摘要:

The Saint‐Santin facility has been operating in its quadristatic configuration since October 1973. A set of 8 days and 7 nights (winter and equinox) ofFregion drift measurements perpendicular to the magnetic field is presented and provides information on the ionospheric electric fields. For quiet magnetic conditions the day‐to‐day variability is found to be weak, and the corresponding daily variations show the dominance of a 50 m/s diurnal oscillation in east‐west drifts and of a 15–20 m/s terdiurnal oscillation in north‐south drifts. None of the presently available models of quiet time electric fields have been found to reproduce this data over 24 hours. Comparison with other mid‐ and low‐latitude electric field results shows a rather good agreement with incoherent scatter results south of Saint‐Santin but a strong contrast with Millstone Hill results despite comparable geographic latitudes. For disturbed magnetic conditions, perpendicular drift velocities appear displaced from their quiet day values with a tendency to westward deviations. On some occasions those displacements reach large values of 100 m/s (4 mV/m electric field) and more over 1 or 2 hours. An interpretation in terms of penetration of the plasmasphere by electric fields associated with magnetospheric subst

ISSN:0148-0227    

DOI:10.1029/JA082i001p00087

年代:1977

数据来源: WILEY

摘要:

Measurements of the location of sources of terrestrial kilometric radiation obtained with the lunar‐orbiting Radio Astronomy Explorer 2 satellite have revealed a class of emission associated with the cusp and dayside magnetosheath. At frequencies near 250 kHz this emission is observed at radial distances between 2 and 20REat magnetic latitudes of 75°–80° and is most often detected during periods of auroral activity (AE≳ 250) and southward orientation of the interplanetary magnetic field vertical component. During very disturbed times the emission at the lowest frequencies (≲200 kHz) appears to come from the dayside magnetosheath at distances of ≳12RE. Whenever the geomagnetic dipole is tilted significantly with respect to the ecliptic pole (≳10°), the cusp emission is confined to the hemisphere containing the subsolar point. The measurements also suggest that the region of cusp emission is rather narrowly confined in longitude to within a few hours of the

ISSN:0148-0227    

DOI:10.1029/JA082i001p00098

年代:1977

数据来源: WILEY

摘要:

Equations are derived which govern modulation of a continuous wave whistler mode transmission by gyroresonant electrons in a region limited in spatial extent. This model is similar to that used to explain the qualitative features of discrete VLF emissions in the geomagnetosphere. It is found that nonlinear wave‐particle interaction results in amplitude modulation of the wave. An integral equation is then derived for the amplitude of the signal leaving the region. Numerical solutions of this equation for a loss cone electron distribution and for parameters typical of the geomagnetosphere atL= 3 result in quasi‐periodic pulsations in the amplitude for sufficiently high densities of resonant electrons. The frequency of these pulsations is in the several‐hertz range, consistent with observations. Similarities of and differences between these calculations and previous theoretical studies of ‘key‐down’ transmissions ar

ISSN:0148-0227    

DOI:10.1029/JA082i001p00105

年代:1977

数据来源: WILEY

摘要:

Relativistic electron precipitation spikes have been observed in the quasi‐trapped population at mid‐latitudes (L≈ 3.5–4.5). The spike electrons are not in the local loss cone but precipitate into the atmosphere upon drift in longitude. In these spikes, often as narrow as 0.3° in invariant latitude, the fluxes of electrons ≳4 MeV may undergo pronounced enhancements, whereas the intensities of electrons in the few hundred keV range may not be significantly affected. This energy selectivity in the formation of the spikes is perhaps more suggestive of wave‐particle interactions, such as the Thorne and Kennel (1971) mechanism for the scattering of relativistic electrons by Doppler‐shifted ion cyclotron waves, rather than of changes in the magnetic field topology. The data were taken from the low‐altitude (∼750 km) polar‐orbiting satellite (1972–076B) with an array of several electron detectors having widely differing geometric factors and energy ranges of response. Energy spectra and pitch angle distributions were measured over the energy range 160 keV to 2.4 MeV with a combination of three spectrometers. Fluxes of energetic (>4 MeV) electrons were measured with a high sensitivity in each of two large (∼3.4 kg) plastic scintillator anticoincidence counters surrounding

ISSN:0148-0227    

DOI:10.1029/JA082i001p00117

年代:1977

数据来源: WILEY

摘要:

It is observed that blanketing type sporadicElayers in the equatorial electrojet region often give rise to strong backscattering of 55‐MHz radar signals. The Doppler spectra of the backscatter signals also show that the drift speeds of the irregularities are small at these times (in comparison to midday values) and that they cannot sustain gradient instabilities of 2.7 m with the normalEregion electron density gradients. It is inferred from these observations that gradient instabilities of 2.7 m are generated at the sharp edges of the thinEslayers even under the conditions of small electric fields. However, the gradient instabilities are observed to disappear close to the time of the electric field reversal. It is further observed that the initial formation of theEslayers takes place only at such times when the drift velocities are small. This observational result and theoretical considerations suggest that the formation ofEslayers in the electrojet region is inhibited by strong vertical drifts. This inhibiting factor and a probable diurnal variation of the ion convergence source result in the formation of blanketingEslayers in the equatorial electrojet region over Trivandrum predominantly in the late afternoon hour

ISSN:0148-0227    

DOI:10.1029/JA082i001p00125

年代:1977

数据来源: WILEY

摘要:

Singly ionized atomic oxygen, O+, was detected in the streaming plasmas within the earth's magnetotail at geocentric radial distances ∼35RE. These measurements were gained with a sensitive electrostatic analyzer on board the earth satellite Imp 7. Identification of the O+ions was possible via distinct and persistent secondary maxima in the energy‐per‐unit‐charge spectra of positive ions. Typical density ranges for H+and O+ions were 1–10 cm−3and 10−3–10−2cm−3, respectively. The plasma bulk flows were ∼200–300 km s−1and were directed generally tailward. Corresponding O+fluxes in the magnetotail were ∼105(cm² s)−1and imply O+upward fluxes in the upper ionosphere of ∼108(cm² s)−1. The kinetic energy of the O+ions is ∼ 1–5 keV. Estimates of the global escape of

ISSN:0148-0227    

DOI:10.1029/JA082i001p00129

年代:1977

数据来源: WILEY

摘要:

During periods of geomagnetic disturbances, VLF emissions and enhancements of low‐energy electrons are simultaneously observed by the equatorial orbiting S³‐A (Explorer 45) satellite. These events are characterized by the following features. (1) The VLF emissions occur outside the plasmasphere in the nightside of the magnetosphere. (2) The VLF emissions consist of two frequency regimes, one below the local electron gyrofrequencyfgand the other abovefg. (3) The VLF emissions belowfgare relatively broadband whistler mode waves characteristic of chorus and frequently have a conspicuous band of ‘missing emissions’ nearfg/2. (4) The emissions abovefgare electrostatic and typically have components near 3fg/2. Occasionally, higher‐frequency components are also observed. (5) The onset of the emissions coincides with abrupt increases outside the plasmasphere (L≳ 4) in 1‐ to 10‐keV electrons to intensities of the order of 108el cm−2s−1sr−1keV−1. Less pronounced enhancements sometimes occur for electrons with energies as high as 70 keV. (6) The cessation of the emissions coincides with a drop in the electron intensities to their preenhancement levels, which are of the order of 106el cm−2s−1sr−1keV−1or less. This drop in low‐energy electron intensities occurs before or when the satellite crosses the plasmapause back into the plasmasphere. These observed features indicate that the VLF emissions are produced by low‐energy (1‐ to 10‐keV) electrons which penetrate into the dusk‐midnight sector of the magnetosphere from the geomagnetic tail during magnetic storms and substorms and drift eastward outside the plasmasphere. In this paper, events observed during geomagnetically disturbed periods in De

ISSN:0148-0227    

DOI:10.1029/JA082i001p00135

年代:1977

数据来源: WILEY

摘要:

The self‐consistent theory of the magnetotail is extended from two dimensions to three. An asymptotic solution for small variation of the field quantities in the direction perpendicular to the normal of the neutral sheet is obtained in closed form. An attempt is made to match the remaining parameters to observational data. The theory contains a number of structural properties of the tail that were not available in the earlier two‐dimensional model, such as the solar magnetosphericycomponent of the magnetic field, tail flaring and plasma sheet variation in theydirection, and field‐aligned cur

ISSN:0148-0227    

DOI:10.1029/JA082i001p00147

年代:1977

数据来源: WILEY

摘要:

A rocket‐borne experiment package was launched over a structured auroral arc from Poker Flat, Alaska, at 0722 UT on February 25, 1972. The results of the flight vector magnetometer data have been detailed by Casserly and Cloutier (1975), who report the detection of a pair of oppositely directed Birkeland current sheets associated with the auroral band. This association has now been extensively investigated, and it has been shown that some observed structures in the arc due to the presence of a fold are also evident in the Birkeland current system. In particular, the field‐aligned current to the east of the fold is at a higher geomagnetic latitude than the current to the west of the fold. Variations in other model current parameters are also shown to be well correlated with changes in the visual arc sys

ISSN:0148-0227    

DOI:10.1029/JA082i001p00155

年代:1977

数据来源: WILEY

摘要:

Over 50 DMSP auroral photographs of bright extended quiet arcs have been analyzed by the method of Holzworth and Meng (1975). An off center circle in corrected geomagnetic‐MLT coordinates is found to be the best fit to these quiet arcs. Several different mathematical methods are used to verify that such an off‐center circle fits the quiet auroral distribution within an accuracy of less than 0.5° in lati

ISSN:0148-0227    

DOI:10.1029/JA082i001p00164

年代:1977

数据来源: WILEY