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Feb. 5th, 2015 at 10:16 PM
The best sprite I've ever seen
A wonderful photo taken last year above Minnesota reveals the clearest glimpse of a very rare phenomenon from the ground, and probably the first depicting their natural colour. These wisps of red fluorescent plasma are very short lived (5 milliseconds), and elusive, so snapping one, along with the aurora borealis (the green glow) and the lightning storm that spawned the sprite is a once in a lifetime event. I'd be surprised if we see the like again even in photo. Careful observation of distant storm fronts and aeroplane flights are your best chance of glimpsing them.
No one knows exactly how they happen, though you have to be well away from the storm to see them, since they shoot up above it from the clouds (normal lightning goes between clouds or cloud to ground) and are usually hidden behind the storm. It is thought that they start when balls of ionised air shoot both down and up (some 50-80km into the stratosphere) in the milliseconds after a conventional lightning strike. They send pulses of electrical energy up toward the edge of space (the electrically charged layer known as the ionosphere) instead of down to Earth’s surface. It is speculated that ions and electrons floating about the atmosphere are heated by this field and glow red in response. They are rich with radio noise, and can sometimes occur in clusters.
They were first filmed in the same state in 1989. University of Alaska space physicist Hans Stenbaek-Nielsen thinks that these sprites may create an electrical conduit between the thunderstorm in the troposphere and the ionosphere. He also says that even though they have been studied for more than 20 years little is known about the sequence of events that causes theses amazing events.
The light is produced by atoms, fluorescing as they are excited by the passing currents, either upwards in the case of jets, or downwards in that of sprites. They are thought to be caused by an EMP propagating in the ionosphere. Their electrical energy could affect atmospheric chemistry by helping gases react with each other. These discharges may represent the missing link in Earth's electrical circuit, connecting the surface with the ionosphere, and accounting for the 300,000 volt potential difference between them.
Since they occur at altitudes too low for satellites (due to atmospheric drag pulling them back down) and too high for balloons or aircraft, only remote studies are currently possible. The European Space Agency was funding a microsatellite in 2010, currently being built by the French CNRS, specifically designed to study these phenomena. Named after Taranis, the Gaulish/Celtic god of thunder, it is slated for launch by Arianespace using a Vega or Soyuz rocket in late 2016. Hopefully our understanding of these wonderful flashes will improve once it's operational. Whatever they are, these mysterious and elusive flashes never cease to wow me.
These phenomena were first reliably reported by pilots in world war 2, though authorities doubted them at the time, and fliers stopped mentioning them for fear of losing their wings, much like early NASA astronauts were reluctant to mention the blue flashes of Cherenkov radiation they saw when cosmic rays struck the aqueous humour in their eyes, for fear of being taken off the flight list. No doubt people have been spotting them throughout history, and they must account for some of the generic reports of weird lights in the sky.
(from The Earth Story on FB)
Image credit: Mike Hollingshead
http://news.stanford.edu/
http://smsc.cnes.fr/
http://www.nature.com/
http://www.albany.edu/
https://
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A movie: elf.gi.alaska.edu/movies/
http://wapo.st/16iBAIR
http://elf.gi.alaska.edu/
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