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| Titel |
Coupled rotational dynamics of Saturn's thermosphere and magnetosphere: a thermospheric modelling study |
| VerfasserIn |
C. G. A. Smith, A. D. Aylward |
| 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. 4 ; Nr. 26, no. 4 (2008-05-13), S.1007-1027 |
| Datensatznummer |
250016075
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| Publikation (Nr.) |
 copernicus.org/angeo-26-1007-2008.pdf |
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| Zusammenfassung |
| We use a numerical model of Saturn's thermosphere to investigate the flow of
angular momentum from the atmosphere to the magnetosphere. The thermosphere
model is driven by Joule heating and ion drag calculated from a simple model
of the magnetospheric plasma flows and a fixed model of the ionospheric
conductivity. We describe an initial study in which our plasma flow model is
fixed and find that this leads to several inconsistencies in our results. We
thus describe an improved model in which the plasma flows are allowed to vary
in response to the structure of the thermospheric winds. Using this improved
model we are able to analyse in detail the mechanism by which angular
momentum extracted from the thermosphere by the magnetosphere is replaced by
transport from the lower atmosphere. Previously, this transport was believed
to be dominated by vertical transport due to eddy viscosity. Our results
suggest that transport within the upper atmosphere by meridional winds is a
much more important mechanism. As a consequence of this, we find that the
rotational structures of the thermosphere and magnetosphere are related in a
more complex way than the eddy viscosity model implies. Rather than the
thermosphere behaving as a passive component of the system, the
thermosphere-magnetosphere interaction is shown to be a two-way process in
which rotational structures develop mutually. As an example of this, we are
able to show that thermospheric dynamics offer an explanation of the small
degree of super-corotation that has been observed in the inner magnetosphere.
These results call into question the usefulness of the effective Pedersen
conductivity as a parameterisation of the neutral atmosphere. We suggest that
a two-parameter model employing the true Pedersen conductivity and the true
thermospheric rotation velocity may be a more accurate representation of the
thermospheric behaviour. |
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