Compton Discovers Unusual High Energy Flashes In The Atmosphere

Scientists at NASA's Marshall Space Flight Center have discovered unusual gamma-ray flashes in the upper atmosphere high above thunderstorms. These high-energy bursts have never been seen before in the Earth's atmosphere or surrounding space, according to Dr. Gerald Fishman of Marshall's Space Science Laboratory. They have now been detected by the Burst and Transient Source Experiment (BATSE), aboard NASA's orbiting Compton Gamma Ray Observatory. "It is suspected that these flashes come from a rare type of powerful electrical discharge, similar to lightning, above large thunderstorm regions," Fishman said. "The flashes are very brief, lasting only a few thousandths of a second, although some of them consist of multiple pulses." They are seen very infrequently: only about twenty have been seen since the observatory was launched in April 1991.

"We saw our first flash of this type the first week that the detectors were turned on. We didn't know what to make of it," said Fishman. Gamma rays must be produced at altitudes above 100,000 feet to be detected with the spaceborne instrument. This is considerably higher than normal weather processes. The observations have been confirmed by other instruments on the observatory. The BATSE detectors were originally designed for sensitive observations of celestial objects in wavelength regions unobservable from the ground. "The gamma-ray observations from the Earth's atmosphere come as a complete surprise to us. Atmospheric scientists are also surprised," said Fishman. "For many years, aircraft pilots have reported upward-going lightning in clear air over thunderstorms. But these reports were either never taken seriously or were never studied in a scientific manner," he said.

In recent years, there have been video observations of electrical discharges above thunderstorms taken from the Space Shuttle and from research aircraft. The new gamma-ray flash observations may be related to these optical observations, Fishman said. "It is becoming apparent that the upper atmosphere is much more electrically active than we ever suspected," he concluded.