Io plasma torus and the source of jovian kilometric radiation (bKOM)

Abstract

One of the many discoveries by Voyagers 1 and 2 during their flyby of Jupiter was the detection of radio emission at kilometric wavelengths1,2 in the frequency range 20–500 kHz. Broadband jovian kilometric radiation bKOM was observed to be beamed away from the zenomagnetic equatorial plane, the beaming angle increasing with increasing frequency1–3. It was suggested that bKOM is created by the linear conversion of electrostatic upper hybrid waves to electromagnetic waves in the density gradients at the lo torus4. The beaming is inherent to the conversion mechanism and depends on the characteristic frequencies of the source plasma. Here I present results, based on this theory, of remote sensing of the lo torus using bKOM observed by Voyager 2 when inbound towards Jupiter. The density profiles obtained are in remarkable agreement with measurements of the torus densities obtained in situ by Voyager 1. This seems to provide very strong evidence that bKOM is produced at the lo torus by the linear mode-conversion mechanism and indicates that the technique used for remote sensing could be a powerful method of determining the torus characteristics when no in situ measurements are available.