共查询到20条相似文献，搜索用时 625 毫秒
1.
O. M. El Mekki 《Solar physics》1982,75(1-2):351-360
Internal atmospheric hydromagnetic planetary-gravity waves propagating through a latitudinally sheared zonal flow and a zonal magnetic field sheared both latitudinally and vertically are studied.It is shown that the waves possess four critical latitudes. At two of them the waves propagate on one side only with their energy and momentum fluxes differing by an additive factor on the two sides of the critical latitude, whereas at the other two they are capable of propagating on both sides and exhibit the value effect behaviour, with their energy and momentum fluxes attenuated by an exponential factor as they cross the critical latitude. 相似文献
2.
O. M. El Mekki 《Solar physics》1983,85(1):83-91
Hydromagnetic planetary-gravity waves propagating on a β-plane through a zonal flow and transverse magnetic field are examined for instability. Such instabilities may be related to same physical phenomena in the atmospheres of the Sun and planets and in the Earth's core. It is found that the onset of instability depends on the directions of the vertical and transverse wave-numbers and the zonal flow. It is also shown that as the magnetic field intensity is kept uniform instability can onset provided that the zonal flow strength does not exceed a certain factor, which depends on the parameters of the medium, and then the zonal wavenumbers that can become unstable are limited to a given range. If the basic Alfvén wave speed is allowed to vary whereas the zonal flow is kept uniform the zonal wavenumbers that can exhibit instability are again limited but the basic Alfvén wave speed can assume any value. 相似文献
3.
G.D. Aburjania Kh.Z. Chargazia G.V. Jandieri A.G. Khantadze O.A. Kharshiladze J.G. Lominadze 《Planetary and Space Science》2005,53(9):881-901
In the present article, the results of theoretical investigation of the dynamics of generation and propagation of planetary (with wavelength 103 km and more) ultra-low frequency (ULF) electromagnetic wave structures in the dissipative ionosphere are given. The physical mechanism of generation of the planetary electromagnetic waves is proposed. It is established, that the global factor, acting permanently in the ionosphere—inhomogeneity (latitude variation) of the geomagnetic field and angular velocity of the earth's rotation—generates the fast and slow planetary ULF electromagnetic waves. The waves propagate along the parallels to the east as well as to the west. In E-region the fast waves have phase velocities (2-20) km s−1and frequencies (10−1-10−4) s−1; the slow waves propagate with local winds velocities and have frequencies (10−4-10−6) s−1. In F-region the fast ULF electromagnetic waves propagate with phase velocities tens-hundreds km s−1 and their frequencies are in the range of (10-10−3) s−1. The slow mode is produced by the dynamoelectric field, it represents a generalization of the ordinary Rossby-type waves in the rotating ionosphere and is caused by the Hall effect in the E-layer. The fast disturbances are the new modes, which are associated with oscillations of the ionospheric electrons frozen in the geomagnetic field and are connected with the large-scale internal vortical electric field generation in the ionosphere. The large-scale waves are weakly damped. The features and the parameters of the theoretically investigated electromagnetic wave structures agree with those of large-scale ULF midlatitude long-period oscillations (MLO) and magnetoionospheric wave perturbations (MIWP), observed experimentally in the ionosphere. It is established, that because of relevance of Coriolis and electromagnetic forces, generation of slow planetary electromagnetic waves at the fixed latitude in the ionosphere can give rise to the reverse of local wind structures and to the direction change of general ionospheric circulation. It is considered one more class of the waves, called as the slow magnetohydrodinamic (MHD) waves, on which inhomogeneity of the Coriolis and Ampere forces do not influence. These waves appear as an admixture of the slow Alfven- and whistler-type perturbations. The waves generate the geomagnetic field from several tens to several hundreds nT and more. Nonlinear interaction of the considered waves with the local ionospheric zonal shear winds is studied. It is established, that planetary ULF electromagnetic waves, at their interaction with the local shear winds, can self-localize in the form of nonlinear solitary vortices, moving along the latitude circles westward as well as eastward with velocity, different from phase velocity of corresponding linear waves. The vortices are weakly damped and long lived. They cause the geomagnetic pulsations stronger than the linear waves by one order. The vortex structures transfer the trapped particles of medium and also energy and heat. That is why such nonlinear vortex structures can be the structural elements of strong macroturbulence of the ionosphere. 相似文献
4.
In the present work, the generation of large-scale zonal flows and magnetic field by short-scale collision-less electron skin depth order drift-Alfven turbulence in the ionosphere is investigated. The self-consistent system of two model nonlinear equations, describing the dynamics of wave structures with characteristic scales till to the skin value, is obtained. Evolution equations for the shear flows and the magnetic field is obtained by means of the averaging of model equations for the fast-high-frequency and small-scale fluctuations. It is shown that the large-scale disturbances of plasma motion and magnetic field are spontaneously generated by small-scale drift-Alfven wave turbulence through the nonlinear action of the stresses of Reynolds and Maxwell. Positive feedback in the system is achieved via modulation of the skin size drift-Alfven waves by the large-scale zonal flow and/or by the excited large-scale magnetic field. As a result, the propagation of small-scale wave packets in the ionospheric medium is accompanied by low-frequency, long-wave disturbances generated by parametric instability. Two regimes of this instability, resonance kinetic and hydrodynamic ones, are studied. The increments of the corresponding instabilities are also found. The conditions for the instability development and possibility of the generation of large-scale structures are determined. The nonlinear increment of this interaction substantially depends on the wave vector of Alfven pumping and on the characteristic scale of the generated zonal structures. This means that the instability pumps the energy of primarily small-scale Alfven waves into that of the large-scale zonal structures which is typical for an inverse turbulent cascade. The increment of energy pumping into the large-scale region noticeably depends also on the width of the pumping wave spectrum and with an increase of the width of the initial wave spectrum the instability can be suppressed. It is assumed that the investigated mechanism can refer directly to the generation of mean flow in the atmosphere of the rotating planets and the magnetized plasma. 相似文献
5.
We show that solitary waves in a planetary, zonal shear have a shape and flow field that are virtually identical to those observed around the Red Spot and numerous other features that have seen in the Jovian atmosphere. We also suggest that the theoretically calculated interaction between solitary waves has many characteristics in common with the observed interactions between these same Jovian features, and show that available atmosphere models are consistent with the very restrictive requirements of the theory. 相似文献
6.
The effect of large Larmor radius on the nonlinear behaviour of Alfvén waves propagating parallel to a uniform magnetic field in a compressible fluid is investigated with the aid of LLR-MHD equations. It is shown that asymptotic evolution of these waves is governed by the modified nonlinear Schrödinger equation. The dispersion is provided by the large Larmor radius effect in the magnetic field equation. It is suggested that these calculations can have a bearing on the investigation of the structure of MHD waves in both laboratory and space plasmas, e.g., imploding pinches, laser-blow-off plasma experiment, recent barium releases in the magnetosphere, plasma flow near small planetary bodies such as comets and plasma dynamic near collisionless shock fronts. 相似文献
7.
Venus Express observations of ULF and ELF waves in the Venus ionosphere: Wave properties and sources
Electrical activity in a planetary atmosphere enables chemical reactions that are not possible under conditions of local thermodynamic equilibrium. In both the Venus and terrestrial atmospheres, lightning forms nitric oxide. Despite the existence of an inventory of NO at Venus like the Earth’s, and despite observations of the signals expected from lightning at optical, VLF, and ELF frequencies, the existence of Venus lightning still is met with some skepticism. The Venus Express mission was equipped with a fluxgate magnetometer gradiometer system sampling at rates as high as 128 Hz, and making measurements as low as 200 km altitude above the north polar regions of Venus. However, significant noise levels are present on the Venus Express spacecraft. Cleaning techniques have been developed to remove spacecraft interference at DC, ULF, and ELF frequencies, revealing two types of electromagnetic waves, a transverse right-handed guided mode, and a linearly polarized compressional mode. The propagation of both types of signals is sensitive to the magnetic field in ways consistent with propagation from a distant source to the spacecraft. The linearly polarized compressional waves generally are at lower frequencies than the right-handed transverse waves. They appear to be crossing the usually horizontal magnetic field. At higher frequencies above the lower hybrid frequency, waves cannot enter the ionosphere from below when the field is horizontal. The arrival of signals at the spacecraft is controlled by the orientation of the magnetic field. When the field dips into the atmosphere, the higher frequency guided mode above the lower hybrid frequency can enter the ionosphere by propagating along the magnetic field in the whistler mode. These properties are illustrated with examples from five orbits during Venus Express’ first year in orbit. These properties observed are consistent with the linearly polarized compressional waves being produced at the solar wind interface and the transverse guided waves being produced in the atmosphere. 相似文献
8.
Cheng Jiu-heng 《Chinese Astronomy and Astrophysics》1994,18(4):374-382
Starting from the equations of motion of a thin magnetic tube, the characteristic curves and velocities and compatibility relations are derived as basis for investigating its motion and for correctly formulating the problem of stationary solution. It is shown that the characteristic velocity of transverse waves is related to the Alfvén Mach number of the flow in the tube. When the flow velocity exceeds the critical value for the Kelvin-Helmholtz instability, transverse waves cease to exist. 相似文献
9.
The propagation of MHD waves is studied when two ideal fluids, thermal and suprathermal gases, coupled by magnetic field are
moving with the steady flow velocity. The fluids move independently in a direction perpendicular to the magnetic field but
gets coupled along the field. Due to the presence of flow in suprathermal and thermal fluids there appears forward and backward
waves. All the forward and backward modes propagate in such a way that their rate of change of phase speed with the thermal
Mach number is same. It is also found that besides the usual hydromagnetic modes there appears a suprathermal mode which propagates
with faster speed. Surface waves are also examined on an interface formed with composite plasma (suprathermal and thermal
gases) on one side and the other is a non-magnetized plasma. In this case, the modes obtained are two or three depending on
whether the sound velocity in thermal gas is equal to or greater than the sound velocity in suprathermal gas. The results
lead to the conclusion that the interaction of thermal and suprathermal components may lead to the occurrence of an additional
mode called suprathermal mode whose phase velocity is higher than all the other modes. 相似文献
10.
《Planetary and Space Science》2007,55(14):2113-2120
The shear-driven electrostatic ion-cyclotron instability (EICI) is studied using the loss-cone distribution function by particle aspect analysis. The effect of the loss-cone distribution on the dispersion relation and growth rate of weak shear-driven EICI is studied. The whole plasma is considered to consist of resonant and non-resonant particles. The wave is assumed to propagate obliquely to the static magnetic field. It is found that the frequency of the EICI is Doppler shifted due to the transverse inhomogeneous flow in the direction of the magnetic field. It is also found that for anisotropic plasma the critical velocity shear needed to excite EICI depends upon the loss-cone distribution index (J). With the increasing values the loss-cone distribution indices (J), the critical value of normalized velocity shear needed to generate EICI in anisotropic plasma, decreases and is of the order of the weak shear. The loss-cone distribution acts as a source of free energy and generates the weak shear-driven EICI at longer perpendicular perturbations. It also lowers the transverse and parallel energy of the resonant ions. The study may explain the frequently observed EICI in the auroral acceleration region. 相似文献
11.
Stratospheric ozone depressions, following intense solar particle events (SPE) observed by the backscattered ultraviolet (BUV) experiment on the Nimbus-4 satellite, indicate the existence of distinct asymmetries between the Northern and Southern Hemispheres. These asymmetries are observed in the magnitude of the depressions above the 5-mb level, their temporal variations, and the spatial (i.e., latitude and longitude) dependence of these variations. Possible causes of asymmetries, shown by two events on 4 August 1972 and 25 January 1971, can be attributed to: (1) tilt of the interplanetary magnetic field (IMF) with respect to the Earth's dipole magnetic field which influences the precipitation of energetic solar particles into the polar atmospheres; (2) differences in ozone chemistry caused by the large change in atmospheric temperature between summer and winter hemispheres; (3) seasonal differences of the stratosphere's dynamic states which are affected by upward propagating planetary waves in winter in contrast to the relatively undisturbed zonal flow in summer; (4) topographic asymmetry between Northern and Southern Hemispheres.These effects are shown by three-dimensional plots of the events in geographic coordinates and by color contour plots of the stratospheric ozone distributions in geomagnetic and geographic polar coordinates, respectively. 相似文献
12.
H. Alinejad 《Astrophysics and Space Science》2012,337(2):637-643
A theoretical investigation is carried out for understanding the basic features of oblique propagation of linear and nonlinear
ion-acoustic waves subjected to an external magnetic field in an electron-positron-ion plasma which consists of a cold magnetized
ion fluid, Boltzmann distributed positron, and electrons obeying a trapped distribution. In the linear regime, two dispersion
curves are obtained. It is shown that the positron concentration causes the both modes to propagate with smaller phase velocities.
Then, owing to the presence of resonant electrons, the modified Korteweg-de Vries equation describing the nonlinear dynamics
of small but finite amplitude ion-acoustic waves is derived. It is found that the effects of external magnetic field (obliqueness),
trapped electrons, positron concentration and temperature ratio significantly modify the basic features of solitary waves. 相似文献
13.
We present a dynamo mechanism arising from the presence of barotropically unstable zonal jet currents in a rotating spherical shell. The shear instability of the zonal flow develops in the form of a global Rossby mode, whose azimuthal wavenumber depends on the width of the zonal jets. We obtain self-sustained magnetic fields at magnetic Reynolds numbers greater than 103. We show that the propagation of the Rossby waves is crucial for dynamo action. The amplitude of the axisymmetric poloidal magnetic field depends on the wavenumber of the Rossby mode, and hence on the width of the zonal jets. We discuss the plausibility of this dynamo mechanism for generating the magnetic field of the giant planets. Our results suggest a possible link between the topology of the magnetic field and the profile of the zonal winds observed at the surface of the giant planets. For narrow Jupiter-like jets, the poloidal magnetic field is dominated by an axial dipole whereas for wide Neptune-like jets, the axisymmetric poloidal field is weak. 相似文献
14.
R. C. Cross 《Planetary and Space Science》1988,36(12):1461-1468
Propagation of torsional Alfvén waves in the magnetosphere is examined for two models of the Earth's magnetic field, one where the field is toroidal, the other being a dipole field. Both models yield magnetically guided torsional wave modes which are strongly localized in all directions transverse to the steady magnetic field. The transverse structure is determined by a self-consistent solution of the ideal MHD equations. It is shown that the torsional wave is guided even when b is finite, where b is the component of the wave magnetic field in a direction parallel to the steady magnetic field. 相似文献
15.
汪景琇 《中国天文和天体物理学报》1986,(3)
本文对充满垂直均匀磁场的等温大气内的磁声重力波做了严格的解析分析,并将其通解表述成广义超几何函数的形式。该解可用于对磁大气内振荡现象的进一步数值模拟研究。对解的分析澄清了若干磁声重力波的传播性质。 相似文献
16.
A. G. Michalitsanos 《Solar physics》1973,30(1):47-61
The magnetohydrodynamic frequency-wavelength relation, derived by McLellan and Winterberg (1968), has been evaluated for an isothermal atmosphere. In particular, the effect which an inclined magnetic field and a finite horizontal wavelength have on the critical sonic and internal-gravity cut-off frequencies has been examined, in which it has been assumed that the magnetic field vector, wave vector, and gravity vector are coplanar. It is shown that the frequency band in which vertical wave propagation is impossible in the non-magnetic photosphere, becomes smaller when an inclined uniform magnetic field is introduced, and that low frequency magnetically coupled internal-gravity waves do not propagate vertically if the horizontal wavelengths associated with this mode are greater than a critical wavelength which decreases with field strength.It is also demonstrated that an inclined magnetic field will inhibit the resonance that occurs at the critical frequency
g in the non-magnetic atmosphere which is a result consistent with recent observations of the wiggly line structure in active regions.This work is supported by the European Space Research Organization.Presently with the Solar Astronomy Group, California Institute of Technology. 相似文献
17.
The paper examines the evolutionary behaviour of acceleration waves in a perfectly conducting inviscid radiating gas permeated by a transverse magnetic field. Solution of the problem in the characteristic plane has been determined. It is shown that a linear solution in the characteristic plane exhibits nonlinear behaviour in the physical plane. Transport equation governing the behaviour of acceleration waves has been derived. The effect of radiative heat transfer under the influence of magnetic field on the formation of shock wave with generalized geometry is analyzed. The critical amplitude of the initial disturbance has been obtained such that the initial amplitude of any compressive wave greater than the critical one always terminates into shock wave. Critical time, when the compressive wave will grow into a shock wave, has been determined. Also, it is assessed as to how the radiative heat transfer in the presence of magnetic field affects the shock formation. 相似文献
18.
The damping of fast kink oscillations of solar coronal loops attributable to the radiation of MHD waves into the surroundings is considered in the thin-tube approximation. The oscillation damping decrement is calculated both by using a new energy method and by solving the dispersion equation for magnetic-tube eigenmodes. The two approaches are in good agreement under appropriate assumptions. The damping is negligible if MHD waves are radiated perpendicular to the magnetic field. The low Q factor of the loop oscillations in active regions found with the TRACE space telescope is associated with the generation of running waves that propagate along magnetic field lines. 相似文献
19.
A fully three-dimensional, nonlinear, time-dependent, multi-layered spherical kinematic dynamo model is used to study the effect on the observable external magnetic field of flow in an electrically conducting layer above a spherical turbulent dynamo region in which the α effect generates the magnetic field. It is shown that the amplitude and structure of an observable planetary magnetic field are largely determined by the magnitude and structure of the flow in the overlying layer. It is also shown that a strong-field planetary dynamo can be readily produced by the effect of an electrically conducting flow layer at the top of a convective core. The overlying layer and the underlying convective region constitute a magnetically strongly coupled system. Such overlying layers might exist at the top of the Earth's core due to chemical or thermal causes, in the cores of other terrestrial planets for similar reasons, and in Saturn due to the differentiation of helium from hydrogen. An electrically conducting and differentially rotating layer could exist above the metallic hydrogen region in Jupiter and affect the jovian magnetic field similar to the overlying layers in other planets. Lateral temperature gradients resulting in thermal winds drive the flow in the overlying layers. All planetary magnetic fields could be maintained by similar turbulent convective dynamos in the field-generation regions of planets with the differences among observable magnetic fields due to different circulations in the overlying electrically conducting layers. 相似文献
20.
S. T. Suess 《Solar physics》1971,18(1):172-175
Some recent observations of the Sun suggest a class of wave-like motions moving both eastward and westward at a uniform velocity with respect to the mean solar angular velocity. It is suggested that these may be hydromagnetic planetary waves. An estimate of the mean toroidal magnetic field is made, based on a theoretical treatment of such waves already in the literature, and a slight correction to the mean rate of rotation of the Sun is inferred. 相似文献