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| Titel |
Auroral current systems in Saturn's magnetosphere: comparison of theoretical models with Cassini and HST observations |
| VerfasserIn |
S. W. H. Cowley, C. S. Arridge, E. J. Bunce, J. T. Clarke, A. J. Coates, M. K. Dougherty, J.-C. Gérard, D. Grodent, J. D. Nichols, D. L. Talboys |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 26, no. 9 ; Nr. 26, no. 9 (2008-09-08), S.2613-2630 |
| Datensatznummer |
250016213
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| Publikation (Nr.) |
 copernicus.org/angeo-26-2613-2008.pdf |
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| Zusammenfassung |
| The first simultaneous observations of fields and plasmas
in Saturn's high-latitude magnetosphere and UV images of the conjugate
auroral oval were obtained by the Cassini spacecraft and the Hubble Space
Telescope (HST) in January 2007. These data have shown that the southern
auroral oval near noon maps to the dayside cusp boundary between open and
closed field lines, associated with a major layer of upward-directed
field-aligned current (Bunce et al., 2008). The results thus support earlier theoretical
discussion and quantitative modelling of magnetosphere-ionosphere coupling
at Saturn (Cowley et al., 2004), that suggests the oval is produced by electron
acceleration in the field-aligned current layer required by rotational flow
shear between strongly sub-corotating flow on open field lines and
near-corotating flow on closed field lines. Here we quantitatively compare
these modelling results (the "CBO" model) with the Cassini-HST data set. The
comparison shows good qualitative agreement between model and data, the
principal difference being that the model currents are too small by factors
of about five, as determined from the magnetic perturbations observed by
Cassini. This is suggested to be principally indicative of a more highly
conducting summer southern ionosphere than was assumed in the CBO model. A
revised model is therefore proposed in which the height-integrated
ionospheric Pedersen conductivity is increased by a factor of four from 1 to
4 mho, together with more minor adjustments to the co-latitude of the
boundary, the flow shear across it, the width of the current layer, and the
properties of the source electrons. It is shown that the revised model
agrees well with the combined Cassini-HST data, requiring downward
acceleration of outer magnetosphere electrons through a ~10 kV
potential in the current layer at the open-closed field line boundary to
produce an auroral oval of ~1° width with UV emission intensities
of a few tens of kR. |
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