Auroral vector electric field and particle comparisons, 1, Premidnight convection topology

Polar 3 (a Nike-Tomahawk) was launched from the Andøya Rocket Range in northern Norway on January 27, 1974. Traversing nearly 3° of latitude, the rocket crossed over a stable IBC II auroral arc in the positive bay region and continued north to a convection boundary which has been identified as the Harang discontinuity. Measurements of the complete electric field vector, of energetic electrons, and of the auroral N2+ (4278 Å) and O I (6300 Å) emissions have been used to study the convection topology in the premagnetic midnight region. The electric field was mainly northerly (about 60 mV/m south of the auroral arc and 20 mV/m or less elsewhere) over most of the flight, rotating to the west in the region of the Harang discontinuity. No evidence of large magnitude ionospheric electric fields parallel to the magnetic field was seen throughout the flight. A strong anticorrelation was observed between the electric field and the precipitating energetic electrons as the rocket passed over the auroral arc. The inverted V nature of the electron precipitations at the convection boundary, compared with the lack of such structure over the arc which was within the positive bay region, leads to the conclusion that auroral arcs are likely to be associated with inverted V type precipitation only at or poleward of convection boundaries and their eddy structures.