The risk of being struck down remains low. But, with the proliferation of extreme weather events, thunderstorms could well threaten our buildings and our homes more and more. Hence the importance of better understanding how lightning strikes. And this is precisely what Australian researchers have managed to do.
The thunderstormsthunderstorms are both violent and fascinating phenomena. An unstable atmosphere. A airair hot at the surface and colder at higher elevations. An ascending current that causes cumulonimbuscumulonimbus electrified. The raging wind and the falling rain. Sometimes in hail. Then the thunder which rumbles, which slams, which rolls. Long flashes that streak the sky. And finally the lightninglightning hitting the ground at more than 400,000 kilometers per hour. This happens more than 450,000 times a year, in mainland France alone.
For a human being, the probability of being struck by lightning is still low. On the order of one in a million. In France, there are approximately 200 people affected each year. But, for buildings, the risk is much greater. L’Empire State Building, for example, is struck down some 25 times a year! It is protected by a system lightning rodlightning rod — generally doubled by a lightning arrester.
A system almost as old as the world. It was invented in 1752, by Benjamin Franklin. It consists of a wire that attracts lightning to the top of the building and directs the associated electrical charge to earth to prevent damage. However, to properly size these lightning rods, it is necessary to better understand the phenomenon.
Researchers have studied thunderstorms extensively. But the lightninglightning, lightning, have long kept their mysteries. In particular that of the zigzags that they like to draw in our sky. The legend even says that the best minds broke their teeth there. Until today and this study published by University of South Australia plasma physicists.
The role of an excited oxygen
In question, they tell us, moleculesmolecules oxygen metastablemetastable singlet-delta. This certainly calls for some explanation. Note first of all that the physicistsphysicists designate by singlet oxygen, a molecule of oxygen (O2) in a excited stateexcited state and which is characterized by a electron configurationelectron configuration different from that of regular oxygen.
At the heart of the storm, a flash takes shape when electronselectrons hit oxygen molecules with enoughenergyenergy to excite them. Accumulation of metastable oxygen molecules results in significant detachment of electrons. These then form like a very conductive step.
“The successive steps combine to form a conductive column that connects the whole to the cloud”
A light walk. A march that redistributes the electric fieldelectric field towards its end, preparing the ground for theemergenceemergence of another market created by ionizationionization. It’s escalation. The successive steps combine to form a conductive column that connects the whole to the cloud. While remaining dark in the regions where the electrons remain attached to classical oxygen molecules.
This work is intended to help engineers better protect us from lightning. “This is particularly important now due to extreme weather events due to climate changeexplains John Lowke, a physicist at the University of South Australia, in a communicated.Especially since the development of environmentally friendly composite materials in aircraft to improve their energy efficiency greatly increases the risk of damage to aircraft caused by lightning. We must therefore consider additional protective measures. And the more we know about how lightning occurs, the better we can design effective systems. »