Researchers at Penn State University have advanced our understanding of lightning formation by identifying the atmospheric events that trigger lightning within thunderclouds. Led by Professor Victor Pasko, the team published their findings in the Journal of Geophysical Research on July 28, 2025.
The study reveals that strong electric fields in thunderclouds accelerate electrons, which then collide with atmospheric molecules like nitrogen and oxygen, producing X-rays. This process initiates a cascade of additional electrons and high-energy photons, leading to lightning strikes. The researchers used mathematical modeling to confirm and explain field observations of photoelectric phenomena in Earth's atmosphere, providing a precise, quantitative explanation for how lightning initiates in nature. This work connects the dots between X-rays, electric fields, and the physics of electron avalanches.
By simulating conditions that replicated observed field conditions, the team offered a complete explanation for the X-rays and radio emissions present within thunderclouds. They demonstrated how electrons, accelerated by strong electric fields in thunderclouds, produce X-rays as they collide with air molecules like nitrogen and oxygen, and create an avalanche of electrons that produce high-energy photons that initiate lightning.
This research enhances our ability to predict and prepare for severe weather, deepening our appreciation for the dynamic forces shaping our world. The implications extend beyond meteorology, informing fields such as aviation safety and the study of atmospheric effects on climate.