NDLI: The Discontinuity Circa 1885 in the Group Sunspot Number

Content Provider	Springer Nature Link
Author	Cliver, E. W. Ling, A. G.
Copyright Year	2016
Abstract	On average, the international sunspot number ( $R_{\mathrm{I}}$ ) is 44 % higher than the group sunspot number ( $R_{\mathrm{G}}$ ) from 1885 to the beginning of the $R_{\mathrm{I}}$ series in 1700. This is the principal difference between $R_{\mathrm{I}}$ and $R_{\mathrm{G}}$ . Here we show that this difference is primarily due to an inhomogeneity in the Royal Greenwich Observatory (RGO) record of sunspot groups (1874 – 1976) used to derive observer normalization factors (called $k$ -factors) for $R_{\mathrm{G}}$ . Specifically, annual RGO group counts increase relative to those of Wolfer and other long-term observers from 1876 – 1915. A secondary contributing cause is that the $k$ -factors for observers who began observing before 1884 and overlapped with RGO for any years during 1874 – 1883 were not based on direct comparison with RGO but were calculated using one or more intermediary or additional observers. We introduce $R_{\mathrm{GC}}$ by rectifying the RGO group counts from 1874 – 1915 and basing $k$ -factors on direct comparison with RGO across the 1885 discontinuity, which brings the $R_{\mathrm{G}}$ and $R_{\mathrm{I}}$ series into reasonable agreement for the 1841 – 1885 interval (after correcting $R_{\mathrm{I}}$ for an inhomogeneity from 1849 – 1867 (to give $R_{\mathrm{IC}}$ )). Comparison with an independently derived backbone-based reconstruction of $R_{\mathrm{G}}$ ( $R_{\mathrm{BB}}$ ) indicates that $R_{\mathrm{GC}}$ over-corrects $R_{\mathrm{BB}}$ by 4 % on average from 1841 – 1925. Our analysis suggests that the maxima of Cycles 10 (in 1860), 12 (1883/1884), and 13 (1893) in the $R_{\mathrm{IC}}$ series are too low by ≈ 10 %.
Starting Page	2763
Ending Page	2784
Page Count	22
File Format	PDF
ISSN	00380938
Journal	Solar Physics
Volume Number	291
Issue Number	9-10
e-ISSN	1573093X
Language	English
Publisher	Springer Netherlands
Publisher Date	2016-02-01
Publisher Place	Dordrecht
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Sun Sunspots Sunspot number Astrophysics and Astroparticles Atmospheric Sciences Space Sciences (including Extraterrestrial Physics, Space Exploration and Astronautics)
Content Type	Text
Resource Type	Article
Subject	Astronomy and Astrophysics Space and Planetary Science

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1	Ministry of Education (GoI), Department of Higher Education	Sanctioning Authority	https://www.education.gov.in/ict-initiatives
2	Indian Institute of Technology Kharagpur	Host Institute of the Project: The host institute of the project is responsible for providing infrastructure support and hosting the project	https://www.iitkgp.ac.in
3	National Digital Library of India Office, Indian Institute of Technology Kharagpur	The administrative and infrastructural headquarters of the project	Dr. B. Sutradhar bsutra@ndl.gov.in
4	Project PI / Joint PI	Principal Investigator and Joint Principal Investigators of the project	Dr. B. Sutradhar bsutra@ndl.gov.in Prof. Saswat Chakrabarti will be added soon
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