A key finding connects lightning initiation with terrestrial gamma-ray flashes, showing gamma-ray production can accompany optically dim or radio-silent regions, uniting TGFs and lightning under the same process.

Researchers describe a runaway chain reaction inside clouds where electric fields accelerate electrons seeded by cosmic rays, producing X-rays that release more electrons via the photoelectric effect, amplifying the cascade until lightning forms.

A new study led by a Penn State researcher provides the first precise, quantitative explanation for how lightning initiates inside thunderclouds, linking strong electric fields, high-energy electrons, X-rays, and gamma rays through a photoelectric feedback mechanism.

Practical implications include improved lightning prediction and storm modeling, enhanced safety for aviation and satellites, and better monitoring of high-energy emissions from storms, with findings published in JGR Atmospheres.

The work represents a global collaboration across multiple institutions and is supported by organizations including the NSF, CNES, and Institut Universitaire de France, marking a major shift in understanding storm energy and atmospheric radiation.

The research also explains other energetic cloud events, such as compact intercloud discharges, as manifestations of the same electron cascade when conditions approach but do not reach full lightning development.

The study uses and validates the Photoelectric Feedback Discharge model, comparing storm-condition recreations with satellite, ground-based, and high-altitude observations, including pre-lightning radiation and radio signals.