NONADIABATIC PARTICLE MOTION AND COROTATION LAG IN THE JOVIAN MAGNETODISK

In the sharply curved magnetic field lines of Jupiter's magnetodisk, energetic ions follow nonadiabatic orbits violating the first and second adiabatic invariants. Even in the corotating reference frame, the energetic ion distribution function is in general anisotropic, as is shown by numerically computed orbits in the Goertz et al. (1976) magnetodisk model. Pitch angle scattering that can be induced by magnetic field irregularities or plasma waves is included in the calculations. This numerically calculated anisotropy of nonadiabatic ions can account for the anistropy of energetic ions measured by Voyager in the Jovian magnetodisk, depending strongly on the radial distribution of particles injected into the current sheet but not strongly on the scattering rate. The measured anisotropy has previously been interpreted as indicating approximate corotation in the outer Jovian magnetodisk, but the present calculations show that the measured anisotropy can be consistent with a substantial corotation lag.