Radio Telescope Reveals How Lightning Begins

"Scientists have never been able to adequately explain where lightning comes from," writes Quanta magazine, sharing a remarkable new animation of a lightning flash recorded by the LOFAR radio telescope network" In a new paper that will soon be published in the journal Geophysical Research Letters, researchers used the observations to settle a long-standing debate about what triggers lightning — the first step in the mysterious process by which bolts arise, grow and propagate to the ground. "It's kind of embarrassing. It's the most energetic process on the planet, we have religions centered around this thing, and we have no idea how it works," said Brian Hare, a lightning researcher at the University of Groningen and a co-author of the new paper.... [T]he electric fields inside clouds are about 10 times too weak to create sparks. "People have been sending balloons, rockets and airplanes into thunderstorms for decades and never seen electric fields anywhere near large enough," said Joseph Dwyer, a physicist at the University of New Hampshire and a co-author on the new paper who has puzzled over the origins of lightning for over two decades. "It's been a real mystery how this gets going." A big impediment is that clouds are opaque; even the best cameras can't peek inside to see the moment of initiation. Until recently, this left scientists little choice but to venture into the storm — something they've been trying since Benjamin Franklin's famous kite experiment of 1752... LOFAR, a state-of-the-art astronomical telescope, can map lighting on a meter-by-meter scale in three dimensions, and with a frame rate 200 times faster than previous instruments could achieve. "The LOFAR measurements are giving us the first really clear picture of what's happening inside the thunderstorm," said Dwyer... Long-time Slashdot reader g01d4 summarizes their results: It seems to be something of a chain reaction starting with clusters of [charged] ice crystals inside the cloud... "More electrons flow in from air molecules that are farther away," according to the article, "forming ribbons of ionized air that extend from each ice crystal tip." These are called streamers which build up numbers until one becomes hot and conductive enough to turn into a leader — a channel along which a fully fledged streak of lightning can suddenly travel. Quanta magazine adds that the key role of ice crystals "dovetails with recent findings that lightning activity dropped by more than 10% during the first three months of the COVID-19 pandemic. Researchers attribute this drop to lockdowns, which led to fewer pollutants in the air, and thus fewer nucleation sites for ice crystals."

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