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Auroras seen as far south as the equator in 1872 after largest known solar storm

In early November, the aurora borealis, typically confined to higher latitudes, graced skies as far south as Italy and Texas. This mesmerizing display of auroras was linked to solar coronal mass ejections impacting Earth’s magnetic field.

While these displays were dramatic, they pale in comparison to the colossal solar storm of February 1872. This historical event’s significance has been recently illuminated by an extensive study conducted by an international team of scientists.

The 1872 Chapman-Silverman storm

The solar storm of February 1872, known as the Chapman-Silverman storm, produced a global display of auroras visible near the equator in locations like Bombay and Khartoum. This extraordinary phenomenon disrupted telegraph communications, showcasing the vulnerability of even the 19th-century technology to solar storms.

In a new study, an international consortium of researchers from nine countries has detailed the solar origins and wide-ranging terrestrial impacts of this event. This storm, alongside others like the Carrington storm of 1859 and the New York Railroad storm of 1921, is now recognized as one of the most extreme geomagnetic events in recent history.

Technological dependencies and risks

Today’s society, highly reliant on technological infrastructure such as power grids and communication systems, faces significant risks from such geomagnetic storms.

“The longer the power supply could be cut off, the more society, especially those living in urban areas, will struggle to cope,” says Designated Assistant Professor Hayakawa, the lead author of the study. The potential disruption to power grids, communication systems, airplanes, and satellites is a cause for concern.  

“Could we maintain our life without such infrastructure?” Hayakawa comments, “Well, let us just say that it would be extremely challenging.” 

Studying an aurora borealis from 1872

The study, spearheaded by Nagoya University, the US National Solar Observatory, and the Royal Observatory of Belgium, involved 22 scientists. They utilized historical records and modern techniques to analyze the Chapman-Silverman storm. Key sources included forgotten sunspot records from Belgian and Italian archives and geomagnetic field measurements from diverse locations.

One significant finding was the storm’s origin in a medium-sized, complex sunspot group. This challenges the assumption that only large sunspot groups can trigger extreme magnetic storms. Over 700 auroral records were examined, revealing that the night sky was illuminated with auroras reaching as far as 20° in latitude in both hemispheres.

“Our findings confirm the Chapman-Silverman storm in February 1872 as one of the most extreme geomagnetic storms in recent history. Its size rivalled those of the Carrington storm in September 1859 and the NY Railroad storm in May 1921,” Hayakawa said. “This means that we now know that the world has seen at least three geomagnetic superstorms in the last two centuries. Space weather events that could cause such a major impact represent a risk that cannot be discounted.” 

Solar storms, aurora borealis, and the future

The study emphasizes the importance of historical records in understanding and preparing for such events. With the Sun approaching the maximum of Solar Cycle 25, recently predicted for 2024, enhanced auroral activity is expected, underlining the need for vigilance and preparedness against potential geomagnetic storms in our increasingly technologically dependent world.

Hayakawa warns of complacency, saying, “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 6 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.”

Recent observations of auroral displays from locations like northern Greece and the northern US serve as reminders of our planet’s ongoing interactions with solar activity. As we approach the peak of Solar Cycle 25, these natural phenomena not only offer a spectacle but also a warning of the potential impacts of solar storms on our modern world.

More about auroras

Auroras, also known as the Northern and Southern Lights, represent one of the most captivating natural phenomena on Earth. These luminous displays of color illuminate the night skies near the poles, offering a breathtaking spectacle. The phenomenon results from interactions between the Earth’s atmosphere and charged particles from the sun.

The science behind auroras

The story of auroras begins with the sun. It continuously emits a flow of charged particles, a phenomenon known as the solar wind. These particles, mainly electrons and protons, journey across the solar system.

Upon reaching Earth, these solar particles encounter the planet’s magnetic field. This magnetic shield redirects the particles towards the Earth’s poles. As they descend, they interact with different gases in the atmosphere, primarily oxygen and nitrogen.

This interaction excites these atmospheric gases, causing them to emit light. Oxygen is responsible for the most common auroral colors — green and red. Nitrogen contributes to blue and purple hues. The varying colors depend on the type of gas and the altitude at which the interaction occurs.

Types of auroras

The Aurora Borealis, or Northern Lights, occur in the northern hemisphere. These are best viewed in high-latitude regions like Norway, Canada, and Alaska.

In the southern hemisphere, the equivalent phenomenon is the Aurora Australis, or Southern Lights. These are visible from high southern latitudes in Antarctica, Chile, and Australia.

Impact of solar activity

The sun undergoes an 11-year cycle known as the solar cycle, which affects auroral activity. During periods of high solar activity, more charged particles reach the Earth, leading to more frequent and intense auroras. The opposite happens during periods of low solar activity.

Auroras and space weather

Auroras are not just a visual marvel; they are also critical in understanding space weather. The study of auroras helps scientists comprehend the interactions between solar wind, Earth’s magnetic field, and the atmosphere. This knowledge is vital for predicting the effects of space weather on satellite operations, communication systems, and power grids.

In summary, auroras are a stunning blend of celestial and atmospheric phenomena. They not only offer a visual feast but also provide insights into the complex interactions between the Earth and the sun. As we continue to explore

The full study was published in The Astrophysical Journal.

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