Modifications of the synchrotron radiation belts of Jupiter: evidence for natural variations in addition to SL9 effects

Regular observations of Jupiter at 21.3, 18.0 and 9.1 cm have been carried out with the Nançay Radio Telescope between 1 April 1994 and 11 April 1996. In July 1994, the collision of comet Shoemaker-Levy 9 with Jupiter produced a large increase of the nonthermal flux density with a hardening of the spectrum at higher frequency. This flux increase was followed in August and September by an increase of the east-west size of the emission region, mostly in the vertical polarization. In April 1995, the radiation belts had not fully recovered their pre-encounter levels. In October 1995, a new surge of the emission occurred characterized by a hardening of the flux and a broadening of the east-west (E-W) size. Two years of monitoring of the jovian synchrotron radiation suggest that the artificial effects induced by the Jupiter/Shoemaker-Levy 9 collision are interwoven with natural variations of the radiation belts.