Pulses of gamma rays and X-rays emitted from the region above thunderstorms, and detectable only from space. The mechanism that produces the necessary exceptionally high energies is currently unknown, although it is suggested that cosmic rays may be involved. Energetic cosmic rays that encounter a powerful electrical field, such as that generated by a positive cloud-to-ground discharge, could produce a shower of secondary electrons (and gamma rays) directed upwards. Such electrons may account for the blue tendrils seen in the lower part of sprites. The gamma-ray events are also known as terrestrial gamma flashes (TGF).
Subjects: Meteorology and Climatology.