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Astron. Astrophys. 347, L47-L50 (1999)

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Letter to the Editor

Mean electromotive force and dynamo action in a turbulent flow

V. Urpin 1,2

1 Department of Mathematics, University of Newcastle, Newcastle upon Tyne, NE1 7RU, UK
2 A.F.Ioffe Institute of Physics and Technology, 194021 St. Petersburg, Russia

Received 26 April 1999 / Accepted 18 June 1999


We derive the expression for the mean electromotive force in a turbulent flow taking into account stretching of turbulent magnetic field lines and streamlines by the mean flow. Shear stresses break the symmetry of turbulence in such a way that turbulent motions become suitable for the dynamo action. The contribution of this effect to the mean electromotive force is proportional to the production of spatial derivatives of the mean magnetic field and the mean velocity thus it cannot be described, in principle, in terms of the conventional alpha-effect.

Key words: Magnetohydrodynamics (MHD) – turbulence – stars: magnetic fields – accretion, accretion disks

Send offprint requests to: V.Urpin

© European Southern Observatory (ESO) 1999

Online publication: June 6, 1999