Solar Physics

, Volume 291, Issue 9–10, pp 3123–3138 | Cite as

Sunspot Numbers from ISOON: A Ten-Year Data Analysis

  • K. S. BalasubramaniamEmail author
  • T. W. Henry
Sunspot Number Recalibration


Sunspot numbers are important tracers of historical solar activity. They are important in predicting the oncoming solar maximum, in the design of lifetimes of space assets, and in assessing the extent of solar-radiation impact on the space environment. Historically, sunspot numbers have been obtained visually from sunspot drawings. The availability of digital images from the US Air Force Improved Solar Optical Observing Network (ISOON) prototype telescope concurrent to observer-dependent sunspot numbers recorded at the National Solar Observatory (NSO) has provided a basis for comparing sunspot numbers determined from the two methods. We compare sunspot numbers from visual and digital methods observed nearly simultaneously. The advantages of digital imagery are illustrated.


Sunspots Solar cycle Sunspot numbers 



This work was supported by the Space Vehicles Directorate, Air Force Research Laboratories (AFRL) and The Air Force Office of Scientific Research; AFRL. We are grateful to Donald Neidig and numerous members of joint AFRL–NSO ISOON Team, the AFRL Space Vehicles Directorate, and the NSO for developing and operating the ISOON prototype telescope for a decade and preserving its data. Particularly, Neidig’s insights into calibration of the data and into sunspot-counting techniques have inspired this article. We thank Ed Cliver, Frédéric Clette, Leif Svalgaard, and numerous colleagues for sustaining the important sunspot-number research through these workshops.

Disclosure of Potential Conflicts of Interest

The authors declare that they have no conflicts of interest.


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Copyright information

© Springer Science+Business Media Dordrecht (outside the USA) 2016

Authors and Affiliations

  1. 1.Air Force Research LaboratorySpace Vehicles DirectorateKirtland AFBUSA
  2. 2.Boston College at Air Force Research LaboratoryKirtland AFBUSA

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