Magnetodisc Structure: Saturn versus Jupiter

We present some recent results of modeling studies undertaken with a dimensionless form of the Jovian magnetodisc model by Caudal (JGR,1986). We have calculated magnetospheric profiles of normalised current density, magnetic field and plasma pressure for reasonable representations of the conditions at Saturn and Jupiter, based on Cassini / Voyager observations. We present and discuss the following two important features which arise in the models: (i) The normalised equatorial current density at Saturn, over distances 5-16 planetary radii, actually exceeds that at Jupiter by factors <~5. The kronian plasmadisc is thus expected to produce a stronger relative perturbation to the background dipole field of the parent planet. (ii) The Jovian outer plasmadisc is clearly a hot pressure-dominated structure, in terms of both force balance and current generation. However, the observed strong variability in hot plasma pressure at Saturn produces a characteristic region in its magnetosphere where the hot pressure gradient may become comparable to or exceed centrifugal force. The size of this region changes significantly according to the assumed mean global value of hot plasma beta.