WAVE PHENOMENA IN THE UPSTREAM REGION OF SATURN

The magnetic field data returned from the Voyager 1 and 2 transit through the upstream region of Saturn have been examined from 0.1 mHz to 0.25 Hz to search for the signatures of waves associated with both the electron and ion foreshocks. In contrast to the Earth, in the ion foreshock of Saturn we find two distinct bands of wave activity at frequencies around 0.5 and 2-mHz in the spacecraft frame. These two waves differ considerably in their properties. The 0.5-mHz waves are right handed, strongly elliptically polarized, while the 2-mHz waves are elliptically or circularly polarized in the left-handed sense. These two different waves may be associated with two different backstreaming particle distributions, possibly those reflected from the shock and those leaking from the hot magnetosheath. We also observe right-hand elliptically polarized upstream waves propagating obliquely to the magnetic field at frequencies between 90 and 150 mHz, which are above the proton gyrofrequency in the spacecraft frame. The frequency of these waves appears to be dependent on the interplanetary magnetic field orientation. Such dependence is characteristic of the 1-Hz waves at Earth. Discrete wave packets associated with shocklets are for the first time observed in the foreshock of an outer planet.