Discovery of a New Class of Optical Discharges in the Lower Atmosphere

Thunderstorms are among nature's most powerful engines, churning out lightning, radio waves, and bursts of high-energy particles that rain down from the sky. For decades, scientists have known that these storms create intense electric fields near the ground, fields so strong they can accelerate electrons to nearly the speed of light. When these speeding electrons crash into air molecules, they can produce flashes of light, a phenomenon researchers have studied for years. However, the lower atmosphere, the space just beneath the storm clouds where humans live and breathe, remains a mysterious frontier. While the upper reaches of storms are well-mapped, the specific ways electricity behaves in the thin gap between the cloud base and the ground have been largely unexplored, leaving a gap in our understanding of how storms start, how they release energy, and how they might trigger the massive lightning bolts we see from afar.

A team of researchers at the Aragats research station in Armenia, perched high on a volcanic plateau, has now peeled back a layer of this mystery. By watching the sky with a suite of synchronized cameras, electric field sensors, and particle detectors, they discovered a new class of optical discharges that had been hiding in plain sight. These are not the familiar, jagged bolts of lightning that strike the ground, nor are they the faint, widespread glows sometimes seen above clouds. Instead, the team identified two distinct types of blue-violet light that appear directly beneath thunderclouds, and they found that the type of light depends entirely on the direction of the electric field just above the ground.

The story of this discovery unfolds through the eyes of cameras and sensors at the Aragats station, located at an altitude of 3,200 meters. Here, the ground is often covered in snow, and the air is thin, but the real drama happens when storm clouds drift low, sometimes hovering just 20 to 100 meters above the station's instruments. During several intense storm events between 2024 and 2026, the researchers watched the sky change its behavior in response to the invisible electric forces at play. They found that when the electric field near the ground pointed upward—a condition known as a positive field—the sky would light up with compact, detached blobs of blue-violet light. These glowing spots looked like isolated knots of energy, sometimes elongated, floating in the air. They were distinct, sharp, and appeared to be suspended at a specific height, hovering roughly 50 to 65 meters above the station.

In stark contrast, when the electric field near the ground flipped to point downward—a negative field—the nature of the light changed completely. The sharp, isolated blobs vanished, replaced by a diffuse, hazy glow that seemed to fill the entire camera view. This light was not a single point but a sprawling, filamentary network that looked like a soft, glowing cloud spreading out from the ground. The researchers observed that these diffuse glows often seemed to originate from the station's own structures, such as metal masts, antennas, and cables, which acted as focal points for the electricity. The light would branch out from these grounded objects, creating a large, fuzzy illumination that could cover a significant portion of the sky.

To understand exactly where these lights were coming from, the team used a technique called stereoscopy, which works much like human binocular vision. By using three cameras spaced apart to look at the same event from different angles, they could calculate the precise height of the glowing objects. The results were clear: the compact blue-violet blobs seen during positive electric fields were indeed elevated, floating in the air between the ground and the cloud base. However, the diffuse glows seen during negative fields could not be pinned down to a single point in the air. This failure to triangulate a single location was not a mistake in the measurement; rather, it confirmed that these glows were not single objects but widespread discharges spreading out from the ground up.

The researchers also tracked the behavior of high-energy particles and radio signals to piece together the full picture. They found that the compact blobs, which appeared during positive fields, were relatively quiet in terms of radio emissions. This silence suggested they were likely the visible heads of "streamers," which are self-propagating fronts of ionization that move through the air. These streamers are thought to be the initial steps of electrical breakdown, the tiny sparks that can eventually grow into a full lightning bolt. The fact that these streamer heads appeared in the gap between the cloud and the ground suggests that the storm's internal electric structure was reaching down, creating a bridge of ionized air.

Conversely, the diffuse glows during negative fields were accompanied by intense, rapid bursts of radio signals. This radio noise indicated a chaotic, high-energy process involving many small discharges happening all at once, consistent with the behavior of "corona" discharges. Corona occurs when the electric field is so strong at a sharp point, like the tip of a metal mast, that it rips electrons away from air molecules, creating a glowing, ionized sheath. The researchers concluded that when the electric field near the ground was negative, the storm was driving these discharges into the station's structures, creating the large, fuzzy glows that filled the sky.

One of the most significant findings was that these two types of light could appear in the same storm, separated by only minutes, as the electric field near the ground flipped back and forth. The team watched a storm on May 29, 2025, where the sky transitioned rapidly from compact, detached blobs to a large, diffuse glow as the electric field reversed. This rapid switching proved that the type of light was not determined by the weather conditions or the thickness of the clouds, but strictly by the polarity of the electric field. When the field pointed one way, the storm produced floating streamer heads; when it pointed the other, it triggered grounded corona discharges.

The study also clarified the relationship between these optical flashes and the high-energy particles that storms produce. While the researchers had previously seen bursts of gamma rays and electrons during storms, they found that these particle bursts could occur during both types of electric fields. This means that the presence of a positive or negative field near the ground does not tell the whole story about what is happening high up in the storm. The electric field near the ground acts more like a window into the lower part of the storm's structure, showing how the electricity is arranged at the bottom, rather than dictating the entire storm's behavior. For instance, the compact blue-violet blobs seen during positive fields were not evidence of a specific type of particle called a positron, as some had hoped, but rather a sign of streamer activity in a specific electric configuration.

By combining these optical observations with measurements of electric fields, particle counts, and radio waves, the researchers have established a new way to diagnose the health and structure of a thunderstorm. They have shown that the lower atmosphere is not a passive stage but an active participant in the storm's life cycle. The electric field near the ground dictates whether the storm creates floating, compact sparks or sprawling, grounded glows. This discovery opens a new window for scientists to watch how electrical discharges form and evolve, offering clues about how the tiny, invisible streamers that start in the lower atmosphere might eventually grow into the massive lightning strikes that define a thunderstorm. The work suggests that by simply watching the color and shape of the light beneath a cloud, and knowing the direction of the electric field, scientists can now distinguish between different fundamental processes of electrical discharge, turning a previously confusing array of sky glows into a clear, understandable map of atmospheric electricity.