Scientists Capture Elusive “Glowing Trees” Phenomenon During Thunderstorms

A long-theorized atmospheric event is finally observed in the wild

For decades, scientists have suspected that something unusual happens in forests during thunderstorms—something largely invisible to the human eye. Now, researchers at Penn State University have confirmed it: a faint electrical glow flickers across treetops as storms pass overhead.

The phenomenon, known as a corona discharge, has been theorized for nearly a century. Until now, however, it had never been directly observed outside controlled laboratory settings. The new findings offer fresh insight into how forests interact with the atmosphere, with potential implications for air quality, ecosystem health, and even storm dynamics.

What causes trees to glow during storms?

When most Americans think of thunderstorms, they picture heavy rain, thunderclaps, and lightning strikes. But beyond these familiar elements, a quieter electrical process is unfolding.

A corona discharge is a weak electrical spark that forms when the electric field in the atmosphere intensifies—such as during a thunderstorm. Unlike lightning, which is powerful and visible, coronas are faint, cool, and short-lived.

They tend to form at sharp points, like the tips of leaves or pine needles. Because they emit mostly ultraviolet (UV) light, they are nearly impossible to see without specialized equipment.

Despite their subtle nature, coronas play an active role in atmospheric chemistry. They generate hydroxyl radicals—molecules that help break down pollutants and improve air quality. In regions with dense forests, such as the southeastern United States, this effect could be more significant than previously understood.

New technology makes the invisible visible

To capture this elusive glow, the Penn State research team developed a specialized instrument mounted on a mobile platform. The system combines a telescope with a UV-sensitive camera capable of detecting extremely faint light in a narrow wavelength range between 255 and 273 nanometers.

This range is key: sunlight at these wavelengths is blocked by the ozone layer and never reaches the Earth’s surface. That means any UV light detected at ground level is almost certainly coming from electrical activity.

Armed with this technology, researchers tracked thunderstorms across multiple states, positioning their equipment near trees and aiming it at the canopy as storms moved in.

Breakthrough observation in North Carolina

The team’s breakthrough came in Pembroke, North Carolina, where they observed a thunderstorm passing directly over a forested area. Focusing first on a sweetgum tree and then a loblolly pine, the researchers recorded hundreds of tiny UV flashes over several hours.

These flashes weren’t stationary. Instead, they moved dynamically across branches and leaves, sometimes following the motion of the wind. Each burst lasted from fractions of a second to a few seconds.

What stood out most was the consistency. Every branch examined showed signs of corona discharge, and both trees displayed similar activity levels.

Additional observations from storms in states ranging from Florida to Pennsylvania revealed the same pattern across different tree species. The findings suggest that this phenomenon is widespread across U.S. forests during thunderstorms.

Measuring electrical activity in trees

By analyzing the UV light captured on camera, scientists were able to estimate the electrical current involved in each discharge. On average, each corona produced about one microamp of current—a very small amount individually.

However, when multiplied across countless leaves and trees in a forest, the cumulative effect becomes significant.

Laboratory experiments using potted spruce and maple trees supported these findings. Researchers confirmed a direct relationship between the brightness of the UV glow and the electrical current flowing through the plant.

This marks the first time scientists can reliably translate visual data—how bright the glow appears—into measurable electrical activity.

Why this discovery matters

While the glow itself may be faint, its implications are substantial.

Air quality improvement

Corona discharges generate hydroxyl radicals, which help remove hydrocarbons and other pollutants from the air. This suggests forests may play a more active role in cleaning the atmosphere during storms than previously recognized.

Tree health concerns

Repeated exposure to these electrical discharges can damage the delicate tips of leaves over time. In regions like the Midwest and Southeast, where thunderstorms are frequent, this could contribute to long-term stress on vegetation.

Potential impact on storm behavior

The charged particles released by coronas may feed energy back into the atmosphere, potentially influencing how thunderstorms develop and behave. While this effect is still being studied, it adds a new layer to understanding storm dynamics.

A hidden layer of nature revealed

For generations, thunderstorms have been viewed as dramatic but straightforward weather events. This research reveals a more complex picture—one where forests quietly interact with atmospheric electricity in ways that have gone unnoticed.

As climate change increases the frequency and intensity of storms across parts of the United States, scientists expect this phenomenon to become even more relevant.

The study, published in Geophysical Research Letters, opens the door to further research on how forests, air chemistry, and weather systems are interconnected.

Conclusion

The discovery of corona discharges glowing across treetops marks a significant advancement in atmospheric science. What was once an invisible and theoretical process is now observable and measurable.

Beyond its scientific novelty, the finding underscores how much remains to be learned about the natural world—even in familiar environments like forests during a thunderstorm.

John Irving

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