Almost 250 years ago, for over two weeks, the skies above parts of Asia lit up in what looked like a burst of fiery red. Those who saw the strange phenomenon kept notes of the event, and now it has been identified as potentially the longest geomagnetic storm ever recorded.
A dim red sky reported to have been observed between the September 16 to 18, 1770 in East Asia was considered one of history’s greatest geomagnetic storms. But now, new materials have come to light suggesting the storm lasted much longer, for nine nights, and covered an area twice as large as originally thought.
A group of Japanese scientists led by Hisashi Hayakawa from Osaka University studied hundreds of historical records dating between September and October 1770, including government records and people’s personal diaries. Using these records, they were able to piece together what happened during the event, and link this to sunspot drawings from the time.
“We believe that this storm is the longest ever known as inferred from the equator-ward extension of the aurora, although magnetic field data is unavailable at that time,” says Hayakawa. He adds that this is the longest storm we now know of, but more historical documents could lead to the discovery of even longer geomagnetic events.
When the group looked at sunspot drawings from the time, they found the area of the Sun covered in sunspots was twice as large as normal. The spots are likely to be where the solar wind came from, creating the aurorae seen from Earth.
A solar storm in 1859, named the Carrington Event after the scientist who discovered it, is generally considered to be one of the most powerful on record. The Carrington Event lasted two nights, the geomagnetic storm in East Asia is now thought to have lasted nine.
Scientists at Nasa have been warning for some time of the dangers of space weather affecting the Earth, and particularly the danger of solar storms. In 1770, disruption caused by such storms was minimal. In 2017, it would be far greater. “Facing such extreme and long-lasting magnetic storms, we have to expect the disturbance of communication, wide-range black outs, radioactive exposure of aircraft, failure of GPS, and so on,” says Hayakawa.
A 2008 study by the US National Research Council estimated the economic impact of the Carrington Event in 1859 today could be up to $2 trillion. “The events in 1770 lasted much longer in scales compatible to Carrington,” says Hayakawa. “We believe we need to expect even more economic and social impacts for this kind of extreme and long-lasting magnetic storms.”
Nobody really knows how the solar wind is created on the Sun. Next year Nasa and ESA are both sending probes towards the Sun to gather data, but looking back also helps. Uncovering more of these high-strength storms will help us understand the long-term pattern of the Sun and its 11-year solar cycle.