Lightning is caused by the buildup and discharge of electrical energy in the atmosphere, typically during thunderstorms. The process involves several key factors:
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Charge Separation: Within a storm cloud, various processes (such as collisions between water droplets, ice particles, and other elements) lead to the separation of positive and negative charges. Generally, smaller ice particles in the upper parts of clouds carry positive charges, while larger water droplets and hailstones in the lower parts of the cloud carry negative charges.
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Electric Field Creation: As the charge separation increases, it creates a strong electric field within the cloud, and between the cloud and the ground. When the electric field strength becomes sufficiently intense, it can overcome the insulating properties of the air.
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Ionization of Air: The strong electric field ionizes the air, creating a conductive path. This ionization process allows electricity to flow through the air, forming what is called a "stepped leader," a series of descending, jagged channels of ionized air.
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Return Stroke: When the stepped leader makes contact with the positive charge on the ground or within the cloud (or between clouds), it completes the circuit. This triggers a powerful discharge of electricity, known as the "return stroke," which is the visible flash of lightning. The return stroke can reach temperatures of around 30,000 Kelvin (approximately 53,540 degrees Fahrenheit or 30,000 degrees Celsius) and emits light across the spectrum, creating the bright flash of lightning.
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Thunder: The rapid heating and expansion of the air from the return stroke creates sound waves, resulting in the thunder that often accompanies lightning.
Lightning can occur within a single cloud (intracloud lightning), between clouds (intercloud lightning), or between a cloud and the ground (cloud-to-ground lightning), with cloud-to-ground lightning being the most well-known.