共查询到20条相似文献，搜索用时 31 毫秒
1.
Akira Hasegawa 《Solar physics》1976,47(1):325-330
Most of the MHD instabilities originating from the nonuniformity of a plasma excite MHD surface wave. When the excited wave has a frequency s which corresponds to the local shear Alfvén wave resonance (s = k
v
a
(x), where v
a
is the Alfvén speed and k
is the wave number in the direction of the magnetic field), the surface wave resonantly mode converts to the kinetic Alfvén wave, the Alfvén wave having a perpendicular wavelength comparable to the ion gyroradius and being able to propagate across the magnetic field. We discuss various linear and nonlinear effects of this kinetic Alfvén wave on the plasma including particle acceleration and heating. A specific example for the case of a MHD Kelvin-Helmholtz instability is given. 相似文献
2.
Shear flow instability is studied in the planar magnetopause boundary layer region by treating the plasma as compressible. A necessary criterion for instability near the cusp resonance is obtained analytically. The criterion depends on plasma, Alfvén Mach numberM
A
and the ratio of the scale lengths of the gradients in the flow and Alfvén velocities. The instability at the cusp resonance layer can be excited rather easily for the low plasma and for shear flow scale length smaller than the typical scale length over which Alfvén velocity varies. The growth rate for instability is obtained for any from a cubic equation. The unstable modes may contribute to the ULF wave activity at the magnetopause. 相似文献
3.
The waves, propagating nearly transverse to the ambient magnetic field, with frequencies near the harmonics of the proton-cyclotron frequency are studied in an inhomogeneous plasma with protons having loss-cone distributions. Three types of drift cyclotron instabilities have been studied: (i) non-flute instability; (ii) B-resonant instability; and (iii) non-resonant instability. Increases of loss-cone and density gradient increase the growth rates of all three instabilities. Increases in the positive temperature gradient and t (ratio of thermal pressure of trapped protons to magnetic field pressure) have a stabilizing effect on the non-flute and non-resonant instabilities and a destabilizing effect on the B-resonant instability. The non-resonant instability has an interesting feature: a particular harmonic can be excited in two separate bands of unstable wave numbers. These instabilities can play an important role in the dynamics of the ring current and the inner edge of the plasma sheet region of the magnetosphere. The discrete turbulence generated by them would give rise to precipitation of protons on the auroral field lines, which may contribute to the excitation of diffuse aurora. These instabilities may be relevant to the observation of harmonic waves at 6R
E by Perrautet al. (1978). 相似文献
4.
G. S. Lakhina 《Astrophysics and Space Science》1985,111(2):325-334
Low frequency electromagnetic lower hybrid waves (so-called hybrid whistlers) propagating nearly transverse to the magnetic field can be driven unstable by a resonant interaction with halo electron distributions carrying solar wind heat flux. The electromagnetic lower hybrid instability is excited when the halo electron drift exceeds the parallel phase velocity of the wave. The growth rate attains a maxima at a certain value of the wavenumber. The maximum growth rate decrease by an increase in e (the ratio of electron pressure to magnetic field pressure) and halo electron temperature anisotropy. At 0.3 AU the growth time of the electromagnetic lower hybrid instability is of the order of 25 ms or shorter, whereas the most unstable wavelengths associated with the instability fall typically in a range of 27 to 90 km. The instability would give rise to a local heating of solar wind ions and electrons in the perpendicular and parallel directions relative to the magnetic field, B0. The observations of low frequency whistlers having high values ofB/E ratios (B andE being the magnitude of the wave magnetic and electric field, respectively) and propagating at large oblique angles to B0 behind interplanetary shocks, can be satisfactorily explained in terms of electromagnetic lower hybrid instability. The instability is also relevant to the generation mechanism of correlated whistler and electron plasma oscillation bursts detected on ISEE-3. 相似文献
5.
De Yu Wang Guang Li Huang C. -G. Fälthammar P. A. Lindqvist L. Blomberg Li Ting Song 《Astrophysics and Space Science》1996,240(2):175-186
Nonlinear kinetic Alfvén waves where m
e
/m
i
, have been solved both with and without the Poisson equation correction. It is found that the ratio of the perpendicular electric field and magnetic field, and the ratio of parallel and perpendicular electric field increase with deepening of the depressive density soliton. The former ratio may be larger than the Alfvén velocity in the case of a large amplitude solitary kinetic Alfvén wave. The Poisson equation correction is important for the nonlinear kinetic Alfvén wave propagating along the magnetic field, which solves a puzzle of Sagdeev potential to approach infinity in the limit ofK
x
0. This correction causes the solitary KAW possessing an electrostatic character along the direction of wave moving frame. These results have been compared with the observations from the Freja satellite in the low aurora. 相似文献
6.
A consistent account of plasma turbulence in magnetohydrodynamics equations describing transport processes across the magnetic field is presented. The structure of the perpendicular shock wave generated in the solar atmosphere, as a result of either local disturbance of the magnetic field or dense plasma cloud motion with a frozen-in magnetic field, has been investigated. The region of parameters in the solar atmosphere at which the electron-ion relative drift velocity u exceeds the electron thermal velocity V
eand generation of radio emission becomes possible, has been determined. The plasma turbulence inside the front has been shown, under conditions of solar corona, not to cause the oscillation structure of shock front to break down. Under chromospheric conditions, the shock profile is aperiodical. Then, the condition u > Vecan be satisfied and shock waves having an Alfvén Mach number M which exceeds the critical value M
c 3.3 for aperiodical shock waves can exist (Eselevich et al., 1971a). Arguments are given in favour of the fact that perpendicular shock waves are generated in the Sun's atmosphere when dense plasma clouds, with a frozen-in magnetic field, are expanded. 相似文献
7.
Nonlinear resonant interactions of different kinds of fast magnetosonic (FMS) waves trapped in the inhomogeneity of a low- plasma density, stretched along a magnetic field (as, for example, in coronal loops) are investigated. A set of equations describing the amplitudes of interactive modes is derived for an arbitrary density profile. The quantitative characteristics of such interactions are found. The decay instability of the wave with highest frequency is possible in the system. If amplitudes of interactive modes have close values, the long-period temporal and spatial oscillations are in the system.For a quantitative illustration, the parabolic approximation of the transverse density profile has been chosen. Dispersion relations of FMS waves trapped in a low- plasma slab with a parabolic transverse density profile are found. The transverse structure of the waves in this case can be expressed through Hermitian polynomials. The interaction of kink and sausage waves is investigated. The sausage wave, with a sufficiently large amplitude, may be unstable with respect to the decay into two kink waves, in particular. The spatial scale of a standing wave structure and the time spectrum of radiation are formed due to the nonlinear interactions of loop modes which contain information about the parameters of the plasma slab. 相似文献
8.
For a cylindrical wave guide, filled with hot collisional and moving plasma, the expression for damping coefficientK
i (imaginary part of the wave vector) has been derived and discussed in case of TM modes. It is observed that due to the effects of ion collisions,K
i remains less than zero for all values of (=/c) and waves suffer strong reflections for 0.5. The damping is however not affected for moderate changes in collision frequencies, while for low values of electron collision frequency and plasma density, the damping coefficient varies in a parabolic fashion with sharp reflections at 0.3. 相似文献
9.
Sergei S. Sazhin 《Astrophysics and Space Science》1993,203(2):317-327
It is pointed out that at frequencies near the plasma cut-off frequencies, the corrections to wave refractive indices in a cold plasmaN
0due to the contribution of ions and relativistic effects can be of the same order of magnitude or greater thanN
0. Expressions for wave refractive indicesN taking into account these corrections are derived in a limiting case |N| I. It is shown that the increase in cut-off frequencies due to effects of ions is negligibly small unless the electron plasma frequency is well below the electron gyrofrequency. The decrease of the cut-off frequencies due to relativistic effects is significant ( 1%) only in a rather hot plasma (T
e 1 keV), which may be observed in a plasma sheet region of the Earth's magnetosphere and in astrophysical conditions. These effects appear to be particularly important in a strongly anisotropic plasma (the electron perpendicular temperature is noticeably greater than the parallel one). 相似文献
10.
G. D. Chagelishvili J. G. Lominadze Z. A. Sokhadze 《Astrophysics and Space Science》1988,141(2):361-374
The specificity of the Parker instability in the disks in the presence of the polytropic connection between the equilibrium pressure and density
is investigated.It is shown that, in contrary to the caseV
A=const., the even and odd (with reference to the disk perpendicular coordinate) modes consist of non-finite sum of the harmonics, and that the zero (fundamental) harmonic of the even mode, which has the definite wave numberK=K
*
will mainly increase. Consequently, this very harmonic will determine the structure, obtained as a result of the Parker instability development. 相似文献
11.
Parameteric instabilities in the relativistic plasma are considered. It is shown that in the electron relativistic plasma (T
em
0e
c
2) the electron mass oscillation in the external electrical field leads to the instability of Langmuir and low frequency aperiodic oscillations as well. In the case of the hot electron ion plasma with relativistic electron temperature the low frequency aperiodic and periodic oscillations are studied. The wave increments for all considered cases are obtained. 相似文献
12.
Satellite observations of the heliospheric current sheet indicate that the plasma flow velocity is low at the center of the current sheet and high on the two sides of current sheet. In this paper, we investigate the growth rates and eigenmodes of the sausage, kind, and tearing instabilities in the heliospheric current sheet with the observed sheared flow. These instabilities may lead to the formation of the plasmoids and kink waves in the solar wind. The results show that both the sausage and kink modes can be excited in the heliospheric current sheet with a growth time 0.05–5 day. Therefore, these modes can grow during the transit of the solar wind from the Sun to the Earth. The sausage mode grows faster than the kink mode for
< 1.5, while the streaming kink instability has a higher growth rate for
> 1.5. Here
is the ratio between the plasma and magnetic pressures away from the current layer. If a finite resistivity is considered, the streaming sausage mode evolves into the streaming tearing mode with the formation of magnetic islands. We suggest that some of the magnetic clouds and plasmoids observed in the solar wind may be associated with the streaming sausage instability. Furthermore, it is found that a large-scale kink wave may develop in the region with a radial distance greater than 0.5–1.5 AU.Also at Department of Earth and Space Science, University of Science and Technology of China, Hefei Anhui 230029, China. 相似文献
13.
V. I. Karpman Ju. K. Alekhin N. D. Borisov N. A. Rjabova 《Astrophysics and Space Science》1973,22(2):267-278
Electrostatic waves with >
c
in a plasma with temperature anisotropy and loss-cone are considered. An analytical asymptotic analysis is made for waves propagating nearly perpendicular to the magnetic field and having wave-length small compared with the Larmor radius. Numerical computations are done for carried out waves with arbitrary direction of propagation. The frequency range of instability, growth damping rates, and dispersion curves have been found. The results can be used for the interpretation of magnetospheric experiments. 相似文献
14.
The thermosolutal instability of a plasma in porous medium in the presence of a vertical magnetic field is considered to include the effects of compressibility and Hall currents. The effects of stable solute gradient and compressibility are found to be stabilizing and the Hall currents have a destabilizing effect. The system is stable for (C
p/g)<1;C
p, , andg denoting specific heat at constant pressure, uniform temperature gradient, and acceleration due to gravity, respectively. In contrast to the non-oscillatory modes in the absence of magnetic field and stable solute gradient, the presence of magnetic field (and, hence, Hall currents) and stable solute gradient introduce oscillatory modes for (C
p/g)>1. The case of overstability is also studied wherein the necessary conditions for the existence of overstability are obtained. 相似文献
15.
The stability of magnetic flux tubes embedded vertically in a convection zone is investigated. For thin tubes, the dominant instability is of the convective type, i.e. it is driven by buoyancy forces associated with displacements along the tube. The stability is determined by = 8P/B
2; if
c
the tube is convectively stable, otherwise it is unstable, where the critical value
c
depends on the stratification of the convection zone. For a solar convection zone model,
c
= 1.83, corresponding to a magnetic field strength of 1350 G at the surface of the Sun. It is concluded that the flux tubes making up the small scale field of the Sun are probably hydrodynamically stable.In tubes with >
c, the instability is expected to transform the tube either into a state of vanishing surface field strength (in the case of an upward flow), or one with a field strength higher than the original value (if the instability sets in as a downward flow). Following Parker, we suggest that this effect is related to the concentrated nature of the observed solar fields.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
16.
The modulational instability of the weakly nonlinear longitudinal Langmuir as well as the transverse electromagnetic waves, propagation in the relativistic plasma without the static fields is described. The nonlinear Schrödinger equation taking account of the nonlinear Landau damping for these waves has been derived by means of the relativistic Vlasov and Maxwell equations. The plasma with the weakly relativistic temperature and that with an ultrarelativistic one has been investigated. In the first case, for the electron-proton plasma with the temperature more than 2.3 KeV we found the regional change of the wave numbers for which the soliton of two types, subsonic and supersonic, can exist. The soliton of the transverse waves can exist when the group velocity of the waves is between the thermal velocity of the electron and ion and the length of the linear waves is less than 2c/
pi
.In the second case the regions of the wave numbers, with the solitons of the Langmuir and transverse waves have been determined.The nonlinear waves in the electron-positron plasma and the waves with the phase velocity, which is about the light one, are also considered in the following paper. 相似文献
17.
Energy accumulation in a current sheet (CS) can occur during the injection of a fast plasma jet in a perpendicular magnetic field. A similar situation can occur in the solar corona when a flux of plasma appears under a magnetic arch. The flare can be produced at the CS disruption. The CS creation during plasma jet interaction with the magnetic field is demonstrated by numerical MHD simulation. The choice of dimensionless parameters Re, Rem,, II, which are suitable for simulation of coronal phenomena, is discussed. When jet injection ceases, the CS evolution produces an unstable state and fast magnetic energy dissipation is observed. 相似文献
18.
P. C. Ram 《Astrophysics and Space Science》1991,175(1):119-123
An analysis of Hall and ion-slip current effects on the MHD free-convection flow of a partiallyionised gas past an infinite vertical porous plate in a rotating frame of reference is carried out. A strong magnetic field is applied perpendicular to the plate and the plate temperature oscillates in time about a constant non-zero mean. The problem has been solved for the velocity and temperature fields and the effects of
e
(the Hall parameter),
i
(the ion-slip parameter),E
r
(rotation parameter), and have been discussed and shown graphically. 相似文献
19.
We consider the problem of ion-acoustic wave generation, and resultant anomalous Joule heating, by a return current driven unstable by a small-area thick-target electron beam in solar flares. With a prescribed beam current evolution, j
b
(t) (and, therefore, a prescribed return current j
p
(t) = –j
b
(t)), and using an approximate local treatment with a two component Maxwellian plasma, and neglecting energy losses, we demonstrate the existence of two quite distinct types of ion-acoustic unstable heating regimes. First, marginally stable heating occurs when the onset of instability occurs at electron-ion temperature ratios T
e
/T
i
> 4.8. Secondly, there exists a catastrophic heating regime for which marginally stable evolution is impossible, when the onset of instability occurs at T
e
/T
i
< 4.8.For the marginally stable case, we solve the electron and ion heating equations numerically and find that rapid anomalous Ohmic heating occurs in a substantial plasma volume. This large hot plasma emits thermal bremsstrahlung hard X-rays ( 20 keV) comparable to, or exceeding, the nonthermal bremsstrahlung which would have been emitted by the beam in a conventional thick target, large area, collisional scenario without anomalous effects. This means that, contrary to the usual assumption, onset of return current instability need not turn off hard X-ray production by a beam, though changing its source from direct to indirect. Indeed with small beam areas, this indirect mechanism can result in a higher hard X-ray bremsstrahlung efficiency than in a conventional collisional thick target.The catastrophic heating regime, for which we expect much larger wave levels, is discussed qualitatively, and preliminary results cited of an alternative approach, incorporating an equation directly describing the electrostatic wave energy level. Which of these two regimes will pertain in any particular case depends (discontinuously) on the beam and atmospheric parameters and we suggest that this effect may manifest itself in the distinctive temporal behaviour of X-ray flares. 相似文献
20.
Joseph V. Hollweg 《Solar physics》1979,62(2):227-240
We consider a horizontally stratified isothermal model of the solar atmosphere, with vertical and uniform B
0, and v
A
2
v
s
2
. The equations of motion are linearized about a background which is in hydrostatic equilibrium. A homogeneous wave equation results for the motions perpendicular to B
0; this wave equation is similar to the equation for the MHD fast mode. On the other hand, the equation for the parallel motions is inhomogeneous, containing driving terms which arise from the presence of the fast mode; the homogeneous form of this equation is identical to the equation describing vertically-propagating gravity-modified acoustic waves. We demonstrate that a resonance can exist between the (driving) fast wave and the (driven) gravity-modified acoustic wave, in such a way that very large parallel velocities can be driven by small perpendicular velocities. Applications of this resonance to solar spicules, jets, and other phenomena are discussed.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献