Lightning Might Be Irradiating Our World Without Ever Showing Its Face. Here’s How.

Here’s what you’ll learn when you read this story:

Scientists have long understood why lightning forms, but the atomic processes at the core of the phenomenon have remained largely a mystery—especially the strange mechanics behind terrestrial gamma-ray flashes (TGFs).
A new study combines ground-based observation with mathematical models to detail the high-energy photons and X-rays responsible for TGFs.
This gives scientists one of the clearest pictures yet of exactly how lightning forms within a thundercloud.

When it comes to lightning, it only takes learning a few facts to learn that these brief moments of raw atmospheric power have precisely zero chill. For one, there are roughly 8.6 million lightning strikes on Earth per day, and those terrifying bolts can temporarily superheat the surrounding air to a toasty 50,000 degrees Fahrenheit (a.k.a. five times hotter than the surface of the Sun). Incredibly, lightning can even briefly produce gamma-rays, which are typically spewed from things like supernovae or black hole jets.

In other words: when lightning goes, it goes hard.

While scientists have a pretty firm grasp on why lightning forms in cumulonimbus clouds, they don’t exactly understand the atomic phenomena underpinning the phenomenon. Why, exactly, does lightning produce electromagnetic energy that rivals some of the most intense celestial ongoings in the universe? Now, in a new study from Pennsylvania State University, scientists used mathematical models combined with ground observations to discern the exact atomic workings that create lightning bolts in the first place. The results of the study were published in the journal JGR Atmospheres.

“By simulating conditions with our model that replicated the conditions observed in the field, we offered a complete explanation for the X-rays and radio emissions that are present within thunderclouds,” Victor Pasko, lead author of the study from Penn State, said in a press statement. “We demonstrated how electrons, accelerated by strong electric fields in thunderclouds, produce X-rays as they collide with air molecules like nitrogen and oxygen, and create an avalanche of electrons that produce high-energy photons that initiate lightning.”

Two years ago, Pasko and his team published a Photoelectric Feedback Discharge model, which simulates conditions ripe for lightning activity. And earlier this year, an unrelated study from the University of Osaka observed and detailed the extremely brief moments of terrestrial gamma-ray flashes, or TGFs, using a multi-sensor set-up. They found that TGFs appeared 31 microseconds before connection of the discharge path with the full burst lasting another 20 microseconds after the two discharge paths—one from the ground and one from the air—meet.

This new study wanted to understand why these TGFs were often produced without flashes of light or radio wave bursts. Driven by the photoelectric effect, which explains how materials or atoms release electrons when struck by light, the variable strength of the runaway chain reaction that occurs in lightning bolts can precisely produce these initially unintuitive conditions.

“In our modeling, the high-energy X-rays produced by relativistic electron avalanches generate new seed electrons driven by the photoelectric effect in air, rapidly amplifying these avalanches,” Pasko said in a press statement. “In addition to being produced in very compact volumes, this runaway chain reaction can occur with highly variable strength, often leading to detectable levels of X-rays, while accompanied by very weak optical and radio emissions. This explains why these gamma-ray flashes can emerge from source regions that appear optically dim and radio silent.”

Lightning has long been an atmospheric phenomenon on Earth, and one leading theory even speculates that it might have helped kickstart life on the planet. Now, a couple billion years later, that life is finally revealing its high-energy secrets.

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