SYMMETRIC AND ASYMMETRIC MOTIONS IN THE BAROTROPIC FILTERED MODEL ATMOSPHERE

By expressing the stream function in terms of the symmetric and the antisymmetric components with respect to the equator,the barotropic vorticity equation can be separated into two equations,one describing the behaviours of the atmospheric symmetric motion,and the other those of the atmospheric antisymmetric motion.From them,for the entire global surface at the equivalent barotropic level,the conservations of several basic quantities,such as vorticity,angular momentum etc.in the symmetric and antisymmetric cases,have been discussed.In addition,the energy budget equations and the energy conservation expressions for the two kinds of motion are given.It can be seen from them that there are not only the conversion between the zonal mean kinetic energy and the disturbed kinetic energy in the atmosphere,but also the conversion between the kinetic energy generated by the symmetric and antisymmetric motions.In the case of including orography and horizontal diffusion into the vorticity equation,a mechanism of the generation of asymmetric behaviours of the atmosphere is proposed.The results show that the asymmetric distribution of orography and that of horizontal diffusion coefficients are likely the causes leading to the asymmetric motion.Finally,a theoretical comparison between the global model and the hemispheric one from the physical point of view is made.     

North Atlantic decadal regimes in a coupled GCM simulation

 The non-stationarity of the North Atlantic atmosphere-ocean coupling is investigated utilizing a long time integration of a coupled atmosphere-ocean general circulation model (GCM) and a consistent atmospheric experiment forced by the climatological sea surface temperature (SST) of the coupled GCM. The temporal behavior of the North Atlantic Oscillation (NAO) is non-stationary with two different decadal regimes being identified: (a) phases with enhanced (active) low-frequency variability of the NAO index are characterized by regional modes with a baroclinic Pacific-North America (PNA) and a dominant barotropic North Atlantic pattern; (b) in phases with reduced (passive) low-frequency variability a global mode connects tropics and midlatitudes. The characteristic space scales are similar in the coupled and the consistent atmospheric experiment; the time scales of the atmospheric eigenmodes are modified by ocean dynamics. In the active (passive) phase the corresponding atmospheric mode is reinforced by the North Atlantic (tropical Pacific) SST. Received: 15 September 2000 / Accepted: 30 March 2001     

正压过滤模式大气中的对称运动和非对称运动

把流函数分成对赤道对称和对赤道反对称的两部分,可以把正压涡度方程分离为描写大气对称运动和反对称运动的两个方程。根据它们,讨论了在全球范围内几种基本物理量,如涡度和绝对角动量等在对称和反对称情况的守恒性。还给出了这两类运动的能量收支方程和能量转换表达式。可以看出,在大气中不仅有纬圈平均动能和扰动动能之间的转换,也有对称运动产生的和反对称运动产生的动能之间的转换。 还在涡度方程中考虑地形和水平扩散的情形下,提出了大气非对称性质产生的机制。结果表明:非对称的地形分布和水平扩散系数的分布可能是导致非对称运动的原因。 最后,还对全球预报和半球预报,从物理观点作了理论比较。     

一个简单的准地转海气耦合模式

文章采用准地转带耗散因子的大气和海洋的动量、热力学方程,建立了一个简单的描写大尺度运动的准地转海气耦台浅水模式,分别在中高纬和低纬地区讨论了海气的耦合效应,分析了耦合低频模(海洋模)的振荡周期随耦合频率和经向波数的变化转征,并由此而说明低频振荡与海气相互作用有关。然后从海洋和大气的频散曲线中揭示出耦合强度对Rossby波传播的影响,还从缓变波列的观点,讨论了两种模之间的转换机制。 结果表明:Newton冷却Rayleigh摩擦对海洋Rossby波起稳定作用。随着耦合频率的增加,耦合低频模的周期也相应增加;经向波数越大,这种增加就越迅速。当耦合频率趋近于临界值时,海洋Rossby波趋于静止。当海气耦合强度增加到一定程度时,海洋Rossby波的传播方向变成与原来相反。通过海气相互作用,海洋Rossby波的一部分将转换成大气Rossby波,本文求解了其能量转换系数。      

EVOLUTION OF LARGE SCALE DISTURBANCES AND THEIR INTERACTION WITH MEAN FLOW IN A ROTATING BAROTROPIC ATMOSPHERE —PART I

The problems on evolution of large-scale disturbances and their interaction with mean flow recently attract much effort of meteorologists due to their practical importance in weather and climate predictions. In this paper, some theoretical results obtained in current investigations of these problems will be reviewed. A barotropic atmosphere is taken in this paper, and the baroclinic atmosphere is left in our second paper.The following aspects are reviewed: First, the general properties of two-dimensional barotropic motion both in the nonlinear and linearized equations and both in the quasi-geostrophic and non-geostrophic models. Second, the evolution and the structure of Rossby wave packet superimposed on a zonal or non-zonal basic flow.In this part, only the above two problems are reviewed. The rernanent problems, i.e., the normal modes and continuous spectra of both quasi-geostrophic and non-geostrophic models, weakly nonlinear theory and the fully nonlinear theory will be discussed in part II (another paper).     

斜压模,正压模和异常海温时间变化的位相关系

利用１９５８－１９９７共４０年ＮＥＣＰ／ＮＣＡＲ再分析大气资料和ＧＩＳＳＴ海表温度资料集,研究了大气斜压模、正压模与海表温度变化这三者之间位相关系,并从大气动力学方程组解释了这些位相关系。指出：大气了斜压西风异常时间变化的位相落略微后于ＳＳＴＡ的变化位相,而正压西风异常的变化位相超前于ＳＳ－ＴＡ变化位相。斜压纬向风异常的变化又超前于正压异常纬向风的变化。斜压纬向风异常与海表温度异常之间存在正相关关     

Synoptic eddy feedback and air–sea interaction in the North Atlantic region

This paper explores the role of synoptic eddy feedback in the air-sea interaction in the North Atlantic region, particularly the interaction between the North Atlantic Oscillation (NAO) and the North Atlantic sea surface temperature anomalies (SSTA) tripole. A linearized five-layer primitive equation atmospheric model with synoptic eddy and low-frequency flow (SELF) interaction is coupled with a linearized oceanic mixed-layer model to investigate this issue. In this model, the “climatological” storm track/activity (or synoptic eddy activity) is characterized in terms of spatial structures, variances, decay time scales and propagation speeds through the complex empirical orthogonal function (CEOF) analysis on the observed data, which provides a unique tool to investigate the role of synoptic eddy feedback in the North Atlantic air–sea coupling. Model experiments show that the NAO-like atmospheric circulation anomalies can produce tripole-like SSTA in the North Atlantic Ocean, and the tripole-like SSTA can excite a NAO-like dipole with an equivalent barotropic structure in the atmospheric circulation, which suggests a positive feedback between the NAO and the SSTA tripole. This positive feedback makes the NAO/SSTA tripole-like mode be the leading mode of the coupled dynamical system. The synoptic eddy feedback plays an essential role in the origin of the NAO/SSTA tripole-like leading mode and the equivalent barotropic structure in the atmosphere. Without synoptic eddy feedback, the atmosphere has a baroclinic structure in the response field to the tripole-like SSTA forcing, and the leading mode of the dynamic system does not resemble NAO/SSTA tripole pattern.     

A simple quasi-geostrophic coupled ocean-atmosphere model

The quasi-geostrophic atmospheric and oceanic equations of momentum and thermodynamics with dissipation factors are used to create a simple coupled ocean-atmosphere model describing the large-scale shallow-water mo-tion. We discuss the ocean-atmosphere coupling effect in mid-high and low latitudes separately and analyze charac-teristics of which the oscillatory periods of coupled low-frequency modes (ocean mode) vary with the coupling fre-quency and latitudinal number. This can interpret the correlation between low-frequency oscillation and ocean-at-mosphere interaction. Then from the dispersion curves of atmosphere and ocean, we reveal effect of the coupling strength on the propagation of Rossby waves. The convection mechanism between the two modes is also discussed in view of the slowly varying wave train.The results show that Newtonian cooling and Rayleigh friction play a stable rule in oceanic Rossby waves, the period of coupled low-frequency mode grows with the increment of the coupling frequency. The larger the latitudinal number is, the more rapidly it grows. When the coupling frequency tends to critical value, the oceanic Rossby waves become static. When the ocean-atmosphere coupling strength grows to some degree, the propagation of oceanic Rossby waves will become opposite to its original direction. One part of the oceanic Rossby waves is converted into atmospheric Rossby waves, the energy conversion coefficient is also solved out.     

An application of equivalent modons to atmospheric blocking

Certain consistent features are demonstrated between a particular strong, vortex pair atmospheric blocking pattern over the eastern North Atlantic Ocean and Europe during January 1963 and an equivalent modon solution of the inviscid equivalent barotropic equation. Modons are uniformly translating, shape preserving, non-linear analytic solutions. The equivalent barotropic model for the atmosphere is derived as a lowest-order truncation of an expansion and projection of the quasigeostrophic equations with the empirical orthogonal pressure modes of the troposphere. The horizontal and vertical structure of the blocking pattern, as well as its intensity, are consistent with the modon dispersion relation. On the other hand, there remain some uncertainties about whether the pressure profile of the mean zonal wind is consistent with modon requirements and whether a stationary theoretical solution adequately reflects the essential dynamics of a fluctuating and regenerative blocking pattern.     

半地转近似下的非线性波

本文应用半地转的概念分析和求解了正压和斜压的大气运动。指出:(1)在水平无辐散或准地转条件下求单波解无法表现非线性作用的困难,可以应用半地转的假定来解决。为了避开上述困难,不得已仅保留部分非线性项,但为了准确表征大尺度运动,最好应用半地转假定,保留全部非线性项。(2)准地转的假定可以滤去快速波动,半地转的假定同样也可以滤去快速波动,而且半地转条件下的Rossby波具有充分的非线性特征。所以,它为讨论非线性问题提供了一个途径。     

斜压性与非线性Ekman抽吸的动力特征

本文利用Ekman动量近似研究了斜压性对Ekman层动力学的影响,得到了一些新的结果。大气斜压性对Ekman层的水平风速分布及近地面的风速矢的水平分量夹角有重要的改变作用。斜压边界层顶部的非线性Ekman抽吸(垂直运动)由三个不同的物理因子决定,第一、正压性的地面地转涡度,第二、斜压性作用产生的热成风涡度,第三、正压性的地面地转涡度与斜压性的热成风涡度的非线性相互作用。这些理论结果为边界层的参数化及数值模拟结果的解释提供物理基础。     

TROPICAL ATMOSPHERIC NONLINEAR STEADY RESPONSE SOLUTION UNDER EFFECTS OF PAIRED HEAT SOURCES OF CONTRASTING NATURE

Based on steady semi-geostrophic model equations,analysis is carried out of the linear and nonlinearmodification/response of the tropical atmosphere to the forcing of ideal paired heat sources of contrasting nature.Re-suits show that the linear part is dominant in the steady response but the nonlinear modification is quite noticable in theneighborhood of the heat source and between the paired sources,and the barotropic mode and second baroclinic modeplay a different role in the modification,with the barotropic(second baroclinic)mode modification depending largely onthe Rossby wave self-interaction(the magnitude due to the Kelvin-Rossby wave interaction)between the pairedsources.     

TROPICAL ATMOSPHERIC NONLINEAR STEADY RESPONSE SOLUTION UNDER EFFECTS OF PAIRED HEAT SOURCES OF CONTRASTING NATURE*

Based on steady semi-geostrophic model equations,analysis is carried out of the linear and nonlinear modification/response of the tropical atmosphere to the forcing of ideal paired heat sources of contrasting nature.Resuits show that the linear part is dominant in the steady response but the nonlinear modification is quite noticable in the neighborhood of the heat source and between the paired sources,and the barotropic mode and second baroclinic mode play a different role in the modification,with the barotropic(second baroclinic)mode modification depending largely on the Rossby wave self-interaction(the magnitude due to the Kelvin-Rossby wave interaction)between the paired sources.     

用自由模对1998年夏季阻塞形势的诊断分析

签于大气自由模和阻塞高压的重要性 ,首先简要介绍阻塞高压与中国夏季降水的关系及 1998年夏季 5 0 0hPa异常环流场 ;然后利用 2 1波菱形截断的谱方法求出无粘性、无强迫正压涡度方程的自由解 ,即和实际大气流场十分接近的大气自由模 ,并讨论其特征 ;最后利用大气自由模的特征诊断分析了实际大气的环流特征 ,并重点用其分析了 1998年夏季的大气环流异常形势。结果表明大气自由模能很好地反映大气环流大尺度特征 ,而略去了中、小尺度涡旋 ;大气自由模的流场和绝对涡度场之间的散点图反映了 (q ,Ψ )的函数关系是分段线性或非线性的 ,尽管实际流场与绝对涡度场之间的点阵图反映两者之间成不同斜率的线性函数关系 ,但点阵比较发散 ,不能突出某些重要系统 ;1998年夏季实际大气自由模态突出了大气环流的重要特征 ,例如 ,越赤道气流、西风急流、副热带高压、阻塞高压及两极的边界效应等 ;通过自由模态的特征可以识别出纬向流及阻塞高压的持续异常 ,利用自由模的稳定性判断阻塞高压的稳定性 ,不稳定模态可以维持一段较长的时间 ,且由于这些不稳定的模存在 ,才使 1998年 6月中旬到下旬的中高纬阻塞高压稳定维持。     

亚洲季风变动与大气正压/斜压运动动能变化的气候特征

使用ＮＣＥＰ／ＮＣＡＲ４０年（１９５８～１９９７年）月平均再分析资料,通过动力学论断研究了大气斜压／正压运动动能的变化及其相互转换,分析了亚洲季风变动与这两种动能变化的联系。指出：季风区大气运动动能的组成和变化具有独特的特征。冬季风时期大气斜压运动动能与正压运动动能具有正相关线性关系,斜压运动能向正压运动动能转换;春、秋季无论是东亚还是印度季风区斜压运动动能与正压运动动能之间转换都处于极小值,只是     

大气动力学方程组的定性理论及其应用

基于完整的湿大气动力学方程组,利用无穷维动力系统的新理论和新方法,系统讨论了强迫耗散的非线性大气系统的定性理论及其应用。将完整的强迫耗散非线性湿大气动力学方程组化为Hilbert空间中一个等价的算子方程,研究了算子的性质及其物理意义,在此基础上得到湿大气系统全局吸引子的存在性定理,揭示出系统向外源的非线性适应特征,并把结果推广到有地形动力作用和非定常外源强迫的情形。同时探讨了大气方程组惯性流形的存在,大气多平衡态产生的根源以及强迫、耗散和非线性对系统解的渐近行为的影响。在理论结果的基础上,提出强迫耗散的非线性动力系统中存在三类时间边界层、方程组简化准则、分解算法的算子约束原则以及支撑吸引子基底的少数自由度的构造方法,探讨了理论在非线性发展方程差分格式的设计和计算稳定性分析、多平衡态的数值分析、数值模式延伸预报的改进、短期气候预测以及一类中尺度系统分析与预测中的应用,指出描述长期过程动力学模式的必备条件,给出初值与模式相协调的合理解释。最后,对今后的研究方向作了展望。     

CISK-rossby wave and the 30-60 Day Oscillation in the Tropics

The 30-60 day oscillation is an important aspect of the atmospheric variance in the tropical area. A number of works have been done on this phenomenon, this article is a further one. A quasi-geostrophic linear model that consists of a two-layer free atmosphere and a well-mixed boundary layer is used to investigate the instability of intraseasonal oscillation, its propagation and vertical structures. Results show that the dynamical coupling and interaction between the barotropic and baroclinic components via boundary layer convergence / divergence are responsible for the appearance of a new kind of low-frequency wave. Such wave is very different from the traditional tropical Rossby wave. It can propagate westward and eastward. Some behaviours of it appear to resemble the observed 30-60 day oscillation mode in many aspects, such,as vertical structures, zonal and meridional propagations. Now many researchers emphasize the direct relationship between CISK-Kelvin mode and the tropical atmospheric 30-60 oscil     

Midlatitude unstable air-sea interaction with atmospheric transient eddy dynamical forcing in an analytical coupled model

While recent observational studies have shown the critical role of atmospheric transient eddy (TE) activities in midlatitude unstable air-sea interaction, there is still a lack of a theoretical framework characterizing such an interaction. In this study, an analytical coupled air-sea model with inclusion of the TE dynamical forcing is developed to investigate the role of such a forcing in midlatitude unstable air-sea interaction. In this model, the atmosphere is governed by a barotropic quasi-geostrophic potential vorticity equation forced by surface diabatic heating and TE vorticity forcing. The ocean is governed by a baroclinic Rossby wave equation driven by wind stress. Sea surface temperature (SST) is determined by mixing layer physics. Based on detailed observational analyses, a parameterized linear relationship between TE vorticity forcing and meridional second-order derivative of SST is proposed to close the equations. Analytical solutions of the coupled model show that the midlatitude air-sea interaction with atmospheric TE dynamical forcing can destabilize the oceanic Rossby wave within a wide range of wavelengths. For the most unstable growing mode, characteristic atmospheric streamfunction anomalies are nearly in phase with their oceanic counterparts and both have a northeastward phase shift relative to SST anomalies, as the observed. Although both surface diabatic heating and TE vorticity forcing can lead to unstable air-sea interaction, the latter has a dominant contribution to the unstable growth. Sensitivity analyses further show that the growth rate of the unstable coupled mode is also influenced by the background zonal wind and the air–sea coupling strength. Such an unstable air-sea interaction provides a key positive feedback mechanism for midlatitude coupled climate variabilities.

     

THE NONDISPERSION SOLUTION OF NONLINEAR SPIRAL PLANETARY WAVES

In this paper,by using the simplified hydrodynamic equations of barotropic nondivergent atmosphere incylindrial coordinates,the nondispersion cnoidal wave solution of spiral planetary waves is discovered.The formulas of wave speed and the diagnostic relationships between wave parameters are obtained,mostof which are consistent with observed facts.It might mean that the nondispersion cnoidal wave does existin the real atmosphere.At least it might be a first approximation to the actual nonlinear wave.