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Uncertainties in the Sunspot Numbers: Estimation and Implications


Sunspot number series are subject to various uncertainties that are still poorly known. The need to understand these better was recently highlighted by the major revision of the international Sunspot Number (Clette et al., in Space Sci. Rev. 186, 35, 2014). We present the first thorough estimation of these uncertainties, which behave as Poisson-like random variables with a multiplicative coefficient that is time- and observatory-dependent. We provide a simple expression for these uncertainties, and reveal how their evolution in time coincides with changes in the observations and processing of the data. Knowing their value is essential for properly building composites out of multiple observations, and for preserving the stability of the composites in time.

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    In the following, “sunspot number” will designate the sunspot number in a generic way, whereas “Wolf number” will refer to the relative sunspot number \([N_{\mathrm{W}}]\) from specific stations, and “international Sunspot Number” will be used for the composite \(S_{\mathrm{N}}\) from SILSO.


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We gratefully acknowledge funding from the European Community’s Seventh Framework Programme (FP7, 2012) under grant agreement no 313188 (SOLID, ). We sincerely thank the anonymous referee for carefully reviewing the manuscript, and for making pertinent comments.

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Correspondence to Thierry Dudok de Wit.

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The authors declare that they have no conflicts of interest.

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Sunspot Number Recalibration

Guest Editors: F. Clette, E.W. Cliver, L. Lefèvre, J.M. Vaquero, and L. Svalgaard

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Dudok de Wit, T., Lefèvre, L. & Clette, F. Uncertainties in the Sunspot Numbers: Estimation and Implications. Sol Phys 291, 2709–2731 (2016).

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  • Sunspots
  • Statistics