Corona discharges represent weak electrical emissions created when atmospheric electrical fields intensify near sharp points, like leaf tips, and ionize surrounding air molecules. Though well-studied in laboratory settings, capturing their presence on living trees outdoors has long eluded researchers due to their tenuous glow and the challenge of isolating them from ambient light conditions during storms. The research, now published in Geophysical Research Letters, overturns century-old scientific assumptions by documenting such discharges under natural thunderstorm conditions for the first time.

The genesis of these woody coronae lies in the interplay between the thunderstorm’s overhead electrical charge and the induced countercharge in the earth below. Thunderstorms often accumulate significant charge within their cloud bases, creating strong electrostatic fields extending toward the ground. This field induces an opposing charge in terrestrial surfaces—especially at elevated points such as tree canopies—leading to an accumulation of electrical charge on leaf tips. When this charge concentration reaches a critical threshold, it causes a discharge of electricity into the surrounding air, ionizing it and creating characteristic corona emissions.

One of the study’s pioneers, Patrick McFarland, a meteorologist based at Pennsylvania State University, recalls how reproducing these coronae in controlled laboratory environments provided a crucial glimpse into their nature. By placing leaves beneath charged plates in near-total darkness, his team observed the faint ultraviolet blue glows characteristic of corona discharges. These displays are typically masked in natural environments by the general brightness of daylight or even twilight, highlighting the challenge faced in detecting them in the wild.

Further experiments revealed that the intensity of UV radiation emitted by coronae correlates closely with the electrical current passing through tree tissues. This finding not only confirms the electrical nature of these discharges but also suggests a possible avenue to non-invasively monitor electrical currents within trees during storms. Past research dating back to the mid-20th century had already flagged such currents as potentially damaging to plants, given that electrical flow can disrupt cellular membranes and degrade chloroplasts responsible for photosynthesis.

To break through the obstacles of field observation, the researchers leveraged an innovative approach: outfitting a 2013 Toyota Sienna minivan with an array of sensitive instruments. This includes an electric field detector, a laser rangefinder, and notably, a roof-mounted periscope channeling light into an ultraviolet-sensitive camera. By catching UV emissions otherwise invisible to human eyes and ordinary cameras, this mobile lab enabled the team to chase thunderstorms and systematically scan treetops for corona activity.

Daily expeditions involved braving intense storms while carefully aiming cameras at specific tree branches—such as those of sweetgum and loblolly pine—across various sites stretching from Florida northward to Pennsylvania. The data accrued demonstrated not sporadic, but rather prolific corona generation. Over 90 minutes of storm monitoring in one instance revealed at least 41 distinct corona discharges flickering intermittently on leaf tips, each lasting up to several seconds and sometimes racing from leaf to leaf in near choreographed patterns.

The ubiquity of corona discharges during thunderstorms is striking. McFarland hypothesizes that these discharges likely illuminate every treetop beneath storm cells, collectively creating a vast, albeit faint, spectacle of blue UV light reminiscent of swarms of bioluminescent insects. Yet, this electrical light show is more than just atmospheric artistry—it carries important biological implications. The repetitive bombardment of coronae can physically scorch leaf tips, evidenced by visible burn marks after only seconds of exposure.

Such damage might go beyond superficial burns. The researchers speculate that corona-induced electrical stress could degrade the cuticle, the protective waxy barrier shielding leaves from UV damage and dehydration. Since trees endure countless thunderstorms annually, the cumulative impact could influence leaf longevity and overall canopy health. This opens intriguing questions about whether trees have evolved structural or physiological traits in response to persistent corona damage to minimize harm over evolutionary time scales.

Looking ahead, McFarland envisions multidisciplinary collaboration to deepen understanding of coronae’s ecological role. Partnerships with forest ecologists and botanists could unravel how these electrical phenomena affect plant physiology, growth patterns, and forest ecosystem dynamics. Assessing whether certain species exhibit adaptations to withstand or mitigate corona effects is another promising frontier.

This paradigm-shifting discovery underscores the complex and intimate connections between atmospheric electricity and terrestrial ecosystems. It illuminates a hidden layer of interaction where thunderstorms not only deliver rain and lightning but also subtly electrify forest canopies in a dazzling yet imperceptible display. As detection technologies advance, researchers anticipate new insights into the electrical life pulsing through forests during storms, with potential ramifications for climatology, plant biology, and forestry management.

Ultimately, this first-ever field documentation of tree corona discharges opens a new chapter in understanding how natural electrical phenomena shape our planet’s biosphere. The faint sparkles of UV coronae serve as a reminder that even the mightiest forces of nature express themselves in subtle, unseen ways—transforming our perception of the stormy mingling between sky and forest.

Subject of Research: Electrical phenomena (corona discharges) from tree canopies during thunderstorms and their ecological impacts
Article Title: Corona Discharges Glow on Trees Under Thunderstorms
News Publication Date: 12-Feb-2026
Web References: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025GL119591
References: McFarland et al., Geophysical Research Letters, 2026
Keywords: corona discharges, thunderstorms, tree canopy, electrical field, ultraviolet emissions, atmospheric electricity, plant physiology, forest ecology, electrical currents in plants, ultraviolet camera, lightning, environmental stress

Lightning, a dynamic and complex physical process, is traditionally perceived as a brief, localized electrical discharge confined to a storm cloud or its immediate vicinity. However, this megaflash shattered those assumptions by traversing an extraordinary horizontal distance. Such an extreme event pushes the boundaries of atmospheric physics and brings to light the intricate electrical structures within vast thundercloud systems. Research spearheaded by Arizona State University’s Professor Randy Cerveny, an expert in geographical sciences and urban planning, underscores the evolving capabilities of our observational technologies and the need to rethink the scale at which atmospheric electricity operates.

Historically, lightning detection relied heavily on ground-based antenna networks designed to capture the radio emissions generated during electrical discharges. These systems triangulate lightning positioning by calculating the time differences at which radio signals arrive at multiple stations. While effective, they were limited in spatial coverage and resolution, often missing or underestimating lightning with extreme horizontal reach. The introduction of space-based lightning detectors, particularly from 2017 onward, has revolutionized the field by enabling continuous and highly accurate monitoring of these transient events on continental and even global scales.

The GOES-16 satellite, positioned in a stable geostationary orbit, carries the Geostationary Lightning Mapper (GLM), a state-of-the-art instrument capable of capturing lightning flashes with millisecond precision. This technological leap allows scientists to document not just the occurrence of flashes but also the complex branching structures and polarity distributions, painting an unprecedentedly detailed electrical map of storms from above. GOES-16 detects roughly one million lightning flashes daily, providing vast amounts of data critical for understanding both routine weather patterns and rare phenomena like the megaflash.

Megaflashes themselves are defined by their extraordinary horizontal extent—stretching at least 60 miles (100 kilometers). The 2017 event far exceeded this threshold, measuring 515 miles, a length that rivals the span of several U.S. states. These massive discharges form primarily within robust, long-lived thunderstorms that persist for upwards of 14 hours and cover areas on the order of thousands of square miles. They are characterized by complex branching, with typically five to seven individual ground-striking pathways radiating from the main lightning channel. Such large-scale electrical activity challenges prevailing models of atmospheric conductivity and charge separation within convective clouds.

The rarity of megaflashes is underscored by satellite data analyses revealing that under 1 percent of thunderstorms produce flashes of this scale. Yet, while they remain exceptional, the existence of megaflashes compels a fresh look at lightning risk assessment. Traditionally, individuals have underestimated the danger posed by lightning, assuming that its reach is closely confined to the immediate vicinity of a storm cloud. Meteorologists now emphasize that lightning can commonly strike far beyond the apparent edges of a thunderstorm, sometimes 10 to 15 miles away, and occasionally over hundreds of miles, as evidenced by megaflash phenomena.

Understanding the mechanics behind megaflashes requires integrating multiple scientific disciplines including atmospheric physics, cloud microphysics, and electrical engineering. The electrical charge structure within a thunderstorm is highly stratified, with positively and negatively charged regions often separated both vertically and horizontally. Megaflashes navigate this complex electrical landscape, propagating through channels of ionized air that can span vast distances, supported by the storm’s enormous energy and dynamic airflow patterns. These discharges reveal intricate details about how charge accumulates, migrates, and dissipates within mesoscale convective systems.

From a technological and observational standpoint, the combined efforts of NOAA’s GOES satellites and similar instruments deployed by European and Chinese space agencies have created comprehensive global coverage of geostationary lightning mapping. This international collaboration not only supports the identification of regional lightning hotspots but also advances data processing algorithms capable of distinguishing true lightning channels from noise and artifacts in massive datasets. Enhanced temporal and spatial resolution empowers meteorologists to track lightning development and evolution in near real-time, critical for weather forecasting and public safety.

The implications of these findings extend beyond academic curiosity. Lightning continues to impose a significant human toll annually, causing between 20 to 30 fatalities and hundreds of injuries in the United States alone. Many of these incidents occur before a storm peaks or after it appears to have passed, times when the perceived threat is diminished. The discovery and characterization of lightning megaflashes bolster the understanding that hazardous electrical activity can persist far from visible storm cores, reinforcing guidelines recommending that individuals wait at least thirty minutes after the last thunderclap before resuming outdoor activity.

In sum, the study of the 2017 record-setting megaflash underscores how emergent satellite technologies and refined analytical tools are reshaping meteorological science. By extending measurement capabilities beyond traditional ground-based networks, researchers now appreciate the multifaceted nature of lightning, stretching across extraordinary distances with complex electrical architecture. Continued monitoring and investigation promise to uncover even more extreme events, refining existing models and ultimately enhancing both scientific knowledge and public safety measures regarding one of nature’s most electrifying spectacles.

This breakthrough discovery not only provides critical insights into the physics of lightning but also serves as a reminder of the persistent unpredictability inherent in atmospheric phenomena. As our observation platforms become more sophisticated and expansive, the potential for identifying previously unknown extremes grows, challenging scientists to develop new theories and adaptation strategies. The 515-mile megaflash stands as a stunning testament to nature’s capacity for scale and power, captured only through the lens of advanced technology and multidisciplinary research collaboration.

Subject of Research: Not applicable
Article Title: [Not provided]
News Publication Date: [Not provided]
Web References:
– https://wmo.int/activities/world-weather-climate-extremes-archive
– http://journals.ametsoc.org/doi/10.1175/BAMS-D-25-0037.1
– https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2023EA002920
References: Bulletin of the American Meteorological Society report
Image Credits: World Meteorological Organization, American Meteorological Society

Keywords

Lightning, Cloud physics, Atmospheric physics, Extreme weather events, Storms, Clouds, Meteorology