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Catastrophic α quenching alleviated by helicity flux and shear View all abstracts by submitter

Axel Brandenburg   Submitted: 2004-08-11 13:50

A new simulation set-up is proposed for studying mean field dynamo action. The model combines the computational advantages of local cartesian geometry with the ability to include a shear profile that resembles the sun's differential rotation at low latitudes. It is shown that in a two-dimensional mean field model this geometry produces cyclic solutions with dynamo waves traveling away from the equator - as expected for a positive α effect in the northern hemisphere. In three dimensions with turbulence driven by a helical forcing function, an α effect is self-consistently generated in the presence of a finite imposed toroidal magnetic field. The results suggest that, due to a finite flux of current helicity out of the domain, α quenching appears to be non-catastrophic - at least for intermediate values of the magnetic Reynolds number. For larger values of the magnetic Reynolds number, however, there is evidence for a reversal of the trend and that α may decrease with increasing magnetic Reynolds number. Control experiments with closed boundaries confirm that in the absence of a current helicity flux, but with shear as before, α quenching is always catastrophic and α decreases inversely proportional to the magnetic Reynolds number. For solar parameters, our results suggest a current helicity flux of about 0.001 G^2/s. This corresponds to a magnetic helicity flux, integrated over the northern hemisphere and over the 11 year solar cycle, of about 1046Mx^2.

Authors: A. Brandenburg & C. Sandin
Projects: None

Publication Status: Astron. Astrophys. (in press)
Last Modified: 2004-08-11 13:50
Go to main E-Print page  Magnetic helicity evolution in a periodic domain with imposed field  Relating Magnetic Field Strengths to Hard X-Ray Emission in Solar Flares  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 

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