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Lightning can light up the sky with a bright flash and take all sorts of shapes, but if you were to draw one, you would almost certainly draw a zigzag. But what gives lightning bolts that branchy shape? Why does lightning zigzag across the sky instead of shooting in a straight line between the thundercloud and the ground?
Many of the mechanisms behind lightning remain a mystery, although researchers are beginning to unravel the causes of lightning’s curvature. “We know all about most things about Earth scientists can predict [lunar and solar] eclipses with an accuracy of a fraction of a second” John Lowke (opens in a new tab), a physicist at the University of South Australia and lead author of a study examining the “stepped pattern” of lightning, told Live Science. “But there are still great mysteries about plain old lightning.”
In a December 2022 study published in the journal Journal of Physics D: Applied Physics (opens in a new tab)Lowke and colleagues suggest that lightning’s distinctive zig-zag pattern is due to its highly conductive form oxygen which accumulates irregularly as the propeller moves towards the ground, sometimes over long distances.
Related: What is the longest recorded lightning bolt?
He said extremely high-speed images of lightning show the lightning is preceded by “leaders” of ionized (electrically charged) air that branches out from the bottom of the thundercloud. In most cases, these leaders are too weak to be seen with the naked eye.
Lowke said it’s these leaders, not the final lightning bolt, that make up the staggered pattern.
Air usually acts as an insulator, but leaders create regions of high concentration of a special form of highly conductive oxygen called “singlet delta oxygen,” which is oxygen molecules with a lower than normal energy state.
Lowke said each “zig” (or “zag”) of the leader – a “step” of about 165 feet (50 meters) – is caused by an electrical charge discharging in such a region.
The powerful magnetic fields from the final stage almost instantaneously create additional singlet delta oxygen molecules from the regular oxygen molecules in the atmosphere, and concentrations of this highly conductive oxygen can branch out in all directions from where the stage ends.
The leader discharges in successive steps over the course of about one millionth of a second, each followed by a fleeting period of “darkness” during which the discharge is not visible in the pictures at all, and finally strikes the ground or a tall object attached to it. The result of this impact are visible (and very loud) lightning “return strike” for about one-thousandth of a second, traveling back along the zig-zag path of highly conductive singlet oxygen delta, he said. The other leaders lose their charge at this point and disappear.
A better understanding of how lightning works can help buildings and people survive storms, Lowke said. For example, it may indicate the placement of lightning rods on tall objects such as buildings, radio masts, and ship superstructures.
Among the lingering questions about lightning is what causes it. Although scientists now assume that lightning is static electricity produced by the movement of ice particles in thunderclouds, this is not certain, Lowke said.
“It’s a very interesting topic,” he said. “The secrets have not been recognized and are not known to the general public.”
