A faint electrical glow on trees during thunderstorms has been directly observed for the first time.
A research team led by Pennsylvania State University has documented the first direct observations of corona discharge—a faint electrical glow—on trees during thunderstorms. The phenomenon, previously theorized but only observed in laboratory settings, was recorded using specialized equipment mounted on a research vehicle.
Observation Method
The team used a modified 2013 Toyota Sienna equipped with a weather station, electric field detector, laser rangefinder, and a roof-mounted periscope. The periscope directed light into an ultraviolet camera sensitive to wavelengths between 255 and 273 nanometers. This wavelength range is typically blocked by the Earth's ozone layer, meaning detected UV light indicates electrical discharge rather than solar radiation.
Field Observations
During a thunderstorm in Pembroke, North Carolina, the instrument was aimed at a sweetgum tree and a loblolly pine. The camera recorded hundreds of UV flashes along branches over several hours. The team documented 41 distinct bursts of UV signals from sweetgum leaves, each lasting between 0.1 and 3 seconds. These bursts moved from leaf to leaf and occasionally repeated on the same leaf. Similar activity was recorded during four additional storms from Florida to Pennsylvania, on different tree types.
Mechanism
Scientists explain that corona discharges form when thunderstorm clouds build up strong negative charges, attracting positive charges on the ground. The positive charge rises through trees, creating an electric field at leaf tips strong enough to produce a weak corona glow. Each corona emitted approximately 100 billion photons at a wavelength of around 260 nanometers per video frame.
Electrical Measurements
By counting UV photons, researchers estimated each corona carried approximately one microamp of current. Laboratory experiments with potted spruce and maple trees confirmed the relationship between UV glow brightness and electrical current, providing a method to estimate electrical current from glow intensity.
Potential Implications
Researchers have identified several areas where these coronae may have effects:
- Atmospheric chemistry: Corona discharges produce hydroxyl radicals, which help remove hydrocarbons and pollutants from forest air.
- Tree health: The discharges can cause gradual damage to leaf tips, particularly in areas with frequent thunderstorms. The long-term effects of repeated electrical surges on trees globally are not yet fully understood.
- Thunderstorm electrification: Charged particles released by coronae may influence thunderstorm behavior by feeding energy back into the storm system.
The research team recommends re-evaluating the impacts of these coronae on atmospheric chemistry, forest ecology, health, evolution, and thunderstorm electrification, particularly as thunderstorm activity may change with climate conditions.
Background
Scientists have theorized about corona discharge on trees for approximately 100 years. Prior to this direct observation, researchers had recreated the glow in laboratory settings and inferred its presence from alterations in electrical fields of forests during storms. The findings were published in the journal Geophysical Research Letters.