一个可供ENSO预测的海气耦合环流模式及1997/1998 ENSO的预测

利用中国科学院大气物理研究所设计发展的具有较高分辨率的热带太平洋和全球大气耦合环流模式,设计了一个初始化方案,建立了ＥＮＳＯ预测系统,进行了系统性的预测试验。预测结果检验评估表明,该预测系统表现出较强的预报能力,赤道中东太平洋地区（Ｎｉｎｏ３和Ｎｉｎｏ３４）海表温度距平预报相关技巧高于０５２的预报可持续１８个月,该预测系统可应用到试验性的海温预测实践中。利用该系统对１９９７／１９９８年ＥＮＳＯ进行了实际预测,表明预测是成功的,预测的海温距平已提供给今年我国夏季降水预测使用,取得了良好的预测效果。     

利用海气耦合模式预测的大尺度环流进行热带气旋年频数的预测试验

基于对热带气旋生成频数和大尺度环流相关关系的分析,利用SINTEX-F海气耦合模式预测的大尺度大气环流信息,通过提取模式预测较好与热带气旋生成密切相关的有用信息,建立了一个基于动力模式预测结果的南海和西太平洋热带气旋年频数预测模型,并对1982—2010年的热带气旋生成频数进行预测试验与检验。SINTEX-F海气耦合模式能够较好预测部分与热带气旋生成密切相关的大尺度环流特征,其中包括热带气旋活动区域的海平面气压、对流层风垂直切变、850 hPa热带辐合带和850 hPa 90 °E附近的越赤道气流。利用这些大尺度环流建立的预测因子与热带气旋生成频数有很好的相关关系,利用这些预测因子建立的多元回归预测模型对热带气旋频数的拟合率为0.8(相关系数,超过99.9%的信度检验)。预测模型的交叉检验结果表明模型整体预测效果较好。交叉检验预测结果与实况热带气旋频数的相关为0.71(超过了99.9%的信度检验),距平同号率为82.8%。但模型对热带气旋异常年的预测误差较大。      

一个海气耦合环流模式中的ENSO循环特征及控制机理

本文利用中科院大气所两层全球大气环流模式和十四层热带太平洋模式的耦合环流模式１００年积分中的后３０年的月平均输出资料,通过分析海表面温度、上层海洋热容量和海表面高度异常的年际变化,揭示了模式ＥＮＳＯ循环（包括其产生、发展、成熟和消亡过程）的特征及其控制机理。结果表明,控制本文耦合环流模式中ＥＮＳＯ循环的机理是“时滞振子”模态,这和由中间复杂程度耦合模式得到的ＥＮＳＯ控制机理是一致的。反映了“时滞振     

模式气候吸引子信息约束下的动力协调初始化方法及其在ENSO预测中的应用

为了改善模式初始场质量,减少初值与模式不协调对ENSO预测的影响,针对国家气候中心NCCo海-气耦合模式原初始化方案动力小协调的问题,从利用模式长期耦合模拟资料中的模式气候吸引子信息的角度出发,发展了一种获取观测资料中与模式相协调分量的信息重构方法,提出了一种模式气候吸引子信息约束下的动力协调初始化方案.对该方案回报检验的结果表明:通过反演NCCo海-气耦合模式模拟资料中的模式气候吸引子信息,有助于获取观测资料中与模式相协调的信息分量特征,实现了初始化过程中动力模式与所同化观测资料间的协调.这种基于信息重构方法的动力协调初始化方案,既可以延续原初始化方案利用观测信息较多的优势,又克服了原方案中观测资料和动力模式不协调的缺陷.这种新的初始化方案,消除了观测资料和模式不协调在初始场中产生的小尺度高频噪声,突出了与NCCo模式动力特征相适应的ENSO尺度信息.进而抑制了初始场中高频噪声所引起的快变预报误差的增长,提高了模式的预测技巧.     

全球热带简单海气耦合模式中的ENSO预报试验

利用一个全球热带简单海气耦合模式(GTSM模式),并选取热带三大洋较强的冷暖事件作为预报对象进行了若干预报试验,分析结果发现:在GTSM模式中由于热带三大洋海气耦合通过大气模式而相互作用和影响,使得该模式对于东大西洋和中东印度洋较强冷暖事件的预报能力,较单独大西洋或单独印度洋耦合模式均有明显提高,预报和观测的ATL3、IND3指数的相关系数达到0.5以上的月份,分别达到9个月和6个月左右;而在东太平洋则和ZC(LDEO1)模式差不多,预报和观测的Nio3指数的相关系数达到0.6以上的月份可以达到15个月左右.     

1月份两类ENSO的海气环流模态分析

本文对1950～2001年1月份的大气风场和大洋流场做了联合复EOF（Empirical Orthogonal Function）分解,用以探讨1月份两类ENSO（El Ni?o-Southern Oscillation）的海气环流及耦合情况,所得结果主要有:该分解第1、2模态空间场分别相应于东部型、中部型ENSO,前者在赤道太平洋东部和中部都有海温动力异常,并以东部异常最强,后者仅在中部存在此异常,两模态的时间系数都与ENSO有很好相关,为此第1、2模态可分别称为东部型、中部型ENSO的风场流场（异常）模态。东部型ENSO模态具有3～6年的年际变化和13～14年的年代际变化,中部型则有明显的7年年际变化和12、17年的年代际变化,两者中约13年的周期与冬季北太平洋NPGO（North Pacific Gyre Oscillation）的周期相同。东、中部型El Ni?o期间,沃克环流上升支分别从印尼东移至赤道西、中太平洋,并有所减弱;南、北支哈得莱环流则分别位于日界线以东及该线附近,且均有所加强,从而使南、北太平洋副热带高压偏强;而在5°S的南美沿岸则分别有垂直运动上升和下沉异常。在海气耦合上,两类ENSO模态在赤道中太平洋均存在西风异常与海洋赤道Kelvin波和Rossby波的波包解耦合,而海温动力异常对大气的影响则都起到负反馈作用,从而有利于ENSO的维持和稳定。     

混合海气耦合模式中的ENSO循环及其形成机制

在无异常外强迫的情况下, 将混合海气耦合模式进行了45年的模拟积分.结果表明:模式能较好地再现类似ENSO循环的热带太平洋海洋、大气的年际振荡, 模式ENSO循环的主周期为4~5年; 探讨了ENSO循环的负反馈机制, 指出:暖态的消亡与El Niño发展过程中太平洋东部不断增强的东风异常所产生的冷水上翻的加强以及纬向向西的冷平流有关; 冷态的消亡主要由赤道波的时滞效应所致.     

一个可描写ENSO循环基本特点的简单热带海气耦合模式

在所构造的海气耦合模式中,采用Zebiak海洋模式框架,并重建了一个海洋数值模式,大气模式采用了Gill模式.在大气模式中保留了时间发展项,潜热加热采用了Kleeman方案.对模式的积分结果表明,海温异常具有3～7年的准周期振荡.在模式El Nino事件的初始阶段,西风异常,海温正距平(SSTA)首先在赤道西太平洋发生,然后向东传播、加强.在模式ENSO循环的位相转换过程中,SSTA的空间分布共有4种不同类型.模式模拟的El Nino事件的初始阶段有两种发展类型,它们是:在初始阶段中西太平洋和东太平洋沿岸各有海表温度的正异常发生.在以后的发展中,一种情况是这两块正SSTA都发展连成一片,形成El Nino事件;另一种情况是中西太平洋地区的正SSTA衰减,中东太平洋地区的正SSTA加强,向西传播,形成El Nino事件.模式模拟的La Nina事件的初始阶段也有两科发展类型,它们的发展过程和El Nino事件初始阶段的发展过程相似.     

ENSO动力学与预测

发生在热带太平洋地区的ENSO现象是海气相互作用的集中表现,是年际气候变化中的最强信号.由于它的发生会在全球许多地区引起严重的气候异常,极大地影响着这些地区的工农业生产和人民生活,因此,对ENSO的机理及其预测的研究一直是大气海洋界的一个热点研究课题.中国科学院大气物理研究所在ENSO的机理及其预测等方面进行了大量的研究,取得了许多研究成果.作者将对中国科学院大气物理研究所在这方面的一些研究成果进行回顾和介绍.     

简单海气耦合模式大气运动方程的非线性对ENSO循环模拟的影响

研究简单海气耦合模式大气运动方程非线性对ENSO循环的影响,即讨论大气运动方程的纬向非线性、经向非线性、纬向和经向非线性对ENSO循环的影响。同时,讨论了ENSO循环对大气运动方程非线性的敏感性问题。数值实验证明,大气运动方程的非线性对ENSO循环的影响明显,并且ENSO循环对大气运动方程的非线性非常敏感。因此,研究简单海气耦合模式中大气运动方程的非线性对ENSO循环的影响,对进一步理解ENSO循环的物理机制,具有一定的理论意义和实用价值。     

一个灵活的海洋——大气耦合环流模式

Based on the National Center for Atmospheric Research (NCAR) Climate System Model version 1(CSM-1), a Flexible coupled General Circulation Model version 0 (FGCM-0) is developed in this study through replacing CSM-1＇s oceanic component model with IAP L30T63 global oceanic general circulation model and some necessary modifications of the other component models. After the coupled model FGCM--0 is spun up for dozens of years, it has been run for 60 years without flux correction. The model does not only show the reasonable long-term mean climatology, but also reproduce a lot of features of the interannual variability of climate, e.g. the ENSO-like events in the tropical Pacific Ocean and the dipole mode pattern in the tropical Indian Ocean. Comparing FGCM-0 with the NCAR CSM-1, some common features are found, e.g. the overestimation of sea ice in the North Pacific and the simulated double ITCZ etc.The further analyses suggest that they may be attributed to errors in the atmospheric model.     

Annual ENSO simulated in a coupled ocean–atmosphere model

Using an output from 200-year integration of the Scale Interaction Experiment of EU project-F1 model (SINTEX-F1), the annual ENSO reproduced in the coupled general circulation model is investigated, suggesting the importance of reproducing an annual cycle in realistically simulating ENSO events. Although many features of the annual ENSO are reproduced, the northward expansion of sea surface temperature anomaly (SSTA) in the eastern tropical Pacific stays south of the equator. It is suggested that this model bias is due to the excitation of the too strong Rossby waves in the southeastern tropical Pacific, which reflect at the western boundary and intrude into the eastern equatorial Pacific. The zonal wind stress anomaly along the equator also plays an important role in generating the equatorial Kelvin waves. The amplitude of SSTA for the annual ENSO mode is reproduced, but its variance is only 20% of the observation; this is again due to the lack of northward migration of seasonal SSTA in the equatorial region and weaker coastal Kelvin waves along South America. Remedies for the model bias are discussed.     

Monsoon circulation related to enso phase-locking

The relation of interannual anomaly of East Asian monsoon to the ENSO cycle is investigated in terms of even and odd symmetry analysis over a tropical heating field based on the past 30-year data. Evidence suggests that odd and even symmetry components related to the monsoon and Walker heating, respectively, effectively describe the East Asian monsoon circulation and Pacific Walker analog, with the monsoon intensity index corresponding to its heating vigor and western Pacific Walker heating vigor to ENSO phase change, both types of heating marked by pro-nounced seasonal variation and phase-locking; the key region for linking monsoon-ENSO interaction is the western Pacific warm pool; the monsoon effect upon ENSO cycle is affected jointly by the seasonal evolution and interannual anomaly of the heating components; the superimposition of an anti-Walker circulation phase produced by interannual winter monsoon perturbation upon a weaker Walker phase on a seasonal basis leads to an El Nino hap-pening in March-April and plays a significant role in maintaining a warm ENSO phase.     

Multi-year predictability in a coupled general circulation model

Multi-year to decadal variability in a 100-year integration of a BMRC coupled atmosphere-ocean general circulation model (CGCM) is examined. The fractional contribution made by the decadal component generally increases with depth and latitude away from surface waters in the equatorial Indo-Pacific Ocean. The relative importance of decadal variability is enhanced in off-equatorial “wings” in the subtropical eastern Pacific. The model and observations exhibit “ENSO-like” decadal patterns. Analytic results are derived, which show that the patterns can, in theory, occur in the absence of any predictability beyond ENSO time-scales. In practice, however, modification to this stochastic view is needed to account for robust differences between ENSO-like decadal patterns and their interannual counterparts. An analysis of variability in the CGCM, a wind-forced shallow water model, and a simple mixed layer model together with existing and new theoretical results are used to improve upon this stochastic paradigm and to provide a new theory for the origin of decadal ENSO-like patterns like the Interdecadal Pacific Oscillation and Pacific Decadal Oscillation. In this theory, ENSO-driven wind-stress variability forces internal equatorially-trapped Kelvin waves that propagate towards the eastern boundary. Kelvin waves can excite reflected internal westward propagating equatorially-trapped Rossby waves (RWs) and coastally-trapped waves (CTWs). CTWs have no impact on the off-equatorial sub-surface ocean outside the coastal wave guide, whereas the RWs do. If the frequency of the incident wave is too high, then only CTWs are excited. At lower frequencies, both CTWs and RWs can be excited. The lower the frequency, the greater the fraction of energy transmitted to RWs. This lowers the characteristic frequency (reddens the spectrum) of variability off the equator relative to its equatorial counterpart. At low frequencies, dissipation acts as an additional low pass filter that becomes more effective, as latitude increases. At the same time, ENSO-driven off-equatorial surface heating anomalies drive mixed layer temperature responses in both hemispheres. Both the eastern boundary interactions and the accumulation of surface heat fluxes by the surface mixed layer act to low pass filter the ENSO-forcing. The resulting off-equatorial variability is therefore more coherent with low pass filtered (decadal) ENSO indices [e.g. NINO3 sea-surface temperature (SST)] than with unfiltered ENSO indices. Consequently large correlations between variability and NINO3 extend further poleward on decadal time-scales than they do on interannual time-scales. This explains why decadal ENSO-like patterns have a broader meridional structure than their interannual counterparts. This difference in appearance can occur even if ENSO indices do not have any predictability beyond interannual time-scales. The wings around 15–20°S, and sub-surface variability at many other locations are predictable on interannual and multi-year time-scales. This includes westward propagating internal RWs within about 25° of the equator. The slowest of these take up to 4 years to reach the western boundary. This sub-surface predictability has significant oceanographic interest. However, it is linked to only low levels of SST variability. Consequently, extrapolation of delayed action oscillator theory to decadal time-scales might not be justified.     

Decadal climate variability simulated in a coupled general circulation model

A 1000 year integration of the CSIRO coupled ocean-atmosphere general circulation model is used to study low frequency (decadal to centennial) climate variability in precipitation and temperature. The model is shown to exhibit sizeable decadal variability for these fields, generally accounting for approximately 20 to 40% of the variability (greater than one year) in precipitation and up to 80% for temperature. An empirical orthogonal function (EOF) analysis is applied to the model output to show some of the major statistical modes of low frequency variability. The first EOF spatial pattern looks very much like that of the interannual ENSO pattern. It bears considerable resemblance to observational estimates and is centred in the Pacific extending into both hemispheres. It modulates both precipitation and temperature globally. The EOF has a time evolution that appears to be more than just red noise. Finally, the link between SST in the Pacific with Australian rainfall variability seen in observations is also evident in the model. Received: 29 August 1998 / Accepted: 31 July 1999     

Ocean-atmosphere interactions and climate drift in a coupled general circulation model

 We have analysed numerical simulations performed with a global 3D coupled atmosphere-ocean model to focus on the role of atmospheric processes leading to sea surface temperature (SST) drift in the tropics. Negative SST errors occur coherently in space and time with large positive errors in latent heat and momentum fluxes at the tropical air-sea interface, as diagnosed from forced SST simulations. The warm pool in the western Pacific disappears after a few years of simulation. Strong SST gradients enforce regions of high precipitation that are thin and stationary north of the equator. We detail the implications for the ocean-atmosphere system of such upheaval in the deep convection location. A sensitivity experiment to empirically formulate air-sea drag coefficient shows that the rapid warm pool erosion is not sensitive to changes in the formulation of the surface drag coefficient over the oceans because the corresponding changes in turbulent heat fluxes and LW cooling approximately cancel one another. In the eastern Pacific, the improvement in SST is striking and caused by feedbacks between SST, surface turbulent fluxes and boundary layer cloud fraction, which decreases as SST warms. Received: 8 December 1998 / Accepted: 6 January 2000     

Mean climate state simulated by a coupled ocean-atmosphere general circulation model

Summary The result of a 100-year integration of a coupled ocean-atmosphere general circulation model (CGCM) is analyzed, and compared with that of a 25-year integration of the corresponding uncoupled atmospheric general circulation model (AGCM) and observed data. The large-scale circulation patterns of mean climate state simulated by the CGCM are in good agreement with the observed ones, although differences exit in the positions and intensities between the simulated and the observed patterns. Having compared the standard deviations of monthly mean sea level pressure simulated by the CGCM to those by the AGCM, we found that the interaction between ocean and atmosphere mainly increases the interannual variability in the tropics especially in summer. The CGCM can also produce El Niño and Southern Oscillation (ENSO) events, whereas the AGCM cannot reproduce the main features of the Southern Oscillation. This implies that the air-sea interaction may be a principal mechanism for the occurrence of ENSO phenomena. The fundamental features of simulated regional climates are also analyzed. The CGCM can reproduce principal characteristics of surface air temperature and precipitation at five selected typical regions (desert region, plain region, monsoon region etc.). The distributions of annual mean surface ait temperature and precipitation in East Asia can also be reasonably simulated.With 9 Figures     

中国业务动力季节预报的进展

利用动力模式开展季节到年际的短期气候预测 ,是目前国际上气候预测的发展方向。自 1996年以来 ,经过 8a多的研制和发展 ,国家气候中心已建立起第 1代动力气候模式预测业务系统 ,其中包括 1个全球大气 海洋耦合模式 (CGCM )、1个高分辨率东亚区域气候模式 (RegCM_NCC)和 5个简化的ENSO预测模式 (SAOMS) ,可用于季节—年际时间尺度的全球气候预测 ;全球海气耦合模式与区域气候模式嵌套 ,可以提供高分辨率的东亚区域气候模式制做季节预测。CGCM对 1982～ 2 0 0 0年夏季的历史回报试验表明 ,该模式对热带太平洋海表面温度和东亚区域的季节预测具有较好的预测能力。RegCM NCC的 5a模拟基本上能再现东亚地区主要雨带的季节进展。利用嵌套的区域气候模式RegCM NCC对 1991～ 2 0 0 0年的夏季回报表明 ,在预报主要季节雨带方面有一定技巧。 2 0 0 1～ 2 0 0 3年 ,CGCM和RegCM NCC的实时季节预报与观测相比基本合理。特别是 ,模式成功地预报了 2 0 0 3年梅雨季节长江和黄河之间比常年偏多的降水。SAOMS模式系统的回报试验表明 ,该系统对热带太平洋海表面温度距平有一定的预报能力 ,模式超前 6～ 12个月的回报与观测的相关系数明显高于持续预报。 1997～ 2 0 0 3年 ,SAOMS多模式集合实时预报与观测的相关系数达到     

The stability of the North Atlantic thermohaline circulation in a coupled ocean-atmosphere general circulation model

 The stability of the Atlantic thermohaline circulation against meltwater input is investigated in a coupled ocean-atmosphere general circulation model. The meltwater input to the Labrador Sea is increased linearly for 250 years to a maximum input of 0.625 Sv and then reduced again to 0 (both instantaneously and linearly decreasing over 250 years). The resulting freshening forces a shutdown of the formation of North Atlantic deepwater and a subsequent reversal of the thermohaline circulation of the Atlantic, filling the deep Atlantic with Antarctic bottom water. The change in the overturning pattern causes a drastic reduction of the Atlantic northward heat transport, resulting in a strong cooling with maximum amplitude over the northern North Atlantic and a southward shift of the sea-ice margin in the Atlantic. Due to the increased meridional temperature gradient, the intertropical convergence zone over the Atlantic is displaced southward and the westerlies in the Northern Hemisphere gain strength. We identify four main feedbacks affecting the stability of the thermohaline circulation: the change in the overturning circulation of the Atlantic leads to longer residence times of the surface water in high-northern latitudes, which allows them to accumulate more precipitation and runoff from the continents. As a consequence the stratification in the North Atlantic becomes more stable. This effect is further amplified by an enhanced northward atmospheric water vapour transport, which increases the freshwater input into the North Atlantic. The reduced northward oceanic heat transport leads to colder sea-surface temperatures and an intensification of the atmospheric cyclonic circulation over the Norwegian Sea. The associated Ekman transports cause increased upwelling and increased freshwater export with the East Greenland Current. Both the cooling and the wind-driven circulation changes largely compensate for the effects of the first two feedbacks. The wind-stress feedback destabilizes modes without deep water formation in the North Atlantic, but has been neglected in almost all studies so far. After the meltwater input stops, the North Atlantic deepwater formation resumed in all experiments and the meridional overturning returned within 200 years to a conveyor belt pattern. This happened although the formation of North Atlantic deep water was suppressed in one experiment for more than 300 years and the Atlantic overturning had settled into a circulation pattern with Antarctic bottom water as the only source of deep water. It is a clear indication that cooling and wind-stress feedback are more effective, at least in our model, than advection feedback and increased atmospheric water vapour transport. We conclude that the conveyor belt-type thermohaline circulation seems to be much more stable than hitherto assumed from experiments with simpler models. Received 31 January 1996/Accepted 22 August 1996