While most people are aware of the destructive power of lightning in forests, few know about the subtle electrical phenomenon known as corona. This weak electrical glow is believed to occur on tree leaves during thunderstorms. Researchers at Penn State University utilized ultraviolet-sensitive equipment to directly observe and measure this intriguing phenomenon in tree species such as sweetgum and celery pine across various U.S. states.
Coronae glow on the tip of a spruce needle caused by a charged metal plate in the laboratory. Image credit: William Bruun.
Lightning strikes have captivated humanity since thunderstorms began sweeping through Earth’s forests, causing everything from trunk splits to wildfires, often turning night into day.
However, scientists are now shifting their focus to the more delicate electrical phenomena that manifest on leaf tips amid thunderstorms.
Unlike lightning, which can heat the air to extreme temperatures, corona represents a weak electrical discharge with a temperature only slightly above that of the surrounding air.
Despite their gentler nature, these electrical sparks can generate significant amounts of hydroxyl, a key oxidant in the atmosphere, potentially harming tree foliage and affecting charged particles within thunderstorm cloud bases.
“We have observed these phenomena, confirming their existence,” stated Dr. Patrick McFarland, a meteorologist at Pennsylvania State University.
“Having tangible evidence is incredibly exciting,” he added.
“In a laboratory setting, when you block all light, you can barely see the corona, which appears as a blue light,” he explained.
For this study, Dr. McFarland and his team designed a portable instrument equipped with multiple components to measure tree canopies and the atmospheric conditions that influence corona formation.
The centralized component is a 25 cm diameter telescope that focuses ultraviolet (UV) radiation onto a solar-blind UV camera sensitive to wavelengths between 255 and 273 nm.
During thunderstorms in North Carolina, scientists succeeded in observing corona on sweetgum and pine trees.
“The corona could potentially travel between leaves or trace along branches swaying in the wind,” the researchers noted.
Similar observations were recorded for various tree species during four additional thunderstorms from Florida to Pennsylvania.
“Our findings illustrate that the corona exhibits glowing patterns in wooded areas during thunderstorms,” the researchers stated.
“These corona effects can alter air quality in forests, subtly damage foliage, and influence storm conditions overhead.”
For further details, refer to the study published on February 12th in Geophysical Research Letters.
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PJ McFarland et al. 2026. Corona discharges glow on trees under thunderstorms. Geophysical Research Letters 53 (4): e2025GL119591; doi: 10.1029/2025GL119591
Source: www.sci.news
