Magnetosphere boundary observations along the Imp 7 orbit. I - Boundary locations and wave level variations

The paper is concerned with magnetosphere boundary phenomena observed by the Imp 7 magnetic field, plasma, and plasma wave instruments in 1972 and 1973. Boundary locations for a 15-month period are surveyed, and the different types of crossings are described. The spacecraft crosses the dawn and dusk boundaries near 25 earth radii downstream, and the physical processes at the Imp 7 magnetopause appear to be intermediate between those observed over the poles and those observed at the lunar orbit. The Imp 7 orbit also traverses a downstream region near where 'fireball' phenomena occur. Electromagnetic wave modes detected in the broad low-frequency channel of the wave instrument are analyzed, and the interpretation of data of this type suggests that the broad low-frequency channel is sensitive to oscillations in the lower hybrid resonance region of the spectrum.