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Ann. Geophys., 24, 2709-2717, 2006
www.ann-geophys.net/24/2709/2006/
© European Geosciences Union 2006
Periodic modulation of gas giant magnetospheres by the neutral upper atmosphere
C. G. A. Smith
Atmospheric Physics Laboratory, Department of Physics and Astronomy, University College, London, UK
Abstract. Periodic signatures present in the magnetospheres of both Jupiter and Saturn
have yet to be fully explained. At Jupiter the unexplained signatures are
related to emissions from the Io torus ("System IV"); at Saturn they are
observed in emissions of kilometric radiation (SKR) and in magnetometer data.
These signatures are often interpreted in terms of magnetic field anomalies.
This paper describes an alternative mechanism by which the neutral atmosphere
may impose such periodic signatures on the magnetosphere. The mechanism
invokes a persistent zonal asymmetry in the neutral wind field that rotates
with the planet. This asymmetry must be coupled to substantial ionospheric
conductivity. It is then able to drive divergent currents in the upper
atmosphere that close in and perturb the magnetosphere. We estimate the
conductivities and wind speeds required for these perturbations to be
significant, and argue that they are most likely to be important at auroral
latitudes where the conductivity may be enhanced by particle precipitation.
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