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SUMMARY:Historical backdrop\, leading to the alpha-effect --- its origins 
 and limitations (Keynote speaker) - Keith Moffatt (University of Cambridge
 )
DTSTART:20220912T090000Z
DTEND:20220912T100000Z
UID:TALK177464@talks.cam.ac.uk
DESCRIPTION:In this introductory lecture\, some historical landmarks in ge
 omagnetism will be reviewed\, in lead-up to a discussion of the &alpha\;-e
 ffect\, 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 magne
 tic Reynolds number Rm of the random motions in the liquid core that contr
 ibute to the &alpha\;-effect is not large\, and a low-Rm approxi-mation ca
 n be exploited with some confidence in determining the crucial param-eter 
 &alpha\;. The situation is very different in solar-type stars where Rm is 
 very large\, and where a satisfactory theory is still lacking. The situati
 on is particularly chal-lenging when the issue of dynamic '&alpha\;-quench
 ing' is addressed. Nevertheless\, mean-field theory in the 'magnetostrophi
 c' approximation is likely to remain in-dispensable for the foreseeable fu
 ture\, given that direct numerical simulation will never be able to come n
 ear to the actual physical parameters of the Earth and the Sun.
LOCATION:Seminar Room 1\, Newton Institute
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