Catastrophic alpha quenching alleviated by helicity flux and shear
Abstract
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 alpha effect in the northern hemisphere. In three dimensions with turbulence driven by a helical forcing function, an alpha effect is self-consistently generated in the presence of an imposed toroidal magnetic field. The results suggest that, due to a finite flux of current helicity out of the domain, alpha quenching is non-catastrophic. Control experiments with closed boundary conditions confirm that in the absence of a current helicity flux, alpha quenching is catastrophic and alpha decreases inversely proportional to the magnetic Reynolds number.Keywords
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