Trees Glow During Thunderstorms: Scientists Capture Electrical Discharges

During a thunderstorm, it’s straightforward to focus on the immediate dangers of lightning and heavy rain. But a subtler, almost magical phenomenon may be occurring right above our heads: treetops emitting a faint glow. This isn’t a latest observation – scientists have long been intrigued by what’s known as Saint Elmo’s fire – but recent research is beginning to reveal how and why trees appear to sparkle with electricity during stormy weather.

A Century-Old Mystery, Newly Illuminated

The phenomenon of Saint Elmo’s fire, a luminous plasma discharge seen on pointed objects like ship masts and aircraft wings, has been documented for centuries. It’s a visible manifestation of a strong electrical field. What’s more recent is the investigation into whether similar electrical discharges occur on trees, specifically at their highest points, during thunderstorms. Researchers at Penn State University have been at the forefront of this inquiry, initially sparked by a simple observation during a lunchtime conversation. As meteorologist Patrick McFarland recounts, his advisor, William Brune, wondered aloud if trees might glow under thunderstorm conditions.

That initial question led to laboratory experiments. McFarland and his team recreated thunderstorm conditions on a smaller scale, using a high-voltage plate to simulate the atmospheric charge and a tree branch grounded with an electrical plate. The result? A faint blue glow, a corona discharge, emanating from the branch. This glow, whereas barely visible, included both blue light and ultraviolet (UV) radiation. The team’s findings were published in the February 28 issue of Geophysical Research Letters. Read more about the research at The New York Times

From Lab to Field: Chasing Thunderstorms in a Retrofitted Van

Confirming the lab results in a natural setting proved challenging. The team needed to detect these faint UV emissions amidst the chaos of a thunderstorm. To do so, they equipped a 2013 Toyota Sienna van with specialized instruments, including a roof-mounted periscope directing light to an ultraviolet camera capable of detecting the coronae. Florida, known for its frequent thunderstorms due to sea breezes from the Atlantic Ocean and the Gulf of Mexico, became their primary hunting ground.

However, simply finding a thunderstorm wasn’t enough. The team needed a location with tall trees, public access, and the time to set up their equipment safely. Serendipity played a role when a storm formed while they were driving back to Pennsylvania, leading them to Pembroke, North Carolina. There, they observed a sweetgum tree and a loblolly pine for 90 minutes, capturing video of the electrical activity.

Dancing Lights: Observing Coronae in the Wild

The video revealed 41 coronae, brief electrical discharges lasting no more than three seconds each. These weren’t static glows; they moved dynamically, flickering and jumping between leaves and branches swaying in the wind. The team also observed similar, though less extensive, coronae during storms in Florida and Pennsylvania, suggesting the phenomenon is widespread.

A corona discharge occurs when the electric field around a pointed object, like a tree branch, becomes strong enough to ionize the air molecules. This ionization releases energy in the form of light. The strength of the electric field is influenced by factors like atmospheric conditions and the shape of the object. MIT News explains how airplanes counteract similar electrical phenomena, known as St. Elmo’s fire, during thunderstorms, offering insight into the principles at play.

What Does This Mean? Understanding the Electrical Landscape of Storms

While the study doesn’t explain the broader implications of these tree-top coronae, it adds another layer to our understanding of the complex electrical processes within thunderstorms. It suggests that trees aren’t simply passive observers of these storms, but active participants in the electrical landscape. The researchers hypothesize that these discharges may play a role in transferring charge between the atmosphere and the ground, potentially influencing lightning initiation. However, more research is needed to confirm this.

It’s important to note the limitations of the study. The observations were made during a limited number of storms, and the equipment’s sensitivity may have prevented the detection of fainter coronae. The study focused on specific tree species; it’s unclear whether other species exhibit similar behavior.

Beyond the Sparkle: The Ongoing Pursuit of Atmospheric Understanding

The team plans to continue their research, aiming to improve their detection capabilities and observe a wider range of storms and tree species. They also hope to investigate the relationship between these coronae and lightning activity. Understanding these processes could have implications for improving lightning prediction and safety measures. Plane + Pilot Magazine details the dangers of lightning strikes and the importance of understanding atmospheric electricity.

The discovery of these tree-top coronae is a reminder that even in well-studied phenomena like thunderstorms, Notice still surprises to be found. It highlights the importance of curiosity-driven research and the power of combining laboratory experiments with real-world observations. As McFarland notes, the initial question arose from a simple observation, demonstrating that sometimes, the most intriguing discoveries begin with just looking up.