Ghostly UV sparks light up forests as thunderstorms pass overhead
Thunderstorms can generate weak electrical discharges on the plants underneath, but until now, they had never been observed in nature
For almost a century, scientists have wondered about how thunderstorms might affect forests below them, with many believing the storm could ignite weak electrical discharges on the plants below, catching at the tips of leaves and along branches. These phenomena, known as coronae, had never been seen in nature—until now.
A new study published earlier this month in Geophysical Research Lettters reveals how the tips of tree leaves burn with ghostly, ultraviolet sparks.
“These things actually happen; we’ve seen them; we know they exist now,” said Patrick McFarland, a meteorologist at The Pennsylvania State University and lead author of the study, in a statement.
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Before this study, scientists had observed in the lab how coronae might form.
“In the laboratory, if you turn off all the lights, close the door and block the windows, you can just barely see the coronae. They look like a blue glow,” McFarland said.
Those observations suggested that the electrical charge of a thunderstorm overhead can induce an opposing charge on the ground below. Attracted to one another, the opposing charge would travel to the highest points it could reach. In the case of forests, this is the tree canopy. The tips of leaves would then discharge the electricity, producing blue sparks or coronae.
To observe the coronae in the wild, McFarland and his team fitted a Toyota Sienna with a mobile weather station, complete with ultraviolet camera. Then they went storm hunting, taking videos as they went. Analyzing the video footage revealed the coronae, glowing on the tips of tree leaves, and even hopping from leaf to leaf.
If humans could see in ultraviolet, McFarland said, it would likely look like the entire tree canopy was aglow. “It’d probably look like a pretty cool light show, as if thousands of UV-flashing fireflies descended on the treetops,” he said.
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