ELF wave production by an electron beam emitting rocket system and its suppression on auroral field lines: Evidence for Alfven and drift waves

Abstract

ELF electric disturbances in the frequency range from DC to 1 kHz produced in the auroral ionosphere by the injection of powerful electron beams have been studied by orthogonal probes on a free‐flying plasma diagnostics payload. Frequency spectrograms have been produced for various pitch angles, pulsing characteristics and other properties of the injected beams. The large‐scale DC ionospheric convection electric field has also been measured, as well as the auroral particle precipitation, the visual auroral forms and the ionospheric parameters. The convection field was strongly attenuated as the experiment system moved northward across discrete arcs but recovered to a higher value north of the arcs where the particle precipitation ceased. The production of ELF waves by beam injection was also strongly reduced in the arcs, and like the DC field, recovered to an even greater intensity north of the arcs. This behavior did not extend into the lower hybrid or whistler mode region. The DC field decrease has been explained by the high Pederson conductivity caused by auroral electron precipitation in the E‐region below the vehicle. It is postulated that the observed ELF waves are in the Alfven and drift modes and are generated by the positive vehicle potential during beam injection. More effective vehicle neutralization in the auroral arcs lowers the vehicle potential and, therefore, reduces wave production. Most features of the experimental observations can be qualitatively explained by this mechanism.