Space Science Reviews

, Volume 94, Issue 1–2, pp 145–152 | Cite as

Modelling solar irradiance variations: Comparison with observations, including line-ratio variations

  • Y.C. Unruh
  • S.K. Solanki
  • M. Fligge


Solar irradiance variations show a strong temporal and spectral dependence. The progression of the Sun through its activity cycle as well as solar rotation are mirrored in the irradiance variations. The spectral dependence is such that the variations are several magnitudes larger in the EUV than in the visible or infrared.

We present a simple 3-component model that is based on the assumption that changes in the solar flux are exclusively due to changes in spot and facular coverage. We compare our model to observations of the spectral solar irradiance variations.

Despite its simplicity, we find that the agreement between our model and the observations is surprisingly good. We also explore the reliability and the limitations of our approach by comparing observations of the solar facular contrast and of the changes in spectral line depths with our calculations.


Spectral Line Solar Irradiance Activity Cycle Spectral Dependence Solar Rotation 
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.


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  1. Auffret, H. and Muller, R.: 1991, A&A 246, 264.Google Scholar
  2. Chapman, G. A. and McGuire, T. E.: 1977, ApJ 217, 657.Google Scholar
  3. Chapman, G. A., Cookson, A. M. and Dobias, J. J.: 1997, ApJ 482, 541.Google Scholar
  4. Fligge, M., Solanki, S. K., Unruh, Y. C., Fröhlich, C. and Wehrli, C.: 1998, A&A 335, 709.Google Scholar
  5. Fligge, M., Solanki, S. K. and Unruh, Y. C.: 2000a, A&A 353, 380.Google Scholar
  6. Fligge, M., Solanki, S. K. and Unruh, Y. C.: 2000b, Space Sci. Rev., this volume.Google Scholar
  7. Fontenla, J. M., Avrett, E. H. and Loeser, R.: 1993, ApJ 406, 319.Google Scholar
  8. Fontenla, J. M., White, O.R., Fox, P.A., Avrett, E. H. and Kurucz, R.L.: 1999, ApJ 518, 480.Google Scholar
  9. Frazier, E. N.: 1971, Solar Phys. 21, 42.Google Scholar
  10. Fröhlich, C. and Lean, J.: 1998, GRL 25, 4377.Google Scholar
  11. Fröhlich, C. et al.: 1997, Solar Phys. 170, 1.Google Scholar
  12. Gray, D. F. and Livingston, W. C.: 1997a, ApJ 474, 802.Google Scholar
  13. Gray, D. F. and Livingston, W. C.: 1997b, ApJ 474, 798.Google Scholar
  14. Kurucz, R. L.: 1991, in Stellar Atmospheres: Beyond Classical Models, L. Crivellari, I. Hubeny, D. G. Hummer (Eds), Kluwer, Dordrecht, p. 441.Google Scholar
  15. Lawrence, J. K. and Chapman, G. A.: 1988, ApJ 335, 996.Google Scholar
  16. Lean, J.: 1997, ARA&A 35, 33.Google Scholar
  17. Libbrecht, K. G. and Kuhn, J. R.: 1985, ApJ 299, 1047.Google Scholar
  18. Mitchell, W. E. Jr. and Livingston, W. C.: 1991, ApJ 372, 336.Google Scholar
  19. Solanki, S. K. and Unruh, Y. C.: 1998, A&A 329, 747.Google Scholar
  20. Taylor, S. F., Varsik, J. R., Woodard, M. F. and Libbrecht, K. G.: 1998, Solar Phys. 178, 1.Google Scholar
  21. Unruh, Y. C., Solanki, S. K. and Fligge, M.: 1999, A&A 345, 635.Google Scholar
  22. Wang, H. and Zirin, H.: 1987, Solar Phys. 110, 281.Google Scholar
  23. White, O.R., Fontenla, J. M. and Fox, P.A.: 2000, Space Sci. Rev., this volume.Google Scholar
  24. Willson, R. C. and Hudson, H. S.: 1991, Nat 351, 42.Google Scholar

Copyright information

© Kluwer Academic Publishers 2000

Authors and Affiliations

  • Y.C. Unruh
    • 1
  • S.K. Solanki
    • 2
  • M. Fligge
    • 3
  1. 1.Institute of AstronomyUniversity of ViennaWienAustria
  2. 2.Max-Planck-Institut für AeronomieKatlenburg-LindauGermany
  3. 3.Institute of AstronomyETH ZentrumZürichSwitzerland

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