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Ann. Geophys., 26, 159-166, 2008
www.ann-geophys.net/26/159/2008/
© European Geosciences Union 2008
Dependence of the open-closed field line boundary in Saturn's ionosphere on both the IMF and solar wind dynamic pressure: comparison with the UV auroral oval observed by the HST
E. S. Belenkaya1, S. W. H. Cowley2, S. V. Badman2, M. S. Blokhina1, and V.V. Kalegaev1
1Institute of Nuclear Physics, Moscow State University, Leninskie Gory, 119991 Moscow, Russia
2Department of Physics {&} Astronomy, University of Leicester, Leicester LE1 7RH, UK
Abstract. We model the open magnetic field region in Saturn's southern polar ionosphere during two compression regions observed by
the Cassini spacecraft upstream of Saturn in January 2004, and compare these
with the auroral ovals observed simultaneously in ultraviolet images
obtained by the Hubble Space Telescope. The modelling employs the paraboloid
model of Saturn's magnetospheric magnetic field, whose parameters are varied
according to the observed values of both the solar wind dynamic pressure and
the interplanetary magnetic field (IMF) vector. It is shown that the open
field area responds strongly to the IMF vector for both expanded and
compressed magnetic models, corresponding to low and high dynamic pressure,
respectively. It is also shown that the computed open field region agrees
with the poleward boundary of the auroras as well as or better than those
derived previously from a model in which only the variation of the IMF
vector was taken into account. The results again support the hypothesis that
the auroral oval at Saturn is associated with the open-closed field line
boundary and hence with the solar wind interaction.
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