Fujiwara no Teika (Sadaie) was an influential poet and courtier who documented the events of his life in the twelfth and thirteenth centuries in Japan. It is in one of his diaries, Meigetsuki, that he recorded an extraordinary event that took place in 1204 C.E.: for three days straight, Kyoto’s sky was cast in red light.
Now, researchers at the Okinawa Institute of Science and Technology (OIST) in Japan have used Teika’s diary to determine the timing of a weather event that occurred almost a thousand years ago. By combining medieval literature with modern scientific approaches, the team discovered a sub-extreme solar proton event occurred between the winter of 1200 C.E. and the spring of 1201 C.E. — a few years prior to Teika’s red lights over Kyoto.
The research published in the journal Proceedings of the Japan Academy, Series B, also led to another surprising discovery. Solar cycles then were markedly shorter than they are today.
Detecting Historic Solar Proton Events
Illustration of Fujiwara no Teika.
(Image Credit: Kikuchi Yosai)
Violent activity on the sun can trigger large expulsions of plasma (coronal mass ejections), which in turn can cause solar particles to hurtle towards Earth at a pace close to the speed of light (solar proton events).
Our magnetic field provides an effective shield, but some particles make it through the barrier, entering at weak points near the poles or when space weather is particularly strong. These particles interact with atmospheric gases, forming carbon-14 and beryllium-10 compounds.
By measuring and dating traces of these compounds, scientists have been able to calculate the timings of particularly powerful solar proton events. The largest detected to date occurred in 775 C.E., 5259 B.C.E., 7176 B.C.E., and 12350 B.C.E., but smaller, sub-extreme events (10 to 30 percent the size of extreme events) are thought to occur more frequently.
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Combining Literature With Science
Like their more extreme counterparts, sub-extreme solar events can be timestamped with high precision by measuring carbon-14 compounds in trees. The problem is that the process is incredibly time-consuming and involves a lot of repetition, and so the challenge becomes knowing where to look.
To narrow their options, the team turned to literature. Teika’s diary included descriptions of what appears to be an aurora in February 1204 C.E. While aurora and solar proton events are not directly linked, both are associated with high levels of solar activity and often occur at the same time.
The particularly striking aspect of this observation was its length: “Each aurora will disappear within 24 hours, so this three-day event suggests recurrent large solar flares had occurred,” Hiroko Miyahara, Professor Hiroko Miyahara from the Solar-Terrestrial Environment and Climate Unit at OIST, told Discover.
A hand-copied version of Fujiwara no Teika’s diary, Meigetsuki.
(Image Credit: National Archives of Japan)
Other historical documents from China, Korea, and Japan record large sunspots and red aurorae at various points throughout 1200 to 1205 C.E., again indicating a period of intense solar activity.
The team analyzed concentrations of carbon-14 found in buried asunaro trees in the northern part of Japan’s main island. While there was nothing that could be specifically linked to the three-day aurora, there was a notable spike that occurred sometime towards the end of 1200 C.E. and the beginning of 1201 C.E., suggesting a sub-extreme solar flare. The team was also able to use the data to reconstruct solar cycles during that period.
“Today, the sun’s activity fluctuates over eleven-year-long cycles, but we’ve found that the cycle was just seven to eight years long back then, indicating a very active sun,” Miyahara said in a statement. “The SPE we have dated occurred at the peak of one of these cycles.”
Predicting Future Events and Why It’s Important
While Artemis II was a success, solar proton events could derail future missions and leave astronauts at risk of hazardous radiation.
“Radiation exposure caused by solar proton events is the greatest barrier to human space exploration,” Miyahara told Discover. “So, it is essential to improve our prediction capabilities, particularly for large events.”
Miyahara hopes the research will improve prediction capabilities. Meanwhile, the team hopes to continue combining literature and science to learn more about solar activity and its influence on weather and climate.
“There are several more records of low-latitude aurorae in literature in Japan,” said Miyahara. “Our venture has just begun.”
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