About 500 of 4.3 million daily lightning strikes produce brief gamma ray bursts in our atmosphere, a mysterious phenomena under investigation by the Firestation instrument on the International Space Station.
White lightning above Kuwait and Saudi Arabia, photographed on December 12, 2013. Want a label-free version for your new wallpaper? Here you go!
Gamma rays are more typically associated with exploding stars or nuclear fusion, but in 1994, we caught them being produced by terrestrial lightning strikes. Only about 500 of the 4.3 million daily lightning strokes have an associated terrestrial gamma-ray flash, and that's about all we know about the process. The Firestation instrument on the International Space Station is a one-year mission to collect multi-wavelength observations on lightning strikes as seen from high above in an effort to learn more about this phenomena.
Lightning flash under a Bolivian thunderstorm, photographed January 9, 2011.
The Firestation instrument on the ISS is designed to observe about 50 lightning strikes a day for a full year. Installed in August of last year, the Firestation has photometers to measure lightning flashes, radio antennas to track the "tell tale, bacon-frying sound of lightning," and a gamma-ray electron detector. A camera takes photographs of the events, helping pinpoint lightning-location, and pick up the red light of sprites or the blue glow of elves along with the bright white of ordinary lightning.
The white glow of a lightning strike over California is clearly distinct from the yellow city-glow from Los Angeles and San Diego.
While lightning strikes about 50 to 70 times a second worldwide, brief bursts of gamma rays are only emitted about once an hour. Theoretically speaking, ordinary lightning should be at least an order of magnitude too weak to produce a gamma ray burst. Current theories for how the bursts happen anyway range from wondering if the bursts are associated with red sprites or blue elves, are a side-effect of lightning triggered by cosmic rays, or maybe even have something to do with the weird high-energy particles sometimes observed in the Van Allen radiation belt. Firestation checked out to start collecting observations as of September 2013, so hopefully we'll be hearing more in coming months as data helps validate some theories while transforming others into discarded relics.
Why is this so fascinating? The various press releases talk about parties raging in the upper atmosphere, and surprise at finding something associated with supernova and solar flares taking place in a cold atmosphere:
"Somewhere in the atmosphere momentarily there's just an incredible amount of energy release and what happens in that region is something of a witch's brew," said Doug Rowland, principal investigator for FireStation at NASA's Goddard Space Flight Center in Greenbelt, Md. "You get antimatter created in the Earth's atmosphere during this interaction, you get energetic neutrons that basically you never see in the quiet atmosphere, that you only associate with nuclear reactions, that are happening in our atmosphere whenever these things go off. That's one of the first fundamental science reasons [to study this phenomenon]—it's part of our planet; we don't understand it; we want to understand it."
That is a good enough reason for me: we don't know why lightning can produce gamma ray bursts, but with a bit of careful observation and dedicated analysis, maybe next year we will.
For more on measuring lightning from the International Space Station, check out the Earth Observatory, or this NASA Science video on Firestation. The photographs in this article were taken by various astronauts on the ISS, not by the Firestation camera. Photography credit to NASA.