Corona Discharges on Trees During Thunderstorms

Introduction

Thunderstorms generate enormous electrical energy that we observe as lightning. Scientists have long suspected that this electricity also flows through tall objects such as trees, producing faint ultraviolet glows known as corona discharges.

These electrical glows were predicted nearly a century ago, but scientists had never directly observed them in natural forests until recently. A new study published in Geophysical Research Letters has provided the first direct evidence of this phenomenon.

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What Are Corona Discharges?

A corona discharge is a type of electrical discharge that occurs when the electric field around an object becomes strong enough to ionise the surrounding air but not strong enough to produce a lightning strike.

Characteristics:

• Produces a faint glow of ultraviolet light

• Occurs around sharp or pointed objects

• Common during high electric fields in thunderstorms

Trees are particularly suitable for corona discharges because:

• branches and leaves have sharp tips

• tall trees are exposed to strong electric fields during storms

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The New Discovery

Scientists from Pennsylvania State University used a new instrument called the Corona Observing Telescope System (COTS).

This mobile system allowed researchers to observe corona discharges directly in forests during thunderstorms.

Key features of COTS

• special ultraviolet-sensitive camera

• mounted on a research vehicle

• capable of detecting light invisible to the human eye

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Why Ultraviolet Detection Was Important

Corona discharges emit ultraviolet radiation.

Normally, detecting UV radiation during daytime is difficult because sunlight also contains UV light.

However, the study took advantage of the Ozone Layer, which blocks a particular wavelength of ultraviolet sunlight.

This allowed the instrument to detect the faint glow produced by electrical discharges.

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Observations in Forests

During a thunderstorm in North Carolina, researchers observed corona discharges on:

• sweetgum trees

• loblolly pine trees

The ultraviolet glow was not stationary. Instead, it:

• jumped between leaves and branches

• followed branches moving in the wind

• lasted from fractions of a second to a few seconds

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Electrical Characteristics

Scientists measured the brightness of the glow and linked it to electrical current.

Key findings:

• A typical discharge produced about 100 billion photons

• Corresponded to roughly one microampere of electrical current

Although this current is very small individually, the researchers found that during thunderstorms:

• corona discharges occur across entire forest canopies

• combined currents may become significant

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Environmental Impact

Corona discharges affect atmospheric chemistry.

They produce Hydroxyl Radical (OH).

This molecule is often called the “detergent of the atmosphere” because it removes pollutants such as hydrocarbons.

Effects include:

• improving air quality

• influencing atmospheric chemistry around forests

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Impact on Trees

The electrical surges associated with corona discharges can also affect vegetation.

Possible effects include:

• burning tiny leaf tips

• causing minor permanent damage to plant tissues

However, these effects are generally small.

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Why This Discovery Matters

This research improves our understanding of:

• interactions between forests and thunderstorms

• atmospheric electricity

• atmospheric chemistry

It also opens a new field of study on how forests influence storm electrification and air chemistry.

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Relevance for UPSC

Prelims

• atmospheric electricity

• ozone layer and ultraviolet radiation

• hydroxyl radical chemistry

GS-III

• environmental science

• atmospheric chemistry

• climate and weather interactions

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Conclusion

The first direct observation of corona discharges on trees represents a major advance in atmospheric science. The discovery shows that forests are not passive during thunderstorms but actively participate in atmospheric electrical processes.

By revealing how corona discharges influence air chemistry and forest ecosystems, the study provides new insights into the complex interactions between weather systems, vegetation, and the atmosphere.