摘要:

Data from ISEE 3, Helios A, and Helios B were used to identify the components of two compound streams and to determine their configurations. (A compound stream is a stream which has formed as a result of the interaction of two or more distinct fast flows.) In one case, ejecta containing a magnetic cloud associated with a disappearing quiescent filament were interacting with a corotating stream. In the second case, ejecta containing a magnetic cloud associated with a 2B flare were overtaking ejecta from a different source. Each of these compound streams produced an unusually large geomagnetic storm, on April 3, 1979, and on April 25, 1979, respectively. The largest geomagnetic storm in the period 1968–1986, which occurred on July 13, 1982, was associated with a compound stream. Thirty geomagnetic storms withAp>90 occurred between 1972 and 1983, and there are interplanetary magnetic field and plasma data for 17 of these events. The data suggest that most large geomagnetic storms are associated with compound streams and/or magnetic cloud

ISSN:0148-0227    

DOI:10.1029/JA092iA06p05725

年代:1987

数据来源: WILEY

摘要:

A two‐dimensional model of the ionosphere of Venus has been constructed by expanding pertinent quantities in Legendre polynomials. The model is simplified by including only a single ion species (O+). Horizontal plasma flow velocity and plasma density have been calculated as a coupled system. The calculated plasma flow velocity is found to be in good agreement with observations and the results of earlier studies. Solar zenith angle dependence of plasma density, particularly on the nightside, shows some features which differ from results of earlier studies and observed values. Effects of raising or lowering the ionopause height and changing the nightside neutral atmosphere have been discusse

ISSN:0148-0227    

DOI:10.1029/JA092iA06p05735

年代:1987

数据来源: WILEY

摘要:

The analysis of in situ plasma electron observations in the Io plasma torus by the plasma science experiment during the Voyager 1 encounter with Jupiter is presented in terms of two components: a thermal (c) Maxwellian component and suprathermal (H) non‐Maxwellian component of the electron distribution function. Average electron temperatures areTe<1 eV in the cold torus (L<5.5), withTe≃ 5–6 eV in the hot torus (5.5

ISSN:0148-0227    

DOI:10.1029/JA092iA06p05741

年代:1987

数据来源: WILEY

摘要:

Pioneer 11 and Voyager 1 and 2 magnetic field measurements over the entire flyby of Saturn's magnetic field have been analyzed by fitting a magnetospheric dipole field (i.e., a dipole field plus the field due to currents in the magnetopause), higher moments of the internal field aligned with the dipole along the rotation axis, and the field due to an equatorial sheet current to the magnetic measurements. We find that a dipole moment of 21,431 nTRs³, a quadrupole moment of 2403 nTRs4, an octopole moment of 2173 nTRs5, and an equatorial sheet current of half thickness 2.0Rsfrom about 5Rsto the solar edge of the magnetopause fit the measurements over the entire magnetosphere with a root mean square deviation of 3.2 nT. (Rsis the planet radius, 66,330 km). The primary feature of our analysis is the explicit inclusion of the calculated magnetopause current field, which reduces the overall root mean square deviation over the entire flyby from σ values of 4.7 and 5.9 nT using previous models to 3.2 nT using our

ISSN:0148-0227    

DOI:10.1029/JA092iA06p05763

年代:1987

数据来源: WILEY

摘要:

An unexpected occurrence following the second lithium release by the AMPTE‐IRM spacecraft in the solar wind on September 20, 1984, was the appearance of electron cyclotron harmonic emissions. These emissions began about 50 s after the release and continued for several minutes. Narrow‐band emissions polarized perpendicular to the magnetic field with amplitudes of approximately 10−5V m−1were observed in each of the first five harmonic bands. Unpolarized diffuse emissions were also present at the same time. The diffuse emissions extended from below the lowest measured frequency channel to above the highest narrow‐band emission with a maximum below the electron cyclotron frequency. It will be shown that these observations are inconsistent with their generation by several ion beam inst

ISSN:0148-0227    

DOI:10.1029/JA092iA06p05768

年代:1987

数据来源: WILEY

摘要:

The barium releases in the magnetotail during the Active Magnetospheric Particle Tracer Explorers (AMPTE) operation were monitored by ground‐based imagers and by instruments on the Ion Release Module. After each release, the data show the formation of a structured diamagnetic cavity. The cavity grows until the dynamic pressure of the expanding ions balances the magnetic pressure on its surface. The magnetic field inside the cavity is zero. The barium ions collect on the surface of the cavity, producing a shell. Plasma irregularities form along magnetic field lines draped over the surface of the cavity. The scale size of the irregularities is nearly equal to the thickness of the shell. The evolution and structuring of the diamagnetic cavity are modeled using magnetohydrodynamics theor

ISSN:0148-0227    

DOI:10.1029/JA092iA06p05777

年代:1987

数据来源: WILEY

摘要:

The stability analysis of two‐dimensional current‐carrying plasmas by use of statistical mechanics is described. This method is applied to a self‐consistent model configuration of the earth's magnetotail. The equations derived are solved analytically, and the results are discussed in view of spontaneous onset of magnetospheric act

ISSN:0148-0227    

DOI:10.1029/JA092iA06p05795

年代:1987

数据来源: WILEY

摘要:

Broadband electrostatic noise (BEN) is commonly observed in the plasma sheet boundary layer in association with ion beams. Here we investigate the generation of these waves in a plasma consisting of an ion beam and a background of hot ions, hot electrons, and cold electrons. The cold electrons are of ionospheric origin. A complete, systematic study of electrostatic ion beam instabilities, including cold electrons, has been done, and it is shown that for the plasma configuration described, four instabilities can be excited. These are the (1) ion acoustic, (2) Buneman, (3) beam resonant, and (4) electron acoustic instabilities. A low and high beam temperature division is shown to exist that separates when different instabilities can be excited. For typically observed parameters in the plasma sheet boundary layer, the ion beams lie in the high‐temperature regime. In this regime, the beam resonant and electron acoustic instabilities are excited, and these instabilities can account for the high‐frequency (>500 Hz), low‐power portion of the BEN spectrum. In the absence of cold electrons, no such wave growth o

ISSN:0148-0227    

DOI:10.1029/JA092iA06p05807

年代:1987

数据来源: WILEY

摘要:

Russell and Elphic (1979) suggested the possibility that flux transfer events (FTEs) generate long‐period micropulsations in the outer, dayside magnetosphere. We examine the reasons for this hypothesis and present results of two pulsation surveys designed to test it. In the first survey, observations of micropulsations by GOES 2 are compared with ISEE 3 and IMP observations of interplanetary magnetic field (IMF) direction; since FTEs are highly correlated with southward IMF, we looked for a similar correlation between pulsations and southward IMF. In the second survey a catalogue of ISEE 1 and 2 magnetopause crossings is compared with magnetometer readings from GOES 2 and 3 to determine whether Pc 4 and Pc 5 pulsations are more likely to occur after FTEs have taken place. Our results indicate that there is a correlation between FTEs and transversely polarized Pc 4 pulsations with periods between 60 and 120 s but not between FTEs and Pc pulsations with periods greater than 120 s. This suggests that the generating (or driving) frequency associated with FTEs lies between 60 and 120

ISSN:0148-0227    

DOI:10.1029/JA092iA06p05820

年代:1987

数据来源: WILEY

摘要:

The AMPTE IRM wave instrument has been applied to the study of flux transfer events (FTE's). This initial investigation concentrates on FTE's observed in the magnetosphere during the fall of 1984. The wave morphology consists of four significant features: at frequencies below the ion gyrofrequency, magnetic fluctuations occur with amplitudes of the order of 1 nT; at frequencies from a few hertz to a few hundred hertz, electric field fluctuations are observed which have a broadband amplitude of a few millivolts per meter, which are perpendicularly polarized at the lowest frequencies, and which are partly electrostatic and partly electromagnetic; in the frequency range from 100 Hz to 10 kHz, broadband spikelike waves occur with a time‐averaged amplitude of about 0.1 mV/m; and near the electron plasma frequency, bursts of waves occur at the boundaries of FTE's. In none of the 25 events surveyed does the total broadband amplitude of all the waves exceed a few millivolts per meter, an amplitude far too small to provide the dissipation required by “traditional” reconnection models in which the dissipation region has a thickness the order of an ion gyroradius. Thus, either all of the FTE's are observed at some distance from the diffusion region, or the observable waves play no significant role in the diffusion process, or “traditional” reconnection models do not apply to reconnection

ISSN:0148-0227    

DOI:10.1029/JA092iA06p05827

年代:1987

数据来源: WILEY