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Blowin' in the Wind, Issue #031 The wonder of thunder: Meteorology lightning bolts - June 1, 2006
June 01, 2006
Electric meteorology lightning boltsIt's that time of year again. When thunder storms and meteorology lightning bolts visit us often. Flash lightning crash thunder. Y'know.
Many wonder - how do lightning bolts form? It's an electrifying story. You'll get a charge out of it. I'm positive.
Lightning and Thunderstorm InformationThe first ingredient in the pre-production of lightning is charge separation. Some say that the ionosphere, an atmosphere layer which includes major parts of the thermosphere and exosphere, (the difference here is that it is defined by its electromagnetic properties rather than air currents), captures charged particles and creates a charged shell around the planet. This shell likes to discharge itself from time to time, forming lightning when possible and using it as a transfer medium.
Others say charges separate due to meteorological forces carrying ions to the top and the bottom of weather systems. Then the whole thing neutralizes itself through the storm. But this mechanism might not be powerful enough. It's still being looked into.
So much for the preamble...
...now for the show.Something starts electrons jumping, possibly cosmic ray strikes from above, perhaps something else. Then a chain of air molecules become successively conductive, forming a charge path, a stepped leader, which will become a wire in the sky. The convective storm is the perfect place for this.
In the earth's surface, following the storm, is a "cloud" of charge, opposite to the one above. It is electrically drawn to the storm cloud and quickly climbs buildings, trees and such, like ants, to get closer to it. Occasionally a positive streamer can jump from one of these high points into the thundercloud. A return stroke occurs when when current goes from this positive leader back into the cloud above, giving a very bright flash.
Meteorology lightning bolts travel as pulses, with short periods of darkness between, giving the flickering effect we see. How much power? It dispenses around 5 Coulombs and 500 megajoules in about 0.2 seconds, giving an average current of around 25 Amperes. As part of the flicker effect described above, its actual "on" time is maybe a thousandth of that value, giving a typical instantaneous current of more like 25 kA, and over a hundred in some cases. With electrical power delivered shooting up to around ten mega-mega watts for a fraction of a millisecond.
What kind of voltagedoes it take to jump through a couple of miles (typical) of air? Hundreds of millions of volts, at least.
Surprised? This lightning has nothing to do with the Ford Explorer, the Chevrolet Thunder or Tampa Bay hockey - meteorology lightning bolts are the real thing.
Catch up on a few meteorological and environmental topics here...
...or re-visit the thought of running your very own
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