What Does Thunder Look Like? If You've Ever Wondered, It's Almost As Cool As Lightning Itself
For most of us, thunder is a distinct sound, and an often terrifying one that makes us hide under our covers. But for a few scientists at the Southwest Research Institute (SwRI) in San Antonio, Texas, thunder is something that they wanted to visualize. The SwRI scientists created images of thunder by manipulating lightning to strike on command and closely examining the process of the phenomenon. With the help of a rocket and 15 microphones, the researchers were able to acoustically image each lightning profile to essentially create an ultrasound of the thunder that followed. The study has made significant strides in understanding lightning and its properties better, which, in turn, might help ease our fears.
In order to study thunder, one must have lightning, but the location and timing of lightning is notorious for being difficult to predict. So, for the study, the SwRI research team took matters into their own hands and manually conjured lightning. This process involved shooting a rocket attached to a copper wire into storm clouds. The wire acts as a conductive channel that triggers lightning to strike in a controlled area, which allowed the team to set up their equipment in one spot and take repeated recordings at the site.
This equipment involved 15 microphones spaced one meter apart lined up 95 meters from the rocket launch pad and lightning target. After picking up the lightning and thunder, the microphones used a processing technique called beamforming to map out ultrasound-like images of the acoustic signatures of nine lightning strikes.
The screen grabs above show a rocket launch, which glows green, and a lightning strike that followed.
In the image above, the green portion is the initial glow of the copper wire and the purple lines are subsequent nine return strokes. On the right is the acoustic data of the signatures of the nine strokes.
These long-exposure optical photographs show two different triggered lightning strikes and their respective acoustic data. You can see how the curve of the lightning bolt on the left is reflected in the acoustic image.
So what exactly do these images explain, and why did they need to visualize thunder in the first place? Dr. Maher A. Dayeh, of the SwRI Space Science and Engineering Division and one of the research scientists who authored the study, explained in a press release:
Lightning strikes the Earth more than 4 million times a day, yet the physics behind this violent process remain poorly understood. 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. A listener perceives thunder largely based upon the distance from lightning. From nearby, thunder has a sharp, cracking sound. From farther away, it has a longer-lasting, rumbling nature.
These images help explain which properties of lightning produce sound, what type of sound, at what volume. As the team continue to study the acoustics of thunder in relation to lightning, rest assured the next time you get woken up by a booming thunder clap that, no, it's not the apocalypse kicking off. Images: University of Florida, Florida Institute of Technology, and Southwest Research Institute