Connections Between Different Types of El Ni~no and Southern/Northern Oscillation

It has long been acknowledged that there are two types of El Ni(n)o events,i.e.,the eastern Pacific El Ni(n)o (EE) and the central Pacific El Ni(n)o (CE),according to the initial position of the anomalous warm water and its propagation direction.In this paper,the oceanic and atmospheric evolutions and the possible mechanisms of the two types of El Ni(n)o events were examined.It is found that all the El Ni(n)o events,CE or EE,could be attributed to the joint impacts of the eastward advection of warm water from the western Pacific warm pool (WPWP) and the local warming in the equatorial eastern Pacific.Before the occurrence of CE events,WPWP had long been in a state of being anomalous warm,so the strength of eastward advection of warm water was much stronger than that of EE,which played a major role in the formation of CE.While for the EE events,most contribution came from the local warming of the equatorial eastern Pacific.It is further identified that the immediate cause leading to the difference of the two types of El Ni(n)o events was the asynchronous variations of the Southern Oscillation (SO) and the Northern Oscillation (NO) as defined by Chen in 1984.When the transition from the positive phase of the NO (NO+) to NO- was prior to that from SO+ to SO-,there would be eastward propagation of westerly anomalies from the tropical western Pacific induced by NO and hence the growth of warm sea surface temperature anomalies in WPWP and its eastward propagation.This was followed by lagged SO-induced weakening of southeast trade winds and local warming in the equatorial eastern Pacific.These were conducive to the occurrence of the CE.On the contrary,the transition from SO+ to SO- leading the transition of NO would favor the occurrence of EE type events.     

The variation of warm pool in the equatorial western pacific and its impacts on climate

1.IntroductionSincetheEINinoeventwasregardedasaresultoftheair--seainteraction(Bjerknes,1969;RasmussonandWallace,1983;Philander,1990),thetropicalPacifichasbeenPaidmuchattentionbymeteorologistsintheclimaticstudies.Particularly,thereisthehighestoceantemperatureintheequatorialwesternPacific,theuwarmpool",andthestrongestconvectionandatmosphericheatingareovertheequatorialwesternPacific,sothattheequatorialwesternPacificisveryimportanttotheclimaticvariationintheglobe.Thenumericalsimulationwithasi…     

热带MJO和ENSO对西北太平洋热带气旋影响研究综述

对西北太平洋热带气旋的活动规律作了综合评述,简单回顾了热带季节内振荡（MJO）特征和厄尔尼诺/南方涛动（ENSO）特征以及两者间关系,较系统地总结了近年来国内外学者关于MJO和ENSO对西北太平洋海域热带气旋活动影响和机理等方面的研究成果。讨论的热带气旋活动特征包括源地、频数、路径、强度、生命期和登陆等几个方面,并简单讨论了目前该领域存在的科学问题和未来可能的研究方向。     

热带太平洋海表温度年际变化对降水季节内振荡的影响

根据 １９８２—１９９２年期间的日平均 ＭＳＵ（Ｓｐｅｎｃｅｒ, １９９３）海洋降水和 ５天平均的ＣＭＡＰ（Ｘｉｅ＆ Ａｒｋｉｎ, １９９７）降水观测资料,分析了热带太平洋大气季节内振荡（ＭＪＯ）的年际变化特征。在太平洋海表温度（ＳＳＴ）年际变化的正常年份（１９８２—８３年, １９８６—８８年, １９９１—９２年）,均有明显的ＭＪＯ信号传到日界线以东并在中、东太平洋维持数月。热带ＭＪＯ活动强度的年际变化与局地ＳＳＴ的变化存在正相关。中、东太平洋降水的季节内振荡的年际变化与热带太平洋ＳＳＴ的最强正相关在Ｎｉｎｏ３区附近。以观测ＳＳＴ场强迫ＣＣＭ３大气模式的数值试验基本上真实地再现了１１年期间热带太平洋降水季节内振荡的年际变化总趋势,但模拟季节内振荡的强度较观测平均偏弱。对比分别采用周平均和月平均ＳＳＴ强迫场的积分结果,发现在中、东太平洋,二个积分模拟的降水季节内振荡强度的年际变化接近并且趋势与观测基本一致,而在西太平洋二个积分的模拟结果差别较大。这表明在热带中、东太平洋,ＳＳＴ强迫的年际变化对ＭＪＯ强度的变化有强的制约。而在ＭＪＯ总体活跃的热带西太平洋,ＳＳＴ强迫场的季节变化对模拟ＭＪＯ活动也有较大影响。ＣＣＭ３模拟     

Teleconnections of inter-annual streamflow fluctuation in Slovakia with Arctic Oscillation,North Atlantic Oscillation,Southern Oscillation,and Quasi-Biennial Oscillation phenomena

The aim of the paper is to analyze a possible teleconnection of Quasi-Biennial Oscillation （QBO）, Southern Oscillation （SO）, North Atlantic Oscillation （NAO）, and Arctic Oscillation （AO） phenomena with longterm streamflow fluctuation of the Bela River （1895-2004） and Cierny Hron River （1931-2004） （central Slovakia）. Homogeneity, long-term trends, as well as inter-annual dry and wet cycles were analyzed for the entire 1895-2004 time series of the Bela River and for the 1931-2004 time series of the Cierny Hron River. Inter-annual fluctuation of the wet and dry periods was identified using spectral analysis. The most significant period is that of 3.6 years. Other significant periods are those of 2.35 years, 13.5 years, and 21 years. Since these periods were found in other rivers of the world, as well as in SO, NAO, and AO phenomena, they can be considered as relating to the general regularity of the Earth.     

Activities of Low-Frequency Waves in the Tropical Atmosphere and ENSO

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中国降水和温度对ENSO响应的特征

该文采用一种较为客观、定量的分析方法,对1951～1990年逐月降水和温度分别转换成Gamma分布和正态分布的百分位数,对10次ENSO事件中各站的降水和温度进行合成。然后计算合成后的第一谐波的振幅和波峰位相,以确定降水和温度对ENSO的响应区域和各响应区域的响应时段,得到了18个降水响应区和7个温度响应区,确定出35个降水响应时段和9个温度响应时段。其中,降水响应最明显的区域在华北区和长江中下游及江南区。温度响应最明显的区域是东北中北部地区。     

The Role of the Solar Cycle in the Relationship Between the North Atlantic Oscillation and Northern Hemisphere Surface Temperatures

The North Atlantic Oscillation （NAO） is one of the leading modes of climate variability in the Northern Hemisphere. It has been shown that it clearly relates to changes in meteorological variables, such as surface temperature, at hemispherical scales. However, recent studies have revealed that the NAO spatial pattern also depends upon solar forcing. Therefore, its effects on meteorological variables must vary depending upon this factor. Moreover, it could be that the Sun affects climate through variability patterns, a hypothesis that is the focus of this study. We find that the relationship between the NAO/AO and hemispheric temperature varies depending upon solar activity. The results show a positive significant correlation only when solar activity is high. Also, the results support the idea that solar activity influences tropospheric climate fluctuations in the Northern Hemisphere via the fluctuations of the stratospheric polar vortex .     

1980～1983年低纬西太平洋、印度洋地区低频振荡的空间型和遥相关分析

利用1980年1月～1983年12月已滤波的OLR资料,采用经验正交函数分析方法,对1980～1981年（正常年）和1982～1983年（异常年）低纬西太平洋和印度洋地区低频振荡的空间分布及遥相关特征进行了研究。结果表明：正常年与异常年,这些地区低频振荡的强度、空间型及时间系数的变化有较大的差异。此外,还发现正常年这些地区存在3种低频遥相关,即赤道西太平洋型,北热带西太平洋型和赤道印度洋型;异常年则仅存在2种低频遥相关,即赤道西太平洋型和南热带西太平洋型。由于受厄尔诺事件的影响,东西向偶极型低频振荡中心的     

21世纪长江中下游梅雨的新特征及成因分析

利用1961—2011年观测资料分析了长江中下游梅雨各特征量的时空变化特征,尤其是21世纪的新特征,指出2000年以来梅雨入梅偏晚,出梅偏早,梅雨长度缩短,强度减弱。统计发现,在这一时段梅雨期内降水日数明显减少,在梅雨长度缩短的同时,降水日数占梅雨期长度的比例也下降,表明梅雨期内强降水越来越集中。梅雨的这种年代际变化可能和2000年以来北太平洋海温处于PDO负位相,且这一时期拉尼娜事件频繁发生有关。在PDO负位相背景下,我国汛期多雨带位置易偏北,同时由于拉尼娜事件频发,热带西太平洋海温增高,使副热带高压偏强偏西偏北,阻止了源自印度洋和孟加拉湾的西南气流向长江中下游地区的输送,迫使水汽输送路径更加偏北偏西至淮河及以北地区,长江中下游地区低层为正散度距平,梅雨降水减少。     

赤道中东太平洋表层水温异常与热带气旋活动的统计关系

利用1950-2005年西北太平洋热带气旋(TC)和赤道中东太平洋表层水温(SST)资料,统计分析了赤道中东太平洋表层水温异常与TC频数、强度、源地和路径等的关系.结果表明,赤道中东太平洋暖异常年:(1)TC发生频数偏少,较常年平均偏少2～3个,但强度偏强,强台风和超强台风发生数偏多,较常年平均偏多1个左右,且随着暖异常强度的增强,TC发生频数偏少,强度增强愈加明显;(2)TC生成位置偏东偏南,145°E以东海区TC生成频数较冷异常年和La Nina年增加明显;(3)TC路径偏东,转向路径出现频次增加,西向路径出现频次减少,从而导致日本东部海区TC通过频数增加,而我国南海和华东沿海TC通过频数减少;(4)在我国登陆的TC频数偏少,较常年平均偏少1～2个.赤道中东太平洋冷异常年,情况基本与上相反.上述影响主要是由于赤道中东太平洋SST异常导致大气环流发生异常造成的.     

Impact of the equatorial Atlantic sea surface temperature on the tropical Pacific in a CGCM

Many coupled general circulation models (CGCMs) suffer from serious model bias in the zonal gradient of sea surface temperature (SST) in the equatorial Atlantic. The bias of the equatorial Atlantic SST (EASST) may affect the interannual variability of the equatorial Atlantic, which in turn may influence the state of the tropical Pacific. In this paper we investigate the impact of the bias and the interannual variability of the EASST on the tropical Pacific in a CGCM. To determine the impact of the interannual variability of the EASST on the tropical Pacific, we compare a run in a fully coupled mode (CTL run) and a run in which the EASST is nudged toward the climatological monthly mean of the SST in the CTL run, but full air-sea coupling is allowed elsewhere (AT_m run). We find that, when the interannual variability of the EASST is excluded, the thermocline depth in the eastern equatorial Pacific is deepened, and the amplitude of the El Niño/Southern Oscillation is reduced by 30 % compared to the CTL run. The impact of the bias of the EASST on the tropical Pacific is investigated by comparing the AT_m run and a run in which the EASST is nudged toward the observed climatological monthly mean SST (AT_o run). It is found that, when the bias of the EASST is removed (i.e. AT_o run), the Gill–Matsuno type response to the warm SST anomalies in the western equatorial Atlantic induces low-level cyclonic anomalies in the eastern South Pacific, which leads to a deeper thermocline and colder SST in the South Pacific as compared to AT_m. The colder SST in the South Pacific reduces the precipitation along the South Pacific convergence zone. Our results of the model experiments demonstrate the importance of the EASST to the tropical Pacific climate.     

赤道东太平洋海温异常对6月中国南方降水影响的数值模拟

利用NCAR CAM3.0大气环流模式,研究6月长江流域及以南地区降水对前期赤道东太平洋海温异常的响应.首先,在赤道东太平洋1997年9月至1998年6月实际海温异常基础上构造的理想化海温异常,依据持续时间不同叠加相应的海温异常值在气候平均外强迫场上,设计第1组敏感性试验;其次,在上组试验中的前期9月至次年6月持续有海温异常的敏感性试验基础上,改变加入模式中的海温异常强度,设计不同强度海温异常对大气环流和降水影响的第2组试验;最后将上述海温异常值取反加入相应的赤道东太平洋区域,设计一组拉尼娜事件的试验.以(25°-30°N,110°-120°E)区域平均的降水距平值代表整个长江流域及其以南地区降水,模拟结果表明:(1)不同的持续时间强迫得到的降水距平峰值在11月,次年6月其值为最小,整体上降水距平有随持续时间的缩短而减小的趋势.表明前期秋季赤道东太平洋较强的厄尔尼诺事件发生时对6月降水有重要影响,证实了前期诊断分析的结论;(2)模式中加入不同强度的厄尔尼诺事件,在长江流域及其以南地区均有明显的降水正距平(最小降水距平为0.287 mm/d,最大为1.98 mm/d),降水正距平范围与实际情况接近,表明模式在模拟该地区异常降水时有较好的稳定性,模拟结果值得信任.另外模拟的降水距平有随着海温异常强度的增强而增大的趋势;(3)当模式中加入不同强度拉尼娜事件的海温异常时,模拟结果不稳定,与厄尔尼诺的影响结果不完全相反,与前期诊断分析结果不符.而只有在拉尼娜相当强时模式才能在长江流域及以南地区模拟出一定范围的降水负距平.     

赤道海温异常与大气的垂直环流圈

本文用实测风资料计算了赤道海面大范围异常增暖和冷却时期太平洋地区的平均径圈环流和赤道附近的平均纬圈环流。结果表明,赤道东太平洋的海面温度变化对这两种垂直环流圈有着显著的影响,并且通过这两种环流圈的相互作用,影响北太平洋付热带高压的长期变化。     

The seasonal cycle of tropical Pacific sea surface temperature in a coupled GCM

 The mechanisms responsible for the seasonal cycle in the tropical central and eastern Pacific sea surface temperature (SST) are investigated using a coupled general circulation model. We find that the annual westward propagation of SST anomalies along the equator is explained by a two-stage process. The first stage sets the phase of the variation at the eastern boundary. The strengthening of the local Hadley Circulation in boreal summer leads to a strengthening of the northward winds that blow across the equator. These stronger winds drive enhanced evaporation and entrainment cooling of the oceanic mixed layer. The resulting change in SST is greatest in the east because the mixed layer is at its shallowest there. As the east Pacific SST cools the zonal SST gradient in the central Pacific becomes more negative. This development signals the onset of the second stage in the seasonal variation of equatorial SST. In response to the anomalous SST gradient the local westward wind stress increases. This increase drives cooling of the oceanic mixed layer in which no single mechanism dominates: enhanced evaporation, wind-driven entrainment, and westward advection all contribute. We discuss the role that equatorial upwelling plays in modulating mixed layer depth and hence the entrainment cooling, and we highlight the importance of seasonal variations in mixed layer depth. In sum these processes act to propagate the SST anomaly westward. Received: 22 February 1999 / Accepted: 20 March 2000     

Correlation analyses between sea surface temperature anomalies in the eastern equatorial Pacific and the world ocean

Based on data from the Comprehensive Ocean-Atmosphere Data Set (COADS), objective analyses of the monthly mean sea surface temperature (SST) were prepared at GFDL for each month of the 110-year period 1870–1979. Time series of various indices characterizing the SST anomalies averaged over the eastern equatorial Pacific (EEP), the tropical oceans and the world ocean are presented for monthly, yearly and decadal time-averaging periods. Global correlations maps are given for each decade of the 1870–1979 period. They show the spatial connections between the monthly SST anomalies in the EEP and in other parts of the world ocean and how these connections vary for the different decades. On the intermonthly time scale the SST anomalies in the EEP and those in the tropical and world oceans are found to be highly correlated, with maximum correlations values of 0.91 at zero lag for the tropical oceans during the 1950–1959 decade and 0.81 for the world ocean during the 1970–1979 decade. Positive correlation values of r0.36 persist on average from about 4 months before to about 8 months after the EEP anomalies occur. There is a clear tendency for the tropical and world ocean anomalies to lag behind the EEP anomalies. Comparing different oceans, we find the tendency for the tropical SST anomalies in the Indian and Atlantic Oceans to lag behind those in the EEP region by about 1 and 3 months, respectively. On the interannual time scale the EEP anomalies are also well correlated with those in the other regions, having an average correlation of 0.84 for the tropical oceans and of about 0.7 for the world ocean.     

北太平洋副热带高压与赤道东部海温的相互作用

本文根据1957—1976年太平洋的月平均海平面气压和海温资料,分析了赤道东部海温与北太平洋海平面气压场的时滞相关。发现赤道海温的变化,就北太平洋而言,主要是受该洋东南部低层副热带及气旋的控制,而赤道海温对副热带高压的反馈,主要是发生在太平洋中部对流层副热带高压中心附近地区。赤道海温向副热带反气旋调整的时间平均为二个月左右,而副热带高压向赤道海温调整的时间平均为四个月左右。前者比后者更快。它们之间相互影响、相互调整形成了一种闭合的负反馈过程。整个过程约历时22个月左右,大致相当于北太平洋副热带高压和赤道海     

北方涛动同北半球温带大气环流的遥相关(一)——基本结构

本文利用1951—1980年逐季的平均值资料(共120个季)讨论了北方涛动和与其相联系的北太平洋海温与北半球海平面气压场、500hPa位势高度场遥相关的基本结构,并与南方涛动和赤道东太平洋海温的结果进行了对比分析.发现北太平洋Namias海区和加利福尼亚海流区海温的变化与北方涛动具有很密切的联系;北方涛动和这两个海区的海温同北半球中高纬度大气环流特别是PNA型和NAO型环流异常存在明显的遥相关关系;南方涛动和赤道太平洋海温同WP型或NPO型环流异常关系比较密切,而与PNA型和NAO型的关系不如北方涛动和Namias海区及加利福尼亚海流区海温的显著.     

基于奇异谱分析的南方涛动指数短期气候预测试验

The Southern Oscillation Index (SOI) time series is analyzed by means of the singular spectrum analysis (SSA) method with 60-month window length. Two major oscillatory pairs are found in the series whose pe riods are quasi-four and quasi-two years respectively. The auto-regressive model, which is developed on the basis of the Maximum Entropy Spectrum Analy sis, is fitted to each of the 9 leading components including the oscillatory pairs. The prediction of SOI with the 36-month lead is obtained from the reconstruction of these extrapolated series. Correlation coefficient between predicted series and 5 months running mean of observed series is up to 0.8. The model can successfully predict the peak and duration of the strong ENSO event from 1997 to 1998. It＇s also shown that the proper choice of reconstructed components is the key to improve the model prediction.     

Correlations between sea surface temperature in eastern equatorial Pacific and rain days over China in summer

Sea-surface temperature (SST) in the eastern, equatorial Pacific and rain days over China in summer are ana-lysed using correlation moments, that is proposed by author and principal component analysis (PCA). Occurrences of the strong rain-day anomalies over China are associated with extreme SSTs in some years. Areas significantly affect-ed by the phenomena include North and Northeast China.