共查询到19条相似文献,搜索用时 78 毫秒
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从包含Rossby波和惯性重力波的大气运动方程组出发,采用弱非线性相互作用近似,推导出耗散大气中这两种尺度相差很大的波动之间的非线性相互作用方程.以此为基础,得到了描述窄角谱Rossby波包和惯性重力波包的非线性时空演变规律的三波相互作用方程.数值分析表明,当一个Rossby波包与两个惯性重力波包发生相互作用时,两个惯性重力波包之间进行快速的能量交换,同时与Rossby波包之间进行缓慢的能量传输.从时间尺度上讲,惯性重力波可以看作Rossby波包运动的背景噪声,因此上述非线性相互作用过程可以理解为大尺度Rossby波包与背景噪声之间的能量交换过程. 相似文献
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从包含Rossby波和惯性重力波的大气运动方程组出发,采用弱非线性相互作用近似,推导出耗散大气中这两种尺度相差很大的波动之间的非线性相互作用方程.以此为基础,得到了描述窄角谱Rossby波包和惯性重力波包的非线性时空演变规律的三波相互作用方程.数值分析表明,当一个Rossby波包与两个惯性重力波包发生相互作用时,两个惯性重力波包之间进行快速的能量交换,同时与Rossby波包之间进行缓慢的能量传输.从时间尺度上讲,惯性重力波可以看作Rossby波包运动的背景噪声,因此上述非线性相互作用过程可以理解为大尺度Rossby波包与背景噪声之间的能量交换过程. 相似文献
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Abstract An analytical spectral model of the barotropic divergent equations on a sphere is developed using the potential-stream function formulation and the normal modes as basic functions. Explicit expressions of the coefficients of nonlinear interaction are obtained in the asymptotic case of a slowly rotating sphere, i.e. when the normal modes can be expressed as single spherical harmonics. 相似文献
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Further observational evidence of normal mode Rossby waves with higher meridional mode numbers is presented with the aid of global data from the troposphere to the stratosphere over the period November 1979 through April 1986.It is shown, without using ana priori assumption of meridional structure, that the third antisymmetric modes of zonal wavenumbers 1 and 2,i.e., (1,4) and (2,4) modes, substantially exist in the real atmosphere. These modes are, however, easily influenced by the nonuniform background field even in the equinoctial season; amplitude submaxima near the equator are apt to be dubious in the upper stratosphere so that the prototype meridional structure becomes obscure. The period of the (1,4) mode often falls into that of the (1,3) mode, about 16 days. Hence, these two modes cannot be classified simply by their periods, but the separation is made by their meridional structure.An appearance calendar of various modes is also presented for the analysis period. It is found that each mode appears irregularly throughout the year and that the year-to-year variation is fairly large. 相似文献
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David N. Straub 《地球物理与天体物理流体动力学》2013,107(2-4):107-130
Abstract Dispersion of linear quasigeostrophic plane waves in a stratified ocean with bottom topography is discussed. Particular emphasis is given to cases for which zonal gradients in the sea floor height are important. As such, the relative importance of the topographic and planetary β-effects is strongly dependent on wave vector orientation. The magnitude of the topographic slopes considered is chosen such that these two effects (topographic and planetary β) are of comparable importance. In the interest of simplicity, stratification is taken to be independent of depth. The eigenvalue problem which must be solved to find the free modes of oscillation has already been treated in the literature (in fact, Charney and Flierl (1981) have treated the effects of a more realistic stratification). The aim of this note is to more fully expose, primarily by example, several dispersive properties of these free wave modes which have been largely overlooked. 相似文献
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R. T. Pierrehumbert 《地球物理与天体物理流体动力学》2013,107(1-4):285-319
Abstract We consider the mixing of passive tracers and vorticity by temporally fluctuating large scale flows in two dimensions. In analyzing this problem, we employ modern developments stemming from properties of Hamiltonian chaos in the particle trajectories; these developments generally come under the heading “chaotic advection” or “Lagrangian turbulence.” A review of the salient properties of this kind of mixing, and the mathematics used to analyze it, is presented in the context of passive tracer mixing by a vacillating barotropic Rossby wave. We then take up the characterization of subtler aspects of the mixing. It is shown the chaotic advection produces very nonlocal mixing which cannot be represented by eddy diffusivity. Also, the power spectrum of the tracer field is found to be k ? l at shortwaves—precisely as for mixing by homogeneous, isotropic two dimensional turbulence,—even though the physics of the present case is very different. We have produced two independent arguments accounting for this behavior. We then examine integrations of the unforced barotropic vorticity equation with initial conditions chosen to give a large scale streamline geometry similar to that analyzed in the passive case. It is found that vorticity mixing proceeds along lines similar to passive tracer mixing. Broad regions of homogenized vorticity ultimately surround the separatrices of the large scale streamline pattern, with vorticity gradients limited to nonchaotic regions (regions of tori) in the corresponding passive problem. Vorticity in the chaotic zone takes the form of an arrangement of strands which become progressively finer in scale and progressively more densely packed; this process transfers enstrophy to small scales. Although the enstrophy cascade is entirely controlled by the large scale wave, the shortwave enstrophy spectrum ultimately takes on the classical k ? l form. If one accepts that the enstrophy cascade is indeed mediated by chaotic advection, this is the expected behavior. The extreme form of nonlocality (in wavenumber space) manifest in this example casts some doubt on the traditional picture of enstrophy cascade in the Atmosphere, which is based on homogeneous two dimensional turbulence theory. We advance the conjecture that these transfers are in large measure attributable to large scale, low frequency, planetary waves. Upscale energy transfers amplifying the large scale wave do indeed occur in the course of the above-described process. However, the energy transfer is complete long before vorticity mixing has gotten very far, and therefore has little to do with chaotic advection. In this sense, the vorticity involved in the enstrophy cascade is “fossil vorticity,” which has already given up its energy to the large scale. We conclude with some speculations concerning statistical mechanics of two dimensional flow, prompted by our finding that flows with identical initial energy and enstrophy can culminate in very different final states. We also outline prospects for further applications of chaotic mixing in atmospheric problems. 相似文献
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Abstract This paper investigates the generation of linear, baroclinic Rossby waves by an imposed current distribution, in a reduced gravity ocean, both with and without an eastern coast. A zonal current is impulsively applied and maintained along the northern edge of the domain of solution. Using Green's function techniques, analytical solutions are found, and these are evaluated for small times. Numerical solutions are obtained for larger times. The upper layer depth field consists of a transient response, due to the sudden application of the current. Maintenance of the current causes a response which is singular along the line of imposed non-zero h y. The interior field decays with time (this is shown asymptotically). The parameters used are appropriate for the mid-latitude North Pacific, and the results are relevant to sudden transport changes in the North Pacific Current. 相似文献
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Michael I. Bergman 《地球物理与天体物理流体动力学》2013,107(1-4):151-176
Abstract The stratification profile of the Earth's magnetofluid outer core is unknown, but there have been suggestions that its upper part may be stably stratified. Braginsky (1984) suggested that the magnetic analog of Rossby (planetary) waves in this stable layer (the ‘H’ layer) may be responsible for a portion of the short-period secular variation. In this study, we adopt a thin shell model to examine the dynamics of the H layer. The stable stratification justifies the thin-layer approximations, which greatly simplify the analysis. The governing equations are then the Laplace's tidal equations modified by the Lorentz force terms, and the magnetic induction equation. We linearize the Lorentz force in the Laplace's tidal equations and the advection term in the magnetic induction equation, assuming a zeroth order dipole field as representative of the magnetic field near the insulating core-mantle boundary. An analytical β-plane solution shows that a magnetic field can release the equatorial trapping that non-magnetic Rossby waves exhibit. A numerical solution to the full spherical equations confirms that a sufficiently strong magnetic field can break the equatorial waveguide. Both solutions are highly dissipative, which is a consequence of our necessary neglect of the induction term in comparison with the advection and diffusion terms in the magnetic induction equation in the thin-layer limit. However, were one to relax the thin-layer approximations and allow a radial dependence of the solutions, one would find magnetic Rossby waves less damped (through the inclusion of the induction term). For the magnetic field strength appropriate for the H layer, the real parts of the eigenfrequencies do not change appreciably from their non-magnetic values. We estimate a phase velocity of the lowest modes that is rather rapid compared with the core fluid speed typically presumed from the secular variation. 相似文献
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CHAO Jiping LIU Lin & YU Weidong . Laboratory of Marine Science Numerical Modeling State Oceanic Administration Qingdao China . National Research Center for Marine Environmental Forecasts State Oceanic Administration Beijing China . Ocean University of China Qingdao China 《中国科学D辑(英文版)》2005,48(10)
Before the 1980s, El Ni?o was believed as the sea surface warming along the coast of Peru in South America. As the positive anomaly strengths, the warm water expands westward along the equator to form large area of anomalous high sea surface temperature. Rasmusson and Carpenter (1982) summarized the de-velopment process of the sea surface warm water and the corresponding wind field[1] during ENSO cylce. However, this canonical El Ni?o was questioned by 1982-1983 warm episode and later dat… 相似文献