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Ann. Geophys., 23, 799-808, 2005
www.ann-geophys.net/23/799/2005/
© European Geosciences Union 2005
Magnetosphere-ionosphere coupling currents in Jupiter's middle magnetosphere: effect of magnetosphere-ionosphere decoupling by field-aligned auroral voltages
J. D. Nichols and S. W. H. Cowley
Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
Abstract. We consider the effect of field-aligned voltages on the
magnetosphere-ionosphere coupling current system associated with the
breakdown of rigid corotation of equatorial plasma in Jupiter's middle
magnetosphere. Previous analyses have assumed perfect mapping of the
electric field and flow along equipotential field lines between the
equatorial plane and the ionosphere, whereas it has been shown that
substantial field-aligned voltages must exist to drive the field-aligned
currents associated with the main auroral oval. The effect of these
field-aligned voltages is to decouple the flow of the equatorial and
ionospheric plasma, such that their angular velocities are in general
different from each other. In this paper we self-consistently include the
field-aligned voltages in computing the plasma flows and currents in the
system. A third order differential equation is derived for the ionospheric
plasma angular velocity, and a power series solution obtained which reduces
to previous solutions in the limit that the field-aligned voltage is small.
Results are obtained to second order in the power series, and are compared
to the original zeroth order results with no parallel voltage. We find that
for system parameters appropriate to Jupiter the effect of the field-aligned
voltages on the solutions is small, thus validating the results of
previously-published analyses.
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