Thunderstorms churn up a ‘boiling pot’ of high-energy gamma rays
Storms, in all their fury, are not merely a dramatic weather spectacle. They are also giant, turbulent engines, churning out high-energy gamma rays as their electrified clouds roil with lightning. And these gamma rays can, at times, shoot out to unexpected heights, creating a vast, invisible sky-high gamma-ray fountain. These recent findings about thunderstorms are giving scientists a fresh look at gamma-ray sources and the ways in which our planet’s own natural processes can generate these exotic rays.
A pair of recent papers — one in *Nature* and the other in *Physical Review Letters* — delved into the puzzling emissions coming from thunderstorms. Using satellites designed to observe the sky in search of gamma rays, scientists have identified a phenomenon in Earth’s upper atmosphere, revealing that storms are an important and underappreciated source of these high-energy photons.
The Electric Energy Behind Gamma Rays
For a decade, scientists had noted gamma-ray bursts originating from Earth’s atmosphere. The initial theory revolved around high-altitude sprites, electrical discharges that occur above active thunderstorms, sparking bursts of gamma rays as a result of lightning’s high energy. But these sprites only occur above strong thunderstorms. Meanwhile, numerous lower-altitude storms, those that weren’t known to produce sprites, also emitted gamma rays. The new studies offer a deeper look at this previously unexplainable mystery.
A group from the University of Kyoto, Japan, used observations from the Fermi Gamma-ray Space Telescope to identify the origin of these low-altitude bursts of gamma rays. They concluded that, while these bursts originate from thunderstorms, the high energy in lightning isn’t responsible for the rays. Instead, the key lies in the thunderstorm’s electrical fields.
The team, led by Yasuyuki Tanaka, suggests that these low-altitude gamma-ray emissions arise from electron-positron pair production — an extremely rare event — within the cloud itself. This production happens as energized electrons, generated within the thunderstorm, interact with gamma-ray photons. When this happens, the photons’ energy gets split between a pair of particles — an electron and a positron, its antiparticle.
“It’s not a one-step process,” says Tanaka, noting that the high-energy electrons also produce more high-energy photons that can then initiate more particle pairs. “It’s a complicated mechanism that we think takes place inside thunderclouds. It’s kind of a boiling pot.” And it’s in that pot that these unexpected high-energy photons are created and eventually sent out, visible only to those sensitive to gamma rays, like space-based telescopes.
These high-energy gamma rays aren’t just confined to the atmosphere. They also interact with Earth’s magnetic field, sometimes creating what appears to be a huge sky-high gamma-ray fountain. The paper by Tanaka’s team in *Nature* observed one such “fountain,” which ascended at an unexpected pace of 48 kilometers (about 30 miles) in just a few minutes.
Cosmic Mysteries and a Stormy Source
The existence of this “fountain” further points to a connection between gamma-ray bursts and terrestrial weather events. It is believed that Earth’s own magnetic field carries these particles across vast distances, eventually funneling them into the atmosphere’s top layer, where they cascade and radiate as visible light — sometimes, producing visual phenomena such as sprites and blue jets. The implications for Earth’s overall energy balance and global atmospheric physics are intriguing.
In the realm of gamma-ray physics, Earth is more than a quiet spectator — it’s an active player in the cosmic dance of high-energy particles. By observing the skies, we are witnessing our own planet generating particles that might shed light on more profound mysteries, even revealing unexpected sources for high-energy cosmic events, including supernova explosions. Our own stormy weather turns out to be not only a captivating meteorological show, but also a source of extraordinary, albeit hidden, phenomena of extreme energy. And those phenomena are revealing just how complex and fascinating the physics behind a seemingly ordinary rainstorm can be.
