Mentions of unusually bright "northern lights" in medieval Japanese and Chinese chronicles helped scientists learn about a series of powerful solar flares in the 11th-12th centuries, the traces of which were "imprinted" in tree rings, according to an article published in Space Weather magazine.
“We found ten cases in these chronicles when the sky over China or Japan was illuminated for several nights by flashes of the northern lights. In the tree rings that formed during the years when these outbreaks occurred, the proportion of 'heavy' carbon-14 is lowered, indicating a high level of solar activity,”says historian Hisashi Hayakawa of Kyoto University, Japan.
The Sun periodically experiences flares - explosive releases of energy in the form of light, heat and X-rays. Powerful flares "pierce" the Earth's magnetic shield. They disrupt the operation of radio communication systems, satellites and threaten the health of astronauts working on the ISS. For example, a solar flare in March 1989 deprived Canada of much of its electricity grid, causing US $ 13.2 million in damage.
It is believed that the most powerful outbreak occurred in 1859 during the so-called "Carrington event". Then about 10 yottojoules (10 to 25 degrees) of energy were released, which is 20 times more than during the fall of a meteorite that destroyed dinosaurs and marine reptiles. NASA predicts that the likelihood of such an event happening again today is about 12%.
For this reason, Hayakawa says, historians, astronomers and physicists are actively trying to find traces of other mega-flares in the fossil and written history of the Earth, which would help us determine how often such events occur and what consequences can be expected from them.
Japanese physicists and historians learned about several powerful flares of this type at once, studying two medieval chronicles - the Japanese Meigetsuki and the Chinese Sun-shi. The first is a diary kept by the court poet Fujiwara Teika, who lived in the XII-XIII centuries, and the second is the history of the Song dynasty, which ruled China in the X-XIII centuries.
While studying these chronicles, Hayakawa and his colleagues came across references to the unusual "red steam", complex figures and radiance in the sky that Teika and his Chinese contemporaries saw on February 21-23, 1204. This radiance, according to Sun-shi, was preceded by the appearance of a particularly large spot on the Sun. A similar "aurora" in mid-latitudes, as noted by scientists, was seen by eyewitnesses of the Carrington event.
These descriptions interested scientists. They completely analyzed the texts of the chronicles and found in them two hundred similar cases, about ten of which were repeated in a suspicious manner after 27 days (one revolution of the Sun around its axis). All of these outbreaks occurred during the supposed maximum solar activity in the 11th-12th centuries, forcing physicists who joined Hayakawa's team to search for traces in the real world.
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In the past, Japanese scientists have already found traces of supernovae and gamma-ray bursts in the annual rings of the most ancient cedars that grew on the territory of the "Empire of the Rising Sun" in the VIII-XII centuries AD. Guided by similar considerations, the researchers compared the contents of the rings that arose during these flares with neighboring layers of wood, and found that the activity of the Sun in those years was indeed extremely high.
Many of these flares, as scientists say, were generated by the same spots on the Sun: they repeated with the same frequency with which the star makes one revolution around its axis. Other flares, lasting five days or more, were apparently generated by several nearly simultaneous coronal ejections on the Sun.
Hayakawa and his colleagues note that they could not find any trends in the frequency of occurrence of large spots and powerful flares, except for the connection with the solar maximum, which generally indicates a random nature of their appearance. Further study of flares, scientists hope, will help to understand how often such events occurred in the early history of mankind, and whether we can expect their return when the Sun once again reaches its peak.