Longitudinal Variations in the Io Torus: a Simple Numerical Model

D. A. Brain, N. M. Schneider, F. Bagenal, A.I.F. Stewart (LASP / University of Colorado)

We present a simple numerical model of the Io torus optimized for the study of longitudinal variation in the torus. Considering a single species in one spatial dimension, we track the mass density of particles in the torus as a function of System III Longitude. In the model, addition of ions and electrons is possible at Io and in a neutral cloud surrounding Io, particle transport occurs via azimuthal diffusion and corotation lag, and loss of particles can happen throughout the torus by several processes. The offset and tilt of Jupiter's dipole magnetic field are included as Io and the model torus are propagated in time.

While other recent models have stressed radial processes or ion chemistry, this model primarily examines longitudinal structure in the torus. It takes a first-order look at the relative roles of each process in maintaining a torus equilibrium in mass and in creating longitudinal torus asymmetry. Preliminary results will be presented with emphasis on comparison of longitudinal variation. Of particular interest are the absence of any observed torus enhancement at tex2html_wrap_inline15 (where the torus and satellite planes intersect), and the presence of a strong parallel ion temperature deficiency at tex2html_wrap_inline17 (Schneider et al., JGR in press, 1997; Brown, JGR 100, 1995, p.21683-95).