Reports of ball lightning have existed for hundreds of years, but footage of the rare phenomenon, which appears transiently in the form of a glowing sphere of electrical activity, has never been acquired outside the lab. Now, a team of Chinese researchers claims it has obtained the first recorded scientific video of ball lightning in action.
Above: The spectrum of a cloud-to-ground lightning strike and of the ball lightning it generated. The ball lightning is the white dot at the far left, and its spectrum is the slightly brighter band of colors at the foot of the irregularly shaped main lightning spectrum. Photo/Caption Credit: J. Cen et al., via Phys. Rev. Lett. 112, 035001 (2014)
Incredibly, the observation was made by accident. Researcher Ping Yuan and his colleagues from Northwest Normal University in Lanzhou, China had set up spectrometers to investigate ordinary lightning on the Plateau of northwest China. One evening, during a thunderstorm in July 2012, a bolt of lightning struck about a kilometer away from their equipment, sending a ball of glowing light about five meters into the air, where it remained for less than two seconds before vanishing. The team was able to record a spectrum and high-speed video footage of the ball. Those observations have now been published in the latest issue of Physical Review Letters.
Footage of the ball lightning, which slows down 1.3 seconds of real-time observation in order to highlight the ball lightning's "shape, color... brightness and its associated specturm" can be seen here:
1.3 seconds of real-time video slowed down to show the ball lightning's evolution in shape, color, and brightness and its associated spectrum. Photo/Caption Credit: J. Cen et al., via Phys. Rev. Lett. 112, 035001 (2014)
A perspective piece published by the American Physical Society provides additional details:
The recorded glow was about 5 meters across—the actual size of the ball was much smaller—and it changed from white to reddish during the second or so that it lasted. Although the darkness prevented the researchers from estimating the ball's altitude, they saw it drift horizontally for about 10 meters and ascend about 3 meters. Yuan says that this is the first time ball lightning has been seen to be created by a cloud-to-ground lightning strike.
The researchers found that the spectrum contained several emission lines from silicon, iron, and calcium—all elements expected to be abundant in soil. One would also expect aluminum to be present, given its abundance in soil minerals. But the researchers couldn't confirm that, as there are no emission lines of neutral aluminum atoms within the spectral range of their instrument (wavelengths of 400–1000 nanometers). The team also used their video data to plot the ball lightning's intensity and apparent diameter as they varied in time, down to the millisecond time-scale.
"I think that this is a unique observation that is probably of ball lightning, or one type of ball lightning," said lightning specialist Martin Uman of the University of Florida in Gainesville, in an interview with The American Physical Society. "There have been many research programs that routinely video or photograph natural and triggered lightning," he says, "but none, as far as I am aware, has stumbled on a ball lightning."