Re-calibration of the Sunspot Number: Status Report

Abstract

We report progress on the ongoing recalibration of the Wolf sunspot number (SN) and Group sunspot number (GN) following the release of version 2.0 of SN in 2015. This report constitutes both an update of the efforts reported in the 2016 Topical Issue of Solar Physics and a summary of work by the International Space Science Institute (ISSI) International Team formed in 2017 to develop optimal SN and GN re-construction methods while continuing to expand the historical sunspot number database. Significant progress has been made on the database side while more work is needed to bring the various proposed SN and (primarily) GN reconstruction methods closer to maturity, after which the new reconstructions (or combinations thereof) can be compared with (a) ``benchmark'' expectations for any normalization scheme (e.g., a general increase in observer normalization factors going back in time), and (b) independent proxy data series such as F10.7 and the daily range of variations of Earth's undisturbed magnetic field. New versions of the underlying databases for SN and GN will shortly become available for years through 2022 and we anticipate the release of next versions of these two time series in 2024.

arXiv comment21 figures, 4 tables. To be published in Solar Physics

References in corpus (75)

• Revisiting the Sunspot Number
• Solar Modulation of Cosmic Rays
• Solar Irradiance Variability and Climate
• The new Sunspot Number: assembling all corrections
• Solar cycle prediction
• A Millennium Scale Sunspot Number Reconstruction: Evidence For an Unusually Active Sun Since the 1940's
• Reconstruction of the Sunspot Group Number: the Backbone Method
• The Maunder minimum (1645--1715) was indeed a Grand minimum: A reassessment of multiple datasets
• A new model of cosmogenic production of radiocarbon 14C in the atmosphere
• A Revised Collection of Sunspot Group Numbers
• Magnitudes and Timescales of Total Solar Irradiance Variability
• Production of cosmogenic isotopes 7Be, 10Be, 14C, 22Na and 36Cl in the atmosphere: Altitudinal profiles of yield functions
• A New Calibrated Sunspot Group Series Since 1749: Statistics of Active Day Fractions
• Visualization of the challenges and limitations of the long-term sunspot number record
• Solar total and spectral irradiance reconstruction over the last 9000 years
• Sunspot positions and sizes for 1825-1867 from the observations by Samuel Heinrich Schwabe
• Solar cyclic activity over the last millennium reconstructed from annual 14C data
• Temporal and Spatial Evolutions of a Large Sunspot Group and Great Auroral Storms around the Carrington Event in 1859
• Solar activity over nine millennia: A consistent multi-proxy reconstruction
• A solar cycle lost in 1793--1800: Early sunspot observations resolve the old mystery
• Revisited sunspot data: A new scenario for the onset of the Maunder minimum
• The Impact of the Revised Sunspot Record on Solar Irradiance Reconstructions
• Heliospheric Magnetic Field 1835-2009
• Level and length of cyclic solar activity during the Maunder minimum as deduced from the active day statistics
• The revised Brussels-Locarno Sunspot Number (1981-2015)
• Analysis of full disc Ca II K spectroheliograms III. Plage area composite series covering 1892-2019
• Sunspot positions, areas, and group tilt angles for 1611-1631 from observations by Christoph Scheiner
• Full-disc Ca II K observations -- a window to past solar magnetism
• An Assessment of Sunspot Number Data Composites over 1845-2014
• Thaddäus Derfflinger's sunspot observations during 1802-1824: A primary reference to understand the Dalton Minimum
• Is the $F_{10.7cm}$ -- Sunspot Number relation linear and stable ?
• Uncertainties in the Sunspot Numbers: Estimation and Implications
• Redefining the limit dates for the Maunder Minimum
• Solar activity: intrinsic periodicities beyond 11 years
• Updated sunspot group number reconstruction for 1749-1996 using the active day fraction method
• A Great Space Weather Event in February 1730
• Sunspot characteristics at the onset of the Maunder Minimum based on the observations of Hevelius
• Robustness of Solar-Cycle Empirical Rules Across Different Series Including an Updated ADF Sunspot Group Series
• The Dalton Minimum and John Dalton's Auroral Observations
• Strong evidence of low levels of solar activity during the Maunder Minimum
• Reconstructed sunspot positions in the Maunder Minimum based on the correspondence of Gottfried Kirch
• Modelling the evolution of the Sun's open and total magnetic flux
• Scrutinizing the relationship between plage areas and sunspot areas and numbers
• Christian Horrebow's Sunspot Observations -- II. Construction of a Record of Sunspot Positions
• The umbra-penumbra area ratio of sunspots during the Maunder Minimum
• Reconstruction of Solar Extreme Ultraviolet Flux 1740-2015
• Iwahashi Zenbei's Sunspot Drawings in 1793 in Japan
• 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
• Dependence of the Sunspot-group Size on the Level of Solar Activity and its Influence on the Calibration of Solar Observers
• Number of Sunspot Groups from the Galileo-Scheiner controversy revisited
• Sunspot Observations Made by Hallaschka during the Dalton Minimum
• Christian Horrebow's Sunspot Observations -- I. Life and Published Writings
• Sunspot Observations and Counting at Specola Solare Ticinese in Locarno since 1957
• Sunspot Catalogue of the Observatory of the University of Coimbra (1929-1941)
• The Sunspot Catalogues of Carrington, Peters, and de la Rue: Quality Control and Machine-readable Versions
• How faculae and network relate to sunspots, and the implications for solar and stellar brightness variations
• 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
• Uncertainty quantification in sunspot counts
• Sunspot Observations by Hisako Koyama: 1945-1996
• Revisiting Kunitomo's Sunspot Drawings during 1835-1836 in Japan
• The lost sunspot cycle: New support from Be10 measurements
• Sunspot Drawings by Japanese Official Astronomers in 1749-1750
• Scale Transfer in 1849 : Heinrich Schwabe to Rudolf Wolf
• A modern reconstruction of Carrington's observations (1853-1861)
• Reconstruction of the Sunspot Number Source Database and the 1947 Zurich Discontinuity
• Sunspot observations by Charles Malapert during the period 1618-1626: a key dataset to understand solar activity before the Maunder minimum
• A Test of the Active Day Fraction Method of Sunspot Group Number Calibration: Dependence on the Level of Solar Activity
• Response of solar irradiance to sunspot area variations
• Revisiting the Amplitude of Solar Cycle 9: The Case of Sunspot Observations by W.C. Bond
• A Sunspot Catalog for the Period 1952-1986 from Observations Made at the Madrid Astronomical Observatory
• Nonparametric monitoring of sunspot number observations: a case study
• Sunspot Records by Antonio Colla just after the Dalton Minimum

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• The 10 October 2024 geomagnetic storm may have caused the premature reentry of a Starlink satellite
• The Extreme Space Weather Event of 1872 February: Sunspots, Magnetic Disturbance, and Auroral Displays
• Analysis of full-disc H alpha observations: Carrington maps and filament properties in 1909-2022
• On the Strength and Duration of Solar Cycle 25: A Novel Quantile-based Superposed Epoch Analysis
• Bošković's method for determining the axis and rate of solar rotation by observing sunspots in 1777
• Reconstruction of annual solar irradiance over the last three millennia
• Solar Irradiance Reconstruction over the Telescopic Era Using a Revised Photospheric Magnetic Field Model
• Sub-surface structural changes associated with successive 11-yr solar activity cycles have been progressively more confined near the surface: new helioseismic results on Cycles 22 -- 25 from BiSON
• Low-Latitude Sunspot Group Tilt Angles in 15-24 Activity Cycles
• Sunspot Observations in 1684-1702: John Flamsteed and Philippe de La Hire