ISS Image: Lightning Above the Middle East

This image of lightning over Kuwait was taken by an astronaut aboard the International Space Station on Dec. 12, 2013.

Credit: NASA Earth Observatory

This stunning image of a lightning strike over Kuwait was captured last December by an astronaut aboard the International Space Station (ISS) and released today (March 24) by NASA's Earth Observatory.

The ISS recently installed Firesation, a new instrument to help study the physics and composition of such bolts in detail on a daily basis.

Firesation being readied

Lightning bolts flash across Earth's atmosphere as often as 50 times per second, which adds up to about 4.3 million times a day and 1.5 billion times a year, NASA officials wrote in an image description.

Some of those strikes emit gamma radiation, a type of radiation more commonly associated with exploding stars and nuclear fusion, in bursts known as terrestrial gamma-ray flashes (TGFs).

The GLAST Burst Monitor (GBM), an instrument aboard NASA's Fermi Gamma-ray Space Telescope, was recently fine-tuned to better catch TGFs, and this allowed scientists to discover that TGFs also emit radio waves.

The scientists will use the new lightning imagery and data from the ISS to try to understand what triggers lightning during storms in general, and what causes these rarer bursts of TGFs

Doug Rowland

"The fact that TGFs exist at all is amazing," Doug Rowland, a space physicist at NASA's Goddard Space Flight Center involved in this new lighting research, said in a statement.

"The electron and gamma-ray energies in TGFs are usually the domain of nuclear explosions, solar flares, and supernovas."

"What a surprise to find them shooting out of the cold upper atmosphere of our own planet."

Researchers think these TGFs may be related to enigmatic red bursts of lightning called red sprites, which travel upward from thunderstorms and can take on ornate shapes that look like jellyfish.

Red sprites are just one of several types of lightning that researchers are still studying to understand their origin and structure.

In fact, lightning, in general, is a mysterious phenomenon, with scientists still not sure exactly how lightning forms.

The working hypothesis suggests it forms when an updraft of warm air reaches a height where the temperature is just above freezing; at this point, ice crystals and frozen particles interact with each other to produce an electric charge separation; when that separation becomes great enough an electrical breakdown occurs i.e. a lightning flash.

Dark Lightning: Terrestrial Gamma Ray Flashes irradiate passengers

"What are the radiation doses to airplane passengers from the intense bursts of gamma-rays that originate from thunderclouds?" Florida Institute of Technology Department of Physics and Space Science faculty members addressed the issue and presented their terrestrial gamma ray flashes (TGFs) research modeling work at a press conference meeting of the European Geosciences Union in Vienna, Austria, April 10, 2013.

Joseph Dwyer

Joseph Dwyer, Ningyu Liu and Hamid Rassoul discussed a new physics-based model of radiation dose calculations and compared the calculations to previous work.

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 (TGFs).

These flashes of gamma-rays are so bright they 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.

Until recently, the work to answer that question was hampered by a poor understanding of exactly how these gamma-rays are generated by thunderstorms, with initial dose estimates ranging from not-so-safe to downright scary.

Ningyu Liu

Now, scientists at Florida Tech have developed a promising physics-based model of exactly how thunderstorms manage to produce high-energy radiation.

According to their 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."

Recent modeling work of dark lightning shows that it can explain many of the observed properties of terrestrial gamma ray flashes.

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.

Hamid Rassoul

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.

"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," said Dwyer.

"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."

It is not known yet how often, if ever, this actually occurs, but ongoing research is working to address this issue.