What Does Thunder Look Like? Now We Know

Michele Berger
Published: May 12,2015



 

Have you ever wondered what thunder looks like? With a little help from a rocket and triggered lightning, scientists from the Southwest Research Institute (SwRI) have for the first time ever created images of the booms, claps and rumbles of thunder. They wanted to understand the physical processes associated with lightning that result in those peals.
“Thunder is a direct consequence of a lightning strike,” Maher A. Dayeh, a research scientist in the SwRI Space Science and Engineering Division, told weather.com. What isn’t known, he added, are the “processes contributing to the thunder that we hear.” In other words, what part of lightning is strong enough to emit an acoustic signature?
Dayeh and colleagues took a seriously awesome approach to answer this question. At the International Center for Lightning Research and Testing at the University of Florida, they went outside in thunderstorm conditions, and with special equipment, monitored the air overhead for electric signals, indicating the imminence of lightning. Then, “right before nature takes its course, we shoot a rocket into the sky,” Dayeh said.
This turns probable lightning into a sure bet, and this particular experiment resulted in nine return strikes. “It’s actually a really good show when you’re so close,” he said. “It’s amazing.” When Dayeh says “close,” he’s not exaggerating: Launch operators are about 165 feet away from where the lightning hits the ground.

Thunder imaged for the first time ever. (University of Florida, Florida Institute of Technology, and Southwest Research Institute)

To go from lightning flash to thunder clap to images on a page required a sophisticated specialized system akin to a “giant ear,” according to Dayeh, one that he built. Fifteen microphones 300 feet or so from the rocket launch site each sat about three feet apart. The mikes picked up the lightning signal, then using a processing technique called beamforming — similar to ultrasound imaging — Dayeh plotted “unique signatures” for the nine lightning strikes.The images don’t look like much, a spectrum of yellows and greens and blues with curved lines in red marking the lightning. But they show something never before seen, a visualization of thunder. Knowing this is feasible is probably the most important result of this experiment, practically speaking, Dayeh said.
Next up, he said he hopes to answer more specific, detailed questions about these storm outcomes, for example how much electric current must be present for an acoustic signal to occur. “People report hearing different types of sounds, clicking, cracking [from thunder],” he said. “It’s not really just one loud boom that you hear.” Thanks to this research, maybe we’ll soon understand why.
And though it has little to do with the thunder visualization research, Dayeh is good-natured about answering one last question, whether thunder and lightning back to back indicates a storm’s close by. “If you see lightning followed by thunder right after,” he said, laughing, “you should not go outside.”
Dayeh presented his research at the joint meeting of American and Canadian geophysical societies in Montreal, Canada, May 3-7.
MORE: Amazing Images of Lightning Strikes