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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 24, issue 10
Ann. Geophys., 24, 2743–2758, 2006
https://doi.org/10.5194/angeo-24-2743-2006
© Author(s) 2006. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 24, 2743–2758, 2006
https://doi.org/10.5194/angeo-24-2743-2006
© Author(s) 2006. This work is distributed under
the Creative Commons Attribution 3.0 License.

  20 Oct 2006

20 Oct 2006

The presence of large sunspots near the central solar meridian at the times of modern Japanese auroral observations

D. M. Willis1,2, R. Henwood3, and F. R. Stephenson4 D. M. Willis et al.
  • 1Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, UK
  • 2Centre for Fusion, Space and Astrophysics, Department of Physics, University of Warwick, Coventry CV4 7AL, UK
  • 3UK Solar System Data Centre, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, UK
  • 4Department of East Asian Studies, University of Durham, Durham DH1 3TH, UK

Abstract. The validity of a technique developed by the authors to identify historical occurrences of intense geomagnetic storms, which is based on finding approximately coincident observations of sunspots and aurorae recorded in East Asian histories, is corroborated using more modern sunspot and auroral observations. Scientific observations of aurorae in Japan during the interval 1957–2004 are used to identify geomagnetic storms that are sufficiently intense to produce auroral displays at low geomagnetic latitudes. By examining white-light images of the Sun obtained by the Royal Greenwich Observatory, the Big Bear Solar Observatory, the Debrecen Heliophysical Observatory and the Solar and Heliospheric Observatory spacecraft, it is found that a sunspot large enough to be seen with the unaided eye by an "experienced" observer was located reasonably close to the central solar meridian immediately before all but one of the 30 distinct Japanese auroral events, which represents a 97% success rate. Even an "average" observer would probably have been able to see a sunspot with the unaided eye before 24 of these 30 events, which represents an 80% success rate. This corroboration of the validity of the technique used to identify historical occurences of intense geomagnetic storms is important because early unaided-eye observations of sunspots and aurorae provide the only possible means of identifying individual historical geomagnetic storms during the greater part of the past two millennia.

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