Lightning has long terrified and fascinated scientists and non-scientists alike. For something so relatively common, the precise atmospheric events that give rise to a lightning strike have been shrouded in mystery, but new research is offering some tantalizing clues.
A team of engineers and meteorologists believe they’ve cracked the curious case of how lightning forms in the cloudtops, and their solution comes from an increasingly influential contender for cracking climate mysteries: mathematical models. The paper describing the new model, published July 28 in the Journal of Geophysical Research, explains the interiors of lightning-imminent thunderclouds.
Within these clouds, powerful electric fields accelerate electrons, producing a harrowing flux of X-rays, electrons, and high-energy photons that crackle into a giant lightning bolt, the new research suggests. In addition to this groundbreaking theoretical insight, the researchers suggest that the unique mechanism creating lightning could pave the way for new X-ray sources.
For the study, a team of engineers and meteorologists built upon a previous model that simulated the physical conditions that produce lightning. Study senior author Victor Pasko, an electrical engineer at Pennsylvania State University, developed this model in 2023. Next, they compared their upgraded mathematical model with field observations collected by other research groups using ground-based sensors, satellite data, and high-altitude spy planes. In particular, they focused on identifying nearby terrestrial gamma-ray flash (TGF) events—invisible bursts of X-rays and radiowaves associated with lightning.
They found that electrons inside thunderclouds radiate energetic photons—X-rays—when the electrical field forces them to crash against the nitrogen and oxygen atoms in the air. This initiates an “avalanche” of new hypercharged electrons that transfer their energy to even more electrons, eventually unleashing a burst of photons that we see as a harrowing arc of light crackling across the sky.
“In addition to being produced in very compact volumes, this runaway chain reaction can occur with highly variable strength,” Pasko said in a statement. This variability also may explain the presence of “optically dim and radio silent” TGFs near thunderclouds, as the uneven distribution of these charged-up electrons is often accompanied by “detectable levels of X-rays, while accompanied by very weak optical and radio emissions.”
The new model also presents the “first fully time-dependent simulations” that can be generally applied to “events observed at different altitudes and quantitative comparisons with observations,” according to the paper. This differs from similar previous studies, which typically modeled a limited and localized area of thunderclouds, explained Zaid Pervez, study co-author and doctoral student at Pennsylvania State University.
Sometimes, the mysteries that are the closest to us take the longest time to explain. For me, what’s really neat about these newfound answers is that they’re often predicated on simple-yet-intuitive mathematical ideas. To list one recent example, scientists finally discovered how static electricity works by calculating shear, or how much a material bends when rubbed against another surface.
Of course, the math used in these studies isn’t like anything we’d see in elementary school, but the central concept driving these complex calculations is to work off a simple starting point. So far, this strategy seems to be working rather well.
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