- Lightning, beyond its stunning visual display and dramatic electrical discharge, also produces a variety of energetic emissions that span across the electromagnetic spectrum. These emissions include radio waves, visible light, ultraviolet (UV) radiation, X-rays, and even gamma rays. The study of these high-energy phenomena, often at the frontier of atmospheric and space physics, reveals that lightning is not only a weather-related occurrence but also a natural source of energetic radiation—some of it as powerful as what is observed in space environments.
- When a lightning bolt forms, it generates extremely high temperatures and electric fields in a matter of microseconds. These conditions accelerate electrons to nearly the speed of light, a process known as runaway electron acceleration. As these high-speed electrons collide with air molecules, they produce bremsstrahlung radiation—a type of X-ray emission caused when fast-moving electrons are suddenly decelerated by atomic nuclei. In some cases, the acceleration is so intense that it results in terrestrial gamma-ray flashes (TGFs)—extremely short bursts of gamma rays that were first discovered by NASA satellites in the 1990s.
- TGFs typically occur at the tops of thunderstorms and last only milliseconds, but they can emit photons with energies exceeding 20 million electron volts (MeV), comparable to emissions from solar flares or even black hole accretion disks. These bursts are often accompanied by energetic electron beams that can travel along Earth’s magnetic field lines, potentially reaching the upper atmosphere or near-Earth space. The presence of TGFs suggests that Earth’s atmosphere can behave like a particle accelerator under the right conditions, a discovery that has significantly changed our understanding of lightning.
- In addition to X-rays and gamma rays, lightning also produces intense radio-frequency emissions, especially in the very low frequency (VLF) and extremely low frequency (ELF) bands. These emissions, known as sferics, can travel vast distances around the planet and are used by researchers to detect lightning strikes from remote locations. The electromagnetic pulses from lightning are also studied for their effects on the ionosphere, the electrically charged layer of Earth’s upper atmosphere. In some cases, lightning-generated radiation can disturb satellite communications, GPS signals, and even trigger sprites and other upper-atmospheric optical phenomena.
- The study of energetic radiation from lightning not only provides insights into the internal structure and behavior of thunderclouds but also has implications for aviation safety, satellite operations, and space weather monitoring. High-energy emissions from lightning can pose a radiation risk to aircraft flying at high altitudes, particularly over storm systems. Furthermore, the interaction between lightning-produced radiation and Earth’s radiation belts is an area of ongoing research, as it may influence the behavior of charged particles in near-Earth space.
- Researchers use ground-based detectors, balloon-borne instruments, and satellites such as NASA’s Fermi Gamma-ray Space Telescope and the Atmosphere-Space Interactions Monitor (ASIM) aboard the International Space Station to study these emissions. These tools help scientists better understand the extreme physical processes occurring in Earth’s atmosphere and their broader environmental impacts.
