Jupiter’s magnetic field as revealed by the synchrotron radiation belts II. Change of the 2-D brightness distribution with DE

We analyze the magnetic equatorial component of Jupiter’s radio synchrotron radiation belts using two-dimensional images recorded by the Australia Telescope Compact Array and the Very Large Array over a period of several years, during which DE , the Earth’s declination seen from Jupiter, changed from DE = −2.9◦ to near 0◦. The brightness distribution of the belts changed markedly. When DE = −2.9◦ there is a pronounced east-west asymmetry where the brightness of a region traversing the east limb is markedly different from that of the same region traversing the west limb, 180◦ of rotation later. At most longitudes λIII the brightness at east limb passage is larger than at west limb passage. However, when DE ≈ 0◦, the eastwest asymmetry essentially disappears. When DE = +2.9◦ it is predicted that the east-west asymmetry will be as at −2.9◦, but reversed. We show how these changes of appearance are simply related to DE and the warp of Jupiter’s field as described by the “magnetic declination”. The radius, latitude and brightness of the locus of maximum intensity is determined by electrons of pitch angle αeq ≈ 90◦, and its longitudinal variation depends entirely on the magnetic field of Jupiter, and not on the energy distribution of the relativistic electrons. We compare the observations with calculations from three magnetic field models and find them to be consistent in general but discrepant in detail. The differences are attributed to uncertainties in the field models, which were generated with few constraints coming from the low latitudes and small radii of the synchrotron radiation belts.