Laure Lefèvre

A Revised Collection of Sunspot Group Numbers

We describe a revised collection of the number of sunspot groups from 1610 to the present. This new collection is based on the work of Hoyt and Schatten (Solar Phys. 179, 189, 1998). The main changes are the elimination of a considerable number of observations during the Maunder Minimum (hereafter, MM) and the inclusion of several long series of observations. Numerous minor changes are also described. Moreover, we have calculated the active-day percentage during the MM from this new collection as a reliable index of the solar activity. Thus, the level of solar activity obtained in this work is greater than the level obtained using the original Hoyt and Schatten data, although it remains compatible with a grand minimum of solar activity. The new collection is available in digital format.

The new Sunspot Number: assembling all corrections

Based on various diagnostics and corrections established in the framework of several Sunspot Number Workshops and described by Clette et al. (Space Sci. Rev.186, 35, 2014), we now assembled all separately derived corrections to produce a new standard version of the reference sunspot-number time series. We explain here the three main corrections and the criteria used to choose a final optimal version of each correction factor or function, given the available information and published analyses. We then discuss the differences between the new corrected series and the original sunspot number, including the disappearance of any significant rising secular trend in the solar-cycle amplitudes after this recalibration. We also introduce the new version management scheme now implemented at the World Data Center Sunspot Index and Long-term Solar Observations (WDC-SILSO), which reflects a major conceptual transition: beyond the rescaled numbers, this first revision of the sunspot number also transforms the former static data archive into a living observational series open to future improvements.

The Revised Brussels–Locarno Sunspot Number (1981 – 2015)

In 1981, the production of the international sunspot number moved from the Zürich Observatory to the Royal Observatory of Belgium, with a new pilot station: the Specola Solare Ticinese Observatory in Locarno, Switzerland. This marked a profound transition in the history of the sunspot number. Those recent decades are particularly important as they provide the link between recent modern solar indices and the entire sunspot-number series extending back to the eighteenth century. However, large variations have recently been identified in the scale of the sunspot number during this recent time period. Here, we refine the determination of those recent inhomogeneities by reconstructing a new average sunspot-number series [SN

Uncertainties in the Sunspot Numbers: Estimation and Implications

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Equivalence Relations Between the Cortie and Zürich Sunspot Group Morphological Classifications

] from a subset of long-duration stations between 1981 and 2015. We also extend this reconstruction by gathering long time series from 35 stations over 1945 – 2015, thus straddling the critical 1981 transition. In both reconstructions, we also derive a parallel group number series [GN

In-depth survey of sunspot and active region catalogs

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Are the sunspots really vanishing? - Anomalies in solar cycle 23 and implications for long-term models and proxies

] built by the same method from exactly the same data set. Our results confirm the variable trends associated with drifts of the Locarno pilot station, which start only in 1983. They lead to a fully uniform SN

Revision of the Sunspot Number(s)

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Survey and Merging of Sunspot Catalogs

-series over the entire 1945 – 2015 interval. By comparing the new SN

Preface to Topical Issue: Recalibration of the Sunspot Number

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