Bright flashes of high-energy radiation (gamma rays) have been seen along with some lightning, usually beamed upwards into space. These “terrestrial gamma-ray flashes” (TGFs) are so bright that someone caught in the middle of one could get a hazardous radiation dose, but that region is generally in the middle of a thundercloud where airplanes seldom go. Smith et al.  report two very similar – but unusual – lightning flashes that went upward into the clouds from the top of a tower in Japan in the winter. One produced an enormously bright downward TGF that paralyzed detectors on the ground while the other produced none at all. The authors present evidence that the TGF occurred in the first case because the electric field was higher than it was during the lightning that didn’t produce radiation.
Citation: Smith, D. M., Bowers, G., Kamogawa, M., Wang, D., Ushio, T., Ortberg, J., et al. . Characterizing upward lightning with and without a terrestrial gamma ray flash. Journal of Geophysical Research: Atmospheres, 123. https://doi.org/10.1029/2018JD029105
—Minghua Zhang, Editor-in-Chief, JGR: Atmospheres