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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 36, issue 4 | Copyright
Ann. Geophys., 36, 1153-1160, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 29 Aug 2018

Regular paper | 29 Aug 2018

Sporadic auroras near the geomagnetic equator: in the Philippines, on 27 October 1856

Hisashi Hayakawa1,2,3, José M. Vaquero4, and Yusuke Ebihara5,6 Hisashi Hayakawa et al.
  • 1Graduate School of Letters, Osaka University, Toyonaka, 5600043, Japan
  • 2Science and Technology Facilities Council, RAL Space, Rutherford Appleton Laboratory, Harwell Campus, Didcot, OX11 0QX, UK
  • 3Japan Society for the Promotion of Science, 5-3-1 Kojimachi, Chiyoda-ku, Tokyo 102-0083, Japan
  • 4Departamento de Física, Universidad de Extremadura, 06800 Mérida, Spain
  • 5Research Institute for Sustainable Humanosphere, Kyoto University, Uji, 6100011, Japan
  • 6Unit of Synergetic Studies for Space, Kyoto University, Kyoto, 6068306, Japan

Abstract. While low-latitude auroral displays are normally considered to be a manifestation of magnetic storms of considerable size, Silverman (2003, JGR, 108, A4) reported numerous sporadic auroras which appear locally at relatively low magnetic latitude during times of just moderate magnetic activity. Here, a case study is presented of an aurora near the geomagnetic equator based on a report from the Philippine islands on 27 October 1856. An analysis of this report shows it to be consistent with the known cases of sporadic auroras, except for its appearance at considerably low magnetic latitude. The record also suggests that an extremely low-latitude aurora is not always accompanied by large magnetic storms. The description of its brief appearance leads to a possible physical explanation based on an ephemeral magnetospheric disturbance provoking this sporadic aurora.

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Short summary
A record has been found of an "aurora" observed on 27 October 1856 in the Philippines, practically at the magnetic equator. An analysis of this report indicates that it could belong to a "sporadic aurora" because of low magnetic activity at that time. We provide a possible physical mechanism that could explain the appearance of this sporadic, low-latitude aurora, according to the analyses on the observational report and magnetic observations at that time.
A record has been found of an "aurora" observed on 27 October 1856 in the Philippines,...