Researchers use ancient literature to track 3,000 years of aurora

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Auroral activity on Earth varies over time. As the magnetic poles drift, auroras can appear at different latitudes around the globe. Solar activity affects them too, with powerful solar storms pushing the aurorae further into mid-latitudes.

In an effort to better understand how the auroras move, how they will move in the future, and when powerful solar storms could pose a threat, a team of researchers have been tracking auroral activity over the past 3,000 years.

Two researchers associated with the National Polar Research Institute and other Japanese institutions have used ancient literature and modern data to map the changing auroral zone over the past three millennia. Finding historical accounts of cultures around the world, they created a video spanning three thousand years of auroral drift.

They published their research in the Journal of Space Weather and Space Climate. The title of the article is “Auroral Zone over the Past 3000 Years” and the first author is Ryuho Kataoka, Associate Professor at the National Polar Research Institute.

Auroral zone reconstructed over the past 3000 years.

“Accurate knowledge of the auroral zone over the past 3,000 years – thanks to ancient aurora witnesses around the world, including those even from the lower latitudes of Japan – helps us understand extreme magnetic storms,” first author Kataoka said in a press release.

Science played a role alongside ancient writings in this study. Paleomagnetism is the study of magnetic evidence in rocks, and researchers have used paleomagnetic models to map the auroral zone of Earth over time. The auroral zone is an oval shape that changes over time. Most auroras occur in a band about 20 to 30 degrees from the poles. But this area can extend further into mid-latitudes when powerful solar storms occur; even in regions like Japan.

“The auroral zone changes over time, and the deformation and sporadic expansion of the auroral oval is recorded in historical records over a thousand years around the world,” Kataoka said.

Estimated overall shape of the auroral zone in 1200 AD (blue) and 1800 AD (red). The contours are field strengths at the top of 49, 173, 474 and 6178 nT, corresponding to 70, 65, 60 and 40 magnetic latitudes. The longitude of Japan (135 E) is down. Image credit: Kataoka and Nakano 2021.

One of the historical documents used by researchers is an Old Norse text called “The King’s Mirror”. It has 70 chapters and is written as a dialogue between father and son. In this case, the father is Haakon IV Haakonsson and the son is Magnus Haakonsson. The text was intended to instruct Magnus in royal affairs and to prepare him for reign. These are mainly questions of court, morality, chivalry, commerce, strategy and tactics. But The King’s Mirror also contains descriptions of auroral activity over Greenland in AD 1200-1300.

The research duo also viewed a Japanese text titled Nippon Kisho-Shiryo, which contains records of aurora and other phenomena. The Nippon Kisho-Shiryo has a cluster of aurora around 1200 AD, which matches what The King’s Mirror shows. Indeed, in the following century, paleomagnetic data shows that the auroral zone moved away from Japan and settled on Greenland. According to the first author, the historical accounts correspond to the paleomagnetic evidence.

Auroral zone reconstructed in 2010 AD (left) and 1200 AD (right).  Image credit: Kataoka and Nakano 2021.
Auroral zone reconstructed in 2010 AD (left) and 1200 AD (right). Image credit: Kataoka and Nakano 2021.

Paleomagnetic data shows another auroral trough in the UK during the 18th century, which also matches written accounts.

Left: Auroral Isochism by Fritz (1881). The documents compiled were from AD 1700 to 1872.
Right: Auroral zone reconstructed in 1800 AD (black) and possible deformation by an integration of 170 years for the time interval between 1700 and 1870 AD (red).

One of the researchers’ goals was to find out whether aurora evidence matches paleomagnetic data. Specifically, they wanted to see if the scientific data supported the idea that the 12th century was the best time in Japan to witness the aurora. They were able to confirm it, and more.

“We concluded that the 12th and 18th centuries were excellent times for Japan and the UK, respectively, to see auroras over the past 3,000 years,” Kataoka said in a press release.

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Kehoe Young

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