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Lightning Varieties

Lightning Varieties

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cloud-to-ground
This is the archetypal lightning bolt, one that arcs out of the sky and smites the ground with a great, often flickering flash of light. Lightning is the sudden release of built-up charge stored in an electric field, though exactly what triggers it remains a mystery (see "How Lightning Works").




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cloud discharge
This is lightning that occurs within a thundercloud, between two thunderclouds, or from a thundercloud to the air. Experts think most cloud discharges take place within an individual cloud, though few data exist to confirm that belief. Cloud discharges are certainly more common than the cloud-to-ground variety: 10 or more cloud flashes may occur before the first one that strikes the earth.




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ball lightning
No scientific documentation such as photos, videos, or other recordings of ball lightning exist, so experts have had to rely on eyewitness accounts, which have been numerous. Judging from such accounts, balls of lightning are typically between a golfball and a basketball in size, about as bright as a 60-watt light bulb, and often red, orange, or yellow in color. Observed shooting through the air, across the ground, and or even into houses, they are fleeting, generally lasting a few seconds before vanishing gradually or abruptly.




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blue jet
Blue jets shoot upward from the tops of thunderclouds. This remoteness, and the fact that they last but a few hundred milliseconds at most, perhaps accounts for why they were not discovered until 1994. The color of sapphires, they are cone-shaped in structure and extend for many miles. Like sprites and elves, blue jets provide a mechanism for energy transfer from lightning and thunderstorms to regions of the atmosphere between thunderclouds and the lower ionosphere.




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red sprites
Red sprites occur above large thunderstorm systems and are generally associated with larger positive cloud-to-ground flashes far below. They are most luminous very high up in the atmosphere, between altitudes of about 25 and 55 miles. Yet even at their most luminous, they are very hard to see, in part because they last for only a few thousandths of a second. Red in color and often bearing faint bluish tendrils extending downward, sprites come in several shapes, designated by colorful names like "carrot," "angel," and "columniform."




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elves
Like celestial halos, elves are circles of light that appear some 50 miles or more above thunderstorms. Triggered by lightning flashes far below, these ephemeral discs spread out radially across the bottom of the ionosphere in the briefest instant, expanding up to hundreds of miles in diameter in less than a millisecond. Experts believe elves are caused by lightning processes that accelerate electrons in the lower ionosphere.




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volcanic lightning
Lightning-like discharges are sometimes observed during volcanic eruptions, with no thunderstorm anywhere nearby. Hundreds or even thousands of feet in length, these bolts can flash to the ground or remain entirely within the ash cloud above the volcano. Here, lightning flashes during an eruption of Japan's Sakurajima Volcano in 1991.




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nuclear lightning
Hydrogen-bomb explosions can generate their own lightning. Ground-level detonations, like this 1952 test of an experimental thermonuclear device on Eniwetok in the South Pacific, cause a negative charge to be deposited in the atmosphere, resulting in long discharges not produced by clouds. This is a frame from movie footage shot at a distance of about 18 miles from ground zero. The lightning channels have been enhanced for visibility.




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triggered lightning
"Triggering lightning at will, at a predetermined place and time, is the old Promethean dream which seems more related to legend than to science," lightning expert Pierre Hubert has written. Yet the technique has taught scientists much about lightning processes and effects. Here, a rocket trailing a thin, grounded copper wire was launched into a thundercloud, triggering a series of lightning bolts that followed the path of the wire, which was vaporized in the process (see smoke-like vapor). Wind has separated the individual bolts.





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