Group Number

Since 2015, we are distributing the Group Number time series next to our primary sunspot data sets. Although the group number is produced completely independently from the Sunspot Number, there are multiple good reasons to offer this extra service. Currently, we are not extending yet the published Group Number series on a monthly basis, like the base Sunspot Number (in preparation).

Archive of raw group counts

This is the current master archive of all base group observations used as input data for building the current group number series.
Reference: Revised collection of the number of sunspot groups from 1610 to 2010.
J.M. Vaquero, L. Svalgaard, V.M.S. Carrasco, F. Clette, L. Lefevre, M.C. Gallego, R. Arlt, A.J.P. Aparicio, J.-G. Richard, and R. Howe, 2016: "Revised collection of the number of sunspot groups from 1610 to 2010", Solar Physics, submitted
SOURCE ARTICLE (DRAFT)
  • Archive of raw daily group counts
  • List of observers/stations
  • Differences between revised and original archive

  • Group Number series VERSION 1.0

    Original group number series by Hoyt & Schatten 1998

    Hoyt, D. V. and Schatten, K. H., 1998a: "Group Sunspot Numbers: A New Solar Activity Reconstruction", Solar Physics, 179, 189-219. DOI: 10.1023/A:1005007527816
    http://link.springer.com/article/10.1023%2FA%3A1005007527816
    Hoyt, D. V. and Schatten, K. H., 1998b: "Group Sunspot Numbers: A New Solar Activity Reconstruction", Solar Physics, 181, 491-512. DOI: 10.1023/A:1005056326158
    http://link.springer.com/article/10.1023%2FA%3A1005056326158

    The corresponding archive of input data can be found at: http://www.ngdc.noaa.gov/stp/space-weather/solar-data/solar-indices/sunspot-numbers/group/daily-input-data/ or ftp://ftp.ngdc.noaa.gov/STP/space-weather/solar-data/solar-indices/sunspot-numbers/group/daily-input-data/


  • Daily group number.
  • Monthly mean group number.
  • Yearly mean group number.

  • Group Number series VERSION 2.0 (Alternate series).

    There is no agreement yet between those recently published series, mostly concerning the long-term evolution over centuries. We just note here that there are two "families" of group numbers sharing similar characteristics:
    - the "backbone" and "error testing" series, without steady secular trend in solar cycle amplitudes, which also agree well with the sunspot number series.
    - the "active-days" series and original V1.0 series, with a rising trend from the 18th to the 20th century that does not match the sunspot number series.

    Svalgaard & Schatten 2015: "backbone" group number

    Svalgaard, L. & Schatten K.H. 2016:Reconstruction of the Sunspot Group Number: The Backbone Method
    Solar Physics, on-line Feb. 2016 DOI: 10.1007/s11207-015-0815-8
    http://link.springer.com/article/10.1007%2Fs11207-015-0815-8
    ArXiv e-print: http://arxiv.org/abs/1506.00755

  • Yearly mean group number.

  • Usoskin et al. 2016: "active-days" group number

    I.G. Usoskin, G.A. Kovaltsov, M. Lockwood, K. Mursula, M. Owens, S.K. Solanki, 2016:
    A New Calibrated Sunspot Group Series Since 1749: Statistics of Active Day Fractions
    Solar Physics, on-line Jan. 2016, DOI: 10.1007/s11207-015-0838-1
    http://link.springer.com/article/10.1007%2Fs11207-015-0838-1
    ArXiv e-print: http://arxiv.org/abs/1512.06421
  • Daily group number.
  • Monthly mean group number.
  • Yearly mean group number.

  • Cliver & Ling 2016: "error testing" group number

    Cliver, E.W. & Ling A.G. 2016: The Discontinuity Circa 1885 in the Group Sunspot Number
    Solar Physics, on-line Feb. 2016, DOI: 10.1007/s11207-015-0841-6
    http://link.springer.com/article/10.1007%2Fs11207-015-0841-6
  • Daily group number.
  • Monthly mean group number.
  • Yearly mean group number.