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Mysterious Cause of Lightning Formation Revealed

The mysterious cause of lightning formation has  been discussed in a new paper. The unprecedented observations are documented in a paper published in Nature Communications.

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Scientists have delved further into the mystery of the formation of lightning. While it is established that lightning is an electric current flowing in the midst of a cloud, or between a cloud and the ground, little is known about how the initial spark is brought into existence; how does it eventually generate powerful bursts of charge?

New observations of a rare type of lightning spark, the powerful narrow bipolar event, made by researchers from Langmuir Laboratory at the New Mexico Institute of Mining and Technology have helped to shed more light on the subject. This study is expected to provide a better understanding of how lightning is caused.

The formation of this powerful form of lightning is triggered by a discharge called fast positive breakdown — this has never been documented before. The researchers believe that this discharge is what causes most lightning events, specially those characteristic of thunderstorms.

The sparks in question travel at incredible speeds considered to be relatively fast for lightning: from 10 to 100 million meters per second. These, in turn, generate extremely powerful radiofrequency (RF) radiation; the researchers think that, of all the natural sources of RF radiation on the planet, they are the strongest.

These findings are in contradiction with simulations of thunderstorm conditions previously conducted by other researchers; according to these experiments, it was thought that lightning breakdown was negative instead of positive. However, as one of the authors of the new paper, William Rison, points out, reproducing such conditions in laboratory is an impossible task. He explains that their results provide a clear demonstration of how the initiation is characterised by a positive breakdown.

Rison also dismisses the well-known proposal that relativistic electrons are behind the initial spark. He says that unlike this type of breakdown which is characterised by an initial upward movement, their findings show that the spread of narrow bipolar events happens downward instead of upward, implying that they are caused by downward-developing positive breakdown.

The next phase will be to determine the physical development of the fast positive breakdown.

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