DMCA
ASTRONOMY AND ASTROPHYSICS The dynamo effect of magnetic flux tubes
BibTeX
@MISC{Ossendrijver_astronomyand,
author = {M. A. J. H. Ossendrijver},
title = {ASTRONOMY AND ASTROPHYSICS The dynamo effect of magnetic flux tubes},
year = {}
}
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Abstract
Abstract. It is shown that toroidal magnetic flux tubes in a rotating star do not provide a net dynamo effect, even if they are subject to random forcing, unless the tubes are unstable to small displacements. The dynamo effect is produced by transverse helical waves that propagate along the flux tube, resulting in an electric current (anti-) parallel to the unperturbed magnetic field, equivalent to an alpha effect. For unstable flux tubes, the alpha effect is enabled by a systematic phase difference between the velocity and magnetic field perturbations. For stable flux tubes subject to random forcing, phase differences do occur, but they vanish in the mean. The requirement for instability is met if the magnetic field strength exceeds a threshold value. Therefore a stellar dynamo based on flux tubes is not self-excited, but needs triggering until the magnetic threshold is surpassed. Key words: Magnetohydrodynamics (MHD) – stars: magnetic fields – stars: late-type – Sun: magnetic fields 1.
Keyphrases
dynamo effect magnetic flux tube alpha effect flux tube magnetic field perturbation magnetic field stellar dynamo rotating star stable flux tube transverse helical wave magnetic threshold toroidal magnetic flux tube key word net dynamo effect phase difference threshold value small displacement magnetic field star systematic phase difference unstable flux tube late-type sun magnetic field strength unperturbed magnetic field
