A Normalized Sunspot-Area Series Starting in 1832: An Update
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A new normalized sunspot-area series has been reconstructed from the series obtained by the Royal Greenwich Observatory and other contemporary institutions for the period 1874 – 2008 and the area series compiled by De la Rue, Stewart, and Loewy from 1832 to 1868. Since the two sets of series do not overlap in time, we used the new version of sunspot index number (Version 2) published by Sunspot Index and Long-term Solar Observations (SILSO) as a link between them. We also present a spectral analysis of the normalized-area series in search of periodicities beyond the well-known solar cycle of 11 years and a study of the Waldmeier effect in the new version of sunspot number and the sunspot-area series presented in this study. We conclude that while this effect is significant in the new series of sunspot number, it has a weak relationship with the sunspot-area series.
KeywordsSolar cycle, observations Sunspots, statistics
Support from the Junta de Extremadura (Research Group Grants GR15137 and GR15146) and from the Ministerio de Economía y Competitividad of the Spanish Government (AYA2014-57556-P) is gratefully acknowledged. We wish to thank the referee for the useful comments that helped to improve this article. Furthermore, we are grateful to the guest editors of this topical issue on Sunspot Number Recalibration (L. Svalgaard and F. Clette) for their useful suggestions.
Disclosure of Potential Conflicts of Interest
The authors declare that they have no conflicts of interest.
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