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.