Thu, Jul 08, 2004 - Page 2 News List

Satellite records elusive sprites and elves

WORLD FIRST Taiwan's satellite has been doing things other than record typhoon damage -- like capturing the first images from space of upper-atmospheric lightning


Images of numerous Transient Luminous Events (TLE), which occur only above clouds, were recorded for the first time by ROCSAT-2, the nation's second satellite.

Images of "sprites," "sprite halos" and "elves" were observed on Sunday by the satellite's onboard "Imager of Sprites: Upper Atmospheric Lightning" (ISUAL) apparatus, which studies phenomena above thunderstorms, the National Space Program Office said.

At a press conference held yesterday in Taipei, images of phenomena occurring at an altitude of 90km to 100km were displayed to the reporters.

The office said that ISUAL recorded Sunday's image when flying over Mindanao in the Philippines. The images showed a large bright patch resulting from cloud-to-ground lightning. Above the patch was a "filamentary sprite," topped by a pancake-shaped sprite halo.

Seven hours after the images were collected, another sprite was recorded, this time shooting over a thunderstorm over the border of Sudan and Chad.

On Monday, ISUAL recorded two more elves, which occurred over Mindanao. On Tuesday, two elves and a sprite were recorded by ISUAL.

"Upper atmospheric lighting occurs more frequently than we thought," said Chang Yeou-shin (張友信), an associate researcher in charge of the ISUAL project.

Alfred Chen (陳炳志), a physicist at National Cheng Kung University who is also participating in the project, said the properties of TLEs have been studied for only a decade.

"More observation of these phenomena from space might help clarify global circuit mechanisms," Chen said.

Chen said that starting next week ISUAL would target areas above other regions, including the US, to learn more about the global distribution of the phenomena, which are rarely visible from ground-based observation stations.

ROCSAT-2 is the first satellite to observe TLEs from space. On June 6, after ROCSAT-2 was tested and sent to mission orbit at 891km above Earth's surface, ISUAL was switched on.

As ISUAL is the first space-based instrument dedicated to the study of TLEs above thunderstorms, technical adjustments have to be made frequently to capture the elusive flashes.

Scientists at the ISUAL project hope to record more TLEs and complete a global distribution map in the next five years.

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