Tuesday, May 13, 2014

Origin of Mysterious 'Sprites' Revealed

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By Tanya Lewis

     Red electrical flashes that mysteriously hover above some thunderstorms have long puzzled scientists, but now, new research reveals how these alien-like atmospheric sprites form.

Sprites form at irregularities in the plasma, or charged particles of gas, in the ionosphere, the layer just above the dense lower atmosphere, about 37 to 56 miles above the Earth's surface, a study found. Since disturbances in the ionosphere can affect radio communication, sprites could be useful for sensing such disturbances remotely, researchers say.

"We would like to know how sprites are initiated and how they develop," Victor Pasko, an electrical engineer at Penn State and author of the study published May 7 in the journal Nature Communications, said in a statement.

Sprites are large electrical discharges that occur above thunderstorms. They resemble reddish-orange jellyfish with bluish tentacles streaming down.

But while sprites require thunderstorms, not all thunderstorms produce sprites. Recent studies suggested that ionosphere irregularities were required for these ghostly flashes to occur, but evidence for them was lacking.

In the study, Pasko and his colleagues studied high-speed video of sprites, and developed a model for how the strange lightning evolves and disappears. They used the model to try to recreate sprite-forming conditions.

Analysis of the videos showed that streamers snake downward from the sprites much more quickly than they spread horizontally, suggesting plasma irregularities were driving the streamer spread. . . .

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