[Photo by Breno Machado on Unsplash]
30 July, 2025 (Wednesday) - By Yeojun Jung
After decades of scientific speculation, a team led by Penn State researchers has identified the precise mechanism behind how lightning begins inside thunderclouds, solving one of atmospheric science’s oldest mysteries.
Published July 28, 2025, in the Journal of Geophysical Research, the study offers the first comprehensive, quantitative model of lightning initiation. It explains how subatomic particle interactions, fueled by intense electric fields and cosmic rays, create a rapid cascade that leads to lightning discharge.
Inside thunderclouds, extreme electric fields accelerate electrons to nearly the speed of light. These high-energy electrons then collide with air molecules like nitrogen and oxygen, triggering a burst of X-rays and creating a shower of new particles in just one-millionth of a second.
The process, known as a relativistic runaway electron avalanche, grows stronger when X-rays knock additional electrons loose from nearby atoms.Researchers call this the photoelectric effect. This self-sustaining chain reaction provides the conditions for a lightning bolt to form.
Cosmic rays, high-energy particles from space, likely initiate the process by seeding the first runaway electrons. The result is an enormous energy release that appears as a flash of lightning.
The research team, led by Professor Victor Pasko, synthesized field data from satellites, aircraft, and ground-based sensors. Doctoral student Zaid Pervez played a major role in matching the model’s predictions to real-world lightning signals, confirming its accuracy across multiple detection platforms.
The model also solves a longstanding paradox: why terrestrial gamma-ray flashes (TGFs), intense energy bursts from thunderstorms, sometimes occur without visible lightning or radio signals. The study shows that these flashes can be triggered by compact, high-energy avalanches that emit X-rays but are too weak to generate the optical or radio emissions typical of lightning.
This deeper understanding of TGFs helps explain how these events can appear to come from “silent” regions of the sky. In such areas, lightning-like activity occurs on a scale too small or brief to be noticed by traditional sensors.
The study introduces the Photoelectric Feedback Discharge model, now available for public research. Its simulations show how individual particles can trigger cascading chain reactions, deepening our understanding of both lightning and broader plasma behavior.
Beyond atmospheric science, the implications could stretch into other fields. Professor Pasko notes that insights from this study could lead to innovations in plasma engineering, including developing compact, high-intensity X-ray sources for future use in technology or medical applications.
The Penn State team has bridged decades of scientific gaps between theory, observation, and simulation by clarifying the physical conditions that spark lightning. Their work not only explains lightning’s beginnings but also lays the groundwork for future explorations of Earth’s upper atmosphere and even space weather phenomena.
