Modelling Planetary Magnetodiscs

There have been two popular approaches in the literature to constructing models of giant planet magnetodiscs. The first assumes an analytical form of the ring current a priori,and computes the corresponding magnetic field structure. The second applies the condition of balance between centrifugal force, magnetic force and plasma pressure in order to acquire a self-consistent field and plasma distribution. In this talk, we shall explore the application of both types of model to observations of planetary fields and plasmas. In particular, we shall see that the force-balance formalism predicts a natural `transition distance' between regions dominated by centrifugal (inertial) currents and pressure-gradient currents. We shall also present this type of model for Jupiter's magnetodisc, and show how the parameters of the model can be used to predict the influence of major reconfigurations of the magnetosphere upon the morphology of the jovian auroral emissions.