National Institute of Polar Research
Centuries-old drawings lead to better understanding of fan-shaped auroras
Released on May 21, 2019 (in Japanese)
Posted on May 31, 2019
Physics researchers and literature researchers have joined together to better understand the rare natural phenomenon of white and red auroras fanning across the night sky in Japan. Armed with drawings and descriptions dating back to the 1700s, microfilm from the 1950s, and today’s spectral image data, they’ve confirmed the accuracy of the older depictions. They’ve also started to understand how the fan-shaped auroras appear, both in the sky and to the eye.
The team published their results on May 17, 2019, in Journal of Space Weather and Space Climate.
An illustration entitled "Aurora Borealis as observed on March 1, 1872 at 9:25 P.M."
Credit: Etienne Leopold Trouvelot (The New York Public Library Digital Collections, https://digitalcollections.nypl.org/items/510d47dd-e6cd-a3d9-e040-e00a18064a99).
Red auroras are fan-shaped auroras characterized by light that appears to begin at the horizon, stretching into white fingers that spread wide across the sky. The fan is infused with a red glow.
"These phenomena are rare, but potentially disrupt man-made ground-based systems, including power grids," said paper author Ryuho Kataoka, an associate professor at National Institute of Polar Research and the Graduate University for Advanced Studies (SOKENDAI) in Tokyo, Japan. "If we understand such auroras, it may help mitigate the possible natural hazard they could produce."
The first depiction of such an aurora appears in a drawing from 1770. On September 17 of that year, the greatest magnetic storm to ever occur over Kyoto, Japan was recorded. During a magnetic storm, more charged particles are violently blown into the Earth's outer atmosphere. As they crash into one another, the energized atmospheric particles lose energy because of emitting light.
"In the modern-day era, one of the strongest solar activities occurred in 1957," Kataoka said. "Auroras appeared over Japan several times in a few years around that event."
On February 11, 1958, several Japanese meteorologists observed red auroras in northern Japan. Some took the first photographs of the fan-shaped auroras while others drew them. Through modern analysis, Kataoka and the team found that the photographs caught more data than might be available to the human eye, such as thin, green pillars dispersed through the aurora.
Sample photograph (left, at 1044 UT) and hand-made sketch (right, at 1037 UT) of the auroras, as observed at Memambetsu Magnetic Observatory on February 11, 1958. Both images are in the all-sky format, where zenith is the center and geographic north is to the top.
The time-lapse photography of the microfilm data of all-sky photographs taken at Memambetsu Magnetic Observatory on February 11, 1958. After digitization of the microfilms, we manually centered, scaled, and rotated the images without altering the contrast or brightness. The final data were saved in an all-sky format, where zenith is the center, geographic north is to the top, and the 90° from the zenith is at the edge of the square.
"It's still challenging to understand the dynamic coupling between the space and atmosphere during the largest magnetic storms," Kataoka said.
The colors of auroras contain trace evidence of which particles crashed where. The bulk motion of the auroras tells us the active coupling between the space and atmosphere in the middle latitude when plasma gets into the atmosphere at a large scale. With this information, researchers may be able to determine the exact nature of the largest magnetic storms.
Next, the researchers plan to simulate the effects of space weather in the outer atmospheres during the special occasion of fan-shaped auroras and to reveal how they were created.
Other contributors from the National Institute of Polar Research are Shiori Uchino; Yasunori Fujiwara, who also has an affiliation with SOKENDAI; and Shigeru Fujita, who also has an affiliation with the Meteorological College in Chiba. Kazuaki Yamamoto of the National Institute of Japanese Literature also contributed.
Original Article
Journal: Journal of Space Weather and Space Climate
Title: Fan-shaped aurora as seen from Japan during a great magnetic storm on February 11, 1958
Authors: Ryuho Kataoka1,2, Shiori Uchino1, Yasunori Fujiwara1,2, Shigeru Fujita1,3 and Kazuaki Yamamoto4
1 National Institute of Polar Research, Japan
2 SOKENDAI (The Graduate University for Advanced Studies), Japan
3 Meteorological College, Japan
4 National Institute of Japanese Literature, Japan
DOI: 10.1051/swsc/2019013
URL: https://www.swsc-journal.org/articles/swsc/full_html/2019/01/swsc180063/swsc180063.html
Publication date: May 17, 2019
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