Why is lightning bolt-shaped?

New research explains why lightning moves in steps and takes on its special shape. The answer may lie in the oxygen molecules in the atmosphere.

Every second beats approx 100 flashes down the world around. Lightning can contain up to a billion volts and moves in segments of about 50 meters each from the clouds down to the ground. But why are the flashes actually zigzag-shaped? A new study now presents an answer.

– There are some textbooks on lightning, but no one explains how the zigzag shape occurs, why the electrically conductive column that connects the different stages of lightning remains dark or how lightning can travel several kilometers, says John Lowke, who is behind the study and is a professor at the University of South Australia, in one press release.

Oxygen molecules account for the explanation

A lightning bolt discharges in stages from an electrically charged cloud until it is close enough to the ground. Then the part moving through the clouds – the pre-discharge – meets with a part from the ground – the capture discharge – and lightning strikes. The process is so fast that the eye does not have time to distinguish the different parts.

The new study sets out to answer why lightning moves in stages and what the dark segments of several microseconds between each stage are due to – the answer lies in the oxygen molecules in the air.

According to the study, lightning occurs when electrons collide with oxygen molecules with high enough energy and form metastable types of singlet oxygen – a reactive form of oxygen with higher energy than ordinary oxygen. The molecules are ionized and the electrons that have been detached form a partial step that is highly electrically conductive. The sub-stage is initially luminous and affects the electric field which increases the voltage at the end of the stage, which in turn enables the next sub-stage.

The calculations are based on a sphere of charged hail particles of 50 centimeters as the origin of the lightning. The metastable oxygen molecules then produce, via detached electrons, a conducting cylinder of ten meters which corresponds to the first stage of lightning.

Although lightning rarely hits people directly, there is a need to develop protection against lightning according to John Lowke. He highlights both the changing climate and technology development in the aviation industry as examples.

– Improving lightning protection is important now because of the more extreme weather events that come with climate change. Furthermore, although the development of environmentally friendly composite materials in aircraft improves fuel efficiency, these materials significantly increase the risk of damage from lightning strikes. We have to look at additional protective measures, he says in the press release.


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