Radio wave emission from the IO torus

Abstract

A theory is proposed to explain radio wave emissions observed by the Voyager spacecraft to have their source in Jupiter's inner magnetosphere. The emissions, termed Jovian kilometric radiation (JKR), are proposed to come from the Io plasma torus - a region of enhanced plasma density circling the planet at the orbit of Io. It is suggested that intense upper-hybrid waves, known to exist at the zenomagnetic equator, couple to the L-O magnetoionic mode at the plasma frequency. In order to produce the observed wave polarisation it is necessary to invoke a distended plasma torus, and ray tracing in a realistic Jovian magnetosphere shows that many characteristics of JKR can be explained by this theory.