e-how: Science - How lightning works
Lightning is a natural phenomenon which occurs as a result of an electrical discharge triggered by a build up of differing charges within a cloud.
Clouds can contain millions of Water Droplets and Ice Particles.
Rising water droplets collide with ice particles. The collision causes the rising droplets to become positively charged and the falling ice to become negatively charged.
The ground and upper section of the cloud gain a strong positive charge whilst the lower section of the cloud gains a strong negative charge. When the bottom of the cloud is charged enough a charge emerges called the Stepped Leader.
When the Stepped Leader gets close to the ground it atracts an upward moving charge called the Upward Leader. When these charges connect they create a bolt of ground-to-cloud lightning called Streamers.
How lightning works image courtesy of science-resources.co.uk
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