摘要:

The cometary plasma in the magnetic barrier just outside the diamagnetic cavity which surrounds the nucleus of comet Halley is virtually stagnant. The outflowing neutral gas exerts an outward ion‐neutral drag force on this plasma, which balances the inward magnetic pressure gradient force in the vicinity of the contact surface. The cometary ions are frictionally heated due to the relative motion of the ion and neutral gases. The ion flow velocity must have a few km/s non‐radial component in order to explain the ion temperatures measured by the ion mass spectrometer on Gio

ISSN:0094-8276    

DOI:10.1029/GL014i010p00983

年代:1987

数据来源: WILEY

摘要:

Based on the ion plasma and magnetic field observations of Vega−1near its closest approach to comet Halley a self‐consistent scenario is developed according to which the observed magnetic field topology, the observed burst of ions at energies 200–600 eV, and the observed directional dependence of the flow of these ions leads to the conclusion that these burst‐particles are cometary ions which have been accelerated by the process of merging of magnetic field lines of opposite p

ISSN:0094-8276    

DOI:10.1029/GL014i010p00987

年代:1987

数据来源: WILEY

摘要:

Possible solar wind sources for a sudden global brightening of Comet IRAS‐Araki‐Alcock are examined. No increases in solar wind momentum flux, solar energetic particles or solar activity occurred coincident with these brightenings. The only change in the solar wind coincident with the brightenings was a rotation of the interplanetary magnetic field to a more flow‐aligned state. If this rotation did not lead to the cometary brightening, the brightening must have been intrinsic to the

ISSN:0094-8276    

DOI:10.1029/GL014i010p00991

年代:1987

数据来源: WILEY

摘要:

Data from the Ion Mass Spectrometer and the magnetometer on the Giotto spacecraft are used to examine the structure of the inbound crossing of the comet Halley bow shock on March 13, 1986. It is found that the velocity decrease, the field strength increase, and the heating of picked up cometary protons occurred over a broad region corresponding to several heavy‐ion gyroradii. The solar‐wind protons and alphas, on the other hand, were compressed and heated at a narrow structure, which might be called a subshock, on the leading edge of the broad shock region. The electrostatic potential difference across the shock was less than 4

ISSN:0094-8276    

DOI:10.1029/GL014i010p00995

年代:1987

数据来源: WILEY

摘要:

The 30‐day reports from the Voyager Ultraviolet Spectrometer team characterize the atomic hydrogen observed near Saturn as a torus with a half width of 7Rsextending from about 8 to 25Rs. The source of this torus was hypothesized to be escape of hydrogen from Titan's atmosphere. Several recent papers propose that the source is actually Saturn's exosphere and that the hydrogen cloud extends inwards to the planet. We model the atomic processes occurring in the inner magnetosphere, including sputtering, ionization, charge exchange, ion‐atom interchange, recombination, and transport, and add a neutral hydrogen source to test the proposal that a hydrogen cloud exists in this region. Plasma observations in the inner magnetosphere are found to be inconsistent with the presence of a dense (20 cm−3) atomic hydrogen cloud. The presence of such a cloud in the observed plasma environment would result in a much larger proton density than observed and would remove nearly all heavy ions from the magnetosphere. Thus we conclude that the hydrogen cloud must be a torus as originally reported, and that the cloud does not extend inward to the orbits of the inner satellites of S

ISSN:0094-8276    

DOI:10.1029/GL014i010p00999

年代:1987

数据来源: WILEY

摘要:

The magnetic reconnection process in a collisionless plasma is studied based on a particle simulation. It is found that the magnetic field reversal and particle energization take place mainly in the midplane of the outflow region and the particle acceleration by slow shocks is not important. This result is consistent with the collisionless reconnection model proposed by Hill [1975].

ISSN:0094-8276    

DOI:10.1029/GL014i010p01003

年代:1987

数据来源: WILEY

摘要:

Empirical models of the average magnetospheric magnetic field, plasma density, and temperature distributions are used to construct a model of the distribution of MHD wave mode speeds within the magnetosphere. Although the MHD wave speeds in general have a smaller dynamic range than the magnetic field intensity or the plasma properties, considerable structure and variability is found which will lead to interesting “optical” effects on the propagation of low frequency waves. A persistent feature of the derived optical structure, which is qualitatively insensitive to known variability of the field or plasma, is a pronounced minimum of the wave speeds in the outer plasmasphere, i.e., a magnetospheric “shoal.” This feature does not map along magnetic field lines, but is confined to the equatorial region, leading to a positive radial gradient of wave speeds near synchronous orbit. The breaking of earthward propagating disturbances in this region may play an essential role in the formation of the substorm injection boundary and in the creation of equatorially trapped warm ion distri

ISSN:0094-8276    

DOI:10.1029/GL014i010p01007

年代:1987

数据来源: WILEY

摘要:

The dominant source of energetic ions upstream of the earth's bow shock remains controversial. Charge Composition Explorer (CCE) energetic (E>10–15 keV) ion and magnetic field measurements near the spacecraft's 8.8 REapogee during a period of greatly increased solar wind dynamic pressure on November 1, 1984 determine the sense of energetic ion streaming in the dayside magnetosphere, the magnetosheath, and the solar wind. The ions stream away from an appropriately compressed model magnetopause at all times in the magnetosheath and solar wind. The flux of energetic ions in the magnetosheath and solar wind rises to, but never exceeds, that in the magnetosphere. The observations are consistent with a magnetospheric, rather than a bow shock (Fermi acceleration) source for the ions in the magnetosheath during this even

ISSN:0094-8276    

DOI:10.1029/GL014i010p01011

年代:1987

数据来源: WILEY

摘要:

During the Spacelab‐2 mission a small satellite carrying various plasma diagnostic instruments was released from the shuttle to co‐orbit at distances up to 300 m. During a magnetic conjunction of the shuttle and the satellite an electron beam modulated at 1.22 kHz was emitted from the shuttle during a 7 min period. The spatial structure of the electromagnetic fields generated by the beam was observed from the satellite out to a distance of 153 m perpendicular to the beam. Electromagnetic radiation at the fundamental and the harmonics of the modulation frequency was observed as well as broad‐banded electrostatic noise. The magnetic field amplitude of the strongest harmonics were comparable to the amplitude of simultaneously observed whistlers, while the electric field amplitudes were estimated to 1–10 mV/m. The observations are related to theories for radiation from pulsed electro

ISSN:0094-8276    

DOI:10.1029/GL014i010p01015

年代:1987

数据来源: WILEY

摘要:

The Active Magnetospheric Particle Tracer Explorers/Charge Composition Explorer (AMPTE/CCE), with a small inclination of 4.8° and an apogee of ∼8.8 RE, is capable of exploring the dynamical behavior of the near‐earth magnetotail current sheet during substorms. At ∼1153 UT on day 240 (August 28), 1986, the spacecraft was on the midplane of the magnetotail near midnight (∼23.4 h LT) at a radial distance of ∼8 RE, when the onset of a substorm took place. The magnetic field data for the ∼3.5‐min interval following the onset indicated a variation of the magnetic field that has not been observed by geostationary satellites or by other spacecraft flown in the near‐earth tail (r≲ 20 RE). The variation was characterized by a large‐amplitude (from less than 10 nT to greater than 40 nT) oscillation of the total field with a period of ∼13 s and also by southward turning of the field during most cycles of the oscillation. At times the magnetic field became strongly southward, and in a few measurements the magnitude of the southward component exceeded 20 nT. The level of high‐frequency perturbations (periods shorter than ∼10 s) was also enchanced during the event. The observations may be due to the formation of an X‐type neutral line and it

ISSN:0094-8276    

DOI:10.1029/GL014i010p01019

年代:1987

数据来源: WILEY