Development of twist in an emerging magnetic flux tube by poloidal field accretion

Chatterjee, P. ; Choudhuri, A. R. ; Petrovay, K. (2006) Development of twist in an emerging magnetic flux tube by poloidal field accretion Astronomy & Astrophysics, 449 (2). pp. 781-789. ISSN 0004-6361

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Official URL: http://www.aanda.org/index.php?option=com_article&...

Related URL: http://dx.doi.org/10.1051/0004-6361:20054401

Abstract

Aims: Following an earlier proposal for the origin of twist in the magnetic fields of solar active regions, we model the penetration of a wrapped up background poloidal field into a toroidal magnetic flux tube rising through the solar convective zone. Methods: The rise of the straight, cylindrical flux tube is followed by numerically solving the induction equation in a comoving Lagrangian frame, while an external poloidal magnetic field is assumed to be radially advected onto the tube with a speed corresponding to the rise velocity. Results: One prediction of our model is the existence of a ring of reverse current helicity on the periphery of active regions. On the other hand, the amplitude of the resulting twist depends sensitively on the assumed structure (diffuse vs. concentrated/intermittent) of the active region magnetic field right before its emergence, and on the assumed vertical profile of the poloidal field. Nevertheless, in the model with the most plausible choice of assumptions a mean twist comparable to the observations results. Conclusions: Our results indicate that the contribution of this mechanism to the twist can be quite significant, and under favourable circumstances it can potentially account for most of the current helicity observed in active regions.

Item Type:Article
Source:Copyright of this article belongs to EDP Sciences.
Keywords:Sun: Interior; Sun: Magnetic Fields; Magnetohydrodynamics (MHD)
ID Code:66567
Deposited On:24 Oct 2011 08:21
Last Modified:18 May 2016 14:03

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