January 2023 saw a team of researchers, led by Yuuki Wada, make a trailblazing find in Kanazawa, Japan. In doing so, they witnessed a lightning discharge that was unequivocally associated with the occurrence of a terrestrial gamma-ray flash. This trend constitutes the first major step toward a deeper understanding of lightning and its role in producing gamma rays. It is the first time that we were able to relate such a specific discharge to this infrequently observed phenomenon.
The incident came about after a bolt of lightning hit a TV transmission tower. Wada and his collaborators set up an array of sensors around two TV broadcast towers. They were gathering information not just in the visible spectrum, but radio frequency and gamma ray wavelengths. Their results showed that the gamma ray burst started at least 31 microseconds before the lightning strike developed.
The scientists tracked both steady and pulseless electrical activity, and detected a downward-propagating lightning leader. This channel, where air ionizes into electrical conduction, moved in parallel with a launching upward-moving leader that descended from the TV tower. This interaction from the two ruling titans produced a brief but powerful burst of gamma rays. This energetic release occurred over at least 90 ms. A visualization of where this collision occurred based on available data, between 800 and 900 meters above ground level. It happened a few hundred meters within the clouds themselves.
Gamma rays are absorbed almost immediately by the atmosphere. Due to this, they generally cannot fly very far at low elevations where the air is most dense. What Wada’s team ended up seeing was an intriguing phenomenon. Creating extremely high concentration electrical fields, which accelerated the electrons in the air, like a massive natural particle accelerator, even as their leaders met at speeds close to 2,700 kilometers per second. That acceleration caused a gamma ray burst, or GRB. It confirmed, for the first time after decades of research, the connection between thunderstorms and gamma-ray production.
The team’s observations add considerably to our understanding of the mechanisms producing terrestrial gamma-ray flashes and their relationship to lightning activity. Now Wada and his colleagues have recorded an example of such a discharge’s link to gamma-ray emissions. This remarkable advancement paves the way for new atmospheric physics and chemical research that has wide-ranging implications.
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