Revisiting the Sunspot Number

  title={Revisiting the Sunspot Number},
  author={Fr{\'e}d{\'e}ric Clette and Leif Svalgaard and Jos{\'e} Manuel Vaquero and Edward W. Cliver},
  journal={Space Science Reviews},
Our knowledge of the long-term evolution of solar activity and of its primary modulation, the 11-year cycle, largely depends on a single direct observational record: the visual sunspot counts that retrace the last 4 centuries, since the invention of the astronomical telescope. Currently, this activity index is available in two main forms: the International Sunspot Number initiated by R. Wolf in 1849 and the Group Number constructed more recently by Hoyt and Schatten (Sol. Phys. 179:189–219… 
Visualization of the challenges and limitations of the long-term sunspot number record
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History of Sunspot Research and Forecast of the Maximum of Solar Cycle 25
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Sunspot observations by Hisako Koyama: 1945–1996
Sunspot records are the only observational tracer of solar activity that provides a fundamental, multicentury reference. Its homogeneity has been largely maintained with a succession of
Revisiting Christoph Scheiner’s Sunspot Records: A New Perspective on Solar Activity of the Early Telescopic Era
Christoph Scheiner was one of the most outstanding astronomers in the history of sunspot observations. His book, Rosa Ursina, is the reference work regarding the study of the earliest sunspot
Evolution of the Sunspot Number and Solar Wind B$B$ Time Series
The past two decades have witnessed significant changes in our knowledge of long-term solar and solar wind activity. The sunspot number time series (1700-present) developed by Rudolf Wolf during the
The Revised Brussels–Locarno Sunspot Number (1981 – 2015)
In 1981, the production of the international sunspot number moved from the Zürich Observatory to the Royal Observatory of Belgium, with a new pilot station: the Specola Solare Ticinese Observatory in
A new look at sunspot formation using theory and observations
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The Impact of the Revised Sunspot Record on Solar Irradiance Reconstructions
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Long-term studies of photospheric magnetic fields on the Sun
We briefly review the history of observations of magnetic fields on the Sun, and describe early magnetograps for full disk measurements. Changes in instruments and detectors, the cohort of observers,
Revisiting the Amplitude of Solar Cycle 9: The Case of Sunspot Observations by W.C. Bond
William Cranch Bond, director of the Harvard College Observatory in mid-19th century, carried out detailed sunspot observations during the period 1847–1849. We highlight Bond was the observer with


A global small sunspot deficit at the base of the index anomalies of solar cycle 23
Context. The variability of the 11-year cycle of solar activity on secular timescales is well established through the sunspot record, but it remains unpredictable. Indeed, the duration of the last
Are the sunspots really vanishing?. Anomalies in solar cycle 23 and implications for long-term models and proxies
Context: The elapsed solar cycle (23) ended with an exceptionally long period of low activity and with unprecedented low levels for various series of solar irradiance and particle flux measurements.
Because of the lack of reliable sunspot observations, the quality of the sunspot number series is poor in the late 18th century, leading to the abnormally long solar cycle (1784–1799) before the
Centennial variations in sunspot number, open solar flux, and streamer belt width: 1. Correction of the sunspot number record since 1874
We analyze the widely used international/Zürich sunspot number record, R, with a view to quantifying a suspected calibration discontinuity around 1945 (which has been termed the “Waldmeier
A new look at wolf sunspot numbers in the late 1700's
Long-term homogeneous observations of solar activity or many solar cycles are essential for investigating many problems in solar physics and climatology. The one key parameter used in most long-term
Long-term evolution of sunspot magnetic fields
Abstract Independent of the normal solar cycle, a decrease in the sunspot magnetic field strength has been observed using the Zeeman-split 1564.8nm Fe I spectral line at the NSO Kitt Peak
Was One Sunspot Cycle Lost In Late Xviii Century
We suggest that one solar cycle was lost in the beginning of the Dalton minimum because of sparse and partly unreliable sunspot observations. So far this cycle was combined with the preceding
Unusual activity of the Sun during recent decades compared to the previous 11,000 years
A reconstruction of the sunspot number covering the past 11,400 years is reported, based on dendrochronologically dated radiocarbon concentrations, and it is pointed out that solar variability is unlikely to have been the dominant cause of the strong warming during the past three decades.