For decades, scientists theorized that thunderstorms could trigger faint electrical discharges on trees, causing sparks to ignite at leaf tips and along branches. These discharges, known as coronas, were only observed in laboratory settings—until now. A new study confirms these ghostly ultraviolet sparks do occur in forests during thunderstorms.
Unseen Electrical Activity
Researchers at Pennsylvania State University, led by meteorologist Patrick McFarland, used specialized ultraviolet cameras mounted on a mobile weather station to observe this phenomenon in real-world conditions. The team drove into storm-prone areas, recording footage as lightning struck nearby.
“These things actually happen; we’ve seen them; we know they exist now,” McFarland stated. The analysis of the captured footage revealed coronas glowing on the ends of tree leaves and even jumping between them.
How It Works: Atmospheric Charge and Tree Canopies
The process begins with the electrical charge of an approaching thunderstorm inducing an opposite charge on the ground below. This opposing charge travels upward, seeking the highest available points—in this case, the tree canopy. The leaves discharge this electricity, producing the ultraviolet sparks.
In a dark laboratory setting, these coronas appear as a faint blue glow. If humans could see ultraviolet light, McFarland explains, it would look like the entire treetop was alight with thousands of UV-flashing “fireflies.”
Why This Matters: Beyond a Cool Light Show
While visually striking, this discovery isn’t just about an interesting natural phenomenon. Understanding these electrical interactions could have implications for forest fire risks. Though the sparks themselves aren’t strong enough to ignite widespread fires, they demonstrate how thunderstorms can electrify vegetation—potentially contributing to the ignition of dry fuels under certain conditions.
The study provides direct evidence of a long-suspected interaction between thunderstorms and forests, bridging a gap between laboratory observations and real-world atmospheric events. This research underscores the complex electrical dynamics at play in natural environments, revealing that even in remote forests, nature is constantly conducting its own silent light show.
