摘要:

We have examined 204 bow shock crossings observed in the magnetic field and plasma data on ISEE 1. Using the measured upstream field and plasma data, we calculated the downstream field magnitudes by using the single‐fluid MHD Rankine‐Hugoniot jump conditions, and we compared the results with the observed downstream field magnitudes. We find that the simple MHD model approach can predict the downstream field magnitude only on the average, but does so quite well if (1) a polytropic index of approximately 5/3 is used in the calculations; (2) the angle between the upstream field and the shock normal is greater than 45°; and (3) the Alfvén Mach (Ma) number is less than about 10. For angles less than 45° the predictions overestimate the observed field strength. ForMa>10 the predictions underestimate the observ

ISSN:0148-0227    

DOI:10.1029/JA090iA05p03925

年代:1985

数据来源: WILEY

摘要:

Electron plasma oscillations in the earth's electron foreshock region are observed to shift above and below the local electron plasma frequency. As plasma oscillations shift downward from the plasma frequency, their bandwidth increases and their wavelength decreases. Observations of plasma oscillations well below the plasma frequency are correlated with times when ISEE 1 is far downstream of the electron foreshock boundary. Although wavelengths of plasma oscillations below the plasma frequency satisfykλDe≈ 1, the Doppler shift due to the motion of the solar wind is not sufficient to produce the observed frequency shifts. A beam‐plasma interaction with beam velocities on the order of the electron thermal velocity is suggested as an explanation for plasma oscillations above and below the plasma frequency. Frequency, bandwidth, and wavelength changes predicted from the beam‐plasma interaction are in good agreement with the observed characteristics of plasma oscillations in the foreshock

ISSN:0148-0227    

DOI:10.1029/JA090iA05p03935

年代:1985

数据来源: WILEY

摘要:

Comprehensive measurements of ion spectra, composition, and anisotropies over the energy range ∼30 keV to ∼5 MeV in Jupiter's foreshock, magnetosheath, and magnetopause were obtained by the low‐energy charged particle instrument during the Voyager 1 and 2 encounters with the planet in 1979. Detailed analyses of the spectral and compositional signatures show the following: (1) The ion spectral form at event onset is described well by a power law in energy (dj/dE=KE−γ) over the range ≲100 keV to ∼2 MeV; the spectrum becomes generally (but not always) harder at the lower (≲200 keV) energies as the event progresses. (2) The ion spectrum is depleted of protons atE≳ 300 keV and is dominated by ions withZ≥ 6 (probably oxygen and sulfur) at higher energies; this fact, taken together with the continuity of the spectrum over a factor of ∼107in intensity, suggests that heavy ions (Z≥ 6) also dominate at low (<300 keV) energies. (3) Spectra of similar form and ion composition are observed inside the magnetosheath and magnetopause. (4) Large (up to 100∶1) variable anisotropies are present throughout all events. (5) Events are seen whenever the projection of the interplanetary magnetic field connects the spacecraft to the bow shock. (6) The overall morphology of ion intensity enhancements resembles that observed upstream of the earth's bow shock in similar energy ranges, including inverse velocity dispersion. These observations lead to the conclusion that ions appearing upstream from Jupiter originate from within Jupiter's magnetosphere. The spectral and compositional features are shown to be consistent with ion escape from the magnetosheath followed byE × Edrift in the solar wind electric field, as suggested byAnderson[1981] for the case of earth. The compositional signatures, together with the large anisotropies and the presence of MeV ions at event onset, preclude the possibility of diffusive, first‐order Fermi acceleration upstream of the shock, as has been proposed for the ions

ISSN:0148-0227    

DOI:10.1029/JA090iA05p03947

年代:1985

数据来源: WILEY

摘要:

Measurements of energetic proton (Ep≥ 520 keV) intensities by The Johns Hopkins University Applied Physics Laboratory instruments on board the Voyagers 1 and 2 deep space probes, during solar flare‐induced shock waves, indicate that the formation of solar energetic storm particle (ESP) events depends critically on the heliolongitudes of different locations on the large‐scale shock front with respect to the source flare site. It is shown that large ESP ion intensity enhancements are observed for solar flare sites to the east of the spacecraft meridian, whereas only weak ESP events are associated with shock crossings where the flare sites are west of the spacecraft meridian. The results are explained in terms of the average “interplanetary magnetic field‐shock front” configurations encountered by the Voyagers at various heliolongitudes of the solar flare‐generated shock wave, i.e., quasi‐perpendicular (quasi‐parallel) shocks for eastern (western) solar flare sites. These configurations suggest that efficient energetic proton acceleration processes operate at quasi‐perpendicular shock fronts consistent with the “grad‐B” shock dri

ISSN:0148-0227    

DOI:10.1029/JA090iA05p03961

年代:1985

数据来源: WILEY

摘要:

Present hydrodynamic models of solar wind streams predict that interactions will cause interplanetary shocks to decay and large‐scale structures to coalesce and smooth out, with a decay length of 10–15 AU for moderate or small‐amplitude shocks. The Pioneer 10 plasma data, extending 1–30 AU, are examined in the light of such predictions. It is found that coalescence of streams into a single stream per solar rotation does occur, in general, but that considerable structure remains by 30 AU. The leading edge of a stream often exhibits a velocity jump of>20 km/s; many of these may be shocks. There is a characteristic velocity‐density‐temperature signature of these distant streams which differs from the close‐in double‐shock signature. A unique transient was seen in July 1982, at 28 AU, with a velocity jump of

ISSN:0148-0227    

DOI:10.1029/JA090iA05p03967

年代:1985

数据来源: WILEY

摘要:

We present results of a detailed analysis of ISEE 3 observations of low‐energy protons (35–1600 keV) and low‐frequency waves (period greater than 6 s) associated with the passage of the large oblique interplanetary shock of April 5, 1979. We observe a foreshock region for several hours prior to the arrival of the shock. Within this region we find (1) a peak in the proton energy spectrum at about 200 keV, (2) the proton energy density (in the range 35–1600 keV) comparable with the total energy density of the magnetic field, (3) a good correlation between the amplitude of the low‐frequency waves and the 200‐keV proton intensity, and (4) a good agreement between the peak in the wave power spectrum and the resonant frequency corresponding to the peak in the proton spectrum, only if large pitch angles are considered, suggesting that the protons are responsible for the waves by virtue of a resonant interaction. Our observations suggest that the high energy density of the high‐energy solar flare protons preceding the shock could be responsible for “seed” waves which provide the scattering centers necessary for the acceleration of the lower‐energy protons via a first‐order Fermi a

ISSN:0148-0227    

DOI:10.1029/JA090iA05p03973

年代:1985

数据来源: WILEY

摘要:

The energetic particle event associated with the quasi‐perpendicular interplanetary shock which passed ISEE 3 on June 6, 1979, is characterized by persistent beamlike antisunward particle fluxes on both sides of the shock. We found that the shock has no significant nonadiabatic effects on the energetic particles near 1 AU. The lack of particles with pitch angles larger than 60° accounts for the absence of signatures of shock drift acceleration. The adiabatic behavior of the bulk of the particles at the shock offers a unique opportunity to understand the role of the postshock magnetic regime. A recently formed magnetic discontinuity just downstream from the shock forms an effective obstacle for particles, particularly those with a small gyroradius. From the spatial dependence of the particle population in front of the magnetic discontinuity we derived the escape probability for particles to cross the discontinuity. Strong anisotropic particle bursts are observed as intensity spikes (duration less than 1 min) both upstream and downstream from the shock. Velocity dispersion in some of these spikes is consistent with impulsive release at the magnetic discontinuity. We propose that the spikes are accomplished by a disturbance propagating along the discontinuity which develops a normal component perhaps accompanied by induced electric fields, thus enabling, in particular, low‐energy particles with their small gyroradii to cross and stream into the upstream region. The energetic particle fluxes in this event are among the highest we have observed at ISEE 3. These fluxes are not produced by shock acceleration near 1 AU, but originate somewhere else far downstream from the magnetic discontinuity. From what we have learned from the unambiguous particle population signatures in this event, we believe that most shock‐associated particle events cannot be understood on the basis of shock interactions alone; rather, the intensity history of energetic particles below 1 MeV is determined by the complete ensemble of magnetic structures embedded in the compressed plasma well behind the

ISSN:0148-0227    

DOI:10.1029/JA090iA05p03981

年代:1985

数据来源: WILEY

摘要:

To understand and explain the Voyager 2 observations of Ganymede's wake‐associated disturbances, an investigation of the electrodynamic interaction of the Jovian magnetospheric plasma with the satellite has been carried out. Two different aspects of the interaction are studied: (1) To see plasma kinematic effects during the interaction of the Jovian plasma and the expansion of the plasma into the cavity, particle‐in‐cell solutions of the electron and ion Vlasov equations are obtained. The disturbances of ions, potentials, and ion and electron thermal and drift energies in the wake region are obtained. (2) To provide explanations of the observed large radial spread of the disturbances, linear Kelvin‐Helmholtz instability theory is applied to the plasma flowing past the boundary of the cavity. Theoretical calculations show that the ambient plasma flow deviates from corotational flow, in both magnitude and direction. Theoretical conditions for the existence of magnetosonic waves and transverse Alfvén waves are also examined. The effect of the distortion of the Jovian magnetic field lines due to the annular current sheet on the charged particle absorption by Ganymede is also

ISSN:0148-0227    

DOI:10.1029/JA090iA05p03995

年代:1985

数据来源: WILEY

摘要:

During an interval of strong interplanetary magnetic field (IMF) By, while ISEE 3 was in the distant magnetotail, the north lobe was observed south of the ecliptic plane. Lobe field lines were strongly bent in the direction of the IMF, and a dense boundary layer plasma was observed. During the interval, magnetopause normals pointed in the z direction, although ISEE 3 was near the dawnside ecliptic plane. The observations are interpreted in terms of field line bending within a twisted and flattened magnetotail.

ISSN:0148-0227    

DOI:10.1029/JA090iA05p04011

年代:1985

数据来源: WILEY

摘要:

We present simultaneous observations of energetic particle measurements from the geosynchronous satellite 1982–019 and magnetic field, electron plasma, and energetic proton and electron measurements obtained with ISEE 3 in the deep tail. The data are supplemented by ground magnetograms. A substorm occurred on March 22, 1983, close to 0300 UT as identified in the ground magnetograms and by a particle injection at geosynchronous orbit. About 10 min later, ISEE 3 observed (at a distance of ∼130REin the deep tail) magnetic field, plasma, and energetic particle signatures consistent with the passage of a plasmoid. After the passage of the plasmoid the satellite enters shortly into a lobelike environment, in which an energetic proton beam is observed. High‐resolution magnetic field data are indicative of small‐scale structures in the postplasmoid plasma sheet. From the plasma sheet flow speed during the plasmoid's passage it is concluded that the 0300 UT substorm is responsible for its origin. This allows an approximate timing of the plasmoid release at a near‐earth neutral line and of the plasma sheet recovery after substorm onset, and it indicates a close relationship between processes in the near‐earth plasma sheet and the deep tail durin

ISSN:0148-0227    

DOI:10.1029/JA090iA05p04021

年代:1985

数据来源: WILEY