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Ball lightning (also called globe lightning) is A rare and randomly occurring bright ball of light observed floating or moving through the atmosphere close to the ground. Observations have widely varying identifying characteristics for ball lightning, but the most common description is that of a sphere having a radius of 15–50 cm, orange or reddish in color, and lasting for only a few seconds before disappearing, sometimes with a loud noise. Most often ball lightning is seen in the vicinity of thunderstorms or a recent lightning strike, which may suggest that ball lightning is electrical in composition or origin. Considered controversial due
How it may occur
A New Zealand scientist may have finally explained the mechanism behind the extraordinary phenomenon of ball lightning.
Associate Professor John Abrahamson, a chemical engineer at the University of Canterbury in Christchurch, explains his theory in the April issue of Physics World Digest.
Ball lightning appears as a glowing, hovering ball of light that moves slowly near the ground before disappearing or exploding. The ball usually measures about 30 cm in diameter, although two park rangers in the Australian outback reported seeing one in 1987 that was 100 metres wide.
There are hundreds of theories about why ball lightning occurs, said Associate Professor Abrahamson — but according to his theory, there are several basic requirements.
The first is regular lightning. Second, the lightning must hit a structure such as a building, soil, or a tree. The struck object must have a metallic or an oxide component.
"Soil contains silicon oxide and carbon," Associate Professor Abrahamson explained. "The lightning reduces this to silicon metal, which is how we make silicon industrially."
The silicon vapour condenses to form silicon nanospheres, which collect together in long strings.
The third requirement is the presence of 'fulgerides' — long sausage-like holes in the soil full of hot vapour. These are created by lightning hitting the ground.
"The lightning strike on soil digs a hole in the ground, forming a very hot channel," said Associate Professor Abrahamson.
"Geologists have dug them up afterwards and found them to be made of frozen molten glass oxides, often in the form of tubes."
The silicon vapour is then ejected back out of the soil, forming a vortex ring — "like a smoker's puff" — which forms a sphere.
Once in this shape, the ball can move long distances, said Associate Professor Abrahamson.
"You have quite a robust structure, which continues to oxidise, and stays hot and visible," he explained.
The layer of oxide on the surface of each of the particles slows the process down, until eventually each particle runs out of metal. At this point the ball either fades away or explodes.
Ball lightning is not as dangerous as regular lightning, but it does carry very high levels of energy.
"People have been killed by ball lightning," Associate Professor Abrahamson warned.
"The metal in the high-energy balls will react with any water-containing substance, including flesh. If you touch ball lightning you could be severely burnt."
Understanding ball lightning is useful because its chemistry relates to that of ordinary lightning, he added.
People haven't thought about the chemistry of ordinary lightning very much — this fills in that part of it."
A simulation of ball lightning
This photo of ball lightning was taken by a student in Nagano, Japan in 1987.
