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blue jet

a faint discharge of blue light from the top of a thunderstorm cloud that propagates upward: extends approximately from the bottom to the top of the stratosphere and is not detectable from the ground.
Also called reverse lightning. Unabridged
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blue-jet in Science
blue jet  
A conical discharge of blue light that starts from the top of active thunderstorm clouds and proceeds upward. Blue jets can last up to several hundred milliseconds and are believed to connect the top of a thundercloud with the ionosphere.
The American Heritage® Science Dictionary
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