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D. E. Huddleston, C. T. Russell, F. Konstantinidis, R. J. Strangeway (UCLA), X. Blanco-Cano (UNAM)
The ions produced at Io and accelerated to corotational velocities by the electric field associated with the plasma of the Io torus, in turn produce copious wave phenomena, reaching 200 nT peak-to-peak at the SO2+ ion gyrofrequency. Measurable waves were seen up to 20 RIo away from Io in the direction perpendicular to the magnetic field. Surprisingly such waves were not observed at Voyager I in 1979 when it passed just 11 Io radii under Io. Thus, even though these waves are propagating nearly parallel to the magnetic field at Io, they do not move very far along those magnetic field lines. An examination of the properties of the waves seen by Galileo reveals that at the highest frequencies the waves travel nearly at right angles to the magnetic field even though at lower frequencies the signals propagate parallel to the field. This suggests that refraction as well as absorption might affect wave propagation in the region close to Io.