By Hannah Grover
Despite how common lightning is — especially in New Mexico — scientists have never quite figured out what triggers a flash, but, thanks to a New Mexico research team, some of the mysteries are beginning to unfold.
Xuan-Min Shao of Los Alamos National Laboratory’s Electromagnetic Sciences and Cognitive Space Applications group hypothesized in a paper published nearly five years ago that high-energy particles from space play a key role in the formation of lightning.
Now Shao has more evidence backing up that hypothesis. Thanks to a radio frequency mapping system developed by Los Alamos scientists in 2021, Shao was better able to visualize what is going on inside a cloud before and during a lightning flash.
This allowed the team to see that a cosmic ray shower creates a type of path that leads up to the flash of lightning.
The researchers published their findings this month in the peer-reviewed journal JGR Atmospheres.
Shao, who has been working at the national lab since 1994, has been interested in lightning and discovering its origins since he was a graduate student pursuing a PhD at New Mexico Institute of Mining and Technology in the early 1990s.
He’s not the first scientist at Los Alamos National Laboratory to seek answers to what leads to flashes of lightning. Researchers at Los Alamos have been looking into the mysteries surrounding lightning for decades and Shao’s team’s discoveries build upon previous work. Shao provided a brief history of past research into what leads to lightning flashes in the introduction to the recent paper.
Lightning starts when opposing electrical charges are separated in clouds and result in a discharge of electricity that forms the lightning flash.
What Shao’s team noticed is the rapid positive discharge of electricity is followed by a faster, more extensive negative discharge.
Shao’s team also noticed that these discharges didn’t just follow the thunderstorm’s electric field, they were guided by ionized paths created by cosmic ray showers.
In the paper, Shao’s team notes that the evidence they documented “strongly favor[s] the inference that most lightning flashes are ignited by [cosmic ray showers].”
Los Alamos’ broadband radio frequency interferometric mapping and polarization system known as BIMAP-3D played a key role in helping Shao’s team tie the lightning flashes to cosmic-ray showers.
The BIMAP-3D system has two stations that are located about seven miles apart and each has four sets of antennas. By combining the 2D measurements from the two stations, scientists are able to construct 3D maps of the lightning flashes.
“All the lighting is starting inside a cloud, so you cannot really see it visually, and so that’s why we use a radio frequency mapping system.” Shao said.
BIMAP-3D allowed the researchers to visualize what is going on inside of the clouds with fairly high resolution.
The research into the origins of lightning ties directly into Los Alamos’ national security mission.
Lightning has similar radio frequency signals to a nuclear explosion.
Gaining a greater understanding of lightning will help the people in charge of nuclear weapons detection distinguish between whether radio frequency signals are caused by natural phenomena or a nuclear explosion.
“We need to understand that background to help us to improve our detection capability,” Shao said.
Shao isn’t done researching lightning and, he said, there are still more unanswered questions he wants to explore.