A team of Penn State researchers has captured the first natural observations of trees emitting faint electrical glows, known as corona discharges, during thunderstorms. The discovery, made in North Carolina, confirms a phenomenon long theorized but never seen outside laboratories. These glows may contribute to air cleaning by producing hydroxyl radicals.
In June 2024, researchers from Penn State University's meteorology and atmospheric science department drove a modified 2013 Toyota Sienna along the East Coast, equipped with a custom telescopic instrument to detect corona discharges from treetops amid storms. After initial challenges in Florida, the team, led by doctoral student Patrick McFarland and distinguished professor William Brune, with assistant research professor Jena Jenkins and former associate research professor David Miller, found success near the University of North Carolina at Pembroke. There, during a two-hour thunderstorm, they targeted a sweetgum tree 100 feet from their van and a nearby long needle loblolly pine as the storm weakened, recording the first field evidence of the phenomenon, as detailed in Geophysical Research Letters in 2026. 859 corona events were captured on the sweetgum tree and 93 on the loblolly pine, each lasting fractions of a second to several seconds, visible mainly in ultraviolet light. The Corona Observing Telescope System, a Newtonian telescope linked to a UV-sensitive camera with atmospheric sensors, enabled the observations by filtering out solar UV. McFarland, the lead author, stated, 'This just goes to show that there's still discovery science being done. For more than half a century, scientists have theorized that corona exists, but this proves it.' Thunderclouds build negative charges, drawing positive charges up through trees to leaf tips, where intense fields spark the discharges. These produce UV radiation that breaks water vapor into hydroxyl, a key atmospheric oxidizer that reacts with pollutants like methane and tree-emitted hydrocarbons, potentially aiding air quality. The team noted minor leaf damage at discharge sites, matching prior lab tests, and plans collaborations with ecologists to study effects on trees and forests. McFarland added, 'It's nearly invisible to the naked eye but our instruments give rise to a vision of swaths of scintillating corona glowing as thunderstorms pass overhead.'
