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The Energy Flux Number and Three Types of Planetary Dynamo

Stevenson, D. J. (1984) The Energy Flux Number and Three Types of Planetary Dynamo. Astronomische Nachrichten, 305 (5). pp. 257-264. ISSN 0004-6337 . https://resolver.caltech.edu/CaltechAUTHORS:20131120-133142684

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Abstract

It is proposed that the existence and nature of a planetary dynamo can be characterized by a dimensionless number Φ ≡ F_eR/ϱλ^2Ω, called the energy flux number, where F_e is the energy flux available for dynamo generation, R is the core radius (or thickness of the dynamo generating region), ϱ is the fluid density, λ is the magnetic diffusivity and Ω is the angular velocity. For Φ ≲ 1, there is no dynamo. For 1 ≲ Φ ≲ 10^(2.5) there is an “energy-limited dynamo”, in which F_e is insufficient to enable the dynamo to reach the dynamically desirable state Λ ≡ B^2/8πϱλΩ ∼ 1, where B is a typical field amplitude (in Gauss). For 10^(2.5) ≲ Φ ≲ 10^5, there is a dynamically determined dynamo (Λ ∼ 1) in which the magnetic Reynolds number of turbulent eddies is small. For Φ ≳ 10^5, there is a turbulent dynamo. Probable planetary examples of these three dynamo states are Mercury (Φ ∼ 10^2-10^3), Earth (Φ ∼ 10^4) and Jupiter (Φ ∼ 10^(11)), respectively.


Item Type:Article
Related URLs:
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http://onlinelibrary.wiley.com/doi/10.1002/asna.2113050512/abstractPublisherArticle
http://dx.doi.org/10.1002/asna.2113050512DOIArticle
ORCID:
AuthorORCID
Stevenson, D. J.0000-0001-9432-7159
Additional Information:© 1984 WILEY-VCH Verlag GmbH & Co. With 2 figures (Received 1983 December 28) Contribution number 4009 of the Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena.
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Caltech Division of Geological and Planetary Sciences4009
Issue or Number:5
Record Number:CaltechAUTHORS:20131120-133142684
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20131120-133142684
Official Citation:Stevenson, D. J. (1984), The energy flux number and three types of planetary dynamo. Astron. Nachr., 305: 257–264. doi: 10.1002/asna.2113050512
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:42596
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:20 Nov 2013 22:09
Last Modified:03 Oct 2019 06:00

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