Ground-level observation of terrestrial gamma-ray bursts initiated by lightning

Terrestrial gamma-ray flashes are intense, brief bursts of gamma rays originating in the Earth's atmosphere. Most of the TGFs have been observed by low-earth orbit satellites, while only a few TGFs have been detected at ground level. By using a NaI(Tl) detector, two bursts of gamma rays were recorded at ground level for the first time in China, when the return strokes of a nearby negative cloud-to-ground lightning flash occurred. The first gamma-ray burst had a duration of 563 μs and the second one had a duration of 353 μs. The time interval of the two bursts was 76.2ms, coincident with the time interval of return strokes as revealed by the synchronous electric field signals.