NUMERICAL-SIMULATION OF TORUS-DRIVEN PLASMA TRANSPORT IN THE JOVIAN MAGNETOSPHERE

The Rice convection model has been modified for application to the tra nsport of Io-generated plasma through the Jovian magnetosphere. The ne w code, called the RCM-J, has been used for several ideal-MHD numerica l simulations to study how interchange instability causes an initially assumed torus configuration to break up. In simulations that start fr om a realistic torus configuration but include no energetic particles, the torus disintegrates too quickly (approximately 50 hours). By addi ng an impounding distribution of energetic particles to suppress the i nterchange instability, reasonable lifetimes were obtained. For cases in which impoundment is insufficient to produce ideal-MHD stability, t he torus breaks up predominantly into long fingers, unless the initial condition strongly favors some other geometrical form. If the initial torus has more mass on one side of the planet than the other, fingers form predominantly on the heavy side (which we associate with the act ive sector). Coriolis force bends the fingers to lag corotation. The s imulation results are consistent with the idea that the fingers are fo rmed with a longitudinal thickness that is roughly equal to the latitu dinal distance over which the invariant density declines at the outer edges of the initial torus. Our calculations give an average longitudi nal distance between plasma fingers of about 15-degrees, which corresp onds to 20 to 30 minutes of rotation of the torus. We point to some Vo yager and Ulysses data that are consistent with this scale of torus lo ngitudinal irregularity.