Reconstruction of the Sunspot Group Number: The Backbone Method

• Published in: Solar physics Vol. 291; no. 9-10; pp. 2653 - 2684
• Main Authors: Svalgaard, Leif, Schatten, Kenneth H.
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.11.2016; Springer Nature B.V
• Subjects: Astrophysics and Astroparticles; Atmospheric Sciences; Counting; Geomagnetism; Intervals; Observers; Physics; Physics and Astronomy; Reconstruction; Rigidity; Solar activity; Solar cycle; Solar physics; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics; Sunspot Number Recalibration; Sunspots; Reconstruction; Sunspot Group Number; Solar Cycle
• ISSN: 0038-0938; 1573-093X
• DOI: 10.1007/s11207-015-0815-8

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.