Key Points
- Los Alamos researchers discovered that cosmic-ray showers help trigger lightning by creating ionized pathways in clouds.
- The team used BIMAP-3D, an advanced 3D mapping system, to monitor lightning discharges.
- They observed a slanted polarization pattern in lightning discharges, deviating from the storm’s electric field.
- The Earth’s magnetic field deflects high-energy electrons and positrons from cosmic rays, affecting the discharge direction.
Researchers at Los Alamos National Laboratory have uncovered compelling evidence that cosmic-ray showers are critical in initiating lightning in thunderstorms. Published in JGR Atmospheres, the study, led by Xuan-Min Shao from the Electromagnetic Sciences and Cognitive Space Applications group, used advanced 3D radio frequency mapping and polarization technology to observe lightning formation.
Traditionally, lightning is understood to begin with a rapid positive electrical discharge as opposing charges within a cloud separate. However, the Los Alamos team observed that these positive discharges were immediately followed by even faster negative discharges, hinting at additional forces at work.
The breakthrough came with BIMAP-3D, a broadband interferometric mapping and polarization system developed at Los Alamos. By deploying two stations about seven miles apart, each outfitted with a Y-shaped array of antennas, the system captured high-resolution 3D maps of lightning. The researchers noticed that the polarization of the discharge currents—the direction in which the currents flowed—was slanted away from the anticipated path defined solely by the thunderstorm’s electric field. Moreover, the polarization direction shifted between the initial positive and the subsequent negative discharges.
This unexpected behavior is attributed to cosmic-ray showers, consisting of high-energy particles from space that generate secondary electrons and positrons upon entering the Earth’s atmosphere. Influenced by the Earth’s magnetic and the storm’s electric fields, these particles follow diverging trajectories, creating the observed slanted polarization. Such interactions further ionize the air in the thunderclouds, forming preferred pathways that allow lightning to propagate more rapidly.
Beyond its scientific significance, the study has important national security implications. Lightning produces optical and radio frequency signals similar to those of a nuclear explosion, and a better understanding of its mechanisms can improve the tools used for nuclear monitoring. This research deepens our understanding of lightning discharge physics and enhances the ability to distinguish natural events from potential security threats.
