In a collaborative effort between the arts and sciences, researchers at Kyoto University and Japan's National Institute of Polar Research (NIPR) and National Institute of Japanese Literature (NIJL) have used historical documents to garner better insight into the patterns of past solar events. The authors of the new study describe a deep search for prolonged intervals of low-latitude aurora sightings in the records extracted from Japanese and Chinese documents dating as far back as the year 510 CE.
Magnetic storms recorded as auroral sightings in Meigetsuki ("The Record of the Clear Moon," ca 1180-1241) by Fujiwara no Teika of Japan, and in Song Shi ("History of Song," commissioned 1343) from China, have given researchers the ability to reconstruct a chronology of past astronomical events.
"An early Japanese record of prolonged auroras, that is, auroras that persisted for two or more nights within one week, was documented February 21 - 23, 1204 in Meigetsuki," says lead researcher Ryuho Kataoka of NIPR. "At the same time in Song Shi, a large sunspot was recorded on the 21st." Such sunspots are an indication of intense magnetic activity on the Sun, including solar flares.
The researchers continued their investigation by looking further into Song Shi to see if there were additional indications of auroras between the years 900 - 1200.
"We found about ten incidents of prolonged auroras during this period," continues Kyoto University historian Hisashi Hayakawa. "When these dates were compared with radiocarbon data from tree rings, we noted decreased levels of carbon-14 - indicating increased levels of solar activity - at these same points."
The team was also able to discern that auroras were more prevalent in the maximal phase of solar cycles rather than the minimum, and that during the Sun's least active cycle (1010 - 1050, Oort Minimum) no auroras were observed.
The multidisciplinary investigation is even casting its literary sources in a new light.
NIJL Deputy Director Tsuneyo Terashima points out that until now, high regard for Meigetsuki's author Fujiwara no Teika has centered on his role in compiling and editing such classics as the Tale of Genji and Ogura Hyakuninisshu - work in which his literary and poetic talents have been key.
"Frankly, his observations of the sky have been regarded mainly in the context of his fiction writing," explains Terashima, "and not really valued for their scientific specificity. We now realize that Meigetsuki, in fact, provides a lucid and accurate account of celestial conditions of the period."
A possible new understanding of classical Japanese literature may even result, expanding the cross-pollinating effects of the research.
Combining data from other studies with new data generated in this study, the authors argue that all but one of the prolonged low-latitude events occurred in either solar maximum or solar cycle decline. Translations of the auroral records indicate that appearance of low-latitude aurora were distressing to the observer(s) and, in at least one case, caused the observer to delay travel plans to avoid any adverse effects of such a "dreadful" event. In addition to the fascinating account of these events, the reference list for this study is an important compilation of historic aurora reports.
"Combining literature, tree ring dating, and space observation, we have uncovered clear patterns in solar activity and astronomical events," says Kyoto University space scientist Hiroaki Isobe.
"In the present day, large solar storms can significantly disrupt power grids and satellites. We are ever more susceptible to solar events, and the insight gained through historical documents allows us to better predict and prepare for the future."
Source: Kyoto University
"Historical space weather monitoring of prolonged aurora activities in Japan and in China" - Ryuho Kataoka, Hiroaki Isobe, Hisashi Hayakawa, Harufumi Tamazawa, Akito Davis Kawamura, Hiroko Miyahara, Kiyomi Iwahashi, Kazuaki Yamamoto, Masako Takei, Tsuneyo Terashima, Hidehiko Suzuki, Yasunori Fujiwara, Takuji Nakamura - Space Weather (2017) - DOI: 10.1002/2016SW001493
Featured image credit: Kyoto University/NASA/TNM