Terrestrial Gamma-Ray Flashes Can Be Detected With Radio Measurements of Energetic In-Cloud Pulses During Thunderstorms.

Many of the details of how terrestrial gamma-ray flashes (TGFs) are produced, including their association with upward-propagating in-cloud lightning leader channels, remain poorly understood. Measurements of the low-frequency radio emissions associated with TGF production continue to provide unique views and key insights into the electrodynamics of this process. Here we report further details on the connection between energetic in-cloud pulses (EIPs) and TGFs. With coordinated measurements from both ground-based radio sensors and space-based gamma-ray detectors on the Fermi and Reuven Ramaty High Energy Solar Spectroscopic Imager spacecraft, we find that all ten +EIPs that occurred within the searched space-and-time window are associated with simultaneous TGFs, including two new TGFs that were not previously identified by the gamma-ray measurements alone. The results in this study not only solidify the tight connection between +EIPs and TGFs, but also demonstrate the practicability of detecting a subpopulation of TGFs with ground-based radio sensors alone. Plain Language Summary Terrestrial gamma-ray flashes (TGFs) are kinds of high-energy emissions produced during thunderstorms and are almost exclusively detected with spacecraft-based gamma-ray detectors. Because of the strong atmospheric gamma-ray attenuation from the low-altitude atmosphere and the geometry-driven short horizontal detection range, the ground detection of TGFs with gamma-ray detectors is challenging. Recently a class of distinct radio emissions during thunderstorms, called energetic in-cloud pulses (EIPs), was found to be closely linked to the production of some TGFs. In this study, we present several additional lines of strong evidence that strengthen the connection between a subpopulation of TGFs and EIPs. Importantly, by identifying EIPs from radio signals, we found two new TGFs that were previously unreported from space-based detection. This demonstrates that some TGFs can be detected from the radio measurements alone when the spacecraft-based detectors are unavailable. [ABSTRACT FROM AUTHOR]