Tech UPTechnologyHow are lightning created?

How are lightning created?

The prelude to a typical lightning strike is the separation of electrical charges in the cloud: the negative charge accumulates at the bottom while the positive charge accumulates at the top, until the negative charge grows enough to overcome the resistance of the lightning bolt. air to circulate electric current through it, something that happens when the potential is about 18,000 volts . Then a stream of electrons begins to descend from the cloud, zigzagging towards the ground .

As they go down, the electrons collide with other atoms and take away part of their electrons, which add to the trip to the surface. This precursor does not cause the lightning strike that we observe. When conducting between 100 and 1,000 amps , that is, between 20 and 200 times the current of an electric iron, it is difficult to see.

On the other hand, something similar happens on land. The proximity of the electrons causes positive charges to begin to accumulate on the ground, which by their nature tend to meet the electrons like two passionate lovers. To start ascending they use any conductive object in the area: buildings, trees or people. At 30 meters above the ground, the tip of the precursor is already in a position to touch the surge of positive current coming from the ground.

It is now when the pyrotechnic display begins. What we have is a kind of short circuit to the beast . In less than a thousandth of a second, 100 trillion electrons reach the earth and the current reaches between 10,000 and 200,000 amps. Although the actual flow of particles is downward, the point of contact between the cloud jet and the ground jet rises to about 80,000 km/s in a movement called backlash . 

This backlash contributes more electrons to the beam as it ionizes the air, in addition to heating it to about 50,000ºC. Thus, each meter of hot air in the lightning channel shines as brightly as a million 100-watt light bulbs. This rising backlash glow is what we see as lightning , only it appears to us as if it is descending.

As the superheated air bursts , a supersonic wave is created : thunder . We might think that everything ends here, but it is not. Backlash hasn’t downloaded to the cloud, so the show isn’t over. A second precursor begins to descend along the same path as the first, which is followed by a second backlash and so on up to four precursor-backlash pairs. 

In short, the flash of lightning is made up of multiple discharges : each precursor-backlash cycle takes two hundredths of a second, too fast for the eye to see them separately but enough to observe the familiar flash of lightning.


Uman, MA (2010) Lighting, Dover Pub


Uman, MA (2010) Lighting, Dover Pub

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