Surprising gamma radiation in large tropical storms

Oct. 2 () –

The gamma radiation produced in thunderstorms is much more common than previously thought and the dynamics that create the radiation contain a treasure of mysteries yet to be solved.

It is the discovery of two new articles published in ‘Nature’ (1) and (2) by a team from Duke University.

“There’s a lot more going on in thunderstorms than we ever imagined,” said Steve Cummer, the William H. Younger Professor of Engineering at Duke University, who was a co-author on both papers. “It turns out that, in essence, all major thunderstorms “they generate gamma rays all day long in many different ways.”

The general physics behind how thunderstorms create high-energy flashes of gamma radiation is not a mystery. As thunderstorms develop, spiraling air currents cause water droplets, hail, and ice to mix and generate an electrical charge similar to that produced by rubbing a balloon against your shirt. Positively charged particles end up at the top of the storm, while negatively charged particles fall to the bottom, creating a huge electric field that It can be as strong as 100 million AA batteries stacked on top of each other.

When other charged particles, such as electrons, are in such a strong field, they accelerate. If they reach high enough speeds and collide with an air molecule, they give off more high-energy electrons. The process occurs in a cascade until the collisions have enough energy to create nuclear reactions, producing extremely strong flashes. and extremely fast gamma rays, antimatter and other forms of radiation.

But that’s not the end of the story of gamma radiation from thunderstorms. Aircraft flying near thunderstorms have also seen a faint glow of gamma radiation coming from clouds. These storms appear to have enough energy to produce a small boil of gamma radiation, but something prevents them from creating an explosion like a kernel of corn bursting. “Several air campaigns were carried out to try to find out whether these phenomena were common or not, but the results were mixed and several campaigns over the United States did not detect any gamma radiation,” says Cummer. “This project was designed to address these issues once and for all.”

The research group secured the use of NASA’s ER-2 high-altitude aerial science aircraft. It is a refurbished U2 spy plane left over from the Cold War and flies at twice the altitude of commercial airliners and about three miles above most thunderstorms. It’s also extremely fast, which gave the team the opportunity to pick the exact thunderstorms they believed were most likely to produce results. “The ER-2 aircraft would be the ultimate platform for observing gamma rays from storm clouds.” , highlights Nikolai Ostgaard, professor of spatial physics at the University of Bergen (Norway) and principal investigator of the project. “By flying at 20 km, we can fly directly over the top of the cloud, as close as possible to the gamma ray source.”

Since ER-2 was the perfect solution and the team was going to fly over the right storms, the researchers figured that if these phenomena were rare, they would hardly see any. But if they were common, they would see many. And they saw many. Over the course of a month, ER-2 made 10 flights over large storms in the tropics south of Florida, and 9 of them returned observations of this hotbed of gamma radiation, which was also more dynamic than expected.

“The dynamics of gamma-ray emitting storm clouds clearly contradict the previous quasi-stationary picture of glows, and rather resemble that of a huge boiling pot emitting gamma rays, both in its pattern and in its behavior“, reveals Martino Marisaldi, professor of physics and technology at the University of Bergen (Norway).

Given the size of a typical storm in the tropics, which is much larger than storms at other latitudes, this suggests that more than half of all storms in the tropics are radioactive. The researchers postulate that this production of low-level gamma radiation acts like steam boiling in a pot of water. and limits the amount of energy that can accumulate inside.

Researchers were also excited to see numerous examples of intense, short-lived bursts of gamma radiation coming from the same thunderstorms. Some of them were exactly the same as those originally detected by NASA satellites. They almost always occurred in conjunction with an active lightning discharge. This suggests that the large electric field created by the lightning is probably overloading the electrons, They already have high energy, allowing them to create high energy nuclear reactions.

But there were also at least two other types of short bursts of gamma radiation that had never been seen before. One type is incredibly short, less than a millisecond, while the other is a sequence of about 10 individual explosions that repeat over the course of about a tenth of a second.

“These two new forms of gamma radiation are the ones that seem most interesting to me,” adds Cummer. “They do not appear to be associated with the development of lightning. They arise spontaneously. There are indications in the data that they might actually be linked to the processes that initiate lightning, that are still a mystery to scientists.

Cummer adds that if anyone is worried about turning into the Hulk because of all this gamma radiation, they shouldn’t worry. The amount of radiation produced would only be dangerous if a person or object were very close to the source. “Radiation would be the least of their problems if it were there. Planes avoid flying into active storm cores because of the turbulence and extreme winds,” Cummer concludes. “Even knowing what we know now, I’m not worried about flying any more than I was before.”