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Positron Annihilation in Thunderstorms

The positron, the antiparticle of the electron, was discovered in 1932 by David Anderson when a shower of cosmic rays hit his cloud chamber [1]. Positrons are fundamental particles, which do not appear in our daily life except for human-made situations in particle accelerators or position emission tomography. On the Earth, known natural production sites of positrons are limited only at cosmic-ray air showers or through beta-plus decays of rare isotope potassium-40. However, we recently spotted lightning that generated positrons in the atmosphere [2]. The new aspect of lightning is opening a new interdisciplinary field of high-energy atmospheric physics [3]. In this article, I introduce new scientific perspectives of high-energy phenomena in lightning and thunderclouds; in particular, results from our observation campaign of winter thunderstorms in Japan as illustrated in Figure 1.