Pennsylvania State University researchers have captured the first outdoor proof that trees produce faint ultraviolet glows during thunderstorms, confirming a hypothesis that scientists had debated for decades without direct field evidence. The team recorded corona discharges hopping from leaf to leaf on treetops along the U.S. East Coast in summer 2024, using a specialized UV camera mounted on a storm-chasing vehicle. Their peer-reviewed findings, published in Geophysical Research Letters, open a new line of inquiry into how electrical activity in storms may alter forest chemistry and air quality across wide regions.
Chasing Storms With a UV Camera
The research team fitted a modified Toyota Sienna with ultraviolet-sensitive imaging equipment and drove it into active thunderstorms, intercepting cells from Florida to Pennsylvania. On two trees in North Carolina, they captured clear footage of corona discharges glowing on treetops as electric fields intensified overhead, an effect described in an American Geophysical Union release on the project. The discharges, which are weak electrical emissions that ionize the air around sharp points like leaf tips, had been reproduced in laboratories but never documented on living trees in a natural storm environment.
What the camera revealed was striking in its detail. Individual discharges jumped from one leaf to another and persisted for up to several seconds at a time, far longer than the near-instantaneous flickers many atmospheric physicists had expected. The coronae emitted approximately 10^11 photons at 260 nanometers and carried currents of roughly 1 microamp, according to the Penn State research dataset compiled for this work. Those numbers are tiny compared to a lightning bolt, but spread across thousands of trees in a forest canopy, the cumulative effect could be significant, especially if storms repeatedly sweep over the same landscapes during peak convective seasons.
Why Decades of Hypothesis Went Unproven
Scientists have long suspected that the strong electric fields beneath thunderclouds should trigger corona discharges on trees. The pointed geometry of leaves and branch tips concentrates charge in much the same way a lightning rod does, and lab experiments had already shown that applying high voltage to foliage produces visible discharge. But confirming the phenomenon outdoors required solving a practical problem: corona light is almost entirely ultraviolet, invisible to the naked eye, and easily overwhelmed by ambient daylight. Standard storm-observation tools were simply not designed to detect it, which helps explain why the effect remained hypothetical in field conditions despite being familiar in controlled laboratory setups.
The breakthrough came from combining a purpose-built UV sensor with the mobility of a storm-chasing vehicle, allowing the team to position themselves close enough to isolated trees while storms passed directly overhead. That approach turned a decades-old theoretical prediction into measurable data. The journal article notes that coronae had been hypothesized to form on trees under thunderstorms but were never directly observed until now, underscoring how instrumental design and field strategy can unlock phenomena that had remained hidden in plain sight. It also exposed a gap in atmospheric science: if corona discharges are as common as the initial observations suggest, researchers may have been missing a persistent source of electrical and chemical activity in forest canopies every time a thunderstorm rolls through.
Chemical Fallout in the Forest Canopy
The outdoor confirmation matters beyond pure physics because corona discharges do not just glow. Earlier laboratory work at Pennsylvania State University demonstrated that electrical discharges on leaves generate hydroxyl radicals (OH) and hydroperoxyl radicals (HO2), highly reactive molecules that drive atmospheric chemistry. That prior study found concentrations of these radicals spiked by 100 to 1,000 times near trees subjected to simulated thunderstorm fields. Hydroxyl radicals are among the most potent oxidizers in the lower atmosphere, capable of breaking down volatile organic compounds emitted by vegetation and, in the process, contributing to ozone formation and other secondary pollutants that influence air quality.
If those lab-scale chemical surges translate to real forests during real storms, the implications are broad. A single thunderstorm passing over a wooded region could trigger ultraviolet sparkles across large swaths of canopy, each discharge site acting as a miniature chemical reactor. The peer-reviewed paper frames these first field measurements as a contribution to emerging research on how electrical discharges affect trees, including potential links to tree damage and limited thunderstorm electrification. Quantifying that effect at landscape scale is the next challenge, and the structured data now available give other research groups a starting point for replication, comparison across ecosystems, and eventual incorporation into regional air-quality and climate simulations.
What a Warming Climate Could Amplify
The timing of this discovery carries weight because thunderstorm frequency and intensity are projected to increase as global temperatures rise, especially in regions prone to severe convective weather. More frequent storms mean more opportunities for corona discharges across forests, which could amplify the radical chemistry described in the lab studies. The authors themselves flag this connection in their analysis, noting that the impacts of coronae and electrical discharges on trees may increase in a warming climate. That framing shifts the finding from a curiosity of atmospheric physics into a variable that climate and air-quality models have not yet fully accounted for, particularly when estimating oxidant production during storm seasons.
Most current models of forest-atmosphere interactions treat thunderstorms primarily as sources of lightning, rain, and mechanical damage from wind and hail. Corona discharges occupy a different niche: they are far weaker than lightning, produce no audible thunder, and leave no visible scorch marks, yet they may be far more widespread during any given storm. If radical production scales with the number of discharge points across a canopy, even modest increases in storm activity could meaningfully shift regional ozone budgets and oxidation capacity. Integrating this process into models will require more observations across diverse tree species, climate zones, and storm types, as well as collaboration among atmospheric chemists, ecologists, and electrical engineers.
Expanding the Research Frontier
The study also highlights the role of scientific infrastructure in bringing such subtle phenomena to light. The work appears under the umbrella of the American Geophysical Union, which supports a broad community of Earth and space scientists and provides peer-reviewed outlets for emerging fields like atmospheric electricity in forested environments. Researchers who want to explore related topics or track follow-up studies can use the advanced search tools in AGU’s publication platform to locate additional papers on corona discharges, thunderstorm chemistry, and tree-atmosphere interactions, building on the initial observations from the Penn State team.
For scientists and students interested in contributing to this line of inquiry, access to journals and collaboration networks is essential. Joining the professional community through an AGU membership portal can facilitate data sharing, conference presentations, and interdisciplinary partnerships that are likely to be necessary as corona-related research expands. Support from donors, including those who give through dedicated fundraising channels, helps sustain the instrumentation, field campaigns, and open-access publishing that make it possible to document elusive phenomena like ultraviolet glows in treetops. As more teams deploy similar UV-sensitive systems in different regions, the ghostly coronae first captured in North Carolina may become a routine, if still invisible, part of how scientists understand the electrical life of forests during storms.
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*This article was researched with the help of AI, with human editors creating the final content.
