The Jovian HOM and bKOM radio emissions observed by Wind/WAVES and by Ulysses/URAP

Abstract

During 1995 and into 1996, both the Jovian hectometric radio emission (HOM) and the Jovian broadband radio emission (bKOM) were received occasionally by the Radio and Plasma Wave Investigation (WAVES) on board the Wind spacecraft and by the Unified Radio and Plasma Experiment (URAP) on board the Ulysses spacecraft. Ulysses was then at distances of 5 AU or more from Jupiter and travelling from south to north of the ecliptic plane. At this distance from the planet, the events are generally weak and much care is needed to distinguish the HOM from weak solar type III emission and, in the Wind/WAVES observations, the bKOM from terrestrial auroral kilometric radiation (AKR). Characteristics of the emission, duration, frequency extent, structure and polarization give new information on the beaming and source location of the HOM and the bKOM. For the period studied, it was found that the bKOM events were observed by Ulysses when the spacecraft was at higher jovicentric latitudes, ( D Uly⩾15°) while HOM events were recorded when the spacecraft was at lower jovicentric latitudes, −12°⩽ D Uly⩽14°. Polarization measurements suggest that, due to beaming, LH polarized radiation from the southern Jovian hemisphere HOM source is beamed towards Ulysses at jovicentric latitudes to the north of some value between −11.7 and −5.3°. Conversely, RH polarized radiation from the northern hemisphere HOM source is beamed away from Ulysses at jovicentric latitudes to the north of some value between −11.7 and −5.3°. For the events studied, if a two-dimensional tilted dipole model is assumed, the emission cone half-angle appears to be about 44° for 940 kHz HOM emission from a source on L-shell about 10. There is no unique value for β that does not involve assumed values of L and f c (Barrow and Lecacheux, Astron. Astrophys. 301 (1995) 903.)