厄尔尼诺

2015-10-31 08:38ElNiLaNiandthenonlinearityoftheirteleconnections
中国学术期刊文摘 2015年14期
关键词:厄尔尼诺

El Niño,La Niña,and the nonlinearity of their teleconnections

Hoerling,MP; Kumar,A; Zhong,M

Nonlinearity and asymmetry of ENSO

An,SI; Jin,FF

ENSO as an integrating concept in Earth science

McPhaden,Michael J; Zebiak,Stephen E; Glantz,Michael H

The impact of global warming on the tropical Pacific ocean and El Niño

Collins,Mat; An,Soon-ll; Cai,Wenju; et al.

两类ENSO事件分类的研究进展*

董宇佳,孟祥凤

(中国海洋大学 海洋环境学院,山东青岛266100)

近百年来的ENSO事件及其强度

王绍武,龚道溢

热点追踪

厄尔尼诺

·编者按·

按照国家气候中心ENSO监测标准,当赤道中东太平洋海水表面温度持续6个月以上比常年同期偏高0.5℃以上,则确认为一次新的厄尔尼诺事件正式形成.2014年5月到现在(2015年7月),赤道东太平洋海温距平持续增暖(超过0.5℃)已经达到15个月,暖海温最大中心位于赤道东太平洋,中心强度超过 3.0℃.基于气候动力和统计模式预测以及诊断分析结果,预计当前的厄尔尼诺事件将至少持续发展到2015/2016年冬季,强度将达到强厄尔尼诺事件标准.这次厄尔尼诺对全球和我国的天气和气候形成显著的影响,2015年5月份以来,我国南方暴雨频繁,北方出现高温天气,今年入汛以来,连续13轮强降雨袭击我国南方,尤其进入6月后,特大暴雨在长江中下游地区和西南地区愈演愈烈;印度高温仍在继续,各地的部分地区气温达到了48℃;2015年3月以来朝鲜半岛降水比常年偏少2~6成,旱情不断发展;5月底,美国得克萨斯州休斯敦市遭受强风暴袭击,布兰科河发生1929年以来最大洪水,造成多人死亡;经历了近85年来最严重干旱的巴西近日旱涝急转、暴雨成灾.

厄尔尼诺(西班牙语:El Niño),又称圣婴现象,是秘鲁、厄瓜多尔一带的渔民用以称呼一种异常气候现象的名词.主要指太平洋东部和中部的热带海洋的海水温度异常地持续变暖,使全球气候模态发生变化,造成一些地区干旱而另一些地区又降雨量过多.正常情况下,热带太平洋区域的季风洋流是从美洲走向亚洲,使西太平洋海水表面保持温暖,给印尼周围带来热带降雨.但这种模态每2~7年会发生一次异常现象,使赤道太平洋风向和洋流发生逆转,海洋表层的热流就转而向东走向美洲,随之便带走了热带降雨,使西太平洋等地区出现大面积干旱,这就是“厄尔尼诺现象”.拉尼娜(西班牙语:La Niña),是厄尔尼诺现象的反相,也称为“反厄尔尼诺”或“冷事件”,它是指赤道附近东太平洋水温反常下降的一种现象,表现为东太平洋明显变冷,同时也伴随着全球性气候异常,总是出现在厄尔尼诺现象之后.

对厄尔尼诺现象形成的原因,目前学术界还没有定论.但有一点可以肯定,即它们是海-气相互作用过程中平衡遭到破坏所致,是海-气系统在全球范围内的异常现象.在正常状况下,北半球赤道附近吹东北信风,南半球赤道附近吹东南信风.信风带动海水自东向西流动,分别形成北赤道洋流和南赤道暖流.从赤道东太平洋流出的海水,靠下层上升涌流补充,从而使这一地区下层冷水上翻,水温低于四周,形成赤道太平洋东西部海温差.但是,一旦东南信风减弱,就会造成太平洋地区的冷水上翻减少或停止,海水温度就升高,形成大范围的海水温度异常增暖.而突然增强的这股暖流沿着厄瓜多尔海岸南侵,使海水温度剧升,冷水鱼群因而大量死亡,海鸟因找不到食物而纷纷离去,渔场顿时失去生机,使沿岸国家遭到巨大损失.目前,对于厄尔尼诺事件发展形成的原因以及冷暖位相的转换机制主要有不稳定海气耦合模态理论、延迟振子理论、充放电振子理论和随机强迫理论.近年来的一些研究还发现厄尔尼诺事件的发生与地球自转速度变化有关.

面对厄尔尼诺,如何趋利避害是全球各国共同面临的问题.国家气候中心的专家针对此次厄尔尼诺提出了应对方案:要做好防范极端天气气候事件的准备,各地应作好暴雨洪涝、高温干旱等气象灾害以及极端天气气候事件的防御准备;江南、华南部分地区须加强防范暴雨洪涝,西南、西北部分地区须防御气象干旱;应该注重综合监测、预测包括厄尔尼诺在内的多种因素的变化,防范可能发生的灾害,争取做到趋利避害.

本专题得到了秦大河院士(中国气象局)、李维京研究员(中国气象局国家气候中心)、陈文研究员(中国气象局国家气候中心)的大力支持.

·热点数据排行·

截至2015年6月20日,中国知网(CNKI)和Web of Science(WOS)的数据报告显示,以“厄尔尼诺(El Niño)或ENSO暖事件(ENSO Warm Events)”为词条可以检索到的期刊文献分别为1614与1701条,本专题将相关数据按照:研究机构发文数、作者发文数、期刊发文数、被引用频次进行排行,结果如下.

研究机构发文数量排名(CNKI)

研究机构发文数量排名(WOS)

作者发文数量排名(CNKI)

作者发文数量排名(WOS)

期刊发文数量排名(CNKI)

期刊发文数量排名(WOS)

根据中国知网(CNKI)数据报告,以“厄尔尼诺”或“ENSO暖事件”为词条可以检索到的高被引论文排行结果如下.

国内数据库高被引论文排行

根据Web of Science统计数据,以“El Niño”或“ENSO Warm Events”为词条可以检索到的高被引论文排行结果如下.

国外数据库高被引论文排行

·经典文献推荐·

基于Web of Science检索结果,利用Histcite软件选取LCS(Local Citation Score,本地引用次数)TOP 30文献作为节点进行分析,得到本领域推荐的经典文献如下.

来源出版物:Geophysical Research Letters,1996,23(1): 57-60

El Niño,La Niña,and the nonlinearity of their teleconnections

Hoerling,MP; Kumar,A; Zhong,M

Abstract: The paradigm of an atmospheric system varying linearly with respect to extreme phases of the EI Niño-Southern Oscillation is questioned. It is argued that the global response to tropical Pacific sea surface temperature forcing will be inherently nonlinear. A physical basis far this intrinsic nonlinearity is the thermodynamic control on deep convection. Climate statistics for warm and cold events of the tropical Pacific are analyzed separately for the northern winter periods during 1950-1996. Composite analysis of 500-mb heights reveal planetary-scale teleconnection patterns,as noted in earlier studies. A new result is the evidence for an appreciable 35 degrees longitude phase shift between the warm and cold event circulation composites,and the two wave trains appear to have different tropical origins. A large nonlinear component in North American surface climate anomalies is also found,which is consistent with such a phase shift in teleconnections. In the Tropics,rainfall anomalies also show evidence of nonlinear behavior. The maximum rain anomalies along the equator are located east of the date line during warm events,but west of the date line during cold events. The interpretation of this behavior is complicated,however,by the fact that composite warm event SST anomalies are not the exact inverse of their cold event counterparts. Idealized atmospheric general circulation model(AGCM)experiments are performed in order to test the question of whether the observed nonlinearity is an intrinsic property of the atmospheric system. The model is forced with a composite SST anomaly that undergoes a realistic seasonally varying ENSO life cycle,as described by E. Rasmusson and T. Carpenter. Both positive and negative phases of the SST anomaly are used,and a 40-member ensemble of warm and cold event model simulations is conducted. A nonlinear climate response in the AGCM is found that closely resembles the observed composites,including a shift in the equatorial positions of the maxmium rain responses and a phase shift of teleconnection patterns in the upper troposphere. Barotropic model experiments indicate that the inherent nonlinearity in the tropical rain response may itself be responsible for the phase shift in the extratropical teleconnection patterns.

来源出版物:Journal of Climate,1997,10(8): 1769-1786

Nonlinearity and asymmetry of ENSO

An,SI; Jin,FF

Abstract: El Niño events(warm)are often stronger than La Niña events(cold). This asymmetry is an intrinsic nonlinear characteristic of the El Niño-Southern Oscillation(ENSO)phenomenon. In order to measure the nonlinearity of ENSO,the maximum potential intensity(MPI)index and the nonlinear dynamic heating(NDH)of ENSO are proposed as qualitative and quantitative measures. The 1997/98 El Niño that was recorded as the strongest event in the past century and another strong El Niño event in 1982/83 nearly reached the MPI. During these superwarming events,the normal climatological conditions of the ocean and atmosphere were collapsed completely. The huge bursts of ENSO activity manifested in these events are attributable to the nonlinear dynamic processes. Through a heat budget analysis of the ocean mixed layer it is found that throughout much of the ENSO episodes of 1982/83 and 1997/98,the NDH strengthened these warm events and weakened subsequent La Niña events. This led to the warm-cold asymmetry. It is also found that the eastward-propagating feature in these two El Niño events provided a favorable phase relationship between temperature and current that resulted in the strong nonlinear dynamical warming. For the westward-propagating El Niño events prior to the late 1970s(e.g.,1957/58 and 1972/73 ENSOs)the phase relationships between zonal temperature gradient and current and between the surface and subsurface temperature anomalies are unfavorable for nonlinear dynamic heating,and thereby the ENSO events are not strong.

Keywords: Niño-southern-oscillation; sea-surface temperature; ocean-atmosphere model; tropical pacific-ocean; El-Niño; equatorial pacific; interannual variability; climate variability; coupled model; La-Niño

来源出版物:Journal of Climate,2004,17(12): 2399-2412联系邮箱:An,SI; sian@hawaii.edu

ENSO as an integrating concept in Earth science

McPhaden,Michael J; Zebiak,Stephen E; Glantz,Michael H

Abstract: The El Niño-Southern Oscillation(ENSO)cycle of alternating warm El Niño and cold La Niña events is the dominant year-to-year climate signal on Earth. ENSO originates in the tropical Pacific through interactions between the ocean and the atmosphere,but its environmental and socioeconomic impacts are felt worldwide. Spurred on by the powerful 1997-1998 El Niño,efforts to understand the causes and consequences of ENSO have greatly expanded in the past few years. These efforts reveal the breadth of ENSO’s influence on the Earth system and the potential to exploit its predictability for societal benefit. However,many intertwined issues regarding ENSO dynamics,impacts,forecasting,and applications remain unresolved. Research to address these issues will not only lead to progress across a broad range of scientific disciplines but also provide an opportunity to educate the public and policy makers about the importance of climate variability and change in the modern world.

Keywords: 1997-1998 EL-NIÑO; sea-surface temperatures; southern-oscillation; LA-NINA; multimodel ensembles; climate forecasts;tropical pacific; united-states; ocean; evolution

来源出版物:Science,2006,314(5806): 1740-1745联系邮箱:McPhaden,Michael J; michael.j.mcphaden@noaa.gov

The impact of global warming on the tropical Pacific ocean and El Niño

Collins,Mat; An,Soon-ll; Cai,Wenju; et al.

Abstract: The El Niño-Southern Oscillation(ENSO)is a naturally occurring fluctuation that originates in the tropical Pacific region and affects ecosystems,agriculture,freshwater supplies,hurricanes and other severe weather events worldwide. Under the influence of global warming,the mean climate of the Pacific region will probably undergo significant changes. The tropical easterly trade winds are expected to weaken; surface ocean temperatures are expected to warm fastest near the equator and more slowly farther away; the equatorial thermocline that marks the transition between the wind-mixed upper ocean and deeper layers is expected to shoal; and the temperature gradients across the thermocline are expected to become steeper. Year-to-year ENSO variability is controlled by a delicate balance of amplifying and damping feedbacks,and one or more of the physical processes that are responsible for determining the characteristics of ENSO will probably be modified by climate change. Therefore,despite considerable progress in our understanding of the impact of climate change on many of the processes that contribute to El Niño variability,it is not yet possible to say whether ENSO activity will be enhanced or damped,or if the frequency of events will change.

Keywords: general-circulation model; sea-surface temperature; ENSO amplitude changes; climate-change; coupled models; atmospheric variability; multimodel ensemble; equatorial pacific; instability-wave; part I

来源出版物:Nature Geoscience,2010,3(6): 391-397联系邮箱:Collins,M; matthew.collins@metoffice.gov.uk

·推荐综述·

两类ENSO事件分类的研究进展*

董宇佳,孟祥凤

(中国海洋大学 海洋环境学院,山东青岛266100)

厄尔尼诺-南方涛动(El Niño-Southern Oseillation,即ENSO)是热带太平洋上最显著的海气藕合信号,也被认为是年际气候变化中的最强信号,它对全球大气环流和气候变化有显著影响,已经引起了各国政府和科学家的关注.Bjerknes[1]最早把厄尔尼诺和南方涛动联系起来,提出这两者事实上是热带太平洋大尺度海气相互作用的一个现象的两个方面,指出应该用大气和海洋双向藕合的观点解析ENSO,这一理论为后来的ENSO研究奠定了重要基础.

Rasmusson and Carpenter[2]对1951—1972年之间发生的6次El Niño事件进行合成分析的结果表明El Niño事件发生时海温增暖首先在南美沿岸出现,然后沿赤道向西传播.符涂斌等[3]指出除增温首先出现在赤道东太平洋的传统El Niño事件以外,还存在另一种增温出现在赤道中太平洋的El Niño事件.传统的El Niño事件首先从赤道东太平洋南美沿岸海域开始增温,然后向西传播至赤道中太平洋,一般情况下不会超过日界线.但是20世纪80年代以来的许多El Niño事件表现出了不同以往的特点,特别是21世纪发生的El Niño事件基本上都不同于传统的El Niño事件,主要表现在其增温首先出现在赤道中太平洋,然后向东传播至赤道东太平洋南美沿岸.这两类El Niño事件对全球气候造成了不同的强烈影响,因而近年来频繁发生的非传统El Niño事件成为科学家们感兴趣的热点问题.有研究认为,中太平洋El Niño事件是传统El Niño事件发生发展的一个阶段[4],但是更多学者则认为这两类事件之间是相互独立的[5-8].到目前为止,学者们针对两类ENSO提出了多种不同的分类方法,本文尝试对这些分类方法进行总结.

1两类ENSO事件的特征

关于两类El Niño事件分别有多种不同的命名,一般将传统El Niño事件称为典型El Niño、冷舌El Niño或东太平洋El Niño;而将非传统El Niño事件称为El Niño Modoki[5]、日界线El Niño[6-7]、中太平洋El Niño[9-10]或暖池El Niño[11].虽然对非传统El Niño事件采用的称呼不一致,但是这些研究基本上描述的是同一现象.

传统El Niño事件的海表增暖(Sea Surface Temperature Anomaly,SSTA)主要出现在赤道东太平洋及南美沿岸附近(图1a),海温异常有显著的传播特征.这类El Niño事件的发展过程受到整个太平洋海盆尺度变化的影响,并同热带印度洋有很强的遥相关.传统El Niño事件主要以2~7a周期年际变化为主,同时也存在如1976/1977年气候跃迁前后的年代际变化[12].

非传统El Niño事件海表增暖主要出现在赤道中太平洋(图1b),在赤道中太平洋表现为暖异常.这类El Niño事件的海温异常、表面风异常和次表层异常都局限于中太平洋,主要在局地发生、发展及消亡,不存在明显的传播特征.另外,这类ENSO事件不涉及温跃层变化,更多的是受大气驱动的影响.非传统El Niño事件除具有年际时间尺度的信号以外还具有年代际时间尺度的信号,近年来这类事件的发生频率显著增加,这可能与全球气候变暖有关[9].此外,两类ENSO事件均有很好的季节锁相特征,虽然开始时间有所不同,但是峰值基本出现在秋末到冬初时期[13].

2两类ENSO事件的判定

2.1定性角度

早期的研究主要从定性角度,通过比较两类事件海表温度异常的主要出现区域、最初发生时间、最初开始的位置等特点来粗略判定ENSO事件类型.

符涂斌[3]等比较早的提出了El Niño事件存在两种类型,通过对Fleet数值海洋中心的整编资料(FCDS)以及实时船舶观测资料进行分析,得到了El Niño事件发生时期赤道太平洋存在两种类型增暖的结论:一种增暖主要位于东太平洋,称之为“东部型”;另一种增暖主要位于日界线附近,称之为“西部型”.减恒范等[14]根据海温异常发生的时间对ENSO事件进行了分类,将明显的海温异常开始于上半年(1~6月)的ENSO事件归为第一类,将明显的海温异常开始于下半年(7~12月)的ENSO事件归为第二类.Xu等[15]认为,春季开始的El Niño事件其合成SSTA暖中心位于东赤道太平洋,而夏季开始的El Niño事件其合成SSTA暖中心位于赤道中太平洋,即东太平洋El Niño事件开始于春季,中太平洋El Niño事件开始于夏季.林学椿等[16]对ENSO事件进行了个例分析,得到不同海水增(降)温过程的两类El Niño(反El Niño事件)事件,将增(降)温最先发生在赤道太平洋130˚W以东的ENSO事件定义为东部型,将增(降)温最先发生在赤道太平洋130˚W以西的ENSO事件定义为中部型.

Niño3指数与Niño4指数分别为SSTA在Niño3区域和Niño4区域的区域平均值,Kug等[11]基于这两个传统对两类事件进行了定性划分,他们指出可以通过比较它们的振幅相对大小来区分两类ENSO事件,当两个指数中的任意一个大于其相应的标准偏差时定义为一次El Niño事件,当Niño3指数大于Niño4指数时为冷舌El Niño事件,反之为暖池El Niño事件.他们还指出,两类La Niña事件SSTA的分布型没有两类El Niño事件SSTA分布型的差异那么显著,这是因为传统的La Niña事件本身就相对于El Niño事件位置更偏西.

曹璐等[17]将Niño3指数和Niño4指数进行3个月滑动平均处理后,作为指数组针对峰值类型和传播类型两方面来对ENSO事件进行分类.峰值类型的判定标准为,当ENSO事件达到峰值时,若标准化的Niño3指数大于标准化的Niño4指数,定义为东太平洋ENSO(Eastern Pacific-ENSO,EP-ENSO)事件,反之则定义为中太平洋ENSO(Central Pacific-ENSO,CP-ENSO)事件.传播类型(即传统意义下的ENSO类型)的判定标准为,若Niño3指数较Niño4指数先达到阈值(±0.5℃)则定义为EP-ENSO事件,反之定义为CP-ENSO事件.若两指数同时达到阈值则以强度大小来作为判定标准,当Niño3指数大于Niño4指数时,定义为EP-ENSO事件,反之则定义为CP-ENSO事件.

另外一些研究也采用Niño3指数和Niño4指数相对大小判定El Niño事件的类型[10,18-19].同时Kug等[11,19]的研究表明,相对于两类El Niño事件来说,两类La Niña事件的区别不那么明显;而Ren等[12]认为,自气候跃迁以后,当去掉强烈的背景年代信号时,两类La Niña事件也是能够明显区分开的.

2.2定量角度

唐佑民等[20]采用聚类分析方法,按海温在El Niño事件过程中的演变特征,根据El Niño事件爆发时海水增温首先出现的位置,将El Niño事件分为两类,I类El Niño事件增暖最初出现在日界线附近,II类El Niño事件最初增暖出现在赤道东太平洋.将El Niño事件发展的不同阶段分别进行合成分析,他们指出,两类El Niño事件海温异常的传播特征存在显著区别.唐佑民等[20]的分类结果与林学椿等[16]结果类似,这是因为在ENSO事件中,海温开始增(降)温位置的不同,在较大程度上决定了海温演变过程中的特征存在差异.

另外一些研究则开始通过定义指数组将其定量化,以期得到更为准确的分类.例如:Ashok等[5]通过经验正交分解(Empirical Orthogonal Function,EOF)方法分析发现El Niño Modoki的热带太平洋海温异常分布呈纬向三极子结构,据此特点他们定义了El Niño Modoki index(EMI指数);Li等[21]在此基础上考虑了不同关键区的贡献不同进一步定义了IEMI指数(improved El Niño Modoki index);陈圣劫等[22]通过多变量经验正交函数分解也发现了三极子的分布结构,同时他们的研究发现El Niño和El Niño Modoki的海气耦合特征存在显著差异,故而选取上层热含量定义了Heat Content El Niño Index(HCEI)和Heat Content El Niño Modoki Index(HCEMI)指数来分别反映和区分两类El Niño事件;Kao等[9]和秦坚肇等[23](待刊)通过联合回归EOF方法定义东太平洋指数/中太平洋指数(Eastern Pacific Index/Central Pacific Index,EPI/CPI);Xu等[24]通过奇异值分解(Singular Value Decomposition,SVD)方法定义东太平洋次表层指数/中太平洋次表层指数(Eastern Pacific Subsurface Index/Central Pacific Subsurface Index,EPSI/CPSI);Ren等[25]对Niño3,Niño4指数进行简单的非线性变换提出描述冷舌ENSO(Cold Tongue-ENSO,CT-ENSO)和暖池ENSO(warm Pool-ENSO,WP-ENSO)的NCT和NWP指数;另外,Yu等[13]选取赤道东太平洋和赤道中太平洋次表层海洋温度定义次表层海温指数组.

2.2.1Niño3.4 /Trans-Niño Index(TNI)

Trenberth等[4]认为,要描述ENSO事件的发展演变过程以及ENSO事件之间的差异需要至少两个自由度,他们指出,可以用Niño3.4指数和TNI来实现这一目的:Niño3.4 SST指数用来描述中东太平洋平均的SSTA,TNI用来描述ENSO事件期间中、东太平洋SSTA的梯度.TNI定义为标准化的Niño l+2(10˚S~0˚,8˚~90˚W)和Niño4(5˚S~5˚N,160˚E~150˚W)SST指数之差.两指数的超前滞后相关分析结果表明它们可以描述过去的100 a间ENSO的发展演化情况,包括1976/77年的气候跃迁.Ashok等[5]年的研究认为,赤道太平洋SSTA的第一、二EOF模态分别与Niño3.4指数和TNI分别密切相关,在所谓的El Niño Modoki事件和传统El Niño事件发生时期,这两个指数的演变特征是不同的,因此可以用这组指数描述两类不同事件.但是TNI的不足之处在于并没有考虑热带西太平洋在描述非传统El Niño事件过程中的重要性.

2.2.2EMI

为了使用单一指数来表征中太平洋ENSO事件,Ashok[5]等困在考虑热带西太平洋SSTA的作用的前提下提出了EMI.对热带太平洋SSTA进行EOF分析的结果表明,前两个EOF模态可以分别代表传统El Niño事件和El Niño Modoki事件.第二EOF模态空间分布型,即El Niño Modoki的分布型,表现为赤道中太平洋为暖异常,暖异常中心两侧的东、西太平洋沿赤道分布有冷异常,且暖异常和冷异常的振幅是相当的;在较高纬度,赤道中太平洋的暖异常在两半球分别向东扩展.可见,在赤道太平洋地区存在三个涉及El Niño Modoki的关键区.基于SSTA分布独特的三极子结构,他们定义了EMI:

公式1右边的方括号分别表示SSTA在区域A(165˚E~140˚W,10˚S~10˚N),B(110˚W~70˚W,15˚S~5˚N),C(125˚E~145˚E,10˚S~20˚N)内的平均.区域A,B,C分别为EOF第二模态空间分布型的3个关键区域,即暖异常区域和左右两侧的冷异常区域.将El Niño Modoki事件定义为指数振幅大于等于0.7倍季节标准偏差的事件.

相关性分析结果表明,EMI同EOF第二模的时间序列PC2(Principal Component,PC)有很高的相关性,说明EMI在很大程度上可以捕捉到赤道太平洋SSTA进行EOF分解得到的第二个模态的分布型,即可以恰当的描述El Niño Modoki事件.EMI同TNI之间的相关性也很高,两者都可以用来表示El Niño Modoki.但是EMI更加有优势,主要表现在两方面,一方面,EMI同PC2的相关性高于TNI同PC2的相关性,这使得EMI更有优势;另一方面,EMI考虑了赤道西太平洋对于El Niño Modoki起到的作用.

2.2.3IEMI

根据Ashok等[5]的方法,Li等[21]对EMI进行改进,提出了IEMI,IEMI表达方式如下:

公式2中的权重系数由线性回归计算得到,Ta,A、Ta,B和Ta,C分别代表SSTA在区域A,B,C中的平均,3个区域的范围同Ashok等[5]提到的区域范围一致,分别是与El Niño Modoki相关的3个关键区.当标准化的指数连续5个月大于等于一个标准偏差时定义为一个El Niño Modoki事件.相对于EMI的0.7个标准偏差来说IEMI将确定El Niño Modoki的阂值提高为一个标准偏差,所以IEMI更能捕捉到El Niño Modoki事件,并且排除传统El Niño信号的干扰.

由公式3和4可以看到,相较于EMI来说,IEMI的改进之处在于考虑了El Niño Modoki时期赤道东、西太平洋区域的SSTA贡献的差异,即在EMI的基础上对各区域添加了不同权重.所以IEMI不仅考虑了热带西太平洋SSTA在捕捉ElNiño Modoki中的作用,同时也考虑到等式右边两项(分别与热带东、西太平洋相关)对EOF第二模态SSTA方差贡献率的不同.因此IEMI能明确地识别出2002/03,2004/05年的El Niño Modoki事件,而在严格意义上,EMI是无法将2002/03,2004/05年确定为El Niño Modoki事件的.相关分析的结果表明,相比于EMI来说IEMI增加了同PC2的相关性的同时也减小了同PC1的相关性,即IEMI同PC1更加正交,这有效的削弱了El Niño信号的干扰IEMI能更好的区分两类El Niño事件.

2.2.4EPI/CPI

Kao等[9]认为SSTA的第二EOF分布型中同时包含了Niñol+2和Niño4的信息,故不能准确的描述新型ENSO事件的主要特征,他们同样基于EOF分析提出了新的指数来描述新型ENSO事件.

他们采用联合回归EOF方法来分离两类ENSO事件,即在进行EOF分析之前,首先从原始SSTA中减去原始SSTA和Niñol+2指数的回归值,对得到的差值SSTA进行EOF分析得到的第一模态即代表CP-ENSO;同理,在进行EOF分析之前,首先从原始SSTA中减去原始SSTA和Niño4指数的回归值,对得到的差值SSTA进行EOF分析可得到代表EP-ENSO的第一EOF模态.将两个EOF第一模态时间序列分别定义为CPI和EPI,当CPI(EPI)超过一个标准偏差时定义为CP(EP)-ENSO.相关性分析结果表明,CPI同Ashok等[5]提出的EMI指数具有很高的相关性,它们都可以识别非传统ENSO事件.CPI和EPI可以较好地描述两类ENSO事件发展的演变过程,但是计算过程却较为复杂繁琐.

秦坚肇等[23]基于Kao等[9]提出的联合回归EOF方法,定义了新的EPI(EP-ENSO Index)和CPI(CP-ENSO Index).

公式5中SSTA[A1]和SSTA[B1]分别表示SSTA在区域A1(5˚S~5˚N,110˚W~80˚W)和区域B1(5˚S~10˚N,150˚E~180˚E)内的平均,权重系数用于平衡各区域面积间的比重,权重系数EA=2/5,EB=3/5;等式6中SSTA[A2]、SSTA[B2]和SSTA[C],分别表示SSTA在区域A2(10˚S~10˚N,170˚E~140˚W)、区域B2(10˚S~5˚N,130˚E~150˚E)和区域C(5˚S~10˚N,100˚W~80˚)内的平均,权重系数CA=10/15,CB=3/15,CC=2/15.他们定义当标准化的EPI0.7≧(≦-0.7)且持续4个月以上的事件定义为EP-EI Niño(La Niña)事件;当标准化的CPI0.8≧(≦-0.8)且持续4个月以上的事件定义为CP-El Niño(La Niña)事件.EPI和CPI之间的相关性很小,可以更加清楚的区分两类ENSO事件.同时指数组可以恰当的展现两类ENSO事件的不同周期,并且能够指示两类ENSO发展演变过程中的各个阶段;两个指数不仅可以很好的描述事件发生时热带太平洋SSTA的发展演变过程,准确的捕捉到两类ENSO事件,超前滞后相关分析的结果也表明,这组指数可以很好的反映气候跃迁前后ENSO的变化.因此,用这个指数组对ENSO事件进行分类有其合理性.另外,这一指数组仅涉及到区域平均值的线性计算,过程更加简单.

2.2.5次表层海温指数

Yu等[13]利用1958—2001年海洋同化资料东太平洋(80˚W~90˚W,5˚S~5˚N)和中太平洋(160˚E~150˚W,5˚S~5˚N)100米以上区域内的平均海温异常得到东太平洋次表层海温指数和中太平洋次表层海温指数.他们指出,上述次表层指数较传统Niño指数具有更强的独立性和更大的偏度,更适合于识别东太型和中太型ENSO特性.基于该指数识别的两类ENSO事件,强El Niño事件主要表现出东太型特征,而强La Niña事件则更趋向于中太型特征;对于弱的El Niño事件和强La Niña事件,则表现出相反的特性.

2.2.6NCP/NWP

由于Niño3指数和Niño4指数之间的相关性很高,不能有效区分两类事件,Ren等[25]提出将Niño3指数和Niño4指数通过变换系数α进行一个简单的非线性变换构造两个新的Niño指数,即冷舌El Niño指数(NCT)和暖池El Niño指数(NWP),来对两类事件进行分类.这对指数可以方便的描述两类ENSO事件的主要SSTA分布型、不同位相的传播特征以及ENSO状态的变化情况,两个新的Niño指数定义为:

公式7和8中N3和N4分别代表Niño3指数和Niño4指数,新的指数组仅是Niño3指数与Niño4指数的简单非线性组合,但是受到ENSO位相的限制.当NWP大于一个阈值,例如一个标准偏差时,视为暖池El Niño事件;当NCT大于一个阈值,例如一个标准偏差时,视为冷舌El Niño事件.相比于Niño3指数和Niño4指数之间很高的相关性,N3和N4之间的相关很小,因此,新的指数能够更好地区分两类ENSO事件.对两个指数进行超前滞后分析,结果表明在赤道SSTA纬向传播方面它们可以有效捕捉到气候跃迁前后ENSO的变化.另外,气候跃迁之后两指数近乎是独立的,这也说明了两类ENSO事件之间的独立性.

2.2.7EPSI/CPSI

Xu等[24]对热带太平洋SST和海洋次表层温度(Subsurface Ocean Temperature,SOT)异常进行奇异值分解,结果表明,SOT的第一、三模态分别同两类ENSO事件密切相关,因此,他们将SOT的第一、三SVD模态时间系数分别定义为EPSI和CPSI.将这组指数同Kao等[11]和Ren等[25]提出的指数组进行比较,相关性分析和小波分析的结果表明,EPSI和NCT具有很高的相关性,并且可以捕捉到EP-ENSO事件的年际变化,另外,CPSI和CP-ENSO事件之间也有一定的关系,可以用来表征CP-ENSO事件.

2.2.8Typical El Niño Index/Central El Niño Index(TENT/CENT)

Li等[26]将SSTA的第一、二EOF模的时间系数同去趋势的冬季SSTA进行回归处理得到它们的SSTA分布型,定义回归的第一、二EOF模态之差为传统El Niño SST分布型,两者之和为中太平洋El Niño SST分布型.相对于单纯的由EOF前两个模态定义两类事件,新的SSTA分布型更接近于观测事实,且它们之间较高的相关性也符合两类事件并不正交这一事实[10].将TENT和CENT分别定义为标准化了的去趋势冬季SSTA向上述两类新的分布型的投影系数.当TENT大于CENT和0.6℃,且热带东太平洋最大SSTA大于1.2℃时定义为一个传统El Niño事件;当CENT大于TENT和0.6℃,且热带中太平洋最大SSTA大于0.9℃时定义为一个中太平洋El Niño事件.虽然这组指数可以描述两类事件的非正交特征以及周期特征,但是计算过程却较复杂.

2.2.9HCEI/HCEMI

由于ENSO事件发生时期,海洋热力异常信号不仅出现在海洋表面,同样存在于海洋内部,而且在海洋内部的信号可能更明显,所以陈圣劫等[22]选取了与海洋表层和次表层海温有关的上层海洋热含量(Heat Content,HC)作为热力特征量来构建区分El Niño事件类型的指数.他们首先对SST, HC, SLP,850 hPa纬向风、850 hPa经向风、200 hPa位势高度和OLR共7个要素场进行多变量经验正交函数分解(Multivariate Empirical Orthogonal Functions MV-EOFs),得到的第一、二模态可以分别代表传统El Niño事件和中太平洋El Niño事件,根据两个模态的空间分布型来确定对两类事件起关键作用的区域,得到的两个指数计算公式如下:

公式9和10中IHCE、IHCEM分别表示ICEH和IHCEM,分别用于判定传统El Niño事件和中太平洋El Niño事件.下标HCA表示热含量距平,下标AE、BE、AEM、BEM、CEM分别代表计算区域,其中,AE(10˚S~10˚N,120˚W~80˚W)和AEM(15˚S~5˚N,170˚E~14˚W)为MV-EOFs得到的前两个模态空间分布型中的正异常值主要分布区域,而BE(10˚S~10˚N,120˚E~160˚E)、BEM(0˚~10˚N,120˚E~140˚E)和CEM(20˚S~5˚S,115˚W~80˚W)则为负异常值主要分布区域.同Kao等[9]、Yu等[13]以及Ren等[25]提出的指数组相比,IHCE和IHCEM之间的相关系数更小,说明由这两个指数分别确定的两类事件具有更高的独立性.另外,这组指数不仅可以对El Niño事件进行分类,同时它们与两类事件发生时期的海气耦合过程是紧密联系的,可以更好的表征事件发生时的海气耦合特征.这对指数对几个有争议的El Niño事件也可以做出更明确的区分.

2.2.10E/C

Takahashi等[27]采用HadlSST数据集对月平均的SSTA计算了EOF模,他们指出EOF的前两个模态无法描述两类不同的ENSO现象,而是描述了ENSO的非线性演化.基于主EOF模态,他们定义了两个新的正交指数E和C,这两个指数分别同东赤道太平洋的极端暖事件以及中赤道太平洋的冷事件和包括El Niño Modoki及CP-El Niño在内的中等暖事件相关,可写为如下形式:

公式11和12中PC1和PC2分别为第一和第二EOF模的时间系数,由于指数C和E分别同中太平洋SST指数(Niño4)以及东太平洋SST指数(Niño1+2)有很好的相关性,因此这组指数可以近似写为如下形式:

公式13和14中,Niño1+2和Niño4分别表示Niño1+2区域以及Niño 4区域SSTA的区域平均值.以C和E为坐标轴构建坐标系时,极端事件沿E轴分布,而中等事件一般沿C轴分布.

3两类ENSO事件与气候跃迁

20世纪70年代后期,伴随着气候跃迁ENSO事件也发生了显著的变化.气候跃迁以前以准4a模为主导,主要是周期为3~4a的冷舌ENSO事件,而暖池ENSO事件是否存在尚有争议;气候跃迁以后,主导模态为准两年模与准四年模共存,暖池ENSO事件出现愈加频繁,冷舌ENSO事件则具有更大的强度,ENSO冷暖事件都可以被清晰的区分为两类事件.因此,当除去掩盖暖池ENSO特征的年代变化时,两类ENSO事件可以体现ENSO特征的变化.

对气候跃迁以后的海表面温度场进行了经验正交分解[5,8],得到的第一EOF模空间分布型表现为异常中心位于赤道东太平洋,并且向赤道中太平洋扩展;而第二EOF空间分布型则表现为在热带中太平洋为暖SSTA,其两侧的热带东、西太平洋为冷SSTA.由于前两个EOF模所解释的方差可以很好的分离[28],并且得到了合成分析以及复杂经验正交分解(Complex EOF,CEOF)分析研究结果的支持,因此这两种空间分布可以代表气候变化的不同模.前两个EOF模分别对应于温度异常中心位于赤道东太平洋的典型El Niño事件以及异常中心位于赤道中太平洋的El Niño Modoki事件.第一EOF模的时间系数同Niño3指数的相关性很高,即第一EOF模可以很好地表征典型El Niño事件,而第二EOF模的时间系数同Niño 3指数的相关性很低,即这一EOF模与典型El Niño事件无关.

4总结

典型El Niño事件的正海温异常主要出现在赤道东太平洋,在赤道西太平洋为负的海温异常;El Niño Modoki事件的正海温异常中心则位于赤道中太平洋.两类ENSO事件海表温度异常中心位置的不同会引起不同的环流异常以及气候效应,因此,在研究EP/CP-ENSO时对事件进行正确的分类是必要的.

早期的研究主要从定型的角度进行分类;在定量研究方面,许多学者根据所关注重点的不同选取了不同指数组对两类事件进行分类,一些直接采用Niño指数或者间接用Niño指数的组合或选取非对称更显著区域的海温指数来划分两类事件,另一些则通过EOF、联合回归EOF、多元变量EOF、SVD等方法得到能够描述两类事件的模态,进而定义能够区分两类事件的指数组.而从物理意义上来讲,基于EOF得来的指数会受到数学正交性的约束,因此并非区分两类事件的理想指数.另外,这些对两类事件的区分能力是有差异的,计算过程的繁简程度也不同,在实际应用的过程中需要根据自己的需要选取不同的指数组进行研究.相对于单一指数来说,指数组虽然可以更好地区分两类事件,但是要将其应用于对ENSO事件进行检测的实际业务工作中就显得过于繁琐了,能否找到可以很好区分两类事件的单一指数以及找到将指数组方便的应用于实际业务预测的方法,有待进一步研究.

·高被引论文摘要·

被引频次:225

近百年来的ENSO事件及其强度

王绍武,龚道溢

利用Niño3区、Niño C区海表温度序列及两个SOI序列,同时考虑SST和SOI建立了1867—1998季分辨率的ENSO指数序列.根据ENSO指数序列,并参考Wright的SOI指数及其它材料,确认了1867—1998年ENSO事件,共确定出32次暖事件(正SST负SOI)及32次冷事件(负SST正SOI)对每次事件的强度分强、中、弱三等进行了评估.虽然1982/1983年暖事件的峰值最高,但从整个事件的平均强度来看,1997/1998年的暖事件则是130年来最强的一次.近20年是暖事件的多发期.

ENSO;强度;季分辨率

来源出版物:气象,1999,25(1): 9-13

被引频次:164

厄尔尼诺的发生与赤道西太平洋暖池次表层海温异常

李崇银,穆明权

摘要:摘要通过资料分析研究了厄尔尼诺事件的爆发与西太平洋暖池次表层海温正异常的重要关系.结果表明,El Niño事件之前暖池次表层海温都有明显的持续升高;这种暖池次表层海温正距平的出现,尤其是它向赤道中东太平洋的传播对El Niño事件的爆发有直接关系,是导致El Niño事件的重要原因.分析还表明,暖池次表层海温正距平的东移原因在于赤道西太平洋地区西风异常的发生和向东扩展.

关键词:厄尔尼诺(El Niño);暖池海温异常

来源出版物:大气科学,1999,23(5): 513-521

被引频次:106

厄尔尼诺与我国汛期降水

林学椿,于淑秋

摘要:本文详细地讨论了厄尔尼诺与我国汛期大尺度降水的关系.指出,厄尔尼诺东部型,北太平洋海温的三个主要正负距平区的结构具有PNA遥相关型;厄尔尼诺中部型,北太平洋海温的三个主要正负距平区分布在赤道东太平洋到千岛群岛一线上.进而指出,厄尔尼诺东部型峰期过后,我国汛期降水的大尺度特征是长江流域降水偏少,江南和华北地区降水偏多.在厄尔尼诺中部型峰期过后则相反,长江流域降水偏多,江南和华北降水偏少.

关键词:厄尔尼诺;北太平洋海温;汛期降水

来源出版物:气象学报,1998,51(4): 434-441

被引频次:97

厄尔尼诺现象对北半球大气环流和中国降水的影响

赵振国

摘要:本文主要讨论了厄尔尼诺现象对北半球大气环流和中国季风降水的影响.研究表明,在厄尔尼诺开始年的春夏季,对流层上部位势高度和副热带高压都处在由弱到强的转变状态,我国东部地区大范围少雨;秋季发生明显的趋势转折,秋季到次年夏季,对流层上部位势高度升高,副高增强西伸,除次年2、3月份全国大范围少雨外,其余月份大都为南多北少的分布型,这种分布形态在开始年秋季最典型.厄尔尼诺开始年、次年,长江中下游入梅期偏晚.

关键词:厄尔尼诺;大气环流;中国;降水;入梅

来源出版物:大气科学,1996,20(4): 422-428

被引频次:93

厄尔尼诺和反厄尔尼诺事件与西北太平洋台风活动

何敏,宋文玲,陈兴芳

摘要:用统计相关和典型年合成方法分析了厄尔尼诺和反厄尔尼诺事件与西北太平洋台风活动的关系,指出厄尔尼诺年台风活动减少,反厄尔尼诺年台风活动增加,而且台风活动与厄尔尼诺、反厄尔尼诺事件起始和终止时间、强度、台风生成区域有关.利用厄尔尼诺和反厄尔尼诺年台风活动频数的统计特征,及台风频数与海温等要素的时滞相关关系,为台风频数的预测提供了有益的信息.还应用奇异值分解方法,分析了高度场和海温场的相关关系.结果表明,厄尔尼诺年海气耦合作用将造成不利于台风发展的环流条件,因此台风偏少,反厄尔尼诺年则出现相反的情况.

关键词:台风;厄尔尼诺和反厄尔尼诺;奇异值分解

来源出版物:热带气象学报,1999,15(1): 17-25

被引频次:84

1998年大气环流异常及其对中国气候异常的影响

李维京

摘要:1998年受ENSO事件和青藏高原冬春季积雪多等因素的影响,北半球大气环流的主要特征是:500 hPa西太平洋副高强大,夏季副高脊线位置偏南;冬夏季风均较弱;赤道辐合带异常偏弱,在西太平洋生成和登陆影响我国的台风和热带风暴异常偏少;夏季亚洲中高纬度经向环流发展,其它季节则以纬向环流为主;这些环流异常是影响1998年中国气候极其异常的主要原因.

关键词:厄尔尼诺;环流异常;气候异常

来源出版物:气象,1999,25(4): 20-25

被引频次:69

我国暖冬气候及其成因分析

孙林海,赵振国

摘要:重点分析了20世纪80年代以来,我国冬季持续偏暖、出现连续暖冬的成因.初步分析表明,我国气温存在着大约30年左右的年代际变化趋势,厄尔尼诺事件的发生、东亚冬季风减弱、西太平洋副热带高压增强、欧亚大陆积雪面积减小、火山活动减少以及温室效应等,都可能是造成我国冬季持续偏暖的主要因素.

关键词:暖冬气候;成因分析;ENSO;西太平洋副高;东亚冬季风

来源出版物:气象,2004,30(12): 57-60

被引频次:64

印度洋海温偶极子和太平洋海温异常

李崇银,穆明权,潘静

摘要:用近百年观测资料分析了赤道印度洋海温(SST)变化,其偶极子型振荡的特征确实存在.这种偶极子型振荡在9~11月最强,而在1~4月最弱;还表现出有年际变化和年代际变化.这个偶极子的正位相型(海温西高东低)一般强于其负位相型(海温东高西低).尽管在极个别年赤道印度洋海温偶极子似乎独立于太平洋厄尔尼诺-南方涛动(ENSO),但总体而论,赤道印度洋海温偶极子与赤道太平洋海温偶极子(类似反ENSO模)有很好负相关.联系它们的主要物理过程主要是赤道大气纬向(Walker)环流的异常.

关键词:印度洋海温偶极子;太平洋海温异常;反ENSO模

来源出版物:科学通报,2001,46(20): 1747-1750

被引频次:64

赤道东太平洋海温与我国江淮流域夏季旱涝的成因分析

励申申,寿绍文

摘要:对赤道东太平洋和西太平洋暖池海温与江淮流域夏季降水的关系作功率谱分析和相关分析.指出秋冬季增暖的厄尔尼诺事件对应江淮流域夏季降水偏多,春夏季开始发展的ENSO事件江淮流域夏季降水偏少.对两种在不同季节增暖的ENSO事件对应的异常流场特征及其对江淮流域降水的影响用1991年和1994年实例作对比分析.不同季节增暖的ENSO事件在太平洋热带地区环流调整的不同阶段可能是影响夏季风活动和东亚夏季天气气候异常的主要原因.

关键词:厄尔尼诺;西太平洋暖池;江淮流域;夏季降水;环流调整

来源出版物:应用气象学报,2000,11(3): 331-338

被引频次:60

1845—1988年期间厄尔尼诺事件与我国西北旱涝

朱炳瑗,李栋梁

摘要:本文应用1958—1988年陕、甘、宁、青四省(区)3~9月的降水量资料,分析了厄尔尼诺事件当年与次年西北降水量的差异性,结果表明在厄尔尼诺事件当年,青海省东部、甘肃有中东部、宁夏全区和陕北降水量明显偏少,而在厄尔尼诺事件次年明显偏多,上述地方降水量差异是显著的.根据Quinn等人划分的历史厄尔尼诺事件资料及西北各省近500年气候历史资料,我们分析了1845—1957年厄尔尼诺事件与西北旱涝的关系,从这些定性或半定量的资料分析中可以看出,上述结论在历史上也是成立的.特别是西北历史上的几个大旱年,基本上出现在连续发生厄尔尼诺事件的年份中.

关键词:厄尔尼诺事件;旱涝;气候变化

来源出版物:大气科学,1992,16(2): 185-192

被引频次:702

Pacific-East Asian teleconnection: how does ENSO affect East Asian climate?

Wang,B; Wu,RG; Fu,XH

Abstract: Observational evidence is presented to show a teleconnection between the central Pacific and East Asia during the extreme phases of ENSO cycles. This Pacific-East Asian teleconnection is confined to the lower troposphere. The key system that bridges the warm(cold)events in the eastern Pacific and the weak(strong)East Asian winter monsoons is an anomalous lower-tropospheric anticyclone(cyclone)located in the western North Pacific. The western North Pacific wind anomalies develop rapidly in late fall of the year when a strong warm or cold event matures. The anomalies persist until the following spring or early summer,causing anomalously wet(dry)conditions along the East Asian polar front stretching from southern China northeastward to the east of Japan(Kuroshio extension). Using atmospheric general circulation and intermediate models,the authors show that the anomalous Philippine Sea anticyclone results from a Rossby-wave response to suppressed convective heating,which is induced by both the in situ ocean surface cooling and the subsidence forced remotely by the central Pacific warming. The development of the anticyclone is nearly concurrent with the enhancement of the local sea surface cooling. Both the anticyclone and the cooling region propagate slowly eastward. The development and persistence of the teleconnection is primarily attributed to a positive thermodynamic feedback between the anticyclone and the sea surface cooling in the presence of mean northeasterly trades. The rapid establishment of the Philippine Sea wind and SST anomalies implies the occurrence of extratropical-tropical interactions through cold surge-induced exchanges of surface buoyancy flux. The central Pacific warming plays an essential role in the development of the western Pacific cooling and the wind anomalies by setting up a favorable environment for the anticyclone-SST interaction and midlatitude-tropical interaction in the western North Pacific.

Keywords: Niño southern oscillation; sea-surface temperature; El-Niño; summer monsoon; biennial oscillation; toga coare; precipitation;atmosphere; winter; model

来源出版物:Journal of Climate,2000,13(9): 1517-1536

被引频次:667

Increased El Niño frequency in a climate model forced by future greenhouse warming

Timmermann,A; Oberhuber,J; Bacher,A; et al.

Abstract: The El Niño/Southern Oscillation(ENSO)phenomenon is the strongest natural interannual climate fluctuation(1). ENSO originates in the tropical Pacific Ocean and has large effects on the ecology of the region,but it also influences the entire global climate system and affects the societies and economies of many countries(2). ENSO can be understood as an irregular low-frequency oscillation between a warm(El Niño)and a cold(La Niña)state,The strong EI Niños of 1982/1983 and 1997/1998,along with the more frequent occurrences of El Niños during the past few decades,raise the question of whether human-induced ‘greenhouse’ warming affects,or willaffect,ENSO3,Several global climate models have been applied to transient greenhouse-gas-induced warming simulations to address this question(4-6)but the results have been debated owing to the inability of the models to fully simulate ENSO(because of their coarse equatorial resolution)(7),Here we present results from a global climate model with sufficient resolution in the tropics to adequately represent the narrow equatorial upwelling and low-frequency waves. When the model is forced by a realistic future scenario of increasing greenhouse-gas concentrations,more frequent El Niño-like conditions and stronger cold events in the tropical Pacific Ocean result.

Keywords: interannual variability; ENSO; event; chaos; cycle

来源出版物:Nature,1999,398(6729): 694-697

被引频次:567

El Niño Modoki and its possible teleconnection

Ashok,Karumuri; Behera,Swadhin K; Rao,Suryachandra A; et al.

Abstract: Using observed data sets mainly for the period 1979-2005,we find that anomalous warming events different from conventional El Niño events occur in the central equatorial Pacific. This unique warming in the central equatorial Pacific associated with a horseshoe pattern is flanked by a colder sea surface temperature anomaly(SSTA)on both sides along the equator. empirical orthogonal function(EOF)analysis of monthly tropical Pacific SSTA shows that these events are represented by the second mode that explains 12% of the variance. Since a majority of such events are not part of El Niño evolution,the phenomenon is named as El Niño Modoki(pseudo-El Niño)(“Modoki” is a classical Japanese word,which means “a similar but different thing”). The El Niño Modoki involves ocean-atmosphere coupled processes which include a unique tripolar sea level pressure pattern during the evolution,analogous to the Southern Oscillation in the case of El Niño. Hence the total entity is named as El Niño-Southern Oscillation(ENSO)Modoki. The ENSO Modoki events significantly influence the temperature and precipitation over many parts of the globe. Depending on the season,the impacts over regions such as the Far East including Japan,New Zealand,western coast of United States,etc.,are opposite to those of the conventional ENSO. The difference maps between the two periods of 1979-2004 and 1958-1978 for various oceanic/atmospheric variables suggest that the recent weakening of equatorial easterlies related to weakened zonal sea surface temperature gradient led to more flattening of the thermocline. This appears to be a cause of more frequent and persistent occurrence of the ENSO Modoki event during recent decades.

Keywords: indian-ocean dipole; sea-surface temperature; pacific decadal variability; tropical pacific; southern-oscillation; equatorial pacific; air-temperature; climate variability; western pacific; global climate

来源出版物:Journal of Geophysical Research-Oceans,2009,112(C11): C11007联系邮箱:Ashok,Karumuri; ashok@apcc21.net

被引频次:536

Variability of El Niño/Southern Oscillation activity at millennial timescales during the Holocene epoch

Moy,CM; Seltzer,GO; Rodbell,DT; et al.

Abstract: The variability of El Niño/Southern Oscillation(ENSO)during the Holocene epoch,in particular on millennial timescales,is poorly understood. Palaeoclimate studies have documented ENSO variability for selected intervals in the Holocene,but most records are either too short or insufficiently resolved to investigate variability on millennial scales(1-3). Here we present a record of sedimentation in Laguna Pallcacocha,southern Ecuador,which is strongly influenced by ENSO variability,and covers the past 12000 years continuously. We find that changes on a timescale of 2-8 years,which we attribute to warm ENSO events,become more frequent over the Holocene until about 1200 years ago,and then decline towards the present. Periods of relatively high and low ENSO activity,alternating at a timescale of about 2000 years,are superimposed on this long-term trend. We attribute the long-term trend to orbitally induced changes in insolation,and suggest internal ENSO dynamics as a possible cause of the millennial variability. However,the millennial oscillation will need to be confirmed in other ENSO proxy records.

Keywords: southern-oscillation; tropical pacific; Niño; ecuador; PERU

来源出版物:Nature,2002,420(6912): 162-165

被引频次:529

The 1990-1995 El Niño Southern Oscillation event: Longest on record

Trenberth,KE; Hoar,TJ

Abstract: 参见本期“经典文献推荐”栏目.

被引频次:520

Remote sea surface temperature variations during ENSO: Evidence for a tropical atmospheric bridge

Klein,SA; Soden,BJ; Lau,NC

Abstract: In an El Niño event,positive SST anomalies usually appear in remote ocean basins such as the South China Sea,the Indian Ocean,and the tropical North Atlantic approximately 3 to 6 months after SST anomalies peak in the tropical Pacific. Ship data from 1952 to 1992 and satellite data from the 1980s both demonstrate that changes in atmospheric circulation accompanying El Niño induce changes in cloud cover and evaporation which,in turn,increase the net heat flux entering these remote oceans. It is postulated that this increased heat flux is responsible for the surface warming of these oceans. Specifically,over the eastern Indian Ocean and South China Sea,enhanced subsidence during El Niño reduces cloud cover and increases the solar radiation absorbed by the ocean,thereby leading to enhanced SSTs. In the tropical North Atlantic,a weakening of the trade winds during El Niño reduces surface evaporation and increases SSTs. These relationships fit the concept of an “atmospheric bridge” that connects SST anomalies in the central equatorial Pacific to those in remote tropical oceans.

Keywords: Asian summer monsoon; southern-oscillation; interannual variability; seasonal-variation; SST anomalies; wind stress; ocean;pacific; circulation; scale

来源出版物:Journal of Climate,1999,12(4): 917-932

被引频次:478

On the weakening relationship between the Indian monsoon and ENSO

Kumar,KK; Rajagopalan,B; Cane,MA

Abstract: Analysis of the 140-year historical record suggests that the inverse relationship between the El Niño-Southern Oscillation(ENSO)and the Indian summer monsoon(weak monsoon arising from warm ENSO event)has broken down in recent decades. Two possible reasons emerge from the analyses. A southeastward shift in the Walker circulation anomalies associated with ENSO events may Lead to a reduced subsidence over the Indian region,thus favoring normal monsoon conditions. Additionally,increased surface temperatures over Eurasia in winter and spring,which area pail of the midlatitude continental warming trend,may favor the enhanced land-ocean thermal gradient conducive to a strong monsoon. These observations raise the possibility that the Eurasian warming in recent decades helps to sustain the monsoon rainfall at a normal Level despite strong ENSO events.

Keywords: Asian summer monsoon; eurasian snow cover; Niño southern oscillation; sea-surface temperatures; air-temperature; rainfall series; variability; climate; model; simulations

来源出版物:Science,1999,284(5423): 2156-2159

被引频次:442

Tropical Atlantic sea surface temperature variability and its relation to El Niño Southern Oscillation

Enfield,DB; Mayer,DA

Abstract: Past analyses of tropical Atlantic sea surface temperature variability have suggested a dipole behavior between the northern and southern tropics,across the Intertropical Convergence Zone(ITCZ). By analyzing an improved 43-year(1950-1992)record of SST [Smith er al.,1996] and other data derived from the Comprehensive Ocean-Atmosphere Data Set(GOADS),it is shown that the regions north and south of the ITCZ are statistically independent of each other at the seasonal to interannual timescales dominating the data,confirming the conclusions of Houghton and Tourre [1992]. Some dipole behavior does develop weakly during the boreal spring season,when there is a tendency for SST anomaly west of Angola to be opposite of that in the tropical North Atlantic. It is further shown that tropical Atlantic SST variability is correlated with Pacific El Niño-Southern Oscillation(ENSO)variability in several regions. The major region affected is the North Atlantic area of NE trades west of 40 degrees W along 10 degrees N-20 degrees N and extending into the Caribbean. There,about 50-80% of the anomalous SST variability is associated with the Pacific ENSO,with Atlantic warmings occurring 4-5 months after the mature phases of Pacific warm events. An analysis of local surface flux fields derived from GOADS data shows that the ENSO-related Atlantic warmings occur as a result of reductions in the surface NE trade wind speeds,which in turn reduce latent and sensible heat losses over the region in question,as well as cooling due to entrainment. This ENSO connection is best developed during the boreal spring following the most frequent season of maximum ENSO anomalies in the Pacific. A region of secondary covariability with ENSO occurs along the northern edge of the mean ITCZ position and appears to be associated with northward migrations of the ITCZ when the North Atlantic warmings occur. Although easterly winds are intensified in the western equatorial Atlantic in response to Pacific warm events,they do not produce strong local changes in SST. Contrary to expectations from studies based on equatorial dynamics,these teleconnected windanomalies do not give rise to significant correlations of SST in the Gulf of Guinea with the Pacific ENSO. As the teleconnection sequence matures,strong SE trades at low southern latitudes follow the development of the North Atlantic SST anomaly and precede by several months the appearance of weak negative SST anomalies off Angola and stronger positive anomalies extending eastward from southern Brazil along 15 degrees-30 degrees S.

Keywords: Northeast Brazil; ocean; circulation; anomalies; prediction; latitudes; rainfall; droughts; model

来源出版物:Journal of Geophysical Research-Oceans,1997,102(C1): 929-945

被引频次:406

El Niño,La Niña,and the nonlinearity of their teleconnections

Hoerling,MP; Kumar,A; Zhong,M

Abstract: 参见本期“经典文献推荐”栏目.

被引频次:376

El Niño in a changing climate

Yeh,Sang-Wook; Kug,Jong-Seong; Dewitte,Boris; et al.

Abstract: El Niño events,characterized by anomalous warming in the eastern equatorial Pacific Ocean,have global climatic teleconnections and are the most dominant feature of cyclic climate variability on subdecadal timescales. Understanding changes in the frequency or characteristics of El Niño events in a changing climate is therefore of broad scientific and socioeconomic interest. Recent studies(1-5)show that the canonical El Niño has become less frequent and that a different kind of El Niño has become more common during the late twentieth century,in which warm sea surface temperatures(SSTs)in the central Pacific are flanked on the east and west by cooler SSTs. This type of El Niño,termed the central Pacific El Niño(CP-El Niño; also termed the dateline El Niño(2),El Niño Modoki(3)or warm pool El Niño(5)),differs from the canonical eastern Pacific El Niño(EP-El Niño)in both the location of maximum SST anomalies and tropical-midlatitude teleconnections. Here we show changes in the ratio of CP-El Niño to EP-El Niño under projected global warming scenarios from the Coupled Model Intercomparison Project phase 3 multi-model data set(6). Using calculations based on historical El Niño indices,we find that projections of anthropogenic climate change are associated with an increased frequency of the CP-El Niño compared to the EP-El Niño. When restricted to the six climate models with the best representation of the twentieth-century ratio of CP-El Niño to EP-El Niño,the occurrence ratio of CP-El Niño/EP-El Niño is projected to increase as much as five times under global warming. The change is related to a flattening of the thermocline in the equatorial Pacific.

Keywords: sea-surface temperature; southern oscillation; pacific RIM; ENSO; sensitivity; anomalies; evolution; events; modoki; oceans

来源出版物:Nature,2009,461(4263): 511-514联系邮箱:Yeh,Sang-Wook; swyeh@kordi.re.kr

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ENSO和北极涛动对东亚冬季气候异常的综合影响

陈文,兰晓青,王林,等

摘要:利用NCEP/DOE再分析资料以及我国温度和降水台站资料,以厄尔尼诺和南方涛动(El Niño and Southern Oscillation,ENSO)冷、暖位相的冬季作为背景,结合北极涛动(Arctic Oscillation,AO)的月际异常,对两者影响东亚冬季气候异常的综合作用进行了研究.结果表明,当El Niño和AO负异常或者La Niña和AO正异常相互配置时,我国北方气候异常主要受AO影响,南方气候异常主要受ENSO影响,并且该气候异常与已经认识到的AO和ENSO影响东亚气候异常的机理相一致.然而,当El Niño和AO正异常或者La Niña和AO负异常相互配置时,尽管我国北方气温仍主要受AO影响,但我国大部分地区,特别是南方的气候异常呈现出与已有认识很不一样的变化模态.进一步的分析认为出现这种差异的原因可能在于平流层和对流层相互作用以及东亚地区中低纬相互作用的不同,这会导致在前者的冬季,大气环流主要表现为纬向对称性,中低纬相互作用偏弱,ENSO和AO对东亚的影响表现出线性的作用;而在后者的冬季,则不利于大气环形模态的维持,导致东亚地区中低纬相互作用偏强,ENSO和AO对东亚的影响呈现出非线性的相互叠加.

关键词:厄尔尼诺和南方涛动;北极涛动;东亚冬季气候;气温与降水异常;平流层与对流层;相互作用

来源出版物:科学通报,2013,58(8): 634-641联系邮箱:陈文,cw@post.iap.ac.cn

厄尔尼诺衰亡年间南亚夏季风在印度洋对西北太平洋遥强迫中的作用

胡海波,洪晓媛,张媛,等

摘要:已有的大量研究给出了印度洋增暖的气候效应,特别是对于西北太平洋反气旋异常的影响.本文利用观测数据和耦合数值模式进一步分析了厄尔尼诺衰亡年印度洋增暖的气候效应,研究了印度洋海温异常与西北太平洋反气旋异常之间的遥强迫形成条件,提出印度洋背景风场的季节性转换对印度洋增暖效应的关键作用.结果表明,只有在有利的背景风场下,即南亚夏季季风完全爆发时,才更有利于印度洋增暖效应的充分体现.可能是由于Kelvin波-Ekman辐散机制,在北印度洋异常增暖所导致的大气热源异常的东侧低层大气中产生了明显的东风异常,这一东风异常对西北太平洋产生遥强迫,使西北太平洋的反气旋异常加强并维持到厄尔尼诺衰亡年夏季.这对于东亚夏季季风的年变率机制研究及预测有着重要意义.

关键词:厄尔尼诺衰亡年;印度洋增暖;南亚夏季风;西北太平洋反气旋异常;东亚夏季风

来源出版物:中国科学:地球科学,2013,43(2): 220-231

华南冬季气温异常与ENSO的关系

伍红雨,潘蔚娟,王婷

摘要:利用1951—2012年华南192个测站逐月气温资料、NCEP/NCAR再分析月资料、NCC的ENSO监测资料,采用相关分析和合成分析等方法分析了华南冬季气温异常与ENSO的关系.结果表明:华南冬季气温对La Niña事件的响应比对E1 Niño事件显著,La Niña事件当年华南冬季气温以偏低为主,极强La Niña事件对应的华南冬季气温显著偏低,而中部型La Niña事件出现过华南冬季气温显著偏高的情况.当La Niña(El Niño)事件为东部型、Niño区海温异常的峰值月份出现在秋冬季,当年华南冬季气温易偏低(高).从年际尺度上,当La Niña发生时,在对流层低层激发西太平洋异常气旋环流和北风异常,对应对流层中层北太平洋高压、乌拉尔山高压脊和东亚大槽南段均加强,西太平洋副热带高压减弱,东亚中高纬经向环流明显,冬季风偏强,导致我国大部分地区包括华南冬季气温偏冷,反之亦然.El Niño事件对华南冬季气温的影响具有年代际差异.对应华南冬季气温年代际变化的海温变化明显的区域位于北太平洋,而与ENSO关系不明显.

关键词:冬季气温;厄尔尼诺;拉尼娜;海温距平;华南

来源出版物:气象,2014,40(10):1230-1239联系邮箱:伍红雨,wuhy@grmc.gov.cn

黑潮入侵南海的强弱与太平洋年代际变化及厄尔尼诺-南方涛动现象的关系

杨龙奇,许东峰,徐鸣泉,等

摘要:在黑潮入侵南海强弱的问题上,到底是太平洋年代际变化(Pacific Decadal Oscillation,PDO)还是厄尔尼诺浦方涛动(El Niño-Southern Oscillation,ENSO)现象在起关键作用,目前还存在着较大争议.本文先以高盐水作为黑潮入侵强弱的示踪物,用1200E断面的高盐水数据和北赤道流分叉点(North Equator Current Bifurcation,NEC-Y)的南北变动进行相关分析,接着,进一步用学者所用的黑潮入侵指数(KI指数,Kuroshio intrusion index和NEC指数,North Equatorial Current index)与北赤道流分叉点南北变动进行相关分析.最后,用EMD(Empirical Mode Decomposition)方法和相关关系分析法分别分析了PD(指数、Niño3.4指数与北赤道流分叉点南北变动的关系并用NECP风场数据探讨其影响机制.结果表明:(1)通过对1200E断面的高盐水的KI指数、NEC指数与NEC-Y的相关分析,表明了北赤道流分叉点的南北变动能够很好地指代黑潮入侵南海的强弱;(2)通过PD(指数和Niño3.4指数与北赤道流分叉点的南北变动的相关性分析,发现PD(指数、Niño3.4指数与北赤道流分叉点的南北变动都具有较好的相关性,都在0.5水平.这些良好的相关性表明了PDO和ENSO对黑潮入侵南海的强弱都具有重要的影响;(3)当处于厄尔尼诺年(拉尼娜)时,赤道太平洋发生西(东)风异常,使得北赤道流分叉点偏北(南),使吕宋岛东侧的黑潮流速减弱(加强),黑潮入侵南海增强(减弱);当PDO处于暖(冷)阶段时,会加强热带太平洋的西(东)风异常,使得黑潮入侵南海增强(减弱).

关键词:黑潮入侵;北赤道流分叉点;太平洋年代际变化;厄尔尼诺—南方涛动

来源出版物:海洋学报,2014,36(7): 17-26联系邮箱:许东峰,xudongfengyh@yahoo.com

热带印度洋-太平洋三极模态的理论探讨

连涛,陈大可,YouMin TANG

摘要:热带太平洋的厄尔尼诺-南方涛动(El Niño-Southern Oscillation,ENSO)现象是过去几十年里海洋与气候研究的重点.随着近年来印度洋偶极子模态(Indian Ocean Dipole,IOD)的提出,热带印度洋中的短期气候变化也逐步被重视.然而,人们对这些现象的研究更多的是局限在单个的海盆之内,而不是将其作为一个整体来思考.观测表明,在年际间尺度上,热带印度洋和热带太平洋的海表温度异常(Sea Surface Temperature Anomaly,SSTA)和海表高度异常(Sea Surface Height Anomaly,SSHA)等物理量的有着很明显的反向变化趋势.对这种反向变化可以给出一个简单的解释:由于双圈沃克环流在暖池区幅聚上升,海表风场在热带印度洋为西风,在热带太平洋为东风;它们通过驱动海水的上翻使得热带西印度洋与东太平洋SSTA变冷,SSHA变低,同时也通过暖水的堆积使得暖池区SSTA升高,SSHA增加.这样就在整个热带印度洋-太平洋地区形成了一个SSTA和SSHA的三极子结构.随着热带印度洋-太平洋上空沃克环流圈的增强或减弱,两个海洋之间的反向梯度关系也会随之做相应的调整,并通过梯度与沃克环流之间的正反馈作用得以维持.这一振荡模态被称为印-太三极子(Indo-Pacific Tripole,IPT).本文将通过资料分析和一个简单的概念模型来讨论IPT模态的发展和变化机制,并着重考虑ENSO与IOD对IPT模态的影响.该模型包含了最基本的海洋与大气的物理变量和他们之间的相互作用,可以为更深层次地理解和研究热带地区短期气候变化提供重要参考.

关键词:厄尔尼诺;印度洋偶极子;印-太三极子

来源出版物:中国科学:地球科学,2014,44(1): 169-186

与厄尔尼诺和拉尼娜相联系的中国南方冬季降水的年代际异常特征

袁媛,李崇银,杨崧

摘要:利用 NCEP/NCAR再分析大气环流资料、哈得来中心海温资料、中国700多站降水资料以及全球格点降水资料,详细分析了中国南方冬季降水异常的特征,并揭示了其所对应的欧亚大气环流和东亚冬季风异常与ENSO事件的联系,以及ENSO暖/冷位相对其影响的非对称性.研究进一步证明了厄尔尼诺是导致中国南方冬季降水偏多的重要外强迫因子,并指出拉尼娜对中国南方冬季降水的影响表现出明显的年代际变化特征.1980年之前的拉尼娜年冬季,东亚冬季风显著偏强,东亚大槽偏深,西北太平洋副热带高压偏弱偏东,中国南方受一致偏北风影响,气温偏低,降水偏少,多表现为冷干的气候特征.但1980年之后的拉尼娜年冬季,东亚大槽偏弱,印缅槽偏强,同时在菲律宾以西激发出异常气旋性环流,使得异常偏东风控制中国南方,有利于热带水汽输送增强,因此降水偏多.同时,1980年之后的拉尼娜事件还使得东亚副热带西风急流偏强偏北,中国南方处于急流人口区的右侧,通过二级环流使得中国南方上空的上升运动偏强,有利于降水偏多.因此,1980年之后的拉尼娜年冬季,中国南方易表现出冷湿的气候特征,有时也容易发生低温雨雪冰冻灾害.进一步分析表明,1980年以后拉尼娜成熟期海温异常空间分布型的变化,以及北半球大气环流的年代际变化可能是导致拉尼娜对东业大气环流的影响在1980年之后发生变化的重要原因.

关键词:东亚冬季风;冬季降水;厄尔尼诺和拉尼娜;非对称性;年代际变化

来源出版物:气象学报,2014,72(2): 237-255联系邮箱:袁媛,yuany@cma.gov.cn

Roles of ENSO and PDO in the link of the East Asian winter monsoon to the following summer monsoon

Wen Chen; Juan Feng; Renguang Wu

Abstract: The present study investigates the roles of El Niño-Southern Oscillation(ENSO)and the Pacific decadal oscillation(PDO)in therelationship between the East Asian winter monsoon(EAWM)and the following East Asian summer monsoon(EASM). The variability of the EAWM is divided into an ENSO-related part named EAWM EN and an ENSO-unrelated part named EAWM res. Corresponding to a weak EAWM EN,an anomalous low-level anticyclone forms over the western North Pacific(WNP)and persists from winter to the following summer. This anticyclone enhances southerlies over the coast of East Asia in summer. Hence,a weak EAWM EN tends to be followed by a strong EASM and vice versa. As such,a link is established between the EAWM EN and the EASM. The persistence of this WNP anticyclone may be mainly attributed to the sea surface temperature anomalies associated with the ENSO-related EAWM part in the tropical Indian Ocean and the extratropical North Pacific. In contrast,corresponding to a weak EAWM res,the anomalous WNP anticyclone is only seen in winter,and there is no obvious relationship between the EAWM res and the following EASM. Therefore,the observed EAWM-EASM relationship is dominated by the winter monsoon variability associated with ENSO. It is found that the EAWM EN-EASM relationship is modulated by the PDO. There tends to be a much stronger EASM after a weak EAWM EN during the positive PDO phases than during the negative PDO phases.

来源出版物:Journal of Climate,2013,26(2): 622-635

A new paradigm for the predominance of standing Central Pacific Warming after the late 1990s

Xiang,Baoqiang; Wang,Bin; Li,Tim

Abstract: Canonical El Niño has a warming center in the eastern Pacific(EP),but in recent decades,El Niño warming center tends to occur more frequently in the central Pacific(CP). The definitions and names of this new type of El Niño,however,have been notoriously diverse,which makes it difficult to understand why the warming center shifts. Here,we show that the new type of El Niño events is characterized by: 1)the maximum warming standing and persisting in the CP and 2)the warming extending to the EP only briefly during its peak phase. For this reason,we refer to it as standing CP warming(CPW). Global warming has been blamed for the westward shift of maximum warming as well as more frequent occurrence of CPW. However,we find that since the late 1990s the standing CPW becomes a dominant mode in the Pacific; meanwhile,the epochal mean trade winds have strengthened and the equatorial thermocline slope has increased,contrary to the global warming-induced weakening trades and flattening thermocline. We propose that the recent predominance of standing CPW arises from a dramatic decadal change characterized by a grand La Niña-like background pattern and strong divergence in the CP atmospheric boundary layer. After the late 1990s,the anomalous mean CP wind divergence tends to weaken the anomalous convection and shift it westward from the underlying SST warming due to the suppressed low-level convergence feedback. This leads to a westward shift of anomalous westerly response and thus a zonally in-phase SST tendency,preventing eastward propagation of the SST anomaly. We anticipate more CPW events will occur in the coming decade provided the grand La Niña-like background state persists.

Keywords: Central Pacific Warming; La Niña-like mean state change; Convection; Low-level convergence feedback

来源出版物:Climate Dynamics,2013,41(2): 327-340联系邮箱:Xiang,Baoqiang; baoqiang@hawaii.edu

Late-twentieth-century emergence of the El Niño propagation asymmetry and future projections

Santoso,Agus; McGregor,Shayne; Jin,Feifei; et al.

Abstract: The El Niño/Southern Oscillation(ENSO)is the Earth’s most prominent source of interannual climate variability,exerting profound worldwide effects(1-7). Despite decades of research,its behaviour continues to challenge scientists. In the eastern equatorial Pacific Ocean,the anomalously cool sea surface temperatures(SSTs)found during La Niña events and the warm waters of modest El Niño events both propagate westwards,as in the seasonal cycle(7). In contrast,SST anomalies propagate eastwards during extreme El Niño events,prominently in the post-1976 period(7-10),spurring unusual weather events worldwide with costly consequences(3-6,11). The cause of this propagation asymmetry is currently unknown(10). Here we trace the cause of the asymmetry to the variations in upper ocean currents in the equatorial Pacific,whereby the westward-flowing currents are enhanced during La Niña events but reversed during extreme El Niño events. Our results highlight that propagation asymmetry is favoured when the westward mean equatorial currents weaken,as is projected to be the case under global warming(12-14). By analysing past and future climate simulations of an ensemble of models with more realistic propagation,we find a doubling in the occurrences of El Niño events that feature prominent eastward propagation characteristics in a warmer world. Our analysis thus suggests that more frequent emergence of propagation asymmetry will be an indication of the Earth’s warming climate.

Keywords: tropical pacific; ENSO dynamics; ocean; model; simulations; evolution; ensemble; feedback; events; impact

来源出版物:Nature,2013,504(7478): 126-130联系邮箱:Santoso,Agus; a.santoso@unsw.edu.au

Sea surface temperature in the north tropical Atlantic as a trigger for El Niño/Southern Oscillation events

Ham,Yoo-Geun; Kug,Jong-Seong; Park,Jong-Yeon; et al.

Abstract: El Niño events,the warm phase of the El Niño/Southern Oscillation(ENSO),are known to affect other tropical ocean basins through teleconnections. Conversely,mounting evidence suggests that temperature variability in the Atlantic Ocean may also influence ENSO variability(1-5). Here we use reanalysis data and general circulation models to show that sea surface temperature anomalies in the north tropical Atlantic during the boreal spring can serve as a trigger for ENSO events. We identify a subtropical teleconnection in which spring warming in the north tropical Atlantic can induce a low-level cyclonic atmospheric flow over the eastern Pacific Ocean that in turn produces a low-level anticyclonic flow over the western Pacific during the following months. This flow generates easterly winds over the western equatorial Pacific that cool the equatorial Pacific and may trigger a La Niña event the following winter. In addition,El Niño events led by cold anomalies in the north tropical Atlantic tend to be warm-pool El Niño events,with a centre of action located in the central Pacific(6,7),rather than canonical El Niño events. We suggest that the identification of temperature anomalies in the north tropical Atlantic could help to forecast the development of different types of El Niño event.

Keywords: NIÑO-southern-oscillation; indian-ocean; warm pool; variability; ENSO; pacific; SST; circulation; rainfall; climate

来源出版物:Nature Geoscience,2013,6(2): 112-116联系邮箱:Ham,Yoo-Geun; jskug@kiost.ac

Improved El Niño forecasting by cooperativity detection

Ludescher,Josef; Gozolchiani,A; Bogachev,Mikhail I; et al.

Abstract: Although anomalous episodic warming of the eastern equatorial Pacific,dubbed El Niño by Peruvian fishermen,has major(and occasionally devastating)impacts around the globe,robust forecasting is still limited to about 6 mo ahead. A significant extension of the prewarning time would be instrumental for avoiding some of the worst damages such as harvest failures in developing countries. Here we introduce a unique avenue toward El Niño prediction based on network methods,inspecting emerging teleconnections. Our approach starts from the evidence that a large-scale cooperative mode-linking the El Niño basin(equatorial Pacific corridor)and the rest of the ocean-builds up in the calendar year before the warming event. On this basis,we can develop an efficient 12-mo forecasting scheme,i.e.,achieve some doubling of the early-warning period. Our method is based on high-quality observational data available since 1950 and yields hit rates above 0.5,whereas false-alarm rates are below 0.1.

Keywords: climate; cross-correlations; dynamic networks; ENSO; spring barrier

来源出版物:Proceedings of the National Academy of Sciences of the United States of America,2013,110(29): 11742-11745

Impact of East Asian winter and Australian summer monsoons on the enhanced surface westerlies over the western tropical Pacific Ocean preceding the El Niño onset

Zheng,Yangxing; Zhang,Renhe; Bourassa,Mark A.

Abstract: Composite analysis from NCEP-NCAR reanalysis datasets over the period 1948-2007 indicates that stronger East Asian winter monsoons(EAWM)and stronger Australian summer monsoons(ASM)generally coexist in boreal winters preceding the onset of El Niño,although the EAWM tend to be weak after 1990,probably because of the decadal shift of EAWM and the change in El Niño events from cold-tongue type to warm-pool type. The anomalous EAWM and ASM enhance surface westerlies over the western tropical Pacific Ocean(WTP). It is proposed that the enhanced surface westerlies over the WTP prior to El Niño onset are generally associated with the concurrent anomalous EAWM and ASM. A simple analytical atmospheric model is constructed to test the hypothesis that the emergence of enhanced surface westerlies over the WTP can be linked to concurrent EAWM and ASM anomalies. Model results indicate that,when anomalous northerlies from the EAWM converge with anomalous southerlies from the ASM,westerly anomalies over the WTP are enhanced. This result provides a possible explanation of the co-impact of the EAWM and the ASM on the onset of El Niño through enhancing the surface westerly over the WTP.

Keywords: atmospheric circulation; forcing; dynamics; monsoons; wind

来源出版物:Journal of Climate,2014,27(5): 1928-1944

Cold Tongue and Warm Pool ENSO Events in CMIP5: Mean State and Future Projections

Taschetto,Andrea S; Sen Gupta,Alexander; Jourdain,Nicolas C; et al.

Abstract: The representation of the El Niño-Southern Oscillation(ENSO)under historical forcing and future projections is analyzed in 34 models from the Coupled Model Intercomparison Project phase 5(CMIP5). Most models realistically simulate the observed intensity andlocation of maximum sea surface temperature(SST)anomalies during ENSO events. However,there exist systematic biases in the westward extent of ENSO-related SST anomalies,driven by unrealistic westward displacement and enhancement of the equatorial wind stress in the western Pacific. Almost all CMIP5 models capture the observed asymmetry in magnitude between the warm and cold events(i.e.,El Niños are stronger than La Niñas)and between the two types of El Niños: that is,cold tongue(CT)El Niños are stronger than warm pool(WP)El Niños. However,most models fail to reproduce the asymmetry between the two types of La Niñas,with CT stronger than WP events,which is opposite to observations. Most models capture the observed peak in ENSO amplitude around December; however,the seasonal evolution of ENSO has a large range of behavior across the models. The CMIP5 models generally reproduce the duration of CT El Niños but have biases in the evolution of the other types of events. The evolution of WP El Niños suggests that the decay of this event occurs through heat content discharge in the models rather than the advection of SST via anomalous zonal currents,as seems to occur in observations. No consistent changes are seen across the models in the location and magnitude of maximum SST anomalies,frequency,or temporal evolution of these events in a warmer world.

Keywords: climate change; climate variability; ENSO; climate models; atmosphere-ocean interaction; model evaluation/performance

来源出版物:Journal of Climate,2014,27(8): 2861-2885联系邮箱:Taschetto,Andrea S; a.taschetto@unsw.edu.au

Holocene history of ENSO variance and asymmetry in the eastern tropical Pacific

Carre,Matthieu; Sachs,Julian P; Purca,Sara; et al.

Abstract: Understanding the response of the El Niño-Southern Oscillation(ENSO)to global warming requires quantitative data on ENSO under different climate regimes. Here,we present a reconstruction of ENSO in the eastern tropical Pacific spanning the past 10000 years derived from oxygen isotopes in fossil mollusk shells from Peru. We found that ENSO variance was close to the modern level in the early Holocene and severely damped similar to 4000 to 5000 years ago. In addition,ENSO variability was skewed toward cold events along coastal Peru 6700 to 7500 years ago owing to a shift of warm anomalies toward the Central Pacific. The modern ENSO regime was established similar to 3000 to 4500 years ago. We conclude that ENSO was sensitive to changes in climate boundary conditions during the Holocene,including but not limited to insolation.

Keywords: El-Niño/southern-oscillation; southern-oscillation; Niño; PERU; variability; climate; record; reconstructions; simulations;midholocene

来源出版物:Science,2014,345(6200): 1045-1048联系邮箱:Carre,Matthieu; matthieu.carre@univ-montp2.fr

Different impacts of various El Niño events on the Indian Ocean Dipole

Wang,Xin; Wang,Chunzai

Abstract: Our early work(Wang and Wang in J Clim 26:1322-1338,2013)separates El Niño Modoki events into El Niño Modoki I and II because they show different impacts on rainfall in southern China and typhoon landfall activity. The warm SST anomalies originate in the equatorial central Pacific and subtropical northeastern Pacific for El Niño Modoki I and II,respectively. El Niño Modoki I features a symmetric SST anomaly distribution about the equator with the maximum warming in the equatorial central Pacific,whereas El Niño Modoki II shows an asymmetric distribution with the warm SST anomalies extending from the northeastern Pacific to the equatorial central Pacific. The present paper investigates the influence of the various groups of El Niño events on the Indian Ocean Dipole(IOD). Similar to canonical El Niño,El Niño Modoki I is associated with a weakening of the Walker circulation in the Indo-Pacific region which decreases precipitation in the eastern tropical Indian Ocean and maritime continent and thus results in the surface easterly wind anomalies off Java-Sumatra. Under the Bjerknes feedback,the easterly wind anomalies induce cold SST anomalies off Java- Sumatra,and thus a positive IOD tends to occur in the Indian Ocean during canonical El Niño and El Niño Modoki I. However,El Niño Modoki II has an opposite impact on the Walker circulation,resulting in more precipitation and surface westerly wind anomalies off Java-Sumatra. Thus,El Niño Modoki II is favorable for the onset and development of a negative IOD on the frame of the Bjerknes feedback.

Keywords: sea-surface temperature; tropical circulation; walker circulation; pacific climate; coupled GCM; variability; ENSO; rainfall;modok I; mode

来源出版物:Climate Dynamics,2014,42(3-4): 991-1005联系邮箱:Wang,Chunzai; chunzai.wang@noaa.gov

Nonlinear precipitation response to El Niño and global warming in the Indo-Pacific

Chung,Christine T. Y; Power,Scott B; Arblaster,Julie M; et al.

Abstract: Precipitation changes over the Indo-Pacific during El Nio events are studied using an Atmospheric General Circulation Model forced with sea-surface temperature(SST)anomalies and changes in atmospheric CO2concentrations. Linear increases in the amplitude of the El Niño SST anomaly pattern trigger nonlinear changes in precipitation amounts,resulting in shifts in the location and orientation of theIntertropical Convergence Zone(ITCZ)and the South Pacific Convergence Zone(SPCZ). In particular,the maximum precipitation anomaly along the ITCZ and SPCZ shifts eastwards,the ITCZ shifts south towards the equator,and the SPCZ becomes more zonal. Precipitation in the equatorial Pacific also increases nonlinearly. The effect of increasing CO2levels and warming SSTs is also investigated. Global warming generally enhances the tropical Pacific precipitation response to El Niño. The precipitation response to El Niño is found to be dominated by changes in the atmospheric mean circulation dynamics,whereas the response to global warming is a balance between dynamic and thermodynamic changes. While the dependence of projected climate change impacts on seasonal variability is well-established,this study reveals that the impact of global warming on Pacific precipitation also depends strongly on the magnitude of the El Niño event. The magnitude and structure of the precipitation changes are also sensitive to the spatial structure of the global warming SST pattern.

Keywords: El-Niño Southern Oscillation; global warming; climate change; climate variability

来源出版物:Climate Dynamics,2014,42(7-8): 1837-1856联系邮箱:Chung,Christine T. Y; c.chung@bom.gov.au

Very early warning of next El Niño

Ludescher,Josef; Gozolchiani,Avi ; Bogachev,Mikhail I; et al.

Abstract: The most important driver of climate variability is the El Niño Southern Oscillation,which can trigger disasters in various parts of the globe. Despite its importance,conventional forecasting is still limited to 6 mo ahead. Recently,we developed an approach based on network analysis,which allows projection of an El Niño event about 1 y ahead. Here we show that our method correctly predicted the absence of El Niño events in 2012 and 2013 and now announce that our approach indicated(in September 2013 already)the return of El Niño in late 2014 with a 3-in-4 likelihood. We also discuss the relevance of the next El Niño to the question of global warming and the present hiatus in the global mean surface temperature.

Keywords: dynamic networks; ENSO; spring barrier

来源出版物:Proceedings of the National Academy of Sciences of the United States of America,2014,111(6): 2064-2066

联系邮箱:Schellnhuber,Hans Joachim; john@pik-potsdam.de

Seasonal Predictability over Europe Arising from El Niño and Stratospheric Variability in the MPI-ESM Seasonal Prediction System

Domeisen,Daniela I. V; Butler,Amy H; Froehlich,Kristina; et al.

Abstract: Predictability on seasonal time scales over the North Atlantic-Europe region is assessed using a seasonal prediction system based on an initialized version of the Max Planck Institute Earth System Model(MPI-ESM). For this region,two of the dominant predictors on seasonal time scales are El Niño-Southern Oscillation(ENSO)and sudden stratospheric warming(SSW)events. Multiple studies have shown a potential for improved North Atlantic predictability for either predictor. Their respective influences are however difficult to disentangle,since the stratosphere is itself impacted by ENSO. Both El Niño and SSW events correspond to a negative signature of the North Atlantic Oscillation(NAO),which has a major influence on European weather. This study explores the impact on Europe by separating the stratospheric pathway of the El Niño teleconnection. In the seasonal prediction system,the evolution of El Niño events is well captured for lead times of up to 6 months,and stratospheric variability is reproduced with a realistic frequency of SSW events. The model reproduces the El Niño teleconnection through the stratosphere,involving a deepened Aleutian low connected to a warm anomaly in the northern winter stratosphere. The stratospheric anomaly signal then propagates downward into the troposphere through the winter season. Predictability of 500-hPa geopotential height over Europe at lead times of up to 4 months is shown to be increased only for El Niño events that exhibit SSW events,and it is shown that the characteristic negative NAO signal is only obtained for winters also containing major SSW events for both the model and the reanalysis data.

Keywords: quasi-biennial oscillation; low-top versions; sudden warmings; southern-oscillation; northern winter; CMIP5 simulations;weather regimes; forecast skill; climate model; ENSO

来源出版物:Journal of Climate,2015,28(1): 256-271联系邮箱:Domeisen,Daniela I. V; daniela.domeisen@zmaw.de

Impacts of variations in the strength and structure of El Niño events on Pacific rainfall in CMIP5 models

Murphy,Bradley F; Ye,Hua; Delage,Francois

Abstract: El Niño-Southern Oscillation(ENSO)plays a dominant role in interannual climate variability in Pacific island countries,directly affecting lives there. Many countries show different rainfall responses depending on the sea surface temperature(SST)structure of different types of El Niño events. El Niño events are classified into three types based on previous studies: those with strongest SST anomalies in theeastern Pacific Cold Tongue region(CTE),in the Western Pacific Warm Pool region(WPE),and those in between,a “Mixed” El Niño(MxE),and results from 30 CMIP5 models are investigated. These models accurately reproduce observed SST and precipitation anomalies for the three El Niño types and La Niña. CMIP5 models simulate much larger ranges in the strength of ENSO events than observed. Results clarify the roles of both the different structures of El Niño SST anomalies and their magnitudes on rainfall in the Pacific,and demonstrate that each of the three El Niño types has different impacts on rainfall in the region. These impacts vary with location,with WPE and CTE producing very different impacts in most Pacific island countries. There is a linear intensification of both the mean and maximum rainfall anomalies in the equatorial Pacific as the events become stronger. Equatorial rainfall shifts eastward in CTE and MxE,westward in La Niña. Both the South Pacific and Intertropical Convergence Zones(SPCZ and ITCZ)shift equatorward in El Niñoand poleward in La Niña,the shifts increasing as events strengthen. WPE show different behaviour to other events,with little east-west shift in equatorial rainfall,and the orientation angle of the convergence zones increases. Identification of models with no erroneous westward bias in SST anomalies has clarified the effect of strong CTE events producing “zonal” SPCZ and shifting rainfall away to the east from western equatorial countries.

Keywords: El Niño; Pacific rainfall; climate variability; CMIP5

来源出版物:Climate Dynamics,2015,44(11-12): 3171-3186联系邮箱:Murphy,Bradley F; B.Murphy@bom.gov.au

Strong influence of westerly wind bursts on El Niño diversity

Chen,Dake; Lian,Tao; Fu,Congbin; et al.

Abstract: Despite the tremendous progress in the theory,observation and prediction of El Niño over the past three decades,the classification of El Niño diversity and the genesis of such diversity are still debated. This uncertainty renders El Niño prediction a continuously challenging task,as manifested by the absence of the large warm event in 2014 that was expected by many. We propose a unified perspective on El Niño diversity as well as its causes,and support our view with a fuzzy clustering analysis and model experiments. Specifically,the interannual variability of sea surface temperatures in the tropical Pacific Ocean can generally be classified into three warm patterns and one cold pattern,which together constitute a canonical cycle of El Niño/La Niña and its different flavours. Although the genesis of the canonical cycle can be readily explained by classic theories,we suggest that the asymmetry,irregularity and extremes of El Niño result from westerly wind bursts,a type of state-dependent atmospheric perturbation in the equatorial Pacific. Westerly wind bursts strongly affect El Niño but not La Niña because of their unidirectional nature. We conclude that properly accounting for the interplay between the canonical cycle and westerly wind bursts may improve El Niño prediction.

Keywords: sea-surface temperature; southern oscillation; tropical pacific; equatorial pacific; conceptual-model; warm pool; La-Nina;ENSO; events; predictability

来源出版物:Nature Geoscience,2015,8(5): 339-345联系邮箱:Chen,Dake; dchen@sio.org.cn

编辑:卫夏雯

The tendency for more frequent El Niño events and fewer La Niña events since the late 1970’s has been linked to decadal changes in climate throughout the Pacific basin. Aspects of the most recent warming in the tropical Pacific from 1990 to 1995,which are connected to but not synonymous with El Niño,are unprecedented in the climate record of the past 113 years. There is a distinction between El Niño(EN),the Southern Oscillation(SO)in the atmosphere,and ENSO,where the two are strongly linked,that emerges clearly on decadal time scales. In the traditional El Niño region,sea surface temperature anomalies(SSTAs)have waxed and waned,while SSTAs in the central equatorial Pacific,which are better linked to the SO,remained positive from 1990 to June 1995. We carry out several statistical tests to assess the likelihood that the recent behavior of the SO is part of a natural decadal-timescale variation. One test fits an autoregressive-moving average(ARMA)model to a measure of the SO given by the first hundred years of the pressures at Darwin,Australia,beginning in 1882. Both the recent trend for more ENSO events since 1976 and,the prolonged 1990-1995 ENSO event are unexpected given the previous record,with a probability of occurrence about once in 2000 years. This opens up the possibility that the ENSO changes may be partly caused by the observed increases in greenhouse gases.

SEA-surface temperature; extratropical response; southern oscillation; northern winter; pacific; organization; atmosphere;transients; anomalies; models

文章题目第一作者来源出版物1The 1990-1995 El Niño Southern Oscillation event: Longest on recordTrenberth,KEGeophysical Research Letters,1996,23(1):57-60 2 El Niño,La Niña,and the nonlinearity of their teleconnections Hoerling,MP 4 ENSO as an integrating concept in Earth science McPhaden,Michael J

The 1990-1995 El Niño Southern Oscillation event: Longest on record

Trenberth,KE; Hoar,TJ

*摘编自《海洋环境科学》2015年34卷3期:473~480页,图、表、参考文献已省略.

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