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Researchers make map of odd lightning phenomena

Three years of observation of atmospheric lightning phenomena — a temporary colorful lightning appearing high in the sky during thunderstorms — recently allowed a research team at National Cheng Kung University’s Department of Physics the be first in the world to present a detailed global map of the events.

In a press release yesterday, the department’s Imager of Sprite and Upper Atmosphere Lightning (ISUAL) research team said that images taken over the past three years by the satellite FORMOSAT-2 showed that 80 percent of the luminous phenomena the team recorded were “elves,” or red bursts of light in the shape of donuts in the sky caused by lightning.

The other 20 percent of the luminous events recorded by the team were made up of “sprites” — a bell-shaped flash of light appearing about 50km to 90km in the air during thunderstorms — and two other types of lightning: “halos” and “gigantic jets,” the release said.

Hsu Ruey-rong (許瑞榮), a professor of physics from the department who was responsible for the research, said that images taken by the satellite had helped the team analyze the locations where “sprites” and “elves” were more likely to be found.

The team found that “elves” usually appeared above the sea, such as the Caribbean Sea, the South China Sea, east Indian Ocean, and the central, west and southwestern Pacific Ocean, while “sprites” tended to show up above land such as central Africa, Hsu said.

Su Han-tzong (蘇漢宗), another professor of physics at the department, said the research team also found that warm seawater — above 26°C — might contribute to “elves.”

“A warm ocean surface can provide the heat source needed to drive intense oceanic lightning with very high peak currents, which usually generate elves in the ionosphere,” Alfred Chen (陳炳志), a professor of astronomy at the school, said in an interview with the New Scientist.

“Elves could have an important global effect on the lower ionosphere and the total electron content,” said Chen.

“Elf hotspots may increase the electron density of the ionosphere by 5 percent or more, which could interfere with ground and space communication as well as navigation systems,” he said.

The university organized the nation’s first “sprite” research team in 1998 and has cooperated with National Central University, National Chiao Tung University, the University of California, Berkeley, and Japan’s Tohoku University, in its research into atmospheric lightning phenomena over the past decade.

The research results of the ISUAL team — which consists of Hsu, Su, Chen and other researchers — was recently publicized in the Journal of Geophysical Research.

ADDITIONAL REPORTING BY CNA
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