摘要:

An electric noise component with anf−1spectrum is observed with the SBH radioastronomy receivers on ISEE 3 at frequencies lower than the plasma frequencyfp. On theZantenna (electrical length for long waves is 7 m) this component is 5–10 times more intense than the predicted thermal noise level. Its spectral density is proportional tofpf−1(Tc)1/2, whereTcis the core electron temperature andfis the observing frequency. On theSantenna (90 m tip to tip) the new component is much weaker and most probably represents the high‐frequency part of a noise spectrum found by Kellogg (1981) with an antenna of the same length. This author interpreted it as mostly due to electron acoustic waves and Doppler shifted ion acoustic waves, but this interpretation has not been confirmed by more accurate calculations (Couturier et al., 1982). Kellogg's spectrum also shows anf−1frequency dependence and, if extrapolated assuming the same law as for theZantenna, approximately fits ourSantenna observations. TheSantennaf−1noise is deeply spin modulated with the minimum electric field in the direction of the solar wind flow as seen in the spacecraft frame of reference. The modulation factor decreases with increasing frequency, becomes negligible when the new component intensity becomes negligible as compared with thermal noise, and increases with the solar wind velocity. Thef−1component shows some of the properties which are expected from shot noise (direction of minimum intensity) but its spectral index is −1 while shot noise is supposed to show a sp

ISSN:0148-0227    

DOI:10.1029/JA087iA11p09025

年代:1982

数据来源: WILEY

摘要:

An interplanetary shock wave that was produced by a solar eruption and its associated coronal transient on May 8, 1979, has been ‘tracked’ through interplanetary space to a rendezvous 2 days later with Venus. The interaction of the shock wave with the ionospheric obstacle at Venus produced a significant compression of the dayside ionosphere. It is believed that the tracking, as it were, was accomplished for the first time via the diagnostic observations provided by Hα and white light imagery near the sun and the plasma and field measurements of two, nearly radially aligned, spacec

ISSN:0148-0227    

DOI:10.1029/JA087iA11p09035

年代:1982

数据来源: WILEY

摘要:

In June 1979 the Pioneer Venus orbiter made its first series of passes through the distant solar wind wake of Venus at distances of 8–12Rvbehind the planet. During this period the plasma analyzer aboard the spacecraft detected disturbed magnetosheath plasma that intermittently disappeared and reappeared, suggesting a tattered, filamentary cavity trailing behind the planet. The magnetosheath dropouts almost always occurred inside the region of ‘magnetotail’ observed by Russell et al. Sporadic bursts of energetic ions (E/q≳ 4 kV) are detected inside and, occasionally, outside the magnetotail; all such bursts are consistent with identification of the ion as O+of planetary origin moving at the local magnetosheath flow speed. The morphology of the plasma dropouts and of the O+bursts is analyzed in detail. The cavity appears to contract at times of high solar wind dynamic pressure. The intensity of the O+component is highly variable, and appears not to be strongly correlated with solar wind dynamic pressure. The most intense bursts correspond to a flux ≲107ions cm−2s−1. This maximum flux, if steady and filling a cylinder 1Rvin radius would correspond to a mass loss rate of ≲1025ions s−1; the intermittency and variability of the flux suggest that the true mean loss rate is very much lower. The kinetic temperature of the O+component is estimated as 105–106K in

ISSN:0148-0227    

DOI:10.1029/JA087iA11p09045

年代:1982

数据来源: WILEY

摘要:

A quantitative model of geomagnetic activity is developed and utilized to investigate the causes of the diurnal, seasonal, and IMF sector variations in theALindex records. This auroral index was chosen for study because of its high sensitivity to the strength of the westward electrojet and, hence, magnetospheric substorm activity. After the introduction of corrections for processes not related to substorms, ability of the functionBs0.85V² to produce the observed variations inALwas examined. The annual variation ofBswas determined by superposing the contributions toBsdue to the inclination of the magnetic axis (Russell and McPherron, 1973) on an empirical mean distribution ofBz.Vwas assumed constant. The predicted values ofALchave been compared with observed averages for 9 years of solar cycle 20. The predicted annual variation ofALcfor toward and away sectors are in good agreement with observation. While the predicted semi‐annual component ofALcis in phase with observation, it is less than half the observed amplitude. The predicted diurnal variation ofALcfor June is in satisfactory agreement with observati

ISSN:0148-0227    

DOI:10.1029/JA087iA11p09054

年代:1982

数据来源: WILEY

摘要:

ISEE 1 observations of the plasmapause are compared with simultaneous observations of the electron plasma sheet and also the auroral oval observed in DMSP photographs. Only a limited amount of appropriate data was available for the comparisons: the plasmapause/plasma sheet inner edge comparisons were restricted to the early and late morning sectors, while there were two satisfactory comparisons of the plasmapause and the equatorward boundary of the auroral oval in the evening sector. However, these examples indicate that the plasmapause location often coincides to within ΔL∼ 0.1–0.2 with both the plasma sheet inner boundary and the field line threading the equatorward boundary of the auroral oval. This co‐location of the plasmapause and the plasma sheet inner edge may be due to shielding of the magnetospheric convection electric field by an Alfvén layer located at the inner edge of the plasma sheet as discussed by Jaggi and Wolf (1973) and

ISSN:0148-0227    

DOI:10.1029/JA087iA11p09059

年代:1982

数据来源: WILEY

摘要:

It is shown that in the post‐noon quadrant, the combination of field‐aligned Currents associated with the eastward auroral electrojet and polar cap currents produces a magnetic field perturbation pattern on the ground and at TRIAD altitude (800 km) in good agreement with observations. This model permits downward net field‐aligned current flow across the post‐noon sector auroral oval while at the same time replicating the observation of a sharp level shift in the east‐west component of the magnetic perturbation field at 800‐km altitude attributed, until now, to net upward field‐aligned current. These results reconcile the contentions of Hughes and Rostoker (1977, 1979) that there is net downward field‐aligned current across the post‐noon auroral oval and of Sugiura and Potemra (1976) that the net current flow in the post‐noon

ISSN:0148-0227    

DOI:10.1029/JA087iA11p09071

年代:1982

数据来源: WILEY

摘要:

A large ion composition data set consisting of 1‐month averages has been assembled for the energy per charge range 0.9–15.9 keV/e. It includes 48 months of data taken by the Ion Composition Experiments on the ESA/GEOS 1 and 2 satellites at or near geostationary orbit. Data were obtained during the rising and maximum phases of the current solar cycle from May 1977 through November 1981 inclusive. Five ion species are routinely identifiable: H+, He++, He+, O++, and O+, above a limiting density ∼10−3ions cm−3. Ion densities exhibit a number of very striking statistical correlations with one another and with bothKpand solar EUV as measured byF10.7. One principal result is that increases in the densities of magnetospheric He+, O++, and O+are observed that are apparently due entirely to increased solar EUV fluxes associated with the rising phase of the current solar cycle. There is a marked rise in O+density by a factor of ∼8 with increasing geomagnetic activity, but no corresponding increase in either He+or O++and only a small increase in H+. The He++/H+ratio is found to be remarkably constant at ≈0.01. Contrary to ion density results, little or no variation is found in mean energy. These observations are interpreted in terms of the composition and dynamics of two sources of magnetospheric plasma: the solar wind and the high‐latitude top

ISSN:0148-0227    

DOI:10.1029/JA087iA11p09077

年代:1982

数据来源: WILEY

摘要:

The ISEE 2 plasma experiment data are used to investigate the properties of the O+ions streams flowing in the earth's magnetotail low latitude boundary layer and northern plasma lobe. The E × B filter is seen to be the organizer of the flow of these ions, after their acceleration in the topside ionosphere. Between XSE=−15 REand −23 REthe velocity of the O+ions is a function of the distance from the center magnetotail axis, the slower flowing closer to this and the faster closer to the magnetopause. The O+stream density is observed to vary with this distance as well. The temperature of the streaming ions is shown to be anisotropic with respect to the ambient magnetic field; a generally unresolved narrow conic pitch angle distribution of the O+ions is suggested to be the cause of this anisotropy. The properties of the O+ions are shown to be consistent with an acceleration mechanism, or a combination of mechanisms, that act orthogonally and parallel to the magnetic f

ISSN:0148-0227    

DOI:10.1029/JA087iA11p09097

年代:1982

数据来源: WILEY

摘要:

To understand observed structure and growth patterns of geostationary Alfvén/ion cyclotron waves, the properties of the hot proton cyclotron instability within a helium rich plasma are explored here. This exploration proceeds with an examination of the net linear wave amplifications that result as a wave propagates through the magnetic gradients of a realistic magnetic field model (linearity is discussed and justified). By taking care in generalizing a single pass model to a multiple pass system, the following conclusions have been reached: (1) The basic structure of the frequency gap that is observed close to the helium cyclotron frequency can be explained by the ‘stop‐gap’ dispersion effect; however, the helium cyclotron resonance effect contributes to the gap formation leading to He+ion energization. (2) The presence of the magnetic gradients virtually insures that helium ion energization (by means of the low frequency wave branch only) is the inevitable consequence of the wave generation process. (3) The energized helium ions will sparsely populate a broad range of geomagnetic latitudes (±15 degrees) but will be concentrated strongly within several (2–4) degrees of the geomagnetic equator. (4) The presence of low percentages of helium ions is most likely to suppress the wave generation process (ATS 6 satellite observations support this conclusion for a portion of the wave

ISSN:0148-0227    

DOI:10.1029/JA087iA11p09107

年代:1982

数据来源: WILEY

摘要:

During the periods after the maximum phase of geomagnetic storms on 2 April 1972 a broadband VLF emission burst has been observed by the equatorially orbiting satellite S³‐A (Explorer 45) along its inbound plasmapause crossings. The frequency band broadening takes place just outside of the nighttime plasmasphere, where the density of cold plasma has been known to be very low during the later phase of a geomagnetic storm. Instead of the gradual broadening of several hours duration, a burst type broadening of VLF emission lasting less than ten minutes was observed in the similar location. The magnetic field component of this emission is very weak and the frequency spreads below the local half electron cyclotron frequency. Corresponding enhancement of the anisotropic ring‐current electrons is also very sudden and limited below the order of 10 keV without significant velocity dispersion, in contrast to the gradual broadening events. The cause of this type of emission band spreading can be attributed to the generation of the quasi‐electrostatic whistler mode emissions of short wavelength by hot bi‐maxwellian electrons surging into the domain of relatively low density magnetized cold plasma. The lack of energy dispersion in the enhanced electrons indicates that the inner edge of the plasma sheet, the source of these hot electrons, is not far from the location of th

ISSN:0148-0227    

DOI:10.1029/JA087iA11p09120

年代:1982

数据来源: WILEY