During thunderstorms, while we may seek shelter, a fascinating phenomenon occurs among the treetops: an invisible light show generated by weak electrical discharges known as coronae. This remarkable occurrence has been captured in unprecedented detail by a team led by Penn State meteorologist Patrick McFarland, who modified a Toyota Sienna to serve as a mobile laboratory for their research.
Using a specialized ultraviolet camera mounted on the vehicle, the researchers recorded the coronae that dance along the tips of leaves during storms. Unlike the intense heat of lightning, coronae produce only a slight increase in temperature, making them difficult to observe without the right equipment. Until recently, their existence was inferred from changes in electric fields rather than direct observation.
Innovative Research Methods
To study these elusive electrical phenomena, McFarland's team first simulated storm conditions indoors. In a controlled environment, they discovered that coronae emit a faint blue glow, detectable only in complete darkness. However, tracking this glow in natural conditions proved challenging due to the overpowering ambient light during thunderstorms.
The team outfitted their modified Sienna with essential instruments, including a GPS and an electric field mill. The highlight of their setup was a roof-mounted periscope that directed light to their UV-sensitive camera, allowing them to observe the coronae in real-time.
The Mechanics of Tree Electrification
The process begins high in the storm clouds, where electrical charges can induce a corresponding charge in the ground below. This attraction causes the charge to travel along the tallest structures, such as tree trunks, and ultimately to the leaf tips. When the electric field intensity reaches a critical point, it discharges into the air, creating the corona effect.
During a storm in Pembroke, North Carolina, the team captured 41 distinct clusters of coronae over 90 minutes, with the discharges lasting from fractions of a second to over three seconds. This phenomenon was not limited to one species; similar behavior was observed in multiple tree types across different locations.
The Broader Implications
These electrical discharges may have significant ecological implications. The hydroxyl radicals produced during corona discharges are known to be powerful oxidizers, playing a crucial role in breaking down greenhouse gases and pollutants in the atmosphere. Early estimates suggest that coronae generate thousands of times more hydroxyl radicals around treetops than all other sources combined.
As climate change leads to more frequent and intense thunderstorms, understanding the relationship between trees and atmospheric electricity could be vital for improving our knowledge of forest ecosystems and their role in air quality. The findings of this research highlight the importance of trees not just as passive organisms but as active participants in the atmospheric chemistry that supports life on Earth.
This groundbreaking study was published in the journal Geophysical Research Letters.
