January 31, 2023

Even weak thunderstorms emit some of the most high-energy light on Earth

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lightningchurchBy Andrew Freedman From Mashable

SAN FRANCISCO — Thunderstorms of all shapes and sized produce high-energy gamma ray bursts, which are potentially harmful to pilots and passengers of aircraft in extraordinarily rare circumstances, scientists reported for the first time on Monday. These bursts of energy, which are thousands of times more intense than typical X-rays, are far more common than once thought as well, occurring on the order of an estimated 1,100 times per day worldwide or more.

The new research, presented at the American Geophysical Union’s annual meeting in San Francisco, wipes clean longstanding assumptions about mysterious high-energy bursts of electrons that have been observed in the upper atmosphere, associated with thunderstorms, since 1994. Gamma ray bursts originating within the planet’s atmosphere are also known as terrestrial gamma flashes, or TGFs. Before the 1990s, it had been assumed that all gamma rays originated outside of the atmosphere, coming toward the Earth from the sun or other high energy sources.

Terrestrial gamma flashes could potentially pose health risks to pilots and airline passengers if they happen to be in the wrong place at the wrong time, which is unlikely, since pilots typically avoid flying into or even very close to thunderstorms due to their previously known other hazards, including extreme turbulence and hail.

Reducing the health risks to frequent fliers is the fact that one would have to be hit directly from the gamma ray burst to be affected, says Joseph Dwyer, a researcher at the University of New Hampshire.

“People don’t need to worry about TGFs when they get on an airplane,” he said at a press conference at the scientific meeting. “It’s safe to fly, don’t let terrestrial gamma flashes stop you from flying.”

gammaraylaunchprocess-640x420If one happens to be on a plane in the wrong place at the wrong time, that person would not get vaporized, or turn into the Incredible Hulk. Instead, they’d receive a whole body CT scan’s-worth of radiation. “This is something that is not necessarily great but it’s not going to kill you,” Dwyer said.

Dwyer said the energy from an upwardly moving gamma ray burst originates within the lightning bolt inside of a thunderstorm — what part and stage of the lightning strike is not yet clear — and is generated in just tens of microseconds of time.

The mystery is how such a huge amount of energy, normally only generated in a particle accelerator, can be created in such a short time in seemingly ordinary atmospheric conditions.

“It’s really a surprise to get such high-energy radiation from a thunderstorm,” he said.

Thunderstorms are “Planet Earth’s most powerful particle accelerator,” said to Themis Chronis, a research associate at UAH’s Earth System Science Center.

By combining data from NASA’s Gamma-ray Burst Monitor with information from ground-based lightning detection networks and weather radars, the researchers were able to do detective work, similar to tracing a phone call, by working backward to locate each storm that emitted a detected gamma ray burst and investigate its structure and intensity. Aiding their investigation was the fact that gamma ray bursts also emit radio signals, as do ordinary lightning strikes, which can be tracked by ground-based sensors. gamma ray bursts also emit radio signals, as do ordinary lightning strikes, which can be tracked by ground-based sensors.

In addition, the researchers also flew an Airbus aircraft through the turbulent inner structure of a major thunderstorm over Italy to conduct measurements from within a storm, which is the first time that had been done in a hunt for gamma rays before. This sickening 5-hour flight through extremely bumpy air helped the researchers confirm that the high energy emissions were coming from lightning, not another source within a thunderstorm.

The storms that caused TGFs ranged in intensity from tall, mature severe storms to storms with less intense rainfall and lower cloud tops, including storms spawned by winter storms.

Most of the detectable TGFs originate in lightning bolts located in the upper part of a thunderstorm, from about seven to nine miles high, Dwyer said, but that does not mean they are not being emitted from lower altitudes too. The hypothesis is that lower altitude gamma ray bursts aren’t easily detectable because their energy is attenuated from the water vapor and ice in the cloud above it.

In other words, gamma rays generated lower in a thunderstorm get trapped in the atmosphere, and don’t make it into space where it can be detected by a satellite sensor.

Complicating research, though, is the fact that despite years of experiments, scientists still don’t know exactly how lightning is triggered during a thunderstorm, although they know how electrical charges build up inside of these storms.

“Lightning strikes the earth something like four million times per day, yet we don’t really know how lightning gets initiated in the storm,” Dwyer said.

Scientists will have a powerful new tool to work with in studying TGFs starting in about a year, when a new U.S. satellite with a specially-designed lightning detection sensor is launched into space.


Lightning steaks across the sky behind the Young Meadows Presbyterian Church in Montgomery, Ala., Monday, March 18, 2013. IMAGE: DAVE MARTIN/ASSOCIATED PRESS

Description of how thunderstorms emit gamma rays into space. IMAGE: JOSEPH DWYER/FIT/NASA

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