对热带不稳定海气相互作用模式的改进

对以前提出的热带海气相互作用模式［１］风应力的参数化作了改进。和以前一样，在这个耦合模式中，滤去了大气和海洋中的重力惯性波，只保留了向西传播的Ｒｏｓｓｂｙ波。但经过海气相互作用后，理论分析指出，在耦合模式中存在着快的和慢的两类波动。快波频率的实部、即其相速度是向西传的，并接近于未经海气相互作用时大气中Ｒｏｓｓｂｙ波的频率；而慢波的性质和以前的结果类似，短波部分是向西传的，长波部分向东传，东传波的临界波数随海气相互作用增强向短波部分位移。与以前结果不同的是，除一个慢波不稳定增长外，另一个快波在长波部分也是不稳定增长的。海气相互作用越强，不稳定增长率和不稳定波所出现的波段范围越大。另外，本文的研究结果还指出，高频和低频不稳定波产生的物理条件是不一样的。     

简单的热海气耦合波──Kelvin波和Rossby波的综合作用

在本文中，考虑到对于研究ＥＮＳＯ事件中的某些现象，人们更感兴趣的是大尺度低频运动的物理性质。为此，本文中引进长波低频近似，这时纬圈运动基本上满足地转平衡。分析表明，对赤道偶对称运动，当经圈结构函数（抛物线柱函数）取ｎ＝０，２时，海气耦合系统中的自由波分别为大气和海洋中的Ｋｅｌｖｉｎ波和Ｒｏｓｓｂｙ波。它们经相互作用后，可以激发出不稳定的海气耦合波。根据海气相互作用强度（αγ）和ε（＝ｃｓ／ｃａ。ｃｓ，ｃａ分别为海洋和大气中的重力波波速）的大小，可以把不稳定区分成三个部分。在ε＜０．１６的强海气相互作用区，不稳定的耦合波，在短波波段是向东传播的，在长波波段则转为向西传播。在ε＞０．１６的弱海气相互作用区中，在长波波段的不稳定耦合波是向东传播的。另外，在ε＞０．１６的强相互作用区中，不稳定耦合波的物理性质较为特殊。在短波波段存在一支向东传播的不稳定波，但由于增长率太大，可以预测波将很快破碎而变成大尺度湍流运动。在长波波段虽然也存在一支频率很高的不稳定波，但其物理性质很难从自由模的比较中追踪出来。文中对由大气和海洋Ｒｏｓｓｂｙ波经相互作用后的对赤道奇对称耦合波也作了讨论。     

简单热带海气耦合模式中的耦合波及其不稳定性（Ⅰ）

西文建立了一处简单的热带海气耦合模式，模式大气和海洋中含了Ｋｅｌｉｖｎ波和长Ｒｏｓｓｂｙ波。在赤道β平面近似下，讨论了取耦合系统中最大径向模时，即大气和海洋中只存在Ｋｅｌｉｎ波时耦合波的性质。结果指出，向东传的耦合Ｋｅｌｖｉｎ波可以出现不稳定性，并且由于海气相互作用，在长波部分可以产生向西传的耦合Ｋｅｌｖｉｎ波。耦合Ｋｅｌｖｉｎ波的性质与模式中所选用的参数有很大关系，当大气与海洋中自由波的频率相差     

边界层动力过程在Madden-Julian振荡发展中的作用

利用包括边界层爱克曼辐合－降水加热过程在内的短期气候变化模式［１］，研究了Ｍａｄｄｅｎ－Ｊｕｌｉａｎ振荡［１１，１２］形成的机制。当经圈方向用抛物圆柱函数展开，并对赤道偶对称解取ｎ＝０，２，４三个截断模时，在长波近似下的自由波解，一为向东的Ｋｅｌｖｉｎ波，另外两支为向西的Ｒｏｓｓｂｙ波。当考虑边界层动力影响后，修正后的Ｋｅｌｖｉｎ波，其向东传播的速度约为１０ｍｓ－１，且在长波波段是不稳定的，最不稳定的波出现在纬向一波附近，不稳定增长率的量级约为Ｏ（１０ｍ－６ｓ－１），理论结果和Ｍａｄｄｅｎ－Ｊｕｌｉａｎ振荡在赤道附近主体环流东传的观测事实接近。另外两支修正后的Ｒｏｓｓｂｙ波，其中经圈尺度较小的那支波，除波长极长的波外，波是阻尼的；但另一支经圈尺度较大的波，在短的波段是不稳定增长的，这似乎可以用来解释Ｍａｄｄｅｎ－Ｊｕｌｉａｎ振荡中大尺度超级云团的西传过程。这些结果表明边界层动力过程在Ｍａｄｄｅｎ－Ｊｕｌｉａｎ振荡的形成中是一种重要的机制。     

低纬热带大气中的Rossby波

从热带大气波动的频率方程出发，详细分析了过去给出的低频Ｒｏｓｓｂｙ波的近似频率公式ω＝－βκ／［（２ｎ＋１）β／ｃ０＋κ＾２］，发现其对热带Ｒｏｓｓｂｙ波的性质有一定程度的歪曲。针对这一问题，经分析得到一个能更精确地表征热带Ｒｏｓｓｂｙ波性质的近似频散公式ω＝－βκ／［（２ｎ＋１）β／ｃ０＋４ｎ（ｎ＋１）／（２ｎ＋１）＾２ｋ＾２］，还简要地比较了热带线性Ｒｏｓｓｂｙ波和孤立Ｒｏｓｓｂｙ波两者的频散     

地形对热带大气超长尺度Rossby波动的影响

应用赤道β平面近似，建立一个简单的正压大气半地转浅水线性模式，在连续方程中引入地形的作用，讨论地形对热带大气超长尺度Ｒｏｓｓｂｙ波的影响。结果分析表明，起伏不平的于形动力抬升作用导致热带大气超长尺度Ｒｏｓｓｂｙ波动不稳定并且影响波动的特性。     

切变基流中赤道Rossby包络孤立波(英文)

利用一个简单的赤道β平面浅水模式和多尺度摄动法，从描写赤道Ｒｏｓｓｂｙ波的正压大气位涡度方程中推导出在切变基本维向流中赤道Ｒｏｓｓｂｙ波包演变所满足的非线性Ｓｃｈｒｏｄｉｎｇｅｒ方程，并得到其单个包络孤立波子波解，并分析基本流切变对非线性赤道Ｒｏｓｓｂｙ孤立子的影响。     

海表温度异常对Madden－Julian振荡的影响

在前文［１］的基础上，进一步研究当海表温度存在经圈方向不均匀分布或偏离气候状态（距平）时，改变水分收支平衡及边界层的湿度辐合这一物理过程对Ｍａｄｄｅｎ－Ｊｕｌｉａｎ振荡的可能影响。结果表明，它对修正的Ｋｅｌｖｉｎ波和Ｒｏｓｓｂｙ波的传播性质影响不大。但当海表温度为正距平时，修正后东传Ｋｅｌｖｉｎ波振幅不稳定增长到ｅ倍的时间约减小了１４．５％，其不稳定增长率随着热源特征宽度的增加而增加，当特征宽度为２倍Ｒｏｓｓｂｙ变形半径时，不稳定增长率达极大，但当特征宽度继续增大时，其不稳定增长率又将减小。当海表温度为负距平时，修正后东传Ｋｅｌｖｉｎ波振幅不稳定增长到ｅ倍的时间约增加２０％，其不稳定增长率随着冷源特征宽度的增加而减小，当特征宽度为２倍Ｒｏｓｓｂｙ变形半径时，其不稳定增长率达极小，此后；随着特征宽度的增加其不稳定增长率随之增加，但始终小于无海表温度异常的情形。经圈尺度较小的那支修正的Ｒｏｓｓｂｙ波除波长极长的波段外，波仍是阻尼的；而经圈尺度较大的那支修正的Ｒｏｓｓｂｙ波，在短的波段内仍是不稳定增长的。     

论陆架波系动力学及其在厄尔尼诺信号传播中的作用

文中讨论了陆架波系和赤道波系在动力学上的相似性，和赤道波系一样，陆架波系也由惯性重力波、Ｋｅｌｖｉｎ波、Ｒｏｓｓｂｙ（长、短）波和有条件的Ｒｏｓｓｂｙ－重力混合波组成。指出，当　海洋三边存在陆架而一边为赤道时（如北太平洋），则陆架波系和赤道波系中的Ｋｅｌｖｉｎ波，　将以逆时针方向携带信号绕海盆一周，而两个波系中的Ｒｏｓｓｂｙ长波，将以顺时针方向绕海盆一周，即通过陆架波和赤道波为海洋中某些信号的传播组织成一个绕海盆的环路。这种物理　过程可望用以解释发生在海洋中的某些长周期现象，如Ｅｌ　Ｎｉ　ｏ现象。文中进一步　讨论了陆架波的各种简化运动。     

热带海气相互作用波及其不稳定性

本文利用一个简单的海气耦合模式,讨论了热带海洋和大气中Rossby波的相互作用。结果指出,海洋和大气中向西传播的Rossby波耦合后,不仅存在着向西传播的波动,而且还可以产生一类向东传的新波。这种向东传播的波动出现在波长较长的波段范围内,这个范围的大小受海气相互作用强度的制约。另外,波动可以出现不稳定性,向西和向东传的波均有不稳定现象发生,不稳定增长率也受海气相互作用强度的制约。最后,根据所得到的海气相互作用波,对ENSO现象作了一个可能的解释。     

Unstable tropical air-sea interaction waves and their physical mechanisms

In this paper, the tropical air-sea interaction is discussed by using a simple air-sea coupled model, in which the inertia-gravity waves are filtered off and only the equatorial Rossby waves are reserved in both the atmosphere and the ocean. There exist two kinds of air-sea interaction waves in the coupled model, that is, the high-frequency fast waves and the low-frequency slow waves. The phase speed of the fast waves is westward and the frequencies are close to those of the equatorial Rossby waves in the atmosphere. The slow waves propagate westward in the part of short wavelengths and eastward in that of long wavelengths. There exist instabilities for both the westward and eastward propagating slow waves. If the fast waves are filtered off, there is little effect on the slow waves which have great in-fluence on the long range process in the tropical air-sea coupled system. According to the tropical air-sea interaction waves we obtain here, a possible explanation to the propagating process of ENSO events is given.     

NUMERICAL EXPERIMENTS ON THE TROPICAL AIR-SEA INTERACTION WAVES

By means of the numerical method,the tropical air-sea interaction waves are studied.The results show that whenthe Kelvin waves are filtered out and only the equatorial Rossby waves are reserved both in the atmosphere and in theocean,the disturbances can also propagate eastward because of the air-sea interaction.The critical wavelength of theeastward propagating waves is related to the intensity of the air-sea interaction.The stronger the air-sea interaction,thelarger the eastward propagating components of the air-sea interaction waves.The results of the numerical experimentsare in good agreement with those of the theoretical analysis(Chao and Zhang,1988).     

THE AIR-SEA INTERACTION WAVES IN THE TROPICS AND THEIR INSTABILITIES

By using a simple air-sea coupled model,the interaction of Rossby waves between the air and sea inthe tropics is discussed.It is shown that the coupling of Rossby waves in the two media produces notonly the westward propagating waves,but also a type of new wave which moves eastward.The eastwardpropagating waves exist in the scope of comparatively long wavelengths and this scope is governed bythe intensity of the air-sea interaction.In addition,instability may appear in both the eastward and west-ward propagating waves,and the wave amplifying rates are also governed by the intensity of the air-seainteraction.In the end,a possible explanation to ENSO events is given in terms of the air-sea interactionwaves.     

The westerly anomalies over the tropical pacific and their dynamical effect on the enso cycles during 1980–1994

In this paper, the zonal wind anomalies in the lower troposphere over the tropical Pacific during 1980–1994 are analyzed by using the observed data. The results show that during the formation of the 1982/83, 1986/87 and 1991 / 92 ENSO events, there were the larger westerly anomalies in the lower troposphere over the equatorial Pacific. Moreover, it is explained by using the correlation analyses that the westerly anomalies over the equatorial Pacific could cause the warm episodes of the equatorial central and eastern Pacific. A simple air-sea coupled model is used to discuss theoretically the dynamical effect of the observed westerly anomalies of wind stress near the sea surface of the equatorial Pacific on the ENSO cycle occurred in the period of 1981–1983. It is shown by using the theoretical calculations of the equatorial oceanic Kelvin wave and Rossby waves responding to the forcing of the observed anomalies of zonal wind stress near the sea surface of the equatorial Pacific that the westerly anomalies of wind stress near the sea surface of the equatorial Pacific make significant dynamical effect on the ENSO cycles occurred in the period of 1982–1983.     

The Westerly Anomalies over the Tropical Pacific and Their Dynamical Effect on the ENSO Cycles during 1980～1994

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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.     

THE EXCITING MECHANISM OF TROPICAL INTRASEASONAL OSCILLATION TO EL NINO EVENT

The data analyses indicated that the occurrence of EL Nino event is closely related to intraseasonal oscillation (ISO) in the tropical atmosphere: The intraseasonal oscillation is very strong in tile tropics (particularly over the equatorial western Pacific) prior to the occurrence of El Nino; But the ISO is evidently reduced and the quasistationary system is enhanced after the outbreak of El Nino. A simple air-sea coupled model study shows that the periodical self-excited oscillation can be produced in the air-sea-coupled system, but the pattern is different from the observed ENSO mode. When there is external (atmospheric) forcing with interannual time scale, a coupled mode, which looks like the ENSO mode, will be excited in the air-sea system. Synthesizing the results in data analyses and the theoretical investigation. the mechanism of ISO in the tropical atmosphere exciting the El Nino event can be suggested : The interannual anomalies (variations) of the tropical ISO play an important role in the exciting El Nino event through the air-sea interaction.     

简单热带海气耦合模式中的耦合波及其不稳定性（II）

为了分析热带海气耦合系统中不稳定扰动究竟由哪种自由波占主导地位，根据本文第I部分提出的热带海气耦合模式，讨论了取耦合系统中不同的径向模时耦合波的性质，即分别讨论了大气长Rossby波和海洋长Rossby波、大气Kelvin波和海洋长Rossby波、大气长Rossby波和海洋Kelvin波的耦合波以及考虑了大气和海洋中所有这些波动时耦合波的性质。结果指出，这些耦合波对海气耦合模式中参数的取值很敏感，不同的参数可以产生性质不同的耦合波。本文的结果也说明了海气耦合系统的性质与热带大气的性质和结构有很大关系。