Goodness gracious, a great ball of lightning seen in China offers the first evidence in nature that the elusive glowing orbs form thanks to vaporised dirt.
Anecdotes about ball lightning stretch back for centuries, but the phenomenon has been hard to study as the balls are unpredictable – and when they do materialise, they last for mere seconds. Lacking detailed observations, explanations have ranged from electrically charged meteorites to hallucinations induced by magnetism during storms.
In 2012, Jianyong Cen and his colleagues at Northwestern Normal University in Lanzhou, China, were observing a thunderstorm in Qinghai, China with video cameras and spectrographs. Purely by chance, they recorded a ball lightning event. When a bolt struck the ground, a glowing ball about 5 metres wide rose up and travelled about 15 metres, disappearing after 1.6 seconds.
The spectrograph revealed that the main elements in the ball were the same as those found in the soil: silicon, iron and calcium. The observations support a theory for making ball lightning put forth in 2000 by John Abrahamson at the University of Canterbury in New Zealand.
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 garnered support in 2006, when scientists at Tel Aviv University in Israel were able to create ball lightning in the lab by firing mock lightning at sheets of silicon oxide. The event in China marks the first time such an orb has been captured in nature with scientific instruments.
The study authors say that other mechanisms could also explain their observations. But Abrahamson thinks the findings are a perfect fit for the soil hypothesis. “Here’s an observation which has all the hallmarks of our theory. This is gold dust as far as confirmation goes,” he says.
Journal reference: Physical Review Letters (accepted for publication)
More on these topics: