Brian Dunbar Headquarters, Washington, D.C. May 27, 1994 (Phone: 202/358-1547) RELEASE: 94-86 UNUSUAL HIGH ENERGY FLASHES SEEN IN EARTH'S ATMOSPHERE Scientists at NASA's Marshall Space Flight Center in Huntsville, Ala., have discovered unusual gamma-ray flashes in the upper atmosphere high above thunderstorms. These high energy bursts have never before been seen in the Earth's atmosphere or surrounding space, according to Dr. Gerald Fishman of Marshall's Space Science Laboratory. These flashes were detected by the Burst and Transient Source Experiment (BATSE), a Marshall instrument 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 observations were published in this week's issue of Science, an international scientific journal. "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 from the Space Shuttle Atlantis. "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. In order to detect gamma rays with space-borne detectors, they must be produced at altitudes above 100,000 feet. This is considerably higher than normal weather processes, according to Fishman. The observations have been confirmed by other instruments on the observatory. The BATSE detectors on the observatory were originally designed for sensitive observations of celestial objects in wavelength regions unobservable from the ground. -more- -2- "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. -end-