Historical backdrop, leading to the alpha-effect --- its origins and limitations (Keynote speaker)

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• Keith Moffatt (University of Cambridge)
• Monday 12 September 2022, 10:00-11:00
• Seminar Room 1, Newton Institute.

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DY2W01 - Dynamos in planets and stars - similarities and differences

In this introductory lecture, some historical landmarks in geomagnetism will be reviewed, in lead-up to a discussion of the α-effect, which, since the 1970s, has played a central role in mean-field dynamo theory. In the case of the Earth (and some other planets) the magnetic Reynolds number Rm of the random motions in the liquid core that contribute to the α-effect is not large, and a low-Rm approxi-mation can be exploited with some confidence in determining the crucial param-eter α. The situation is very different in solar-type stars where Rm is very large, and where a satisfactory theory is still lacking. The situation is particularly chal-lenging when the issue of dynamic ’α-quenching’ is addressed. Nevertheless, mean-field theory in the ‘magnetostrophic’ approximation is likely to remain in-dispensable for the foreseeable future, given that direct numerical simulation will never be able to come near to the actual physical parameters of the Earth and the Sun.

This talk is part of the Isaac Newton Institute Seminar Series series.

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