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1.
G.D. Aburjania Kh.Z. Chargazia O.A. Kharshiladze 《Journal of Atmospheric and Solar》2010,72(13):971-981
The generation and further linear and nonlinear dynamics of planetary ultra-low-frequency (ULF) waves are investigated in the rotating dissipative ionosphere in the presence of inhomogeneous zonal wind (shear flow). Planetary ULF magnetized Rossby type waves appear as a result of interaction of the medium with the spatially inhomogeneous geomagnetic field. An effective linear mechanism responsible for the intensification and mutual transformation of large scale magnetized Rossby type and small scale inertial waves is found. For shear flows, the operators of the linear problem are not self-conjugate, and therefore the eigenfunctions of the problem may not be orthogonal and can hardly be studied by the canonical modal approach. Hence, it becomes necessary to use the so-called nonmodal mathematical analysis. The nonmodal analysis shows that the transformation of wave disturbances in shear flows is due to the non-orthogonality of eigenfunctions of the problem in the conditions of linear dynamics. Using numerical modeling, the peculiar features of the interaction of waves with the background flow as well as the mutual transformation of wave disturbances are illustrated in the ionosphere. It has been shown that the shear flow driven wave perturbations effectively extract an energy of the shear flow increasing the own energy and amplitude. These perturbations undergo self-organization in the form of the nonlinear solitary vortex structures due to nonlinear twisting of the perturbation’s front. Depending on the features of the velocity profiles of the shear flows the nonlinear vortex structures can be either monopole vortices or vortex streets and vortex chains. 相似文献
2.
G. D. Aburdzhaniya O. A. Kharshiladze Kh. Z. Chargaziya 《Geomagnetism and Aeronomy》2013,53(4):471-478
The linear mechanism by which internal gravity waves (IGWs) are generated and subsequently intensified in a stably stratified dissipative ionosphere in the presence of an inhomogeneous zonal wind (shear flow) has been studied. In the case of shear flows, the operators of linear problems are nonself-adjoint and the corresponding eigenfunctions are nonorthogonal; a canonical approach can hardly be used to study such motions. It is more adequate to apply the so-called nonmodal calculation. Dynamic equations and equations of energy transfer of IGW disturbances in the ionosphere with a shear flow have been obtained based on a nonmodal approach. Exact analytical solutions for the constructed dynamic equations have been found. The growth rate of the IGW shear instability has been determined. It has been established that IGW disturbances are intensified in an algebraically power manner rather than exponentially in the course of time. The effectiveness of the linear mechanism by which IGWs are intensified when interacting with an inhomogeneous zonal wind is analyzed. It has been indicated that IGWs effectively obtain the shear flow energy during the linear evolution stage and substantially increase (by an order of magnitude) their amplitude and energy. The frequency and the wave vector of generated IGW modes depend on time; therefore, a wide spectrum of wavelike disturbances, depending on the linear, rather than nonlinear, turbulent effects, is formed in the ionosphere with a shear flow. Thereby, a new degree of freedom appears, and the turbulent state of atmospheric—ionospheric layers can be formed on IGW disturbances. 相似文献
3.
The generation and further nonlinear dynamics of internal gravity wave (IGW) structures in a dissipative ionosphere in the presence of an inhomogeneous zonal wind (shear flow) have been studied. The effectiveness of the IGW amplification mechanism during the interaction with an inhomogeneous zonal wind is analyzed based on the corresponding model system of nonlinear dynamic equations constructed in (Aburjania et al., 2013). It has been indicated that IGWs effectively obtain the shear flow energy at the initial linear evolution stage and substantially (by an order of magnitude) increase their amplitude and, correspondingly, energy. The nonlinear self-localization mechanism starts operating with increasing amplitude, and the process terminates with the self-organization of nonlinear solitary strongly localized vortex structures. A new degree of system freedom and the disturbance evolution trend in a medium with a shear flow appear in such a way. Nonlinear IGW structures can be a purely monopoly vortex, a transverse vortex chain, and/or a longitudinal vortex path against the background of an inhomogeneous zonal wind, depending on the shear flow velocity profile. The accumulation of such vortices in the ionospheric medium can generate a strongly turbulent state. 相似文献
4.
Inertial waves as oscillatory motions in rotating fluids generate internal shear layers at critical latitudes. We investigated
the nonlinear interaction of inertial waves for global flows (3D flows) in dependence on the Ekman number. When the value
of the Ekman number decreases, the influence of the Ekman layers to the flow pattern increases. Critical latitudes, the attractor
flow pattern and certainly internal shear layers are observable mainly at greater values of the Ekman number. Although, with
decreasing the Ekman number smaller flow structures become visible, nonlinear interactions in shear layers drive an axisymmetric
flow whose amplitude diverges at the limit of the vanishing Ekman number. We show that this conclusion is valid not only for
zonal wind driven by inertial modes but also for similarly driven global flows. 相似文献
5.
G. D. Aburjania Z. O. Guguchia A. G. Khantadze O. A. Kharshiladze 《Geomagnetism and Aeronomy》2007,47(4):442-451
The generation and further dynamics of the planetary magnetized Rossby waves and inertial waves in a dissipative ionosphere in the presence of a smooth inhomogeneous zonal wind (shear flow) have been studied. The magnetized Rossby waves are caused by the interaction with the spatially inhomogeneous geomagnetic field and represent the ionospheric manifestations of usual tropospheric Rossby waves. The effective linear mechanism of amplification and mutual transformation of the Rossby and inertial waves has been revealed. For shear flows, the operators of linear problems are not self-adjoint, and the corresponding eigenfunctions are non-orthogonal; therefore, a canonical modal approach is of little use in studying such motions. It becomes necessary to apply the so-called nonmodal mathematical analysis, which has actively been developed for the last years. The nonmodal approach makes it possible to reveal that the transformation of wave-like disturbances in shear flows is caused by the nonorthogonality of eigenfunctions in the problem of linear dynamics. Thus, there appear a new degree of the system freedom and a new way of disturbance evolution in the medium. 相似文献
6.
We study stratified shear flow instability where the density profile takes the form of a staircase of interfaces separating uniform layers. Internal gravity waves riding on density interfaces can resonantly interact due to a background shear flow, resulting in the Taylor-Caulfield instability. The many steps of the density profile permit a multitude of interactions between different interfaces, and a rich variety of Taylor-Caulfield instabilities. We analyse the linear instability of a staircase with piecewise-constant density profile embedded in a background linear shear flow, locating all the unstable modes and identifying the strongest. The interaction between nearest-neighbour interfaces leads to the most unstable modes. The nonlinear dynamics of the instabilities are explored in the long-wavelength, weakly stratified limit (the defect approximation). Unstable modes on adjacent interfaces saturate by rolling up the intervening layer into a distinctive billow. These nonlinear structures coexist when stacked vertically and are bordered by the sharp density gradients that are the remnants of the steps of the original staircase. Horizontal averages remain layer-like. 相似文献
7.
切变基本纬向流中非线性赤道Rossby长波 总被引：5，自引：1，他引：4
为了解决观测和理论研究中的一些问题以及更好地了解热带大气动力学 ,有必要进一步研究基本气流的变化对大气中赤道Rossby波动的影响 .本文研究分析基本气流对赤道Rossby长波的影响 ,利用一个简单赤道 β平面浅水模式和摄动法 ,研究纬向基本气流切变中非线性赤道Rossby波 ,推导出在切变基本纬向流中赤道Rossby长波振幅演变所满足的非线性KdV方程并得到其孤立波解 .分析表明 ,孤立波存在的必要条件是基本气流有切变 ,而且基流切变不能太强 ,否则将产生正压不稳定 . 相似文献
8.
A corresponding model system of nonlinear dynamic equations for the lower ionosphere has been constructed in order to study the generation and further nonlinear dynamics of internal gravity wave (IGW) structures in a dissipative ionosphere in the presence of a nonuniform zonal wind (shear flow). The criterion for the development of the IGW shear instability in the ionosphere has been obtained. 相似文献
9.
G. D. Aburjania Z. O. Guguchia A. G. Khantadze O. A. Kharshiladze 《Geomagnetism and Aeronomy》2007,47(4):452-460
The specific features of the amplification and mutual transformation of wave modes in a linear regime have been revealed based on an analysis of the numerical solution to the set of equations describing the interaction of the magnetized Rossby wave and the inertial wave with the spatially inhomogeneous zonal wind (shear flow) in the ionospheric D, E, and F regions. It has been established that the presence of the geomagnetic field and Hall and Pedersen currents in the ionosphere improves the interaction and energy exchange between the waves and shear flow. 相似文献
10.
The broadband electrostatic turbulence generally observed in the high-latitude ionosphere is a superposition of nonlocal waves of ion-acoustic and ion-cyclotron types. In the presence of a shear of ion parallel velocity, ion-acoustic modes can be induced by an instability emerging due to an inhomogeneous distribution of energy density. This paper is devoted to the studies of excitation of oblique ion-acoustic wave in background configurations with inhomogeneous profiles of both electric field and ion parallel velocity. A numerical algorithm has been developed, and instability was simulated at various parameters of background plasma. The general possibility of oblique ion-acoustic wave generation by a gradient of ion parallel velocity is shown. In this case, the wave spectrum is found to be broadband, which agrees with satellite observations. 相似文献
11.
Gregory M. Zhikharev 《地球物理与天体物理流体动力学》2013,107(3-4):259-279
Abstract A spectral low-order model is proposed in order to investigate some effects of bottom corrugation on the dynamics of forced and free Rossby waves. The analysis of the interaction between the waves and the topographic modes in the linear version of the model shows that the natural frequencies lie between the corresponding Rossby wave frequencies for a flat bottom and those applying in the “topographic limit” when the beta-effect is zero. There is a possibility of standing or eastward-travelling free waves when the integrated topograhic effect exceeds the planetary beta-effect. The nonlinear interactions between forced waves in the presence of topography and the beta-effect give rise to a steady dynamical mode correlated to the topographic mode. The periodic solution that includes this steady wave is stable when the forcing field moves to the West with relatively large phase speed. The energy of this solution may be transferred to the steady zonal shear flow if the spatial scale of this zonal mode exceeds the scale of the directly forced large-scale dynamical mode. 相似文献
12.
Abstract The linear stability of a non-divergent barotropic parallel shear flow in a zonal and a non-zonal channel on the β plane was examined numerically. When the channel is non-zonal, the governing equation is slightly modified from the Orr-Sommerfeld equation. Numerical solutions were obtained by solving the discretized linear perturbation equation as an eigenvalue problem of a matrix. When the channel is zonal and lateral viscosity is neglected the problem is reduced to the ordinary barotropic instability problem described by Kuo's (1949) equation. The discrepancy between the stability properties of westward and eastward flows, which have been indicated by earlier studies, was reconfirmed. It has also been suggested that the unstable modes are closely related to the continuous modes discretized by a finite differential approximation. When the channel is non-zonal, the properties of unstable modes were quite different from those of the zonal problem in that: (1) The phase speed of the unstable modes can exceed the maximum value of the basic flow speed; (2) The unstable modes are not accompanied by their conjugate mode; and (3) The basic flow without an inflection point can be unstable. The dispersion relation and the spatial structure of the unstable modes suggested that, irrespective of the orientation of the channel, they have close relation to the neutral modes (Rossby channel modes) which are the solutions in the absence of a basic shear flow. The features mentioned above are not dependent on whether or not the flow velocity at the boundary is zero. 相似文献
13.
《Journal of Atmospheric and Solar》2002,64(8-11):1251-1261
A numerical simulation of secondary waves generated by nonlinear interaction has been used to interpret the behaviour of planetary waves observed by a meteor radar in the UK (53°27′N, 1°35′W) during the summer of 1992. A new explanation is proposed for the long-period variability of the (3,0) mode quasi-two-day wave in the mesosphere and lower-thermosphere, involving the (2,0) Rossby-gravity mode and pseudo-two-day secondary waves with the same zonal wavenumbers as those of the primary (2,0) and (3,0) modes. These pseudo-two-day secondary waves arise from the nonlinear interaction of the Rossby-gravity modes with long-period oscillations of the zonally averaged flow in the equatorial stratosphere, which can be generated by the interaction between the 10 and 16 day planetary waves. Other maxima existing in the neutral wind power spectra can be identified with various secondary waves originating from nonlinear interaction between the quasi-two-day and long-period planetary waves. 相似文献
14.
Field observations of tidally driven stratified flow in the sill area of Knight Inlet (British Columbia) revealed a very complicated structure, which includes solitary waves, upstream bifurcation, hydraulic jump and mixing processes. Recent observations suggest that the flow instabilities on the plunging pycnocline at the lee side of the sill may contribute to solitary wave generation through a subharmonic interaction. The present study reports on a series of numerical experiments of stratified tidal flow in Knight Inlet performed with the help of a fine resolution fully non-linear non-hydrostatic numerical model. The model reproduces all important stages of the baroclinic tidal dynamics observed in Knight Inlet. Results demonstrate that solitary waves are generated apart from the area of hydrodynamic instability. Accelerating tidal flux forms a baroclinic hydraulic jump just above the top of the sill, whereas the bifurcations and zones of shear instabilities are formed downstream of the sill. The first baroclinic mode having the largest velocity escapes from the generation area and propagates upstream, disintegrating further into a packet of solitary waves reviling the classical “non-subharmonic” mechanism of generation. The remaining part of the disturbance (slow baroclinic modes) is arrested by tidal flow and carried away to the lee side of the obstacle, where shear instability, billows and mixing processes are developed. Some sensitivity runs were performed for different value of tidal velocity. 相似文献
15.
Abstract Barotropic instability of weakly non-parallel zonal flows with localized intense shear regions is investigated numerically. The numerical integrations of the linear stability problem reveal the existence of unstable localized wave packets whose spatial structure and eigenfrequencies depend on two parameters which measure the degree of supercriticality and the zonal length-scale of the shear region. The results indicate that the structure of the instability is determined by conditions that ensure the decay of the wave packet at infinity and the transition from long to short waves across a turning point (critical layer) region which is controlled by non-parallel effects. The controlling influence exerted by the weak non-parallel effects on the evolution of the instability underlines the weakness of the parallel flow assumption which can be used locally, away from critical layers, as a diagnostic tool only. 相似文献
16.
We investigate numerically kinematic dynamos driven by flow of electrically conducting fluid in the shell between two concentric differentially rotating spheres, a configuration normally referred to as spherical Couette flow. We compare between axisymmetric (2D) and fully 3D flows, between low and high global rotation rates, between prograde and retrograde differential rotations, between weak and strong nonlinear inertial forces, between insulating and conducting boundaries and between two aspect ratios. The main results are as follows. Azimuthally drifting Rossby waves arising from the destabilisation of the Stewartson shear layer are crucial to dynamo action. Differential rotation and helical Rossby waves combine to contribute to the spherical Couette dynamo. At a slow global rotation rate, the direction of differential rotation plays an important role in the dynamo because of different patterns of Rossby waves in prograde and retrograde flows. At a rapid global rotation rate, stronger flow supercriticality (namely the difference between the differential rotation rate of the flow and its critical value for the onset of nonaxisymmetric instability) facilitates the onset of dynamo action. A conducting magnetic boundary condition and a larger aspect ratio both favour dynamo action. 相似文献
17.
《Journal of Atmospheric and Solar》2008,70(10):1336-1350
Planetary waves with periods between two and four days in the middle atmosphere over Antarctica are characterized using one year of data from the medium-frequency spaced antenna (MFSA) radars at Scott Base, Rothera, and Davis. In order to investigate the origin of the observed waves, the ground-based data are complemented by temperature measurements from the Earth Observing System Microwave Limb Sounder (EOS MLS) instrument on the Aura satellite as well as wind velocity data from the United Kingdom Met. Office (UKMO) stratospheric assimilation. Observed characteristics of waves with a period of approximately two days in summer are consistent with the quasi-two-day wave (QTDW) generally found after the summer solstice at low- and mid-latitudes. The Scott Base observations of the QTDW presented here are the highest-latitude ground-based observations of this wave to date. Waves with preferred periods of two and four days occur in bursts throughout the winter with maximum activity in June, July, and August. The mean of the two- and four-day wave amplitudes is relatively constant, suggesting constant wave forcing. When several waves with different periods occur at the same time, they often have similar phase velocities, supporting suggestions that they are quasi-non-dispersive. In 2005, a “warmpool” lasts from late July to late August. An alternative interpretation of this phenomenon is the presence of a structure propagating with the background wind. Consideration of the role of vertical shear (baroclinic instabilities) and horizontal shear (barotropic instabilities) of the zonal wind suggests that instabilities are likely to play a role in the forcing of the two- and four-day waves, which are near-resonant modes and thus supported by the atmosphere. 相似文献
18.
The specific features of the generation and intensification of internal gravity wave structures in different atmospheric-ionospheric regions, caused by zonal local nonuniform winds (shear flows), are studied. The model of the medium has been explained and an initial closed system of equations has been obtained in order to study the linear and nonlinear dynamics of internal gravity waves (IGWs) when they interact with the geomagnetic field in a dissipative ionosphere (for the D, E, and F regions). 相似文献
19.
Starting out with two interacting Rossby-Haurwitz waves, the generation of zonal flow is discussed. It is shown that zonal flow cannot be generated by first or second order interactions between two such waves, unless they are exchanging energy with a third wave within a resonant triad. The generation of zonal flow at second order through resonant triad interactions is subsequently established and studied. 相似文献
20.
Charles A. Lin 《地球物理与天体物理流体动力学》2013,107(4):227-259
Abstract A high vertical resolution model is used to examine the instability of a baroclinic zonal flow and a finite amplitude topographically forced wave. Two families of unstable modes are found, consisting of zonally propagating most unstable modes, and stationary unstable modes. The former have time scale and spatial structure similar to baroclinic synoptic disturbances, but are localized in space due to interaction with the zonally asymmetric forcing. These modes transport heat efficiently in both the zonal and meridional directions. The second family of stationary unstable modes has characteristics of modes of low frequency variability of the atmosphere. They have time scales of 10 days and longer, and are of planetary scale with an equivalent barotropic vertical structure. The horizontal structure resembles blocking flows. They are maintained by available potential energy of the basic wave, and have large zonal heat fluxes. The results for both families of modes are interpreted in terms of an interaction between forcing and baroclinic instability to create favoured regions for eddy development. Applications to baroclinic planetary waves are also considered. 相似文献