Octupole model of Jupiter's magnetic field from Ulysses observations

Abstract

A spherical harmonic model of the planetary magnetic field of Jupiter is obtained from the Ulysses encounter observations. The magnetic field in the Jovian magnetosphere is represented using a degree and order 3 spherical harmonic for the planetary (``internal'') field, and an explicit model of the magnetodisc for the field (``external'') due to distributed currents. The model is obtained by partial solution of the underdetermined inverse problem using generalized inverse techniques. Dipole, quadrupole, and a subset of the octupole spherical harmonic coefficients are determined and compared with those obtained using Voyager and Pioneer observations. The model requires a less intense magnetodisc current, in early 1992, compared with that observed during the Voyager 1 encounter in 1979 and the Pioneer encounters of 1973 and 1974.