Interdecadal Variations of Phase Delays Between Two Ni(n)o Indices at Different Time Scales

Phase delays between two Nino indices-sea surface temperatures in Nino regions 1+2 and 3.4(1950-2001)-at different time scales are detected by wavelet analysis. Analysis results show that thereare two types of period bifurcations in the Nino indices and that period bifurcation points exist only in the region where the wavelet power is small. Interdecadal variation features of phase delays between the two indices vary with different time scales. In the periods of 40-72 months, the phase delay changes its sign in 1977: Nino 1+2 indices are 2-4 months earlier than Nino 3.4 indices before 1977, but 3-6 months later afterwards. In the periods of 20-40 months, however, the phase delay changes its sign in another way:Nino 1+2 indices are 1-4 months earlier before 1980 and during 1986-90, but 1-4 months later during 1980-83 and 1993-2001.     

1470—2019年中国东部旱涝年代际变化及其与太平洋海表温度的关系

基于中国东部地区（30°—40°N,105°E以东）19个代表站1470—2019年旱涝等级序列、古气候代用资料定量重建的北太平洋海表温度年代际振荡指数以及Nino3.4指数,通过经验正交函数分解、小波分析和集合经验模态分解方法分析了中国东部旱涝年代际变化特征及其与太平洋海温的关系。结果表明,（1）1470年以来中国东部旱涝变化的主模态为全区一致型（方差贡献率为25.2%）,变率中心主要位于黄河中下游,其时间系数的小波分析和集合经验模态分解揭示出全区旱涝存在10—30 a的准周期;该模态长期趋势揭示17—18世纪中国东部整体偏涝,而19世纪以后出现干旱化趋势。（2）寒冷背景下中国东部旱涝一致变化更明显,在17世纪前、中期和19世纪中、后期的小冰期寒冷期全区一致型模态的方差贡献率为35%—40%,且这两个时段10—30 a的年代际变化信号尤为显著;而旱涝的变率中心则表现出冷期偏北,暖期偏南或偏西的特征。（3）中国东部旱涝的年代际变化与北太平洋和赤道中东太平洋海表温度异常有关,表现为偏涝（旱）气候对应于北太平洋海表温度年代际振荡的冷（暖）相位,以及年代际尺度上的冬季Nino3.4区海表温度的异常偏低（高）;在小冰期的寒冷期,旱涝的年代际变化可能与Nino3.4区海表温度异常关系更密切。      

甘肃空中水汽含量演变特征

为揭示甘肃空中水汽的时空演变,采用EOF、REOF、小波分析和计算Petitt变点等方法,研究了该区域大气中水汽含量在近40 a的变化.结果表明：甘肃水汽变化存在4个敏感区（空间型）,东部、西部是最敏感地区,中部敏感程度次之;在时间变化上阶段性明显,1977、1987年发生突变,1977年之前呈明显下降趋势,1977～1987年间波动,1987年后呈明显上升趋势;小波分析表明水汽变化存在2～4 a为主的振荡,20世纪70年代以前变幅大,80年代以后变幅小.     

SPATIAL/TEMPORAL FEATURES OF DROUGHT/FLOOD IN FUJIAN FOR THE PAST FOUR DECADES

41a (1961 - 2001) seasonal Z index series of 25 representative weather stations are investigated by virtue of EOF, FFT, continuous wavelet transformation (CWT) and orthogonal wavelet transformation (OWT). It shows that: (1) Fujian drought/flood (DF) has a significant 2 - 3a cycle for the periods 1965 - 1975 and 1990's; (2) the pattern, which represents the opposite DF trend between the southern and northern parts, has 1a and 3 - 4a cycles since the middle of 1980's; (3) EOF3, which denotes the reverse change between the middle-west region and other areas, has significant 1 - 2a cycle for the period from 1985 to 1998 and 9 - 13a cycle since 1980s; (4) there is an obvious drought trend for the last 40a (especially in the 1990's), which is more outstanding in the south (east) than in the north (west); (5) the 1960's and 1980's are in relatively wet phases and the 1970's and 1990's are in drought spells.     

THE FREQUENCY CHARACTERISTICS OF WARM AND COLD EPISODES IN THE NI(N)O REGIONS

On the basis of NOAA/CPC data of sea surface temperature anomaly in the Nino regions during Jan. 1950 - Dec. 2003, the wavelet power spectrum of SST were studied with significance and confidence testing at different scales in this paper. It shows that the SST are provided with multi-time scales structure nested one another, and vary on scales of 2 - 7 years, 8 - 20 years and ＞30 years. The most significant variation of the warm and cold episodes is in the 4-year band of period. The power, frequency structure and confidence of the same episode are different in different Nino regions. The intensity of oscillations is increasing at low frequency bands and decreasing at high frequency bands from east to west in the Nino regions, especially after 1970.     

Nino海区SSTA的时频结构特征

根据1950～2003年Nino海区SSTA资料，采用小波变换方法分析了SST变化的多尺度结构及其强度变化。结果表明，Nino海区的SSTA序列表现为多层次相互嵌套的时频结构，存在着2～7a、8～20a和30a以上时间尺度的变化，经检验显著变化周期为2～7a，10a以上和1a以下的周期信号较弱。冷暖事件的能量主要集中在2～7a的尺度上，以准4a尺度的周期振荡最为显著。同一事件在不同海区的频率结构也不相同，1970年以后各尺度上冷暖事件的强度明显增大，有向低频发展的趋势。     

热带太平洋与印度洋相互作用的年代际变化

利用全球海表海温资料（GISST）和NCEP／NCAR再分析资料,研究了热带太平洋与印度洋之间的相互作用及其在不同年代二者作用关系的变化。结果表明：热带印度洋偶板子指数超前热带太平洋Nin03指数2月时相关最大,印度洋单板子指数滞后Nin03指数3～4月时相关最大。印度洋偶板子在一定程度上影响E1 Nino事件的发生,而E1 Nino事件的发生、发展会影响印度洋单板子事件的发生。热带印度洋偶板子事件与热带太平洋ENSO事件的相互作用在1961年发生了明显跃变,其原因可能是1961年之前热带印度洋偶板子对热带太平洋上空的纬向风影响很小,而1961年以后其影响明显加强。热带印度洋单板子事件与热带太平洋ENSO事件的相关一直显著,没有明显跃变。     

Indices of El Nino and El Nino Modoki： An Improved El Nino Modoki Index

In recent years, El Nino Modoki (pseudo-El Nino) has been distinguished as a unique large-scale ocean warming phenomenon happening in the central tropical Pacific that is quite different from the traditional El Nino. Empirical Orthogonal Function (EOF) analysis is used to successfully separate El Nino and El Nino Modoki. The abilities of the NINO3 index, NINO3.4 index, NINO1+2 index and NINO4 index in characterizing the El Nino are explored in detail. It is suggested that the NINO3 index is comparatively optimal to monitor the El Nino among the four NINO indices, since other NINO indices either cannot well distinguish El Nino and El Nino Modoki signals or are easily disturbed by El Nino Modoki signals. Further, an improved El Nino Modoki index (IEMI) is introduced to better represent the El Nino Modoki that is captured by the second leading EOF mode of monthly tropical Pacific sea surface temperature anomalies (SSTA). The IEMI is an improvement of the El Nino Modoki index (EMI) through adjusting the inappropriate weight coefficients of the three boxes of EMI, and it effectively overcomes the lack of EMI in monitoring the two historical El Nino Modoki events and also avoids the possible risk of EMI in excluding the interference of El Nino signal, indicating the realistic and potential advantages.     

三类厄尔尼诺事件对东亚大气环流及中国东部次年夏季降水的影响

利用全球海表温度(SST)资料、ONI(Oceanic Nino Index)序列以及中国160站逐月降水资料,研究了不同类型El Nino事件的主要特征及其对东亚大气环流及中国东部次年夏季逐月及季节降水的影响。结果表明:1)据El Nino事件期间SST最大正异常所在区域,将El Nino事件分为Nino3、Nino4和Nino3.4型。2)El Nino事件次年6月,Nino3型时降水显著正异常区主要位于鄱阳湖和洞庭湖流域,Nino4型时位于鄱阳湖流域、桂粤湘三省交界及广西西部,Nino3.4型时位于洞庭湖流域。7月Nino3型降水显著正异常区北移至长江流域,8月则呈西多东少反相分布。从次年6月至8月,Nino4型降水显著正异常区逐渐北移,Nino3.4型降水显著正异常区则从南到北再移向东北。3)在整个次年夏季,Nino3、Nino4和Nino3.4型降水显著正异常区在中国东部呈自南向北分布。无论逐月或季节降水,均是Nino4型降水正异常最强、Nino3.4型最弱。4)不同类型事件次年夏季和各月环流特征存在一定差异,总体而言,对于南亚高压,Nino3型、Nino4型事件后呈偏强、东伸和北抬的特点,且后者较前者时更强;Nino3.4型事件后主要呈减弱、西退特征。对于西太平洋副热带高压,Nino3型、Nino4型事件后主要呈偏强、西伸、北抬特征,后者较前者更强,西伸、北抬也更明显;Nino3.4型后,副高以东撤、北抬特征为主。     

Equatorial pacific SSTA-related decadal variations of potential predictability of ENSO and interannual climate

Summary Based on analysis of NCEP reanalysis data and SST indices of the recent 50 years, decadal changes of the potential predictability of ENSO and interannual climate anomalies were investigated. Autocorrelation of Nino3 SST anomalies (SSTA) and correlation between atmospheric anomalies fields and Nino3 SSTA exhibit obvious variation in different decades, which indicates that Nino3 SSTA-related potential predictability of ENSO and interannual climate anomalies has significant decadal changes. Time around 1977 is not only a shift point of climate on the interdecadal time scale but also a catastrophe point of potential predictability of ENSO and interannual climate. As a whole, ENSO and the PNA pattern in boreal winter are more predictable in 1980s than in 1960s and 1970s, while the Nino3 SSTA-related potential predictability of the Indian monsoon and the East Asian Monsoon is lower in 1980s than in 1960s and 1970s. Received October 19, 1999 Revised December 30, 1999     

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

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

Connection of the stratospheric QBO with global atmospheric general circulation and tropical SST. Part II: interdecadal variations

The interdecadal variation of the association of the stratospheric quasi-biennial oscillation (QBO) with tropical sea surface temperature (SST) anomalies (SSTA) and with the general circulation in the troposphere and lower stratosphere is examined using the ERA40 and NCEP/NCAR reanalyses, as well as other observation-based analyses. It is found that the relationship between the QBO and tropical SSTA changed once around 1978–1980, and again in 1993–1995. During 1966–1974, negative correlation between the QBO and NINO3.4 indices reached its maximum when the NINO3.4 index lagged the QBO by less than 6?months. Correspondingly, the positive correlations were observed when the NINO3.4 index led the QBO by about 11–13?months or lagged by about 12–18?months. However, maximum negative correlations were shifted from the NINO3.4 index lagging the QBO by about 0–6?months during 1966–1974 to about 3–12?months during 1985–1992. During 1975–1979, both the negative and positive correlations were relatively small and the QBO and ENSO were practically unrelated to each other. The phase-based QBO life cycle composites also confirm that, on average, there are two phase (6–7?months) delay in the evolution of the QBO-associated anomalous Walker circulation, tropical SST, atmospheric stability, and troposphere and lower stratosphere temperature anomalies during 1980–1994 in comparison with those in 1957–1978. The interdecadal variation of the association between the QBO and the troposphere variability may be largely due to the characteristic change of El Ni?o-Southern Oscillation. The irregularity of the QBO may play a secondary role in the interdecadal variation of the association.     

Bivariate Wavelet Analysis of Asia Monsoon and ENSO

This paper employs some recently developed bivariate wavelet analysis techniques to study the correlation between Asia monsoon and E1 Nino southern oscillation (ENSO).Various energy spectral densities are defined for waveiel transforms,analogous to those used in conventional Fourier analysis.Some comparisons are made by applying both wavelet and Fourier spectral methods (o the data.The wavelet analysis shows evidence of some relationship between Asia monsoon and ENSO,which the Fourier analysis resolves poorly.Correlation on several time scales,ranging from 2-4 years,11 years,and 22 years,become apparent with the wavelet cross-spectrum.Finally,the warelet cross-transform provides time localization of the distinctive features within the data record.     

中国东部夏季主要降水型的年代际变化及趋势分析

针对中国东部夏季降水存在着20世纪50和60年代为“南旱北涝”、80和90年代为“南涝北旱”的相反形势,该文应用小波分析等方法对华北和长江中下游地区近54 a来的夏季降水进行分析,发现二者都具有不同周期的年代际变化。对于周期小于24 a的年代际变化,其morlet小波分析表明两地夏季降水的位相关系并不是固定的。对于更长的时间尺度,用正交小波分析了周期大于28 a的年代际变化,这种长周期的年代际变化能较好地体现出“南旱北涝”和“南涝北旱”两种形势,说明两地降水还存在着更长时间尺度的准周期变化。对于两地降水的这种长周期变化,分别选用不同位相的17 a为代表进行海温、环流形势的合成分析,对比发现两阶段所对应的海温、环流形势具有极明显的差异。最后,用近期的海温、环流形势与上述两种位相的海温、环流形势进行对比,讨论了未来降水型的可能演变趋势。     

ENSO 循环过程中逐月海温异常的合成分析

文章基于UK和MIT 1990年整编的12年（1968～1977年和1982～1983年）逐月5°×5°经纬网格点的海温（SST）距平资料，对其间发生的4次El Nino事件和3次La Nina事件作了逐月全球SST异常分布的合成分析。合成结果表明:在El Nino事件的形成阶段，赤道中太平洋存在明显的东传暖性低频扰动；而在La Nina事件的形成阶段，南北美沿岸有稳定增强的冷中心向西发展。     

PROCESS OF TRANSITION BETWEEN COLD AND WARM PERIODS AND ITS PREDICTION

The oscillation of multi-time scales and the process of transition between cold and warm periods over most parts of China and its 6 regions (the Northeast,North China,Changjiang River Valley,South China,the Southwest,the Northwest) were analyzed with wavelet transformation and by computing the variances of the wavelet components for the temperature grade series during January 1911 to February 2001,The prediction model for cold and warm periods has been developed and the trend of cold and warm change in the coming 10 years is predicted.The results show that the oscillation with periods of around 30-40 years was the strongest in the last 100 years and the 3-year oscillation in both winter and summer was also stronger,especially in winter.The transition time of cold and warm periods in terms of winter mean did not coincide with that of annual mean,but the difference between summer mean and annual mean is less.The processes of transition of 6 regions are somewhat different,their main characteristics are that the beginning year of significant warming for 1980s to 1990s was very different for the southern and the northern part of China.It is found that the stronger oscillation with 3-year period causes cooling in Northeast China in recent several winters.The experimental predictions show that the models used in the paper can project the major transition between high and low temperature periods.     

Trends and periodicity of daily temperature and precipitation extremes during 1960–2013 in Hunan Province,central south China

In this study, the trends and periodicity in climate extremes are examined in Hunan Province over the period 1960–2013 on the basis of 27 extreme climate indices calculated from daily temperature and precipitation records at 89 meteorological stations. The results show that in the whole province, temperature extremes exhibit a warming trend with more than 50% stations being statistically significant for 7 out of 16 temperature indices, and the nighttime temperature increases faster than the daytime temperature at the annual scale. The changes in most extreme temperature indices show strongly coherent spatial patterns. Moreover, the change rates of almost all temperature indices in north Hunan are greater than those of other regions. However, the statistically significant changes in indices of extreme precipitation are observed at fewer stations than in extreme temperature indices, forming less spatially coherent patterns. Positive trends in indices of extreme precipitation show that the amount and intensity of extreme precipitation events are generally increasing in both annual and seasonal scales, whereas the significant downward trend in consecutive wet days indicates that the precipitation becomes more even over the study period. Analysis of changes in probability distributions of extreme indices for 1960–1986 and 1987–2013 also demonstrates a remarkable shift toward warmer condition and increasing tendency in the amount and intensity of extreme precipitation during the past decades. The variations in extreme climate indices exhibit inconstant frequencies in the wavelet power spectrum. Among the 16 temperature indices, 2 of them show significant 1-year periodic oscillation and 7 of them exhibit significant 4-year cycle during some certain periods. However, significant periodic oscillations can be found in all of the precipitation indices. Wet-day precipitation and three absolute precipitation indices show significant 1-year cycle and other seven provide significant power at the 4-year period, which are mainly found during 1970–1980 and after 1992.     

Interannual relationships between Indian Summer Monsoon and Indo-Pacific coupled modes of variability during recent decades

Various SST indices in the Indo-Pacific region have been proposed in the literature in light of a long-range seasonal forecasting of the Indian Summer Monsoon (ISM). However, the dynamics associated with these different indices have never been compared in detail. To this end, the present work re-examines the variabilities of ISM rainfall, onset and withdrawal dates at interannual timescales and explores their relationships with El Ni?o-Southern Oscillation (ENSO) and various modes of coupled variability in the Indian Ocean. Based on recent findings in the literature, five SST indices are considered here: Ni?o3.4 SST index in December?CJanuary both preceding [Nino(?1)] and following the ISM [Nino(0)], South East Indian Ocean (SEIO) SST in February?CMarch, the Indian Ocean Basin (IOB) mode in April?CMay and, finally, the Indian Ocean Dipole (IOD) averaged from September to November, also, both preceding [IOD(?1)] and following the ISM [IOD(0)]. The respective merits and associated dynamics of the selected indices are compared through various correlation and regression analyses. Our first result is a deceptive one: the statistical relationships with the ISM rainfall at the continental and seasonal scales are modest and only barely significant, particularly for the IOD, IOB and Nino(?1) indices. However, a detailed analysis shows that statistical relationships with the ISM rainfall time series are statistically biased as the ISM rainfall seems to be shaped by much intraseasonal variability, linked in particular to the timing of the onset and withdrawal of the ISM. Surprisingly, analysis within the ISM season shows that Nino(?1), IOB and SEIO indices give rise to prospects of comparatively higher ISM previsibility for both the ISM onset and the amount of rainfall during the second half of the ISM season. The IOD seems to play only a secondary role. Moreover, our work shows that these indices are associated with distinct processes occurring within the Indian Ocean from late boreal winter or early spring onwards. The regression analyses also illustrate that these (local) mechanisms are dynamically and remotely linked to different phases of ENSO in the equatorial Pacific, a result which may have useful implications in terms of forecasting strategies since the choice of the better indices then hinges on the concurrent phasing of the ENSO cycle.     

1976/1977年前后热带印度洋海表温度年际异常的变化

基于1948～2005年NCEP/NCAR（美国大气研究中心/环境预测中心）再分析资料,讨论了1976/1977年前后的年代际气候变化对热带印度洋海表温度（SST）年际变率特征的影响,结果表明:在气候变化前后,ENSO都能导致热带印度洋SSTA（海表面温度异常）出现全海盆同号的变化,这种模态在冬季最强;气候变化前与变化后相比,该模态对该地区海温年际变率的方差贡献大22.1%, 达到最强的时间早2个月。气候变化前,秋季热带印度洋SSTA的主导年际变率模态表现为全海盆同号,变化后则表现为“偶极子模态”（IODM）。导致上述SSTA特征变化的重要原因,是气候变化前后印度洋风场对ENSO的响应不同。在气候变化前,与ENSO相关联的热带印度洋东风异常首先在夏季出现,而变化后则首先在春季出现,并且有一反气旋性环流异常维持在热带东南印度洋。     

ECMWF seasonal forecast system 3 and its prediction of sea surface temperature

The latest operational version of the ECMWF seasonal forecasting system is described. It shows noticeably improved skill for sea surface temperature (SST) prediction compared with previous versions, particularly with respect to El Nino related variability. Substantial skill is shown for lead times up to 1?year, although at this range the spread in the ensemble forecast implies a loss of predictability large enough to account for most of the forecast error variance, suggesting only moderate scope for improving long range El Nino forecasts. At shorter ranges, particularly 3?C6?months, skill is still substantially below the model-estimated predictability limit. SST forecast skill is higher for more recent periods than earlier ones. Analysis shows that although various factors can affect scores in particular periods, the improvement from 1994 onwards seems to be robust, and is most plausibly due to improvements in the observing system made at that time. The improvement in forecast skill is most evident for 3-month forecasts starting in February, where predictions of NINO3.4 SST from 1994 to present have been almost without fault. It is argued that in situations where the impact of model error is small, the value of improved observational data can be seen most clearly. Significant skill is also shown in the equatorial Indian Ocean, although predictive skill in parts of the tropical Atlantic are relatively poor. SST forecast errors can be especially high in the Southern Ocean.