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Lightning can light up the sky in a bright flash and take on a variety of shapes, but if you were to draw it, you’d almost certainly scratch a zigzag. But what gives thunderbolts this branch shape? Why does lightning zigzag across the sky, instead of striking in a straight line between a thundercloud and the ground?
Many lightning mechanisms remain a mystery, although researchers are beginning to unravel the reason for the twisting of lightning. “We know everything about most things about Earth — scientists can predict [lunar and solar] eclipses in 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 looking at the “staircase model” of lightning, told Live Science. “But there are still great mysteries about the common old thunderbolt.”
In the study, study published in December 2022 in the Journal of Physics D: Applied Physics (opens in a new tab)Lowke and colleagues suggest that the characteristic zigzag pattern of lightning is caused by a highly conductive form of oxygen which builds up irregularly as the bolt travels towards the ground, sometimes over great distances.
Related: What is the longest lightning bolt ever recorded?
Extremely fast photographs of lightning show that a flash is preceded by “leaders” of ionized (electrically charged) air that branch out from the bottom of a thundercloud, he said. In most cases, these rulers are too weak to be seen with the naked eye.
It is these leaders, not the last flash, that form the staircase pattern, Lowke said.
Air generally acts as an insulator, but leaders create regions with high concentrations of a special form of highly conductive oxygen called “delta singlet oxygen” – that is, oxygen molecules with a energy state lower than normal.
Each “zig” (or “zag”) of a leader – a “step” about 165 feet (50 meters) long – is caused by an electrical charge discharging in such a region, Lowke said.
The strong magnetic fields of the last stage almost instantly create additional delta singlet oxygen molecules from the regular oxygen molecules in the atmosphere, and concentrations of this highly conductive oxygen can branch out in all directions from the end of the stage, he explained.
The leader discharges through successive stages in about a millionth of a second, each followed by a fleeting “dark” period where photographs show no visible discharge, and finally hits the ground or a tall object connected to it. This impact translates into the visible (and very noisy) the lightning “return hit” for about a thousandth of a second, returning along the zigzag path of the highly conductive delta singlet oxygen, he said. The other leaders lose their charge at this point and disappear.
A better understanding of how lightning works can help structures and people survive thunderstorms, Lowke said. For example, it can inform the placement of lightning rods on large 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 created by the movement of ice particles in thunderclouds, this is not known for certain, Lowke said.
“It’s an incredibly interesting subject,” he said. “The mysteries have not been recognized and are not known to the general public.”
