From a statistical study of 500‐ to 1000‐kev electrons at synchronous orbit, it is concluded that near local midnight there exists a ‘fault line,’ west of which substorms are accompanied by geomagnetic inflation and east of which they are accompanied by collapse. Published studies have shown that the large, transient, substorm‐associated fluxes of 50‐ to 150‐kev electrons observed at synchronous orbit are produced near local midnight and subsequently drift longitudinally to other local times. A study of these lower‐energy electron spikes and the concurrent geomagnetic data indicates that the electrons are produced during and within the geomagnetic collapse. Using measured magnetic data, it is concluded that the collapse is an inward convective surge of field lines with an average convective velocity estimated at 0.5 RE/min. Magnetotail plasma particles of initial energies up to 10‐20 kev are convected inward and energized tenfold; protons drift longitudinally westward (producing the observed evening inflation, and perhaps establishing a partial ring current), and electrons drift eastward. The model proposed is similar in many respects to others already proposed. However, our model exhibits the asymmetric inflation and collapse behavior about the fault line shown by observations at synchronous orbit.

This paper presents preliminary results of measurements of 50 to 1000 keV electrons at the geomagnetic equator at 6.6 Re. Quiet‐day electron fluxes exhibit a diurnal dip in intensity at local midnight accompanied by a softening of the electron spectrum. During geomagnetically disturbed times the 50 to 150 keV electrons exhibit large fluctuations in intensity; we have denoted these fluctuations as “spikes.” These spikes are largest just after local midnight and decrease in intensity as local time increases. They have a duration of about 1 hr and tend to recur with about a 2‐hr period. The electron spectrum softens considerably during the spikes. Generally the variations in intensity of the electrons correlates excellently with the Kp index.

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During magnetically disturbed times, large intensity variations are observed for electrons of energies 50· to 150-ke V at the geostationary orbit of the ATS-1 satellite. Simultaneously, the correlation experiment at the magnetic conjugate region of the satellite has shown that large fluxes of brems· strahlung X-rays from precipitated energetic electrons are observed on high-altitude balloons while magnetic bays are recorded on the ground. The conclusion reached is that the magnetospheric substorm is responsible for the simultaneous intensification of the trapped particle population at 6.6 · R, equatorial plane and of precipitated energetic electrons at the magnetic conjugate region.

Measurements were made with a magnetic deflection electron spectrometer of electrons in the range 50–150 kev at the boundary of the magnetosphere on January 14, 1967. At this time, the magnetopause was compressed inside the orbit of the ATS 1 geostationary satellite, which was located at 6.6 RE in the subsolar region of the magnetosphere. The first crossing of the trapping boundary and magnetic field reversal was followed by many transient count rate increases and magnetic field variations. Owing to the rapid sampling of electrons on the spinning satellite it was possible to determine the azimuthal distribution associated with electron concentration gradients at the various boundaries and to determine the direction in space of the gradients and of the trapping boundary surfaces. In one case the trapping boundary was found to be approximately perpendicular to the earth's surface. In another case a transient region was found that appeared to be moving over the spacecraft from the solar direction. The energetic electron trapping boundary was usually separated from the magnetic field reversal by the order of four cyclotron radii. The electron flux dropped from 1.4 × 104 to 3.2 × 10² (electrons cm−2 sec−1 ster−1 kev−1) in two cyclotron radii at one of these boundaries.