Scientists Observe Trees Emitting Ultraviolet Light During Thunderstorms
For the first time, meteorologists have caught a glimpse of the tiny bursts of ultraviolet light emitted by trees during thunderstorms. This invisible phenomenon, known as a corona, is believed to be the result of electric currents induced in trees by passing storm charges.
While the existence of tree coronae had been suspected for some time, it wasn’t until a team led by Pennsylvania State University meteorologist Patrick McFarland went storm-chasing to gather hard evidence that it was confirmed. The glow produced by the build-up of charge in leaf tips had previously been recreated in a lab setting and inferred from changes in the electrical fields of forests during storms.
Thunderstorms are structures of immense electrical turbulence, with cumulonimbus clouds containing charges that can lead to lightning strikes. However, during less dramatic exchanges of charge, the imbalance can travel up a tree, building up at the leaves and emitting a faint corona of ultraviolet light.
McFarland and his team first observed tree coronae in the lab by simulating the phenomenon using small spruce and maple trees placed beneath charged metal plates. They then ventured into the wild, equipped with specialized tools mounted on a vehicle to capture the phenomenon in action.
The resulting video footage revealed clusters of ultraviolet signals across the branches of sweetgum and loblolly pine trees, with distinct bursts of light lasting from 0.1 to 3 seconds. These bursts behaved sporadically, moving from leaf to leaf and occasionally repeating on the same leaf.
Each corona emitted approximately 100 billion photons at a wavelength of around 260 nanometers per frame of the video. The researchers believe that similar effects can be observed in forests across the US east coast during thunderstorms.
The implications of these coronae on atmospheric chemistry, forest ecology, and thunderstorm electrification are still unclear. The team suggests that further research is needed to understand the potential impact of these electrical currents on trees and the environment, especially as thunderstorms are expected to increase in a warming climate.
The groundbreaking research on tree coronae was recently published in the journal Geophysical Research Letters.
