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There is something in the series of meanders that involves random chaos. However, blue lightning strikes not only the same places with regularity, but successive discharges often reuse exactly the same channel.
It has never been quite clear how the path traced by a lock stuck for repeated performance, but new research has uncovered persistent pockets of charge as a result of a lightning strike, which could provide a map for more to follow.
An international team of physicists has collected an unprecedented level of detail on lightning radio waves to determine why charged air pockets that trace the path of lightning behave in the same way.
Using a radio telescope network called Low-Frequency Array, or LOFAR, the researchers were able to collect data allowing nanometric resolution of impacts over an area of several thousand square kilometers.
"These data allow us to detect the spread of lightning on a scale where, for the first time, we can distinguish the primary processes," says physicist Brian Hare from the University of Groningen in the Netherlands.
"In addition, the use of radio waves allows us to look inside the storm cloud where most flashes are."
In spite of its dazzling and bright, lightning is actually only an electric spark of grandfather caused by a difference of positive and negative charges.
The opposite charges are separated by air currents swirling around small hailstorms called graupels, forcing them to physically move and crush their electrons in a weather game of passing the package.
Regular accumulation of hundreds of millions of volts can occur in and between separate clouds, or between a cloud and the ground. However, wherever it is formed, lightning has the ability to jump, but only if conditions are met.
What we see as the zig-zagging lock is only the end of a complex process that we are rebuilding.
The first step involves the formation of a small pocket of plasma – a drop of heated gas composed of charged particles. This tiny seed of lightning ramifies rapidly in many directions, with one or more channels forming a channel several kilometers long that acts like a giant wire hanging in the sky.
The ends of this chain, called leaders, can be positive or negative, each of them moving uniquely according to its load.
Negative leaders tend to move discontinuously, which is called step by step, producing a high frequency radio signal when they jump. Positive leaders do not act the same way, so do not produce the same signal as they grow up. Yet their channels still buzz with a distinctive pattern in radio waves.
These contrasting signals provide researchers with insight into the rapid generation of lightning, from the growth of the plasma channel to the climatic light show at the end.
A curious observation made in the past has been positive: leaders can be separated from their plasma channel. Nobody knows why this split occurs like this, largely because most studies to date have not found the necessary resolution.
The vast complex of antennas that LOFAR composes, however, provided researchers with everything they needed to focus on the finer details of a branched plasma channel.
"Near the central area of LOFAR, where the antenna density is the highest, the spatial accuracy was about one meter," says the physicist of the University of Groningen, Olaf Scholten.
With such a high level of detail, the researchers were able to map the dynamic changes that occurred in the plasma channels as they reached the distance, which allowed the team to make a discovery. rather strange.
When leaders arrive in areas where the voltage difference is sufficient, the electrons pass through the plasma, causing the air to reach temperatures higher than the Sun's surface.
It turns out that all this current does not reach the same end points. Part of the residual charge escapes through gaps in the main discharge channel, trailing in small, thin structures called needles.
"This discovery contrasts sharply with the current situation, in which the charge flows along plasma channels directly from one part of the cloud to another, or up to the ground," said Scholten.
"These needles can be 100 meters in length and less than five meters in diameter, too small and too short for other lightning detection systems," says Hare.
If the voltage difference is reconstituted in the cloud in a relatively short period of time, these charged needles can provide a map for other keystrokes, which is why we could often see flashes of copy-cat hitting the same mark several times.
The clip below shows a slow-motion strike, with each yellow dot representing a radio pulse describing the path of the dump. At the very top of the clip, you can see the positive leaders twinkle when they meet the needles of a previous bolt.
"From these observations, we see that part of the cloud is being recharged, and we can understand why a lightning discharge on the ground can be repeated several times," says Hare.
For a force as primordial as we have always been amazed, it is astonishing to think that we are still learning as much about the operation of lightning.
This research was published in Nature.
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