The European Physical Journal D

, Volume 53, Issue 2, pp 205–212 | Cite as

Fibrillation of solar magnetic fields

  • J. M.A. AshbournEmail author
  • L. C. Woods
Plasma Physics


Solar magnetic structures are often observed in the form of flux tubes composed of a number of smaller elements called fibres or threads, although theoretically such concentrations should not appear but should be flattened by magnetic diffusivity into a uniform, low intensity field. In this paper we describe a mechanism which may be responsible for the fibrillation and also for the very large diffusivity which dissipates magnetic flux tubes in hours instead of years. Firstly, the electric current associated with magnetic field gradients usually increases the local electron temperature and reduces the resistivity, so that the current becomes concentrated into sheets or streamers. Secondly, the magnetic field gradients continue to increase until the current magnitude reaches its limit, which is determined by the electron-ion streaming instability. Then with appropriate temperature and number densities, the Larmor radius of the ions overlaps the near discontinuity in Bz and generates a sharply peaked fluid motion at the edge that is close to the thermal speed. Finally, the resulting vorticity generates an axial magnetic field opposing Bz in the term \(\partial B_z/\partial t\), and if this is sufficient to change the sign of this term, the very unstable backward heat equation results. This instability repeatedly switches on and off and maintains the magnetic structure in the fibrillated form. Such structures are eventually eliminated by magnetic diffusivity in the usual way, but because of the fluctuations in Bz, this occurs at a vastly increased rate. We show that this phenomenon increases the magnetic diffusivity, D, by a factor ~ 108 in agreement with some observations of plasma loops and supergranules.


96.60.-j Solar physics 96.60.Hv Electric and magnetic fields, solar magnetism 41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems 


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  1. M.J. Aschwanden, R.W. Nightingale, D. Alexander, Astrophys. J. 541, 1059 (2000)Google Scholar
  2. C.J. Schrijver, C. Zwann, Solar and Stellar Magnetic Activity (Cambridge Univ. Press, Cambridge, 2000)Google Scholar
  3. H. Zirin, Astrophysics of the Sun (Cambridge Univ. Press, Cambridge, 1988)Google Scholar
  4. R.J. Bray, L.E. Cram, C.J. Durrant, R.E. Loughhead, Plasma Loops in the Solar Corona (Cambridge Univ. Press, Cambridge, 1991)Google Scholar
  5. J.H. Thomas, N.O. Weiss, S.M. Tobias, N.H. Brummell, Nature 420, 390 (2002)Google Scholar
  6. D. Laveder, T. Passot, P.L. Sulem, Phys. Plasmas 9, 293 (2002)Google Scholar
  7. M.J. Tildesley, N.O. Weiss, Mon. Not. R. Astron. Soc. 350, 657 (2004)Google Scholar
  8. J.M.A. Ashbourn, L.C. Woods, Phys. Scr. 74, 349 (2006)Google Scholar
  9. L.C. Woods, Physics of Plasmas (Wiley-VCH, Weinheim, 2004)Google Scholar
  10. J.R. Ockendon, S.D. Howison, A.A. Lacey, A.B. Movchan, Applied Partial Differential Equations (Oxford Univ. Press, Oxford, 1999)Google Scholar
  11. N.A. Krall, A.W. Trivelpiece, Principles of Plasma Physics (McGraw-Hill Book Co., New York, 1973)Google Scholar
  12. L.C. Woods, Principles of Magnetoplasma Dynamics (Oxford Univ. Press, Oxford, 1987)Google Scholar
  13. E.R. Priest, C.J. Schrijver, Sol. Phys. 190, 1 (1999)Google Scholar
  14. M.J. Aschwanden, R.W. Nightingale, Astrophys. J. 633, 599 (2005)Google Scholar
  15. G.A. Gary, Sol. Phys. 203, 71 (2001)Google Scholar
  16. K. Shibasaki, Astrophys. J. 557, 326 (2001)Google Scholar

Copyright information

© EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2009

Authors and Affiliations

  1. 1.Mathematical Institute, University of OxfordOxfordUK

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