A research team led by Kyoto University, in collaboration with a network of citizen supporters, collected data from gamma-ray glows—the phenomenon in which high-energy photons from thunderstorms hit the ground—that could illuminate the origins of lightning.
In fact, thunder is caused by lightning. As Mark Twain wrote in 1908, “Thunder is good, thunder is striking; but lightning is what works.” But what causes lightning still remains a mystery.
In the collaborative Thundercloud project, recording devices called “Kogamo”—short for compact gamma-ray monitor—are installed at each supporter’s home in a multi-point monitoring network in Kanazawa, near the Sea of Japan coast. In addition to environmental high-energy radiation data, Kogamo records and transmits real-time temperature, humidity, and light data to a web server.
“Gamma rays indicate that lightning has a strong electric field where electrons can be accelerated to relativistic speeds,” says project leader Teruwaki Enoto of Kyoto’s Department of Physics. Their paper, “Citizen Science Observations of Gamma-Ray Glow Associated with Lightning Initiation,” was published on July 3, 2023. Geophysical Research Letters.
Combining radio and radar observations, a lightning bulb lit up in the researchers’ heads, confirming the origin of lightning discharges in the field of accelerated electrons.
“Furthermore, we are trying to check whether cosmic rays interact with this strong electric field to trigger lightning,” adds Miwa Tsurumi, lead student in the research team.
The image of bolts fired by Zeus may not be so far-fetched: high-energy particles from deep space — cosmic rays — collide with atmospheric atoms, creating an air shower of massive amounts of electrons and other particles. Thunderstorms accelerate and accelerate high-energy electrons, which emit gamma rays as a result of successive collisions.
Enotto’s team suggests that a series of these air shower processes may be related to the activity of lightning discharges.
Although phenomena such as the high-energy particle nature of thunderstorms are not easy to observe, partly due to rapid absorption in the atmosphere, gamma rays travel farther than electrons, and as a result, are characteristic of winter thunderstorms along the coast near Kanazawa. It was this glow that inspired the team’s hypothesis about lightning impulses.
“The Kogamo system alerts Twitter whenever the server detects a gamma-ray glow, so citizen supporters are helpful: the bigger the network of detectors, the bigger the collective power and the fulfillment of citizen science,” concludes Yuko Ikatai of Kanazawa University.
M. Tsurumi et al, Citizen Science Observation of a Gamma-Ray Glow Associated with the Initiation of a Lightning Flash, Geophysical Research Letters (2023). DOI: 10.1029/2023GL103612