Lightening is a giant spark of electricity in the atmosphere between clouds, air or ground. When water vapor condenses into small ice crystals when it moves upwards in the cumulonimbus cloud. The ice crystals continues to grow till they gather enough mass to overcomes buoyance force this leads to a system where small ice crystals move up, while bigger ice crystals comes down resulting in the collision that triggers release of electron similar to ionization. More free electrons causes more collision and a chain reaction starts.
The process results in a situation in which the top layer of the cloud gets positively charged while the middle and bottom layers are negatively charged. The potential difference can be on the order of 109-1010 volts. In little time a huge current of order of 105-106 amperes starts to flow between the layers. It produces heat, leading to heating of air coloum. It is because of this heat the cloud looks red during the lightening. As this air heated it causes to expand and creates shock waves that results in thunder.
Thunder is the sound caused by the discharge of atmosphere electrical charge by lightening. The channel pressure of the electric charge exceeds the ambient pressure of surrounding and channel expends at a supersonic speed. The resultant sock wave decays rapidly with distance and is eventually heard as thunder once it slows to the speed of sound. Thunderbolt is a flash of lightening accompanied by a crash of thunder.
Electric discharge :-
- Cloud to ground :- This type of lightening is commonly called as ‘thunderbolt’ or cloud-ground lightening that occurs between the cloud and ground. It is typically appears to follow a course and is usually branched downwards from a distinct main channel. It is initiated when downward moving -ve charge ‘stepped ladder’ connects with a streamer of +ve charge reaching upward. Once channel is established a massive electrical discharge follows. This is the ‘return stroke’ and is most luminous discharge.
It can also travel many kilometers to strike the ground as the so called ‘bolt form the blue’ (clear air lightening). Ground to cloud discharge initiated by an upward moving ladder can sometimes originate from objects on the ground such as tall towers and skyscrapers.
2. Cloud to cloud :- This type of lightening popularly called as ‘sheet lightening’ because it lights up the sky with a sheet of light that occurs within a thunderstorm. (Either intracloud or intercloud) Sometimes lightening discharges originating below or within anvil can be seen to move horizontally for some distance generating multiple tree-like branches. These are known as anvil crawlers.
3. Cloud to air :- This type of lightening also sometimes called as ‘streak lightening’ and occurs as sinuous discharges passing from a thundercloud to the air and not striking the ground. Discharge often divides into branches but with a distinct main channel. It frequently includes a long quasi-horizontal part.
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