Trees Aglow in Weather and Lightning Research

Each year, lightning strikes cause significant damage to trees in our landscapes. When lightning travels from the treetop to the ground, it often leaves us unsure whether the tree will recover over the coming years or gradually decline due to the intense heat and energy of the strike. It is well known that negative electrical charges in thunderstorm clouds meet positive charges rising from the ground, resulting in the lightning we see.

Beyond lightning, a more subtle interaction between the electrical charge in the atmosphere around thunderstorms and sharp objects extending into the air from the ground can occur, appearing as a subtle glow of blue or violet light around. This phenomenon is often referred to as St. Elmo's Fire and typically is observed around flagpoles, ship masts, airplane wings, or spires on top of buildings. The glow is the result of a corona discharge of the electrical charge in the atmosphere. Recent research has found that this electrical discharge may be happening across our forest canopies during thunderstorms.

In 2025, meteorological researchers at Penn State University – Patrick McFarland, William Brune, D.O. Miller, and J.M. Jenkins – used a special instrument called the Corona Observing Telescope System (COTS). In the laboratory, the researchers were able to reproduce and photograph tiny discharges of ultraviolet (UV) rays that matched the amount of electrical current passing through trees exposed to high voltage during naturally occurring thunderstorms. These halo effects may damage leaf surfaces and interfere with normal plant function, but appear to be a common occurrence trees must live with. The researchers then moved from the lab to real-world settings, using the COTS tool attached to a modified minivan to photograph these brief electrical events while tracking storms from Florida to Pennsylvania.

Read more of their work and findings in this press release from the American Geophysical Union.