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Posted at 12:00 PM ET, 09/17/2012

Red sprites, blue jets, and elves: What are these mysterious, elusive phenomena?


A sprite glows red in this image captured by astronauts on the International Space Station on April 30, 2012. (NASA)

During World War II (and probably before), high flying pilots were reported to have observed unexplained aerial phenomena (UAP), often now called transient luminous events (TLE’s), particularly in the vicinity of thunderstorms. But at the time, scientists believed that such observations had little credibility. The pilots, they thought, while good at what they were trained to do, lacked the ability to properly identify fleeting aerial phenomena, such as (what we now know are) red sprites, blue jets, and elves, if, in fact, they existed at all.

As a result, pilots were reluctant to come forward, believing that their reputations were at stake and that some might think them delusional. In short, the pilots wanted to keep their “wings.”

Although instances of TLE’s can be traced back much earlier than WW II, it’s only during the last few decades--especially after 1989--that they’ve begun to be taken seriously,. That’s the year when University of Minnesota Physics Professor John R. Winckler made a startling discovery when testing a video camera for a research rocket flight. When the tape was played, it unexpectedly revealed “two giant columns of light towering high above distant thunderstorms in northern Minnesota.” Finally, the centuries-old mystery about mysterious lights above thunderstorms was solved.

Today, although quite enigmatic and elusive, red sprites, and their cousins, blue jets, and elves, are revealing some of their secrets. Even so, it’s a challenge to photograph them. Recently, U.S. astronauts were lucky (as was Professor Winckler in 1989), when a time-lapse video revealed a red sprite rocketing outward into space from a brilliant lightning discharge over Burma and Malaysia (see top image).


First color photo (1994) of a red sprite. (NASA)

So, as far as we know, what is the exact nature of these bizarre phenomena scientists have dubbed “red sprites, blue jets, and elves?** For one thing, it’s known that when red sprites occur, it’s always over thunderstorms, particularly very intense ones, and they can shoot outward, often in clusters, from a starting point as much as 25 miles or more above the tops of thunderstorms. They can reach 50-60 miles into space and penetrate downward into the middle of the stratosphere (15-20 miles high) with jellyfish-like tendrils.

Since red sprites only last a few milliseconds, form at a great altitude, and are usually obscured, they are much more difficult to see or detect than normal lightning. According to NASA scientists, following is the genesis of a “red sprite”:

“a neutrally charged cloud discharges some …. electricity to [the] ground. Normally [a] negative charge is carried from the cloud to the ground, but about one out of every ten times it’s [a] positive charge -- and that leaves the top of the cloud negatively charged. With this one in ten chance, the electric field above the cloud is “just right” to produce the sprite, an electrical discharge 50 miles above the thunderstorm.”

The reddish-orange coloration is caused by “electrons in the mesosphere being accelerated by the sudden electrical change. Their rapid movement produces heat, ionization and red light when the electrons collide with nitrogen molecules,” according to the Stanford University News Service.

“Blue jets” and “elves” are also associated with thunderstorms, but not in the same way as “sprites.” Whereas sprites are directly related to cloud-to-ground lightning strikes and form far above a thundercloud, blue jets (source: University of Albany) “emerge directly from the top of a thundercloud,…..propagate upward in narrow cones of about 15 degrees, fan out, and disappear at heights of about 25-30 miles, with a lifetime of a couple of tenths of a second.”

Although a sprite’s duration is nothing special to write home about, the duration of an elf is even shorter—less than a millisecond. Therefore, unlike sprites, which, on rare occasions can be seen by the naked eye, elves cannot. If one could see an elf, it would probably look like a giant, expanding ring—about 300 miles across--emanating from a point 60-65 miles in altitude and expanding outward. They seem to occur above areas of active cloud-to-ground lightning when an energetic electromagnetic pulse extends up into the ionosphere.

Such is the story of red sprites, blue jets and elves, not to mention the stories of “blue starters, sprite halos, trolls, gnomes, pixies, gigantic jets, tipps, and gamma ray bursts,” all, in one way or another associated with thunderstorms, except for the last two. See diagram below.


Red sprites, blue jets, and elves Courtesy NASA and adapted from Carlos Moralles (AeroVironment and Tom Nelson (FMA). View full size.

*Also, see the actual video (although the sprite is not apparent) at:

** The term “sprite” was first coined in 1994 by Prof. David Sentman of the University of Alaska-Fairbanks, who believed their fleeting nature was reminiscent of the mythical “sprite,” Puck, in Shakespeare’s Midsummer Night’s Dream. The term “blue jet” speaks for itself, and “elves” is an acronym for emission of light and very low frequency perturbations due to electromagnetic pulse sources. Of course, it didn’t hurt that an elf is emblematic of the transient, pixie-like nature of the whole class of these amorphous, luminous phenomena.

By  |  12:00 PM ET, 09/17/2012

Categories:  Latest, Lipman, Science, Thunderstorms

 
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