The lightning phenomenon

For thousands of years, lightning has always mystified and scared mankind as it was perceived as a sign of divine intervention. In the XVIIth century, it was revealed that this natural phenomenon consists in an electrostatic discharge.
Each year, about 20 people along with tens of thousands of farm animals are killed as a result of the million of lightning strikes reported in France. In the meantime, a major amount of electronic and electric equipment is destroyed yearly.

Lightning storms

When two air masses with very different temperatures collide, it favors the conditions required for the formation of a cumulonimbus. Violent vertical air streams reaching up to 15 km appear within the clouds and form ice fragments, water drops and hail. These elements will then start to lose electrons when colliding each other. As long as the cloud grows bigger, it cumulates a high number of electrical loads thus becoming a giant capacitor. Such difference in terms of electrical loads can appear within the same cloud, between different clouds and between the lower part of a cloud and the ground. Electrostatic fields can then reach very high levels from 10 to 25kV/m: the lightning strike is imminent.

Lightning bolt

In fact, a lightning bolt is a very complex process which can be divided in several phases. Small quantities of energy are expelled from both the cloud and the ground and progress one leap after another with a speed of 200 km/s: this creation of upward and downward leaders is barely perceptible to the naked eye. These leaders “breach” into a micro ionized tunnel. Once the upward leader is close enough to the downward leader, a connection between the tunnels occur. The cloud will be discharged through this ionized path. A lightning bolt is the result of repeated consecutive discharges which can be compared to a stroboscopic effect.

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