Storm loads trigger tiny lightning bolts on leaves and needles, new study reports
Thunderstorms can bring much more than rain and gloom. The same forces that cause thunder and lightning also makes treetops sparkle in ultraviolet light, like a Christmas tree topper invisible to the human eye.
For almost a century, scientists have discussed a phenomenon called Saint Elmo’s firewhere electrical discharges cause a bluish glow from sharp objects such as ship masts during thunderstorms. More recently, researchers have wondered whether thunderstorms might cause weak electrical discharges from treetops. These releases were detected in the laboratory, and now they have been spotted in nature.
The tips of wild trees emit an electrical charge with a blue and ultraviolet glow in response to an opposing charge in the atmosphere during a thunderstorm, scientists report in February 28. Geophysical research letters.
The question of whether these discharges could form in treetops was raised a few years ago over lunch, says Patrick McFarland, a meteorologist at Penn State. McFarland’s advisor, William Brune, “kind of leaned back from the picnic table where we were sitting, and he looked up at the top of the tree right above us, and kind of posited, you know, ‘Hmm, I wonder if these trees glow in thunderstorms,'” McFarland says.
“That afternoon we grabbed a branch from a tree, brought it into our lab, put a high-voltage plate on it,” McFarland says. The team placed the high-voltage plate on top of the branch, creating a negative charge in the air around it, and attached the branch to a positively charged electrical plate to simulate the ground. “And of course we saw him shine.”
The glow, part of an electrical discharge called a corona, was barely visible, emitting a pale blue light as well as invisible UV light. Detecting this in the lab made researchers even more curious, McFarland says: “Are we also seeing these glows under thunderstorms?
To answer that question, the group outfitted a 2013 Toyota Sienna pickup truck with all the instruments they would need. find a stormplus a camera capable of detecting the distinct UV light emitted by a crown. In the summer of 2024, it was time to hit the road.
“We built this van and drove it around Florida for about a month,” McFarland says. Florida experiences the most thunderstorms in the United States due to sea breezes coming from the Atlantic Ocean and the Gulf of Mexico. “There are storms almost every day. »
Although thunderstorms were common, finding a storm was just one factor when searching for crowns, McFarland said. “Then you have to find a public place to set up with trees that look relatively tall. And then you have to set it all up and, you know, turn the instrument on and point it at the tree. So it’s really, really difficult.”
A happy coincidence led them to their best storm. “This storm in North Carolina formed by chance as we were heading back to Pennsylvania,” McFarland says. The team found a location in the coastal plains town of Pembroke, North Carolina. She set up her equipment and recorded video of a gum tree and a loblolly pine for 90 minutes.
In the video, the team identified 41 crowns, none of which lasted more than three seconds. And the flashes didn’t stay localized in one place. They danced and darted like twinkling lights, jumping between the leaves and along the branches swaying in the wind.
While the study primarily focused on data collected during the North Carolina storm, the team notes that the coronas appeared during storms in Florida and Pennsylvania and had the same fleeting flickering appearance. “These glows seem to be really widespread,” McFarland says. “There may be many more coronas that we just don’t have the sensitivity to see.”
