Extreme Solar Storms May Be More Frequent Than Previously Thought

An international team consisting of scientists from nine countries has published a detailed study on a lesser-known solar storm—named Chapman-Silverman event after two astronomers who collected the first data—that hit Earth in February 1872. Their findings confirm that solar storms powerful enough to directly impact our infrastructure are more common than previously thought.

Coronal mass ejections or flares are powerful outbursts of charged particles traveling towards Earth. When such a flare hits Earth, it can cause a solar storm disrupting the planet’s magnetic field.

The largest solar storm recorded so far occurred in 1859 and is known as the Carrington Event. British astronomer Richard Christopher Carrington was the first to observe a gigantic flare on the solar surface. In the following weeks, polar lights were observed during daylight as far as the equator. At the time, long before mobile telecommunications and the widespread use of electronic devices, damage was fortunately very limited.

Today the National Oceanic and Atmospheric Administration’s Space Weather Prediction Center monitors solar activity and its impact on our infrastructure. Power grids and satellite communications are at a high risk of interference and jamming.

The researchers linked hundreds of accounts of unusual light phenomena with geomagnetic field measurements and sunspot records, showing they were all connected to a peak in solar activity.

Combing through records in libraries, archives and reports of observatories around the world, the team found more than 700 accounts that indicated that the night sky was illuminated by magnificent auroral displays in Japan, the U.S., Australia, India, Mexico, Madagascar and Europe. An aurora occurs when the charged particles coming from the sun react with the gases in Earth’s atmosphere. To be visible over such a large area, the solar storm behind the 1872 aurora must have been quite powerful.

At the same time, geomagnetic field measurements recorded in places as diverse as Bombay in India, Tiflis in Georgia and Greenwich in the U.K. showed strong variations in Earth’s magnetic field.

The storm was big enough to affect the technological infrastructure even in the tropics. Telegraph communications on the submarine cable in the Indian Ocean were disrupted for hours. Similar disturbances were reported on the landline between Egypt and Sudan.

To prove a connection with solar activity, the group turned to largely forgotten Belgian and Italian sunspot records. These findings suggest that even a medium-sized sunspot activity triggered one of the most extreme geomagnetic storms in history.

“Our findings confirm the Chapman-Silverman storm in February 1872 as one of the most extreme geomagnetic storms in recent history. Its size rivaled those of the Carrington storm in September 1859 and the New York Railroad storm in May 1921,” explains Hisashi Hayakawa, Assistant Professor at Nagoya University and Harwell Campus (U.K.) and the lead author of the study.

“Such extreme events are rare. On the one hand, we are fortunate to have missed such superstorms in the modern time. On the other hand, the occurrence of three such superstorms in six decades shows that the threat to modern society is real. Therefore, the preservation and analysis of historical records is important to assess, understand, and mitigate the impact of such events,” Hayakawa concludes.

Recent auroral displays have been observed from northern U.S to southern Europe. Currently, the sun is experiencing a solar cycle, predicted to peak in 2024, and we may expect enhanced solar activity in the coming years.

The study “The Extreme Space Weather Event of February 1872: Sunspots, Magnetic Disturbance, and Auroral Displays” was published in The Astrophysical Journal (2023). Additional material and interviews provided by Nagoya University.

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