"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.