DIRECTION FINDING STUDY OF JOVIAN HECTOMETRIC AND BROAD-BAND KILOMETRIC RADIO EMISSIONS - EVIDENCE FOR THEIR AURORAL ORIGIN

Taking advantage of the direction finding capabilities of the Ulysses unified radio and plasma wave (URAP) experiment we derive the source l ocations and emission characteristics of the Jovian hectometric (HOM)a nd broadband kilometric (bKOM) emissions. Unlike previous studies we a dditionally determine the systematic error-of the source direction due to the uncertainty of the antenna/receiver calibration parameters. To obtain maximum accuracy when doing direction finding, we use HOM and bKOM events observed close to the Ulysses encounter with Jupiter. It i s found that both emissions have their sources at the auroral zones of Jupiter, at dipole L shells between 7 and 11 for HOM in the northern hemisphere, and between 9 and 15 for the bKOM radiation observed at hi gh southern latitudes after the Ulysses Jupiter encounter. For the ana lyzed HOM events the source location is usually between 40 degrees and 130 degrees central meridian longitude (CML) and 2200 and 0600 local time (LT), but probably there exist emissions from other longitudes an d local times too. In contrast, the bKOM is emitted from a wide range of longitudes and local times as well. There is some evidence that bot h the kilometric and hectometric emissions are composed of a dominant component in the fast extraordinary (R-X) mode and a weaker ordinary ( L-O) mode component. Due to the uncertainty in source direction determ ination the emission's cone half-angle (i.e. half-angle of the cone in which the emission is beamed) cannot be accurately determined. It is some 30 degrees-90 degrees for the HOM and about 40 degrees-80 degrees for the bKOM. The source location of bKOM is likely to be associated with open magnetospheric field lines whereas the HOM is located at fie ld lines that connect the HOM radio sources with the inner Jovian plas ma sheet and/or outer plasma torus. There is some evidence that the bK OM radio emissions are correlated with ultraviolet auroral activity.