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Reducing the non-axisymmetry of a planetary dynamo and an application to Saturn

Stevenson, D. J. (1982) Reducing the non-axisymmetry of a planetary dynamo and an application to Saturn. Geophysical and Astrophysical Fluid Mechanics, 21 (1-2). pp. 113-127. ISSN 0309-1929. doi:10.1080/03091928208209008.

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If a conducting fluid shell is undergoing spin-axisymmetric differential rotation and overlies the dynamo generating region of a planet then it is capable of greatly reducing the non-spin-axisymmetric components of the generated field, provided the appropriate magnetic Reynolds number is large. The model, closely related to the electromagnetic skin effect, is quantified and applied to Saturn. The observed small dipole tilt (~1°) of Saturn's magnetic field can be explained because of the presence of a stably stratified conducting layer overlying the dynamo region. This layer is a predicted consequence of the thermal evolution, arises because of the limited solubility of helium in metallic hydrogen (Stevenson, 1980), and appears to be required by the Voyager infrared observations indicating depletion of helium from Saturn's atmosphere. The much larger dipole tilt angles of Jupiter and the Earth indicate the absence of any such stable, differentially rotating layer with a large magnetic Reynolds number.

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Stevenson, D. J.0000-0001-9432-7159
Additional Information:© 1982 Gordon and Breach Science Publishers Inc. Received: 30 Jul 1981; Accepted: 30 Dec 1981; Published online: 18 Aug 2006. I thank an anonymous reviewer for pointing out the work of Crane. This work is supported by NASA grant NAGW-185. Contribution number 3660 from the Division of Geological and Planetary Sciences, Pasadena, California 91125.
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Caltech Division of Geological and Planetary Sciences3660
Issue or Number:1-2
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ID Code:39022
Deposited On:21 Jun 2013 17:58
Last Modified:09 Nov 2021 23:41

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