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Sprites from Space

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gigantic blue jet

Gigantic blue jet of 22 July 2002 rose to 90 km in half a second and flashed for mere milliseconds.

National Cheng Kung University
Red sprites, blue jets, gnomes, trolls and the other electrical events in the middle atmosphere are all called TLEs by the people who research them. That's for Transient Luminous Events. Every year in early December, the small community of TLE researchers convenes at the Fall Meeting of the American Geophysical Union.

The first of these gatherings was sensational as hundreds of scientists crowded in large rooms to gawk and gasp at videos of red sprites and blue jets. The idea of electrical phenomena hidden high above thunderstorms captivated everyone. That was in 1994. The 2001 session had an attendance of a few dozen, and those present marked the death of John Winckler, who was the first to capture a sprite in 1989.

Since then the crowds have begun to rebound, and the 2003 session, on December 11, presented new observations from the ill-fated space shuttle Columbia, which had been destroyed 10 months earlier. After briefly telling what the experiment had meant historically, sprite expert David Sentman led the group in a minute of silence to honor shuttle scientist Ilan Ramon, who led the experiment, and the six others who died with him. "We are them," he said, "and they are us."

Space shuttle observations in 1989 laid a foundation for TLE science, but none were done in the years since until researchers got the chance to piggyback upon a shuttle experiment in 2003. During daylit parts of Columbia's orbit, the Mediterranean Israeli Dust Experiment (MEIDEX) observed dust in the atmosphere with a pod of cameras in the shuttle's open cargo bay. At night the shuttle was rotated to face large thunderstorm centers and astronauts aimed a video camera at them. Forecasting the storms and rotating the spacecraft was carefully coordinated just hours in advance using near-real-time data on the Internet.

When the first recordings were lucky enough to capture a sprite image the researchers were pleased and the astronauts were engaged, said Yoav Yair of Israel's Open University. The great majority of the data, including 392 minutes of videotape, was downloaded from the shuttle and saved. Another usable tape survived the crash and was found on the ground. Astronaut Ramon, once an Israeli fighter pilot, said in an email that the thrill of the sprite hunt was much like that of air combat.

While only 20 percent of the MEIDEX data had been checked, Yair said it shows that sprites and elves may be more common than we thought, especially over the open ocean. In one pass over the Congo, meteors were seen entering the atmosphere moments before sprite displays. This observation may confirm a long-standing suspicion that meteors play a role in some TLEs. Yair pointed out that the meteors were part of the Quadrantid shower.

Other talks at the session reported advances. Walter Lyons, who runs the sprite observation station in northern Colorado, has been putting the data from the breakthrough 2000 campaign into a database. While reviewing the tapes he has found many more events, and his growing database is confirming that sprites arise not just from positive cloud-to-ground (CG) lightning, but from positive CG strokes with a large change in charge moment.

A team from Taiwan found a new type of TLE last year that they call "gigantic blue jets." Han-Tzong Su said that this year's campaign spent 80 nights looking for more but came up empty. His team's research into the 2002 batch, however, showed that they are apparently NOT related to positive CG lightning. Rather, he suspects that they arise from negative cloud-to-ionosphere discharges, making them a very different kind of creature.

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