For the first time, researchers have directly observed and measured faint electrical discharges, known as coronae, flickering from tree leaves during thunderstorms, confirming a phenomenon long suspected but never documented in the wild.
The groundbreaking study, led by Patrick McFarland, a meteorologist at Pennsylvania State University, recorded the near-invisible discharges across multiple tree species along the US East Coast during the summer of 2024.
The findings were published in Geophysical Research Letters, a journal of the American Geophysical Union.
Scientists have theorised for nearly a century that thunderstorms could induce weak electrical discharges in plants. When a storm builds overhead, it creates a strong electric field that induces an opposite charge in the ground. That charge travels upward to the highest points, typically leaf tips in treetops, where it releases as a faint electrical glow known as a corona.
“In the laboratory, if you turn off all the lights, you can just barely see the coronae. They look like a blue glow,” McFarland said. “To finally have concrete evidence that these things actually happen in nature is what I think is the most fun.”
To capture the elusive phenomenon, the team transformed a 2013 Toyota Sienna into a storm-chasing mobile lab, equipping it with an electric field detector, weather station, laser rangefinder and a roof-mounted periscope feeding into an ultraviolet camera.
The UV camera proved critical, as even dim storm light overwhelms the glow in the visible spectrum.
During one storm in Pembroke, North Carolina, researchers documented 41 corona events on leaf tips within 90 minutes. The glows lasted up to three seconds and often appeared to hop between leaves as branches swayed in the wind. Similar activity was recorded on sweetgum and loblolly pine trees across multiple storms between Florida and Pennsylvania.
The implications could be significant. Coronae can scorch leaf tips within seconds, and laboratory studies suggest repeated electrical currents may damage cell membranes and chloroplasts, potentially affecting photosynthesis.
While a single event appears harmless, repeated exposure across entire canopies during frequent storms could shape how trees evolve to minimise electrical damage.
“If you had superhuman vision,” McFarland said, “you’d probably see a swath of glow on the top of every tree under a thunderstorm, like thousands of UV-flashing fireflies.”
