Scientists reveal what thunder 'looks' like

Tuesday, May 5, 2015, 6:32 PM - For the first time, scientists have visually captured the sound waves created by thunder produced from artificially triggered lightning.

Lightning strikes the Earth more than 4 million times a day – but there’s still a lot to learn about the phenomenon. 

While researchers understand the general mechanics of thunder, they aren’t sure how lightning contributes to what we hear – and why thunder sounds like a sharp crack from nearby and a rumble from far away. 

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Researchers from the Southwest Research Institute (SwRI) simulated lightning to study the acoustic power radiated from different portions of a lightning channel in an effort to learn more about the origins of thunder and the energetic processes associated with lightning. 

EXPLANATION FROM SwRI: This long-exposure photograph (left) shows a triggered lightning event. The initial copper wire burn glows green, while nine subsequent return strokes are more purplish. Southwest Research Institute scientists plotted acoustic data (right) measured at the array that clearly show the unique signatures of the nine return strokes (RS) associated with the triggered lightning event. The 'curved' appearance of the RS signatures is associated with sound speed propagation effects. A secondary acoustic signature after the first RS (b) is the result of an electric current pulse associated with the return stroke. Courtesy: University of Florida, Florida Institute of Technology, and Southwest Research Institute

"Thunder and lightning are fascinating, wild, and unpredictable," said Dr. Maher A. Dayeh of SwRI in a statement.

"Because of their erratic nature, the phenomena are best studied using triggered events."

Researchers launched a small rocket trailing a copper wire into thunderclouds. This created a predictable path for lightning, allowing the research team to perform repeatable experiments.

The study was conducted in Gainsville, Florida, home to the most lightning strikes per year in the U.S.

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A series of microphones were used to study the acoustics of thunder, along with fifteen microscopes lined up 95 metres away from the rocket launch pad.

Dr. Dayeh used processing techniques to create a visual representation of the data captured by the gadgets.

"At first I thought the experiment didn't work," Dr. Dayeh said in a statement.

"The initial constructed images looked like a colorful piece of modern art that you could hang over your fireplace."

Further analysis, however, revealed a distinct signature of thunder generated by the lightning.

It's hoped the findings will allow scientists to gain a better understanding of the relationship between thunder and lighting, while creating a method to analyze the probable acoustic signature of lightning discharge.

Source: Phys.org