It can sound like a loud clap or low rubble, but unlike the bright lightning bolts it usually accompanies, it has never been seen.
That is, until now – as a team of scientists from the Southwest Research Institute in Texas have unveiled what they say are the world’s first images of thunder.
Dr. Maher Dayeh, a research scientist at the Institute’s Space Science and Engineering Division, presented the images in Montreal this week at the 2015 Joint Assembly, which brings together American and Canadian scientific researchers.
“This tells us more about the origins of thunder, which in turn allows us to better understand the energetic processes associated with lightning,” he told the Star via e-mail.
A team of researchers placed 15 microphones 95 metres from a simulated lightning site and captured the acoustic power coming from the bolt. The lightning was triggered by launching a small rocket trailing a copper wire, which acted as a conductive channel, into the clouds.
“We created a ‘special ear’ that can amplify sounds coming from a specific direction,” Dayeh said. “This enabled us to collect and amplify sound signals coming from specific portions of the lightning channel.”
The resulting image shows acoustic sound waves that appear purple interacting with the path of the lightning channel – the copper wire – which glows green.
The scientific process is known as “beamforming,” Dayeh said, and it is similar to an ultrasound taking images of infants in their mothers’ wombs. “But this is the first time this technology has been applied to understand thunder and lightning.”
Thunder accompanies lightning, which emerges in the sky as a result of static charges inside clouds. The air around lightning quickly expands at extremely-high temperatures, and this process – which forms what is known as a lightning channel – is where thunder comes from.
Since light travels faster than sound, thunder is heard several seconds after lighting is seen, depending on how far away the bolt struck.
Dayeh said he hoped the images will help scientists better understand what parts of lightning contribute to thunder’s boom.
“In this case, we may be able to learn more about the faster processes (lightning) by looking at the slower response (thunder). For instance, we can tell if the branches of lightning create acoustic signatures or not,” he said.
“Anytime you have a new tool, you can learn more.”