Although lightning is the most dramatic electrical force in a thunderstorm, it may not be the only thing that touches the forest canopy.

Scientists have observed for the first time that tree leaves emit tiny electrical sparks during active storms, revealing that the entire tree canopy can leak tiny electrical currents into the air.

In forests, instead of a single lightning strike, there can be thousands of subtle flickers of electricity, almost invisible electrical discharges that change the surface of leaves and can change the chemistry of the local atmosphere.

The researchers used an ultraviolet telescope mounted in a van to track bursts of coronal discharges that flitted across leaf tips as the storm passed overhead.

Meteorologist Patrick McFarland pennsylvania state university Repeated flashes have been recorded across multiple storms and tree species, suggesting that this silent exchange between sky and tree canopy may be more common than once thought.

Where electrical sparks occur

One summer thunderstorm provided the sunniest window ever. For 90 minutes, the ultraviolet camera remained fixed on three branches of a sweetgum tree as dark clouds loomed overhead.

During this period alone, researchers recorded 41 weak electrical leaks radiating from the sharp leaf tips.

Some flashes lasted up to three seconds, and the light frequently bounced from leaf edge to leaf edge as the storm charge moved higher into the sky.

“These things do happen. We’ve seen it. We know they exist now,” McFarland said.

recharge the canopy

Above the storm cloud, positive and negative charges drift apart, and opposite charges begin to build up on the ground below.

The accumulated charge moves through the roots and trunk of the tree towards the highest point and is concentrated at the tips of the leaves, where the air begins to conduct electricity.

When electrical charge leaks from a sharp edge, it forms a corona (short for corona discharge), emitting a faint glow much weaker than lightning.

Even if the secretion remains cool and localized and does not shatter the wood, it can still change the leaf surface.

UV light reveals hidden currents

Outdoors, the visible glow from the corona will be dimmed to be unnoticeable under storm clouds. So the researchers tuned their cameras to ultraviolet light (a band invisible to the human eye), allowing them to capture flashes that would otherwise go unnoticed.

A laboratory calibration then converted that ultraviolet light brightness into an electrical current, measuring about one millionth of an ampere drawn from a single electrical current. tree branch.

This step was critical because it is the electrical current, not the glow itself, that determines the amount of energy reaching the leaf.

The energy is concentrated in the sharp tips of the leaves. In laboratory tests, the corona appears to cause tissue charring and damage the cuticle, a waxy coating that helps leaves retain water.

A single burst may leave only a small scar, but repeated storms can gradually spread the damage to more leaves.

What is not yet clear is how the trees will react over time. Scientists still don’t know which species will recover quickly and which may lose their ability to photosynthesize for weeks or seasons if they don’t carefully check the site after a storm.

Electrical sparks reshape the air

In addition to scorching the tips of leaves, corona can also change the shape of the air that forests breathe during storms.

Charge leaking from the sharp edges of the wood can cause the formation of reactive chemicals. A 2022 study found that corona discharge can increase levels of hydroxyl radicals. Hydroxyl radicals are short-lived but powerful molecules that help scrub. pollutants Because of the atmosphere.

A surge in these chemical reactions can rapidly break down the natural gas released by the leaves, increasing local ozone and particle levels.

The effects may be concentrated near the tops of trees, as fast-moving storms and rainfall quickly weaken and wash out the explosion.

Still, each flicker represents a tiny pulse of atmospheric chemistry that repeats over and over again each time a thundercloud passes overhead.

Difficult to measure electric sparks in wood

The storm’s winds keep the leaves in constant motion, twisting and tilting their tips toward or away from the sky. The corona tends to flare where the leaf is most pointed straight up, and even small changes in angle can change the strength of the charge concentration.

Wet surfaces can also change the direction of the current to new edges, causing the glow to bounce unexpectedly from tip to tip. pine needleshad naturally sharp tips and exhibited similar flickering alongside hardwood species such as sweetgum.

This movement makes it difficult to understand the phenomenon. Ultraviolet telescopes could only frame small slices of the tree canopy at a time, and overlapping leaves sometimes blocked each other out.

The weak discharges likely fell below the camera’s detection threshold, making undercounts almost inevitable when estimating forest-wide activity.

Still, similar signals appeared across multiple tree species during four additional storm tracks from Florida to Pennsylvania.

“It will probably look like a pretty cool light show, like thousands of flashing ultraviolet light fireflies descending on the tree tops,” McFarland said.

Mapping sparks throughout the forest

With confirmation in the field, scientists can now move beyond proof of concept and begin tracking how often corona appears in different forests and how leaves react in the following days.

Working with ecologists, McFarland hopes to combine ultraviolet imaging with detailed leaf surveys to monitor surface damage and dryness after storms.

Add an air sensor nearby treetop While it could reveal how powerful each chemical burst can be, storm data could help link corona events to specific cloud settings.

Estimates of forest-wide impacts will remain rough until researchers map shine across stands and repeat those measurements over many storms.

Still, this study changed the way scientists think about storm-forest interactions, showing that trees and weather are connected through more than lightning, and that once-hidden electrical processes can be directly measured to improve tree health research and local atmospheric models.

This study Geophysical Research Letters.

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