Space Science Reviews

, 214:56 | Cite as

Evolution of the Sunspot Number and Solar Wind \(B\) Time Series

  • Edward W. CliverEmail author
  • Konstantin Herbst
Part of the following topical collections:
  1. The Scientific Foundation of Space Weather


The past two decades have witnessed significant changes in our knowledge of long-term solar and solar wind activity. The sunspot number time series (1700-present) developed by Rudolf Wolf during the second half of the 19th century was revised and extended by the group sunspot number series (1610–1995) of Hoyt and Schatten during the 1990s. The group sunspot number is significantly lower than the Wolf series before ∼1885. An effort from 2011–2015 to understand and remove differences between these two series via a series of workshops had the unintended consequence of prompting several alternative constructions of the sunspot number. Thus it has been necessary to expand and extend the sunspot number reconciliation process. On the solar wind side, after a decade of controversy, an ISSI International Team used geomagnetic and sunspot data to obtain a high-confidence time series of the solar wind magnetic field strength (\(B\)) from 1750-present that can be compared with two independent long-term (> ∼600 year) series of annual \(B\)-values based on cosmogenic nuclides. In this paper, we trace the twists and turns leading to our current understanding of long-term solar and solar wind activity.


Sunspot number solar wind magnetic field strength 



E.W.C. thanks Daniel Baker, André Balogh, Tamás Gombosi, Hannu Koskinen, Rudolf von Steiger, and Astrid Veronig for organizing the ISSI Workshop on The Scientific Foundation of Space Weather and the invitation to speak on long-term solar variability. He is grateful to ISSI for supporting both this Workshop and, previously, the Svalgaard, Lockwood, and Beer International Team on Long-term reconstruction of Solar and Solar Wind Parameters. He thanks Leif Svalgaard for the translation of the Wolf (1856) article. K.H. thanks Jürg Beer, Ken McCracken, Bernd Heber, and Raimund Muscheler for their support and many insightful discussions over the past years.


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© Springer Science+Business Media B.V., part of Springer Nature 2018

Authors and Affiliations

  1. 1.National Solar ObservatoryBoulderUSA
  2. 2.Christian-Albrechts-Universität zu KielKielGermany

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