首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 46 毫秒
1.
Relativistic effects on parallel whistler-mode propagation and instability are considered analytically in some limiting cases relevant to magnetospheric and/or astrophysical conditions. The corresponding wave dispersion equation for a weakly relativistic anisotropic plasma is expressed in terms of generalized Shkarofsky functions. Asymptotic presentation of these functions is found in the limit of large wave refractive indices. Based on this presentation, a new analytical expression for whistler-mode refractive index is obtained and analysed. It is pointed out that relativistic effects increase the value of anisotropy above which the waves are unstable, in agreement with the results of the earlier numerical analysis. This increase is particularly important for whistler-mode propagation in a rarefied, hot plasma but could be potentially observed in the magnetosphere of the Earth in the region outside the plasmasphere.  相似文献   

2.
The nonlinear frequency shift arising from the interaction of the quasimono- chromatic whistler-mode wave with resonant particles in an inhomogeneous plasma is derived. The modulational instability caused by this shift is investigated. The results are applied to the propagation of long-duration VLF whistler-mode signals along the magnetic field in the magnetosphere. It is shown that the modulational instability of these waves in the equatorial region leads to pulsations very similar to those observed experimentally  相似文献   

3.
In the equatorial plasmasphere, plasma waves are frequently observed. To improve our understanding of the mechanism generating plasma waves from instabilities, a comparison of observations, linear growth-rate calculations, and simulation results is presented. To start the numerical experiments from realistic initial plasma conditions, we use the initial parameters inferred from observational data obtained around the plasma-wave generation region by the Akebono satellite. The linear growth rates of waves of different modes are calculated under resonance conditions, and compared with simulation results and observations. By employing numerical experiments by a particle code, we first show that upper hybrid-, Z-, and whistler-mode waves are excited through instabilities driven by a ring-type velocity distribution. The simulation results suggest a possibility that energetic electrons with energies of some tens of keV confined around the geomagnetic equator are responsible for the observed enhancements of Z- and whistler-mode waves. While the comparison between linear growth-rate calculations and observations shows the different tendency of wave amplitude of Z-mode and whistler-mode waves, the wave amplitude of these wave modes in the simulation results is consistent with the observation.  相似文献   

4.
An approximate formula is derived for the refractive index of a whistler-mode wave propagating in a hot anisotropic plasma with wave normal angle close to the resonance cone angle (θR). Approximations used during the derivation are generally satisfied for magnetospheric conditions. It is pointed out that the derived formula can be considered to be complementary to the corresponding formula for quasilongitudinal whistler-mode propagation in a hot anisotropic plasma which was derived by Sazhin and Sazhina (1982). The limits of applicability of a cold plasma model when determining the height of generation of saucer emissions and V-shaped hiss are discussed.  相似文献   

5.
The process of quasi-electrostatic whistler-mode propagation is interpreted in terms of the periodic energy exchange between wave field and perturbed electron currents.  相似文献   

6.
PIERRE  F.  SOLOMON  J.  CORNILLEAU-WEHRLIN  N.  CANU  P.  SCIME  E. E.  BALOGH  A.  FORSYTH  R. J. 《Solar physics》1997,172(1-2):327-334
We present a study of whistler-mode wave generation and wave particle interaction in the vicinity of interplanetary shocks as observed by the Ulysses spacecraft. Generally the whistler-mode waves (measured in the frequency range 0.22–448 Hz) are observed downstream of the shocks where they persist for some hours. From the electron distribution functions (EDF) in the energy range 1.6 to 862 eV measured by the spacecraft, we compute the wave growth rate of the electromagnetic electron cyclotron and Landau instabilities for the case of oblique propagation of the waves with respect to the interplanetary magnetic field (IMF) B. In general, in agreement with the wave measurements, the instability grows mostly downstream of the shock fronts. Following the wave activity, velocity space diffusion of the electrons results in a marginally stable state with some sporadic fluctuations.  相似文献   

7.
  相似文献   

8.
A new approximation of the real part of the nonrelativistic plasma dispersion function ?Z of a real argument ξ0 is proposed: namely, $$\Re Z_A (\xi _0 ) = \frac{{2\xi _0 }}{{1 - 2\xi _0^2 }}.$$ This approximation gives the exact value for ?Z when d2?Z/dξ 0 2 = 0 and gives the correct expressions for the first two terms of its expansion for large ξ0. On the basis of this approximation, a new approximate expression for whistler-mode refractive index is derived for the case of wave propagation parallel to the magnetic field in a hot anisotropic and dense plasma. Under certain conditions this expression is more convenient for practical applications in magnetospheric and/or astrophysical conditions than other approximate expressions. The approximation ?Z A was also used in deriving the approximate expression for whistler-mode instability or damping (γ), although in this case it seems to have little merit when compared with the previously used expressions for γ.  相似文献   

9.
An approximate analytical expression for wave normal angle g0, at which whistler-mode group velocity is directed along magnetic field line in a hot anisotropic plasma, is derived. This expression is simple enough for practical applications in the magnetospheric conditions and is compatible with the results of numerical analysis for wave frequencies below but not close to the half of electron gyrofrequency.  相似文献   

10.
A numerical application to the extreme cases of high and low degree of ionization of the binary collision theory of Burgers (1960) and the multiple collision theory of Shkarofsky (1960) shows very good agreement in the values of the magnetic tensor components for solar electrical conductivity. It is pointed out that the inclusion of ion motions in Burgers theory favors its use in the future evaluation of the solar thermal conductivity tensor.The research reported in this paper was sponsored by the Air Force Cambridge Research Laboratories, AFSC, under Contract F19628-70-C-0192-P00001, but the report does not necessarily reflect endorsement by the sponsor.  相似文献   

11.
An analytical solution of the general plasma wave dispersion equation is obtained for the parameters close to those for which the numerical or analytical solution of this equation is known. This solution is further applied to parallel whistler-mode waves in an anisotropic plasma observed in the Earth's magnetosphere.Now at the Dept. of Physics, University of Sheffield, England.  相似文献   

12.
The range of applicability of an improved quasilongitudinal approximation for whistler-mode waves in the equatorial magnetosphere (4 L 6.6) is specified based on the direct comparison between numerical solutions of the hot electromagnetic dispersion equation with the corresponding analytical quasilongitudinal solutions. It is pointed out that this approximation can be used at frequencies ω less than but not close to the electron gyrofrequency Ω (ω 0.6 Ω) and wave normal angles θ less than but not close to the resonance cone angle θR. At ω = 0.8 Ω the analytical results deviate considerably from numerical ones due to the strong damping of the waves, and so the quasilongitudinal solution becomes no longer valid.  相似文献   

13.
An approximate expression is derived for the maximum deviation of the direction of the quasi-electrostatic whistler-mode group velocity from the external magnetic field. This derivation takes into account finite electron density, temperature, and ion effects. It is pointed out that ions cannot be neglected at low frequencies . For close to half the electron gyrofrequency the contribution of these effects is about 10% for parameters typical for the inner magnetosphere and should be taken into account in an accurate analysis of whistler mode propagation.  相似文献   

14.
The resonant interaction of electrons with a coherent whistler-mode wave in the magnetosphere, and corresponding particle precipitation through the loss-cone, are considered. We show that, due to the inhomogeneity of the magnetic field, the phase untrapped resonant electrons play a basic role in the precipitation process. An effective change of their pitch-angles near the loss-cone is calculated and particle fluxes are estimated for quiet magnetospheric conditions (weak diffusion without the wave). It appears that observation of the precipitation caused by a single whistler-mode wave is within the scope of experimental possibilities. The duration of the precipitation process is of the order of the electron bounce period. It is also shown that precipitating current may produce an observable magnetospheric disturbance with a time characteristic of the order of the bounce period.  相似文献   

15.
A theory of VLF noise excitation by electron beams in the polar magnetosphere is proposed. Two modes of excited oscillations are considered: waves with frequencies in the vicinity of the lower hybrid resonance (LHR) from about 50 to 1000 kHz and whistler-mode waves in the frequency range of several kHz.The spectral distribution and the level of turbulent noise, having been excited by means of two counterstreaming electron beams, are deduced in magnetized plasma at the LHR frequency. It is also shown that the growth of noise up to the quasistationary level oscillates with time. Energy density of oscillations at the LHR frequency in the region of the dayside polar cusp agrees with the experimental data.The processes of whistler excitation by electron beams are discussed. The growth rate of excitation of whistler-mode by electrostatic oscillations at the LHR frequency is calculated.  相似文献   

16.
The one-dimensional, steady-state equation of transport for cosmic rays including convection, diffusion and adiabatic deceleration is separated for a spatial diffusion coefficient with an arbitrary momentum dependence and for an arbitrary spatial dependence of the convection velocityV, and applies for planar, cylindrical and spherical geometries. As an application, the previously obtained spherically symmetric steady-state Green's functions, describing the propagation of cosmic rays in interplanetary space, are generalized to the case where the convection velocity is a function of position.  相似文献   

17.
We present a numerical analysis of free-space propagation of the beams inside a long-baseline optical/infrared interferometer. Unlike the models of beam propagation used in most previous studies, our analysis incorporates the effects of atmospheric seeing on the wavefronts entering the interferometer. We derive results for the changes in throughput, coherence loss and fringe-detection signal-to-noise ratio arising from diffraction along the propagation path. Our results for conditions of moderate seeing show that although the flux throughput decreases with propagation distance for a given beam diameter, the fringe contrast increases at the same time. In this case it becomes possible for diffraction to increase the signal-to-noise ratio of the fringe measurements. Previous studies have only considered an arrangement where all the apertures in the beam-propagation system have the same diameter. If the light at the end of the propagation path is collected with a fixed size aperture, we find that in many cases the signal-to-noise ratio for fringe detection is maximized when the initial beam diameter is approximately 30 per cent smaller than the final collector diameter. We discuss the implications of our results in the context of future interferometer designs.  相似文献   

18.
In this paper, general sufficiently analytical formulae are developed for the arbitrary order generalized relativistic Fermi-Dirac (FD) functions. Analytical assessment of relativistic FD function is very important for various fields of physics especially in the theory of relativistic nondegenerate and degenerate electron gas systems. One of the more appropriate and correct approximations is based on a binomial expansion method and incomplete Gamma functions that have been used in the calculations of the generalized relativistic FD functions. Note that, the established expression in special cases of specific values of parameters becomes the evaluation formulae of other type FD functions. Calculation results of the generalized relativistic FD functions are compared with the other approximations methods and available numerical approaches and demonstrated satisfactory agreement.  相似文献   

19.
Westward electric fields of 0–0.4 mV/m well inside the plasmasphere (L ~ 2.3) are found from the measured doppler shifts and group delay times of whistler-mode signals during quiet times.  相似文献   

20.
Nonlinear ion acoustic solitary wave structures in electron-positron-ion (e-p-i) magnetized rotating plasmas is studied. The electron and positron species are assumed to be nonthermal and follow the kappa distribution function. The Korteweg de Vries (kdV) equation is derived by employing the reductive perturbation technique for solitary wave in the nonlinear regime. The variation in the amplitude and width of the solitary wave are discussed with the effects of positron concentration, temperature ratio of kappa distributed electrons to positrons, spectral index of the positrons, direction of propagation of the wave with magnetic field and effective gyrofrequency of the rotating nonthermal plasmas. The numerical results are also presented for illustration.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号