Positron acceleration in thunderstorms

Imagine the sky during a thunderstorm not just as a place where rain falls, but as a giant, natural particle factory. Usually, scientists know this factory churns out bursts of high-energy electrons and gamma rays, a phenomenon called a Thunderstorm Ground Enhancement (TGE). It's like a cosmic firework show happening right above your head. But a new study from the Aragats Observatory in Armenia suggests that sometimes, this factory produces something even stranger: positrons.

Think of a positron as the "evil twin" or the antimatter mirror image of an electron. If an electron is a tiny ball of negative charge, a positron is its positive counterpart. When they meet, they annihilate each other in a flash of energy, creating a specific type of gamma ray called the 511-keV line.

For a long time, scientists thought these positrons were just a side effect, a messy byproduct of the main electron show. But the researchers, Chilingarian and Sargsyan, found evidence that positrons might have their own spotlight, their own stage, and their own timing.

The Mystery of the "Late Bloomer"

On May 16 and 17, 2026, the team at Aragats (sitting high up in the mountains of Armenia) watched the sky like hawks. They saw three distinct events, and the timing told a fascinating story.

In two of the events, the "ordinary" electron fireworks peaked first. But then, about 12 minutes later, a massive surge of positrons arrived. It was as if the main band finished their set, packed up their instruments, and then a surprise solo artist took the stage.

This delay is the smoking gun. If positrons were just a simple byproduct of the electron explosion, they would have happened at the exact same time. The fact that they waited suggests they are being driven by a completely different mechanism.

The "Two-Stage" Thundercloud

To explain this, the authors propose a clever model involving two separate "dipoles" (think of these as electrical magnets with a positive and negative end).

1. The Big Magnet (The Electron Dipole): This is the classic setup. A huge negative layer high up in the cloud pulls electrons down toward the ground. This creates the standard TGE electron bursts we've known about for years.
2. The Tiny, Localized Magnet (The Positron Dipole): This is the new discovery. Near the very bottom of the cloud, a small pocket of positive charge (called a Lower Positive Charge Region, or LPCR) forms. This pocket is often linked to graupel (soft hail) falling from the cloud.

Here's the magic part: This tiny positive pocket creates its own little electrical field right above the ground. Because it's positive, it acts like a magnet for the negative electrons, slowing them down. But for the positive positrons? It acts like a slide, accelerating them straight down toward the detectors.

The Perfect Storm Conditions

The paper notes that these "positron slides" only appear under very specific, almost cozy conditions:

• Extremely Low Clouds: The cloud base was so low it was only 38 to 50 meters above the detectors. That's like the cloud hovering just over the roof of a two-story house!
• Positive Electric Fields: The electric field near the ground flipped to positive, which is the signature of that lower positive pocket.
• Graupel Rain: The presence of soft hail confirmed the microphysics needed to build that lower pocket.

In one of the events (May 16), the electron burst was almost non-existent, yet the positron signal was still there, boosting the 511-keV line by about 15%. In the second event (May 17 at 14:26), the positron signal was even stronger, jumping 35% above normal levels, all while the electron signal was only a modest 5.9%.

What This Rules Out

The authors are careful to say this isn't just a fluke or a simple mix-up. They explicitly rule out the idea that the positrons are just a delayed echo of the main electron avalanche. If that were true, the peaks would happen together. They also distinguish these positrons from radon gas (a natural radioactive element in the air). While the storm did lift radon particles (seen in other gamma-ray lines), the timing and behavior of the positrons were different, proving they weren't just riding the same wind as the radon.

The Takeaway

So, what did we learn? Thunderstorms are more complex than we thought. They aren't just one giant accelerator for electrons. Instead, they can act like a multi-layered system where a small, localized pocket of charge near the ground can create a dedicated "positron highway."

The data suggests that when the cloud base drops low, soft hail falls, and the electric field near the ground turns positive, the storm temporarily creates a zone where antimatter (positrons) gets a head start, zooming down to Earth while the electrons get held back. It's a dynamic, shifting dance of charges that turns a thunderstorm into a temporary, localized factory for antimatter acceleration.

The authors measured these events directly with their detectors, so this isn't just a guess or a computer simulation; it's a real observation of nature doing something unexpected. While we don't know exactly how often this happens or how big these positron pockets get, the evidence from those two days in May 2026 strongly suggests that positron acceleration is a distinct, real phenomenon with its own rules.