In 1960, the Soviet Union shot down American pilot Francis Gary Powers’ plane while flying over Yekaterinburg. The aviator was captured alive and sentenced to 10 years in prison, while the remains of the fuselage were displayed in public. That was called the U2 incident, after the name of the spy plane that Powers piloted, which had been designed at the request of the CIA to fly at high altitude and photograph Communist arsenals without being detected.
Six decades later, the same type of plane, converted for scientific use, has made it possible to observe what happens inside a thunderstorm like never before. Despite the ability to study these processes from Earth and from space, it is unknown how the rays are triggered, capable for an instant of heating the atmosphere to 20,000 degrees, three times more than the surface of the Sun.
In July 2023, the United States Space Agency carried out 10 flights with its ER-2 aircraft, the same type as the U2s of the Cold War. Its objective was to carry out an unprecedented experiment: climb up to 20 kilometers and fly over as many times as possible the worst tropical storms that were at that time in the Caribbean and Central America. This jet plane is capable of gliding for hours loaded with scientific instruments. On Earth, a team of researchers, meteorologists and soldiers guide the aviator and warn him where the next electric shock is going to occur with a code word: “glow!” The pilot passes just two and a half kilometers from the clouds and their electrical discharges. It’s the closest science has come to a storm.
NASA’s ER-2 aircraft.NASA
The results of the campaign reveal that storms generate radioactivity in the form of gamma rays, the type of radiation that is also produced by nuclear explosions or the disintegration of elements such as uranium. Although other experiments had demonstrated the existence of this phenomenon, the dimensions observed by the NASA spy plane are never seen before. The storms generate gamma rays for hours and cover areas of more than 9,000 square kilometers, almost the size of all of Europe.
in two studies published this wednesday in Naturea reference for the best world science, scientists compare the phenomenon to a pot of boiling water. Each bubble would correspond to a glow of gamma rays that lasts fractions of a second, and that lights up the sky with flashes of light invisible to the human eye.
Due to its design, only one pilot can fly inside the ER-2, clad in a pressurized suit like that of astronauts. One of them said that the clouds had “a strange purple color due to the crazy rhythm at which the lightning discharged,” Steve Cummer, an electrical engineer at Duke University (United States), and co-author of the first study, explains to this newspaper. “For the first time we know that this process is very common, so that rays, a spectacular visual process, and gamma rays, invisible without the appropriate equipment, work in unison to discharge the energy,” he details.
Storm clouds are the largest natural particle accelerators on Earth, summarizes Martino Marisaldia physicist at the University of Bergen in Norway, and co-author of the second study. “At all times, on the planet we have about 2,000 active storm clouds and about 45 lightning strikes occur every second. It is one of the most powerful processes we can imagine and it is essential to understand how it happens,” he highlights.
The great unknown about lightning is that to produce it, electric fields ten times greater than those that have so far been observed within storms are required, so it is not known how the burst of electricity is actually triggered.
A thunderstorm near Santa Marta, Colombia. Oscar van der Velde
These scientists have discovered a new type of gamma ray within the storm called a flickering gamma ray flash (TGF). This phenomenon is “the missing link” that connects the two types of gamma rays already known, glows, which can last more than a minute, and ground flashes, which are more intense but last microseconds. TGFs happen just after flashes and before lightning. This implies that there is a until now unknown process that discharges part of the energy in the form of gamma rays, and that in turn could be the previous step for lightning to form.
“If this process did not occur, the storms would be much more electrified and would probably generate much more powerful and dangerous discharges,” Cummer acknowledges. The new information fits well with what was known from a cosmological point of view: gamma rays are the most powerful radiation in the universe and in fractions of a second they release more energy than all the stars in the universe.
Another process with a science-fiction movie name also happens within storm clouds: an avalanche of out-of-control relativistic electrons. They are relativistic because they travel at almost the speed of light, the maximum limit allowed in the universe, according to Albert Einstein’s theory of relativity. When those electrons collide with air molecules, they generate high-energy electrons and photons. The potential within the cloud becomes so great that positrons, the antimatter particles complementary to the electron, but with opposite charges, are also created. “We now know that many storms glow with gamma rays and create antimatter,” Cummer summarizes.
Those responsible for the work believe that they are now a little closer to understanding exactly how lightning is generated. “For the first time we see that gamma rays are not a scientific curiosity, but a fundamental process that probably occurs in all storms with sufficiently large electric fields,” highlights Marisaldi. This would include not only tropical ones, but also those that can be produced in Europe, he says. “This work now shows us the way to continue investigating how the production of energetic particles generates lightning, one of the greatest enigmas of atmospheric physics,” he adds.
Scientists believe that gamma ray storms pose no risks to people. You would have to be very close to one of these flashes to receive a significant dose. What does entail risks is getting closer to a storm. The most dangerous thing about putting a plane in one of these storms would be the enormous turbulence, which could knock the ship over. Lightning, on the other hand, is not too worrying. It is relatively common for a commercial airplane to receive an electrical shock—it happens about twice a year—, and in most cases there is no damage.
These two new works are part of an emerging field: high-energy atmospheric physics, explains the physicist and mathematician in an independent comment. Joseph Dwyerfrom the University of New Hampshire (United States). “It is amazing that two decades into the beginning of the 21st century, the Earth’s atmosphere has enough surprises in store to inaugurate a whole new field of science.” Studies carried out with devices like NASA’s old spy plane could be “a revolution in our understanding of the electrification of storms and lightning,” he adds.
