Extreme Solar Storm of 1872 Holds a Warning for the Near Future

solar sun

In early November of this year, auroras were observed in unexpectedly low-latitude regions such as Austria, Italy, and Texas. Such auroras visible so far south indicate a stronger coronal mass ejection from the sun, with correspondingly significant effects on Earth’s magnetic field and atmosphere.

As unusual as this recent display of light and colors was, it pales in comparison to the auroras that appeared after a massive solar storm in February 1872. During that event, auroras were observed even in equatorial locations like Bombay and Khartoum.

An international team of scientists from nine countries has now published a detailed study on this historically significant event. The study shows that this storm significantly disrupted the primitive telecommunication of the time. Additionally, the results confirm that such extreme storms occur more frequently than previously thought, serving as a warning given the predicted solar activities for 2024 and 2025.

In the modern world, we rely increasingly on technical infrastructures such as power grids, communication systems, and satellites. This dependence makes us more vulnerable to the impacts of large geomagnetic storms. “The longer the power supply could be interrupted, the more society, especially urban residents, will struggle with it,” says Hisashi Hayakawa (University of Nagoya), the lead author of the new study in the Astrophysical Journal. Such storms could be powerful enough to, in the worst case, disrupt power grids, communication systems, airplanes, and satellites.

The Third “Superstorm”

World map showing all the places where auroras were documented in February 1872
World map showing all the places where auroras were documented in February 1872.

Extremely intense storms are rare. In the past two centuries, two such storms stand out: the Carrington Event in September 1859 and the geomagnetic storm of May 1921. The new study suggests that the event of February 1872 should also be classified in this category. The solar storm at that time was potent enough to impact technical infrastructure, even in tropical regions. Telegraphic communication on the undersea cable in the Indian Ocean between Bombay (Mumbai) and Aden was interrupted for hours. Similar disruptions were reported on the landline connection between Cairo and Khartoum.

For their new study, the group led by Hayakawa utilized historical records and modern techniques to investigate the solar storm, from its solar origin to its terrestrial impacts. For the solar origin, the group accessed largely forgotten sunspot records from historical archives, particularly Belgian and Italian documentation.

Regarding the Earth’s impacts, they used geomagnetic field measurements recorded at diverse locations such as Bombay (Mumbai), Tbilisi, and Greenwich to assess the temporal development and intensity of the storm. They also examined hundreds of reports of visual auroras in various languages caused by the storm.

More than 700 Records

coronal mass ejection
A medium-sized solar flare and a coronal mass ejection that erupted from the same large active region of the sun in 2017. According to the new study, even medium-sized sunspot groups can have serious consequences for the Earth. Image: NASA.

One of the most interesting aspects of the 1872 storm was that it likely originated in a medium-sized but complex sunspot group near the center of the solar disk, as confirmed by analyses of sunspot records from Belgium and Italy. These results suggest that even a medium-sized sunspot group can trigger an extreme magnetic storm. In total, the team identified more than 700 aurora records, indicating that the night sky was illuminated by spectacular auroras from polar regions to the tropics (up to about 20 degrees of geographical latitude in both hemispheres).

Such extreme events are rare,” concludes Hayakawa. “On the one hand, we can consider ourselves fortunate that we have been spared from such superstorms in today’s time. On the other hand, the occurrence of three such superstorms within six decades shows that the threat to modern society is real. Therefore, preserving and analyzing historical records is crucial to assessing, understanding, and mitigating the impacts of such events.

The recent auroras in early November were likely just a prelude to much stronger solar storms originally expected for 2025. Currently, the Sun is approaching the peak of the 25th solar cycle. According to a recent study in the Monthly Notices of the Royal Astronomical Society: Letters, we may reach the maximum as early as 2024, and we may be fortunate that this cycle is expected to be relatively weak to moderate.

Let’s hope that a geomagnetic superstorm like those of 1859, 1872, or 1921 will not occur in the next two years.