O-Mode Emission at the Io Torus: A Real or Virtual Source?

Abstract

We examine the nature of an ordinary (o-mode) emission observed near the Io plasma torus during the 1992 Ulysses encounter with Jupiter. The emission appears to intensify by factors of 10-100 in local torus density depletions. We examine whether these intensifications are due to local generation within the density depletion or reflection of a remotely generated emission. Based on the observed emission spectra, we find that a virtual source is most consistent with the character of the local enhancements. This virtual source observation near the dense torus may be relevant to the understanding of a newly discovered torus-related hectometric emission by the Galileo orbiter.