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Elves are rapidly expanding disk-shaped regions of glowing that can be up to 300 miles across. They last less than a thousandth of a second, and occur above areas of active cloud to ground lightning. Scientists believe elves result when an energetic electromagnetic pulse extends up into the ionosphere. Elves were discovered in 1992 by a low-light video camera on the Space Shuttle.
Red Sprites can appear directly above an active thunderstorm as a large but weak flash. They usually happen at the same time as powerful positive CG lightning strokes. They can extend up to 60 miles from the cloud top. Sprites are mostly red and usually last no more than a few seconds, and their shapes are described as resembling jellyfish, carrots, or columns. Because sprites are not very bright, they can only be seen at night. They are rarely seen with the human eye, so they are most often imaged with highly sensitive cameras.
Blue jets emerge from the top of the thundercloud, but are not directly associated with cloud-to-ground lighting. They extend up in narrow cones fanning out and disappearing at heights of 25-35 miles. Blue jets last a fraction of a second and have been witnessed by pilots.
John Harrison, another witness, described how he looked out of his landing window and saw a “massive ball of light with tentacles going right down to the ground” over the wind farm. He said: “It was huge. With the tentacles it looked just like an octopus.”
The mechanics of sprites With negative cloud-to-ground (CG) lightning strikes, electrons move from the clouds to the Earth (and, by definition, current moves upward). In a positive CG, electrons move upward.
While all of this might be interesting to devoted lightning researchers, red sprite aficionados are most curious about the physics happening above the clouds. And the new research, produced by Stanford University's Christopher Barrington-Leigh and colleagues, changes the perception of what's going on up there. "Our observation of negative CG sprites suggests that the normal mechanism for sprites does not depend greatly on the sign of the charge moved by the lightning, but only on how much charge is moved by the lightning," Barrington-Leigh told space.com. "The scarcity of negative CG sprites must then lie in the fact that most negative CG lightning just doesn't often move enough charge around." Every second of every day, on average, lightning hits Earth about 50 times. Barrington-Leigh points out that the majority of that activity involves negative CG strikes, of the type he's just observed to be associated with red sprites.
This raises the possibility that sprites may be far more prevalent than previously suspected. The possibly higher frequency could alter our understanding of numerous upper-atmosphere phenomena. Some researchers have speculated that sprites might create nitric oxide, which destroys the protective ozone layer.
And there are other possible relationships. "We have seen evidence that sprites, and the electromagnetic pulses from lightning, may be able to both increase and decrease [respectively] the populations of high-energy particles in the Earth's radiation belts," said Barrington-Leigh. "These remarkable effects could thus affect the rate at which satellites in low- and middle-Earth orbit are being bombarded by electrons." It's also possible that similar discharges might occur on other planets -- Jupiter and Venus being likely candidates. "Differences in how the analogies to sprites and lightning appear in other planetary atmospheres could serve as a diagnostic for the nature of extraterrestrial ionospheres, atmospheres, and electrification processes," Barrington-Leigh said. "The study is quite significant," said Matt Heavner, an atmospheric electricity researcher at the University of Alaska, Fairbanks.
Heavner, noting that we still understand very little about the lightning that comes out of the bottom of clouds, said knowledge of red sprites is growing rapidly, considering researchers have only been on the trail for a decade.