Galileo evidence for rapid interchange transport in the Io torus

Anomalous plasma signatures were detected by the Galileo particles and fields instruments during the initial transit through the Io torus. These unusual events are characterized by abrupt changes in the magnetic field, enhanced levels of broadband low frequency electromagnetic waves and a pronounced change in both the flux and pitch angle anisotropy of energetic particles. Here we present a coordinated study of one of the events which occurred near 6.03R_J, just after 17:34 UT on December 7, 1995. The available data are consistent with the concept of rapid inward transport, and this is interpreted as the first evidence for the predicted interchange motions in the region exterior to the orbit of Io. Theoretical arguments indicate that the interchanging flux tube is characterized by substantially reduced plasma density, a spatial scale comparable to 10³ km, and an inward radial velocity comparable to 102 km/s.