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A Note on Solar Cycle Length Estimates


Recently, new estimates of the solar cycle length (SCL) have been calculated using the Zurich Sunspot Number (RZ) and the Regression-Fourier-Calculus (RFC)-method, a mathematically rigorous method involving multiple regression, Fourier approximation, and analytical expressions for the first derivative. In this short contribution, we show estimates of the solar cycle length using the RFC-method and the Group Sunspot Number (RG) instead the RZ. Several authors have showed the advantages of RG for the analysis of sunspot activity before 1850. The use of RG solves some doubtful solar cycle length estimates obtained around 1800 using RZ.

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  1. Benestad, R.E.: 2005, Geophys. Res. Lett. 32, L15714. DOI: 10.1029/2005GL023621.

  2. Damon, P.E. and Laut, P.: 2004, Eos Trans. AGU 85, 370.

  3. Friis-Christensen, E. and Lassen, K.: 1991, Science 254, 698.

  4. Hathaway, D.H., Wilson, R.M., and Reichmann, E.J.: 2002, Solar Phys. 211, 357.

  5. Hoyt, D.V. and Schatten, K.H.: 1998, Solar Phys. 179, 189 (reprinted with figures from Solar Phys. 181, 491).

  6. Kane, R.P.: 2002, Solar Phys. 205, 383.

  7. Krivova, N.A., Solanki, S.K., and Beer, J.: 2002, Astron. Astrophys. 396, 235.

  8. Laut, P.: 2003, J. Atmos. Sol. Terr. Phys. 65, 801.

  9. McKinnon, J.A.: 1987, Sunspot Numbers: 1610–1985, National Geophysical Data Center, NOAA, Boulder, Colorado.

  10. Mursula, K. and Ulich, Th.: 1998, Geophys. Res. Lett. 25, 1837.

  11. R Development Core Team: 2004, R: A Language and Environment for Statistical Computing, R Foundations for Statistical Computing, Vienna, Austria (available at http://www.R-project.org.

  12. Solanki, S.K., Krivova, N.A., Schussler, M., and Fligge, M.: 2002, Astron. Astrophys. 396, 1029.

  13. Usoskin, I.G., Mursula, K., and Kovaltsov, G.A.: 2001, Astron. Astrophys. 370, L31.

  14. Usoskin, I.G., Mursula, K., and Kovaltsov, G.A.: 2002, Geophys. Res. Lett. 29, 2183. DOI:10.1029/2002GL015640.

  15. Usoskin, I.G., Mursula, K., and Kovaltsov, G.A.: 2003, Astron. Astrophys. 403, 743.

  16. Usoskin, I.G. and Kovaltsov, G.A.: 2004, Solar Phys. 224, 37.

  17. Vanlommel, P., Cugnon, P., van der Linden, R.A.M., Berghmans, D., and Clette, F.: 2004, Solar Phys. 224, 113.

  18. Vaquero, J.M.: 2004, Solar Phys. 219, 379.

  19. Vaquero, J.M., Trigo, R.M., and Gallego, M.C.: 2005, Astron. Nachr. 326, 112.

  20. Waldmeier, M.: 1947, The Sunspot Activity in the Years 1610–1960, Zurich Schulthess and Company AG.

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Correspondence to J. M. Vaquero.

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Vaquero, J.M., García, J.A. & Gallego, M.C. A Note on Solar Cycle Length Estimates. Sol Phys 235, 433–437 (2006). https://doi.org/10.1007/s11207-006-0102-9

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  • Fourier
  • Solar Cycle
  • Cycle Length
  • Sunspot Number
  • Group Sunspot