A terrestrial gamma-ray flash recorded at the Lightning Observatory in Gainesville, Florida

• TGF was associated with an intense negative cloud-to-ground flash.
• TGF occurred 202μs after the return-stroke onset.
• TGF lasted for 16μs with photon energies ranging from 95 keV to 13 MeV.

A terrestrial gamma-ray flash (TGF) observed at ground level is presented. It was recorded at the Lightning Observatory in Gainesville, Florida, on June 13, 2014. Ground-based observations of TGFs are very rare. To date, only two positively identified ones are found in the literature. Our TGF was associated with a single-stroke negative cloud-to-ground discharge. It had a duration of 16μs and consisted of 6 pulses, two of which exceeded the upper measurement limit of 5.7 MeV. The pulses apparently corresponded to individual photons, which is a characteristic feature of TGFs. The TGF began 191μs after the return-stroke electric field peak. The stepped leader duration was as short as 3.9 ms. There was essentially no energetic radiation detected during the leader process. The NLDN-reported return-stroke peak current was as high as 224 kA. The characteristics and occurrence context of the LOG-recorded TGF are compared to those of the two similar events found in the literature. In all three cases there was evidence of a channel carrying appreciable current to ground at the time of TGF, and the associated (preceding or concurrent) cloud-to-ground discharge processes were unusually intense.