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Astron. Astrophys. 360, L21-L24 (2000)


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Letter to the Editor

Torsional oscillations in the solar convection zone

E. Covas 1, R. Tavakol 1, D. Moss 2 and A. Tworkowski 3

1 Astronomy Unit, School of Mathematical Sciences, Queen Mary and Westfield College, Mile End Road, London E1 4NS, UK (eoc,reza@maths.qmw.ac.uk)
2 Department of Mathematics, The University, Manchester M13 9PL, UK (moss@ma.man.ac.uk)
3 MRC, School of Mathematical Sciences, Queen Mary and Westfield College, Mile End Road, London E1 4NS, UK (ast@maths.qmw.ac.uk)

Received 28 June 2000 / Accepted 18 July 2000

Abstract

Recent analysis of the helioseismic observations indicate that the previously observed surface torsional oscillations extend significantly downwards into the solar convection zone.

In an attempt to understand these oscillations, we study the nonlinear coupling between the magnetic field and the solar differential rotation in the context of a mean field dynamo model, in which the nonlinearity is due to the action of the azimuthal component of the Lorentz force of the dynamo generated magnetic field on the solar angular velocity. The underlying zero order angular velocity is chosen to be consistent with the most recent helioseismic data.

The model produces butterfly diagrams which are in qualitative agreement with the observations. It displays torsional oscillations that penetrate into the convection zone, and which with time migrate towards the equator. The period of these oscillations is found to be half that of the period of the global magnetic fields. This is compatible with the observed period of the surface torsional oscillations. Inside the convection zone, this is a testable prediction that is not ruled out by the observations so far available.

Key words: Sun: magnetic fields – chaos – magnetic fields

Send offprint requests to: E. Covas

© European Southern Observatory (ESO) 2000

Online publication: August 17, 2000

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