Solar Physics

, Volume 173, Issue 2, pp 427–439 | Cite as


  • M. Fligge
  • S. K. Solanki


Most of the present models and reconstructions of solar irradiance use the concept of Photometric Sunspot Index (PSI) to account for the influence of sunspots on solar brightness. Since PSI is based on measured sunspot areas a firm database of such areas is essential. We show, however, that a significant disagreement exists between the data provided by the Royal Greenwich Observatory (from 1874 to 1976) and newer measurements provided by the observatories of Rome, Yunnan, Catania, and the US Air Force. The overlap of the time intervals over which sunspot areas were measured at Greenwich and Rome allows us to quantify the difference between the Greenwich and other data sets. We find that the various data sets differ, at least in a statistical sense, mainly by a correction factor of between 1.15 and 1.25.

The revised time series of sunspot areas correlates well with the Zürich sunspot relative numbers over the last 120 years, with the relationship between sunspot areas and sunspot numbers changing only slightly from one cycle to the next. In particular, no indication exists for any extraordinary magnetic behavior of the Sun during the last 2 decades, as might falsely be concluded if the various sunspot area data sets are uncritically combined. There are, however, some indications that cycles 15 and 16 deviate from the rest. We expect that our results should have a significant influence on the reconstruction of the historical solar irradiance.


Time Series Correction Factor Present Model Relative Number Sunspot Number 
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  1. Albregtsen, F. and Maltby, P.: 1978, Nature 274, 41.Google Scholar
  2. Bodgan, T. J., Gilman, P. A., Lerche, I., and Howard, R.: 1988, Astrophys. J. 327, 451.Google Scholar
  3. Brandt, P. N., Stix, M., and Weinhardt, H.: 1994, Solar Phys. 152, 119.Google Scholar
  4. Chapman, G. A.: 198, Ann. Rev. Astron. Astrophys. 25, 633.Google Scholar
  5. Chapman, G. A., Cookson, A. M., and Dobias, J. J.: 1994, Astrophys. J. 432, 403.Google Scholar
  6. Covington, A. E.: 1954, J. Geophys. Res. 59, 163.Google Scholar
  7. Covington, A. E.: 1959, in R. N. Bracewell (ed.), Paris Symposium on Radio Astronomy, Stanford University Press, Stanford, California, p. 159.Google Scholar
  8. Covington, A. E.: 1969, J. Roy. Astron. Soc. Can. 63, 125.Google Scholar
  9. Foukal, P.: 1981, in L. E. Cram and J. H. Thomas (eds.), The Physics of Sunspots: Sunspots and Changes in the Global Output of the Sun, Sacramento Peak Observatory Conference, p. 391.Google Scholar
  10. Foukal, P. and Lean, J.: 1986, Astrophys. J. 302, 826.Google Scholar
  11. Foukal, P. and Lean, J.: 1988, Astrophys. J. 328, 347.Google Scholar
  12. Foukal, P. and Lean, J.: 1990, Science 247, 556.Google Scholar
  13. Fröhlich, C.: 1992, in R. F. Donnelly (ed.), The Proceedings of Solar Electromagnetic Radiation Study for Cycle 22, NOAA/ERL/SEL, Boulder, CO, p. 1.Google Scholar
  14. Fröhlich, C.: 1994, in J. Pap, C. Fröhlich, H. S. Hudson, and S.K. Solanki (eds.), ‘The Sun as a Variable Star: Solar and Stellar Irradiance Variations’, IAU Colloq. 143, 28.Google Scholar
  15. Frö;hlich, C., Pap, J. M., and Hudson, H. S.: 1994, Solar Phys. 152, 111.Google Scholar
  16. Hudson, H. S., Silva, S., and Woodard, M.: 1982, Solar Phys. 76, 211.Google Scholar
  17. Kuhn, J. R. and Libbrecht, K. G.: 1991, Astrophys. J. 381, L35.Google Scholar
  18. Lean, J. and Foukal, P.: 1988, Science 240, 906.Google Scholar
  19. Pap, J., Willson, R. C., Frö;hlich, C., Donelly, R. F., and Puga, L.: 1994, Solar Phys. 152, 13.Google Scholar
  20. Tapping, K. F.: 1987, J. Geophys. Res. 92, 829.Google Scholar
  21. Steinegger, M., Brandt, P. N., Pap, J., and Schmidt, W.: 1990, Astrophys. Space Sci. 170, 127.Google Scholar
  22. Waldmeier, M.: 1978, Astronomische Mitteilungen der Eidgenössischen Sternwarte Zürich 358.Google Scholar
  23. Willson, R. C. and Hudson, H. S.: 1988, Nature 332, 810.Google Scholar
  24. Willson, R. C. and Hudson, H. S.: 1991, Nature 351, 42.Google Scholar
  25. Willson, R. M., Rabin, D., and Moore, R. L.: 1987, Solar Phys. 111, 279.Google Scholar
  26. Woodard, M. and Hudson, H. S.: 1983, Nature 305, 589.Google Scholar

Copyright information

© Kluwer Academic Publishers 1997

Authors and Affiliations

  • M. Fligge
    • 1
  • S. K. Solanki
    • 1
  1. 1.Institute of Astronomy, ETH-Zentrum 8092ZürichSwitzerland

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