For centuries, the dramatic spectacle of lightning striking trees has captured human attention. However, scientists have now confirmed a far more subtle, yet significant, electrical phenomenon: corona discharges – a faint glow occurring on tree leaves during thunderstorms. Researchers at Pennsylvania State University have directly observed and measured these discharges on species like sweetgum and loblolly pine across multiple U.S. states, revealing a previously undocumented interaction between trees and atmospheric electricity.
Beyond Lightning: The Subtle Power of Coronae
While lightning is characterized by intense heat and destructive force, coronae are weak electrical discharges that barely elevate the surrounding air temperature. Despite their subtlety, these sparks generate extreme amounts of hydroxyl, the primary oxidizer in the atmosphere, potentially damaging leaves and introducing charged particles into thunderstorm clouds.
“To finally have concrete evidence of that…is what I think is the most fun,” said Dr. Patrick McFarland, a meteorologist involved in the study. In controlled laboratory conditions, these discharges appear as a barely visible blue glow when all other light sources are eliminated.
How the Observation Was Made
The research team developed a specialized mobile instrument to detect coronae on treetops. The core of this setup was a 25-cm telescope that focused ultraviolet (UV) radiation onto a solar-blind UV camera, sensitive to wavelengths between 255 and 273 nm. This allowed them to observe the discharges during thunderstorms in North Carolina, documenting how they “hopped among leaves and sometimes followed a branch as it swayed in the wind.”
Similar observations were made under four additional storms spanning from Florida to Pennsylvania.
Implications for Forests and Storms
The findings suggest that coronae occur widely beneath thunderstorms, potentially altering air quality in forested areas, causing subtle damage to foliage, and even contributing to the electrical charge within storm clouds.
“Our observations indicate that corona shimmer on the swath of trees beneath a thunderstorm,” the authors wrote in their report.
This research highlights that the electrical interactions between thunderstorms and forests are more complex than previously understood. The faint glow of coronae, though often unseen, may play a surprisingly important role in atmospheric chemistry and storm dynamics.
The study, published February 12 in Geophysical Research Letters, expands our understanding of how forests respond to storms. This provides new context for forest health, atmospheric science, and the broader effects of lightning on the natural world.
