University of Oulu

Clette, F., Lefèvre, L., Chatzistergos, T. et al. Recalibration of the Sunspot-Number: Status Report. Sol Phys 298, 44 (2023).

Recalibration of the sunspot-number : status report

Saved in:
Author: Clette, F.1; Lefèvre, L.1; Chatzistergos, T.2;
Organizations: 1World Data Center SILSO, Royal Observatory of Belgium, 3 avenue Circulaire, 1180, Brussels, Belgium
2Max Planck Institute for Solar System Research, Justus-von-Liebig-weg 3, 37077, Göttingen, Germany
3Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, 4648601, Japan
4Institute for Advanced Research, Nagoya University, Nagoya, 4648601, Japan
5Space Physics and Operations Division, RAL Space, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Oxford, Didcot, Oxfordshire, OX11 0QX, UK
6Nishina Centre, Riken, Wako, 3510198, Japan
7Departamento de Física, Universidad de Extremadura, E-06006, Badajoz, Spain
8Leibniz-Institut f. Astrophysik Potsdam, An der Sternwarte 16, 14482, Potsdam, Germany
9National Solar Observatory, 3665 Discovery Drive, 3rd Floor, Boulder, CO, 80303, USA
10LPC2E, CNRS/CNES/University of Orléans, 45067, Orléans, France
11International Space Science Institute, Hallerstrasse 6, 3012, Bern, Switzerland
12Rudolf Wolf Society, Ahornweg 29, 3123, Belp, Switzerland
13Ulugh Beg Astronomical Institute, Uzbekistan Academy of Sciences, 33 Astronomicheskaya str., 100052, Tashkent, Uzbekistan
14Laboratory for Atmospheric and Space Physics, University of Colorado, 3665 Discovery Dr., Boulder, CO, 80303, USA
15Department of Meteorology, University of Reading, Earley Gate, PO Box 243, Reading, RG6 6BB, UK
16ISBA/LIDAM, UCLouvain, Pl. de l’Université 1, 1348, Ottignies-Louvain-la-Neuve, Belgium
17Division of Solar System Science, Southwest Research Institute, Boulder, CO, USA
18Code 671, NASA Goddard Space Flight Center, Greenbelt, MD, 20771, USA
19Hansen Experimental Physics Lab, Stanford University, Stanford, CA, 94305, USA
20Space Physics and Astronomy Research Unit and Sodankylä Geophysical Observatory, University of Oulu, 90014, Oulu, Finland
21Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK
22Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, F-92195, Meudon, France
23Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Konkoly Thege út 15-17, H-1121, Budapest, Hungary
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 6.1 MB)
Persistent link:
Language: English
Published: Springer Nature, 2023
Publish Date: 2023-09-25


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 reconstruction 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 the next versions of these two time series in 2024.

see all

Series: Solar physics
ISSN: 0038-0938
ISSN-E: 1573-093X
ISSN-L: 0038-0938
Volume: 298
Issue: 3
Article number: 44
DOI: 10.1007/s11207-023-02136-3
Type of Publication: A2 Review article in a scientific journal
Field of Science: 115 Astronomy and space science
Funding: Open Access funding enabled and organized by Projekt DEAL. F. Clette and L. Lefèvre are supported by the Belgian Solar-Terrestrial Center of Excellence (STCE) funded by the Belgian Science Policy Office. L. Lefèvre acknowledges funding from the Belgian Federal Science Policy Office (BELSPO) through the BRAIN VAL-U-SUN project (BR/165/A3/VALU-SUN). T. Chatzistergos acknowledges support by the German Federal Ministry of Education and Research (Project No. 01LG1909C). H. Hayakawa acknowledges financial support by JSPS Grant-in-Aids JP20K22367, JP20K20918, JP20H05643, and JP21K13957, JSPS Overseas Challenge Program for Young Researchers, and the ISEE director’s leadership fund for FY2021, Young Leader Cultivation (YLC) programme of Nagoya University, Tokai Pathways to Global Excellence (Nagoya University) of the Strategic Professional Development Program for Young Researchers (MEXT), and the young researcher units for the advancement of new and undeveloped fields, Institute for Advanced Research, Nagoya University of the Program for Promoting the Enhancement of Research Universities. I. Usoskin acknowledges partial support of the Academy of Finland (project ESPERA No. 321882). L. van Driel-Gesztelyi acknowledges the Hungarian National Research, Development and Innovation Office grant OTKA K-131508.
Academy of Finland Grant Number: 321882
Detailed Information: 321882 (Academy of Finland Funding decision)
Copyright information: © 2023 The Authors. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit