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Dark lightning — gamma-rays (pink in this simulated image) that result from waves of electrons (one shown, yellow) colliding with atoms in the air — may sporadically strike airplanes and briefly expose passengers to radiation, new research suggests.
NASA Goddard Space Flight Center, J. Dwyer/Florida Institute of Technology
CHICAGO — More than electricity can illuminate a thundercloud.
Brilliant bursts of gamma radiation, known as dark lightning or terrestrial gamma-ray flashes, also explode in lightning storms. And on rare occasions, those powerful blasts — the most energetic radiation to naturally arise on Earth — might even strike a passing airplane, researchers reported December 13 at the American Geophysical Union meeting. The zap could briefly expose passengers to unsafe levels of radiation.
First reported in 1994, dark lightning is estimated to flash around the world about a thousand times each day. But scientists have only a hazy understanding of how it initiates. They generally agree dark lightning is sparked by the electric fields generated by thunderstorms and lightning bolts. These fields can spur electrons to velocities approaching the speed of light, amassing breakneck electron avalanches. When the streaming particles smash into airborne atoms, gamma radiation is unleashed.
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Dark lightning often occurs around 10 to 15 kilometers high in the sky, altitudes frequented by airlines. The new analysis combines dark lightning observations and airline routes to suggest that dark lightning might strike near a plane around once every 1 to 4 years, atmospheric scientist Mélody Pallu said at the meeting. However, that’s probably “an upper limit of the real probability,” or even 10 times the actual rate, she said, largely because the calculations didn’t factor in pilots’ avoidance of thunderstorms.
Previous computer simulations have revealed that passengers flying within 200 meters of a strong terrestrial gamma-ray flash’s initiation point may become exposed to radiation doses exceeding 0.3 sieverts, said Pallu, now at the Astroparticle and Cosmology Laboratory in Paris. Such levels would surpass the occupational safety level of 0.02 sieverts per year put forth by the International Commission on Radiological Protection.
Though somewhat nebulous, the findings make one thing clear: Further investigations are needed to figure out how dark lightning impacts passengers flying through the sky.
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M. Pallu. Radiation risk assessment associated with TGFs for aircraft passengers: estimations of the probability for a commercial flight to be hit by a TGF. American Geophysical Union meeting, Chicago, December 13, 2022.
M. Pallu et al. Estimation of radiation doses delivered by terrestrial gamma ray flashes within leader-based production models. Journal of Geophysical Research: Atmospheres. Vol. 126, April 27, 2021, e2020JD033907. doi: 10.1029/2020JD033907.
M.S. Briggs et al. Terrestrial gamma-ray flashes in the Fermi era: Improved observations and analysis methods. Journal of Geophysical Research: Space Physics. Vol. 118, June 2013, p. 3805. doi: 10.1002/jgra.50205.
G.J. Fishman et al. Discovery of intense gamma-ray flashes of atmospheric origin. Science. Vol. 264, May 27, 1994, p. 1313. doi: 10.1126/science.264.5163.1313.
U.S. Department of Health and Human Services: Radiation Emergency Medical Management – International Commission on Radiological Protection (ICRP) Guidance for Occupational Exposure
Nikk Ogasa is a staff writer who focuses on the physical sciences for Science News. He has a master’s degree in geology from McGill University, and a master’s degree in science communication from the University of California, Santa Cruz.
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