**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
(where the torus and satellite planes
intersect), and the presence of a strong parallel ion temperature
deficiency at (Schneider et al., *JGR*
in press, 1997; Brown, *JGR* 100, 1995, p.21683-95).