Visualization of the challenges and limitations of the long-term sunspot number record

Abstract

The solar cycle periodically reshapes the magnetic structure and radiative output of the Sun and determines its impact on the heliosphere roughly every 11 years. Besides this main periodicity, it shows century-long variations (including periods of abnormally low solar activity called grand minima). The Maunder Minimum (1645-1715) has generated significant interest as the archetype of a grand minimum in magnetic activity for the Sun and other stars, suggesting a potential link between the Sun and changes in terrestrial climate. Recent reanalyses of sunspot observations have yielded a conflicted view on the evolution of solar activity during the past 400 years (a steady increase versus a constant level). This has ignited a concerted community-wide effort to understand the depth of the Maunder Minimum and the subsequent secular evolution of solar activity. The goal of this Perspective is to review recent work that uses historical data to estimate long-term solar variability, and to provide context to users of these estimates that may not be aware of their limitations. We propose a clear visual guide than can be used to easily assess observational coverage for different periods, as well as the level of disagreement between currently proposed sunspot group number series.

References in corpus (8)

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Cited by in corpus (30)

• Re-calibration of the Sunspot Number: Status Report
• Long-term modulation of solar cycles
• Nonlinear mechanisms that regulate the solar cycle amplitude
• Cosmic Ray Extremely Distributed Observatory
• Thaddäus Derfflinger's sunspot observations during 1802-1824: A primary reference to understand the Dalton Minimum
• Robustness of Solar-Cycle Empirical Rules Across Different Series Including an Updated ADF Sunspot Group Series
• Sunspot characteristics at the onset of the Maunder Minimum based on the observations of Hevelius
• The Dalton Minimum and John Dalton's Auroral Observations
• Strong evidence of low levels of solar activity during the Maunder Minimum
• The Solar Corona during the Total Eclipse on 16 June 1806: Graphical Evidence of the Coronal Structure during the Dalton Minimum
• Reanalyses of the Sunspot Observations of Fogelius and Siverus: Two "Long-Term" Observers during the Maunder Minimum
• Revisiting Christoph Scheiner's Sunspot Records: a New Perspective on Solar Activity of the Early Telescopic Era
• Number of Sunspot Groups from the Galileo-Scheiner controversy revisited
• Christian Horrebow's Sunspot Observations -- I. Life and Published Writings
• Modeling stellar Ca II H & K emission variations. I. Effect of inclination on the S-index
• Over seven decades of solar microwave data obtained with Toyokawa and Nobeyama Radio Polarimeters
• The effect of telescope aperture, scattered light, and human vision on early measurements of sunspot and group numbers
• Stephan Prantner's Sunspot Observations during the Dalton Minimum
• Daniel Mögling's sunspot observations in 1626 - 1629: A manuscript reference for the solar activity before the Maunder Minimum
• Soonspot: Software to Determine Areas and Sunspot Positions
• Candidate Auroral Observations during the Major Solar-Terrestrial Storm in May 1680: Implication for Space Weather Events during the Maunder Minimum
• Sunspot observations by Charles Malapert during the period 1618-1626: a key dataset to understand solar activity before the Maunder minimum
• Reconstruction of the Sunspot Number Source Database and the 1947 Zurich Discontinuity
• Revisiting the Amplitude of Solar Cycle 9: The Case of Sunspot Observations by W.C. Bond
• On the use of naked-eye sunspot observations during the Maunder Minimum
• Comparison of solar activity proxies: eigen vectors versus averaged sunspot numbers
• Planetary Influences on the Solar Cycle: A Nonlinear Dynamics Approach
• Sunspot Records by Antonio Colla just after the Dalton Minimum
• Recovery of the Solar Cycle from Maunder-like Grand Minima Episodes: A Quantification of the Necessary Polar Flux Threshold through Solar Dynamo Simulations
• Low-Latitude Sunspot Group Tilt Angles in 15-24 Activity Cycles