Burn, Bang, Burp
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Hi I'm Bryan Yeaton and this is the Weather Notebook. Ball lightning is usually seen during thundery weather. Witnesses describe a floating globe, often about the size of a basketball, and typically white or yellow -- sometimes with a bluish glow over the surface.

It might last as much as a minute before either fading away or - sometimes -- exploding. Correspondent Allan Coukell takes you into the lab for some recent ball lightning experiments.

Alan: The dancing, glowing spheres known as ball lightning are a scientific mystery. The latest theory comes from John Abrahamson, of University of Canterbury in New Zealand, who has been trying to create ball lighting in the high voltage lab. He calls his theory the "bang, burp, burn bang" theory of ball lightning.

John Abrahamson: "The bang is the normal lightning strike, which you hear as thunder."

Alan: It starts when ordinary forked lightning blasts the ground.

JA: "It goes underground, it goes through the soil. During that passage it heats the soil intensely, vapourising some of the soil."

Alan: The burp comes when the heat of expanding gases propels the hot soil vapour into the air.

JA: "The burp [FX: Whoof] is the jet from beneath the soil."

Alan: A cloud of circulating gases and soot is formed. According to the theory, this then begins to burn.

JA: "The material which condenses within that little sphere above the soil, that starts burning in a special way. And that's the ball lightning."

Alan: The burning sphere might then exhaust its fuel and fade away [music fades] or it might overheat and explode‹the final "bang" of the bang-burp-burn-bang theory of ball lightning.

That's Allan Coukell of Auckland, New Zealand. The Weather Notebook is a production of the Mount Washington Observatory and is underwritten by Subaru of America and the National Science Foundation.