The dirty secret behind ball lightning is dirt

Image (left corner) and spectrum of a serendipitous ball lightning event in China, the first time such a measurement has ever been performed.

J. Cen, P. Yuan, and S. Xue, Phys. Rev. Lett. (2014)

Ball lightning is an odd phenomenon. The few, fortunate people who have seen an incident describe the lightning as a roughly spherical glowing object that travels horizontally for a few seconds before vanishing. However, while several experiments have reproduced something resembling the phenomenon, the physical mechanism behind ball lightning is somewhat mysterious.

Now, a team of researchers serendipitously observed ball lightning at a time when they had the right equipment to study it. Jianyong Cen, Ping Yuan, and Simin Xue were in the field measuring the properties of ordinary lightning when they happened to catch ball lightning with both their high-speed cameras and their spectrographs. They found the chemical composition of the event matched that of soil. That strongly supports the hypothesis (proposed nearly fifteen years ago) that ball lightning is basically a dirt clod dislodged and heated to incandescence by a cloud-to-ground lightning strike.

Ordinary lightning occurs due to the ionization and dissociation of molecules in the air (a process with the awesome name "dielectric breakdown"), which occurs during a static electric discharge between clouds and the ground. Ball lightning is much rarer, to the point where some have even postulated it's actually a hallucination rather than a real weather phenomenon. As the name suggests, it appears as a spherical or spheroidal ball of light, between one centimeter and one meter in size, and variously colored as purple, green, white, or orange.