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Nature

27
Jan

Great Lightning Balls of Fire

Balls of lightning that meander close to the ground during storms: myth, or reality?

Chilling anecdotes regarding these spheres of light—typically purple, green, white, or orange in color—have been passed around for centuries. Australia’s Aborigines call them “Min Min Lights,” and British occultist Aleister Crowley saw one while sheltering in a cottage during a 1916 thunderstorm on Lake Pasquaney in New Hampshire. And perhaps most famously, Czar Nicholas II of Russia witnessed a flaming orb during a church service in the 19th century.

But because incidences of ball lightning are so unpredictable, scientists have never captured data on them. In fact, some experts have attributed sightings to hallucinations induced by magnetism during storms.

In 2012, though, Jianyong Cen and his colleagues at Northwestern Normal University in Lanzhou, China, were observing a thunderstorm in Qinghai, China with video cameras and spectrographs. By chance, they recorded a ball lightning event and found that the event’s chemical composition matched that of soil. The discovery confirms a nearly 15-year-old theory first proposed by chemical engineer John Abrahamson in 2000: that ball lightning forms when a strike whisks up and scorches a small clod of dirt.

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Image (left) and associated visual spectrum—used to identify chemical components—of ball lightning event in China.

Michael Slezak, writing for New Scientist:

Abrahamson surmised that when lightning hits the ground, the sudden, intense heat can vaporise silicon oxide in the dirt, and a shockwave blows the gas up into the air. If there’s also carbon in the soil, perhaps from dead leaves or tree roots, it will steal oxygen from the silicon oxide, leaving a bundle of pure silicon vapour. But the planet’s oxygen-rich atmosphere rapidly re-oxidises the hot ball of gas, and this reaction makes the orb glow briefly.

The theory gained support when scientists were able to simulate ball lightning in a lab, but the Chinese storm discovery marks the first time experts have identified its cause through spectral analysis. Here’s Matthew Francis, writing for ArsTechnica:

At its origin, the ball was a bright white-violet in color, but then it faded to orange and then red before vanishing. Analyzing the spectrum, the researchers identified silicon, iron, and calcium—three of the major chemical components in soil. (Aluminum is another common element in soil, but the authors pointed out that their cameras weren’t able to spot the appropriate wavelengths to identify it.)

Watch high-speed footage of the ball lightning event and the accompanying spectrum:

Learn about another kind of electrical phenomenon produced not by thunderstorms, but by earthquakes.