News•May 7, 2015

Boom! Here's What Thunder Looks Like

During a thunderstorm, launching a rocket with copper wire attached to it is pretty much the exact opposite of what any sane person would do.

But when it’s the only way to answer one of the mysteries of science, even scientists, usually the most rational of people, are willing to make an exception.

Last July, researchers from the Southwest Research Institute (SWRI) based in San Antonio, Texas, made the trip to Florida to do exactly that. Their mission? To capture the uncapturable, an image of thunder, specifically the sound waves that propagate from thunder’s flashier counterpart.

Lightning already hits the planet 100 times a second and recent findings suggest that lightning will increase as the world warms. Understanding the dynamics of this already familiar phenomenon is clearly of scientific interest.

Scientists compared long-exposure optical photographs of two different triggered lightning events (on top) with acoustically imaged profiles of the discharge channel (below), corrected for sound speed propagation and atmospheric absorption effects. The apparent tilt of the lightning bolt in the left photo is also seen in the acoustic image.
Credit: SWRI

There’s no shortage of images of lightning. But capturing a visual of the more outspoken thunder required specialized microphones and a bit of science ingenuity to coax lightning toward the microphones.

A long-exposure photograph of the lightning strike scientists monitored for the acoustic image of thunder.
Click image to enlarge. Credit: SWRI

SWRI scientist Maher A. Dayeh and colleague set up camp on Camp Blanding, a U.S. Army base in Gainesville, Fla., that’s home the International Center for Lightning Research and Testing (yes, there is such a thing). They laid out 15 special microphones and a rocket launch pad and then waited a storm.

On July 14, that storm materialized and Dayeh sent his rocket with a spool of copper wire up into the air as a ladder for lightning to descend. It goes without saying that this is an experiment you should not try at home.

The resulting images of lightning are cool in their own right, but data from the microphones was what Dayeh was really after.

After some processing in the digital darkroom, a picture of thunder emerged. The thunder, perhaps not surprising, follows the lightning bolt down. But the loudest part is when it approaches the ground.

The next step for scientists is to attempt to get a picture of thunder in its natural habitat with lightning that tends to zig and zag more than the rocket and copper-fueled lightning in this study. And if projections of a more shocking world are accurate, there will be no shortage of opportunities.