It is not well known how lightning starts in a thunderstorm. With the newly developed 3D mapping and polarization system, physicists at the Los Alamos National Laboratory observed that some lightning not only began with positive high-speed discharges, but also faster and wider negative discharges soon began. Surprisingly, the signal polarization is tilted from the direction of the discharge propagation, and the polarization of the two opposite discharges rotates towards each other, indicating that the initiating high-speed discharge is not driven solely by the storm electric field. The authors analyzed these observations in a cosmic ray shower and found that these seemingly strange features could be consistently explained.
Lightning starts with a positive fast discharge followed by a faster, broader negative discharge observed in 3D. The signal polarization from the direction of discharge propagation tilts and rotates between two opposite high-speed discharges. These functions are through a cosmic ray shower that pretreats the discharge path and directs the direction of the discharge current. Image credit: ELG21.
“Scientists still don’t fully understand how lightning starts in a thunderstorm,” says Dr. Xuan-Min Shao, the lead author of the study.
“We noticed an unusual pattern of how lightning started using 3D radio frequency mapping and polarization techniques. Instead of a speedy electrical discharge, the flash of lightning quickly, faster, and negative emissions followed.”
Generally, after the opposition to electrical charge (positive and negative) is separated by clouds, lightning begins, resulting in the emissions that people consider lightning.
In their study, utilizing an innovative, Los Alamos-developed mapping and polarization system called BIMAP-3D, Dr. Xiao and colleagues observed that signal polarization from these discharges had a diagonal pattern from the direction of propagation.
This indicates that something other than the electric field played a role in the initiation of lightning.
In addition to being oblique, physicists have noticed that the direction of polarization has changed between positive and negative emissions.
They attribute this behavior to cosmic ray showers, high-energy particles from spaces entering the Earth’s atmosphere.
These cosmic rays can generate secondary high-energy electrons and positrons in the atmosphere, further ionizing the air, creating paths into thunder, and travel faster after lightning.
Researchers found that high-energy electrons and positrons are pushed in different directions by the Earth’s magnetic field and the cloud’s electric field, leading to oblique discharge currents, i.e. tilted polarization from the path of the cosmic ray shower.
Positrons and electrons were deflected in different directions of the electromagnetic field, explaining why they behaved differently between fast positive and negative discharges.
“This concept can also explain the common case that involves only high-speed positive discharges, and therefore the onset of most lightning flashes,” the scientist said.
Their result It was released on March 3rd Journal of Go Physical Research: Atmosphere.
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Xuan-Min Shao et al. 2025. 3D radio frequency mapping and polarization observations show that a flash of lightning was ignited by a cosmic ray shower. JGR atmosphere 130 (5): E2024JD042549; doi: 10.1029/2024JD042549
Source: www.sci.news
