Lightning no longer a mystery, physicist publishes landmark paper revealing clues about phenomenon
Ever wondered why lightning zig-zags? Or how it is connected to the thundercloud ago? You might have tried looking up the many textbooks on the lightning but failed to find a definite and convincing answer.
That is, until now.
A University of South Australia physicist just published a landmark paper that solved both mysteries.
According to Dr. John Lowke, former CSIRO scientist and now UniSA Adjunct Research Professor, lightning has been a puzzling subject even to the best scientific minds.
Singlet-delta metastable oxygen molecules behind the mystery
But first, why is this important?
The solution to protecting buildings from lightning strikes has remained the same for hundreds of years. It is essential to understand how lightning works so that buildings, airplanes, skyscrapers, and people can be protected more effectively.
Though the lightning rod invented by Benjamin Franklin in 1752 continues to be erected on structures, the "uncertain factor is how many are needed on each structure," Lowke said in a statement.
"There are a few textbooks on lightning, but none have explained how the zig-zags (called steps) form, why the electrically conducting column connecting the steps with the cloud remains dark, and how lightning can travel over kilometers," Lowke said.
Lowke figured that singlet-delta metastable oxygen molecules were behind the phenomenon.
The results are published in the Journal of Physics D: Applied Physics.
Improving lightning protection is so important due to extreme weather events
When electrons hit oxygen molecules with sufficient energy, they create high-energy singlet delta oxygen molecules. Once they've collided, the "detached" electrons form a "conducting step – initially luminous – that redistribute the electric field, causing successive steps," as per the release.
When electrons attach themselves to neutral oxygen molecules, the conducting column connecting the step to the cloud remains dark. After this, the electrons immediately detach themselves by singlet delta molecules.
The study could create a significant change - with new Australian lightning protection standards recommending that building roofs be earthed.
"Improving lightning protection is so important now due to more extreme weather events from climate change. Also, while the development of environmentally-friendly composite materials in aircraft is improving fuel efficiency, these materials significantly increase the risk of damage from lightning, so we need to look at additional protection measures," said Lowke.
"The more we know about how lightning occurs, the better informed we will be in designing our built environment," he added.
An unresolved issue in the physics of lightning is an explanation for lightning proceeding to the ground by successive luminous steps separated by "dark" times of many microseconds. There is also no explanation of the structure of the dark column connecting the streamer step with the cloud that can be km in length, is electrically conducting, yet has a very low sustaining electric field. It is proposed that these two processes can be explained by the accumulation of singlet delta metastable oxygen molecules excited in the corona pulses of lightning. The step time is necessary for the excitation of large metastable densities to produce significant metastable detachment of electrons from negative ions. The detached electrons form a highly conducting step, initially luminous, that causes a redistribution of electric fields and an increase in the potential and electric fields at the end of the step to make possible a further step by ionization. These features are supported by calculations of densities of electrons, positive ions, negative ions and singlet delta metastable oxygen molecules for the first 7 s of a discharge chosen to be initiated by a 50 cm sphere of charged hail particles. The calculated corona streamers produce metastable densities of 1017 cm-3 near the corona source. These metastables, by electron detachment, produce a conducting cylinder 10 m long with a radius of 1 cm and an electron density ~ 1012 cm-3 that is attributed to being the first step and a lightning "leader". These conducting regions develop within them very low electric fields. Successive steps combine to form the long conductive column that exists before the return stroke. Electron densities in the leader and the column are an equilibrium between electron production by metastable detachment and electron loss by attachment to neutral oxygen molecules, requiring no electric field.