Study reveals how lightning often strikes twice

Lightning often strikes twice, contrary to popular belief, and a new international study shows how.

It comes down to what the research team call ‘needles’, which store a negative charge along the main lightning channel that can cause repeated strikes.

The research team led by the University of Groningen in the Netherlands and involving a scientist from The Australian National University (ANU) used a low frequency radio telescope to crack the long-running lightning mystery.

Lightning strikes when electricity built up in a cloud is strong enough to break through the ionised air. The lightning bolt hits the ground within a fraction of a second after passing through a channel. According to the Bureau of Meteorology, lightning causes up to 10 deaths every year in Australia.

ANU Emeritus Professor Harvey Butcher said the team studied the development of lightning flashes in unprecedented detail, creating extremely high definition 3D images.

“The reason why a lightning channel is reused had been a mystery until now,” said Professor Butcher, a former Director of the ANU Research School of Astronomy and Astrophysics.

“This new research shows the negative charges inside a thundercloud are not drained all in one flash but are, in part, stored alongside breaks in the main lightning channel.

“This happens in structures called needles that have never been described before. Through these needles, a negative charge may cause a repeated discharge to the ground.”

Professor Butcher led the development of the telescope used by the team. The radio telescope, LOFAR (LOw Frequency ARray), is made of thousands of simple antennas spread across Northern Europe.

These antennas are connected with a central computer through fibre-optics, which means they can operate together to form a radio camera able to focus on both the distant Universe and on phenomena in the Earth’s atmosphere.

The findings are published in Nature.

Lead author Dr Brian Hare from the University of Groningen, said the data collected by LOFAR allowed the team to detect lightning activity within clouds and the surrounding environment at a scale where, for the first time, scientists can distinguish the primary processes.

“From these observations we see that a part of the cloud is re-charged, and we can understand why a lightning discharge to the ground may repeat itself a few times,” he said.

“The use of radio waves allows us to look inside the thundercloud, where most of the lightning resides.”

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