The energy needed for thunderstorms can come from an avalanche of electrons sown by extraterrestrial cosmic rays, new research argues.
Scientists already knew that lightning was an electrical discharge between thunder and the Earth’s surface, but they knew that storm clouds would remain a mystery for centuries of electric fields powerful enough to throw bolts at them.
Now, new research uses computer models to reveal that lightning strikes as a result of a powerful chain reaction that begins in space. Researchers published their findings in the Journal of Geophysical Research: Atmospheres on July 28th.
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“Our findings provide an initial, accurate, quantitative explanation of how lightning essentially starts,” author author Victor Pasco, professor of electrical engineering in Pennsylvania and computer science, said in a statement. “It connects the dots between the physics of X-rays, electric fields, and electron avalanches.”
The electrical properties of Lightning were famously confirmed in 1752 by Benjamin Franklin. Franklin’s iconic, often misrepresented, experiments flew a kit connected to a 1-foot (0.3 meters) wire at one end, pasting fur strings attached to the key Franklin held in a silk ribbon. When the storm arrived, the kit was electrified and the thread was wet, so a small spark jumped at my fingers stretched out of the key.
Despite this discovery, data recorded by planes and weather balloons shows that the electric field required to cascade electrons to the Earth is about ten times greater than what was actually measured within storm clouds.
Related: “Killer Electronics” play pinball in space weather around Earth
There are two competing theories to explain how lightning actually occurs. The initial atmospheric static electricity pools until friction between the ice in the storm cloud separates negatively charged electrons from the atoms, ionizing the particles in the atmosphere beneath them, and frees enough electrons to compete with the ground along multiple forking paths.
In the second theory, this initial ionization is achieved by cosmic rays – high-energy subatomic particles (mainly protons) from the universe that strike the upper atmosphere. These rays come from the sun. An explosion of a star called a supernova. A rapidly spinning neutron star called a pulsar. and other unknown sources. When space particles strike the atmosphere, they create runaway electron failures that end in a cascade of ground strikes.
In the new study, researchers pooled data from ground-based sensors, satellites and high-altitude spy surfaces, matching information to mathematical models that simulated conditions for storm clouds before the strike.
Model simulations support cosmic ray theory and show that electrons generated by fast protons accelerated along the field lines and multiplied by atmospheric molecules such as nitrogen and oxygen. This leads to an avalanche of electrons, producing high-energy photons that initiate lightning, researchers say.
Surprisingly, this model also explains why gamma ray flashes and x-rays occur before lightning strikes.
“In our modelling, the high-energy X-rays produced by relativistic electron avalanches produce new seed electrons driven by photoelectric effects in the air, amplifying these avalanches quickly,” Pasco said. “In addition to being produced in very compact volumes, this runaway chain reaction can occur at a very diverse range of intensities, often with very weak optical and radio emissions.
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