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How does lightning occur?

Lightning is the result of a large charge separation within a cloud. Clouds are composed of millions of ice particles and water droplets. These particles collide with other condensing moisture as it rises, and when they do, electrons are knocked loose. These electrons build up at the bottom of a cloud and make it negatively charged. The rising moisture molecules, now missing electrons, become positively charged and gather at the top of the cloud. This creates a charge separation, which has an electric field that is negative at the bottom and positive at the top. As the collisions continue, the electric field builds so strong that it gives the planet's surface a positive charge. When these charges become powerful enough, the cloud's electricity is discharged toward the Earth's surface, which results in lightning.
The most common thunderstorm cloud is a tall cloud which is precipitating, called a cumulonimbus cloud (cumuli- meaning tall, high altitude, and nimbus meaning precipitation). These clouds form when conditions include upward winds, rather moist air, and cooling temperatures. Within this cloud, there are many electrons giving off their charges. The tendency of charges within a cloud is to have positive charges gather toward the upper portion and negative charges in the bottom of the cloud.
When the difference between these charges is great enough to overcome the air's natural insulation, which keeps these charges from mixing, a lightning flash can take place. This charge difference builds up to millions of volts before the stoke of lightning takes place. The lightning bolt actually happens because nature tries to maintain equilibrium, a state of balance between all things. This is why the lightning that you see is a discharge of energy in the form of electricity.


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