摘要:

IMP electron data are compared to several predictions of a steady state theory of solar wind electrons which assumes that transport is controlled by the macroscopic interplanetary electric and magnetic fields and elastic Coulomb collisions with the solar wind protons and thermal electrons. One of the predictions based on these assumptions is that the ratio of forward to backward phase space density of field‐aligned extrathermal electrons should be 6∶1. In contrast, measurements of electron distributions within the only steady state solar wind flow identified to date, the high‐speed solar wind, show this ratio to be typically about an order of magnitude larger. Based on a larger set of assumptions, the theory further predicts an anticorrelation between the solar wind bulk speed and (1) the fractional density of extrathermal electrons, (2) the component of the temperature of the extrathermal electrons parallel to the interplanetary magnetic field, and (3) the total heat flux. These anticorrelations are not found in the IMP electron data set. Good agreement between the predictions and the observations may require modification of a number of assumptions of the theory. Most important may be the need to include inelastic Coulomb and/or wave‐electron col

ISSN:0148-0227    

DOI:10.1029/JA087iA09p07355

年代:1982

数据来源: WILEY

摘要:

The velocities of helium, oxygen, and hydrogen ions have been recorded over a full range of solar wind conditions by the ion composition instrument (ICI) and Los Alamos National Laboratory plasma instrument (LANLPI), respectively, aboard the ISEE 3 spacecraft between August 1978 and December 1979. Interspecie velocity differences were observed frequently. For solar wind velocities between 300 and 400 km s−1the helium velocity exceeded the hydrogen velocity by 5 km s−1on the average. For solar wind velocities between 400 and 500 km s−1the average difference was 14 km s−1; however, no evidence was found for a systematic nonzero average velocity difference between helium and oxygen ions even at the higher velocities. Velocity differences were examined in a number of streams and across a number of interplanetary shocks. Helium‐hydrogen velocity differences are generally bounded by the Alfvén speed. Velocity differences show abrupt changes across interplanetary discontinuities, presumably tangential. Differences between the speeds of differently charged minor ions appear also to result from the electrostatic potential differences across the interplanetary shocks. The potential difference, calculated from the energy jump condition for a perpendicular hydromagnetic shock, is of the correct magnitude to produce the observ

ISSN:0148-0227    

DOI:10.1029/JA087iA09p07363

年代:1982

数据来源: WILEY

摘要:

Helium abundance (A(He)) enhancements observed with Los Alamos instruments on IMP 6, 7, and 8 during the 1972–1978 interval have been investigated. Statistical analysis of 73 large events with A(He) ≥ 10% (HAEs) provides evidence for a close link between helium enhancements at 1 A.U. and transient coronal mass ejections. HAE events are sporadic, sometimes clustered in time, and their frequency of occurrence is approximately in phase with the solar cycle. Nearly 50% of HAEs are associated with interplanetary shocks and/or geomagnetic activity sudden commencements, but the plasma pattern associated with A(He) enhancements is independent of shock occurrence. This pattern features high magnetic field strength, low alpha‐proton velocity difference, and low proton temperature. These plasma properties suggest that the enhancement is embedded in a ‘closed,’ magnetically dominated structure that expands adiabatically. In fact, HAEs are likely to be still evolving dynamically at 1 A.U. Evidence of a significant association between helium enhancements at 1 A.U. and type II and IV radio bursts in the corona is presented. We interpret these results to mean that most HAE events originate in transient coronal disturbances in which the magnetic field strength is

ISSN:0148-0227    

DOI:10.1029/JA087iA09p07370

年代:1982

数据来源: WILEY

摘要:

Following the recent discovery of large fluxes of He+in the solar wind, a systematic search of solar wind energy/charge (E/Q) spectra was initiated, using plasma data from IMP 7, IMP 8, ISEE 1, and ISEE 3 that covered the time period from October 1972 to February 1980. A technique of vertically stacking successiveE/Qspectra made it possible to detect systematic trends in the spectra that were indicative of ion species beyond the He++peak down to the one count level. A search of nearly 8 years of data yielded only three distinct events with identifiable levels of He+. These events occurred on July 29, December 1, and December 4, 1977, all within 1 year and during the rising phase of solar cycle 21. We believe more events would have been detected if the instruments had been more sensitive and tracking more complete. Two of the events occurred within driver gas, following interplanetary shocks, while the third event occurred in a noncompressive density enhancement (NCDE). For all three the abundances of various minor ions, including He++, were enhanced in comparison to normal solar wind abundances. One unusual feature found in these three He+events, in contrast to normal solar wind, was the appearance of ionization states corresponding to both warm and very cold coronal freezing‐in conditions within the same plasma. In addition to the unusual appearances of large fluxes of He+ions, iron ions ranging from Fe+10to Fe+5were observed. Evidence was found for the appearance of C+4ions, and in one event the data can be interpreted as containing O+2and O+3at detectable levels. One of the phenomenological results following from these observations is that certain unusual transient events eject both hot and unusually cold coronal plasma mixed and coexisting on the same magnetic field line

ISSN:0148-0227    

DOI:10.1029/JA087iA09p07379

年代:1982

数据来源: WILEY

摘要:

The Pioneer 10 and 11 Jet Propulsion Laboratory vector helium magnetometer and the University of Chicago 0.5‐ to 1.8‐MeV proton telescope data are used to examine the relationship between low‐energy proton increases and corotating interaction regions (CIR's) in the heliosphere between 1 and 6.3 AU. The 0.5‐ to 1.8‐MeV proton flux enhancements are correlated with the forward and reverse shocks bounding the CIR's. Fifty to sixty percent of all identified shocks are accompanied by time‐coincident proton events. Conversely, almost all proton events occurring at CIR boundaries are associated with shocks: 92% of all proton events detected at the leading boundary are accompanied by forward shocks, and 72% of the proton events near the trailing CIR edge are associated with reverse shocks. Proton intensities are highest when the shock normal angle with respect to the magnetic field direction is ≥80°, for both forward and reverse shocks. One long lasting CIR, which persisted for more than 14 rotations, is studied to determine detailed field‐particle relationships and their evolutionary changes with time (and distance from the sun). The CIR recurs with a sidereal period of 24.7±0.1 days, a value comparable to the average period of magnetic features near the sun's equator. Considerable variation in the CIR field intensity and associated proton count rate occurs from rotation to rotation, indicating a variability in the high‐speed stream interaction properties and in the overall efficiency of the proton acceleration mechanism(s). A general correlation between the maximum CIR field intensity and the maximum proton count rate is noted. The evolution of proton flux characteristics, with time and distance, is studied. Initially, the characteristic double peaks in proton intensity, associated with the forward and reverse shocks, are approximately equal in magnitude. With time, the second, trailing peak becomes significantly larger. The two peaks are not always coincident with the shocks but are often found inside the CIR. The minimum proton flux, located between the two proton maxima, appears to be correlated with the maximum field strength of the CIR. The proton flux in this minimum region increases with time, presumably due to cross‐field diffusion of protons from the neighboring maximum regions. Spectral softening and large proton‐to‐helium ratios are characteristic of the particles near the leading CIR edge, but not of the trailing edge. Proton anisotropies are often large and field aligned. The ‘flow’ is generally away from the forward and reverse shocks, indicating that the shocks are the source of particle acceleration. Upstream of forward shocks, the proton flow is in the solar direction. Protons are found to stream in the antisolar direction within the CIR. The distribution is isotropic upstream of the reverse shock. Intense magnetohydrodynamic fluctuations are present within the CIR, indicated by large field variances. Although the variances are orders of magnitude larger within the CIR than in the quiet regions outside CIR's, the relative field fluctuation, given by the value σ²/B², is generally less inside the CIR than outside. The evidence presented in this paper strongly supports shock acceleration as the primary source of the 1‐MeV protons. A schematic figure, which incorporates many of the features deduced in this report, is given to illustrate the relationship between the energetic protons, the forward and reverse shocks, and the interplanetary magnetic field structure. The predictions of various theories and mechanisms for interplanetary nucleon acceleration are discussed in light of

ISSN:0148-0227    

DOI:10.1029/JA087iA09p07389

年代:1982

数据来源: WILEY

摘要:

A study of the effects of the transfer of momentum of the shocked solar wind to the Venus ionosphere near the terminator region is presented. It is shown that the deficiency of momentum flux within the velocity boundary layer in the ionosheath is comparable to the momentum flux present in the upper ionosphere near the terminator. Using the observed concentration of planetary O+ions in the wake it is also shown that mass loading processes are not sufficient to account for the loss of momentum flux above the ionopause and that, instead, an efficient coupling must exist between the plasma above and below that boundary. With reasonable values of the thickness and length of the velocity boundary layer it is possible to estimate an effective viscosity coefficient of the flow and the energy released through viscous dissipation. The results indicate that a column integrated energy deposition of the order of 10−2ergs cm−2sec−1can be predicted near the terminator. This number is comparable to that required to heat up the nightside ionosphere as assumed in the modeling studies of Knudsen et al (1979), Cravens et al (1980), Hoegy et al (1980), and Merritt and Thompson (

ISSN:0148-0227    

DOI:10.1029/JA087iA09p07405

年代:1982

数据来源: WILEY

摘要:

It is proposed that the so‐called radial spokes observed in rotation across Saturn's B ring are composed of fine charged dust levitated off the surfaces of larger bodies by electrostatic forces when the latter are sporadically charged to high electrostatic potentials. From the observed wedge‐shaped morphology of these spokes it is deduced that the dust grains are negatively charged. The dynamical structure of a spoke feature consisting of grains of different sizes is considered. It is shown that the surface density of dust within these wedge‐shaped spokes is not uniform. Each spoke has a fine structure consisting of a number of almost straight sharp ‘ribs’ radiating out from points on the synchronous orbit. The time evolution of a spoke can be likened to the continuous unfolding of a fan whose vertex is at the synchronous orbit and one of whose edges (the corotating one) is fixed in the radial direction. The model also predicts that the measured spoke velocities correspond to phase velocities rather than particle velocities, as is generally believed. According to this model, the angular velocity of the leading edge of the fan depends on the age of the spoke. Inside the synchronous orbit it is super‐Kepler up to about 2.5 hours after formation, but sub‐Kepler between 2.5 hours and 6 hours. Those spokes surviving the ring plane crossing will once again have a super‐Kepler leading edge after 6 hours. Outside the synchronous orbit the reverse would be the case. Consequently the model anticipates the observed scatter of the measured velocities about the Kepler value as real rather than due to errors of measurement, although they lie within the expected error bars. Finally, it is shown that the resettling of the grains on the larger bodies in the ring plane following their initial levitation results in a differential transport of grains across the ring plane. A consequence of this is the establishment of different multimodal size distributions of dust within the spokes at different planetoce

ISSN:0148-0227    

DOI:10.1029/JA087iA09p07413

年代:1982

数据来源: WILEY

摘要:

Charged particle motion in the guiding center approximation is analyzed for models of the Jovian and Saturnian magnetospheric magnetic fields based on Voyager magnetometer observations. Field lines are traced and shown to exhibit the previously recognized (Connerney et al., 1981a,b) distention that arises from azimuthally circulating magnetospheric currents. The spatial dependencies of the guiding center bounce period and azimuthal drift rate are investigated for the model fields. The bounce period may be shorter or longer by a factor of 1–3 than in the field of the planetary dipole alone depending on whether a particle mirrors close to the magnetic equator and experiences predominantly an enhanced mirror force or at high latitude and is affected principally by the extended length of the field line. Nondipolar effects in the gradient‐curvature drift rate are most important at the equator and affect particles with all mirror latitudes. The effect is a factor of 10–15 for Jupiter with its strong magnetodisc current and 1–2 for Saturn with its more moderate ring current. Limits of adiabaticity are discussed and are shown to occur at quite modest kinetic energies for protons and heavi

ISSN:0148-0227    

DOI:10.1029/JA087iA09p07421

年代:1982

数据来源: WILEY

摘要:

A general stability analysis is performed for the Kelvin‐Helmholtz instability in sheared magnetohydrodynamic flow of finite thickness in a compressible plasma. The analysis allows for arbitrary orientation of the magnetic fieldB0, velocity flowv0, and wave vectorkin the plane perpendicular to the velocity gradient, and no restrictions are imposed on the sound or Alfvén Mach numbers. The stability problem is reduced to the solution of a single second‐order differential equation, which includes a gravitational term to represent coupling between the Kelvin‐Helmholtz mode and the interchange mode. In the incompressible limit it is shown that the Kelvin‐Helmholtz mode is completely stabilized for any velocity profile as long as the condition is satisfied, whereV0is the total velocity jump across the shear layer. Numerical results are obtained for a hyperbolic tangent velocity profile for the transverse (B0⊥v0) and parallel (B0∥v0) flow configurations. Only modes withkΔ<2 are unstable, where Δ is the scale length of the shear layer. The fastest growing modes occur forkΔ ∼ 0.5‐1.0. Compressibility and a magnetic field component parallel to the flow are found to be stabilizing effects. For the transverse case, only the fast magnetosonic mode is destabilized, but ifk · B0≠ 0, the instability contains Alfvén‐mode and slow‐mode components as well. The Alfvén component gives rise to a field‐aligned current inside the shear layer. In the parallel case, both Alfvén and slow magnetosonic components are present, with the Alfvén mode confined inside the shear layer. The results of the analysis are used to discuss the stability of sheared plasma flow at the magnetopause boundary and in the solar wind. At the magnetopause boundary, the fastest growing Kelvin‐Helmholtz mode has a frequency of 0 (V0/2Δ), which overlaps with the frequency range of geomagnetic pulsations (Pc 3‐5). It is suggested that the MHD Kelvin‐Helmholtz instability could serve as a dynamo process driving small‐scale field‐aligned currents in the presence of t

ISSN:0148-0227    

DOI:10.1029/JA087iA09p07431

年代:1982

数据来源: WILEY

摘要:

In order to understand certain aspects of the plasma sheet dynamics, a numerical study of the nonadiabatic behavior of particles in a model field geometry is performed. The particle's magnetic moment as a function of time is calculated for various initial parameters, corresponding to various particle energies and degrees of field curvature. It is shown that the magnetic moment changes as the particle passes through the plasma sheet and that the magnitude of the change is related to the curvature of the field at the middle of the plasma sheet. The relation of the magnitude of the change in magnetic moment to the particle's pitch and phase angles as it passes through the sheet is numerically resolved. The nature of the change may be considered as a mechanism for pitch angle diffusion, and the diffusion coefficient is calculated. This scattering mechanism is significant for plasma sheet ions (1–10 keV) as well as energetic electrons (⩾100 k

ISSN:0148-0227    

DOI:10.1029/JA087iA09p07445

年代:1982

数据来源: WILEY