EDP Sciences
Free access
Volume 449, Number 2, April II 2006
Page(s) 781 - 789
Section The Sun
DOI http://dx.doi.org/10.1051/0004-6361:20054401
A&A 449, 781-789 (2006)
DOI: 10.1051/0004-6361:20054401

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

P. Chatterjee1, A. R. Choudhuri1, 2 and K. Petrovay1, 2, 3

1  Department of Physics, Indian Institute of Science, Bangalore 560012, India
2  Eötvös University, Department of Astronomy, Budapest, Pf. 32, 1518, Hungary
    e-mail: K.Petrovay@astro.elte.hu
3  Department of Applied Mathematics, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH, UK

(Received 24 October 2005 / Accepted 8 December 2005 )

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.

Key words: Sun: interior -- Sun: magnetic fields -- magnetohydrodynamics (MHD)

© ESO 2006

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access.

An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account.
    In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.