Meteorologists have, for the first time, captured tiny bursts of ultraviolet light emitted by trees during intense thunderstorms. Scientists had long suspected this invisible phenomenon existed, theorizing it was triggered by electrical current flowing through plants as a storm front passed nearby, as reported by ScienceAlert.
This glowing effect, known as a corona, arises because electrical charge accumulates at the very tips of the leaves. Previously, this phenomenon could only be reproduced in controlled laboratory settings or inferred from peculiar shifts in the electrical fields within forests during inclement weather. To secure tangible proof, a team of experts led by meteorologist Patrick McFarland from Penn State University set out to chase active thunderstorms.
“These things actually happen; we’ve seen them; now we know they exist,” stated Patrick McFarland. Thunderstorms represent regions of massive electrical turbulence. Tall clouds contain ice and dust particles that segregate electrical charges, much like an enormous battery. When the potential difference between these charges becomes sufficiently great, lightning streaks across the sky.
However, the electrical exchange between the ground and the sky is not always so overt and visible. Sometimes, a charge imbalance can travel through a nearby tree, as its moist trunk and branches act as excellent conductors. The charge builds up on the plant’s foliage, where it weakly radiates a corona of ultraviolet light.
Initially, the researchers simulated this process in the lab. They positioned small firs and maples beneath charged metal plates designed to mimic thunderclouds, and then shut off the lights. “In the lab, if you turn off all the ambient light, close the door, and block the windows, you can just barely make out the coronas. They look like a faint blue glow,” the scientist explained.
Next, the team sought these nearly invisible sparks in the wild. They outfitted a vehicle as a mobile weather station, equipped with an electric field detector, a laser rangefinder, and a specialized rooftop periscope that piped light into a UV camera. During a severe storm video captured in North Carolina, the specialists recorded 41 distinct flashes of light on tree branches, lasting between 0.1 and 3 seconds each.
The flashes behaved erratically, jumping from leaf to leaf, which perfectly aligned with previous laboratory findings. Similar occurrences were observed across various tree species along the entire Eastern Seaboard of the US. “I believe you would see this band of light on top of every tree during a thunderstorm,” McFarland commented. He added that the sight resembles thousands of luminous fireflies descending upon the canopy. Each such corona expelled approximately 100 billion photons.
It remains unclear what specific impact this strong electrical current may have on global forests. For instance, regular exposure to such voltage surges could potentially inflict damage on the upper branches of trees. “The effect these coronas have on atmospheric chemistry, forest ecology, tree health, and even thunderstorm electrification needs to be re-evaluated and understood, especially as thunderstorms become more frequent amid a warming climate,” the researchers concluded in their scientific paper.
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