Scientists find gamma-ray surprise

Because terrestrial gamma-ray flashes seem to only occur in the vicinity of large-scale thunderstorms, scientists believe the two phenomena are somehow related

May 27, 1999
Web posted at: 11:30 AM EDT

While monitoring bursts of gamma-ray energy coming toward Earth from the depths of space, NASA scientists have accidentally discovered a different phenomenon: gamma-ray energy bursts flashing away from Earth that are associated with severe storm systems.

The finding has baffled researchers, who are working to find a reason behind the phenomenon.

Terrestrial gamma-ray flashes (or TGFs) are short blasts of gamma-ray energy associated with thunderstorms. They only last a few milliseconds and can only be detected by satellites orbiting the Earth.

"We came across these (TGFs) totally by accident," said Jerry Fishman, principal investigator on the Burst and Transient Source Experiment (BATSE) aboard the Compton Gamma-Ray Observatory. "We designed BATSE to collect gamma-rays from the deepest recesses of space, which it does very well. What we didn't know it would do was also collect gamma rays released from severe weather systems on Earth."

In 1991 NASA launched the Compton Gamma Ray Observatory carrying BATSE. BATSE was designed specifically for the study of the enigmatic gamma ray bursters but accidentally discovered the TGFs shortly after launch of the satellite.

The weather images produced by BATSE revealed that each time a TGF was detected, a massive thunderstorm was in the same vicinity. Because TGFs seem to only occur in the vicinity of large-scale thunderstorms, scientists believe the two phenomena are somehow related.

Now, after eight years of observations, the BATSE team has recorded approximately 70 TGFs. However, because BATSE observes in all directions, portions of the Earth are inevitably in its field of view. Thus, the scientists believe that many more TGFs may be occurring in locations that are invisible to the observatory.

Earlier this year, researchers discovered sprites and jets — huge flashes of red and blue light associated with upward-moving lightning. Many scientists believe that these phenomena and TGFs are probably somehow related, however, according to NASA, no TGF has ever been directly observed in conjunction with an upward moving sprite.

The scientists hope to confer on the subject at the upcoming International Conference on Atmospheric Electricity in Guntersville, Ala., June 7-11.

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