摘要:

Plasma observations near comet Halley indicate that around 1.6×105km from the nucleus a newly discovered sharp boundary (cometopause) separates the solar wind controlled external and the heavy cometary ion dominated internal regions. Such a discontinuity was previously not predicted by theoretical models. Inside the cometopause (in the cometary plasma region) the protons and heavy ions move with different speeds: the heavy ion velocity is less than a few km/s throughout this region, while the protons decelerate from several tens of km/s (observed near the cometopause) to a few km/s (near 1.5×104km

ISSN:0094-8276    

DOI:10.1029/GL013i007p00613

年代:1986

数据来源: WILEY

摘要:

During the Uranus ring plane crossing at 4.57 Uranus radii, the PRA instrument aboard Voyager 2 recorded a characteristic intense noise extending 104km perpendicular to the ring plane. This is interpreted as due to impact ionization of dust grains striking the spacecraft. The noise level is smaller by a factor ∼ 170 than the same kind of event recorded during Voyager 2 Saturn encounter just outside the G‐ring. The results indicate a maximum concentration of about 10−9cm−3of grains larger than 1 µm with a scale height ∼ 150 km across the ring plane. The distribution is asymmetrical, extending farther on the sunlit side. The inferred geometric optical depth is of

ISSN:0094-8276    

DOI:10.1029/GL013i007p00617

年代:1986

数据来源: WILEY

摘要:

In the magnetosphere of a planet which has its rotation axis aligned with the solar wind flow direction and its magnetic dipole axis significantly tilted to its rotation axis, solar‐wind‐driven magnetospheric convection can transport plasma throughout the magnetosphere; although corotation is present, it does not produce a closed flow region (normally identified with the plasmasphere) and thus does not Impede penetration of convection into the inner magnetosphere. The difference from the conventional theory of plasmasphere formation lies in the fact that, with the assumed geometry, the spatial pattern of magnetospheric convection is steady in the corotating rather than in the fixed frame of reference. Uranus at the present epoch closely approximates to this geometry, and hence magnetospheric convection is expected to be the dominant transport process in the Uranian magnetosphere, leading to transport times comparable to the estimated flow times of 30‐40

ISSN:0094-8276    

DOI:10.1029/GL013i007p00621

年代:1986

数据来源: WILEY

摘要:

We investigate the formation of plasmaspheres in planetary magnetospheres with arbitrary orientations of the rotation and magnetic dipole axes. A traditional plasmasphere with closed orbits inside the plasmapause and open trajectories outside it only occurs for the limiting case of aligned rotation and dipole axes. A time variable plasmapause exists if the rotation axis is perpendicular to the solar wind flow direction. In any other case no definite plasmapause exists. Solar wind driven convection transports plasma throughout the magnetosphere with an effectiveness which increases as the orientation becomes further from one of the two limiting cases of strict plasmapause formation. Our analysis is applied to Earth and Uranus using the actual orientations of the rotation and dipole axes. Particle trajectories at Earth deviate only slightly from those obtained with traditional models. Uranus has no plasmasphere, and plasma convects sunwards throughout the inner magnetosphere.

ISSN:0094-8276    

DOI:10.1029/GL013i007p00624

年代:1986

数据来源: WILEY

摘要:

We have made a semi‐empirical analysis of our extensive body of observed cosmic ray intensity data from Pioneers 10 and 11 and related spectral information from other authors in order to infer the radius R of the modulation region surrounding the sun. During the period 1972‐1985 the inferred values of R vary with time systematically and in a manner generally similar to that of sunspot numbers. The range of values of R is from 42 AU at the time of minimum solar activity (∼ 1976) to 88 AU about 1.5 yr following the time of maximum solar activity (∼ 1980). A specific, testable prediction is that Pioneer 10 will reach the modulation boundary in 1988 and will remain in its vicinity for several years the

ISSN:0094-8276    

DOI:10.1029/GL013i007p00628

年代:1986

数据来源: WILEY

摘要:

A few hours after the onset of a large geomagnetic storm on September 4, 1984, energetic molecular ions in the mass range 28‐32, predominantly NO+and O2+, have been discovered in the outer ring current at L ∼ 7. The data have been obtained with the time‐of‐flight spectrometer SULEICA on the AMPTE/IRM spacecraft. We find at 160 keV/e a mean abundance ratio of the molecular ions relative to O+ions of 0.031±0.004. During quiet times no molecular ions are observed, the 1 σ upper limit of the ratio derived by averaging over several quiet periods is 0.003. The observations demonstrate the injection of ionospheric plasma into the storm time ring current and the subsequent acceleration to energies of several hundred keV on a time scale of a few hours after the onset of the magne

ISSN:0094-8276    

DOI:10.1029/GL013i007p00632

年代:1986

数据来源: WILEY

摘要:

Central plasma sheet (CPS) ion conies are oxygen dominated with peak energies ranging from tens to hundreds of eV centered around pitch‐angles between 115 and 130 degrees. Because of the lack of correlation between the CPS conics and the observed currents and/or electron beam‐like structures, it is not likely that all of these conies are generated by interactions with electrostatic ion cyclotron waves or lower hybrid waves. Instead, we suggest that the observed intense broad band electric field fluctuations in the frequency range between zero and a hundred Hz can be responsible for the transverse energization of the ions through cyclotron resonance heating with the left‐hand polarized electromagnetic waves. This process is much more efficient for heating the oxygen ions than hydrogen ions, thus providing a plausible explanation of the oxygen dominance in CPS conies. Simple algebraic expressions are given from which estimates of conic energy and pitch angle can be easily calculated. This suggested mechanism can also provide some preheating of the oxygen ions in the boundary plasma sheet (BPS) where discrete aurorae

ISSN:0094-8276    

DOI:10.1029/GL013i007p00636

年代:1986

数据来源: WILEY

摘要:

The relationship between proton temperature and momentum flux density per unit mass at 1 AU is examined using Helios 1 solar wind data from 1974 to 1980. In high‐speed plasma (V>500 km s−1)Tpincreases with increasingn0V², wheren0andTpare the density and proton temperature at 1 AU andVis the flow speed. In low‐speed plasma (V<500 km s−1),Tpdoes not increase with increasingn0V², and perhaps tends to decrease slightly. These basic relationships betweenTpandn0V² are not significantly affected by stream interactions. A qualitative explanation of these results is offered in the context of a solar wind model that includes deposition of momentum and energy extending well outward into the interplanet

ISSN:0094-8276    

DOI:10.1029/GL013i007p00640

年代:1986

数据来源: WILEY

摘要:

Plasma waves observed during the March 21, 1985, AMPTE magnetotail barium release are described. Electron plasma oscillations provided local measurements of the plasma density during both the expansion and decay phases. Immediately after the explosion the electron density reached a peak of about 4 × 105cm−3, and then started decreasing approximately as t−2.4as the cloud expanded. About 6 minutes after the explosion the electron density suddenly began to increase, reached a secondary peak of about 2.4 × 10² cm−3, and then slowly decayed down to the pre‐event level over a period of about 15 minutes. The density increase is believed to be caused by the collapse of the ion cloud into the diamagnetic cavity created by the initial expansion. The plasma wave intensities observed during the entire event were quite low. In the diamagnetic cavity electrostatic emissions were observed near the barium ion plasma frequency, and in another band at lower frequencies. A broadband burst of electrostatic noise was also observed at the boundary of the diamagnetic cavity. Except for electron plasma oscillations no significant wave activity was observed outside of the diamagne

ISSN:0094-8276    

DOI:10.1029/GL013i007p00644

年代:1986

数据来源: WILEY

摘要:

Magnetic field observations on ISEE‐1 and 2 in and near the neutral sheet about 20 Re down the near‐Earth magnetotail reveal the occurrence of structures resembling magnetic flux ropes. Both electric field and fast plasma data show that these structures convect across the spacecraft at speeds of 200 ‐ 600 km/s, and that they have scale sizes of roughly 3 ‐ 5 Re. The rope axis orientation is across the tail, approximately in the −Y GSM direction. Their magnetic structure is strikingly similar to magnetic flux ropes observed in the Venus ionosphere, and to flux transfer events observed at the dayside magnetopause. The total field‐aligned current within these ropes may approach a million amps. These structures may arise because of patchy reconnection within the plasma sheet, or may be tearing islands formed when the plasma sheet magnetic field has a cross‐tail component. Plasma sheet flux ropes are not a common feature at ISEE orbital altitudes; this suggests that near‐Earth neutral line formation within ISEE apogee (22 Re) may

ISSN:0094-8276    

DOI:10.1029/GL013i007p00648

年代:1986

数据来源: WILEY