Lightning is a massive electrostatic discharge caused by unbalanced electric charges in the atmosphere, and resulting in a strike, from a cloud to itself, a cloud to a cloud or a cloud to ground, and accompanied by the loud sound of thunder. A typical cloud to ground lightning strike jumps a 5 km (3 mi) gap through the air. A typical thunderstorm has three or more strikes per minute at its peak. Lightning is usually produced by cumulonimbus clouds based 5–6 km (3-4 mi) above the ground and that are themselves up to 15 km (9 mi) in height. Lightning also occurs during snow storms (thundersnow), volcanic eruptions, dust storms, forest fires or tornadoes. Hurricanes typically generate some lightning, mainly in the rainbands as much as 160 km (100 mi) from the center. When the local electric field exceeds the dielectric strength of damp air (about 3 million volts per meter), electrical discharge results in a strike, often followed by commensurate discharges branching from the same path. (See image, right.) Mechanisms that cause the charges to build up to lightning are still a matter of scientific investigation. Lightning may be caused by the circulation of warm moisture-filled air through electric fields. Ice or water particles then accumulate charge as in a Van de Graaff generator. The science of lightning is called fulminology. The fear of lightning is called astraphobia. THUNDER
Thunder is the sound caused by lightning. Depending on the nature of the lightning and distance of the listener, thunder can range from a sharp, loud crack to a long, low rumble (brontide). The sudden increase in pressure and temperature from lightning produces rapid expansion of the air surrounding and within a bolt of lightning. In turn, this expansion of air creates a sonic shock wave, similar to a sonic boom, which produces the sound of thunder, often referred to as a clap, crack, or peal of thunder. The distance of the lightning can...
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