A great space weather event in February 1730

¹ Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, UK
e-mail: hisashi.hayakawa@stfc.ac.uk
² Graduate School of Letters, Osaka University, Toyonaka, 5600043, Japan (JSPS Research Fellow)
e-mail: hayakawa@kwasan.kyoto-u.ac.jp
³ Research Institute for Sustainable Humanosphere, Kyoto University, Uji, 6100011, Japan
⁴ Unit of Synergetic Studies for Space, Kyoto University, Kyoto, 6068306, Japan
⁵ Departamento de Física, Universidad de Extremadura, 06800 Mérida, Spain
⁶ Graduate School of Science, Kyoto University, Kyoto, 6068501, Japan
⁷ Departamento de Física, Universidad de Extremadura, 06071 Badajoz, Spain
⁸ Faculty of Engineering, The University of Tokyo, Tokyo, 1130033, Japan
⁹ Oriental Astronomical Association, 6500021 Kobe, Japan
¹⁰ National Institute of Japanese Literature, Tachikawa, 1900014, Japan
¹¹ Kwasan Observatory, Kyoto University, Kyoto, 6078471 Japan
¹² Graduate School of Advanced Integrated Studies in Human Survivability, Kyoto University, Kyoto, 6068306 Japan

Received: 30 January 2018
Accepted: 23 April 2018

Abstract

Aims. Historical records provide evidence of extreme magnetic storms with equatorward auroral extensions before the epoch of systematic magnetic observations. One significant magnetic storm occurred on February 15, 1730. We scale this magnetic storm with auroral extension and contextualise it based on contemporary solar activity.

Methods. We examined historical records in East Asia and computed the magnetic latitude (MLAT) of observational sites to scale magnetic storms. We also compared them with auroral records in Southern Europe. We examined contemporary sunspot observations to reconstruct detailed solar activity between 1729 and 1731.

Results. We show 29 auroral records in East Asian historical documents and 37 sunspot observations.

Conclusions. These records show that the auroral displays were visible at least down to 25.8° MLAT throughout East Asia. In comparison with contemporary European records, we show that the boundary of the auroral display closest to the equator surpassed 45.1° MLAT and possibly came down to 31.5° MLAT in its maximum phase, with considerable brightness. Contemporary sunspot records show an active phase in the first half of 1730 during the declining phase of the solar cycle. This magnetic storm was at least as intense as the magnetic storm in 1989, but less intense than the Carrington event.