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| Titel |
Differential Rotation Dynamos: An Application to Saturn |
| VerfasserIn |
J. Wicht, P. Olson |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250040615
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| Zusammenfassung |
| Most planetary dynamo are thought to be driven be convection, and numerical simulations
have confirmed that the associated chaotic flows can indeed account for many of the observed
planetary magnetic field features. Saturn’s dynamo, however, seems exceptional, producing a
highly axisymmetric and relatively simple magnetic field. Its octupole is also much stronger
and of opposite sign than typical for convectively driven dynamos. We have used numerical
simulations to examine the dynamo action of the flow between two differentially rotating
co-axial spheres, the so-called spherical-Couette system. When the differential rotation
exceeds a critical value the stationary and axisymmetric Couette shear flow becomes instable.
The non-axisymmetric instabilities can induce magnetic fields which are highly
axisymmetric and concentrated in two flux bundles around both poles. Sub-rotation
of the inner boundary preferentially results in an equatorially asymmetric field.
Super-rotation of the inner boundary produces an equatorially antisymmetric magnetic field
which shares many similarities with Saturn’s magnetic field. It is not only highly
axisymmetric but also produces a strong octupole component of the correct sign. We
speculate that the super-rotation in Saturn’s interior may be sustained by Helium
precipitation. Extrapolation of our results indicates that vary small amount of differential
rotation, or order one part in 107, could suffice to yield the respective dynamo action. |
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