What happened
A team from Northwest Normal University in Lanzhou was measuring ordinary cloud-to-ground lightning on the Qinghai Plateau, at an altitude of about 2,500 m above sea level. During an evening thunderstorm in July 2012, after a lightning bolt struck the ground about 900 meters from the equipment, cameras fitted with spectrographs recorded a ball of light about 5 meters in diameter. The ball moved horizontally for a dozen or so meters and went out after 1.64 seconds, changing color along the way. The researchers also had footage from a high-speed camera recording 3,000 frames per second, which captured the final phase of the phenomenon. They published their results in January 2014 in “Physical Review Letters” – it was the first measurement of the spectrum of natural ball lightning.
Witnesses
A team of scientists from Northwest Normal University in Lanzhou; the phenomenon was recorded by two cameras equipped with spectrographs.
Explanations and hypotheses
The ball’s spectrum showed lines of silicon, iron, and calcium – elements typical of soil – which supports the hypothesis of John Abrahamson and James Dinniss: lightning vaporizes silica in the ground, and the resulting cloud of silicon nanoparticles slowly oxidizes and glows. The measurement, however, concerns a single event and does not explain all accounts, such as balls appearing inside aircraft. The mechanism of ball lightning is still debated.
Disputed A likely explanation exists, but some of the facts are still disputed.
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