摘要:

The stability of the Kippenhan‐Schluter model prominence to ideal MHD perturbations is analyzed. It is shown that all modes withg· ▽v1= 0, wheregis the gravitational field andv1the perturbed velocity, are stable. The analysis is done by self‐consistently taking into account the spatial variation of equilibrium quantities (density, magnetic field) and looking for bounded eigenmodes. Some consequences (of the derived stability of perturbations) are drawn with regards to observed prominence phe

ISSN:0148-0227    

DOI:10.1029/JA087iA10p08057

年代:1982

数据来源: WILEY

摘要:

We demonstrate that (tangential) discontinuities in the magnetic field direction can support MHD surface waves. The surface waves resemble the usual Alfvén wave, but there are some important differences: (1) The surface waves exhibit a low‐frequency cutoff. (2) The velocity and magnetic field fluctuations are elliptically, and sometimes circularly, polarized. They may account for the solar wind helicity spectrum. (3) The surface waves are compressive, but there are special cases where they are noncompressive. (4) The wave vectork, the local normals to the surfaces of constant phase, and the magnetic minimum variance direction (mvd) do not all coincide. (5) There is a tendency for the mvd to align itself with the mean magnetic field direction. (6) The waves can be intrinsically nonplanar. (7) Equipartition between magnetic and kinetic energies is not obeyed locally. These properties of the surface waves lead us to believe that surface waves may be common in the solar wi

ISSN:0148-0227    

DOI:10.1029/JA087iA10p08065

年代:1982

数据来源: WILEY

摘要:

Electron plasma waves with amplitudes as high as 10 mV/m have been measured in the electron foreshock region of the earth's bow shock. It is shown that a population of stable suprathermal electrons of the type observed can produce the measured level of enhanced fluctuations without becoming unstable. The steady state wave level is given by the balancing between emission and absorption. The apparent association of fluctuation enhancements with sharp changes in electron fluxes can be understood in terms of modification of the electron distribution due to acceleration processes. The expected 2ωperadiation from the model is consistent with the observations

ISSN:0148-0227    

DOI:10.1029/JA087iA10p08077

年代:1982

数据来源: WILEY

摘要:

This paper summarizes the evidence from the Pioneer 10 plasma analyzer that plasma derived from Europa was present in the Jovian magnetosphere in December 1973. Plasma detected between 1900 UT and 2100 UT on December 3, 1973, shows a number of significant phenomena near the expected position of Europa'sLshell. Mass addition to the magnetospheric plasma is suggested by a local increase in density apparently superimposed on the density gradient of Iogenic plasma. This increase in plasma density is unlike any phenomenon observed when the spacecraft is not close to a lunarLshell. The density shows fluctuations which allow an estimate of the net outflow speed of magnetospheric ions per Jovian rotation. We estimate a radial flow speed in 1973 of 0.37 km/s from the Pioneer data and we estimate 1 km/s in 1979 from Voyager 2 data, thus indicating a significant change. The mass addition from Europa is consistent with the expected derivation of oxygen ions (or OH+or H2O+) from the icy surface of Europa by sputtering or other processes or with the derivation of recycled sulphur ions from Europa. Evidence from other peaks in the plasma spectra also argues for the identification of the most prominent peak in these spectra as havingM/Qin the range of 16–18. The estimate of the bulk plasma speed obtained by combining this identification with the absolute energies of the peaks and the spacecraft trajectory information indicates that at this time the corotation speed is substantially higher than the expected corotation speed for a large number of spectra. If the most prominent peak in the spectra were associated withM/Qvalues of 32, then the corotation speed would be consistent with rigid corotation. These results contrast with the Voyager 1979 observations and are more evidence for a large change in magnetospheric conditions between the 1973 and 1979 observations. We can account partially for the increased corotation speed of the plasma during the Pioneer 10 encounter by use of momentum conservation and compression of the magnetosphere by the solar win

ISSN:0148-0227    

DOI:10.1029/JA087iA10p08081

年代:1982

数据来源: WILEY

摘要:

We interpret the plasma density enhancements observed during the Voyager 1 Titan encounter in terms of a single plume of plasma wrapped around Saturn by corotation. We consider the radial motions of the plume driven by fluctuations in solar wind pressure and the dispersal of the plasma by the centrifugal interchange instability, by heating and by azimuthal acceleration. We show that Saturn cannot readily impose corotation directly on the plume and incidentally, that the total dissipation associated with the Titan‐magnetosphere interaction is insufficient to supply the power to produce the observed Titan ultraviolet airglow. A pickup velocity of 8 km/s is inferred from the observed velocity and a standing wave model. We note that the Voyager plasma observations are consistent with the predictions of the mode

ISSN:0148-0227    

DOI:10.1029/JA087iA10p08091

年代:1982

数据来源: WILEY

摘要:

The pronounced depletion of energetic ions observed by Voyager outside the orbit of Io can be understood as a steady state balance between particle loss and inward diffusion. For ions above 1 MeV/nuc (nucleon) G sweeping loss by Io itself is unimportant; rather the removal mechanisms involve processes associated with the extensive torus of neutral and ionized gas emanating from the satellite. There is compelling evidence to suggest that losses throughout an extended region in the outer torus, exterior to the orbit of Io, occur at a rate comparable to the upper limit imposed by strong pitch angle diffusion; although the plasma waves responsible for such scattering have yet to be detected. This is by far the dominant process for removing energy from the inner Jovian magnetosphere, and it also provides a viable energy source for exciting intense Jovian auroral emissions. Charge exchange removal of equatorially trapped lower‐energy (≲10 MeV/nuc G) heavy ions (e.g., O+or S+) can become significant over a limited region near and just inside the orbit of Io, but this process appears to have little overall effect on the energetics of the Jovian system. The trapped particle distribution function in fact exhibits little evidence for effective loss inside the orbit of Io, presumably due to the absence of intense plasma waves. An equilibrium solution for the ion phase space density requires a pronounced increase in the rate of radial diffusion between the orbit of Io and the outer torus (L>7). This suggests a change in the dominant mechanism for cross‐Ltransport consistent with the anticipated onset of rapid centrifugally driven interchange diffusion withDLL≈ 5×10−6(L/8)4RJ²/s in the outer torus. In contrast, the diffusion rate near Io is substantially slower,DLL(L≃ 6) ≈ 2×10−7RJ²/s. This is comparable to the value deduced earlier from Pioneer 11 data by Thomsen et al., who suggested neutral winds in the Jovian ionosphere as

ISSN:0148-0227    

DOI:10.1029/JA087iA10p08105

年代:1982

数据来源: WILEY

摘要:

When radial flow is generated in the rapidly rotating magnetosphere of Jupiter, angular velocity of the magnetospheric plasma departs from the corotational value on account of the conservation of the angular momentum. This causes twisting of magnetic field lines in the magnetosphere and Joule heating in the ionosphere. We have estimated the energy storage and dissipation rates by using a model in which finite transit time of the signals between the equatorial plasma disc and the ionosphere as well as the reflection of the signal at the ionosphere are taken into account. In the case of the inward flow produced by the magnetospheric compression the energy stored in the magnetic field and dissipated in the ionosphere while the compression is in progress both amount to 1017∼18

ISSN:0148-0227    

DOI:10.1029/JA087iA10p08111

年代:1982

数据来源: WILEY

摘要:

The effects of the solar wind compression of the dayside Venus ionosphere are simulated numerically. The initial ionosphere is assumed to be in pressure equilibrium with the (shocked) solar wind at the upper boundary of the ionosphere. Composition, densities, and temperatures of ions and electrons in the ionosphere are chosen in accordance with Pioneer Venus data. A spherically symmetric Lagrangian hydrodynamic code using a two‐fluid model of the ionosphere consisting of O+and electrons is employed to simulate the effects on the ionosphere of rapid changes in solar wind pressure. Sudden increases in solar wind pressure are found to generate shock waves in the ions that propagate from the ionopause downward into the ionosphere with velocities as high as 5 km/s. The effect of shock waves on ionospheric density profiles is dramatic with distinct ‘ledges’ developing in the ionosphere at the shock front. Comparison of density profiles from our simulation with select Pioneer Venus ion mass spectrometer data suggest possible agreement between shock produced ionospheric ledges resulting from rapid solar wind compression and observed ionospheric l

ISSN:0148-0227    

DOI:10.1029/JA087iA10p08118

年代:1982

数据来源: WILEY

摘要:

The variations of the plasma parameters and of the magnetic field in the vicinity of the stream line passing the subsolar point at the magnetopause are calculated by using a special flow pattern of the plasma which is the result of the formation of a stagnation line at the nose part of the magnetopause. The calculations indicate a rotation of the direction of the magnetic field across the magnetosheath. The displacement of the magnetopause due to the penetration of the solar wind magnetic field into the magnetosphere is discussed.

ISSN:0148-0227    

DOI:10.1029/JA087iA10p08131

年代:1982

数据来源: WILEY

摘要:

ISEE 1 and 2 magnetic field data obtained during dayside magnetopause crossings have been analyzed using a minimum variance technique in order to determine the characteristics of the rotation of the magnetic field across the magnetopause. Only a small fraction of the magnetopause crossings examined present a sufficiently coherent structure that they can be compared with theoretical predictions, and only a few of the hodograms of the magnetic field at the crossings show the ideal rotation expected for a rotational discontinuity structure. Observed senses of rotation are not consistent with the predictions of the electron whistler polarization theory. Rotations greater than 180° are very seldom observed; they usually occur across multiple crossings, either as 360° rotation about the minimum variance direction or, occasionally, in more complicated patterns associated with ‘S’‐shaped hodograms. These observations suggest that the sense of the magnetic field rotation through the magnetopause is controlled by the relative orientation of the magnetosheath and magnetospheric field and that the angular rotation is minimized when the magnetic field changes from one orientation to th

ISSN:0148-0227    

DOI:10.1029/JA087iA10p08139

年代:1982

数据来源: WILEY