Detailed Footage Finally Reveals What Triggers Lightning

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during summer A significant lightning bolt shone over a network of radio telescopes in Hurricane, Netherlands, in 2018. Detailed recordings from the telescopes, which were recently processed, reveal something no one has seen before: lightning is actually starting inside a thunderstorm.

In a new paper which will soon be published in the journal Geophysical Research PapersIn this article, researchers used the observations to settle a long-standing debate about what triggers lightning—the first step in the mysterious process by which bolts are generated, grow, and spread across 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 don’t know how it works,” he said Brian Hare, a power researcher at the University of Groningen and a co-author of the new paper.


The picture from the school book is that, during a thunderstorm, hail falls as light snow crystals rise. The hail rubs off the negatively charged electrons of the ice crystal, leaving the top of the cloud positively charged while the bottom becomes negatively charged. This creates an electric field that increases until a giant spark jumps across the sky.

Yet the electric fields inside clouds are about 10 times weak enough to produce sparks. “People have been sending balloons, rockets and airplanes for thunderstorms for decades and have never seen electric fields anywhere near as massive,” 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 electricity for more than two decades. “It’s been a real mystery how it’s going.”

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One major obstacle is that clouds are opaque; Even the best cameras can’t peek inside to see the moment of initiation. Until recently, scientists had no choice but to enter a storm—something they’ve been trying to do since Benjamin Franklin’s famous kite experiment of 1752. (According to a contemporary account, Franklin attached a key to a kite and flew it under a thunderstorm, noting that the kite became electrified.) More recently, weather balloons and rockets made their way to the interior. Snapshots are introduced, but their presence artificially interferes with data by creating sparks that would not occur naturally. “For a long time we haven’t really known what causes thunderstorms at the time and place of lightning,” Dwyer said.

The obscurity of storm clouds has recently prevented scientists from seeing how lightning begins.Photo: George Rose/Getty Images

So Dwyer and his team turned to the Low Frequency Array (LOFAR), a network of thousands of tiny radio telescopes, mostly in the Netherlands. LOFAR typically looks at distant galaxies and exploding stars. But according to Dwyer, “the same goes for measuring electricity to work really well.”

When thunderstorms roll upward, there is little useful astronomy that LOFAR can do. So instead, telescopes tune their antennas to detect a barrage of a million or so radio pulses that each emit a flash of lightning. Unlike visible light, radio pulses can pass through dense clouds.

Using radio detectors to map lightning is nothing new; purpose-built radio antennas Long-Seen Hurricanes in New Mexico, But those images are low-resolution or only in two dimensions. LOFAR, a state-of-the-art astronomical telescope, can map lighting on a meter-by-meter scale in three dimensions, and achieve that with a frame rate 200 times faster than previous instruments. “LOFAR measurements are giving us the first really clear picture of what’s happening inside a thunderstorm,” Dwyer said.

A physically lightning bolt produces millions of radio pulses. To recreate a 3D lightning image from a jumble of data, the researchers used an algorithm similar to the one used in the Apollo moon landings. The algorithm continually updates what is known about the state of an object. While a single radio antenna can only indicate the rough direction of the flash, adding data from a second antenna updates the position. By looping continuously across the LOFAR’s thousands of antennas, the algorithm produces a clear map.

When researchers analyzed lightning data in August 2018, they saw that all radio pulses emanated from a 70-meter-wide area inside the storm cloud. He quickly hypothesized that the pattern of pulses supports one of two leading theories as to how the most common types of lightning start.

a thought It holds that cosmic rays – particles from outer space – collide with electrons in thunderstorms, causing electron avalanches that strengthen electric fields.

New observations point to rival theory, It begins with clusters of ice crystals inside the cloud. Turbulent collisions between needle-shaped crystals brush off some of their electrons, leaving one end of each ice crystal positively charged and the other negatively charged. The positive end draws electrons from nearby air molecules. More electrons flow from the air molecules that are further away, creating ribbons of ionized air that extend from each ice crystal tip. These are called streamers.

LOFAR, a large network of radio telescopes mostly in the Netherlands, records lightning when it is not doing astronomy.Photograph: Loafer / Astron

Each crystal tip gives rise to a multitude of streamers, with individual streamers repeatedly branching out. The streamers heat the surrounding air, ripping electrons from the air molecules as they flow over the massive ice crystals. Eventually a streamer that becomes hot and conductive turns into a leader—a channel along which a fully developed streak of lightning can suddenly travel.

“This is what we’re seeing,” said Christopher Sterpka, first author on the new paper. In a movie showing the onset of the flash, from researchers data, the radio pulse accelerates, possibly due to a deluge of streamers. “After the avalanche stops, we see a lightning leader nearby,” he said. In recent months, Sterpka has been compiling more lightning initiation movies than it ever seemed.

The important role of ice crystals coincides with Recent Findings That the electrical activity declined by more than 10 percent during the first three months of the COVID-19 pandemic. Researchers attribute this decline to the lockdown, which has led to fewer pollutants in the air, and thus fewer nucleation sites for ice crystals.

“The steps set out by LOFAR are certainly very important,” said ute aberte, a physicist at the National Research Institute for Mathematics and Computer Science and Eindhoven University of Technology in the Netherlands who studies the initiation of electricity but was not involved in the new work. She said LOFAR’s initiation movies provide a framework for creating accurate lightning models and simulations, which have so far been held back by a lack of high-resolution data.

However, Ebert notes that despite its resolution, the initiation film described in the new paper does not directly image the ice particles ionizing the air – it only shows what happens shortly thereafter. “Where is the first electron coming from? How does the discharge begin near the ice particle?” he asked. Some researchers still support the rival theory that cosmic rays initiate electricity directly, but cosmic rays may still play a secondary role in creating electrons. . which triggers the first streamer Those connect to the ice crystals, Ebert said. Hare added that exactly how streamers turn into leaders is also “a subject of great debate.”

Dwyer expects LOFAR to be able to resolve these millimeter-scale processes. “We’re trying to see the first little sparks that come out [ice crystals] To capture the initiation action itself at the very beginning,” he said.

Initiation is the first of many complex steps that lightning takes on its way to the ground. “We don’t know how it spreads and grows,” Hare said. “We don’t know how it connects to the ground.” The scientists hope to map the entire sequence with the LOFAR network. “This is an entirely new capability, and I think it will increase our understanding of lightning by leaps and bounds,” said Julia Tills, a lightning researcher at Sandia National Laboratories in New Mexico.

origin story reprinted with permission from quanta magazine, an editorially independent publication of Simmons Foundation whose mission is to enhance public understanding of science by covering research developments and trends in mathematics and the physical and life sciences.

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