Reconstruction of the Sunspot Group Number: the Backbone Method

TL;DR

This paper reconstructs the sunspot group number using a novel backbone method based on original sources, providing a pure solar activity index that challenges claims of recent exceptional activity.

Contribution

It introduces the backbone method for reconstructing sunspot groups, relying solely on original sources without external proxies, offering a more direct solar activity measure.

Findings

Solar activity levels have remained consistent over the last three centuries.

Recent decades are not unusually active compared to historical levels.

The method provides a robust, source-based reconstruction of solar activity.

Abstract

We have reconstructed the sunspot group count, not by comparisons with other reconstructions and correcting those where they were deemed to be deficient, but by a re-assessment of original sources. The resulting series is a pure solar index and does not rely on input from other proxies, e.g. radionuclides, auroral sightings, or geomagnetic records. 'Backboning' the data sets, our chosen method, provides substance and rigidity by using long-time observers as a stiffness character. Solar activity, as defined by the Group Number, appears to reach and sustain for extended intervals of time the same level in each of the last three centuries since 1700 and the past several decades do not seem to have been exceptionally active, contrary to what is often claimed.