Corona Discharges - Electrical Storms

Introduction to Corona Discharges

Scientists have directly observed tiny electrical discharges, known as coronae, glowing and moving across tree leaves during thunderstorms, confirming a phenomenon suspected for more than 70 years.

Using a specially equipped research vehicle fitted with an ultraviolet camera, researchers recorded 859 electrical signals on a sweetgum tree and another 93 on a loblolly pine in North Carolina.

Background and History

The concept of corona discharges on trees has been a topic of interest for scientists for over seven decades, with initial suspicions arising from observations of unusual electrical activity during thunderstorms.

However, it wasn't until the development of advanced technology, such as ultraviolet cameras and mobile measurement systems, that researchers were able to directly observe and record these events.

Methodology

The research team developed a mobile measurement system called the Corona Observing Telescope System (COTS) to detect the faint ultraviolet radiation produced by corona discharges.

The equipment was mounted vertically inside a research vehicle, allowing the telescope to observe treetops through a periscope installed on the vehicle's roof.

The system included a specialised ultraviolet camera capable of detecting wavelengths between 255 and 273 nanometres.

Key Equipment

• GPS receiver
• Electric field mill
• Weather station
• Laser rangefinder

Results

On 27 June 2024, researchers observed electrical discharges on two trees during a thunderstorm at the University of North Carolina Pembroke in North Carolina.

Using a specially equipped research vehicle, they first monitored a sweetgum tree from approximately 32 metres away for around 1.5 hours before moving to a loblolly pine tree 28 metres away for another 20 minutes.

During the sweetgum observations, the team recorded 859 ultraviolet signals across three branches, grouped into 41 corona clusters.

Corona Discharge Movement

The researchers found that corona discharges did not remain in one location on a tree.

Instead, they appeared intermittently across different leaves and branches.

Some ultraviolet signals followed the movement of leaves and branches as they swayed in the wind, helping the team confirm that the emissions were associated with the trees rather than unrelated sources of radiation.

Implications

The study also established a relationship between the intensity of corona discharges and the electrical current flowing through trees.

To investigate this connection, researchers conducted separate laboratory experiments using approximately one-metre-tall spruce and maple trees exposed to enhanced electrical fields.

By measuring the electrical current through the trees and comparing it with the ultraviolet signals detected by the COTS camera, they developed a way to estimate the current associated with the observed discharges.

Potential Effects on Forest Environments

The findings also raise questions about the effects of these electrical discharges on forest environments.

Coronae and their ultraviolet radiation can produce hydroxyl radicals, known as OH, which play an important role in atmospheric chemistry.

Previous research cited in the study estimated that coronae could produce approximately 10¹⁷ to 10¹⁸ hydroxyl radical molecules around a treetop during a thunderstorm.

Expert Perspective

According to experts in the field, the discovery of corona discharges on trees has significant implications for our understanding of forest ecosystems and atmospheric chemistry.

Further research is needed to fully understand the effects of these discharges and to explore potential applications in fields such as forestry and environmental science.

Implications for Readers in India

The study's findings have global implications, including for readers in India, where thunderstorms are a common occurrence during the monsoon season.

Understanding the effects of corona discharges on trees and forest environments can inform strategies for sustainable forestry and environmental management in India and other countries.

What to Watch Next

As researchers continue to explore the phenomenon of corona discharges on trees, several areas of study are likely to emerge as key priorities.

These include investigating the effects of corona discharges on different tree species, exploring the relationship between corona intensity and electrical current, and examining the potential applications of this research in fields such as forestry and environmental science.

Conclusion

The researchers concluded that their work provides the first direct observations of corona discharges on trees during thunderstorms, along with measurements of their ultraviolet emissions and estimated electrical currents.

They also noted that further research is needed to establish a universal relationship between corona intensity, electrical current and the electric fields surrounding treetops across different tree species and forest environments.