Looking out the airplane window, it can be unnerving to see lightning flashes inside thunderclouds. But, according to scientists, there’s also another kind of lightning emanating from thunderclouds that’s invisible. It’s called “dark lightning.” Scientists say that this dark lightning hits plane passengers with gamma rays without their even knowing it.
However, these outbursts don’t seem to reach dangerous levels, scientist say.
Scientists have known for almost a decade that thunderstorms are capable of generating brief but powerful bursts of gamma-rays called terrestrial gamma-ray flashes, or TGFs. These flashes of gamma-rays can blind instruments many hundreds of kilometers away in outer space.
Because they can originate near the same altitudes at which commercial aircraft routinely fly, scientists have been trying to determine whether or not terrestrial gamma ray flashes present a radiation hazard to individuals in aircraft.
Researchers from Florida Institute of Technology addressed the issue and presented their work at the European Geosciences Union meeting in Vienna, Austria, on April 10.
According their new computer model, instead of creating normal lightning, thunderstorms can sometimes produce an exotic kind of electrical breakdown that involves high-energy electrons and their anti-matter equivalent called positrons. The interplay between the electrons and positrons causes an explosive growth in the number of these high-energy particles, emitting the observed terrestrial gamma ray flashes while rapidly discharging the thundercloud, sometimes even faster than normal lightning. Even though copious gamma-rays are emitted by this process, very little visible light is produced, creating a kind of electrical breakdown within the storms called “dark lightning.”
The model also calculates the radiation doses received by individuals inside aircraft that happen to be in exactly the wrong place at the wrong time. Near the tops of the storms, for the types of terrestrial gamma-ray flashes that can be seen from space, the radiation doses are equivalent to about 10 chest x-rays, or about the same radiation people would receive from natural background sources over the course of a year.
Florida Tech researcher Joseph Dwyer said:
However, near the middle of the storms, the radiation dose could be about 10 times larger, comparable to some of the largest doses received during medical procedures and roughly equal to a full-body CT scan. Although airline pilots already do their best to avoid thunderstorms, occasionally aircraft do end up inside electrified storms, exposing passengers to terrestrial gamma ray flashes. On rare occasions, according to the model calculation, it may be possible that hundreds of people, without knowing it, may be simultaneously receiving a sizable dose of radiation from dark lightning.
Bottom line: What are the radiation doses to airplane passengers from dark lightning – the intense bursts of gamma-rays that originate from thunderclouds? Florida Institute of Technology researchers addressed the issue and presented their research at the European Geosciences Union meeting in Vienna, Austria, April 10, 2013.
Eleanor Imster has helped write and edit EarthSky since 1995. She was an integral part of the award-winning EarthSky radio series almost since it began until it ended in 2013. Today, as Lead Editor at EarthSky.org, she helps present the science and nature stories and photos you enjoy. She also serves as one of the voices of EarthSky on social media platforms including Facebook, Twitter and G+. She and her husband live in Tennessee and have two grown sons.