Solar Physics

, Volume 149, Issue 1, pp 1–21 | Cite as

Intermediate degree p-mode frequency splittings near solar maximum

  • R. S. Ronan
  • B. J. Labonte
Article

Abstract

We report on observations of global solar Ca K-line intensity oscillations taken in May 1991 from Mees Solar Observatory, Hawaii. We measurep-mode frequency splittings for modes of spherical harmonic degrees between 20 and 129 averaged over the radial order of the modes. Our measurement of the antisymmetric component of the splittings is comparable with previous measurements and thus indicates a decrease in the latitudinal differential rotation with depth into the convection zone and the upper radiative zone. We find evidence for a 1% variation in the rotation rate of the upper convection zone roughly in phase with the solar activity cycle. Our measurement of the symmetric component of the splittings is of the same order as was reported from the previous solar maximum and is an order of magnitude larger than has been measured near solar minimum. From the degree dependence of the symmetric component of the splittings, we find evidence for an aspherical fractional sound speed perturbation located at a depth of 0.85 ± 0.05 solar radii. This perturbation has a magnitude ofδc/c ≈ +9 × 10−4 at the equator relative to the poles. Additionally, there is evidence for a near-surface aspherical sound speed perturbation of smaller magnitudeδc/c ≈ +4 × 10−4 at the equator relative to the poles. If an intense global magnetic field were the dominant source of the observed symmetric component of the splittings, instead of latitudinal gradients in the sound speed, then global fields of order 105 G would be required in the convection zone.

Keywords

Convection Zone Solar Minimum Solar Maximum Differential Rotation Solar Observatory 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Brown, T. M.: 1985,Nature 317, 591.Google Scholar
  2. Brown, T. M. and Morrow, C. A.: 1987,Astrophys. J. 314, L21.Google Scholar
  3. Brown, T. M., Christensen-Dalsgaard, J., Dziembowski, W. A., Goode, P., Gough, D. O., and Morrow, C. A.: 1989,Astrophys. J. 343, 526.Google Scholar
  4. Christensen-Dalsgaard, J., Duvall, T. L., Jr., Gough, D. O., Harvey, J. W., and Rhodes, E. J.: 1985,Nature 315, 378.Google Scholar
  5. Dziembowski, W. A. and Goode, P. R.: 1992,Astrophys. J. 394, 670.Google Scholar
  6. Duvall, T. L., Jr. and Harvey, J. W.: 1984,Nature 310, 19.Google Scholar
  7. Duvall, T. L., Jr., Harvey, J. W., and Pomerantz, M. A.: 1986,Nature 321, 500.Google Scholar
  8. Duvall, T. L., Jr., Dziembowski, W. A., Goode, P. R., Gough, D. O., Harvey, J. W., and Leibacher, J. W.: 1984,Nature 310, 22.Google Scholar
  9. Fisher, G. H., Chou, D. Y., and McClymont, A. N.: 1989, in J. H. Waite, J. L. Burch, and R. L. Moore (eds.),Solar System Plasma Physics, AGU, Washington, D.C., p. 47.Google Scholar
  10. Gilman, P. A. and Howard, R.: 1984,Astrophys. J. 283, 385.Google Scholar
  11. Goode, P. R., Dziembowski, W. A., Korzennik, S. G., and Rhodes, E. J., Jr.: 1991,Astrophys. J. 367, 649.Google Scholar
  12. Gough, D. O.: 1988, in E. J. Rolfe (ed.),Seismology of the Sun and Sun-like Stars, ESA Publications Division, Noordwijk, The Netherlands, p. 679.Google Scholar
  13. Gough, D. O.: 1990, in Y. Osaki and H. Shibahashi (eds.),Progress of Seismology of the Sun and Stars, Springer-Verlag, Berlin, p. 283.Google Scholar
  14. Gough, D. O. and Thompson, M. J.: 1990,Monthly Notices Roy. Astron. Soc. 242, 22.Google Scholar
  15. Hansen, C. J., Cox, J. P., and Van Horn, H. M.: 1977,Astrophys. J. 290, 765.Google Scholar
  16. Jefferies, S. M., Pomerantz, M. A., Duvall, T. L., Jr., Harvey, J. W., and Jaksha, D. B.: 1988, in E. J. Rolfe (ed.),Seismology of the Sun and Sun-like Stars, ESA Publications Division, Noordwijk, The Netherlands, p. 279.Google Scholar
  17. Korzennik, S.: 1990, Ph.D. Thesis, University of California, Los Angeles.Google Scholar
  18. Kuhn, J. R.: 1988,Astrophys. J. 331, L131.Google Scholar
  19. Leighton, R. B., Noyes, R. W., and Simon, G. W.: 1962,Astrophys. J. 135, 474.Google Scholar
  20. Libbrecht, K. G.: 1989,Astrophys. J. 336, 1092.Google Scholar
  21. Libbrecht, K. G. and Woodard, M. F.: 1990,Nature 345, 779.Google Scholar
  22. Libbrecht, K. G. and Zirin, H.: 1986,Astrophys. J. 308, 413.Google Scholar
  23. Ronan, R. S. and LaBonte, B. J.: 1993, in T. M. Brown (ed.),GONG 1992: Seismic Investigation of the Sun and Stars, Astronomical Society of the Pacific Conference Series, Volume 42, San Francisco, p. 93.Google Scholar
  24. Ronan, R. S., Harvey, J. W., and Duvall, T. L., Jr.: 1991,Astrophys. J. 369, 549.Google Scholar
  25. Ronan, R. S., LaBonte, B. J., and Kupke, R.: 1991,Bull. Amer. Astron. Soc. 323, 1442.Google Scholar
  26. Snodgrass, H. B.: 1983,Astrophys. J. 270, 288.Google Scholar
  27. Tomczyk, S.: 1988, Ph.D. Thesis, University of California, Los Angeles.Google Scholar
  28. Ulrich, R. K.: 1970,Astrophys. J. 162, 993.Google Scholar

Copyright information

© Kluwer Academic Publishers 1994

Authors and Affiliations

  • R. S. Ronan
    • 1
  • B. J. Labonte
    • 2
  1. 1.Center for Space Science and AstrophysicsStanford UniversityStanfordUSA
  2. 2.Institute for AstronomyUniversity of HawaiiHonoluluUSA

Personalised recommendations