SYNCHROTRON EVIDENCE FOR AMALTHEAS INFLUENCE ON JUPITERS ELECTRON-RADIATION BELT

High-resolution radio images of Jupiter at wavelength lambda = 20 cm o btained with the Very Large Array (VLA) in June 1994 (a few weeks befo re comet Shoemaker-Levy 9 collided with the planet) are compared with detailed model calculations. All major features of the radio emission can be explained or simulated through model calculations. In particula r, we infer how the pitch angle distribution of high-energy electrons varies with L value. The electron pitch angle distribution seems to un dergo a dramatic change at Amalthea's orbit: A fraction of the electro n population is redistributed in pitch angle (isotropized) there, so t hat fewer electrons mirror near the magnetic equator and more electron s mirror off the equator at L less than or similar to 2.65 than beyond . The isotropic component leads to the high-latitude emission regions, while the decreased number of equatorially mirroring electrons result s in a ''shoulder'' or flattening in the radio intensity pattern at L similar to 2.5, as is observed. Perhaps Amalthea's motion through Jupi ter's magnetic field induces Alfven or whistler wings or electrostatic high-frequency waves which lead to the ''observed'' pitch angle scatt ering. Jupiter's ring absorbs 80%-100% of electrons with small pitch a ngles that diffuse through the region it occupies. The observed effect of this absorption is that the high-latitude emission peaks remain di stinct from the equatorial maximum. Ring absorption causes nearly all electrons at L less than or similar to 2 to be narrowly confined to th e magnetic equator, a distribution which accounts for the east-west as ymmetry, which is very prominent at certain central meridian longitude s. The azimuthal variation (east-west asymmetry) over a Jovian rotatio n is completely determined by the magnetic field configuration, as was suspected by many researchers in the past but never modeled succesful ly before. We infer, however, that Connemey's O-6 magnetic field model from 1992-1993 is slightly oversimplified, since the radiation charac teristics cannot be completely matched at all Jovian longitudes: Devia tions appear in particular at longitudes lambda(cml) similar to 140 de grees-180 degrees and lambda(cml) similar to 300 degrees-340 degrees ( corresponding to lambda(III) similar to 30 degrees-90 degrees and lamb da(III) similar to 210 degrees-270 degrees in Jovicentric coordinates) .