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Ann. Geophys., 25, 1215-1226, 2007
www.ann-geophys.net/25/1215/2007/
© European Geosciences Union 2007
IMF dependence of the open-closed field line boundary in Saturn's ionosphere, and its relation to the UV auroral oval observed by the Hubble Space Telescope
E. S. Belenkaya1, I. I. Alexeev1, M. S. Blokhina1, S. W. H. Cowley2, S. V. Badman2, V. V. Kalegaev1, and M. S. Grigoryan1
1Institute of Nuclear Physics, Moscow State University, Vorob'evy Gory, 119992 Moscow, Russia
2Department of Physics & Astronomy, University of Leicester, Leicester LE1 7RH, UK
Abstract. We study the dependence of Saturn's magnetospheric
magnetic field structure on the interplanetary magnetic field (IMF),
together with the corresponding variations of the open-closed field line
boundary in the ionosphere. Specifically we investigate the interval from 8
to 30 January 2004, when UV images of Saturn's southern aurora were obtained
by the Hubble Space Telescope (HST), and simultaneous interplanetary
measurements were provided by the Cassini spacecraft located near the
ecliptic ~0.2 AU upstream of Saturn and ~0.5 AU off the
planet-Sun line towards dawn. Using the paraboloid model of Saturn's
magnetosphere, we calculate the magnetospheric magnetic field structure for
several values of the IMF vector representative of interplanetary
compression regions. Variations in the magnetic structure lead to different
shapes and areas of the open field line region in the ionosphere. Comparison
with the HST auroral images shows that the area of the computed open flux
region is generally comparable to that enclosed by the auroral oval, and
sometimes agrees in detail with its poleward boundary, though more typically
being displaced by a few degrees in the tailward direction.
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