More than 4 million lightning discharges occur daily. The breathtakingly powerful and beautiful spectacle is particularly fatal in the United States, claiming more lives than tornadoes or hurricanes each year.

The nature of lightning is still subject for debate. As recently as the 1990s, NASA’s Compton Gamma Ray Observatory found something unexpected in lightning: terrestrial gamma-ray flashes, or TGFs for short. Scientists excitedly began studying the phenomenon.

If you don’t follow atmospheric physics, you might be a little shocked to learn that lightning is more than electricity. In fact, thunderstorms produce powerful flashes of radiation! This isn’t news to Joseph Dwyer, however. A professor from the University of New Hampshire, he is well acquainted with the problems of high-energy atmospheric physics and lightning.

According to Dwyer, the presence of TGFs took most everyone by surprise. Studies have found both X-ray and gamma-ray bursts in thunderstorms on Earth, but many physicists associate them more readily with exploding stars, black holes, and other “less mundane” events.

Benjamin Franklin is rumored to have flown a kite in a thunderstorm to test his theories about electricity. Dwyer and his colleagues at the University of Florida launch small rockets that trail Kevlar-coated copper wire. They were among the first to register the presence of x-ray radiation in thunderstorms, as a result of their experiments. Additionally, they measured the amount of radiation produced.

Dwyer’s accomplishments, although far from the public eye, are notable in their area. Recently, he was named the University of New Hampshire’s Paul Chair (Fall 2014), and continues to actively pursue a deeper understanding of runaway electron physics. Thanks to his efforts and those of scientists chasing similar pursuits, we now know that terrestrial thunderstorms emit much more than electricity – including x-rays and gamma rays.

This physics stuff is interesting, but if your focus isn’t atmospheric science, you might be rolling your eyes and wondering what any of this has to do with you. The answer, if you fly a lot, is more than you think. Dark lightning, another term for TGFs, can affect you directly.

In 2009, a team of researchers studying the potential for commercial plane exposure to high levels of radiation, determined that some risk to flyers existed. Their research assumed that the probability of a plane being struck by TGF was low – after all, at that point TGFs were thought to be rare. Incidentally, Dwyer was a part of that research.

And the quantity of energy discussed is staggering.

When you go to a hospital for an x-ray or CT scan, your body is largely protected from excess radiation. High levels of radiation pose significant health risks. If the 2009 study is correct, passengers who are exposed to a TGF could receive the equivalent of ten rem – the same amount of radiation produced by 400 chest x-rays or three CT scans, and the estimated safety limit for radiation exposure over a human lifetime. Commercial planes are struck by lightning a few times each year, but the jury is still out on how many TGFs commercial flight passengers are exposed to when flying.

References:

1. Session AE33A - Energetic Radiation from Lightning and Thunderstorms II, Wednesday December 17, 2014. AGU Fall Meeting. San Francisco, CA.

2. Personal Communications and interview with Dr. Themistoklis Chronis. December 19-24th, 2014.

3. http://news.ufl.edu/archive/2009/12/lightning-produced-radiation-a-potential-health-concern-for-air-travelers.html

4. http://www.smithsonianmag.com/innovation/8-things-weve-learned-lately-about-thunder-and-lightning-80165586/?no-ist

5. http://www.scientificamerican.com/article/thunderclouds-make-gamma-rays-shout-out-matter/