Media release

From: Springer Nature

Striking discoveries about thunderstorm gamma rays

Gamma ray generation from thunderstorms may be more common and take more forms than previously thought, according to two studies published in Nature. The papers offer new insights into how the various types of emission are interrelated, with clues as to their origin.

Previous research has reported two types of gamma-ray emissions by thunderclouds — high intensity bursts known as terrestrial gamma-ray flashes (TGFs), and moderate intensity longer-duration gamma-ray glows. However, characteristics of these emissions and how they are produced are not fully understood. Using data collected by aircraft during ten flights in July 2023, researchers investigated gamma-ray emissions produced during ocean and coastal thunderstorms over the Caribbean and Central America.

Nikolai Østgaard and colleagues identified a different type of gamma-ray emission called flickering gamma-ray flashes (FGFs), which consist of pulses with a longer duration than those of TGFs (FGFs lasted up to 250 milliseconds, compared to up to 100 microseconds for TGFs). In total, 24 FGFs were observed while passing over thunderclouds emitting gamma-ray glows during five of the ten flights; 17 of these FGFs were followed by lightning activity. The authors suggest that FGFs may start as gamma-ray glows before increasing suddenly in intensity and becoming a sequence of pulses, and may also have a role in some lightning initiation. As FGFs share similar features to gamma-ray glows and TGFs, the authors propose that FGFs could provide evidence of links between the two phenomena.

In an accompanying paper, Martino Marisaldi and colleagues investigated the properties of gamma-ray glows detected by the aircraft. These included a thundercloud system occupying an area of more than 9,000 square kilometres that was observed glowing for at least three hours. The authors found that emissions were common and not uniform over a glowing region. More than 500 individual gamma-ray glows were observed over the entire study area during nine of the ten flights, with each glow each lasting between one and 10 seconds. These findings contradict those of previous studies, which reported that gamma-ray glows last up to hundreds of seconds and are emitted uniformly over areas of up to 20 kilometres.

Together, the findings improve our understanding of gamma-ray emissions from thunderclouds, suggesting a causal link between the glows and the flashes, and a possible role for these emissions in the subsequent initiation of lightning.