共查询到20条相似文献，搜索用时 31 毫秒
1.
Y. Hobara S.N. Walker M. Dunlop M. Balikhin O.A. Pokhotelov H. Nilsson H. Rme 《Planetary and Space Science》2007,55(15):2257-2260
Using multipoint measurements from the Cluster mission wave identification techniques are applied to observations of ULF waves made in the terrestrial foreshock with the aim of identifying the modes and properties of the waves taking into account the effects of a high beta plasma. The wave properties in the spacecraft and plasma rest frames are experimentally derived using minimum variance analysis. Two waves with periods of 30 and 3 s dominate the dynamic frequency spectrum. The results indicate that these waves propagate in the fast magnetosonic and Alfvén/Ion Cyclotron modes, respectively. Both waves propagate in the upstream direction in the plasma rest frame but are convected downstream in the spacecraft frame. The measured wave properties in the plasma rest frame are in good agreement with those obtained from the theoretical kinetic dispersion relation taking into account the effects of different plasma beta. The dispersion results show a rather significant deviation from fluid model, especially when high beta plasma conditions occur. These experimentally derived foreshock ULF wave properties are in good agreement with previous results but when the effects of a high beta plasma are considered it is not as straight forward to choose the correct wave mode branch. 相似文献
2.
The relation between the ejected plasma cloud and the shock wave propagating ahead of it is examined for 27 pairs of such events. The flare sprays and the eruptive prominences observed in H line as well as the fast-moving sources of type-IV radio bursts have been considered as such ejected plasma clouds. Propagation of the shock wave in the solar corona has been examined from the observations of type-II radio bursts. Using the Parker model of the propagation of a shock wave, the shock wave velocity has been compared with the plasma cloud velocity. Energy interconnection between these two events has been studied. In the majority of the investigated cases there exists an energetic interconnection between the plasma cloud and the shock wave. 相似文献
3.
This paper investigates wave properties of hot plasma in a Veselago medium. For the Schwarzschild black hole, the 3+1 GRMHD
equations are re-formulated which are linearly perturbed and then Fourier analyzed for rotating (non-magnetized and magnetized)
plasmas. The graphs of wave vector, refractive index and change in refractive are used to discuss the wave properties. The
results obtained confirm the presence of Veselago medium for both rotating (non-magnetized and magnetized) plasmas. This work
generalized the isothermal plasma waves in the Veselago medium to hot plasma case. 相似文献
4.
M. S. Ruderman 《Solar physics》1991,131(1):11-24
Surface magnetohydrodynamic wave propagation on a magnetic interface in a cold plasma is studied. The anisotropic ion viscosity is taken into account. Only long waves damping weakly in a wave period are considered. The dispersion equation is obtained. This equation is shown always to have exactly one root if there is no viscosity. The dependences of phase velocity, penetration depth and damping decrement of waves on the parameters of undisturbed plasma and wave propagation direction are investigated. The resulting application for describing of surface wave damping in the solar corona is discussed. 相似文献
5.
The problem of a one-dimensional, nonlinear, circularly polarized wave in a collisionless plasma is solved for the case in which the group velocity of the localized wave is zero relative to the plasma frame.For an electron-positron plasma the ponderomotive potential is repulsive, and both small and large amplitude waves in the presence of reflected and transmitted particles is discussed.The inclusion of an external magnetic field such that the cyclotron frequency is smaller than the wave frequency does not alter qualitatively the results of the fieldless case, except for the fact that an electrostatic potential is generated.For the case in which the cyclotron frequency is larger than the wave frequency, the resulting potential is attractive, and it is shown that no localized waves can coexist with confined and transmitted particles. If, however, an ionic component is presnt in the electron-positron plasma, such as may be the case in pulsar magnetospheres, localized waves may again be possible. 相似文献
6.
《Planetary and Space Science》1999,47(8-9):1111-1118
Particle aspect analysis is extended for kinetic Alfven waves in an inhomogeneous magnetoplasma in the presence of a general loss-cone distribution function. The effect of finite Larmor radius is incorporated in the finite temperature anisotropic plasma. Expressions for the field-aligned current, perpendicular current (to B), dispersion relation, particle energy and growth rate are derived and effects of steepness of loss-cone distribution and plasma density inhomogeneity are discussed. The treatment of the kinetic Alfven wave instability is based on the assumption that the plasma consists of resonant and non-resonant particles. It is assumed that resonant particles support the oscillatory nature of the wave. The excitation of the wave is treated by the wave particle energy exchange method. The applicability of the investigation is discussed for auroral acceleration phenomena. © 1999 Elsevier Science Ltd. All rights reserved. 相似文献
7.
A one-dimensional model for thinning of the plasma sheet is developed on the basis of launching a fast mode MHD rarefaction wave propagating in the tailward direction along the plasma sheet. Behind the rarefaction wave the pressure is reduced, leading to thinning of the plasma sheet and also to an Earthward plasma flow with a speed on the order of the sound speed a0. The plasma sheet thickness is reduced by a factor of 2 if an Earthward plasma flow speed of 0.8a0 is induced. The predictions of the model are in reasonable agreement with observations. 相似文献
8.
C. C. Harvey 《Solar physics》1976,46(2):509-509
An attempt is made to explain the observed frequency-time profiles of type III solar radiobursts in terms of a rapid plasma wave decay rate combined with the exciter model recently proposed by the author. The decay rate is assumed to be sufficiently rapid for the plasma wave energy density profile to be similar to the excitor power density time profile; this is consistent with the exciter model, the rapid decay being caused by Landau damping on the electrons of the modified high energy tail of the ambient plasma electron velocity distribution. The model is compared with radio observations by making simple assumptions about the dependence of the radio intensity upon the plasma wave energy. A comparison is made with simultaneous radio and electron observations by further assuming a simple power-law velocity distribution for the electrons at their point of ejection from the Sun. 相似文献
9.
Nonlinear Alfvén wave in a hot rotating and strongly magnetized electron-positron plasma is considered. Using relativistic two fluid equations, the dispersion relation for Alfvén wave in the rotating plasma is obtained. Large amplitude Alfvén solitons are found to exist in the rotating pulsar plasma. Rotational effects on solitons are discussed. 相似文献
10.
Dean F. Smith 《Astrophysics and Space Science》1976,42(2):261-283
A general scheme is established to examine any magnetohydrodynamic (MHD) configuration for its acceleration potential including the effects of various types of plasma waves. The analysis is restricted to plasma waves in a magnetic field with electron cyclotron frequency less than, but comparable to, the electron plasma frequency (moderate field). The general role of electron plasma waves is examined in this paper independent of a specific MHD configuration or generating mechanism in the weak turbulence limit. The evolution of arbitrary wave spectra in a non-relativistic plasma is examined, and it is shown that the nonlinear, process of induced scattering on the polarization clouds of ions leads to the collapse of the waves to an almost one-dimensional spectrum directed along the magnetic field. The subsequent acceleration of non-relativistic and relativistic particles is considered. It is shown for non-relativistic particles that when the wave distribution has a negative slope the acceleration is retarded for lower velocities and enhanced for higher velocities compared to acceleration by an isotropic distribution of electron plasma waves in a magnetic field. This change in behavior is expected to affect the development of wave spectra and the subsequent acceleration spectrum.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
11.
Investigation of nonlinear wave modulation of electron-acoustic solitary wave packets in planar as well as nonplanar geometry is carried out for an unmagnetized two temperature plasma composed of cold and hot (featuring q-nonextensive distribution) electrons with stationary ions. It is shown that in such plasma, propagation of EA wave packets is governed by a modified NLSE which accounts for the geometrical effect and the nonextensivity of the hot electron species. It is found that the nature of the modulational instabilities would be significantly modified due to the geometrical effects, density ratio α of the hot-to-cold electrons species as well as their temperature ratio θ. Also, there exists a modulation instability period for the cylindrical and spherical envelope excitations, which does not exist in the one-dimensional case. Furthermore, spherical EA solitary wave packets are more structurally stable to perturbations than the cylindrical ones. The relevance of the current study to EA wave modulation in auroral zone plasma is highlighted. 相似文献
12.
The Rayleigh-Taylor instability in a rotating plasma of variable density has been investigated to include simultaneously the effects of viscosity and the finiteness of the ion Larmor radius. It is shown that, for a plasma in which the density is stratified along the vertical, the solution is characterized by a variational principle. Making use of this, proper solutions have been otained for a semiinfinite plasma in which the density varies exponentially. The dispersion relation has been solved numerically and it is found that the influence of the effects of both FLR and viscosity is stabilizing. The Coriolis forces are found to have a dual role, stabilizing for small wave numbers and destabilizing for large wave numbers. The range of the small wave numbers, over which the Coriolis forces have a stabilizing influence, is found to increase with Coriolis forces. 相似文献
13.
Bifurcations of nonlinear electron acoustic solitary waves and periodic waves in an unmagnetized quantum plasma with cold and hot electrons and ions has been investigated. The one dimensional quantum hydrodynamic model is used to study electron acoustic waves (EAWs) in quantum plasma. Applying the well known reductive perturbation technique (RPT), we have derived a Korteweg-de Vries (KdV) equation for EAWs in an unmagnetized quantum plasma. By using the bifurcation theory and methods of planar dynamical systems to this KdV equation, we have presented the existence of two types of traveling wave solutions which are solitary wave solutions and periodic traveling wave solutions. Under different parametric conditions, some exact explicit solutions of the above waves are obtained. 相似文献
14.
An instability associated with the magnetosonic wave driven unstable due to coupling with electron and ion drift modes has been considered as a potential source for driving the hydromagnetic turbulence observed in Giacobini-Zinner (G-Z) Cometary plasma. The instability has good growth rate for propagation perpendicular to plasma inhomogeneities and exists for all wave numbers. The wave period for waves propagating perpendicular to the gradients is about a few times ion-gyroperiod and higher values of plasma beta (
e
lead to stronger instability. 相似文献
15.
S. K. El-Labany W. M. Moslem N. A. El-Bedwehy R. Sabry H. N. Abd?El-Razek 《Astrophysics and Space Science》2012,338(1):3-8
Rogue wave in a collisionless, unmagnetized electronegative plasma is investigated. For this purpose, the basic set of fluid
equations is reduced to the Korteweg-de Vries (KdV) equation. However, when the frequency of the carrier wave is much smaller
than the ion plasma frequency then the KdV equation is also used to study the nonlinear evolution of modulationally unstable
modified ion-acoustic wavepackets through the derivation of the nonlinear Schr?dinger (NLS) equation. In order to show that
the characteristics of the rogue wave is influenced by the plasma parameters, the relevant numerical analysis of the NLS equation
is presented. The relevance of our investigation to the Titan’s atmosphere is discussed. 相似文献
16.
《Planetary and Space Science》2007,55(10):1358-1367
Propagation of plasma-acoustic wave has been studied in magnetized plasma contaminated with dust charged grains. It has shown that, because of the configuration of magnetized plasma contaminated with dust charge fluctuation, pseudopotential method fails to derive nonlinear wave equation. We thus exercise an alternate approach to yield wave equation in the form of Sagdeev-like potential equation which enables the success to study the nonlinear waves. Again a modified mathematical formalism known as tanh-method has the merit to evaluate the soliton features in relation to its expectation in space. The method has its success in finding the solitary waves along with other exciting formation of shock-like wave, soliton radiation in soliton propagation. The results have more realistic interpretation in showing explicitly the interaction of magnetic field and impurity caused by dust charge variation. 相似文献
17.
We consider a model of a coronal loop in the form of a cord surrounded by a coaxial shell. Two slow magnetosonic waves longitudinally propagate within a thin flux tube on the m=0 cylindrical mode with velocities close to the tube velocities in the cord and the shell. One wave propagates inside the cord, while the other propagates inside the shell. A peculiar feature of the second wave is that the plasma in the cord and the shell oscillates with opposite phases. There are two fast magnetosonic waves on each of the cylindrical modes with m>0. If the plasma density in the shell is lower than that in the surrounding corona, then one of the waves is radiated into the corona, which causes the loop oscillations to be damped, while the other wave is trapped by the cord, but can also be radiated out under certain conditions. If the plasma density in the shell is higher than that in the cord, then one of the waves is trapped by the shell, while the other wave can also be trapped by the shell under certain conditions. In the wave trapped by the shell and the wave radiated by the tube, the plasma in the cord and the shell oscillates with opposite phases. 相似文献
18.
The nonlinear wave structure of arbitrary amplitude ion acoustic solitary waves (IASWs) are studied in the Sagdeev’s pseudopotential framework for an ultra-relativistic degenerate dense plasma comprising cold and hot electrons and inertial ultra-cold ions. By employing standard normal-mode analysis the dispersion relation for linear waves is studied. The numerical results are presented to understand the features of ion acoustic solitary wave structures. It is shown that the present plasma model supports IASWs having positive potential well. Also, it is found that the small amplitude rarefactive double layer solution can exist in such a plasma system in some parametric region. It is shown that solitary structures and double layers are affected by relevant plasma parameters. 相似文献
19.
In this paper we examine the wave properties of a hot plasma living in a Schwarzschild magnetosphere. The 3+1 GRMHD perturbation
equations are formulated for this scenario. These equations are Fourier analyzed and then solved numerically to obtain the
dispersion relations for a non-rotating, rotating non-magnetized and rotating magnetized plasma. The wave vector is evaluated,
which is used to calculate the refractive index. These quantities are shown in graphs which are helpful to discuss the dispersive
properties of the medium near the event horizon. 相似文献
20.
Properties of a guided MHD-wave propagating in a magnetic field tube with the plasma density differing from the ambient density are studied. Like the Alvén wave this wave propagates along the magnetic field and is connected with the field-aligned currents flowing at the periphery of the oscillating tube. The guided wave is accompanied by the magnetic field compression, nevertheless the wave moves without attenuation. The guided wave velocity is between the Alvén velocities inside and outside the oscillating tube. In a tube of elliptical cross-section the propagation velocity depends on the polarization of the wave. 相似文献