Many details of how thunderstorms generate terrestrial gamma ray flashes (TGFs) and other forms of high‐energy radiation remain uncertain, including the basic question of where they are produced. We exploit the association of distinct low‐frequency radio emissions with generation of terrestrial gamma ray flashes (TGFs) to directly measure for the first time the TGF source altitude. Analysis of two events reveals source altitudes of 11.8 ± 0.4 km and 11.9 ± 0.9 km. This places the source region in the interior of the thunderstorm between the two main charge layers and implies an intrinsic TGF brightness of approximately 1018 runaway electrons. The electric current in this nontraditional lightning process is found to be strong enough to drive nonlinear effects in the ionosphere, and in one case is comparable to the highest peak current lightning processes on the planet.

We investigated National Lightning Detection Network reports and lightning radio waveforms in a 44 day observation period to analyze the in‐cloud (IC) events producing currents above 200 kA. The results show that there are two distinct classes of IC lightning events with very high peak currents: the well‐known narrow bipolar events, and a previously unreported type that we call energetic in‐cloud pulses (EIPs). Their temporal and spatial context shows that EIPs are generated from existing negative polarity leaders that are propagating usually upward but sometimes downward. The nearly identical characteristics of EIPs and some previously reported terrestrial gamma ray flashes (TGFs) indicate a likely connection between the two, which further suggests the possibility of downward directed TGFs. These very high peak current IC events also suggest the association of EIPs with ionospheric perturbations and optical emissions known as elves.

Radio emissions continue to provide insight into the production of terrestrial gamma ray flashes (TGFs) by thunderstorms, including the critical question of the conditions under which they are generated. We have identified several TGF-associated lightning radio emissions in which the altitudes of in-cloud lightning leader pulses that precede and follow the TGF can be measured. We combine these with high absolute timing accuracy TGF observations from the Fermi satellite to determine the development of the lightning channel before, during, and after the TGF production. All of these TGFs were produced several milliseconds after the leader had initiated and when the leaders reached 1-2 km in length. After the TGFs, the leaders all continued to ascend for several more kilometers with no dramatic change in their characteristics, although they all exhibited high average velocities of 0.8-1.0 × 10 6 m/s. Implications in the context of TGF models are discussed. These results paint the first clear picture of the lightning processes that occur before, during, and after TGF production.

Terrestrial gamma ray flashes (TGFs) are brief bursts of energetic gammy‐ray photons generated during thunderstorms, which have been detected almost exclusively by satellite‐based instruments. Here we present three lines of evidence which includes the three out of three simultaneously observed pairs, the same occurrence contexts, and the consistent estimated occurrence rate, which indicate a direct relationship between a subset of TGFs and a class of energetic radio signal easily detectable by ground‐based sensors. This connection indicates that these gamma ray and radio emissions are two views of the same phenomenon and further enable detection of these TGFs from ground distant radio signals alone. Besides dramatically increasing the detection rate of TGFs, this ground detection approach can identify TGFs in continental and coastal areas that are at latitudes too high for present TGF‐detecting satellites and will provide more insights into the mechanism of TGF production.

Do terrestrial gamma‐ray flashes (TGFs) produce their own radio signatures? To explore this question, we analyze TGF data from the Fermi Gamma‐ray Burst Monitor, independent lightning geolocation data from the National Lightning Detection Network, and low‐frequency (LF) magnetic field waveforms, to determine the relationship between TGF generation and LF waveforms. LF waveforms associated with six TGFs are found to contain a clear and isolated slow pulse (~80‐μs duration) within a sequence of multiple fast pulses (<10‐μs risetime). We find that the slow LF pulse is produced simultaneously with the observed gamma rays, with an uncertainty as small as 7 μs. Simultaneity implies a consistent TGF source altitude range of approximately 10–15 km, which is consistent with previous estimates. These findings provide important evidence that the slow LF pulse, when observed, is associated with TGF production and perhaps produced by the electron acceleration itself.