Solar Physics

, Volume 246, Issue 2, pp 295–307 | Cite as

The 27-Day Signal in Sunspot Number Series and the Solar Dynamo

  • Jean-Louis Le Mouël
  • Mikhail G. Shnirman
  • Elena M. BlanterEmail author


We analyze the Wolf number daily series WN (1849 to present) as well as two other related series characterizing solar activity. Our analysis consists in computing the amplitude of a given Fourier component in a sliding time window and examining its long-term evolution. We start with the well-known 27.03- and 27.6-day periods and observe strong decadal variations of this amplitude as well as a sharp increase of the average value starting around 1905. We then consider a packet of 31 lines with periods from 25.743 to 28.453 days, which is shown to be a better representation of the synodic solar rotation. We first examine the temporal evolution of individual lines, then the energy of the packet. The energy of the packet increases sharply at the beginning of the 20th century, leading by more than two decades the well-known increase of the Wolf number. The nonaxisymmetry of sunspots increases before the total increase of activity and may be considered as a precursor. We discuss briefly and tentatively this observation in terms of solar dynamo theory.


Sunspots Sunspot number Solar activity Solar cycle Synodic rotation 27 days variation Solar magnetic field Solar dynamo 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Blanter, E., Le Mouël, J.L., Perrier, F., Shnirman, M.: 2006, Solar Phys. 237, 329. CrossRefADSGoogle Scholar
  2. Chulliat, A., Blanter, E., Le Mouël, J.L., Shnirman, M.: 2005, J. Geophys. Res. 110, A05301. CrossRefGoogle Scholar
  3. Cowling, T.G.: 1933, Mon. Not. Roy. Astron. Soc. 94, 39. zbMATHADSGoogle Scholar
  4. de Toma, G., White, O.R., Harvey, K.L.: 2000, Astrophys. J. 529, 1101. CrossRefADSGoogle Scholar
  5. Dorch, S.B.F., Nordlund, A.: 2001, Astron. Astrophys. 365, 562. CrossRefADSGoogle Scholar
  6. Gilman, P.A.: 1986, In: Sturrock, P.A. (ed.) The Solar Interior I, Reidel, Dordrecht. Google Scholar
  7. Hoyt, D.V., Schatten, K.H.: 1998, Solar Phys. 181, 491. CrossRefADSGoogle Scholar
  8. Kane, R.P.: 2002, Solar Phys. 209, 207. CrossRefADSGoogle Scholar
  9. Krause, H., Rädler, K.H.: 1980, Mean Field Magnetohydrodynamics and Dynamo Theory, Pergamon, Oxford. zbMATHGoogle Scholar
  10. Le Mouël, J.L., Blanter, E., Chulliat, A., Shnirman, M.G.: 2004, Ann. Geophys. 22, 985. ADSCrossRefGoogle Scholar
  11. Mordvinov, A.V., Plyusnina, L.A.: 2000, Solar Phys. 197, 1. CrossRefADSGoogle Scholar
  12. Mursala, K., Hiltula, T.: 2004, Solar Phys. 224, 133. CrossRefADSGoogle Scholar
  13. Neugebauer, M., Smith, E.J., Ruzmaikin, A., Feyman, J., Vaughan, A.H.: 2000, J. Geophys. Res. 105, 2315. CrossRefADSGoogle Scholar
  14. Ossendrijver, M.: 2003, Astron. Astrophys. Rev. 11, 287. CrossRefADSGoogle Scholar
  15. Parker, E.N.: 1979, Cosmical Magnetic Fields, Cambridge University Press, Cambridge. Google Scholar
  16. SIDC team: 1850 – 2005, Monthly Report on the International Sunspot Number,
  17. Solanki, S.K.: 2003, Astron. Astrophys. Rev. 11, 153. CrossRefADSGoogle Scholar
  18. Temmer, M., Veronig, A., Hanslmeier, A.: 2002, Astron. Astrophys. 390, 707. CrossRefADSGoogle Scholar
  19. Thompson, M.J., Christensen-Dalsgaard, J., Miesch, M.S., Toomre, J.: 2003, Ann. Rev. Astron. Astrophys. 41, 599. CrossRefADSGoogle Scholar
  20. Tobias, S.M., Brummel, N.H., Clune, T.L., Toomre, J.: 1998, Astrophys. J. 502, 177. CrossRefADSGoogle Scholar
  21. Tobias, S.M., Hugues, D.W.: 2004, Astrophys. J. 603, 785. CrossRefADSGoogle Scholar
  22. Tobias, S.M., Weiss, N.O.: 2007, In: Hughes, D.W., Rosner, R., Weiss, N.O. (eds.) The Solar Tachocline, Cambridge University Press, Cambridge. Google Scholar

Copyright information

© Springer Science+Business Media B.V. 2007

Authors and Affiliations

  • Jean-Louis Le Mouël
    • 1
  • Mikhail G. Shnirman
    • 1
    • 2
  • Elena M. Blanter
    • 1
    • 2
    Email author
  1. 1.Equipe de GéomagnétismeInstitut de Physique du Globe de ParisParis Cedex 05France
  2. 2.International Institute of Earthquake Prediction Theory and Mathematical GeophysicsMoscowRussia

Personalised recommendations