Sat. Jan 22nd, 2022


So Doyer and his team went back to the Low Frequency Array (LOFAR), a network of thousands of small radio telescopes, mostly in the Netherlands. LOFAR usually looks at distant galaxies and exploding stars. But according to Dwyer, “it also works really well for measuring lightning.”

When a thunderstorm passes over the head, there is very little useful astronomy that can LOFAR. Instead, the telescope tuned its antennas to detect a barrage of one million or more radio vibrations emanating from each flash of lightning. In contrast to visible light, radio pulses can pass through dense clouds.

Using radio detectors to map lightning is not new; There are purpose-built radio antennas The longest observed storm in New Mexico. But those images are low-resolution or only two-dimensional. The LOFAR, a state-of-the-art astronomical telescope, can map three dimensions of light on a meter-by-meter scale and achieve 200 times faster than previous instruments with a frame rate. “The LOFAR measurement is giving us the first really clear picture of what’s happening inside the thunderstorm,” Dwyer said.

A physical thunderbolt produces millions of radio pulses. To reconstruct a 3D lightning image from data clusters, researchers have used an algorithm used to land on the Apollo moon. The algorithm constantly updates what is known about the position of an object. Where a single radio antenna can only point the rough direction of the flash, adding data from a second antenna updates the position. By looping steadily across thousands of LOFAR antennas, the algorithm creates a clear map.

When researchers analyzed data from a lightning strike in August 2018, they found that radio pulses emanated from a 70-meter-wide region deep in all storm clouds. They quickly guess that the pattern of the pulse supports one of the two main theories about how the most common type of lightning starts.

An idea Suppose that cosmic rays – particles from space collide with electrons inside the thunderstorm, the electron initiates snowfall which strengthens the electric fields.

Indications of new observations Rival theory. It starts with a bunch of ice crystals inside the clouds. The turbulent collision between the needle-shaped crystals causes some of their electrons to stop, each end of the ice crystal charging positively and the other negatively. Draw electrons from air molecules near the positive edge. More electrons flow from distant air molecules, forming ionized air ribbons 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.Photo: LOFAR / ASTRON

Each crystal tip raises a group of streamers, with which the individual streamers are repeatedly closed. Streamers heat the surrounding air, scattering electrons from the air molecules so that a large current flows over the ice crystals. Eventually a streamer became hot and conductive enough to become a leader – a channel with which a whole stream of lightning could suddenly travel.

“This is what we’re looking at,” he said Christopher Starpka, The first author of the new paper. In a movie showing researchers the beginnings of flash made from data, radio pulses grew rapidly, probably due to the demise of the streamer. “After the snow stopped, we saw a thunderbolt leader nearby,” he said. In recent months, Sterpka has been compiling more Lightning Initiation movies that look like the first.



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