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 synchrotron radiation belts from Very Large Array observations at 20 cm. As in earlier observations with the Australia Telescope Compact Array, this reconstruction shows that the equatorial belt is not symmetric or planar, but is warped. The warp is related to the φ component of the magnetic field, or equivalently the magnetic declination at Jupiter’s magnetic equator: Dmag. We show that there is a well defined maximum of intensity at a radius that ranges from about 1.4 to 1.7 RJ, and that the brightness variation with longitude is anticorrelated with |Dmag| at the magnetic equator. The observed magnetic equatorial radius, jovicentric latitude and brightness are compared with calculations of radius, jovicentric latitude and magnetic declination at the magnetic equator on a locus of constant B = 1.2 G in two field models: H4 and VIP4. The agreement between the observed and model quantities is generally good. However, there are discrepancies that suggest inadequacies in the models, particularly at longitudes where the non-dipolar field elements are pronounced. Until now, observations have provided very few constraints at small radii (R . 2) and low latitudes (. 15◦) for the generation of magnetic field models. Therefore it is not surprising that they are accurate at high latitudes but not at low. The observations of this paper should provide useful constraints for improved models.