Ghostly UV sparks light up forests as thunderstorms pass overhead

Ghostly UV sparks light up forests as thunderstorms pass overhead

By Claire Cameron edited by Jeanna Bryner

For nearly a century, scientists have wondered how thunderstorms might affect the forests beneath them, and many have believed that a storm might ignite weak electrical discharges on plants that would catch on the tips of their leaves and along their branches. These phenomena, known as coronas, had never been seen in nature – until now.

A new study published earlier this month in Geophysical Research Letters 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,” Patrick McFarland, a Pennsylvania State University meteorologist and lead author of the study, said in a statement.

On supporting science journalism

If you like this article, please consider supporting our award-winning journalism by subscribes. By purchasing a subscription, you help secure the future of impactful stories about the discoveries and ideas that shape our world today.

Before this study, researchers had observed in the laboratory how such electrical discharges can be formed.

“In the lab, if you turn off all the lights, close the door and block the windows, you can just barely see the coronas. They look like a blue glow,” McFarland said.

These observations suggested that the electrical charge of an overhead thunderstorm could induce an opposite charge on the ground below. Attracted by the thunderstorm’s charge, the opposing charge would travel to the highest points it could reach. In the case of forests, this will be the tree crown. The tips of the blades would then discharge the electricity, producing blue sparks or coronas.

To observe the coronas in nature, McFarland and his team equipped a Toyota Sienna with a mobile weather station, complete with ultraviolet camera. Then they went storm hunting and took videos as they went. Analyzing the video footage revealed the coronas glowing on the tips of tree leaves and even jumping from leaf to leaf.

If humans could see in ultraviolet, McFarland said, it would likely appear to observers as if the entire tree canopy was glowing. “It would probably look like a pretty cool light show, like thousands of UV flashing fireflies descending on the treetops,” he said.

It’s time to stand up for science

If you liked this article, I would like to ask for your support. Scientific American has served as an advocate for science and industry for 180 years, and right now may be the most critical moment in its two-century history.

I have been one Scientific American subscriber since I was 12 years old, and it helped shape the way I see the world. SciAm always educates and delights me, and inspires a sense of awe for our vast, beautiful universe. I hope it does for you too.

If you subscribe to Scientific Americanyou help ensure our coverage is centered on meaningful research and discovery; that we have the resources to report on the decisions that threaten laboratories across the United States; and that we support both budding and working scientists at a time when the value of science itself is too often not recognised.

In return, you receive important news, captivating podcasts, brilliant infographics, can’t-miss newsletters, must-see videos, challenging games, and the world of science’s best writing and reporting. You can even give someone a subscription.

There has never been a more important time for us to stand up and show why science is important. I hope you will support us in that mission.