Structure of the magnetopause at 6.6<i>R_E</i>in terms of 50- to 150-keV electrons

Abstract

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.