The genesis of lightning within thunderstorms remains an area of considerable scientific obscurity. Leveraging a sophisticated, newly engineered system for 3D spatial representation and polarization analysis, investigators at the Los Alamos National Laboratory have ascertained that certain lightning discharges commence not only with a rapid positive polarity surge but are subsequently and instantaneously succeeded by an even more accelerated and extensive surge of negative polarity. Intriguingly, the observed polarization alignment deviates from the trajectory of the discharge’s propagation, and the polarization characteristics of these two opposing discharges exhibit a mutual rotation, thereby suggesting that the initial rapid discharges were not solely dictated by the ambient electrical field of the storm. A comprehensive analysis by the research team, correlating these findings with the phenomenon of cosmic-ray showers, has revealed that these seemingly anomalous features can be elucidated in a coherent manner.
Lightning initiates with a swift positive charge expulsion, followed by an even more rapid and widespread negative charge expulsion, as documented in three dimensions; the polarization signals diverge from the discharge’s path and rotate relative to each other between the two opposing rapid discharges; these characteristics are attributable to cosmic-ray showers that pre-established the discharge conduit and dictated the current’s direction. Image courtesy of ELG21.
“The precise mechanisms by which lightning originates within tumultuous atmospheric conditions are not yet fully comprehended by the scientific community,” stated Dr. Xuan-Min Shao, the principal investigator of this research endeavor.
“Employing our advanced 3D radio frequency mapping and polarization instrumentation, we detected an atypical sequence in the initial phases of lightning; rather than a solitary rapid positive electrical discharge, the lightning events were swiftly followed by an even swifter discharge of a negative electrical nature.”
Fundamentally, lightning genesis transpires subsequent to the separation of opposing electrical potentials—positive and negative—within cloud formations, culminating in an electrical discharge perceived by observers as lightning.
During their investigation, which utilized a novel mapping and polarization apparatus, designated BIMAP-3D, developed at Los Alamos, Dr. Shao and his associates meticulously recorded the signal polarization emanating from these discharges. They observed that this polarization exhibited a lateral orientation relative to the direction of propagation, indicating that factors beyond the storm’s inherent electric field were influential.
This observation strongly implies that influences extraneous to the prevailing electrical field played a significant role in initiating the lightning phenomenon.
Beyond the peculiar slanting, the physicists further discerned that the orientation of the polarization underwent a transformation between the positive and negative discharge phases.
This observed behavior was posited to be a consequence of cosmic-ray showers, which consist of high-energy subatomic particles originating from outer space that traverse Earth’s atmosphere.
These incoming cosmic rays engender secondary, energetic electrons and positrons within the atmospheric medium. These particles, in turn, further ionize the air, thereby establishing conductive pathways within cumulonimbus clouds, which facilitates the initiation and rapid progression of lightning.
The researchers deduced that the high-energy electrons and positrons were subject to disparate directional influences from both the Earth’s geomagnetic field and the electrical field present within the clouds. This differential influence resulted in a diagonally oriented discharge current, which corresponds to the observed slanted polarization originating from the trajectories established by the cosmic-ray showers.
The positrons and electrons, being deflected in divergent paths by the electromagnetic field, were responsible for the differentiated behavior observed between the swift positive and negative discharge events.
“This theoretical framework is also capable of accounting for prevalent scenarios involving only the rapid positive discharge, thereby explaining the initiation mechanism for the majority of observed lightning flashes,” the research team commented.
Their scholarly findings were formally disseminated on March 3rd within the esteemed pages of the Journal of Geophysical Research: Atmospheres.
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Xuan-Min Shao et al. 2025. 3D Radio Frequency Mapping and Polarization Observations Show Lightning Flashes Were Ignited by Cosmic-Ray Showers. JGR Atmospheres 130 (5): e2024JD042549; doi: 10.1029/2024JD042549
