For the first time, scientists have "seen" thunder, visually capturing the sound lightning creates, including how sound radiates along the length of a lightning bolt.
"We all know what lightning looks like, and all hear the thunder that comes out from the lightning strike," said Maher Dayeh, a research scientist at the Southwest Research Institute in San Antonio. These first images of thunder allow us to see what we hear, he said.
Why bother? "Lightning strikes the Earth more than 4 million times a day, yet the physics behind this violent process remain poorly understood," Dayeh said.
"While we understand the general mechanics of thunder generation, it's not particularly clear which physical processes of the lightning discharge contribute to the thunder we hear," he said.
Since thunder and lightning are unpredictable, Dayeh and his team artificially triggered lightning strikes at an outdoor laboratory in central Florida last summer. Scientists fired off a small rocket into the thunderclouds. Like fish biting a baited hook, lightning was attracted to a copper wire attached to the rocket.
Dayeh put out a sophisticated array of 15 microphones to study the thunder. The microphones were lined up 103 yards from the rocket launch pad where the triggered lightning hit.
It turned out that the loudest thunder was near the ground, not up in the clouds. "That's where the lightning channel is attaching into the ground," Dayeh said.
Scientists hope the work opens the door for other experiments that will help to improve understanding of lightning.
"Whenever we can come up with a new tool for studying lightning or seeing it in a new way, that's a good thing," said Joseph Dwyer, an atmospheric physicist at the University of New Hampshire-Durham. "That's what this new acoustic imaging does."
This study was presented last week at a meeting of American and Canadian geophysicists in Montreal.