During any given thunderstorm, the forest canopy above you is likely flickering with a faint, violet light. This is not folklore, but a newly documented reality. A study recently published in Geophysical Research Letters confirms that St. Elmo’s Fire, a phenomenon once relegated to the eerie tips of ship masts and church spires, is a widespread and constant feature of electrified skies. It paints entire forests in a ghostly glow completely invisible to the human eye.
The Unseen Corona
St. Elmo’s Fire is a physical process, not a supernatural one. It occurs when a powerful electric field, like the one generated in a thunderstorm, concentrates around a sharp, conductive point. This intense field supercharges the surrounding air molecules, stripping them of electrons and creating a low-temperature plasma that emits a characteristic blue or violet light. For centuries, scientists speculated whether the trillions of needles and leaf tips in a forest could act as focal points for this discharge. The answer is now clear.
Patrick McFarland, a meteorologist at Pennsylvania State University, and his team didn’t wait for a chance sighting. They brought the phenomenon into the controlled environment of their lab. Taking a branch from a campus spruce tree, they exposed it to strong electric fields. “And sure enough, it glowed,” McFarland reported. The waxy tips of the conifer’s needles became adorned with glowing balls of purple plasma. It was proof of concept. But a lab is not a forest. The real challenge was capturing this fleeting event in the wild, amidst the chaos of a live thunderstorm.
The Storm-Chasing Minivan
To hunt for the glow, the research team engineered a mobile observatory out of a 2013 Toyota Sienna. (A practical choice). They removed a seat to install a telescope and cut a twelve-inch hole in the roof for a periscope connected to a highly sensitive ultraviolet camera. The vehicle was also outfitted with an electric field detector and a Faraday cage to shield the instruments from electrical interference. “Totally killed the resale value of the car,” McFarland noted. For much of the summer of 2024, this modified minivan became their base of operations as they chased storms up and down the East Coast.
Back in the lab, the analyzed footage was revelatory. What the human eye missed, the instruments captured with stunning clarity. “Every single tree that we looked at under a thunderstorm had very similar amounts or frequencies of this corona glow,” McFarland stated. They hadn’t just seen one or two isolated flickers. They saw hundreds of points of light bursting across canopies in pulses that lasted up to three seconds, sometimes appearing to leap from one leaf to the next. The implication is staggering. This is happening constantly, everywhere.
A New Atmospheric Variable
The discovery moves beyond mere curiosity and into the fundamental mechanics of atmospheric science. Richard Zare, a chemistry professor at Stanford University not involved with the study, underscored its importance for understanding how our atmosphere is formed. These countless tiny electrical discharges are actively creating ozone and nitrogen oxides right at the leaf-atmosphere boundary. This represents a previously unaccounted-for chemical factory operating on a planetary scale. “It might be very important,” Zare commented, pointing to a new variable that must be factored into climate and atmospheric models.
The implications extend to the trees themselves. Loïc D’Orangeville, a forest ecologist at Laval University, explained that such chemical compounds, especially in high concentrations, can be harmful to plant life. While he suspects forests have evolved adaptations to this constant electrical fizz, the sheer scale of the phenomenon opens a new field of inquiry into forest health and resilience. “There are around 1,800 thunderstorms occurring at any given moment on Earth,” he said. “So that’s quite a significant amount of those coronas occurring at all times.” For ecologists like D’Orangeville, the finding is profound. “It’s neat to discover something new that’s going on with the trees that I had absolutely no clue existed.” We now know the forest is not just a passive bystander in a storm. It is an active participant, lit from within by its own invisible fire.