Currents in Saturn's magnetosphere

A model of Saturn's magnetospheric magnetic field is obtained from the Voyager 1 and 2 observations. A representation consisting of the Z3 zonal harmonic model of Saturn's planetary magnetic field together with an explicit model of the equatorial ring current fits the observations well within r < 20 Rs, with the exception of data obtained during the Voyager 2 inbound pass. The exception is attributed to a time variation of Saturn's magnetosphere driven by a drop in solar wind ram pressure. The magnetohydrodynamic momentum equation is used to obtain, from the magnetic field model, estimates of the plasma pressure and mass density at radial distances of 8 < r < 16 Rs. These estimates are generally consistent with those obtained by the Pioneer 11 and Voyager plasma investigations. The Voyager 1 observations suggest the presence of a global field-aligned current of ∼107 A flowing into the (southern) auroral zone in the evening sector. No evidence of such a field-aligned current system is found in the Voyager 2 observations obtained a year later.

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