摘要:

Results of determining the shape and location of the heliospheric current sheet from a potential field model and from K‐coronameter observations are compared. Interplanetary magnetic field polarities as observed by IMP 8, Helios 1 and 2, and Voyager 2 spacecraft were used to test the two methods over the period May 1976 to August 1977 throughout 18 Carrington rotations. The computed heliospheric current sheets from both methods had a quasi‐stationary four‐sector structure and very similar shapes. Agreement between interplanetary magnetic field polarity and the results from the potential field model was found on 79% of the days, while agreement between the interplanetary field polarity and the polarities derived from the K‐coronameter data was found on 87% of t

ISSN:0148-0227    

DOI:10.1029/JA089iA07p05381

年代:1984

数据来源: WILEY

摘要:

We first discuss theoretically the relative importance and the behavior of the two basic terms adding to the total angular momentum flux, the angular momentum of the particles (electrons, protons and alpha particles) and of the magnetic field stresses, respectively. Second, we analyze these two quantities with respect to their dependence on heliocentric distance by using the Helios 1 and 2 plasma and interplanetary magnetic field observations between 0.3 and 1 AU classified according to low‐speed (600 km s−1) solar wind for the 1975–1976 epoch. Applying now these results as well as various combinations of the constants of motion for the solar wind (such as the total angular momentum flux, the mass flux, and the magnetic flux) and their observational constraints, as deduced earlier by Marsch and Richter (1984), we finally present various methods (1) to derive the values of several characteristic solar wind plasma and magnetic field parameters at the Alfvén critical points, (2) to estimate their locations above the solar surface, and (3) to obtain the radial slope of the associated solar wind velocity profiles for the three solar wind clas

ISSN:0148-0227    

DOI:10.1029/JA089iA07p05386

年代:1984

数据来源: WILEY

摘要:

ISEE 3 magnetic field and proton data are used to study the properties of rotational and tangential discontinuities in the solar wind. A Sonnerup‐Cahill minimum variance analysis of the magnetic field data is used to determine the direction of the normal to each discontinuity. The discontinuities are then classified as rotational (RD), tangential (TD), or either (ED), depending on the relative values of the normal field component and the change of field magnitude across them. This process yields substantially more RD's than TD's, in agreement with earlier studies using this method of classification. Other field and plasma parameters are then examined for each of these three groups. The field magnitude passes through a local minimum while the field direction is changing for some TD's but not for RD's. The first and second adiabatic invariants for protons and the helium abundance are approximately conserved across RD's but not across TD's, although the helium abundance is observed to change at a small fraction of the RD's. The product of plasma density times the anisotropy factor tends to be conserved across all three types, The relative directions of the velocity and field changes across all three types of discontinuity are consistent with the propagation of RD's outward from the sun, even though no such relation is predicted for TD's. The magnitude of the velocity change at RD's is smaller than that predicted by MHD theory, and the use of a two‐stream fit to the proton data reduces, but does not remove, this discrepancy. The speeds of the alpha particles and the secondary proton beam relative to the primary proton beam result in little interaction between the alphas and RD's, while the primary and secondary proton beams flow through RD's in opposite directions and have oppositely directed velocity changes. The plasma conditions at ED's show a closer resemblance to RD's than to T

ISSN:0148-0227    

DOI:10.1029/JA089iA07p05395

年代:1984

数据来源: WILEY

摘要:

Suprathermal ions with energies between solar wind thermal energies and ∼29 keV are occasionally observed ahead of outward propagating interplanetary shocks with the Los Alamos/Garching fast plasma experiment on ISEE 1 and 2. Compared with suprathermal ion velocity distributions observed upstream from the earth's bow shock, the upstream interplanetary shock ion velocity distributions are relatively structureless, and the particle fluxes are less intense. Typically the suprathermal ion distribution emerges smoothly from the solar wind thermal distribution and is nearly isotropic in the solar wind frame. Such distributions are observed with the fast plasma experiment only in association with interplanetary shocks. Field‐aligned beams, kidney‐bean‐shaped distributions, shells of ions in velocity space, and bunches of gyrating ions—all common to the upstream region of the earth's bow shock—have not been observed ahead of interplanetary shocks. Highly structured ion velocity distributions observed upstream of the earth's bow shock apparently are caused directly or indirectly by the nearly specular reflection of solar wind ions at the shock, a consequence of the generally high Mach number of the solar wind flow at 1 AU. By way of contrast, most interplanetary shocks at 1 AU have low, subcritical Mach numbers, and solar wind ion reflection at these shocks does not appear to play a role in producing upstream suprathermal ion distributions at 1 AU. Nevertheless, solar wind ions are accelerated to high energies at interplanetary shocks. Leakage of shocked thermal plasma across these low‐Mach‐number shocks from the downstream region may play an important role in producing upstream suprathermal ion populations and may therefore constitute the first step in the acceleration of solar wind ions to high energies

ISSN:0148-0227    

DOI:10.1029/JA089iA07p05409

年代:1984

数据来源: WILEY

摘要:

This paper assembles ISEE 1, 2, and 3 observations of the interplanetary magnetic and electric fields, plasma, magnetohydrodynamic waves, electromagnetic and electrostatic plasma waves, 1‐ to 6‐keV protons and electrons, and>30‐keV/Qions for the interplanetary shock of November 12, 1978. The shock was high speed (640 km s−1), supercritical, quasi‐parallel, and an efficient accelerator of energetic protons. The flux of>35‐keV protons increased by a factor of 15 in the last 45 min and 270REbefore shock encounter. The>10‐keV proton energy density approached that of the magnetic field and thermal plasma upstream of the shock. The shock was inside a closed magnetic structure that was connected at both ends to the shock. The intensity of ion acoustic and low‐frequency MHD waves increased inside the closed

ISSN:0148-0227    

DOI:10.1029/JA089iA07p05419

年代:1984

数据来源: WILEY

摘要:

An objective of this paper is to determine the jump in plasma parameters across the November 12, 1978, interplanetary shock, sufficiently accurately to test in a subsequent paper a major prediction of shock acceleration theory: the dependence of the energetic ion spectral index upon the density compression ratio. We use ISEE 1 and 3 measurements of the magnetic field and electron and proton densities, temperatures, and bulk velocities, as well as ISEE 3 alpha particle measurements, and confirm the ISEE 1 electron densities using plasma wave measurements. We solve for the shock normal using four independent methods and show that the upstream and downstream flow parameters are consistent to better than 10% with γ = 5/3 Rankine‐Hugoniot jump conditions. We conclude that the November 12, 1978, shock was a high‐speed (612 km s−1), supercritical, quasi‐parallel (θBn= 41°) shock of moderate strength (fast Mach number of 2.8) propagating into an upstream plasma whose total β was 1.14 and whose electron‐to‐proton temperature ratio was 2.8. This shock had three dissipative scale lengths one of a few Larmor radii associated with its magnetic field jump, one of about 10REassociated with electron equilibration, and one of about 30REassociated with an energetic p

ISSN:0148-0227    

DOI:10.1029/JA089iA07p05436

年代:1984

数据来源: WILEY

摘要:

The Jovian magnetosphere is a rapid rotator in the sense that the corotation velocity exceeds the gyrovelocity for most of the low‐energy plasma particles. Ordinarily, an electric drift velocity greater than the gyrovelocity will destroy the near periodicity of the bounce motion, so the parallel invariantJwill no longer be valid. However, this paper shows thatJinvariance actually remains valid in rapidly rotating magnetospheres so long as departures from rigid rotation are not too great. Northrop and Birmingham have already provedJinvariance for the case of rapid but exactly rigid rotation, and this paper extends their results to nonrigid, rapid rotation with corotation lag and/or convection. These results allow the magnetic field to be arbitrarily asymmetric. The guiding‐center equations in the rotating frame are also used to obtain conditions for plasma corotation in arbitrarily asymmetric but rigidly rotating magnetic fields. The plasma bulk velocity equals the corotation velocity for any trapped particle population that is steady state in the corotating frame providedE+ (Ω×r) ×B/c= 0 and all first‐order drifts are negligible. These conditions are satisfied, and corotation is expected, for a steady‐state cold plasma on equipotential field lines of any geometry threading a rigidly rotating central

ISSN:0148-0227    

DOI:10.1029/JA089iA07p05453

年代:1984

数据来源: WILEY

摘要:

Considerable evidence exists from data obtained by artificial satellites of Venus describing the detached bow shock wave which develops at Venus due to the interaction of the super‐Alfvenic, supersonic solar wind. However, there is no such direct evidence for any bow shock wave at Titan due to the interaction with the corotating Saturnian magnetosphere. This is because the fast mode MHD Mach number was less than unity at the time of Voyager 1 close flyby. In spite of this difference in plasma regimes, there is a certain striking similarity in these two interactions. (1) Both obstacles to plasma flow have appreciable ionospheres and are globally nonmagnetic, (2) Downstream from both obstacles, an induced bipolar magnetic tail is formed with a central field reversal region which is analogous to the earth's neutral sheet‐plasma sheet region. This paper will discuss plasma and magnetic field data from the Venera 9 and 10 spacecraft at Venus and from Voyager 1 at Titan which lead to new conclusions regarding the magnetic tail structure of their induced magnetospheres: (3) There appears to be evidence for magnetic merging in these induced tails so that magnetic reconnection between the oppositely directed tail lobes occurs. The single tail crossing at Titan shows evidence of merging while the repeated tail crossings at Venus indicate that similarly observed merging there is not a permanent feat

ISSN:0148-0227    

DOI:10.1029/JA089iA07p05461

年代:1984

数据来源: WILEY

摘要:

Associations of geomagnetic activity in the auroral zone with thinnings and expansions of the magnetotail plasma sheet are examined statistically in this paper. We first identified many plasma sheet thinnings and expansions in plasma and particle data from VELA satellites and from OGO 5 without reference to ground magnetic data. These events were grouped according to the location of the detecting satellite in the magnetotail. For each such group the times of thinning or expansion were then used as fiducial times in a superposed‐epoch analysis of the geomagneticALindex values that were recorded in 8‐hour intervals centered on the event times. The results show that many plasma sheet thinnings and expansions are related to discrete negative bay structures that are the classical signature of substorms. Furthermore, they support earlier findings that plasma sheet thinning and expansion at the VELA orbit (r≈ 18RE) tend to be associated with the onset of the auroral zone negative bay and the beginning of its subsidence, respectively. Earthward ofr≈ 13–15RE, plasma sheet expansion occurs near the time of the onset of the negative bay, again in agreement with earlier findings. A large fraction of plasma sheet expansions to half thicknesses of ≳ 6REat the VELA orbit are associated not with a baylike geomagnetic disturbance but with subsidence of a prolonged interval of disturbance. The study also shows that many plasma sheet expansions are related simply to generally enhanced geomagnetic activity showing no baylike or other distincti

ISSN:0148-0227    

DOI:10.1029/JA089iA07p05471

年代:1984

数据来源: WILEY

摘要:

Electron motion in the distant tail current sheet is evaluated and found to violate the guiding center approximation at energies ≳ 100 eV. Most electrons within the energy range ˜10−1‐ 10² keV that enter the current sheet become trapped within the magnetic field reversal region. These electrons then convect earthward and gain energy from the cross‐tail electric field. If the energy spectrum of electrons entering the current sheet is similar to that of electrons from the boundary layer surrounding the magneto tail, the energy gain from the electric field produces electron energy spectra comparable to those observed in the earth's plasma sheet. Thus current sheet interactions can be a significant source of particles and energy for plasma sheet electrons as well as for plasma sheet ions. A small fraction of electrons within the current sheet has its pitch angles scattered so as to be ejected from the current sheet within the atmospheric loss cone. These electrons can account for the electron precipitation near the high‐latitude boundary of energetic electrons, which is approximately isotropic in pitch angle up to at least several hundred keV. Current sheet interaction should cause approximately isotropic auroral precipitation up to several hundred keV energies, which extends to significantly lower latitudes for ions than for electrons in agreement with low‐altitude satellite observations. Electron precipitation associated with diffuse aurora generally has a transition at 1–10 keV to anisotropic pitch angle distributions. Such electron precipitation cannot be explained by current sheet interactions, but it can be explained by pitch angle diffusion driven by pl

ISSN:0148-0227    

DOI:10.1029/JA089iA07p05479

年代:1984

数据来源: WILEY