Advertisement

Solar Physics

, Volume 205, Issue 1, pp 63–92 | Cite as

The Orientational Relaxation of Bipolar Active Regions

  • Dana Longcope
  • Arnab Rai Choudhuri
Article

Abstract

In the mean, bipolar active regions are oriented nearly toroidally, according to Hale's polarity law, with a latitude-dependent tilt known as Joy's Law. The tilt angles of individual active regions deviate from this mean behavior and change over time. It has been found that on average the change is toward the mean angle at a rate characteristic of 4.37 days (Howard, 1996). We show that this orientational relaxation is consistent with the standard model of flux tube emergence from a deep dynamo layer. Under this scenario Joy's law results from the Coriolis effect on the rising flux tube (D'Silva and Choudhuri, 1993), and departures from it result from turbulent buffeting of the tubes (Longcope and Fisher, 1996). We show that relaxation toward Joy's angle occurs because the turbulent perturbations relax on shorter time scales than the perturbations from the Coriolis force. The turbulent perturbations relax more rapidly because they are localized to the topmost portion of the convection zone while the Coriolis perturbations are more widely distributed. If a fully-developed active region remains connected to the strong toroidal magnetic field at the base of the convection zone, its tilt will eventually disappear, leaving it aligned perfectly toroidally. On the other hand, if the flux becomes disconnected from the toroidal field the bipole will assume a tilt indicative of the location of disconnection. We compare models which are connected and disconnected from the toroidal field. Only those disconnected at points very deep in the convection zone are consistent with observed time scale of orientational relaxation.

Keywords

Flux Tube Convection Zone Toroidal Field Toroidal Magnetic Field Orientational Relaxation 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Achterberg, A.: 1996, Astron. Astrophys. 313, 1008.Google Scholar
  2. Caligari, P., Moreno-Insertis, F., and Schüssler, M.: 1995, Astrophys. J. 441, 886.Google Scholar
  3. Choudhuri, A. R.: 1989, Solar Phys. 123, 217.Google Scholar
  4. Choudhuri, A. R. and Dikpati, M.: 1999, Solar Phys. 184, 61Google Scholar
  5. Choudhuri, A. R. and Gilman, P. A.: 1987, Astrophys. J. 316, 788.Google Scholar
  6. Choudhuri, A. R., Schüssler, M., and Dikpati, M.: 1995, Astron. Astrophys. 303, L29.Google Scholar
  7. Dikpati, M. and Charbonneau, P.: 1999, Astrophys. J. 518, 508.Google Scholar
  8. D'Silva, S. and Choudhuri, A. R.: 1993, Astron. Astrophys. 272, 621.Google Scholar
  9. D'Silva, S. and Howard, R. F.: 1993, Solar Phys. 148, 1.Google Scholar
  10. Durney, B. R.: 1995, Solar Phys. 160, 213.Google Scholar
  11. Durney, B. R.: 1997, Astrophys. J. 486, 1065.Google Scholar
  12. Fan, Y., Fisher, G. H., and DeLuca, E. E.: 1993, Astrophys. J. 405, 390.Google Scholar
  13. Fan, Y., Fisher, G. H., and McClymont, A. N.: 1994, Astrophys. J. 436, 907.Google Scholar
  14. Hale, G. E., Ellerman, F., Nicholson, S. B., and Joy, A. H: 1919, Astrophys. J. 49, 153.Google Scholar
  15. Howard, R. F.: 1992, Solar Phys. 137, 205.Google Scholar
  16. Howard, R. F.: 1996, Solar Phys. 169, 293.Google Scholar
  17. Howard, R. F., Gilman, P. A., and Gilman, P. I.: 1984. Astrophys. J. 283, 373.Google Scholar
  18. Longcope, D. W. and Fisher, G. H.: 1996, Astrophys. J. 458, 380.Google Scholar
  19. Lundquist, L. L. and Fisher, G. H.: 2001, AGU, Sping Meeting 2001.Google Scholar
  20. Moreno-Insertis, F., Schuessler, M., and Ferriz-Mas, A.: 1996, Astron. Astrophys. 312, 317.Google Scholar
  21. Nandy, D. and Choudhuri, A. R.: 2001, Astrophys. J. 551, 576.Google Scholar
  22. Press, W. H., Flannery, B. P., Teukolsky, S. A., and Vetterling, W. T.: 1986, Numerical Recipes: The Art of Scientific Computing, Cambridge University Press, Cambridge.Google Scholar
  23. Ryutov, D. A. and Ryutova, M. P.: 1976, Soviet Phys. JETP 43, 491.Google Scholar
  24. Spruit, H. C.: 1974, Solar Phys. 34, 277.Google Scholar
  25. Spruit, H. C.: 1981, Astron. Astrophys. 98, 155.Google Scholar
  26. Spruit, H. C., Title, A. M., and van Ballegooijen, A. A.: 1987, Solar Phys. 110, 115.Google Scholar
  27. Wang, Y.-M. and Sheeley, N. R.: 1989, Solar Phys. 124, 81.Google Scholar
  28. Wang, Y.-M., Nash, A. G., and Sheeley, N. R.: 1989, Astrophys. J. 347, 529.Google Scholar

Copyright information

© Kluwer Academic Publishers 2002

Authors and Affiliations

  • Dana Longcope
    • 1
  • Arnab Rai Choudhuri
    • 2
  1. 1.Department of PhysicsMontana State UniversityBozemanU.S.A
  2. 2.Department of PhysicsIndian Institute of ScienceBangaloreIndia

Personalised recommendations