Magnetic field changes in the inner magnetosphere of Jupiter Original Research Article

While the outer magnetosphere of Jupiter is very dynamic, powered ultimately by mass loading at the moon, Io, the magnitude of the magnetic field in the inner and middle magnetospheres is very steady. Small deviations with orbit to orbit variations of typically 5 nT do occur, presumably caused by variations in the magnetodisk current. We develop an index of the magnetodisk current from models of the interior and exterior field subtracting these models from the observations, adjusting for long term effects while leaving the orbit to orbit variations. While we use the radial range from 11 to 12 jovian radii for computing our index, the same values for the index would be obtained over a wide range of radial distances. The present internal field as deduced from the Galileo fluxgate magnetometer data differs somewhat from earlier models. Whether this is due to secular variation or due to errors in the original models is difficult to determine. We obtain a dipole longitude of 160.0° ± 0.6° and a tilt of 9.8° ± 0.1°.