Jupiter's magnetic field as revealed by the synchrotron radiation belts - I. Comparison of a 3-D reconstruction with models of the field

We use tomographic techniques to make a 3-D reconstruction of Jupiter's syn chrotron radiation belts from Very Large Array observations at 20 cm. As in earlier observations with the Australia Telescope Compact Array, this reco nstruction shows that the equatorial belt is not symmetric or planar, but i s warped. The warp is related to the phi component of the magnetic field, o r equivalently the magnetic declination at Jupiter's magnetic equator: D-ma g. We show that there is a well defined maximum of intensity at a radius th at ranges from about 1.4 to 1.7 R-J, and that the brightness variation with longitude is anticorrelated with \D-mag\ at the magnetic equator. The obse rved magnetic equatorial radius, jovicentric latitude and brightness are co mpared with calculations of radius, jovicentric latitude and magnetic decli nation at the magnetic equator on a locus of constant B = 1.2 G in two fiel d models: H4 and VIP4. The agreement between the observed and model quantit ies is generally good. However, there are discrepancies that suggest inadeq uacies in the models, particularly at longitudes where the non-dipolar fiel d elements are pronounced. Until now, observations have provided very few constraints at small radii ( R less than or similar to 2) and low latitudes (less than or similar to 15 degrees) for the generation of magnetic field models. Therefore it is not s urprising that they are accurate at high latitudes but not at low. The obse rvations of this paper should provide useful constraints for improved model s.