general properties
As far as studying ball lightning as a scientific phenomenon, scientists have been limited by the inability to recreate these objects in the laboratory. The entirety of data on the subject consists of the thousands of eye-witness accounts of ball lightning which go back as far as the Middle Ages. The 'average' ball lightning is somewhere between the size of a golf ball and a beach ball, lasting about 15 seconds (ranging from 2 to 50 seconds) before it suddenly fades out or explodes. The ball may be spherical or dumb-bell shaped and may pulsate or shine steadily. It can come in various colors but is usually yellowish with brightness of a 100-watt light bulb. It will float around making little or no noise and can scorch wooden objects and has been known to injure or kill people, so it is a considerable source of energy. Its motion is not dictated by wind and usually floats close to the ground, although cases have been documented where it appears in closed rooms or even in airplanes. It will bounce when it hits the ground or comes close to electric fields.
the burning ball of silicon fluff model
Several models exist which describe many of the properties of lightning balls, but few are able to explain all, or even most of them. Generally, it has been suggested that the ball is made up of a cloud of plasma (ionized air) that forms due to the electrical discharge during a thunderstorm. The plasma may be sustained through the absorption of radio waves, but this is unsubstantiated. Other theories suggest that the source of the energy is anything from the flow of current from the ground to the cloud to even focused cosmic ray particles. However, these theories do not adequately explain how ball lightning appears in closed containers such as an airplane.
A theory, recently published in the journal Nature suggests that ball lightning is caused by burning balls of silicon nanoparticles, liberated when lightning strikes the ground. This is similar to the process people used to form semiconductor silicon from sand. For this to occur, the critirea include 3000 K temperatures (room temp is around 300 K) and the carbon present at the site of the lightning strike is twice as prevalent as silicon dioxide. The authors checked soils from various sites, finding some did have the appropriate ratio of materials. It is also known that the point of lightning strikes can easily reach temperatures above 3000K. The free silicon cools rapidly after impact into nanoparticles, which then further assemble, forming long chains or even spherical dendritic balls. Calculating the physical properties of a 30 centimeter burning ball of silicon nanostrings, the authors find that the duration, brightness and density all correspond well to the observed behavior of ball lightning in nature.
See: Abrahamson & Dinnis - Nature v 403 2000 p 519-521
The following are an eye-witness accounts of ball lightning:
I saw ball lightning during a thunderstorm in the summer of 1960. I was 16 years old. It was about 9 PM, very dark, and I was sitting with my girlfriend at a picnic table in a pavilion at a public park in upstate New York. The structure was open on three sides and we were sitting with our backs to the closed side. It was raining quite hard. A whitish-yellowish ball, about the size of a tennis ball, appeared on our left, 30 yards away, and its appearance was not directly associated with a lightning strike. The wind was light. The ball was eight feet off the ground and drifting slowly towards the pavilion. As it entered, it dropped abruptly to the wet wood plank floor, passing within three feet of our heads on the way down. It skittered along the floor with a jerky motion (stick-slip), passed out of the structure on the right, rose to a height of six feet, drifted ten yards further, dropped to the ground and extinguished non-explosively. As it passed my head, I felt no heat. Its acoustic emission I likened to that of a freshly struck match. As it skittered on the floor it displayed elastic properties (a physicist would call them resonant vibrating modes). Its luminosity was such that it was not blinding. I estimate that it was like staring at a less than 10-watt bulb. The whole encounter lasted for about 15 seconds. I remember it vividly even today, as all eyewitnesses do, because it was so extraordinary. Not until ten years later, at a seminar on ball lightning, did I realize what I had witnessed.
- Graham K. Huber Naval Research Lab, Washington D.C.
in Nature 2000 v403 p 487
About 16 years ago, when I was a child and lived with my family in Russia, a curious thing happened. My mother and I were sitting in our 13th floor flat, when we heard a sizzling noise and I saw a ball of fire about 5 centimeters in diameter right behind my mother's head. It stayed there a few seconds, then went "pop" like an exploding light bulb and vanished. It was not raining that day, but was cloudy and quite stuffy. The windows were closed at the time of the incident.
- Maria A Bennet, Aberdeen, England
in the NewScientist - last word
My wife and I bought an old house at the foothills of a central mountain range in AZ. It had been a mining shack that had been refurbished and an elderly couple was living there. The husband related the following story, and there were burn marks on a tree and in the linoleum to back up his story. The man was peeling potatoes in the small kitchen and a mountain thunderstorm arrived as they do in the summer time. He stated that there was a huge clap of thunder that stunned him. Almost immediately there was a blue ball of light that started to richochet around in the kitchen. He said that he had to lift up his feet so that the ball did not hit him. There was a small wood burning stove against one wall with a piece of galvanized time behind it to shield the wooden wall from the heat of a fire. The lightening blasted one of nails holding the metal sheet out of the wall onto the linoleum and burnt the bent shape of an 8 penny nail into the flooring. The burn mark was still visible when we bought the house. Outside the damage was greater. The lightening had struck a huge cottonwood tree leaving a major scar in the wood and bark that is still visible twenty years later. There was a wire clothes line from the tree to the house that was vaporized. The clothes pins were neatly aligned on the ground where they had fallen from the clothes line. It was presumed that the lightening was carried to the wall of the house by the wire clothes line, and then blasted the nail from the wall. How or what the blue ball of energy was that was bouncing around the kitchen is anyone's guess. BUT it fits the description of ball lightening. The man who told me the story was not known to tell tall tales, and he was very convincing when he told the story to me. My father-in-law described "sheet lightning" that he saw in NW Missouri during a major thunderstorm, but that is a different thing.
- Gordon Bradshaw Mayer, AZ
http://www.amasci.com/weird/unusual/bl.html