What causes lightning strikes? Researchers find the missing link
New research into what causes lightning strikes could lead to a better understanding and real-time forecasting of thunderstorms in the future.
Groundbreaking new research has discovered a new type of radiation present in thunderclouds; flickering gamma-ray flashes (FGFs), a type of ionising radiation emission produced by lightning.
FGFs may be more common, complex, diverse and dynamic in thunderclouds than previously thought and the findings could help real-time forecasting of thunderstorms.
The missing link
Two different hard radiation phenomena are known to originate from thunderclouds: terrestrial gamma-ray flashes (TGFs), which are high intensity bursts; and gamma-ray glows, which are less intense, but longer-duration. However, the characteristics of these emissions and how they are produced is not fully understood.
Researchers have discovered a third phenomenon that bridges the gap between the two: FGFs. These are pulses of gamma-rays which do not coincide with any detectable optical or radio signals, with certain distinct characteristics, and may have a role in lightning initiation.
“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", says lead author, Professor Nikolai Østgaard, of the University of Bergen.
Flying into the storm
The discovery is the result of observations taken during a flight campaign called ALOFT (Airborne Lightning Observatory for FEGS and TGFs), a collaboration between NASA and the University of Bergen.
A NASA-equipped ER-2 plane was flown in airspace above thunderclouds over the Gulf of Mexico, Central America and the Caribbean during the summer of 2023. It carried lightning detectors, gamma-ray scintillators, and a mixture of passive and/or active microwave sensors. A total of 10 flights took place.
“The precise factors that initiate lightning strikes have until now remained an enigma,” says Dr Martin Fullekrug, a Reader in the University of Bath’s Department of Electronic & Electrical Engineering who helped plan the mission and interpret the results.
“Studying lightning initiation is very difficult,” he continues. “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.”
Fullekrug says this study is a “massive step forward in recognising the role of ionising radiation at the very early stages of lightning initiation.” He believes that over time, and with further research and better, targeted instrumentation, it may be possible to improve early warnings for lightning protection.
News references
Østgaard, N., Mezentsev, A., Marisaldi, M. et al. (2024) Flickering Gamma-Ray Flashes, the Missing Link between Gamma Glows and TGFs, Nature.
Marisaldi, M., Østgaard, N., Mezentsev, A. et al. (2024) Highly dynamic gamma-ray emissions are common in tropical thunderclouds, Nature.