Twelfth century literature and space-age data help map 3,000 years of auroras

"The Poetic Edda," an Old Norse collection of poems believed to have been most likely drawn up between 1000 and 1100 AD, contains the gods and giants of ancient Scandinavian lore but lacks perhaps the most magical of real phenomena -- auroras. A century later, another Old Norse text, called "The King's Mirror," describes auroras over modern-day Greenland. Around the same time, auroras were witnessed across Japan, including written records of red and white curtain-like lights just north of Kyoto.

Why the discrepancy? Researchers set out to better understand the auroral zone and its movement over the last 3,000 years in an effort to predict how it might change in the future. The team published maps indicating how the auroral zone has moved over the last three millennia on Aug. 20 in the Journal of Space Weather and Space Climate.

"The accurate knowledge of the auroral zone over the past 3,000 years -- via worldwide old witness record of auroras, including those even from low-latitude Japan -- helps us understand the extreme magnetic storms," said first author Ryuho Kataoka, associate professor at the National Institute of Polar Research.

The researchers used the latest models of paleomagnetism, which can estimate Earth's magnetic field in history by examining magnetic evidence contained in rocks, to map the auroral zone. Most auroras occur in a band roughly 20 to 30 degrees from the planet's magnetic poles. The band is an oval, according to Kataoka, that can sporadically expand toward middle-latitude regions, such as Japan, during extreme magnetic storms.

"The auroral zone changes over time, and the deformation and sporadic expansion of the auroral oval are recorded in historical documents over a thousand years from across the world," Kataoka said.

For example, the map of the auroral zone in the 11th to 12th century indicates a notch up from over Norway, where "The Poetic Edda" originated, but a dip toward Japan at the same time. The next century, the auroral zone started moving away from Japan but settled over Greenland. The historical literature matches the paleomagnetism records, according to Kataoka.

The researchers also found similar consistencies in witness accounts in the United Kingdom during the 18th century, matching how the auroral zone dipped over Europe.

"We concluded that the 12th and 18th centuries were excellent periods for Japan and the United Kingdom, respectively, to observe auroras in the last 3,000 years," Kataoka said.

The researchers are now exploring how to use their maps to predict how the auroral zone may behave in the future, to help avoid potentially negative effects on worldwide power grids.

The paper was co-authored by Shin'ya Nakano, associate professor at The Institute of Statistical Mathematics and the Center for Data Assimilation Research and Applications, Joint Support Center for Data Science Research. Both Kataoka and Nakano are also affiliated with the Graduate University for Advanced Studies (SOKENDAI).