Octupole model of Jupiter's magnetic field from Ulysses observations

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.