STRUCTURE WITHIN JOVIAN HECTOMETRIC RADIATION

Observations of Jovian hectometric radio emission (HOM) by the Voyager planetary radio astronomy (PRA) experiment at frequencies from 300 kH z to 1.3 MHz indicate persistent dynamic spectral features that had no t been previously studied. The features of interest appear as ''lanes' ' of decreased emission intensity within the otherwise persistent HOM. The lanes are apparent in intensity and occurrence probability spectr ograms of frequency versus Jovian System III (1965) longitude. In the investigation of the morphology of these features, we use inbound and outbound Voyager 2 data at Jupiter to show that the lane occurrence an d characteristics do not depend on local time over the range sampled. Occurrence probability spectrograms of frequency versus magnetic latit ude are created from the portion of the data when the spacecraft was b etween 0 degrees and +10 degrees magnetic latitude. These spectrograms represent both the inbound and outbound passes and are quite similar despite the different longitude ranges. A simple extension of decametr ic (DAM) arc features into the HOM wavelength does not account for all the lane features, giving further evidence that HOM is an independent emission component. Polarization signatures for the data show that th e polarization is predominantly right-hand circular and that it does n ot reverse across the lanes, suggesting the emission is from the same hemisphere. In addition, we investigate possible effects due to solar wind variations and find that the occurrence of the lanes appears to b e independent of times of low and high solar wind densities. The inten sity of the HOM emission on either side of the lanes is comparable, im plying that the lane is probably not a result of a gap between fundame ntal and second harmonic emission regions. We present these data and a nalyses asa morphological study to establish that the lane features ar e an important part of the HOM emission and should be considered in HO M emission models. At this time, no theory of the source of the lanes explains all the observed features.