Advertisement

Solar Physics

, Volume 264, Issue 1, pp 31–44 | Cite as

The Mount Wilson Ca ii K Plage Index Time Series

  • L. Bertello
  • R. K. Ulrich
  • J. E. Boyden
Open Access
Article

Abstract

It is well established that both total and spectral solar irradiance are modulated by variable magnetic activity on the solar surface. However, there is still disagreement about the contribution of individual solar features for changes in the solar output, in particular over decadal time scales. Ionized Ca ii K line spectroheliograms are one of the major resources for these long-term trend studies, mainly because such measurements have been available now for more than 100 years. In this paper we introduce a new Ca ii K plage and active network index time series derived from the digitization of almost 40 000 photographic solar images that were obtained at the 60-foot solar tower, between 1915 and 1985, as a part of the monitoring program of the Mount Wilson Observatory. We describe here the procedure we applied to calibrate the images and the properties of our new defined index, which is strongly correlated to the average fractional area of the visible solar disk occupied by plages and active network. We show that the long-term variation of this index is in an excellent agreement with the 11-year solar-cycle trend determined from the annual international sunspot numbers series. Our time series agrees also very well with similar indicators derived from a different reduction of the same data base and other Ca ii K spectroheliograms long-term synoptic programs, such as those at Kodaikanal Observatory (India), and at the National Solar Observatory at Sacramento Peak (USA). Finally, we show that using appropriate proxies it is possible to extend this time series up to date, making this data set one of the longest Ca ii K index series currently available.

Keywords

Chromosphere, active Solar activity, observations, data analysis 

References

  1. Chapman, G.A., Boyden, J.E.: 1986, Astrophys. J. Lett. 302, 71. CrossRefADSGoogle Scholar
  2. de Vaucouleurs, G.: 1968, Appl. Opt. 7, 1513. CrossRefADSGoogle Scholar
  3. Ermolli, I., Solanki, S.K., Tlatov, A.G., Krivova, N.A., Ulrich, R.K., Singh, J.: 2009, Astrophys. J. 698, 1000. CrossRefADSGoogle Scholar
  4. Fligge, M., Solanki, S.K., Unruh, Y.C.: 2000, Space Sci. Rev. 94, 139. CrossRefADSGoogle Scholar
  5. Foukal, P.: 2003, EOS Trans. 84, 205. ADSGoogle Scholar
  6. Foukal, P., Lean, J.: 1988, Astrophys. J. 328, 347. CrossRefADSGoogle Scholar
  7. Foukal, P., Milano, L.: 2001, Geophys. Res. Lett. 28, 883. CrossRefADSGoogle Scholar
  8. Foukal, P., Bernasconi, P., Eaton, H., Rust, D.: 2004, Astrophys. J. Lett. 611, 57. CrossRefADSGoogle Scholar
  9. Foukal, P., Fröhlich, C., Spruit, H., Wigley, T.M.L.: 2006, Nature 443, 161. CrossRefADSGoogle Scholar
  10. Foukal, P., Bertello, L., Livingston, W.C., Pevtsov, A.A., Singh, J., Tlatov, A.G., Ulrich, R.K.: 2009, Solar Phys. 255, 229. CrossRefADSGoogle Scholar
  11. Fröhlich, C.: 2009, Astron. Astrophys. 501, L27. CrossRefADSGoogle Scholar
  12. Fröhlich, C., Lean, J.: 2004, Astron. Astrophys. Rev. 12, 273. CrossRefADSGoogle Scholar
  13. Johannesson, A., Marquette, W.H., Zirin, H.: 1998, Solar Phys. 177, 265. CrossRefADSGoogle Scholar
  14. Lean, J.L.: 2001, Geophys. Res. Lett. 28, 4119. CrossRefADSGoogle Scholar
  15. Solanki, S.K.: 2003, AGU, Fall Meeting, SH31C-01. Google Scholar
  16. Solanki, S.K., Fligge, M.: 2002, Adv. Space Res. 29, 1933. CrossRefADSGoogle Scholar
  17. Solanki, S.K., Unruh, Y.C.: 1998, Astron. Astrophys. 329, 747. ADSGoogle Scholar
  18. Stott, P.A., Tett, S.F.B., Jones, G.S., Allen, M.R., Ingram, W.J., Mitchell, J.F.B.: 2000, Space Sci. Rev. 94, 337. CrossRefADSGoogle Scholar
  19. Tlatov, A.G., Pevtsov, A.A., Singh, J.: 2009, Solar Phys. 255, 239. CrossRefADSGoogle Scholar

Copyright information

© The Author(s) 2010

Authors and Affiliations

  1. 1.National Solar ObservatoryTucsonUSA
  2. 2.Department of Physics and AstronomyUniversity of CaliforniaLos AngelesUSA

Personalised recommendations