Please use this identifier to cite or link to this item: http://hdl.handle.net/2381/10870
Title: Oscillation of Saturn's southern auroral oval
Authors: Nichols, Jonathan D.
Clarke, J.T.
Cowley, S.W.H.
Duval, J.
Farmer, A.J.
Gérard, J.-C.
Grodent, D.
Wannawichian, S.
First Published: 7-Nov-2008
Publisher: American Geophysical Union (AGU)
Citation: Journal of Geophysical Research - Space Physics, 2008, 113, A11205 (12)
Abstract: Near-planetary-period oscillations in the Cassini plasma and magnetic field data have been observed throughout Saturn's magnetosphere despite the fact that Saturn's internal magnetic field is apparently highly axisymmetric. In addition, the period of the Saturn kilometric radiation has been shown to vary over time. In this paper we present results from the recent Hubble Space Telescope observations of Saturn's southern ultraviolet auroral emission. We show that the center of the auroral oval oscillates with period 10.76 h +/- 0.15 h for both January 2007 and February 2008, i.e., close to the periods determined for oscillations in other magnetospheric phenomena. The motion of the oval center is described for 2007 by an ellipse with semimajor axis similar to 1.4 degrees +/- 0.3 degrees oriented toward similar to 09-21 h LT, eccentricity similar to 0.93, and center offset from the spin axis by similar to 1.8 degrees toward similar to 04 h LT. For 2008 the oscillation is consistent with an ellipse with semimajor axis similar to 2.2 degrees +/- 0.3 degrees oriented toward similar to 09-21 h LT, eccentricity similar to 0.99, and a center offset from the spin axis by similar to 2.2 degrees toward similar to 03 h LT. The motion of the auroral oval is thus highly elliptical in both cases, and the major oscillation axis is oriented toward prenoon/premidnight. This result places an independent constraint on the magnitude of the planet's dipole tilt and may also indicate the presence of an external current system that imposes an asymmetry in the ionospheric field modulated close to the planetary period.
DOI Link: 10.1029/2008JA013444
ISSN: 0148-0227
Links: http://www.agu.org/pubs/crossref/2008/2008JA013444.shtml
http://hdl.handle.net/2381/10870
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: Copyright © 2008 by the American Geophysical Union. Deposited with reference to the publisher's archiving policy available on the SHERPA/RoMEO website.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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