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

We analyze the magnetic equatorial component of Jupiter's radio synchrotron radiation belts using two-dimensional images recorded by the Australia Tel escope Compact Array and the Very Large Array over a period of several year s, during which D-E, the Earth's declination seen from Jupiter, changed fro m D-E = -2.9 degrees to near 0 degrees. The brightness distribution of the belts changed markedly. When D-E = -2.9 degrees 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 degrees of rotation later. At most longitudes lambda(III) the brightnes s at east limb passage is larger than at west limb passage. However, when D -E approximate to 0 degrees, the east-west asymmetry essentially disappears . When D-E = +2.9 degrees it is predicted that the east-west asymmetry will be as at -2.9 degrees, but reversed. We show how these changes of appearance are simply related to D-E and the w arp of Jupiter's field as described by the "magnetic declination". The radi us, latitude and brightness of the locus of maximum intensity is determined by electrons of pitch angle alpha(eq) approximate to 90 degrees, and its l ongitudinal variation depends entirely on the magnetic field of Jupiter, an d not on the energy distribution of the relativistic electrons. We compare the observations with calculations from three magnetic field models and fin d them to be consistent in general but discrepant in detail. The difference s 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.