by The electrical effects of a thunderstorm are not just limited to high in the atmosphere. Close to the ground, Earth’s atmosphere buzzes with intense electric fields that accelerate particles and toss electrons around in ways that force atoms to glow with gamma rays.
From the top of a mountain in Armenia, scientists have taken a closer look at this mysterious meteorological phenomenon.
At the Alikhanyan National Science Laboratory’s cosmic ray facility on Mount Aragats, physicist Ashot Chilingarian and his colleagues have been working to understand Thunderstorm Ground Enhancements, or TGEs.
This electromagnetic amplification, Chilingarian says, has been overlooked in thunderstorm research, but it could be a piece of the puzzle in our understanding of the physical universe, from thunderstorms here on Earth to the cosmic rays that travel vast distances through space takes.
“There are 40,000 thunderstorms every day. Countless networks that detect atmospheric discharges and satellites with precise optical instruments monitor lightning flashes. But when we started TGE research, no one contained the enormous flow of megaelectronvolt (MeV) electrons the holes that bombard our planet and the space above it,” he told ScienceAlert.
“We established the SEVAN particle detector network ten years ago to monitor TGEs in Eastern Europe, Germany and Armenia. Electron accelerators with energies of tens of MeV cover enormous volumes in the atmosphere and many square kilometers on the Earth’s surface.
“This massive current accompanies life on Earth throughout its billions of years of evolution and certainly affects all aspects of geospace and the biosphere.”
TGEs consist of electric fields in the atmosphere, generated by thunderstorms. Within these electric fields, electrons are accelerated to high speeds – speeds approaching that of light in a vacuum, or relativistic speeds.
These are known as relativistic runaway electron avalanches, propelled by the electric field, both towards the ground and up into the atmosphere. It is these electrons that produce the radiation.
When they suddenly slow down, deflected by a collision with an atomic nucleus in the atmosphere, the energy loss manifests as gamma rays – a form of radiation known as bremsstrahlung.
Using their network of detectors, Chilingarian and his colleagues collected data on thunderstorms across Europe in 2023, making detailed measurements of the electrons and gamma rays that occurred during the 56 intense TGEs they recorded.
The most intense TGEs usually occurred from May to July, with the most powerful one recorded in May on Mount Lomnický štít in Slovakia. For this one event, the particle flux was 100 times normal fair weather levels. In total, there were seven events that exceeded the fair weather flux by more than 75 percent.
“We measure the stable electron flux on the Earth’s surface, which covers a hundred thousand square meters. Some mechanism ensures this stability for a minute or more,” Chilingarian explains.
“A huge electron beam emerges in the thundercloud, where the charge structure changes on the second scale. Atmospheric discharges cancel out the potential difference, but the flux is stable. It was exciting to measure!”
Surprisingly, the researchers also found that the electric field is much closer to the ground than they expected. They measured a strong electric field strength up to 50 meters above the ground.
“This discovery was astonishing to meteorologists, who did not believe it until we presented the exhaustive evidence,” Chilingarian noted.
The consistency of the acceleration, which can maintain the particle flow for several minutes, as well as the low height of the electric field, reveals new details about the structure of atmospheric electric fields and thunderstorms that we did not know before.
For example, TGEs can provide a path for lightning strikes to reach the ground. And their role in geophysics needs to be explored. The researchers have made available an open-access TGE database for the scientific community to explore and analyze.
Their thunderstorm research is just part of the work being done on Aragats. This year the sun has entered a frenzy as it approaches solar maximum, the peak of its activity cycle, sending particles into space powered by coronal mass ejections.
Chilingarian and his colleagues have also detected solar events with the mountaintop equipment, publishing three papers and a fourth on the way.
‘Violent explosions in our Milky Way also send ultra-high energy particles into the solar system. Recently, Pevatrons, sources of 1015 eV gamma rays were discovered. We critically analyzed this discovery based on our knowledge of atmospheric physics,” Chilelingarian told ScienceAlert.
“The synergy of atmospheric, space and solar accelerators is important for understanding nature!”
The findings will be published shortly Physical examination D.
