Long radiation bursts generated by thunderstorms don't always culminate in lightning, although the reasons why are not fully understood. Tatsuo Torii at the Japan Atomic Energy Agency in Tokyo and his group tracked one such burst under a thunder cloud at the tip of Japan's Tsuruga Peninsula. They observed a moving, hemispherical source of radiation, probably caused by an intense electric field inside the thunder cloud, with a radius of 700 metres and reaching to just 300 metres above sea level.
The cloud emitted radiation — but no lightning — for several minutes as it moved southwards. This was probably because the radiation hemisphere was so close to the ground, the team suggests.
Geophys. Res. Lett. http://dx.doi.org/10.1029/2011GL049731 (2011)
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Thunder but no lightning. Nature 480, 8 (2011). https://doi.org/10.1038/480008a