How and why does thunder make sound?
Jake Porento, Riverwoods, Ill.
Dear Jake,
Thunder is the sensation that we register when pressure waves in air–“sound waves”–that are generated by lightning impinge upon the eardrum within our ears.
A lightning stroke heats the air through which it passes (a channel less than one inch in diameter) to above 50,000 (degrees) F within a few millionths of a second, a duration of time so short that the heated air does not have time to expand. A channel of extreme pressure (possibly 100 times in excess of normal atmospheric pressure) is thereby generated and it then blasts into the surrounding air, traveling for the first ten yards or so as a shock wave faster than the speed of sound, and after that as ordinary sound waves.
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Tom Skilling is chief meteorologist at WGN-TV. His forecasts can be seen Monday through Friday on WGN-TV News at noon and 9 p.m.
Write to: ASK TOM WHY, 2501 Bradley Pl., Chicago, IL 60618 or asktomwhy@wgntv.com (Mail volume precludes personal response.)
WGN-TV meteorologists Steve Kahn, Richard Koeneman and Paul Dailey plus weather producer Bill Snyder contribute to this page.
