BLUE JETS, which are restricted to the part of the atmosphere below about 40 kilometers altitude, are comparatively difficult to observe. A color image (right) shows that the jets give off a deep-blue light, which does not penetrate the atmosphere readily--quite unlike the reddish hues that dominate sprites and elves. So observation requires going above the dense lower atmosphere. Sentman and Wescott recorded such eerie cones of blue light for the first time while flying over an intense storm in Arkansas in 1994. This sequence of video images from a sensitive monochromatic camera (A-D) reveals how these lights jet upward from the top of thunderclouds at speeds of about 120 kilometers per second. Researchers are still trying to reconcile competing theories to explain exactly how blue jets come about. 
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Image: Daniel L. Osborne, University of Alaska-Fairbanks

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Images: Stephen B. Mende