Ulysses observations of auroral hiss at high Jovian latitudes

Abstract

During the Ulysses flyby of Jupiter, a whistler‐mode emission was periodically detected by the Unified Radio and Plasma wave (URAP) experiment during intervals when the spacecraft extended to high magnetic latitudes. The signal was detected between the local electron plasma frequency and lower hybrid resonance and appears as a funnel‐shaped structure on frequency‐versus‐time spectrograms; these characteristics are very reminiscent of whistler‐mode auroral hiss observed at high latitudes at Earth. Ray tracing of the emission occurrences suggests the emission source is on magnetic field lines extending out to at least 65 RJ. This location associates the emission with the boundary between open and closed field lines — not the Io torus. The emission radiates about 107 W of power. Consequently, the auroral input power derived from the solar wind to drive the emission is believed to be 1010‐12 W (or about 1% of the energy associated with Io torus electrical processes).