New observations from a modified U2 spy plane reveal a surprising amount and variety of gamma rays produced in large tropical thunderstorms. NASA satellites were originally designed to detect high-energy particles in the universe, but accidentally discovered gamma ray bursts originating from thunderstorms on Earth. Subsequent research conducted by NASA using the U2 spy plane found that these gamma rays are common in thunderstorms, manifest themselves in various forms, and are related to the electrical activity in thunderstorms. The discovery reveals a complex dynamic process involving high-speed electrons and nuclear reactions that may also influence the formation of lightning.
In the 1990s, NASA satellites built to detect high-energy particles from supernovae and other celestial bodies discovered a surprise - high-energy gamma ray bursts from Earth.
While it didn't take researchers long to figure out that these radioactive supercharged particles came from thunderstorms, how this phenomenon occurs so commonly remains a mystery. Satellites are not designed to detect gamma radiation from Earth; they have to be in the right place at the right time to detect gamma radiation.
After years of using less-than-ideal platforms for the task, a group of scientists now got the chance to fly a modified U2 spy plane owned by NASA over the storm to take a proper look. In two new papers published October 3 in Nature, the team found that gamma rays produced in thunderstorms are much more common than thought, and that the dynamics that produce the radiation hold as yet unsolved mysteries.
"There's a lot more going on in thunderstorms than we thought," said Steve Cummer, the William H. Young Distinguished Professor of Engineering at Duke University. "It turns out that essentially all large thunderstorms produce gamma rays in many different forms throughout the day."
The general physics behind how thunderstorms produce high-energy gamma ray flashes are not mysterious. When thunderstorms occur, swirling air currents sweep water droplets, hailstones and ice into the mix, creating an electrical charge like a balloon rubbing against your shirt. The positively charged particles end up at the top of the storm, while the negatively charged particles fall to the bottom, creating a massive electric field with the strength of 100 million AA batteries stacked end-to-end.
When other charged particles, such as electrons, find themselves in such a strong electric field, they accelerate. If they accelerate to a high enough speed and happen to hit air molecules, they will knock out more high-energy electrons. This process progresses step by step until the energy generated by the collision is enough to cause a nuclear reaction, producing extremely strong and fast gamma rays, antimatter and other forms of radiation.
But that's not the end of the story about thunderstorm gamma radiation. Planes flying near thunderstorms have also seen faint glows of gamma radiation in the clouds. These storms appear to have enough energy to produce low-altitude simmers of gamma radiation, but something prevents them from producing explosive bursts like popping corn kernels.
"Several aircraft have tried to find out if these phenomena are common, but have had mixed results, and several flights over the United States have not detected any gamma radiation at all," Cuomo said. "This project is designed to address these issues once and for all."
The research team obtained access to NASA's ER-2 high-altitude airborne science aircraft. A modified U2 spy plane left over from the Cold War, it flies twice as high as a commercial aircraft and about three miles above most thunderstorms. It's also very fast, giving the team the opportunity to accurately select the thunderstorms they think are most likely to produce results.
"The ER-2 aircraft will be the ultimate platform for observing gamma rays in thunderclouds," said Nikolai Østgaard, professor of space physics at the University of Bergen in Norway and lead researcher on the project. "Flying at an altitude of 20 kilometers (12.4 miles), we can fly directly over the cloud tops and get as close as possible to the gamma ray source."
Since ER-2 was the perfect solution and the team would fly over suitable storms, the researchers figured they would see few if any of the phenomena if they were rare. But if these phenomena are common, they're going to be seen a lot.
Over the course of a month, ER-2 flew 10 times over large storms in tropical southern Florida. On nine of those occasions, it observed this simulated gamma radiation, which was also more dynamic than expected.
Martino Marisaldi, professor at the Department of Physics and Technology at the University of Bergen, said: "The dynamics of gamma-ray luminescence thunderclouds are completely opposite to previous images of quasi-static luminescence, and are more like a giant gamma-ray luminescence boiling pot in pattern and behavior."
Considering that typical thunderstorms in the tropics are much larger than those at other latitudes, this suggests that more than half of thunderstorms in the tropics are radioactive. The researchers speculate that the production of this low-level gamma radiation acts like steam boiling in a pot of water, limiting the accumulation of energy inside.
Equally exciting to the researchers, they also discovered many short, intense gamma-ray bursts originating from the same thunderstorm. Some of them are very similar to the gamma-ray bursts originally detected by NASA satellites. These phenomena almost always occur simultaneously with active lightning discharges. This suggests that the large electric fields generated by lightning likely supercharge the already energetic electrons, enabling them to produce high-energy nuclear reactions.
But there are at least two other types of short gamma-ray bursts that have never been seen before. One was incredibly short, less than a thousandth of a second, while the other was a series of about 10 separate gamma-ray bursts that repeated over about a tenth of a second.
"These two new forms of gamma radiation are the ones I find most interesting," Cuomo said. They don't appear to be related to the development of lightning. They appear spontaneously in some way. The data suggests that they may actually be related to the process that triggers lightning, which remains a mystery to scientists. "
If anyone is worried about being turned into the Hulk by all this gamma radiation, don’t be. The amount of radiation produced is only dangerous if a person or object is in close proximity to the source. "If you find yourself there, radiation will be the least of your worries. Aircraft will avoid flying in the center of active thunderstorms due to extreme turbulence and high winds," Cuomo said. "Even knowing what we know now, I wouldn't be any more concerned about flying than I was before."
Compiled from /scitechdaily