High‐Energy Radiation From Natural Lightning Observed in Coincidence With a VHF Broadband Interferometer

This work presents the first simultaneous X‐ray measurements from natural lightning in coincidence with a very high frequency (VHF) broadband interferometer. During an observational campaign in north‐central Colombia, five intense X‐ray bursts were detected from negative stepped leaders and two X‐ray emissions from a dart leader. Thanks to the high angular and time resolution of the interferometer, it was possible to locate the origin of high‐energy radiation during the lightning leader propagation. We study the correlation with VHF pulses and the two‐dimensional speed of the leader channels. A strong temporal correspondence has been observed between the high‐energy emissions and the most intense VHF pulses, which suggests the runaway electrons as a shared mechanism. The observations show that an X‐ray burst can have multiple high‐energy sources belonging to different leader branches, that can be several hundreds of meters apart. Therefore, from a spatial point of view, not a unique origin has to be searched, but an extensive origin of the X‐ray burst should be considered. We hypothesize similar conclusions in particular for downward TGFs and maybe for TGFs in general. Plain Language Summary It is well known that lightning can produce high‐energy emissions. In particular, a phenomenon has been observed from space called “Terrestrial Gamma‐ray Flash (TGF),” which consists of an intense burst of gamma radiation that can be produced during thunderstorms. This phenomenon has met with considerable interest in the scientific community and its mechanism is still not fully understood. Beyond space observations, in order to investigate TGFs, ground‐based measurements can provide complementary information to better understand under which conditions high‐energy emissions are produced. In this research context, this work presents some accurate ground‐based observations of the location of high‐energy emissions during natural cloud‐to‐ground lightning. Key Points X‐ray bursts were detected simultaneously with a lightning imaging obtained with a very high frequency (VHF) broadband interferometer A strong temporal correspondence has been observed between the high‐energy radiation and the most intense VHF pulses Measurements suggest an extensive spatial origin of Terrestrial Gamma‐ray Flashes (TGFs) due to a multiplicity of high‐energy sources