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Balloon-measured electric-field data for five-hour periods during each of 19 substorms near local midnight have been analyzed and averaged. Results are applied to an improved model of the magnetospheric substorm in which the origin of the electric fields, the flow of cold plasma and magnetic-field lines, and many observed particle phenomena are more naturally explained.
Demonstration that large-amplitude linearly or elliptically polarized Alfven waves propagating parallel to the average magnetic field can be dissipated by nonlinear Landau damping. The damping is due to the longitudinal electric field associated with the ion sound wave which is driven (in second order) by the Alfven wave. The damping rate can be large even in a cold plasma (beta much less than 1, but not zero), and the mechanism proposed may be the dominant one in many plasmas of astrophysical interest.
By means of an energy conservation approach, this paper analyzes the growth rates of whistlers with arbitrary frequency and direction of propagation in a cold plasma permeated by a dilute energetic electron population. Numerical results are obtained for whistler frequencies and plasma characteristics prevailing at the onset of artificially stimulated emissions. It is found that the growth rates do not in general maximize for propagation along the static magnetic field, and a criterion for the existence of maximal growth at this direction is derived. An application to artificially stimulated emissions is discussed.
Whistler propagation in the magnetosphere was studied in detail to find accurate and economical means of determining the path latitude and the electron concentration along the path from whistler parameters of nose frequency and travel time at the nose. Longitudinal propagation in field aligned whistler ducts of cold plasma was assumed, and the earth's magnetic field was approximated by a centered dipole. The effects of whistler propagation in the earth-ionosphere waveguide and through the conjugate ionospheres were treated as small perturbations. Several alternative methods are described so that the most economical method may be chosen depending on the desired accuracy and the availability of a computer or a calculator.
The current state of the theory of Jupiter's outer atmosphere is briefly reviewed. The similarities and dissimilarities between the terrestrial and Jovian upper atmospheres are discussed, including the interaction of the solar wind with the planetary magnetic fields. Estimates of Jovian parameters are given, including magnetosphere and auroral zone sizes, ionospheric conductivity, energy inputs, and solar wind parameters at Jupiter. The influence of the large centrifugal force on the cold plasma distribution is considered. The Jovian Van Allen belt is attributed to solar wind particles diffused in toward the planet by dynamo electric fields from ionospheric neutral winds, and the consequences of this theory are indicated.
Resonance phenomena have been observed in swept frequency experiments carried out on two mother-daughter Nike-Tomahawk rocket flights at auroral latitudes. The experimental method is briefly described and characteristic samples of the results are presented. A possible interpretation of some main resonances is offered, involving cold plasma cone resonances.
A new formulation of the one-dimensional Vlasov equation is derived which is analogous to the Kalman-transformed cold-plasma equations. The equations are shown to yield nonsecular, nonlinear approximations to a source or boundary-value problem. It is suggested that the formulation may have other applications in nonlinear plasma theory.
Explicit difference equations are presented for the solution of a signal of arbitrary waveform propagating in an ohmic dielectric, a cold plasma, a Debye model dielectric, and a Lorentz model dielectric. These difference equations are derived from the governing time-dependent integro-differential equations for the electric fields by a finite difference method. A special difference equation is derived for the grid point at the boundary of two different media. Employing this difference equation, transient signal propagation in an inhomogeneous media can be solved provided that the medium is approximated in a step-wise fashion. The solutions are generated simply by marching on in time. It is concluded that while the classical transform methods will remain useful in certain cases, with the development of the finite difference methods described, an extensive class of problems of transient signal propagating in stratified dispersive media can be effectively solved by numerical methods.
An investigation is conducted concerning the conditions encountered during a Javelin sounding rocket experiment conducted on Apr. 3, 1970 at Fort Churchill, Canada. Evidence is presented that near the equatorward edge of the auroral arc an intense beam of cold plasma ions was flowing parallel to the earth's magnetic field. The beam was associated with intense narrow band electric field oscillations near the local ion gyrofrequency. The data support the hypothesis that intense electrostatic ion cyclotron waves were driven unstable by field-aligned currents.
An idealized two-dimensional model of the distorted electric field configuration, in the limit of a perfectly conducting satellite or satellite ionosphere, has been constructed. This model has been used to trace the adiabatic guiding-center trajectories of energetic protons and electrons across Jupiter's magnetic-field lines, which are taken as rectilinear. The adiabatic trajectories of very low-energy particles (cold-plasma) are thus found to avoid the satellite and escape absorption. In the limit of very high particle energies the adiabatic trajectories are undistorted, and absorption proceeds as if Io were an insulator. The particle absorbing characteristics of an electrically conducting Jovian satellite are found to depend on both the species and the energy of the incident particle, and the satellite's particle-absorbing cross section differs systematically from its geometric cross section.
The electrostatic field associated with the rotation of Jupiter, relative to the rest frame of Io, would be distorted if the satellite were an electrical conductor. An idealized two-dimensional model of the distorted electric-field configuration, in the limit of a perfectly conducting satellite or satellite ionosphere, has been constructed and used to trace the adiabatic guiding-center trajectories of energetic protons and electrons across Jupiter's magnetic field lines, which are taken as rectilinear. The adiabatic trajectories of very low-energy particles (cold plasma) are found to avoid the satellite and escape absorption. In the limit of very high particle energies, the adiabatic trajectories are undistorted, and absorption proceeds as if Io were an insulator. The interpolation between these limits is monotonic for protons, such that Io sweeps out a drift shell half as wide as the satellite for first invariants of the order of 1 GeV per gauss. The situation for electrons is more complicated, and no absorption from adiabatic trajectories is found at first invariants not exceeding 46 GeV per gauss. Electrons having first invariants of at least 50 GeV per gauss are typically swept out of drift shells wider than the satellite itself. However, electrons can impact only a portion of Io's exposed hemisphere for first invariants of 50-200 GeV per gauss. Thus, the particle-absorbing characteristics of an electrically conducting Jovian satellite are found to depend on both the species and the energy of the incident particle, and the satellite's particle-absorbing cross section differs systematically from its geometric cross section.
The solution to the equation of transfer of polarized radiation in a steady-state homogeneous rarefied medium is applied to self-absorbed synchrotron sources. Relativistic electrons (independent of the presence of any cold plasma) can quite easily produce in such sources significant Faraday rotation and/or conversion of linear to circular polarization. Structural inhomogeneities do not obviate the importance of these phenomena in compact nonthermal sources. Contrary to the calculation of Pacholczyk and Swihart (1975), the circular polarization for a homogeneous source changes sign just below the self-absorption turnover as the source becomes opaque, even when polarization conversion dominates; however, for a physically realistic source, structural inhomogeneity may alter this behavior. The observational evidence bearing upon these effects is reviewed.
High time resolution measurements made inside the magnetopause from L = 7 to L = 14 by the flux gate magnetometer aboard the Ogo 5 satellite, which demonstrate that the Pc 1-2 magnetic field oscillations are present in the outer magnetosphere, are examined. The solar wind dynamic pressure and the magnetospheric cold plasma were enhanced, and the IMF had a southward component 2 hours before the events, but there was no significant correlation between the time of the events and either storm recovery phase or substorm onset. The magnetic field perturbations in each event were transverse to the ambient field with amplitudes from 2 to 8 gamma, and most of the transverse perturbations showed left-handed polarization. Excursions into the magnetosheath during two events revealed a disturbed magnetic field with significant power in frequencies of minimum 0.1 Hz, and although the magnetosheath was a source of free energy for waves at Pc 1-2 frequencies, the data within the magnetosphere suggest that the observed pulsations were ion cyclotron waves generated at the geomagnetic equator at large radial distances.
Possible thermal models for solar, hard X-ray emission, consisting of small volumes in which the electrons are rapidly heated to 400 million K, are examined to determine under what conditions such models can be more efficient than nonthermal models. The analysis is restricted to one dimension by supposing that the hot electrons are confined in a flux tube and that conduction and convection act only along the magnetic field. A conduction front, thin in relation to other length scales involved, separates the hot electrons from the relatively cold plasma. The range of conduction-front velocity is studied by systematizing the present knowledge of heat conduction and applying it first to a simple model in which convection is neglected, and then to a detailed numerical model in which convection is included. Convection in which mass motion goes to zero at the conduction front does not lead to a change in the conduction-front velocity compared to conduction alone, but does constitute another nonradiative energy loss which reduces the source efficiency.
Despite the malfunctioning of the digital portion of the experiment which is encoding the absolute amplitude of the wave spectrum with a fixed bias of approximately 20 dB, the analog portion of the instrument is acquiring excellent data concerning the wave function and relative amplitude. Results obtained over a 2-year period which have important implications for magnetospheric wave-particle interactions are examined in the areas of emission generation by nonconducted coherent waves, and cold plasma distribution in the inner magnetosphere.
The presence of whistler mode waves in, and upstream from, the bow shock has been well established by observation. Theoretical descriptions of the mode under solar wind conditions have been relatively meagre, however, and it may not be generally appreciated how readily whistler waves generated in the shock could occupy most of the region ahead of the shock most of the time. Graphic descriptions of phase and group velocities and group velocity directions for typical solar wind parameters are presented by using the cold plasma approximation over all appropriate frequencies and directions with respect to the IMF. The relations of whistler phase and group velocities to observations of a quasi-perpendicular shock crossing by ISEE are illustrated.
An estimate of Jupiter's planetary magnetic field is obtained from the Voyager 1 observations of the Jovian magnetosphere. An explicit model for the magnetodisc current system is combined with a spherical harmonic model of the planetary field with both sets of parameters determined simultaneously using a nonlinear generalized inverse methodology. The resulting model fits the observations extremely well throughout the analysis interval (r 20 Jovian radii). The Jovian internal field model obtained from the Voyager 1 data is very similar to the octopole Pioneer 11 models. The best fitting magnetodisc lies in the centrifugal equator, 2/3 of the way between the rotational and magnetic equators, as appropriate for centrifugal loading of the magnetosphere by a cold plasma.
The present investigation has the objective to study the precipitation of energetic electrons into the ionosphere due to the interaction of these particles with short-duration VLF waves in the magnetosphere. The physics of the interaction is considered, taking into account the wave structure, the energetic particle distribution, wave-particle interaction, and the computation of the precipitated flux versus time. The obtained formulation is applied to various different magnetospheric conditions. Attention is also given to peak flux and total deposited energy. The results of the investigation demonstrate the role of the energetic particle distribution function, the normalized wave frequency, the L value of the path of propagation, the cold plasma density, and the wave intensity. The precipitated energy flux that would be observed at 1000-km altitude is presented as a function of time relative to the injection of the wave pulse at the same point.