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and now, thanks to a Dutch radio telescope network called the Low Frequency Array (
LOFAR), scientists have a better idea why.
An international team used the array to study the development of lightning flashes in unprecedented detail, and discovered that the negative charges inside a thundercloud are not discharged in a single flash.
Some are stored inside structures the researchers have called needles, making a repeated discharge to the ground quite possible.
"This finding is in sharp contrast to the present picture, in which the charge flows along plasma channels directly from one part of the cloud to another, or to the ground", says Olaf Scholten, from the University of Groningen in The Netherlands.
And it hasn't been noticed before because there wasn't equipment powerful enough to do so.
"These needles can have a length of 100 metres and a diameter of less than five metres, and are too small and too short-lived for other lightning detections systems," says Brian Hare, also from the University of Groningen.
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