What exactly is lightning? And how does it occur?

Although a deadly phenomenon, lightning is perhaps the largest source of energy after the Sun, as far as Earth is concerned. The scientific world is desperately looking for ways to tap the great amount of energy produced during lightning and channel it in productive ways.
What exactly is lightning? And how does it occur? The scientists had started to pursue the answers centuries ago. However, the satisfying theories about the phenomenon were put forward by G C Simpson (1927) and CTR Wilson (1929). Their inferences are widely accepted in the science world.
Lightning is actually an electric discharge between two charged spots. It can happen in three ways; within a cloud, between two clouds, and between a cloud and the Earth. It occurs mostly during storm or rain.
A cloud is a collection of condensate water molecules. Due to the friction between these molecules, a build-up of charges is formed. The positive charges pool above the cloud while the heavier negative charges (electrons) assemble in the downside. An electric field is created between these charges and when it is big enough, an electric current occurs between these charges. The water vapor acts as a medium here. This can happen inside a cloud or between two clouds. A large amount of heat and pressure is produced during the lightning. This causes a rapid expansion of the air in the nearby areas and produces a shock wave. The sound of this wave is what is heard as thunder. Since light travels far swifter than sound, the thunder is heard only after the lightning is seen, although both take place simultaneously.
Another way of lightning is between the cloud and Earth, which is also the least common type of the phenomenon. When the polarization happens in the clouds, the Earth also undergoes some changes. Due to electromagnetic induction, a pool of positive charges is formed on the ground directly under the negative charges in the cloud. According to the movement of cloud, this pool also moves. The opposite charges attract each other and when this attraction is great enough to overcome the resistance of air, electrons travel from the cloud to Earth through the path with the least resistance. It is the principle behind the cloud to ground lightning. The speed of lightning is around 45000 km per second and the temperature can rise up to 30000 degree Celsius.
The frequency of lightning around the world is very large. It is estimated that more than 50 lightning flashes occur in a second. Around 4000 million kilowatts of electricity is produced during an average lightning.

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