Modifications of the electrodynamic interaction between Jupiter and Io due to mass loading effects

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Abstract
The electrodynamic interaction between Jupiter and Io is investigated by means of three‐dimensional resistive MHD simulations with Jupiter being modeled as an aligned rotator situated in the origin of a cylindrical coordinate system. For numerical reasons, however, only qualitative statements can be made, which do not allow quantitative comparisons with observations. The main topic is the generation of electric currents parallel to the magnetic field. In consideration of the fact that some observational features cannot be qualitatively understood with present theories, the rôle of the plasma production from lo's atmosphere as well as by ionization in the plasma torus is investigated. If these two plasma sources are significantly cooler than the plasma environment, they can be shown to cause a torus corotational lag, in consequence of which a field‐aligned current system develops. If microinstabilities occur along this system, anomalous resistivity regions may be built up where the electric field attains a component parallel to the magnetic field. Thus ionization within the torus might explain the observed decametric radiation upstream of Io's current position. Furthermore, plasma production from Io's atmosphere shows a strong influence on the MHD modes excited by the Io/torus interaction. The pressure signatures generated by slow mode perturbations disclose the formation of a tail‐like structure in the wake behind Io. Thus previous conceptions about a new current systems in Io's wake can be confirmed by self‐consistent MHD simulations. Finally, the correlations between this current and gradients in angular velocity and density are studied in detail.