Researchers have recently observed an intriguing phenomenon known as corona discharge, where tiny electrical bursts emerge at the tips of leaves, causing trees to emit a faint glow in the ultraviolet (UV) spectrum. For over 70 years, scientists have hypothesized that forests might exhibit this behavior during storms due to unique electric field activities, but concrete evidence had previously eluded them.
The Quest for Evidence
A team of scientists, including William Brune, a renowned professor of meteorology, and doctoral student Patrick McFarland, aimed to document these natural corona discharges for the first time. They selected Florida, known for its frequent thunderstorms, as their study site. However, the weather was not favorable, with short-lived storms thwarting their initial efforts for three weeks.
Breakthrough in North Carolina
As the team prepared to return to Pennsylvania, they encountered favorable storm conditions near the University of North Carolina at Pembroke. They quickly set up their instruments to observe a sweetgum tree about 100 feet away. A thunderstorm lasting nearly two hours provided the perfect opportunity to capture corona discharges, marking the first confirmed detection of this phenomenon in a natural environment. Their findings were subsequently published in Geophysical Research Letters.
"This shows that there's still discovery science happening," remarked McFarland, the lead author. "For decades, scientists have theorized about corona, but now we have proof."
Understanding the Formation of Corona Discharges
Corona discharges occur due to significant electrical imbalances during storms. Thunderclouds generate large negative charges, attracting positive charges from the ground. This positive charge ascends through trees, concentrating at the tips of leaves. The resulting electric field is intense enough to produce a faint glow visible in both visible light and UV.
The UV radiation created can break apart water vapor molecules, resulting in the formation of hydroxyl, a crucial atmospheric oxidizer. Hydroxyl plays an essential role in removing pollutants by reacting with airborne chemicals, transforming them into less harmful substances.
Implications for Air Quality
Previous research has indicated that corona discharges could significantly contribute to hydroxyl production within forest canopies, potentially influencing air quality and climate processes. This discovery highlights the importance of understanding these electrical phenomena for environmental health.
Innovative Observation Techniques
The researchers developed a Corona Observing Telescope System, a specialized instrument equipped with a UV-sensitive camera and atmospheric sensors. This system enabled them to capture 859 corona events on the sweetgum tree and 93 on a nearby loblolly pine, with each event lasting from mere seconds to several seconds.
"It's nearly invisible to the naked eye, but our instruments reveal vast areas of scintillating corona as thunderstorms pass," McFarland explained. "These widespread coronae could affect the removal of hydrocarbons emitted by trees and have broader implications for forest and atmospheric health."
Future Research Directions
While the confirmation of corona discharges is a significant step, many questions remain. Researchers are exploring whether these electrical events are beneficial or harmful to trees and how they might influence forest ecosystems. Collaborations with ecologists and biologists will further enhance understanding of these interactions.
This groundbreaking study was supported by the U.S. National Science Foundation, with contributions from Brune, Jenkins, and Miller as co-authors.
