Volume 427, Number 1, November III 2004
|Page(s)||13 - 21|
|Published online||25 October 2004|
Catastrophic alpha quenching alleviated by helicity flux and shear
NORDITA, Blegdamsvej 17, 2100 Copenhagen Ø, Denmark e-mail: email@example.com
2 Astrophysical Institute Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany e-mail: CSandin@aip.de
Accepted: 21 July 2004
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 a finite imposed toroidal magnetic field. The results suggest that, due to a finite flux of current helicity out of the domain, alpha 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, alpha quenching is always catastrophic and alpha decreases inversely proportional to the magnetic Reynolds number. For solar parameters, our results suggest a current helicity flux of about . This corresponds to a magnetic helicity flux, integrated over the northern hemisphere and over the 11 year solar cycle, of about .
Key words: magnetohydrodynamics (MHD) / turbulence / Sun: magnetic fields
© ESO, 2004
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.