In a recent study published in the Journal of Geophysical Research: Atmospheres, scientists from Los Alamos National Laboratory found that cosmic-ray showers appear to be a major factor in causing lightning strikes.
Scientists at Los Alamos National Laboratory are studying the origins of lightning. Image Credit: Los Alamos National Laboratory
Scientists still do not fully understand how lightning starts in thunderstorms. Using our 3D radio frequency mapping and polarization technology, we noticed an unusual pattern in how lightning begins; instead of just fast positive electrical discharge, the lightning flashes were quickly followed by an even faster, negative discharge.
Xuan-Min Shao, Lead Author, Electromagnetic Sciences and Cognitive Space Applications Group, Los Alamos National Laboratory
Lightning occurs when opposing electrical charges—positive and negative—separate within a cloud, creating a discharge that is visible as a flash of light.
The team's research, which made use of a cutting-edge mapping and polarization system called BIMAP-3D developed by Los Alamos, showed that the signal polarization—or the orientation of the discharge current—displayed a slanted pattern away from the direction of propagation, indicating that they were not just following the electric field of the thunderstorm. This suggests that lightning was triggered by an element other than the electrical field.
According to the research team, this behavior was caused by cosmic-ray showers—high-energy particles from space that enter Earth's atmosphere.
The secondary, high-energy electrons and positrons produced by these cosmic rays in the atmosphere further ionize the air and form pathways in thunderclouds, which accelerate the speed of lightning.
The research team found that positrons and electrons behaved differently during fast positive and negative discharges due to their deflection in opposite directions within the electromagnetic field. High-energy electrons and positrons were influenced by both Earth's magnetic field and the cloud's electric field, pushing them in different directions. This interaction led to a slanted discharge current, or slanted polarization, along the pathways of cosmic-ray showers.
Using a 3D Mapping System to Discover Lighting’s Origins
The broadband radio frequency interferometric mapping and polarization system (BIMAP-3D), created by Los Alamos in 2021, offers a previously unheard-of capacity for high-resolution, three-dimensional lightning source mapping and source polarization detection for in-depth research on the physics of lightning discharge.
BIMAP-3D records lightning in three dimensions by identifying radio wave bursts released by lightning during its formation and development. This allows users to see the location of lightning strikes and follow their path throughout the storm.
The system is located at Los Alamos National Laboratory and consists of two stations spaced roughly seven miles apart. To map lightning in two dimensions, each station has four sets of antennas that combine to form a Y-shaped interferometer array. The scientists can create complete 3D lightning maps by combining the 2D measurements from the two stations.
“This system is unique in that it simultaneously detects polarization in 3D, enabling us to see not only where lightning happens but also the direction of the discharge current inside the cloud,” Shao added.
The National Security Implications of Lightning
Lightning can produce optical and radio frequency signals that resemble those from a nuclear explosion. Los Alamos National Laboratory studies lightning to determine whether the signals are the result of a nuclear event or lightning.
Scientists at Los Alamos use lightning as part of their global security mission to help improve nuclear monitoring instruments while also learning a great deal about the phenomenon of lightning, which is still poorly understood.
The study was funded by the Laboratory Directed Research and Development Program.
Journal Reference:
Shao, -M. X., et al. (2025) 3D Radio Frequency Mapping and Polarization Observations Show Lightning Flashes Were Ignited by Cosmic-Ray Showers. Journal of Geophysical Research: Atmospheres. doi.org/10.1029/2024JD042549.