Versions of Time Series for Classical Solar Indices and an Adequate Description of Solar Activity

Abstract

This article discusses issues relevant to the 2015 recalibration of the time series of classical solar indices. It shows that the Wolf numbers WN and the group numbers GN are sensitive to the quality of the observations underpinning the reconstructions of the relevant time series, given the intermittent recordings in the 17th and 18th centuries. The authors suggest that research efforts should focus on the compilation of a long series of total sunspot areas (absolute sunspot magnetic flux), because, on the one hand, this series is less sensitive to poor-quality observations, while, on the other hand, it reflects a clear physical index.