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Astron. Astrophys. 364, 339-347 (2000)


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Magnetic dynamo due to turbulent helicity fluctuations

N.A. Silant'ev

Instituto Nacional de Astrofísica, Óptica y Electrónica, Apartado Postal 51 y 216, Z.P. 72000, Pue. México (silant@inaoep.mx)
Main Astronomical Observatory of Russian Academy of Sciences, 196140-St. Petersburg, Russia

Received 16 June 2000 / Accepted 11 September 2000

Abstract

Using the large-scale or long-time averaged magnetic field diffusion equation, we show that the inhomogeneous distribution of the turbulent helicity fluctuations (more correctly, the fluctuations of the [FORMULA]-coefficient) gives rise to the large-scale enhancement of the mean magnetic field. This effect occurs even if the mean helicity is absent. This newly reported dynamo mechanism requires the differential rotation of an atmosphere and does not depend on the action of the Coriolis force. The estimations show that the [FORMULA]-coefficients due to helicity fluctuations have the same (or greater) magnitude compared to the usual [FORMULA]-coefficients, related to the action of the Coriolis force. However, this mechanism works in the regions of the convective zone where the inhomogeneity of the fluctuation distribution is most prominent. It is very anisotropic in character and is described by the [FORMULA]-tensor. The possible effect of this mechanism in the Sun is discussed.

Key words: magnetic fields – turbulence – Sun: magnetic fields – stars: magnetic fields


© European Southern Observatory (ESO) 2000

Online publication: December 15, 2000

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