A recent study by Professor Victor Pasco from Pennsylvania and his team reveals the method for determining the robust electric field associated with thunder, which collides with molecules such as nitrogen and oxygen, resulting in x-rays that trigger intense storms through additional electrons and high-energy photons.
NASA’s high-population ER-2 plane is equipped with instruments for the fly-eye Earth Intake Mapper Simulator and the Ground Gamma Ray Flash (ALOFT) Mission, which records gamma rays from ThunderClouds (illustrated in purple). Image credit: NASA/ALOFT team.
“Our research provides an accurate and quantitative explanation of the initial processes leading to lightning,” stated Professor Pasco.
“It connects the underlying physics of X-rays, electric fields, and electron avalanches.”
In their study, Professor Pasco and colleagues employed mathematical modeling to validate and elucidate field observations related to photoelectric phenomena within the Earth’s atmosphere.
This phenomenon, known as terrestrial gamma-ray flashes, consists of invisible, naturally occurring bursts of x-rays along with their associated radio emissions.
“By creating a simulation that mirrors the observed field conditions, we offered a comprehensive explanation of the x-rays and radio emissions occurring inside Thunderclouds,” added Professor Pasco.
“Our research illustrates how electrons, accelerated by lightning’s strong electric field, can generate x-rays upon colliding with air molecules like nitrogen or oxygen, leading to an avalanche of electrons that create high-energy photons to initiate lightning.”
Through their model, the researchers analyzed field observations gathered by various research teams utilizing ground-based sensors, satellites, and high-altitude surveillance platforms to simulate thunderstorm conditions.
“We elucidated the mechanisms of photoelectric events, the triggering conditions for electron cascades in thunder, and the sources of diverse radio signals detected in clouds preceding a lightning strike,” explained Professor Pervez.
“To validate the lightning initiation explanation, I compared our findings with previous models, observational studies, and my own investigations into lightning bolts, specifically intercompact cloud discharges that typically occur within limited regions of Thunderclouds.”
This process, termed photoelectric feedback discharge, models the physical conditions where lightning is likely to happen.
The equations employed to develop the model are available in the published papers, enabling other researchers to apply them in their own studies.
Besides elucidating the onset of lightning, the scientists clarified why ground-level gamma-ray flashes can often occur without the accompanying light and radio emissions that signify lightning in rainy conditions.
“In our simulations, the high-energy X-rays generated by relativistic electron avalanches create new seed electrons driven by photoelectric phenomena in the air, rapidly amplifying these avalanches,” Professor Pasco remarked.
“Moreover, while this runaway chain reaction is generated in a compact volume, it can happen across a varied range of intensities, often with minimal optical and radio emissions but detectable X-ray levels.”
“This explains why these gamma-ray flashes originate from regions that are visually dim and appear silent in wireless frequency.”
The team’s findings will be published in the Journal of Geophysical Research: Atmospheres.
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Victor P. Pasco et al. 2025. The photoelectric effect in the air accounts for the initiation of lightning and the occurrence of terrestrial gamma rays. JGR Atmosphere 130 (14): E2025JD043897; doi: 10.1029/2025JD043897
Source: www.sci.news
