Low latitude auroras: the storm of 25 September 1909 |
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| Institution: | 1. University of Iowa, Dept. of Physics and Astronomy, Iowa City, IA 52242, USA;2. LESIA, Observatoire de Paris, CNRS, UPMC, Universit Paris Diderot, Meudon, France;3. Imperial College of Science, Technology and Medicine, Space and Atmospheric Physics Group, Department of Physics, London SW7 2BW, UK;4. University of Leicester, Department of Physics and Astronomy, Leicester LE1 7RH, UK;5. Central Arizona College, Department of Science, Coolidge, AZ 85128, USA;6. Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109, USA;7. Space Environment Technologies, Planetary and Space Science Division, 320 N. Halstead Street, Suite 110, Pasadena, CA 91107, USA;8. Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, 1234 Innovation Drive, Boulder, CO 80303, USA;1. School of Computer Science and Technology, Tianjin University, Tianjin 300072, China;2. Department of Basic Courses, Academy of Military Transportation, PLA, Tianjin 300161, China;3. Tianjin Key Laboratory of Cognitive Computing and Application, Tianjin 300072, China;4. School of Computer Science and Software, Hebei University of Technology, Tianjin 300130, China;5. School of Computer and Information Technology, Henan Normal University, Xinxiang 453007, China;1. Department of Computer Science, Electrical, and Space Engineering, Luleå University of Technology, Box 812, Rymdcampus, S-981 28 Kiruna, Sweden;2. Institute for Aerospace Studies, University of Toronto, Toronto M3H 5T6, Canada;1. School of Materials Science and Engineering, Southeast University, Nanjing 211189, China;2. Jiangsu Key Laboratory of Advanced Metallic Materials, Nanjing 211189, China;3. College of Materials Science and Engineering, Nanjing Tech University, 5 Xinmofan Road, Nanjing 210009, China;4. School of Information Science and Engineering, Southeast University, Nanjing 210096, China |
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| Abstract: | Visual auroras at low latitudes are rare, documented for only five occasions since 1859. They are important from a theoretical point of view in terms of the lowest latitude at which particle precipitation can been observed. One of the great magnetic storms of the past 150 yr occurred on 25 September 1909, during the prolonged solar activity minimum around the beginning of the present century. A report of an auroral sighting at Singapore, not far from the magnetic equator, the lowest latitude ever reported for a visual aurora. has focussed attention on this event. This paper compiles and discusses the solar, magnetic, auroral, and telegraphic disturbance data related to the event. The data show that the lowest credible magnetic latitude for this event was between 30° and 36°. I conclude that the report of a visual auroral observation at Singapore, based on a single Australian newspaper item, was almost certainly not auroral at all, but rather resulted from cable disturbances, known to be associated with auroras, and confused with the aurora itself. Furthermore, consideration of the height at which particle precipitation would be observed leads to an estimate of a threshold magnetic latitude for a visual auroral event of the order of 15°, greater than that of 'Singapore. This result removes the necessity of theories of major storms to account for such a low latitude sighting. |
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