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Thunderstorms and Lightning
Australia Natural Disasters

How is lightning caused?


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September 22, 2014 9:20PM

Lightning occurs as a discharge of energy from charged air masses in clouds, and can be from cloud to cloud or from a cloud to the ground.

How Lightning Occurs

The first process in the generation of lightning is the forcible separation of positive and negative charges within a cloud or air. The mechanism by which this happens is still the subject of research, but one widely accepted theory is the polarization mechanism. This mechanism has two components: the first is that falling droplets of ice and rain become electrically polarized as they fall through the atmosphere's natural electric field, and the second is that colliding ice particles become charged by electrostatic induction. Once charged, by whatever mechanism, work is performed as the opposite charges are driven apart and energy is stored in the electric fields between them. The positively charged crystals tend to rise to the top, causing the cloud top to build up a positive charge, and the negatively charged crystals and hailstones drop to the middle and bottom layers of the cloud, building up a negative charge. Cloud-to-cloud lightning can appear at this point.

Cloud-to-ground lightning is less common. It occurs when a "step leader" from a cloud ionizes a path for the discharge of large electrostatic charges. Negative charges usually migrate from a cloud to the ground and positive charges from the ground to a cloud, and they can involve many different areas in the cloud at once.

Cumulonimbus clouds that do not produce enough ice crystals usually fail to produce enough charge separation to cause lightning.

Depending on the medium, lightning can travel up to 75 km/sec, so even though it creates light it is a release of energy, so it doesn't travel at the speed of light.
Through friction in the clouds

particles rub together creating an electrical charge in the clouds.