印度洋-太平洋暖池海域表层水温分析

利用1951~2003年HadISST资料集的表层海水温度（SST）资料,讨论了印度洋-西太平洋暖池（IPWP）海域,尤其是印度尼西亚贯穿流（ITF）及其周边海域SST的季节及年际变化的时空特征.研究结果表明,整个研究海域SST的年际变化均与ENSO相关,但印度洋与南海的响应特征与西太平洋的相反且不同步.前者海温变化滞后Nio3指数3~6个月,而热带太平洋西边界和ITF流经海域海温则超前1~3个月.沿ITF及其东印度洋出口,SST的年际变化规律不同于热带印度洋而与太平洋的相似,分析表明其在较大程度上受到ITF海洋桥的影响.在季节尺度上,印度洋和太平洋赤道海域SST的波动规律也有明显不同.以巽他岛弧（苏门答腊、爪哇和小巽他群岛）为界,从赤道西太平洋向西沿ITF流径,太平洋一侧SST的季节变化以0.5a周期的波动占主导,印度洋一侧则以1a周期占主导.     

全球海洋环流模式中上层海洋对表面强迫的响应和调整Ⅰ.年际变率

利用一个较高分辨率的全球海洋环流模式在COADS 1945～1993年逐月平均资料的强迫下对海温和环流场进行了模拟试验,研究了全球热带海洋(主要是热带太平洋)海温和环流场的年际变化特征及模式ENSO冷暖事件演变的控制机理.结果表明,模式成功地再现了和观测一致的海温和环流的年际变化以及ENSO演变特征.其中热带印度洋年际SST变率的主要模态表现为与ENSO相联系的海盆尺度的一致性增暖或变冷现象,次级模态为热带印度洋偶极子模态;热带大西洋的SST年际变率表现为类ENSO的年际振荡现象.在热带太平洋,SST年际变化主要表现为ENSO型,环流的年际变率表现为与ENSO相对应的热带海洋质量循环圈的年际异常.对应于暖(冷)事件,前期赤道海洋垂直环流圈显示出减弱(增强)的特征.其中南赤道流异常的位相较Nino3区海温总体要超前5个月左右的时间;赤道上翻流异常的位相在表层要超前4个月,并随时间由上至下扩展;赤道潜流的异常则显示出东传特征,其中最早的较为显著的异常发生ENSO成熟前3个月180°附近.在模式ENSO冷暖事件的演变过程中,次表层海温异常沿赤道的东传起了关键作用,模式的ENSO模态主要表现为"时滞振子"模态.     

一个简单的印-太海气耦合模式

本文基于一层半海洋模式和SVD(Singular Value Decomposition)大气模式构建了一个简单的海气耦合模式, 引入热通量的作用, 分析ENSO影响热带印度洋地区的动力学和热力学耦合过程。其中, 使用统计大气模式, 由给定的SST(Sea Surface Temperature)异常得到风应力异常, 进而驱动海洋环流反馈给SST, 完成海气的动力耦合; 使用块体经验公式由SST异常和风场异常计算热通量异常, 直接作用于SST, 实现海气的热力学耦合。动力耦合实验揭示, 太平洋第一EOF(Empirical Orthogonal Functions) 模态与观测基本吻合。并且模拟Ni?o 3指数存在两年左右的谱峰周期。这说明, 海气动力学耦合是ENSO生成的主要因素。热力耦合的加入是为了考察ENSO影响热带印度洋的热力学效应。同时考虑动力和热力耦合的实验结果表明, 热带太平洋暖异常中心更加接近观测值, 热带印度洋出现海盆尺度海温正异常。这意味着热带太平洋的ENSO信号通过海气界面的热量交换实现对热带印度洋地区的遥强迫, 导致印度洋海盆尺度增暖。     

How does the Indian Ocean subtropical dipole trigger the tropical Indian Ocean dipole via the Mascarene high？

The variation in the Indian Ocean is investigated using Hadley center sea surface temperature(SST)data during the period 1958–2010.All the first empirical orthogonal function(EOF)modes of the SST anomalies(SSTA)in different domains represent the basin-wide warming and are closely related to the Pacific El Ni o–Southern Oscillation(ENSO)phenomenon.Further examination suggests that the impact of ENSO on the tropical Indian Ocean is stronger than that on the southern Indian Ocean.The second EOF modes in different domains show different features.It shows a clear east-west SSTA dipole pattern in the tropical Indian Ocean(Indian Ocean dipole,IOD),and a southwest-northeast SSTA dipole in the southern Indian Ocean(Indian Ocean subtropical dipole,IOSD).It is further revealed that the IOSD is also the main structure of the second EOF mode on the whole basin-scale,in which the IOD pattern does not appear.A correlation analysis indicates that an IOSD event observed during the austral summer is highly correlated to the IOD event peaking about 9 months later.One of the possible physical mechanisms underlying this highly significant statistical relationship is proposed.The IOSD and the IOD can occur in sequence with the help of the Mascarene high.The SSTA in the southwestern Indian Ocean persists for several seasons after the mature phase of the IOSD event,likely due to the positive wind–evaporation–SST feedback mechanism.The Mascarene high will be weakened or intensified by this SSTA,which can affect the atmosphere in the tropical region by teleconnection.The pressure gradient between the Mascarene high and the monsoon trough in the tropical Indian Ocean increases(decreases).Hence,an anticyclone(cyclone)circulation appears over the Arabian Sea-India continent.The easterly or westerly anomalies appear in the equatorial Indian Ocean,inducing the onset stage of the IOD.This study shows that the SSTA associated with the IOSD can lead to the onset of IOD with the aid of atmosphere circulation and also explains why some IOD events in the tropical tend to be followed by IOSD in the southern Indian Ocean.     

The Indian Ocean’s asymmetric effect on the coupling of the Northwest Pacific SST and anticyclone anomalies during its spring–summer transition after El Niño

By comparing different climatologies in El Niño decaying summer with regard to the presence of Indian Ocean Basin (IOB) warming, we studied the effect of IOB warming on the Northwest Pacific sea surface temperature (SST) anomalies and the coupling process with the surface wind. Zonal asymmetric coupling feedback in the west and east of the Northwest Pacific were caused by the asymmetric spring–summer transition of the background tropical atmospheric circulation. Although the westward wind anomaly caused by the remote effect of IOB warming is found in the whole Northwest Pacific, reversal of the mean background surface winds in the western part leads to negative wind-evaporation SST (WES), whereas sustained trade winds lead to positive WES in the eastern part. The east–west SST gradient resulting from this zonal asymmetric evolution of SST sets off more positive feedback that strengthens the local anticyclone easterly anomalies.     

Why was the 2008 Indian Ocean Dipole a short-lived event?

In this paper, the role of equatorial oceanic waves in affecting the evolution of the 2008 positive Indian Ocean Dipole (IOD) event was evaluated using available observations and output from a quasi-analytical linear wave model. It was found that the 2008 positive IOD was an early matured and abruptly terminated event: developed in April, matured in July, and diminished in September. During the development and the maturation of the 2008 positive IOD event, the wind-forced Rossby waves played a dominant role in generating zonal current anomalies in the western equatorial Indian Ocean, while a complex interplay between the wind-forced upwelling Kelvin waves and the eastern-boundary-generated Rossby waves accounted for most of the variability in the eastern basin. The latter induced eastward zonal current anomalies near the eastern boundary during the peak phase of the event. The 2008 positive IOD event was abruptly terminated in mid-July. We found that there were strong eastward zonal currents in mid-July, though the surface wind anomalies in the eastern basin continued to be westward (upwelling favorable). Our analysis shows that these eastward zonal currents mainly resulted from the easternboundary-generated upwelling Rossby waves, although the contribution from the wind-forced downwelling Kelvin waves was not negligible. These eastward zonal currents terminated the zonal heat advection and provided a favorable condition for surface heat flux to warm the eastern basin.     

热带印度洋SST海盆模态的“充电/放电”作用——对夏季南亚高压的影响

根据观测资料和海气耦合模式初值试验结果,通过比较分析热带太平洋SST主模态(ENSO模)和热带印度洋SST主模态(海盆模)对夏季南亚高压的影响,揭示了印度洋海盆模的"充电/放电"作用:赤道中东太平洋海温异常首先对印度洋进行"充电",形成热带印度洋SST对太平洋EN-SO的响应模态——海盆模。该模态在ENSO发生翌年春季达到峰值位相,而且有很好的持续性,可以从春季持续到夏季,该暖(冷)模态可以引起大气的"Matsuno-Gillpattern"响应,并通过亚洲夏季平均西南季风的异常水汽输送等使得夏季南亚高压偏强(弱),即为"放电"过程。而赤道中东太平洋海温异常对夏季南亚高压的直接影响并不显著,并指出了夏季南亚高压和超前3~12个月Nio3指数之间高的显著正相关关系只是一个表象,并不是太平洋海温异常对南亚高压的直接影响结果,而是通过印度洋海盆模态的"充电/放电"作用引起的。     

Estimates of the mutual influence of variations in the sea surface temperature in tropical latitudes of the Pacific,Atlantic, and Indian Oceans from long-period data series

Based on the concept of the Wiener&–Granger causality, a seasonal trivariate analysis of directional couplings between sea surface temperature variations in tropical latitudes of the Pacific, Atlantic, and Indian Oceans has been performed. These variations are related to significant modes of regional and global climatic variability. We have analyzed time series of monthly indices of Pacific Ocean processes of the El Ni&ño/Southern Oscillation (ENSO), equatorial Atlantic mode (EAM), and Indian Ocean Dipole (IOD)&—along with its western and eastern poles for the period of 1870&–2015. A scheme of interactions between the processes under study where coupling strength estimates are presented, along with estimates of the season of its maximal value and the coupling coefficient sign, has been developed. We have found the seasonal influences of ENSO on the western and eastern poles of IOD, the eastern pole of IOD on ENSO, EAM on ENSO, and IOD on EAM to be the most significant couplings.     

ENSO variability and the eastern tropical Pacific: A review

El Niño-Southern Oscillation (ENSO) encompasses variability in both the eastern and western tropical Pacific. During the warm phase of ENSO, the eastern tropical Pacific is characterized by equatorial positive sea surface temperature (SST) and negative sea level pressure (SLP) anomalies, while the western tropical Pacific is marked by off-equatorial negative SST and positive SLP anomalies. Corresponding to this distribution are equatorial westerly wind anomalies in the central Pacific and equatorial easterly wind anomalies in the far western Pacific. Occurrence of ENSO has been explained as either a self-sustained, naturally oscillatory mode of the coupled ocean–atmosphere system or a stable mode triggered by stochastic forcing. Whatever the case, ENSO involves the positive ocean–atmosphere feedback hypothesized by Bjerknes. After an El Niño reaches its mature phase, negative feedbacks are required to terminate growth of the mature El Niño anomalies in the central and eastern Pacific. Four requisite negative feedbacks have been proposed: reflected Kelvin waves at the ocean western boundary, a discharge process due to Sverdrup transport, western Pacific wind-forced Kelvin waves, and anomalous zonal advections. These negative feedbacks may work together for terminating El Niño, with their relative importance being time-dependent.ENSO variability is most pronounced along the equator and the coast of Ecuador and Peru. However, the eastern tropical Pacific also includes a warm pool north of the equator where important variability occurs. Seasonally, ocean advection seems to play an important role for SST variations of the eastern Pacific warm pool. Interannual variability in the eastern Pacific warm pool may be largely due to a direct oceanic connection with the ENSO variability at the equator. Variations in temperature, stratification, insolation, and productivity associated with ENSO have implications for phytoplankton productivity and for fish, birds, and other organisms in the region. Long-term changes in ENSO variability may be occurring and are briefly discussed. This paper is part of a comprehensive review of the oceanography of the eastern tropical Pacific.     

Analysis of the global relationship of biennial variation of sea surface temperature and air-sea heat flux using satellite data

We investigated the phase difference and the cross correlation coefficient between the band-pass filtered biennial variations of sea surface temperature (SST) and air-sea heat flux estimated by the monthly mean 2°×2° satellite data of Advanced Very High Resolution Radiometer (AVHRR) and Special Sensor Microwave/Imager (SSM/I) from July 1987 to June 1991. Judging from the phase difference, it can be determined whether the biennial variation of SST is controlled by local thermal air-sea interaction or oceanic processes of horizontal transport. When the local air-sea heat flux controls the biennial variation of SST, the phase of SST advances /2 (6 months) against that of the air-sea heat flux. In contrast, when the biennial variation of SST is controlled by the oceanic process, the phase difference between the SST and the air-sea heat flux becomes 0 or (12 months). In this case, two types of the phase differences are determined, depending on which variability of SST and air-sea heat flux is larger. The close thermal air-sea interaction is noticeable in the tropics and in the western boundary current region. The phase difference of /2 appears mainly in the north Pacific, the southeast Indian Ocean, and the western tropical Pacific; zero in the eastern tropical Pacific and the northeast and equatorial Atlantic; and that of in the central equatorial Pacific and north of the intertropical convergence zone (ITCZ) of the Atlantic. Phase differences of 0, , or /2 are possible in the western boundary current regions. This fact indicates that each current plays a different role to the biennial variation of SST. It is inferred that SST anomalies in the tropics are mutually correlated, and the process in which marked SST anomalies in the tropics are transferred to the remote area was probed. In the equatorial Pacific, the SST anomaly is transferred by the long planetary wave. On the other hand, it is found from the phase relationship and the horizontal correlation of SST that the SST anomaly in the central and western equatorial Pacific is connected through atmospheric mediation. It is suggested that the biennial variation of SST in the eastern Indian Ocean is affected by heat transport due to the Indonesian throughflow from the western tropical Pacific. It is found that the mentioned pattern of the interannual variation of SST in the tropical Atlantic as a dipole is not tenable.     

西太平洋暖池海温异常年夏季东亚大气环流特征

利用NCEP/NCAR逐月再分析资料对西太平洋暖池区海表水温冷、暖异常年夏季东亚大气环流作了合成分析,与气候平均比较后发现:夏季暖池区暖异常时,在西太平洋上空的对流层低层产生一个强的反气旋偏差环流,因而不利于南海南部和赤道太平洋地区的西风发展,使热带夏季风强度减弱;在南海西部和中南半岛东部有偏差气流转向大陆,因而增强了偏南风,使副热带夏季风强度增强;在对流层中、下层副高脊线位置偏南,大约以400hPa为分界线,低层副高强度增强,高层副高强度减弱。西太平洋暖池冷异常年夏季东亚大气环流特征大致与上述情况相反,且强度或变化幅度小于暖异常年夏季。另外,与气候平均比较,暖异常年纬向Walker环流上升支大幅西移,而冷异常年该环流上升支则东移。     

南印度洋偶极子及其影响研究进展

回顾了对南印度洋副热带海气相互作用的研究,总结了南印度洋偶极子事件背景下的气候变化。印度洋海表温度的方差表明南印度洋是整个印度洋海温变率最强的区域,年际海温变化最显著的特征就是海温呈现西南—东北向的偶极子型分布,被称为南印度洋偶极子(Southern Indian Ocean Dipole, SIOD)。南印度洋海温偶极子的形成主要是受大尺度大气环流调整的影响。南印度洋副热带反气旋环流异常引起了印度洋热带东风异常和副热带西风异常的变化,影响了潜热通量、上升流和Ekman热输送,进而引起了海温变化。SIOD对热带和热带外大气环流也有影响,尤其会影响亚洲夏季风降水异常,例如我国的降水异常和南印度洋偶极子海温异常具有显著相关关系。此外,SIOD模态所引起的经向环流异常与南海、菲律宾地区的反气旋环流异常也有紧密联系。     

印度洋波浪诱导的水体输运效应及其对赤道SST异常的影响

波浪诱导的水体输运会对海洋产生大尺度影响。结合波浪大尺度效应的研究现状和印度洋涌浪分布的事实,利用ECMWF-CERA20的波浪、海表面温度(SST)及风场数据,采用多种统计分析方法,研究了波浪输运与赤道印度洋SST的潜在关系。结果显示:中高纬度波浪输运异常的低频信号在空间、周期上与赤道SST异常均有高度相似性;Stokes漂流纬向、经向异常呈现出南—北、东—西的振荡,其第二模态时间序列与印度洋偶极子(Indian Ocean Dipole,IOD)指数存在强相关性并在La Ni a次年的负IOD事件中达到最高:相关系数在ACC区域纬向异常超前6个月时接近0.6,中纬度区域经向异常在超前3个月时达到0.7。在La Ni a次年的负IOD中,波浪经向输运异常的相位(超前三个月)与赤道SST异常相位呈全年反相位,经向浪致输运异常造成的东—西热量输运差异对赤道SST异常分布有不可忽略的贡献。     

热带太平洋与热带大西洋海表温度主模态的相互作用

根据英国Hadley气候中心的海表温度资料和美国NCEP/NCAR中心的大气资料,研究了热带太平洋与热带大西洋海表温度主模态的相互作用。热带太平洋的ENSO可以导致大西洋Nino模态或经向偶极子模态,这主要是通过热带海洋-大气相互作用,或大气的太平洋-北美遥相关过程实现的。大西洋Nino模态的暖(冷)位相会导致赤道中东太平洋的海表温度降低(升高)。这可能是通过两种途径完成的:一种可能是大西洋Nino使印度洋增暖(变冷),进而引起赤道中太平洋的东(西)风异常,通过海洋-大气相互作用正反馈机制能发展成为La Nina(El Nino),使赤道东太平洋海温降低(升高);另一种可能是大西洋Nino直接可以导致太平洋Walker环流增强(减弱),从而使赤道东太平洋海温降低(升高)。     

春季青藏高原感热通量对不同海区海温强迫的响应及其对我国东部降水的影响

本文利用在青藏高原适用性较好的ERA-interim地表感热通量资料,研究了1981-2010年青藏高原春季地表感热通量的年际变率与前期不同海区海温强迫的联系,以及这种联系对我国东部降水可能造成的影响。结果表明,春季青藏高原地表感热通量的年际变化有两个主要的模态,分别与前期太平洋以及印度洋海温有密切联系。与冬季ENSO事件相应的赤道中东太平洋海温强迫可以激发一个向极向西的波列,通过改变青藏高原南侧的环流和降水异常,形成一个纬向偶极型分布的高原感热第一模态,其对应的时间序列主要表现为准5 a的振荡,与ENSO事件的周期较为吻合;而春季印度洋的三极型海温分布可以强迫出一个跨越南北半球的波列,使青藏高原主体表现为东风异常,减弱背景西风,从而形成一个青藏高原主体与周围反相关的回字形感热第二模态,其主要呈现5~7 a的振荡周期。ENSO事件以及印度洋海温分布分别与青藏高原春季感热两个主模态相联系,并且冬春季海温与高原春季感热主模态对我国东部春季降水有协同影响,对于我国北方降水异常而言,高原的贡献相对海洋更重要。     

赤道太平洋海域上层海洋热含量及其变化机制的诊断分析*

基于1992—2015年国际共享的ECCO v4 (Estimating the Circulation and Climate of the Ocean Version 4)同化产品, 利用热含量控制方程定量地诊断赤道太平洋(118°E—75°W, 5°S—5°N, 0~300m)和Niño 3.4区(170°W—120°W, 5°S—5°N, 0~80m)这两块区域热含量变化机制。对于去掉季节平均后的年际变化, 在赤道太平洋地区, 时间趋势项主要由经向输送和海表热通量项共同驱动。通过5°N断面的输送决定了时间趋势项的幅值和正负符号。在Niño 3.4区, 时间趋势项主要由海表热通量项和热量输送项共同驱动, 其中垂向输送对总输送贡献最大。赤道太平洋地区经向热量输送异常领先于Niño 3.4区垂向热量输送异常, 这解释了在年际尺度上赤道太平洋热含量异常领先Niño 3.4指数变化的原因。尽管EP(Eastern Pattern)型El Niño和CP(Central Pattern)型El Niño有许多不同之处, 合成分析表明, 两类El Niño的共同点为: 在赤道太平洋地区, 两类El Niño事件的热量输送异常在发展期和衰退期由经向输送主导; 在Niño 3.4区, EP型El Niño和CP型El Niño的热量输送在发展期和衰退期由垂向输送主导。     

赤道太平洋-印度洋海温异常综合模与次表层海温异常

通过对1958-2001年的SODA海温资料进行经验正交函数分解,得到了太平洋-印度洋海温异常综合模态,该模态在海表及次表层的时空演变特征的分析表明,在赤道西印度洋、中东太平洋的海温偏高(低)时,赤道西太平洋、东印度洋的海温偏低(高)。该综合模态既有年际变化特征,还有年代际变化特征,在20世纪70年代中后期由以负指数为主转变为以正指数为主。对1958-2001年强正、负指数事件合成分析结果得知,综合模也存在着显著的年变化特征,在2-4月份偏弱,最强出现在10月份。西太平洋暖池次表层与赤道东太平洋次表层、赤道东印度洋次表层与西印度洋次表层有一种反位相的变化。次表层海温异常在东太平洋、西印度洋分别沿着南北纬10°左右向西太平洋、东印度洋传播并向赤道扩展,西太平洋、东印度洋的次表层海温异常则分别沿赤道向东太平洋、西印度洋传播汇聚。     

Can an atmospherically forced ocean model accurately simulate sea surface temperature during ENSO events?

The performance of an atmospherically forced ocean general circulation model (OGCM) in simulating daily and monthly sea surface temperature (SST) is examined during the historical El Niño Southern Oscillation (ENSO) events during the time period 1993–2003. For this purpose, we use the HYbrid Coordinate Ocean Model (HYCOM) configured for the North Pacific north of 20°S at a resolution of ≈9 km. There is no assimilation of (or relaxation to) SST data and no date-specific assimilation of any data type. The ability of the model in simulating temporal variations of SST anomalies is discussed by comparing model results with two satellite-based SST products. The HYCOM simulation gives a basin-averaged monthly mean bias of 0.3 °C and rms difference of 0.6 °C over the North Pacific Ocean during 1993–2003. While the model is able to simulate SST anomalies with mean biases  <0.5 °C  in comparison to observations during most of the ENSO events, limitations in the accuracy of atmospheric forcing (specifically, net short-wave radiation) have some influence on the accuracy of simulations. This is specifically demonstrated during the 1998 transition period from El Niño to La Niña, when a record large SST drop of  ≈7 °C  occurred in the eastern equatorial Pacific Ocean.     

太平洋表层海温的年代际变化

众所周知，ENSO(El Nino/ Southern Oscillation)是发生在热带太平洋的年际时间尺度上最强的气候信号，与 El Nino (La Nina)相应的正(负)海温距平(SSTA)主要分布于赤道中东太平洋地区(Rasmusson et al.，1982)。相对于热带太平洋的年际ENSO现象，人们注意到北太平洋海平面气压(SLP)存在更长周期的年代际变化(Trenberth et al.，1994)，有人认为这与北太平洋的表层温度(SST)变化有关(Latif et al.，1994)，也有人认为与热带SST的异常关系更为密切(Jacobs et al.，1994)。20世纪80年代后的ENSO事件和20世纪60，70年代有明显的差别(Wang，1995)，20世纪90年后El Nino发生频数增加，并且在1997和1998年出现了20世纪最强的一次Nino事件(McPhaden，1999)。 因此，不论是作为大气年代际变化可能的一个驱动因子，还是作为年际ENSO的背景场，从整体上了解太平洋SST的年代际时间尺度上的时、空变化特征都是十分重要的。