ENSO Frequency Asymmetry and the Pacific Decadal Oscillation in Observations and 19 CMIP5 Models

Using observational data and the pre-industrial simulations of 19 models from the Coupled Model Intercomparison Project Phase 5（CMIP5）, the El Ni o（EN） and La Ni a（LN） events in positive and negative Pacific Decadal Oscillation（PDO） phases are examined. In the observational data, with EN（LN） events the positive（negative） SST anomaly in the equatorial eastern Pacific is much stronger in positive（negative） PDO phases than in negative（positive） phases. Meanwhile,the models cannot reasonably reproduce this difference. Besides, the modulation of ENSO frequency asymmetry by the PDO is explored. Results show that, in the observational data, EN is 300% more（58% less） frequent than LN in positive（negative）PDO phases, which is significant at the 99% confidence level using the Monte Carlo test. Most of the CMIP5 models exhibit results that are consistent with the observational data.

The Impact of Global Warming on the Pacific Decadal Oscillation and the Possible Mechanism

The response of the Pacific Decadal Oscillation （PDO） to global warming according to the Fast Ocean Atmosphere Model （FOAM） and global warming comparison experiments of 11 IPCC AR4 models is investigated. The results show that North Pacific ocean decadal variability, its dominant mode （i.e., PDO）, and atmospheric decadal variability, have become weaker under global warming, but with PDO shifting to a higher frequency. The SST decadal variability reduction maximum is shown to be in the subpolar North Pacific Ocean and western North Pacific （PDO center）. The atmospheric decadal variability reduction maximum is over the PDO center. It was also found that oceanic baroclinic Rossby waves play a key role in PDO dynamics, especially those in the subpolar ocean. As the frequency of ocean buoyancy increases under a warmer climate, oceanic baroclinic Rossby waves become faster, and the increase in their speed ratio in the high latitudes is much larger than in the low latitudes. The faster baroclinic Rossby waves can cause the PDO to shift to a higher frequency, and North Pacific decadal variability and PDO to become weaker.

Phase Transition of the Pacific Decadal Oscillation and Decadal Variation of the East Asian Summer Monsoon in the 20th Century

This paper focuses on the relationship between the phase transition of the Pacific decadal oscillation （PDO） and decadal variation of the East Asian summer monsoon （EASM） in the twentieth century. The first transition occurred in the 1940s, with an enhanced SST in the North Pacific and reduced SST in the tropical eastern Pacific and South Indian Ocean. In agreement with these SST changes, a higher SLP was found in most parts of the Pacific, while a lower SLP was found in the North Pacific and most parts of the Indian Ocean. In this case, the EASM was largely enhanced with a southerly anomaly in the lower troposphere along the east coast of China. Correspondingly, there was less rainfall in the Yangtze River valley and more rainfall in northern and southern China. An opposite change was found when the PDO reversed its phase in the late 1970s. In the tropical Indian Ocean and western Pacific, however, the SST was enhanced in both the 1940s and 1970s. As a result, the western Pacific subtropical high （WPSH） tended to extend westward with a larger magnitude in the 1970s. The major features were reasonably reproduced by an atmospheric general circulation model （IAP AGCM4.0） prescribed with observed SST and sea ice. On the other hand, the westward extension of the WPSH was exaggerated in the 1970s, while it was underestimated in the 1940s. Besides, the spatial pattern of the simulated summer rainfall in eastern China tended to shift southward compared with the observation.

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.

Influence of the Pacific Decadal Oscillation on regional sea level rise in the Pacific Ocean from 1993 to 2012

The rate of regional sea level rise(SLR) provides important information about the impact of human activities on climate change.However,accurate estimation of regional SLR can be severely affected by sea surface height(SSH) change caused by the Pacific Decadal Oscillation(PDO-SSH).Here,the PDOSSH signal is extracted from satellite altimeter data by multi-variable linear regression,and regional SLR in the altimeter era is calculated,before and after removing that signal.The results show that PDO-SSH trends are rising in the western Pacific and falling in the eastern Pacific,with the strongest signal confined to the tropical and North Pacific.Over the past 20 years,the PDO-SSH accounts for about 30%-40%of altimeter-observed SLR in the regions 8°-15°N,130°-160°E and 30°-40°N,170°-220°E.Along the coast of North America,the PDO-SSH signal dramatically offsets the coastal SLR,as the sea level trends change sign from falling to rising.

Response of Growing Season Gross Primary Production to El Nino in Different Phases of the Pacific Decadal Oscillation over Eastern China Based on Bayesian Model Averaging

Gross primary production(GPP) plays a crucial part in the carbon cycle of terrestrial ecosystems.A set of validated monthly GPP data from 1957 to 2010 in 0.5°× 0.5° grids of China was weighted from the Multi-scale Terrestrial Model Intercomparison Project using Bayesian model averaging(BMA).The spatial anomalies of detrended BMA GPP during the growing seasons of typical El Nino years indicated that GPP response to El Nino varies with Pacific Decadal Oscillation(PDO) phases: when the PDO was in the cool phase,it was likely that GPP was greater in northern China(32°–38°N,111°–122°E) and less in the Yangtze River valley(28°–32°N,111°–122°E);in contrast,when PDO was in the warm phase,the GPP anomalies were usually reversed in these two regions.The consistent spatiotemporal pattern and high partial correlation revealed that rainfall dominated this phenomenon.The previously published findings on how El Nino during different phases of PDO affecting rainfall in eastern China make the statistical relationship between GPP and El Nino in this study theoretically credible.This paper not only introduces an effective way to use BMA in grids that have mixed plant function types,but also makes it possible to evaluate the carbon cycle in eastern China based on the prediction of El Nino and PDO.

Twentieth-century Pacific Decadal Oscillation simulated by CMIP5 coupled models

太平洋年代际振荡(PDO)是影响亚洲—太平洋气候,乃至全球气候变化非常重要的海洋模态之一。目前为止,有关PDO形成的动力根源及机制仍不清楚。本文聚焦20世纪PDO的空间模态和时间序列演变,系统分析了CMIP5框架下25个耦合模式开展的109个历史时期模拟试验的结果。结果显示,大多数耦合模式可以成功模拟出20世纪PDO"马蹄形"海表温度距平,其中BNUESM,CanESM2,CCSM4,CESM1-FASTCHEM,GFDL CM3,MIROC5,NorESM1-M等模式和中国科学院大气物理研究所的FGOALS-g2模拟的PDO太平洋海表温度遥相关型空间分布与观测相似度较高;耦合模式模拟的PDO时间序列与观测相差较大,表明现有的耦合模式几乎不能模拟出20世纪PDO的位相演变特征。

Potential Correlation between the Decadal East Asian Summer Monsoon Variability and the Pacific Decadal Oscillation

This study discusses the potential contribution of the Pacific decadal oscillation(PDO)to the weakening of the East Asian summer monsoon(EASM)and the evident correlation between the positive PDO and"Southern flood and Northern drought(SFND)"summer rainfall pattern over East China.The mechanism behind this contribution is also discussed.

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.

Response of Japanese anchovy(Engraulis japonicus)to the Pacific Decadal Oscillation in the Yellow Sea over the past 400 a

Quantitative identification of long-term changes in the abundance of Japanese anchovy(Engraulis japonicus)in the Yellow Sea is particularly important for understanding evolutionary processes of the Yellow Sea ecosystem.Unfortunately,the driving mechanisms of climate variability on the anchovy are still unclear due to the lack of long-term observational data.In this study,we used the fish scale deposition rate in the central Yellow Sea to reconstruct the time series of the anchovy stock over the past 400 a.On this basis,we further explored the impacts of the Pacific Decadal Oscillation(PDO)on the anchovy.Our results show that the anchovy stock is positively correlated with the PDO on a decadal time scale.In addition,anchovy abundance was relatively high during1620–1860 AD(the Little Ice Age,LIA),though in a state of constant fluctuation;anchovy abundance maintained at a relatively low level after~1860 AD.In particular,followed by overfishing since the 1980 s,the anchovy stock has declined sharply.Based on these findings,we infer that fluctuations of the anchovy stock may be regulated by basin-scale“atmosphere–ocean”interactions.Nevertheless,the role of overfishing should not be ignored.

Precipitation Regime Shift Associated with the Pacific Decadal Oscillation in the Maritime Continent

Recent changes in precipitation regime in South-East Asia are a subject of ongoing discussion. In this article, for the first time, evidence of a precipitation regime shift during the mid-1970s in the Northern Hemispheric part of South-East Asia is demonstrated. The detection of regime shifts is made possible by using a new comprehensive dataset of daily precipitation records (South-East Asian Climate Assessment and Dataset) and applying a novel Bayesian approach for regime shift detection. After the detected regime shift event in the mid-1970s, significant changes in precipitation distribution occurred in the Northern Hemispheric regions—Indochina Peninsula and the Philippines. More specifically, dry days became up to 10% more frequent in some regions. However, no precipitation regime shift is detected in Southern Hemisphere regions—Java and Northern Australia, were the number of observed dry days increased gradually.

Global influenza in cold phase of Pacific Decade Oscillation

Based on the study of the cold phase of the Pacific Decade Oscillation, pandemic influenza is related to climate. The relation of low temperature, Pacific Decade Oscillation, strongest earthquake, Influenza, hurricane and El Nino is researched in this study. In the cold period of Pacific Decade Oscillation, the strongest earthquake, hurricane with La Nina, Pandemic Influenza with El Nino will occur stronger and stronger. From 1950 to 1976, the strongest dust-storm is connected with Pandemic Influenza one by one. So, dust-storm is one of factors to spread pandemic influenza viruses.

CMIP 6 models simulation of the connection between North/South Pacific Meridional Mode and ENSO

The subtropical North and South Pacific Meridional Modes(NPMM and SPMM)are well known precursors of El Niño-Southern Oscillation(ENSO).However,relationship between them is not constant.In the early 1980,the relationship experienced an interdecadal transition.Changes in this connection can be attributed mainly to the phase change of the Pacific decadal oscillation(PDO).During the positive phase of PDO,a shallower thermocline in the central Pacific is responsible for the stronger trade wind charging(TWC)mechanism,which leads to a stronger equatorial subsurface temperature evolution.This dynamic process strengthens the connection between NPMM and ENSO.Associated with the negative phase of PDO,a shallower thermocline over southeastern Pacific allows an enhanced wind-evaporation-SST(WES)feedback,strengthening the connection between SPMM and ENSO.Using 35 Coupled Model Intercomparison Project Phase 6(CMIP6)models,we examined the NPMM/SPMM performance and its connection with ENSO in the historical runs.The great majority of CMIP6 models can reproduce the pattern of NPMM and SPMM well,but they reveal discrepant ENSO and NPMM/SPMM relationship.The intermodal uncertainty for the connection of NPMM-ENSO is due to different TWC mechanism.A stronger TWC mechanism will enhance NPMM forcing.For SPMM,few models can simulate a good relationship with ENSO.The intermodel spread in the relationship of SPMM and ENSO owing to SST bias in the southeastern Pacific,as WES feedback is stronger when the southeastern Pacific is warmer.

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.

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.

Response of North Pacific and North Atlantic decadal variability to weak global warming

和平的十的摆动(PDO ) 和大西洋 Multidecadal 可变性(AMV ) 是在气候系统的二个主导的低频率的模式。这研究在弱全球温暖下面集中了于这二个模式的反应。观察数据从冰和海表面温度数据集(HadISST ) 和联合模型从联合模型 Intercomparison 工程阶段 5 输出的哈德利中心海(CMIP5 ) 被导出。在 PDO 和 AMV 的变化与长弱的全球温暖情形(RCP2.6 ) 用四个模型(bcc-csm1-1， CCSM4， IPSL-CM5A-LR，和 MPI-ESM-LR ) 被检验。这些模型在工业化前的跑和 RCP2.6 跑捕获了二个低频率的模式。在弱全球温暖下面，当振幅仅仅稍微减少了时， PDO 和 AMV 的时间规模显著地减少了。有趣地，诺思太平洋海表面温度异例(SSTA ) 的标准差仅仅在十的时间规模减少了，并且诺思大西洋 SSTA 的在 interannual 和十的时间规模两个都减少了。联合系统由一个慢海洋部件组成，它有十的时间规模，和一个快大气的部件，它由减去是计算的从总数十。结果建议在全球温暖下面， PDO 变化被海洋动力学统治，并且 AMV 变化被强迫的海洋动力学和随机的空气统治。

Analysis of Decadal Climate Variability in the Tropical Pacific by Coupled GCM

This study presents the spatial and temporal structures of the decadal variability of the Pacific from an extended control run of a coupled global climate model (GCM).The GCM used was version-g2.0 of the Flexible Global Ocean Atmosphere Land System (FGOALS-g2.0) developed at LASG/IAP.The GCM FGOALS-g2.0 re-produces similar spatial-temporal structures of sea surface temperature (SST) as observed in the Pacific decadal os-cillation (PDO) with a significant period of approximately 14 years.Correspondingly,the PDO signals were closely related to the decadal change both in the upper-ocean temperature anomalies and in the atmospheric circulation.The present results suggest that warm SST anomalies along the equator relax the trade winds,causing the SSTs to warm even more in the eastern equatorial Pacific,which is a positive feedback.Meanwhile,warm SST anomalies along the equator force characteristic off-equa-torial wind stress curl anomalies,inducing much more poleward transport of heat,which is a negative feedback.The upper-ocean meridional heat transport,which is asso-ciated with the PDO phase transition,links the equatorial to the off-equatorial Pacific Ocean,acting as a major mechanism responsible for the tropical Pacific decadal variations.Therefore,the positive and negative feedbacks working together eventually result in the decadal oscilla-tion in the Pacific.

Decadal variations of the North Pacific Tropical Water at 137°E

The decadal variations of the North Pacifi c Tropical Water (NPTW) at 137°E in the western North Pacific Ocean are investigated based on the repeated hydrographic observations along with two global gridded ocean products. The results indicate that the maximum salinity of NPTW experiences signifi cant quasi-decadal variations, having maxima around 1979, 1987, 1995, 2004, and 2012, while minima around 1974, 1983, 1991, 1999, and 2008 during the period of interest. The NPTW area also shows similar quasidecadal variation, expanding/shrinking as its maximum salinity increases/decreases at the 137°E section. These variations are induced mainly by changes in the mixed layer salinity in the source region and largescale circulation in the northwestern tropical Pacific Ocean, both of which are related to the Pacific Decadal Oscillation. The underlying processes at work are further confi rmed through conducting the subsurface salinity budget analysis. Besides, short-term processes are also at work through nonlinear interactions, especially after 2000.

Climate-Related Variations in Autumn Cohort of Japanese Common Squid Todarodes pacificus

The Japanese common squid Todarodes pacificus is widely distributed in the Sea of Japan,the East China Sea and the Northwest Pacific Ocean,and is largely exploited by the Asia-Pacific countries.In this study,the impacts of regime shift of the Pacific Decadal Oscillation(PDO)during 1977-2015 on the autumn cohort of T.pacificus were assessed by examining the variations in vertical water temperatures at depths of 0 m(Temp_0 m),50 m(Temp_50 m)and 100 m(Temp_100 m)and the distribution pattern of preferred spawning ground(SSG).Spatial and temporal correlation analysis revealed that the PDO index exhibited a significantly negative relationship with vertical water temperatures at different depths and was negatively related to catch-per-unit-effort(CPUE)and stock biomass of T.pacificus.In addition,water temperatures in the specific three water layers were positively associated with CPUE.The PDO regime shift strongly affected the thermal condition and spawning ground of T.pacificus.Comparing to the negative PDO,the waters from the surface to the deep became cool in the positive PDO phase;correspondingly,the area of SSG largely contracted at different depths.Consequently,the CPUE and stock biomass of T.pacificus profoundly decreased.From the results it can be concluded that the PDO regime shift-driven changes in vertical thermal condition and SSG ranges can yield substantial impacts on T.pacificus abundance.

Evaluation of CMIP6 model performance in simulating the PDO and its future change

本文基于40个CMIP6模式输出结果,系统评估了模式对历史时期太平洋年代际振荡(PDO)的模拟性能,并利用其中17个模式的4种共享社会经济路径情景数据预估了PDO未来可能变化趋势.结果表明,CMIP6模式能够合理再现PDO相关海表温度异常的空间模态,但模式模拟PDO位相演变的能力普遍较弱.多模式集合能够合理再现PDO的50年左右周期,但无法模拟出其20年左右周期,并且低估了PDO的变化幅度.在未来变暖情景下,PDO可能在2050左右出现由负位相向正位相的转变,同时其50年左右周期也将明显缩短.