Source characteristics of Jovian hectometric radio emissions

Abstract

Direct confirmation that low‐frequency Jovian hectometric (HOM) radio emissions centered near 0° central meridian longitude consist of distinct, oppositely polarized northern and southern beams has been achieved using data from the Unified Radio and Plasma Wave (URAP) experiment on the Ulysses spacecraft during the Ulysses‐Jupiter encounter in early February 1992. Distinct northern and southern beams were observed in the frequency range from ∼300 kHz to 1 MHz for at least eight Jovian rotations during the Ulysses inbound pass at distances from 100 to 40 RJ. The radiation from the two magnetic hemispheres was measured from different Jovigraphic longitudes and magnetic (or centrifugal) latitudes. Observed temporal variations in the radio intensities, with time scales on the order of 30 min, may result either from longitudinal variations of the HOM sources or from longitudinal density variations in the Io plasma torus. Using the URAP direction‐finding capabilities and assuming a tilted dipole planetary magnetic field model, the three‐dimensional HOM source locations, the L shell through these source locations, and the beam opening angles were independently deduced. The HOM sources were found to originate at ∼3 RJ and on low L shells (L ∼ 4 to 6), with beam opening angles ranging from 10° to 50°.