, most IOD events have a zonal gradient perturbation on a uniform positive SSTA. However, there are three exceptionally strong positive IOD events （1982, 1994, and 1997）, with opposite SSTA in the western and eastern Indian Ocean, accompanied by an El Nifio event. Consequently, two anomalous reversed Walker cells are located separately over the Indian Ocean and western-eastern Pacific; the one over the Indian Ocean is much stronger than that during other positive IOD events.     

太平洋年代际振荡的研究进展

作者以太平洋年代际振荡(PDO)现象为重点,系统地回顾了太平洋年代际变率观测、模拟和理论研究的国内外进展.在PDO时空结构方面,总结了PDO的基本观测事实,在PDO成因方面,从海洋大气相互作用观点出发比较了三类PDO形成机制的理论或假说,讨论了现有理论或假说中存在的若干问题,并提出了未来研究的方向和需要解决的关键科学问题.作者也简要介绍了东亚及中国气候年代际变化的特征及其和太平洋海表温度异常的联系,并讨论了东亚大气环流异常在PDO形成中的可能作用.     

Simulation of the 2014 Anomalous Warming in the Northeast Pacific

The Nucleus for European Modelling of the Ocean (NEMO) numerical model was used to simulate the North Pacific Ocean beginning in January 1960. The model had a horizontal resolution of 0.25^o, 46 vertical levels, and employed a spectral nudging assimilation scheme that, unlike standard nudging, nudges only specific frequency and wavenumber bands. This simulation was nudged to the mean and monthly Levitus climatology of potential temperature and salinity. The model was forced with mean monthly winds, net heat flux, and precipitation from the National Centers for Environmental Prediction (NCEP). The simulation was used to study a recent intrusion of much warmer and less saline water than normal from the west into the Gulf of Alaska, beginning in December 2013 and lasting until at least the early summer of 2014. The observed surface temperature anomalies were more than 4 standard deviations above normal. The model reproduced these anomalies in both a qualitative and quantitative manner, reproducing the same scale of anomalies over the region. An anomalous increase in the North Pacific Current (NPC) was found in the model in 2012 and the beginning of 2013, in agreement with observations. This increase in the NPC is associated with the positive phase of the North Pacific Gyre Oscillation. The causes of the temperature anomalies in the Gulf of Alaska could be due to three key factors: (i) an anomalously high, positive, surface heat flux in 2013 over the greater North Pacific; (ii) a significant decrease in the eastward flow of the NPC starting in late 2013 (with an accompanying decrease in cold water advection) after a period of historically strong eastward flow; and (iii) weaker winds throughout most of 2013 accompanied, however, by a shift to stronger northward winds (with an accompanying increase in warm water advection) in late 2013.     

Upper Water Column Nitrous Oxide Distributions in the Northeast Subarctic Pacific Ocean

This is the first study to investigate the magnitude and distribution of N₂O concentrations along the Line P oceanographic transect in the Northeast (NE) subarctic Pacific Ocean. Concentrations of N₂O were measured from the surface to 600 m depth at five stations between 126°W and 145°W. Although nitrification within the mixed layer may produce some N₂O, we conclude that mixing and diffusion processes, which vertically transport N₂O upwards from below the mixed layer, are the primary sources of N₂O to the surface waters of the NE subarctic Pacific Ocean. Below the mixed layer, nitrification appears to be the dominant source of N₂O, and based on correlations of excess N₂O (ΔN₂O) versus apparent oxygen utilization and NO₃ ^? concentrations, we estimated that the N₂O yield from nitrification was approximately 0.028 to 0.040%. The longitudinal distributions of N₂O concentrations below the mixed layer were variable and we consider the potential role that different transiting water masses may play in contributing to this variability. Finally, we estimated that the regional average sea-to-air N₂O flux was 4.37 mol of N₂O km^?2 d^?1, a value which is approximately four times that of the global average seawater-to-air flux rate. Our N₂O yield estimates are within the range of those expected under oxic conditions, leading us to conclude that decreasing dissolved O₂ concentrations in the NE subarctic Pacific Ocean, and the water masses that influence this region, over the past 50 years have yet to produce a substantial increase in N₂O production. Given the expectation that dissolved O₂ concentrations in the subarctic Pacific Ocean will continue to decrease during this century, this study has provided an important baseline from which future studies will be able to track changes in seawater N₂O concentrations and fluxes to the atmosphere.

[Traduit par la rédaction] La présente étude est la première à s'intéresser à la valeur et à la distribution des concentrations de N₂O le long du transect océanographique de la ligne P dans le Pacifique Nord-Est subarctique. Les concentrations de N₂O ont été mesurées de la surface jusqu’à une profondeur de 600 m à cinq stations entre 126°O et 145°O. Bien que la nitrification à l'intérieur de la couche de mélange puisse produire du N₂O, nous concluons que le mélange et les processus de diffusion, qui transportent verticalement le N₂O vers le haut à partir d'en dessous de la couche de mélange, sont les sources principales de N₂O pour les eaux de surface du Pacifique Nord-Est subarctique. En dessous de la couche mélange, la nitrification semble être la principale source de N₂O, et d'après les corrélations de l'excès de N₂O (ΔN₂O) par rapport à l'utilisation apparente d'oxygène et aux concentrations de NO₃ ^?, nous avons estimé que le rendement en N₂O de la nitrification était approximativement de 0,028 à 0,040%. Les distributions longitudinales des concentrations de N₂O en dessous de la couche de mélange étaient variables et nous considérons le rôle possible que des différentes masses d'eau transitoires peuvent avoir à jouer dans cette variabilité. Finalement, nous avons estimé que la moyenne régionale du flux mer–air de N₂O était de 4,37 moles de N₂O km^?2 j^?1, une valeur qui est environ quatre fois celle du taux planétaire moyen du flux eau de mer–air. Nos estimations du rendement en N₂O sont de l'ordre de celles attendues dans des conditions oxyques, ce qui nous amène à conclure que la diminution des concentrations d'oxygène dissout dans le Pacifique Nord–Est subarctique, et dans les masses d'eau qui influencent cette région, au cours des cinquante dernières années ont encore à produire une augmentation substantielle de production de N₂O. Étant donné qu'on s'attend à ce que les concentrations d'oxygène dissout dans le Pacifique subarctique continuent à diminuer durant le présent siècle, cette étude a fourni une importante base de référence à partir de laquelle de futures études pourront suivre les changements dans les concentrations de N₂O dans l'eau de mer et dans ses flux vers l'atmosphère.     

Decadal Changes in Interannual Dependence of the Bay of Bengal Summer Monsoon Onset on ENSO Modulated by the Pacific Decadal Oscillation

Interannual variations of the Bay of Bengal summer monsoon (BOBSM) onset in association with El Ni?o?Southern Oscillation (ENSO) are reexamined using NCEP1, JRA-55 and ERA20C atmospheric and Hadley sea surface temperature (SST) reanalysis datasets over the period 1900?2017. Decadal changes exist in the dependence of the BOBSM onset on ENSO, varying with the Pacific Decadal Oscillation (PDO). A higher correlation between the BOBSM onset and ENSO arises during the warm PDO epochs, with distinct late (early) onsets following El Ni?o (La Ni?a) events. In contrast, less significant correlations occur during the cold PDO epochs. The mechanism for the PDO modulating the ENSO?BOBSM onset relationship is through the variations in SST anomaly (SSTA) patterns. During the warm PDO epochs, the superimpositions of the PDO-related and ENSO-related SSTAs lead to the SSTA distribution of an El Ni?o (La Ni?a) event exhibiting significant positive (negative) SSTAs over the tropical central?eastern Pacific and Indian Ocean along with negative (positive) SSTAs, especially over the tropical western Pacific (TWP), forming a strong zonal interoceanic SSTA gradient between the TWP and tropical Indian Ocean. Significant anomalous lower tropospheric easterlies (westerlies) together with upper-tropospheric westerlies (easterlies) are thus induced over the BOB, favoring an abnormally late (early) BOBSM onset. During the cold PDO epochs, however, the superimpositions of PDO-related SSTAs with El Ni?o-related (La Ni?a-related) SSTAs lead to insignificant SSTAs over the TWP and a weak zonal SSTA gradient, without distinct circulation anomalies over the BOB favoring early or late BOBSM onsets.     

The Decadal Shift of the Summer Climate in the Late 1980s over Eastern China and Its Possible Causes

In this paper, it is pointed out that a notable decadal shift of, the summer climate in eastern China occurred in the late 1980s. In association with this decadal climate shift, after the late 1980s more precipitation appeared in the southern region of eastern China （namely South China）, the western Pacific subtropical high stretched farther westward with a larger south-north extent, and a strengthened anticyclone at 850 hPa appeared in the northwestern Pacific. The decadal climate shift of the summer precipitation in South China was accompanied with decadal changes of the Eurasian snow cover in boreal spring and sea surface temperature （SST） in western North Pacific in boreal summer in the late 1980s. After the late 1980s, the spring Eurasian snow cover apparently became less and the summer SST in western North Pacific increased obviously, which were well correlated with the increase of the South China precipitation. The physical processes are also investigated on how the summer precipitation in China was affected by the spring Eurasian snow cover and summer SST in western North Pacific. The change of the spring Eurasian snow cover could excite a wave-train in higher latitudes, which lasted from spring to summer. Because of the wave-train, an abnormal high appeared over North China and a weak depression over South China, leading to more precipitation in South China. The increase of the summer SST in the western North Pacific reduced the land-sea thermal contrast and thus weakened the East Asian summer monsoon, also leading to more precipitation in South China.     

The Effect of Regional Ocean-Atmosphere Coupling on the Long-term Variability in the Pacific Ocean

A fully coupled ocean-atmosphere model is applied to highlight the mechanism of the long-term variability (including decadal and longer time scales) in the Pacific Ocean. We are interested in the effect of ocean-atmosphere coupling of different regions during these processes. The control run successfully simulates the Pacific long-term variability, whose leading modes are the Pacific (inter) Decadal Oscillation (PDO) and the North Pacific mode (NPM). Furthermore, three numerical experiments are conducted, s...     

Interdecadal Change of the Northward Jump Time of the Western Pacific Subtropical High in Association with the Pacific Decadal Oscillation

In this paper, the northward jump time of the western Pacific subtropical high(WPSH) is defined and analyzed on the interdecadal timescale. The results show that under global warming, significant interdecadal changes have occurred in the time of the WPSH northward jumps. From 1951 to 2012, the time of the first northward jump of WPSH has changed from "continuously early" to "continuously late", with the transition occurring in 1980. The time of the second northward jump of WPSH shows a similar change, with the transition occurring in 1978. In this study, we offer a new perspective by using the time of the northward jump of WPSH to explain the eastern China summer rainfall pattern change from "north-abundant-southbelow-average" to "south-abundant-north-below-average" at the end of the 1970 s. The interdecadal change in the time of the northward jump of WPSH corresponds not only with the summer rainfall pattern, but also with the Pacific decadal oscillation(PDO). The WPSH northward jump time corresponding to the cold(warm) phase of the PDO is early(late). Although the PDO and the El Nino–Southern Oscillation(ENSO)both greatly influence the time of the two northward jumps of WPSH, the PDO’s effect is noticed before the ENSO’s by approximately 1–2 months. After excluding the ENSO influence, we derive composite vertical atmospheric circulation for different phases of the PDO. The results show that during the cold(warm)phase of the PDO, the atmospheric circulations at 200, 500, and 850 h Pa all contribute to an earlier(later)northward jump of the WPSH.     

A New Method for Predicting the Decadal Component of Global SST

A simple approach that considers both internal decadal variability and the effect of anthropogenic forcing is developed to predict the decadal components of global sea surface temperatures (SSTs) for the three decades 2011-2040. The internal decadal component is derived by harmonic wave expansion analyses based on the quasiperiodic evolution of the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO), as obtained from observational SST datasets. Furthermore, the external decadal component induced by anthropogenic forcing is assessed with a second-order fit based on the ensemble of projected SSTs in the experiments with multiple coupled climate models associated with the third Coupled Model Intercomparison Project (CMIP3) under the Intergovernmental Panels on Climate Change (IPCC) Special Reports on Emissions Scenario (SRES) A1B. A validation for the years from 2002 to 2010 based on a comparison of the predicted and the observed SST and their spatial correlation, as well as the root mean square error (RMSE), suggests that the approach is reasonable overall. In addition, the predicted results over the 50°S-50°N global band, the Indian Ocean, the western Pacific Ocean, the tropical eastern Pacific Ocean, and the North and the South Atlantic Ocean are presented.     

Decadal/interdecadal variations of the ocean temperature and its impacts on climate

Decadal/interdecadal climate variability is an important research focus of the CLIVAR Program and has been paid more attention. Over recent years, a lot of studies in relation to interdecadal climate variations have been also completed by Chinese scientists. This paper presents an overview of some advances in the study of decadal/interdecadal variations of the ocean temperature and its climate impacts, which includes interdecadal climate variability in China, the interdecadal modes of sea surface temperature (SST) anomalies in the North Pacific, and in particular, the impacts of interdecadal SST variations on the Asian monsoon rainfall. As summarized in this paper, some results have been achieved by using climate diagnostic studies of historical climatic datasets. Two fundamental interdecadal SST variability modes (7– 10-years mode and 25–35-years mode) have been identified over the North Pacific associated with different anomalous patterns of atmospheric circulation. The southern Indian Ocean dipole (SIOD) shows a major feature of interdecadal variation, with a positive (negative) phase favoring a weakened (enhanced) Asian summer monsoon in the following summer. It is also found that the China monsoon rainfall exhibits interdecadal variations with more wet (dry) monsoon years in the Yangtze River (South China and North China) before 1976, but vice versa after 1976. The weakened relationship between the Indian summer rainfall and ENSO is a feature of interdecadal variations, suggesting an important role of the interdecadal variation of the SIOD in the climate over the south Asia and southeast Asia. In addition, evidence indicates that the climate shift in the 1960s may be related to the anomalies of the North Atlantic Oscillation (NAO) and North Pacific Oscillation (NPO). Overall, the present research has improved our understanding of the decadal/interdecadal variations of SST and their impacts on the Asian monsoon rainfall. However, the research also highlights a number of problems for future research, in particular the mechanisms responsible for the monsoon long-term predictability, which is a great challenge in climate research.     

Model Evidence for Interdecadal Pathway Changes in the Subtropics and Tropics of the South Pacific Ocean

Numerical simulations using a version of the GFDL/NOAA Modular Ocean Model(MOM 3) are analyzed to demonstrate interdecadal pathway changes from the subtropics to the tropics in the South Pacific Ocean.After the 1976-77 climate shift,the subtropical gyre of the South Pacific underwent significant changes,characterized by a slowing down in its circulation and a southward displacement of its center by about 5-10 latitude on the western side.The associated circulation altered its flow path in the northwestern part of the subtropical gyre,changing from a direct pathway connecting the subtropics to the tropics before the shift to a more zonal one after.This effectively prevented some subtropical waters from directly entering into the western equatorial Pacific.Since waters transported onto the equator around the subtropical gyre are saline and warm,such changes in the direct pathway and the associated reduction in equatorward exchange from the subtropics to the tropics affected water mass properties downstream in the western equatorial Pacific,causing persisted freshening and cooling of subsurface water as observed after the late 1970s.Previously,changes in gyre strength and advection of temperature anomalies have been invoked as mechanisms for linking the subtropics and tropics on interdecadal time scales.Here we present an additional hypothesis in which geographic shifts in the gyre structure and location(a pathway change) could play a similar role.     

Structure and Evolution of Decadal Spiciness Variability in the North Pacific during 2004-20,Revealed from Argo Observations

Ocean spiciness is referred to as density-compensated temperature and salinity variations with warm(cool)and salty(fresh)waters having high(low)spiciness,respectively.The structure and evolution of density-compensated(warm/salty or cool/fresh)spiciness anomalies are investigated in the North Pacific thermocline using Argo observations during the period 2004-20.Two well-organized decadal spiciness events are identified through isopycnal surface analyses.One warm/salty spiciness anomaly of about 0.15°C and 0.05 g kg^?1temperature and salinity perturbations on the 25 kg m^?1isopycnal surface appeared in the eastern subtropical North Pacific at(18°-30°N,120°-150°W)in 2007,which then migrated southwestward along the mean circulation and arrived in the western tropics at(~15°N,145°E-175°W)in 2012-13,with the reduced salinity perturbation of about 0.043 g kg^?1.Another cool/fresh spiciness anomaly of about?0.2°C and?0.07 g kg^?1temperature and salinity perturbations originated from the eastern subtropics at(120°-150°W,~30°N)in 2014 and followed a similar advective pathway during the period from 2014-15 to 2019-20.The subduction pathway can be adequately determined by the mean Montgomery stream function on the isopycnal surface;the propagation direction and speed are in good agreement with the expectation for the role played by advection due to the mean geostrophic current.Moreover,the subducted decadal spiciness anomalies can have negative feedback on sea surface temperature(SST)variability in the western tropical Pacific through the diapycnal processes.The identifications of these density-compensated spiciness anomalies and their propagation pathways provide a clear illustration of the oceanic extratropics-tropics interactions in the North Pacific Ocean.     

东亚夏季风降水年代际变异模态及其与太平洋年代际振荡的关系

利用全球陆地月平均降水资料、英国气象局哈德莱中心的月平均海表温度距平(SSTA)资料及NCEP/NCAR再分析大气环流资料,探讨东亚夏季风降水年代际变率及其与太平洋年代际振荡(PDO)的联系。研究指出:东亚夏季风降水年代际变异模态以及PDO均在1976年前后呈现显著的年代际转折,并且东亚夏季风降水与PDO在年代际尺度上具有较好的相关关系。PDO能够在对流层低层激发出与年代际东亚夏季风环流较为相似的大气环流异常特征,表明东亚夏季风环流的年代际变化可能受大气外强迫因子PDO在对流层低层的外源强迫作用影响,最终导致东亚夏季风降水发生年代际变化。     

太平洋年代际振荡冷、暖背景下ENSO循环的特征

利用英国气象局哈德莱中心的月平均海温距平资料、美国Scripps海洋研究所联合环境分析中心(JEDAC)的海表和次表层海温观测资料以及NCEP/NCAR再分析资料,研究了太平洋年代际振荡(PDO)不同背景下ENSO循环的特征.结果表明,PDO为ENSO循环提供了一个年代际气候背景,在PDO的暖位相时期,El Nino事件发生的频率较高,强度较强;反之,在PDO的冷位相时期,La Nina事件发生的频率较高,强度较强.而且在不同的太平洋年代际振荡背景下,ENSO循环表现出不同的特征.在PDO冷位相时期,发生El Nino(La Nina)事件时,正(负)的SOTA从西太平洋沿温跃层向东传播,正(负)的SSTA从赤道东太平洋向西扩展到中太平洋,ENSO事件先在赤道东太平洋爆发.在PDO的暖位相时期,发生El Nino(La Nina)事件时,正(负)的SOTA首先出现在赤道中太平洋,然后沿温跃层向东传播,正(负)的SSTA从赤道中太平洋向东扩展到东太平洋,ENSO事件首先在中太平洋爆发.这为ENSO预测提供了新的线索.