共查询到20条相似文献，搜索用时 46 毫秒
1.
The equations of dynamics of eddy—wave disturbances of two-dimensional stratified flows in an ideal incompressible fluid that are written in a Hamiltonian form are used to study the resonant interaction of waves of discrete and continuous spectra. A gravity—shear wave generated at a jump of the density and vorticity of the undisturbed flow and a wave generated at a weak vorticity jump, which is similar to a wave of a continuous spectrum, participate in the interaction. The equations are written in terms of normal variables to obtain the system of evolution equations for the amplitudes of the interacting waves. The stability condition for eddy—wave disturbances is derived within the framework of the linear theory. It is shown that a cubic nonlinearity may lead to the stabilization of unstable disturbances if the coefficient of the nonlinear term is positive. 相似文献
2.
讨论简单热带海气耦合模式中的低频海洋扰动。研究结果表明,挟卷对海洋Ｒｏｓｂｙ波的发展起抑制作用,而平流有利于海洋Ｒｏｓｓｂｙ波的发展;挟卷和平流都有利于与海温距平相对应的扰动Ｕ的发展 相似文献
3.
M. V. Kalashnik 《Izvestiya Atmospheric and Oceanic Physics》2018,54(2):109-113
The quasi-geostrophic dynamics of disturbances of a flow with a vertical shear is described by a transfer equation for potential vorticity. Wave solutions of this equation are represented by edge baroclinic waves (modes in a discrete spectrum) and singular modes in a continuous spectrum. When frequencies of these modes coincide, the effect of resonant excitation occurs in which the amplitude of baroclinic waves increases linearly. This paper studies this effect in the presence of Ekman bottom friction. It is shown that friction suppresses linear wave growth and gives rise to baroclinic waves of finite amplitude. 相似文献
4.
By using the theories on Stokes multicolored water waves and taking the two- layer ocean as a basic model of stratified ocean, the paper analyzes the problems related to the effects of the nonlinear water wave on offshore structures. A mathematical expression is presented to describe second order wave radiation conditions. Using integral principle, the analytical integral solutions are given to evaluate second order scattered wave loads on general vertical circular cylinders in the two-layer ocean, and the special recurrence formulas for infinite integrals over free and stratified surfaces are derived. 相似文献
5.
A model for a two-layer ocean is applied to consider, in terms of the geometrical optics approximation, the effect of mean
flows propagating within the upper layer upon the dynamics of Rossby waves. The case is theoretically analysed, with the depth
of the ocean's upper layer much smaller than that of the underlying layer. In this case, the flow's impact upon the baroclinic
mode of Rossby waves is ubiquitous, with the exception of synchronicity. Depending on the parameters, four types of wave packets'
behaviour in the vicinity of synchronicity points are singled out, namely, the elimination of the peculiarity, shadowing,
and convective/absolute instability. For the mean flow profile simulating cyclonic and anticyclonic gyres, we have obtained
wave packet trajectories and have studied the wave packet's interaction with the current. Specifically, it has been demonstrated
that, given some modulus of the wave packet, vigorous energy exchange between the wave vector and the flow takes place.
Translated by Vladimir A. Puchkin. 相似文献
6.
The phase pattern of inertia-gravity waves that form a wake in the ocean behind a moving hurricane is investigated using a kinematic theory. In the framework of the model of a two-layer ocean, simple analytical expressions are obtained for phase surfaces (surfaces of the ridges and troughs of wave structure) and the dependence of the semiangle of a wave cone on the speed of the hurricane is determined. It is shown that the observed asymmetry of the wave wake in the horizontal plane may be related to inhomogeneity in the distribution of the Coriolis parameter with latitude. 相似文献
7.
The instability of oscillatory flows in a two-layer fluid where the two layers differ in density and viscosity has been analysed using a perturbation method for long waves with special interest on effects of viscosity, time scale, density and depth of the fluid. The flow of a fluid with homogeneous density can be unstable, when the kinematic viscosity of the upper fluid layer is different from that of the lower one. Viscosity stratification results in unstable oscillatory flows. Two limiting cases of single-layer flow are also considered. 相似文献
8.
M.A.C. Teixeira 《Ocean Modelling》2011,36(1-2):149-162
The structure of turbulence in the ocean surface layer is investigated using a simplified semi-analytical model based on rapid-distortion theory. In this model, which is linear with respect to the turbulence, the flow comprises a mean Eulerian shear current, the Stokes drift of an irrotational surface wave, which accounts for the irreversible effect of the waves on the turbulence, and the turbulence itself, whose time evolution is calculated. By analysing the equations of motion used in the model, which are linearised versions of the Craik–Leibovich equations containing a ‘vortex force’, it is found that a flow including mean shear and a Stokes drift is formally equivalent to a flow including mean shear and rotation. In particular, Craik and Leibovich’s condition for the linear instability of the first kind of flow is equivalent to Bradshaw’s condition for the linear instability of the second. However, the present study goes beyond linear stability analyses by considering flow disturbances of finite amplitude, which allows calculating turbulence statistics and addressing cases where the linear stability is neutral. Results from the model show that the turbulence displays a structure with a continuous variation of the anisotropy and elongation, ranging from streaky structures, for distortion by shear only, to streamwise vortices resembling Langmuir circulations, for distortion by Stokes drift only. The TKE grows faster for distortion by a shear and a Stokes drift gradient with the same sign (a situation relevant to wind waves), but the turbulence is more isotropic in that case (which is linearly unstable to Langmuir circulations). 相似文献
9.
The generation of internal waves by the barotropic tide in a two-layer ocean of variable depth is studied within the framework of the linear theory of long waves in view of the Coriolis force. The relationships between the internal wave amplitude, the angle of climb of the barotropic tide, and the bottom elevation geometry are studied.Translated by Mikhail M. Trufanov. 相似文献
10.
A European Space Agency＇ s ENVISAT advanced synthetic aperture radar （ASAR） image covering Zhejiang coastal water in the East China Sea （ECS） was acquired on 1 August 2007. This image shows that there are about 20 coherent internal solitary wave （ISW） packets propagating southwestward toward Zhejiang coast. These ISW packets are separated by about 10 kin, suggesting that these ISWs are tide-generated waves. Each ISW packet contains 5-15 wave crests. The wavelengths of the wave crests within the ISW packets are about 300 m. The lengths of the leading wave crests are about 50 km. The ISW amplitude is estimated from solving KdV equation in an ideal two-layer ocean model. It is found that the ISW amplitudes is about 8 m. Further analysis of the ASAR image and ocean stratification profiles show that the observed ISWs are depression waves. Analyzing the tidal current finds that these waves are locally generated. The wavelength and amplitude of the ECS ISW are much smaller than their counter- parts in the South China Sea （SCS）. The propagation speed of the ECS ISW is also an order of magnitude smaller than that of the SCS ISW. The observed ISWs in the ECS happened during a spring tide period. 相似文献
11.
A. I. Shavlyugin 《Izvestiya Atmospheric and Oceanic Physics》2011,47(5):619-627
A quasi-geostrophic contour dynamics model permitting one to study flows induced by a system of vortex patches in a two-layer ocean with round shore boundaries in the presence of specified background flows caused by the bottom relief, the β effect, and sources and sinks at the boundaries is proposed. The principal relations of the model are presented and the algorithm of its numerical realization is described. Some experimental results of the study of the evolution of unstable two-layer vortices are demonstrated. 相似文献
12.
Alternating zonal flows in an idealized wind-driven double-gyre ocean circulation have been investigated using a two-layer
shallow-water eddy-permitting numerical model. While the alternating zonal flows are found almost everywhere in the time-mean
zonal velocity field, their meridional scales differ from region to region. In the subpolar western boundary region, where
the energetic eddy activity induces quasi two-dimensional turbulence, the alternating zonal flows are generated by the inverse
energy cascade and its arrest by Rossby waves, and the meridional scale of the flows corresponds well to the Rhines scale.
In the eastern part of the basin, where barotropic basin modes are dominant, the zonal structure is formed through the nonlinear
effect of the basin modes and is wider than the Rhines scale. Both effects are likely to form zonal structure between the
two regions. These results show that Rossby basin modes become an important factor in the formation of alternating zonal flows
in a closed basin in addition to the arrest of the inverse energy cascade by Rossby waves. The wind-driven general circulation
associated with eddy activities plays an essential role in determining which mechanism of the alternating zonal flows is possible
in each region. 相似文献
13.
海洋是多尺度强迫-耗散系统,机械能主要在大尺度输入,在小尺度耗散。在大、中尺度运动的能量向小尺度湍流传递过程中,内波扮演着重要角色。内波的生成和破碎可打破海洋动力平衡,而在陆架区,内波（主要是内孤立波）的浅化演变与耗散则是驱动湍流混合的关键过程。通过长期的理论、观测与数值模拟研究,目前已认识到内波浅化过程中主要发生如下演变：波形调制、极性转变、裂变、破碎与耗散。相较于直接发生破碎,浅化演变过程中的裂变及其引发的剪切不稳定和对流不稳定是内孤立波在陆架区的主要耗散机制,显著调制陆架区的跃层混合。从能量串级的角度讲,内孤立波浅化裂变为动力不稳定的高频内波是潮能串级的重要通道。本文简要回顾南海北部陆架区内波的研究历史,并着重总结内波在陆架区演变与耗散机制的研究进展。 相似文献
14.
The transformation of internal waves over the oceanic shelf of variable depth is studied analytically within a linear theory
of a two-layer flow. It is shown that, at a specific character of depth variation, the internal wave propagates without reflection
from the slope even if it is sufficiently steep. The properties of such progressive waves are studied—their form and the current
structure in the upper and lower layers. The transformation of the wave propagating from the open ocean, where the depth is
assumed to be constant, is considered. It is shown that the wave is transformed at the shelf edge and does not change its
form in the course of time during its further propagation over the shelf. The height and form of the internal wave are calculated
at the interface of the transition of the two-layer flow into the one-layer flow. Applications of the developed analytical
theory to the estimation of internal wave transformation over a real shelf are discussed. 相似文献
15.
Study of the generation of non-stationary non-linear long waves by atmospheric pressure disturbances
In a non-linear statement, this paper considers the generation of long waves by periodic atmospheric pressure disturbances in a confined basin of variable depth filled with homogeneous fluids. The study is conducted using a non-stationary finite-difference model. The contribution of dissipative forces to the development and stabilization of fluid oscillations is analysed. The paper also considers how the growth of the amplitude of atmospheric pressure disturbances may enhance the non-linearity of the wave process. It is shown that as the pressure amplitude becomes larger, the number of significant harmonics with multiple frequencies in the spectrum of sea level elevations increases. For the weakly non-linear case, wave velocities and free surface elevations, with oscillations stabilized, are compared with their counterparts derived through the perturbation technique.Translated by Vladimir A. Puchkin. 相似文献
16.
本文采用无海底地形但考虑海洋跃层和剪切背景流的二维非静力准不可压缩方程组的数值模式，开展失稳垂向剪切背景流下线性和非线性对称型海洋内波生成演变的数值实验，并对结果进行分析、比较和讨论。研究结果表明，线性内波强度随积分时间始终呈指数增长，并有内波的对称不稳定；而非线性内波强度则在发展期呈准线性增长，最终进入稳定期。线性增长比非线性增长要快得多，非线性效应具有维稳作用。对该线性和非线性对称型内波，在跃层附近位密度扰动均有大值中心，即其为跃层所俘获，这与实际观测相一致；流函数与位密度扰动两者均有很好配合，位密度扰动的正、负中心分别相应于流函数的上升、下沉运动，表明有从海底向上的斜对流发生，且以跃层为顶盖。对线性内波来说，随积分时间增加，其波形大体不变，其正、负振幅也大体相同，并有符号相反原地增长的两个倾斜环流圈，而在它们之间则有较强倾斜上升流。非线性内波波形随积分时间改变，倾斜环流圈数目也在增加，最终形成负环流强于正环流的结果，并导致流函数、位密度扰动水平梯度剧增，其可视为间断。 相似文献
17.
V. V. Lyahov 《Izvestiya Atmospheric and Oceanic Physics》2007,43(3):308-316
The effect of a real departure of the atmosphere from the adiabaticity condition on the generation and dissipation of acoustic-gravity waves (AGWs) throughout the entire height of the atmosphere up to the mesopause (≈90 km) is studied. The results of solving the derived dispersion equation can be helpful in the formation of boundary conditions during simulation of the propagation of wave disturbances in the thermosphere and above. Unlike an adiabatic model, in a nonadiabatic model of the atmosphere, the frequencies (the roots of the dispersion equation) are complex and waves attenuate in some atmospheric layers, whereas other layers are unstable with respect to the onset of the corresponding AGW modes. As the height increases, the phase velocities of both acoustic and gravity branches of AGWs decrease and dissipation is enhanced. It is shown that macroscopic flows, along with periodic disturbances, are generated in a nonadiabatic atmosphere. 相似文献
18.
Ａｔｈｒｅｅ－ｄｉｍｅｎｓｉｏｎａｌｏｃｅａｎｇｅｎｅｒａｌｃｉｒｃｕｌａｔｉｏｎｍｏｄｅｌｆｏｒｍｅｓｏｓｃａｌｅｅｄｄｉｅｓ──ⅠＭｅａｎｄｅｒｓｉｍｕｌａｔｉｏｎａｎｄｌｉｎｅａｒｇｒｏｗｔｈｒａｔｅ￥ＷａｎｇＪｉａａｎｄＭｏｔｏＩｋｅｄａ（Ｒ... 相似文献
19.
The scattering of plane surface waves by bottom undulations in an ice-covered ocean modelled as a two-layer fluid consisting of a layer of fresh water of lesser density above a deep layer of salt water, is investigated here by using a simplified perturbation analysis. In such a two-layer fluid there exist waves of two different modes, one with higher mode propagates along the interface and the other with lower mode propagates along the ice-cover. An incident wave of a particular mode gets reflected and transmitted by the bottom undulations into waves of both the modes so that transfer of wave energy from one mode to another takes place. The first-order reflection and transmission coefficients of two different modes are obtained due to incident waves of again two different modes by employing Fourier transform technique in the mathematical analysis. For sinusoidal bottom topography these coefficients are depicted graphically against the wavenumber. These figures show how the transfer of energy from one mode to another takes place. 相似文献
20.
Interfacial waves and wave-induced tangential stress are studied for geostrophic small amplitude waves of two-layer fluid with a top free surface and a flat bottom. The solutions were deduced from the general form of linear fluid dynamic equations of two-layer fluid under the f-plane approximation, and wave-induced tangential stress were estimated based on the solutions obtained. As expected, the solutions derived from the present work include as special cases those obtained by Sun et al. (2004. Science in China, Ser. D, 47(12):1147-1154) for geostrophic small amplitude surface wave solutions and wave-induced tangential stress if the density of the upper layer is much smaller than that of the lower layer. The results show that the interface and the surface will oscillate synchronously, and the influence of the earth''s rotation both on the surface wave solutions and the interfacial wave solutions should be considered. 相似文献