ISEE 1 and 2 observations of an oscillating outward moving current sheet near midnight

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Abstract
An outward moving current sheet is examined with the ISEE 1 and 2 magnetometers. It is found that the current sheet is moving outward with a velocity of about 17 km/s, a thickness of about 1300 km, and with the current flowing into the ionosphere. Oscillations observed in the magnetic field profile indicate the presence of a wave traveling along the current sheet from midnight toward the east with a velocity of 400 km/s. The oscillations of the plasma normal to the current sheet associated with this wave are sufficient to explain the amplitude of the electric field oscillations in the plane of the current sheet observed by the University of California‐Berkeley (UCB) electric field detector. In addition a strong electric field is observed normal to the sheet, corresponding to a flow along the sheet of 400 km/s, which is consistent with the velocity of the wave deduced from the intersatellite timing of the oscillations. Thus the wave is stationary in the frame of the current sheet plasma. This oscillating current sheet model explains the observed behavior of both the magnetic and electric field observations. The potential drop across the current sheet was very large at this time, 41±26 kV, and is comparable to the total normal potential drop across the polar cap.