At the lab where lightning always strikes twice, scientists fire rockets into thunderstorms like impatient Benjamin Franklins. Now, researchers from the Southwest Research Institute have used the University of Florida’s ECE Lightning Research Laboratory to get the first images of the boom after the flash — this is what thunder looks like:
(Left) Long-exposure photograph of a triggered lightning strike vaporizing the copper wire sent up into the clouds via rocket. The purplish lines are the return strokes (RS). (Right) Acoustic data showing the increased sound pressure (in decibels) surrounding each of the nine return strokes. Click to enlarge.
These images, reported at a joint meeting of American and Canadian geophysical societies in Montreal, Canada, show the very genesis of the cracks and rumbles that follow lightning strikes. When that much electricity rips through the atmosphere, the air around the main bolt channel and return strokes rapidly heats up. This in turn increases the surrounding air pressure (shown in red above) and creates the pressure waves that eventually hit us as the sound of thunder.
To map the acoustic signatures of thunder, Dr. Maher A. Dayeh and his team set up an array of of fifteen microphones, a meter apart, spiraling outwards from the site of the triggered lightning strikes. Using a few different processing techniques and a focus on higher sound frequencies, Dayeh eventually uncovered a distinct thunder signature. The technique represents a new way of looking at the energetics of thunder, and will likely help us answer one of the great mysteries of the phenomenon: how does lightning start?
Head here for more information on the lightning lab.
IMAGES: University of Florida, Florida Institute of Technology, and Southwest Research Institute