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1.
A system of equations has been derived for the modes of free oscillation of the magnetosphere when it is regarded as an adiabatic magnetic dipole trap filled with cold inhomogeneous plasma. The limiting case of infinite longitudinal conductivity corresponding to the assumption that the electric field is orthogonal to the geomagnetic field has been studied. The boundary at the ionosphere is supposed to be perfectly conducting.The eigenmode spectrum has been found to have discrete and continuous components. The eigenmodes of the discrete component correspond to quasi-magnetosonic modes and the eigenmodes of the continuous component to quasi-Alfvén modes.Assuming the magnetosphere to be axisymmetric, a general expression in the form of a Frobenius series has been derived for quasi-Alfvén oscillations of magnetic shells near resonant magnetic surfaces. 相似文献
2.
A consistent theory of excitation, stabilization, and propagation of electromagnetic oscillations in a relativistic one-dimensional electron-positron plasma flowing along curved magnetic field lines is presented. It is shown that in such a medium which is typical of the magnetosphere of a neutron star there exist unstable natural modes of oscillations. Nonlinear saturation of the instability leads to an effective energy conversion into transverse oscillations capable of leaving the magnetosphere of a pulsar. The polarization spectrum and the directivity pattern of generated radiation are determined. A comparison with observations has shown that the theory makes it possible to explain practically all the basic characteristics of observed pulsar radio emission. 相似文献
3.
Isointensity contours of 630 nm auroral emission are traced into the magnetosphere, using two different empirical magnetic field models, the Mead-Fairfield model, and the Hedgecock-Thomas model. The auroral data are for a specific ISIS-II satellite pass, and so the starting points are expressed in geographic latitude and longitude coordinates, at a specific universal time. The magnetic field models are constructed from satellite magnetometer measurements, and those used correspond to magnetically quiet times. The projections are found to agree reasonably well with direct plasma measurements of the plasma sheet. The projections of the dayside contour connect to widely different regions of the magnetosphere, providing an interpretation that is consistent with observations of the dayside aurora. It is concluded that field line projections of the aurora into the magnetosphere using these models is a valid procedure, but only under quiet-time conditions. 相似文献
4.
K.D. Cole 《Planetary and Space Science》1974,22(7):1075-1088
Some new ideas on the interaction of the solar wind with the magnetosphere are brought forward. The mechanism of reflection of charged particles at the magnetopause is examined. It is shown that in general the reflection is not specular but that a component of momentum of the particle parallel to the magnetopause changes. A critical angle is derived such that particles whose trajectories make an angle less than it with the magnetopause enter the magnetosphere freely, so transferring their forward momentum to it. Spatially or temporally non-uniform entry of charged particles into the magnetosphere causes electric fields parallel to the magnetopause which either allow the free passage of solar wind across it or vacuum reconnection to the interplanetary magnetic field depending on the direction of the latter. These electric fields can be discharged in the ionosphere and so account qualitatively for the dayside agitation of the geomagnetic field observed on the polar caps. The solar wind wind plasma which enters the magnetosphere creates (1) a dawn-dusk electric field across the tail (2) enough force to account for the geomagnetic tail and (3) enough current during disturbed times to account for the auroral electrojets. The entry of solar wind plasma across the magnetosphere and connection of the geomagnetic to interplanetary field can be assisted by wind generated electric field in the ionosphere transferred by the good conductivity along the geomagnetic field to the magnetopause. This may account for some of the observed correlations between phenomena in the lower atmosphere and a component of magnetic disturbance. 相似文献
5.
Ernazar B. Abdikamalov Bobomurat J. Ahmedov John C. Miller 《Monthly notices of the Royal Astronomical Society》2009,395(1):443-461
Just as a rotating magnetized neutron star has material pulled away from its surface to populate a magnetosphere, a similar process can occur as a result of neutron-star pulsations rather than rotation. This is of interest in connection with the overall study of neutron star oscillation modes but with a particular focus on the situation for magnetars. Following a previous Newtonian analysis of the production of a force-free magnetosphere in this way Timokhin et al., we present here a corresponding general-relativistic analysis. We give a derivation of the general relativistic Maxwell equations for small-amplitude arbitrary oscillations of a non-rotating neutron star with a generic magnetic field and show that these can be solved analytically under the assumption of low current density in the magnetosphere. We apply our formalism to toroidal oscillations of a neutron star with a dipole magnetic field and find that the low current density approximation is valid for at least half of the oscillation modes, similarly to the Newtonian case. Using an improved formula for the determination of the last closed field line, we calculate the energy losses resulting from toroidal stellar oscillations for all of the modes for which the size of the polar cap is small. We find that general relativistic effects lead to shrinking of the size of the polar cap and an increase in the energy density of the outflowing plasma. These effects act in opposite directions but the net result is that the energy loss from the neutron star is significantly smaller than suggested by the Newtonian treatment. 相似文献
6.
We use the specific scintillations of jovian decametric radio sources (modulation lanes), which are produced by plasma inhomogeneities in the vicinity of that planet, to probe the inner magnetosphere of Jupiter. The positions and frequency drift of 1762 lanes have been measured on the DAM spectra from archives. A special 3D algorithm is used for space localization of field-aligned magnetospheric inhomogeneities by the frequency drift of modulation lanes. As a result, the main regions of the lane formation are found: the Io plasma torus; the magnetic shell of the Gossamer Ring at Thebe and Amalthea orbits; and the region above the magnetic anomaly in the northern magnetosphere. It is shown that modulation lanes reveal the depleted magnetic tubes in practically unvisited, innermost regions of the jovian magnetosphere. The local and probably temporal plasma enhancement is found at the magnetic shell of Thebe satellite. Hence, the modulation lanes are a valuable instrument for remote sensing of those parts of jovian magnetosphere, which are not studied yet in situ. 相似文献
7.
J. F. McClay 《Planetary and Space Science》1970,18(12):1673-1690
Certain classes of micropulsations are customarily explained in terms of guided (toroidal) and isotropic (poloidal) hydromagnetic waves m the magnetosphere. The physical properties of these waves are not well understood and their utility in explaining observed polarization patterns is questionable. In an effort to understand and explain the physics underlying these modes, a study is made of a cylindrical cavity (the hydromagnetic wedge), filled with a plasma having a large but finite conductivity and magnetized by an azimuthal magnetic field. Coupling between the toroidal and poloidal modes is effected by the inclusion of the Hall current in the generalized Ohm's law. Physically meaningful solutions to the wave equation are obtained and the toroidal eigenfunctions are demonstrated to be non-degenerate and well-behaved throughout the configuration, and exhibit for each mode a unique spatial resonance whose location, given by a line of force, is specified by the corresponding eigenvalue. The non-degenerate, discrete and spatially independent eigenvalues for the modes are shown to obey a selection rule that limits the spectrum. For a given mode, the states of polarization of the transverse field are determined and it is shown (as has been observed) that, depending on the line of force singled out, the magnetic polarization may be linear, elliptical or circular, right or left-handed, and whatever the state, it is immutable along the line of force. More complicated polarization patterns are derived and explained by superposing different modes vectorially. Classical concepts such as guided and isotropic modes and vibrating field lines are reinterpreted and evaluated in terms of the model. To examine the dependence of modal amplitude on source, the amplitude is expressed in terms of a sinusoidal driving pressure for a simple steady-state case. Symmetries of the model and the magnetosphere are specified and the detailed numerical results are ‘scaled’ for plasmaspheric application. The resonant spectrum, encompassing pc 2–4, is described and the variation of period spectrum with magnetic latitude and activity is presented. The agreement between the semi-quantitative analysis and the observational results is sufficiently close to indicate that the basic physics of the model encompasses the fundamental dynamics of pc activity. 相似文献
8.
MHD problems of solar wind interaction with the Earth's magnetosphere on the day-side are investigated. These ideas are used for the analysis of satellite data on the day-side magnetopause crossing. It is shown that the observed regularities may be adequately explained within the bounds of MHD-flow theory which includes the stagnation line at the nose of the magnetosphere. The ratio k of the magnetic field pressure to the plasma pressure in the vicinity of the subsolar point of the magnetosphere, which determines the magnitude of the interplanetary magnetic field penetrating into the magnetosphere, was estimated. 相似文献
9.
Hu Wen-Rui 《Planetary and Space Science》1981,29(6):695-702
A mechanism of the Earth's magnetospheric substorm is proposed. It is suggested that the MHD waves may propagate across the magnetopause from the magnetosheath into the magnetotail and will be dissipated in the plasma sheet, heating the plasma and accelerating the particles. When the solar wind parameters change, the Poynting flux of the waves transferred from the magnetosheath into the tail, may be greater than 1018 erg s?1. The heated plasma and accelerated particles in the plasma sheet will be injected into the inner magnetosphere, and this may explain the process of the ring current formation and auroral substorm.The Alfvén wave can only propagate along the magnetic force line into the magnetosphere in the open magnetosphere, but the magnetosonic wave can propagate in both the open and closed magnetosphere. When the IMF turns southward, the configuration of the magnetosphere will change from a nearly closed model into some kind of open one. The energy flux of Alfvén waves is generally larger than that of the magnetosonic wave. This implies that it is easy to produce substorms when the interplanetary magnetic field (IMF) has a large southward component, but the substorm can also be produced even if the IMF is directed northward. 相似文献
10.
Under the purely centrifugal approximation (gravity and pressure force are neglected), stellar magnetospheres are classified into three main types of different physical properties in the two-dimensional parameter space. They are characterized essentially by the strength of the magnetic field and the plasma density, at the base of the magnetosphere. Among the three types, the type II magnetosphere has moderate surface densities for a given field strength, and is expected to possess a centrifugal wind blowing across the magnetic field lines without affecting them appreciably. Such a situation may be realized through a modification of the electric field from that under the ideal-MHD condition, owing to the inertia of a plasma. In order to illustrate this mechanism, the type II magnetosphere is taken up for a numerical simulation. The effect of artificial viscosity is avoided by integrating the characteristic equations for both components of the plasma, instead of solving the fluid equations directly. Our model reproduces a disk-like outflow of the centrifugal wind across the magnetic field lines which are closed through the equatorial plane. 相似文献
11.
By using an image-dipole magnetic field model for a variety of plasma density profiles we have studied the latitude effect of the 0.1–1.0-Hz hydromagnetic wave propagation in the Earth's magnetosphere. On comparing the results of signal group delay time calculations for dipole and model magnetic fields with ground and satellite observations we obtain some propagation characteristics of Pc1s and localize the regions of their generation. Our results show that most high-latitude Pc1 events are generated in the outer magnetosphere in accordance with ground and satellite observations and theoretical considerations. The non-dipole geometry of the geomagnetic field in the outer magnetosphere (at geomagnetic latitudes φ0 > 66°, L > 6) has a significant effect on the hydromagnetic wave propagation. 相似文献
12.
Nobuki Kawashima Kazunori Akai Yukio Murasato Susumu Sasaki 《Astrophysics and Space Science》1984,106(1):117-123
In an electron beam emission experiment on board the EXOS-B (JIKIKEN) satellite (200 V, 1 mA-maximum), several types of waves are strongly excited by the beam such as plasma frequency, upper hybrid frequency, electron cyclotron frequency, their harmonics and nonlinear coupling of these waves. Measurements of these waves give information on local plasma density and magnetic field strength and it is revealed that the electron beam emission from the spacecraft is a powerful diagnostic tool in the magnetosphere. A long term observation in this electron beam experiment has provided us with the average plasma density profile in the magnetosphere. It is also useful for the detection of the plasmapause. Plasma density measurements down to the order of 10 cm–3 are possible. The instrument itself is very simple and compact, so that it will be a powerful plasma diagnostic tool in future magnetospheric and planetary explorations. 相似文献
13.
Walter J. Heikkila 《Planetary and Space Science》1978,26(2):121-129
Reconnection involves singular lines called X-lines on the day and night sides of the magnetosphere, and the reconnection rate is proportional to the component of the electric field along the X-line. Although there is some indirect support for this model, nevertheless direct support is totally lacking. However, there are two distinct pieces of clearly contradictory observational evidence on the dayside. First is the failure to account for the implied energy dissipation by the magnetopause current, over 1011 W, which should be easily observable as heating or enhanced flow of the plasma near the magnetopause. In marked contrast to this prediction, HEOS-2 satellite data reveal a plasma with decreased energy density and reduced flow. Second, the boundary of closed magnetic field lines is in the wrong location. In the reconnection process the plasma outflow would cut across open field lines toward higher latitudes; there should be a band of open field lines equatorward of the cleft. Observations of trapped energetic particles indicate closed field lines within the entry layer and cleft. Either one of these pieces of evidence is sufficient by itself to require drastic revision, even rejection, of the reconnection model. There is also contradictory evidence on the night side. The last closed field line capable of trapping energetic particles is poleward of auroral arcs. The implication is that the X-line is at the distant magnetopause, and not in the plasma sheet. Consequently, even if the reconnection process were operative at the nightside X-line, it would be isolated from steady state plasma sheet and auroral processes. On the other hand, substorm phenomena, in which stored magnetic energy is converted into particle kinetic energy, necessarily involve an induced electric field; that is excluded in theories of the reconnection process in which it is assumed that curl E = 0. Nevertheless, the observed easy access of energetic solar flare particles to the polar caps, and especially the preservation of interplanetary anisotropies as differences between the two polar caps, argues strongly for an open magnetosphere, with interconnection between geomagnetic and inter-planetary magnetic field lines. It is suggested that the resolution of this apparent paradox involves electric fields parallel to the magnetic field lines somewhere on the dawn and dusk sides of the magnetosphere, with an equipotential dayside magnetopause. 相似文献
14.
15.
The behaviour of energetic electrons in the distant magnetosphere near the midnight meridian during polar substorms has been studied for the period March 5th–April 4th, 1965, using data from two end window Geiger counters flown on the IMP 2 satellite (apogee 15.8 Earth radii) and magnetic records from a chain of auroral zone stations around the world at magnetic latitudes equivalent to L = 7.4 ± 2.0.
When the satellite was in the distant radiation zone or in the plasma sheet which extends down the Earth's magnetic tail, sudden decreases in the horizontal magnetic field component at ground stations near the midnight meridian (negative magnetic bays) were followed by sudden increases in 40 keV electron fluxes (electron islands) at the satellite. When the satellite was at high latitudes in the magnetic tail ‘bays’ often were not followed by ‘islands.’ When the satellite was near the centre of the plasma sheet, energetic electron fluxes were observed even during magnetically quiet periods. The time delay between the sharp onset of magnetic bays in the auroral zone and the corresponding rapid increase in energetic electron intensity at the satellite, typically some tens of minutes, was least when the satellite was close to the Earth and increased with its increasing radial distance from the Earth. The delay was also a function of distance of the satellite from the centre of the plasma sheet, and of the magnitude of the intensity increase (smaller delays for larger intensity increases). We deduce that the disturbance producing the magnetic bays and associated particle acceleration originates fairly deep in the magnetosphere and propagates outward to higher L values, and down the plasma sheet in the Earth's magnetic tail on the dark side of the Earth. It is unlikely that the accelerated electrons are themselves drifting away from the Earth, because the apparent velocity with which the islands move away from the Earth decreases with increasing distance from the Earth.
It is suggested that the polar substorm and the associated particle acceleration are part of an impulsive ejection mechanism of magnetospheric energy into the ionosphere, rather than an impulsive injection mechanism of solar wind energy into the magnetosphere. 相似文献
16.
Pulsars are presently believed to be rotating neutron stars with large frozen-in magnetic fields normally assumed to be dipole fields. It has been shown that such a star must possess a magnetosphere if it rotates sufficiently rapidly. By assuming that the magnetic field is dipolar, and unaffected by the trapped particles in the magnetosphere, and that the field dipole axis is parallel to the rotation axis, Goldreich and Julian determined many of the properties of the magnetosphere. In this paper is given a self-consistent model of the closed field lines of a pulsar magnetosphere. Using this model, it is shown that, close to the star, the above assumptions of Goldreich and Julian are justified. Their results are extended to the oblique rotator as well as to stars with magnetic multipoles of arbitrary order and arbitrary orientation.Supported in part by the U.S. Atomic Energy Commission under Grant 2171T. 相似文献
17.
Yu. D. Zhugzhda 《Astronomy Letters》2018,44(5):331-336
The conditions under which the subphotospheric slow-wave resonator can be responsible for the local oscillations in a sunspot have been determined. A rich spectrum of local 3-min oscillations can be produced by the subphotospheric resonator only if the magnetic field in the resonator magnetic flux tube is much weaker than the surrounding sunspot magnetic field. Convective upflows of hot plasma in the sunspot magnetic field satisfy this condition. Consequently, there must be a correlation between the local oscillations and umbral dots, because the latter are produced by convective flows. Various modes of operation of the subphotospheric resonator give rise to wave packets of 3-min oscillations and umbral flashes. It is shown that giant local umbral flashes can emerge under certain conditions for the excitation of oscillations in the subphotospheric resonator. 相似文献
18.
Plasma irregularities present in the solar wind are plasmoids, i.e. plasma-magnetic field entities. These actual plasmoids differ from ideal magnetohydrodynamic (MHD) filaments. Indeed, (1) their “skin” is not infinitely thin but has a physical thickness which is determined by the gyromotion of the thermal ions and electrons, (2) they are of finite extent and their magnetic flux is interconnected with the interplanetary magnetic flux, (3) when they penetrate into the magnetosphere their magnetic field lines become rooted in the ionosphere (i.e. in a medium with finite transverse conductivity), (4) the external Lorentz force acting on their boundary surface depends on the orientation of their magnetic moment with respect to the external magnetic field, (5) when their mechanical equilibrium is disturbed, hydromagnetic oscillations can be generated. It is also suggested that the front side of all solar wind plasmoids which have penetrated into the magnetosphere is the inner edge of the magnetospheric boundary layer while the magnetopause is considered to be the surface where the magnetospheric plasma ceases to have a trapped pitch angle distribution. 相似文献
19.
20.
Elena S. Belenkaya 《Astrophysics and Space Science》2001,277(1-2):289-292
When a highly conducting magnetized plasma passes an object with lower conductivity, or a body with inhomogeneous conductivity,
2-D structures are formed, the so-called `Alfvén wings'. These structures may arise, for example, at a Jovian moon without
an intrinsic magnetic field (Callisto). In this case, Alfvén wings could be generated in the magnetized Jovian magnetospheric
plasma flow owing to the in homogeneity of the moon's ionosphere/atmosphere conductivity. Such Alfvén wings may be considered
as a satellite magnetosphere; the satellite magnetospheric magnetic field is a disturbed field of the Jovian magnetospheric
plasma flow. An analytical solution is obtained in a simple proposed model.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献