Stormy weather

What is a geomagnetic storm? 6 incredible facts you need to know

How solar flares could cause blackouts and more.

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The National Oceanic and Atmospheric Administration issued a geomagnetic storm warning for October 11, which may leave you with one question...

What on Earth does that mean?

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1. First, the basics:

A geomagnetic storm is a disturbance of the Earth’s magnetosphere caused by coronal mass ejections or solar flares. These flares send charged solar wind toward Earth, where it can disturb our planet’s magnetic field.

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The October 11 warning comes from a coronal mass ejection on October 9.

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2. Geomagnetic storms are rated G1–G5 for severity, with G5 being the strongest.

The October 11 storm is rated G2.

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According to NOAA, the impact you’re mostly like to feel in a G2 geomagnetic storm is a slight disruption of the power grid, which could damage transformers if the storm lasts long enough.

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A G2 geomagnetic storm could also throw off satellites’ orientation, meaning they’d have to be directed manually from the ground.

Stronger storms could disable power grids worldwide, knock out the internet, and destroy satellites.

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On the brighter side, a G2 storm could make aurorae visible as far south as New York. In a G5 storm, they could reach all the way to Florida.

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3. One of the biggest geomagnetic storms in recent history happened in August 1972. Far-reaching aurorae, radio blackouts, and power disruption through the U.S. followed.

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The storm is believed to have detonated around 25 sea mines off the coast of Vietnam, which were designed to explode based on magnetic field changes.

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4. The largest recorded geomagnetic storm occurred in 1859. It’s called the Carrington storm, after astronomer Richard Carrington, who first observed the solar flare that caused it.

In the Carrington storm, bright aurorae filled the sky as far south as central Mexico.

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Electrical and telegraph systems were severely damaged. There are reports of telegraph operators feeling shocks and recording tape catching fire at telegraph stations.

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A 2013 report by Lloyd’s of London and Atmospheric and Environmental Research, Inc. claims a Carrington-level storm today could leave up to 40 million people in the U.S. without power, some for up to two years.

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5. Solar storms operate on a roughly 11-year cycle of waxing and waning intensity, beginning with the Sun’s entire magnetic field flipping poles.

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The last cycle began in 2019. Solar activity tends to pick up around the middle of a cycle, so we could be in for more geomagnetic storms in the coming years.

6. Scientists know a lot more about solar flares than they did in 1859 or even 1979 — but there’s still a lot they don’t understand.

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We still can’t predict when the flares that cause geomagnetic storms will occur, or what causes them in the first place.

Recent research into understudied regions of the Sun could help explain both of those mysteries, but a major breakthrough hasn’t happened yet.

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For now, we’re stuck hoping the next Carrington-level storm doesn’t hit before we’re ready — and that the aurora it brings is worth it. NOAA predicts “aurora may be visible as low as New York to Wisconsin to Washington state.”