ELECTRODYNAMICS OF THE PLASMA FLOW REVERSAL IN THE LATE EVENING AURORAL OVAL

Electric and magnetic field measurements taken by two Nike-Tomahawk sounding rockets, launched from Andoya, Norway in early 1977 into the late evening auroral oval, are presented. Flight 18.1005, launched into quiet magnetic conditions, passed over a quiet auroral arc and over a region of plasma flow reversal. The flow reversal was interpreted as the Harang discontinuity. The second flight, 18.1004, was launched into a breakup aurora and through the westward electrojet. Horizontal current strengths were inferred from dc magnetic field measurements and calculated from the measured dc electric field and calculated conductivities for both flights. The calculated currents disagreed with the magnetic field measurements. The disagreement was larger for flight 18.1004, supporting the conclusion that neutral winds play a role in driving horizontal currents. A major emphasis was placed on the performance of the tri-axial fluxgate magnetometer as compared to the proton precession magnetometer. It was shown that northward and vertical magnetic field components could be obtained with some difficulty, but that determination of the eastward component was not possible. Suggestions for the improvement of the tri-axial fluxgate's capabilities are presented.