Research into the causes of lightning strikes, which could lead to better understanding and real-time forecasting of thunderstorms in the future, has been released.
Two studies published in Nature conclude that gamma ray generation from thunderstorms may be more common and take more forms than previously thought.
Artistic view of a Nasa plane flying over gamma ray-glowing clouds in the Caribbean during the July 2023 flight campaign. Image: UiB/Mount Visual.
Type of ionising radiation emissions
The papers detail the discovery of flickering gamma-ray flashes, or FGFs, a type of ionising radiation emissions produced by lightning – and establishes that gamma rays emitted by thunderclouds are much more common, complex, diverse and dynamic than previously thought.
Dr Martin Fullekrug, a reader in the Bath’s Department of Electronic & Electrical Engineering, said: “The precise factors that initiate lightning strikes have until now remained an enigma. The results of this study are a massive step forward in recognising the role of ionising radiation at the very early stages of lightning initiation.
“Over time, and with further research and better, targeted instrumentation, it could help us to improve on early warnings for lightning protection.”
Two different hard radiation phenomena have so far been known to originate from thunderclouds: high intensity bursts known as terrestrial gamma-ray flashes (TGFs) and less intense, but longer-duration gamma-ray glows. The characteristics of these emissions and how they are produced are not fully understood.
FGFs are a third phenomenon that bridges between the two, while at the same time revealing certain distinct characteristics, and may have a role in lightning initiation. Most noteworthy is that FGFs are pulses of gamma-rays which do not coincide with any detectable optical or radio signals.
“We think that FGFs could be the missing link between TGFs and gamma-ray glows, whose absence has been puzzling the atmospheric electricity community for two decades," said lead author, Professor Nikolai Østgaard, of the University of Bergen.
Detection on high-altitude flights
The groundbreaking research is based upon observations taken during a flight campaign entitled ALOFT (Airborne Lightning Observatory for FEGS and TGFs).
A collaboration between Nasa and the University of Bergen, ALOFT was carried out by flying a specially equipped Nasa ER-2 plane from MacDill Air Force Base in Florida, USA, to airspace above thunderclouds over the Gulf of Mexico, Central America and the Caribbean during the summer of 2023.
The payload consisted of lightning detectors, gamma-ray scintillators, and a mixture of passive and/or active microwave sensors. A total of 10 flights were conducted.
Dr Fullekrug helped to plan the mission, organising a workshop in Bath in July 2023. He also helped to interpret the results and in the writing of the research paper.
He said: “Studying lightning initiation is very difficult. Ionising radiation, a crucial part in the creation of lighting, is absorbed in the atmosphere so quickly that observations from the ground or satellites had until now missed the abundance of ionising radiation effects observed here, from an aircraft cruising directly above thunderstorm cloud tops.”
A large team of researchers helped to author the research paper, led by the University of Bergen, Norway and Nasa in the USA.
Published in Nature, Flickering Gamma-Ray Flashes, the Missing Link between Gamma Glows and TGFs (DOI: 10.1038/s41586-024-07893-0), is co-authored by University of Bath academic and lightning expert Dr Martin Fullekrug. The other paper, also published in Nature is titled Highly dynamic gamma-ray emissions are common in tropical thunderclouds (DOI: 10.1038/s41586-024-07936-6).