It has been recently discovered that x-rays are emitted by lightning. Aircraft and ground-based measurements at the International Center for Lightning Research and Testing (ICLRT) are being used to investigate these emissions. In particular, rocket-triggered lightning is measured using the Thunderstorm Energetic Radiation Array (TERA).
The Thunderstorm Energetic Radiation Array (TERA) is an experiment designed to measure energetic radiation (x-rays and gamma rays) from thunderclouds and lightning. The Thunderstorm Energetic Radiation Array is also part of an experiment called the MSE (Multiple Station Experiment), which is used to study the electric and magnetic fields from rocket-triggered lightning and nearby natural lightning. Besides the x-ray detectors, the MSE/TERA stations are also equipped with instrumentation to measure electric fields and their derivatives as well as magnetic fields using flat plate antennas and loop antennas. The flat plate antennas are used to measure the vertical component of the electric field and its derivative for nearby storms. Due to some charge movement during the leader formation process, a process which is still not yet fully understood, electromagnetic pulses are produced; these pulses are picked up by the sensitive antennas. After accounting for the propagation delay through the fiber optics and the electronics, the radiation source of these pulses is located using TOA techniques that are based on the arrival times of the dE/dt pulses. The 24 Thunderstorm Energetic Radiation Array instruments are distributed at different stations across the ~1 km2 ICLRT site, centered on the rocket launch tower. Monte Carlo simulations are compared with data form a Thunderstorm Energetic Radiation Array to infer properties of the x-ray emissions from lightning as well as properties of the lightning leaders.