|Jason Ahrns, University of Alaska Fairbanks|
I like to cover ongoing mysteries in science, and the topic of Sprites is a good one! Although they were reported in scientific literature as far back as 1886, it wasn't until 1925 that the theoretical underpinnings were discussed. Experimental proof didn't come for almost 7 decades!
This recent photo was taken by Jason Ahrns of the University of Alaska Fairbanks who was working with an airborne team of researchers from NCAR, using a 'normal' dSLR camera with an image intensifier and settings of f/1.8, ISO 6400, 3/4 second exposure. They use more sophisticated equipment for the actual research, but bring their personal cameras along to get shots like this which are nicer to look at!
So, what are they?
Sprites are a form of electrical discharge in the upper atmosphere, called the "mesosphere" in the range of 50 to 90 km above Earth. They are not lightning, but are related to lightning strikes. As I said in the intro, they are a mystery and we have just begun to get a rough idea about them. Here's a bullet list of what we do know so far:
- they are a cold plasma phenomenon
- they were named after "air spirits", for their rare sightings
- they are red-orange at the tops, and bluish at their bottoms
- they tend to appear in clusters of at least 2
- they can be preceded by an orange halo above
- they last for just milliseconds
- they can be produced by both positive and negative (cloud to ground) lightning strikes, but are most often produced by the more rare positive strikes
- positive lightning produces 7 to 10 times more halos than negative
- every lightning strike 'tries' to create them
- initial estimates of their energy were low by a factor of 50
- they produce VLF & ELF radio waves
- they consist of balls of ionization that move downward at ~10% of the speed of light, followed by upward moving balls
- they were theoretically anticipated by C.T.E. Wilson, Cavendish Laboratory, in 1925
- they were first captured in images by J.R. Winckler, University of Minnesota in 1989
If you're interested in using Sprites for classroom material, I recommend this publication: THE DISCOVERY OF RED SPRITES AS AN OPPORTUNITY FOR INFORMAL SCIENCE EDUCATION
References (including above):
UPDATE: August 18, 2013
Some of the comments from a G+ version of this story
UPDATE: Sept 17, 2013
A new video from NASA talks about their Firestation experiment aboard the ISS, which has started operations recently.
In recent decades researchers have discovered some strange things happening in the cloud tops. High above ordinary lightning, exotic forms known as red sprites and blue elves shoot toward the heavens, cold cousins to the fiery bolts below. In some places jets of antimatter fly upwards, triggering the detectors on NASA's orbiting high-energy observatories. And as often as 500 times a day, Earth briefly mimics a supernova, producing a powerful blast of gamma-rays known as a Terrestrial Gamma-ray Flash or TGF.
No know knows exactly how these phenomena are related either to each other or to the lightning down below.
A new experiment called "Firestation" onboard the ISS aims to find out. Firestation is a package of sensors designed to explore the links between TGFs, ordinary lightning, and sprites.
Something up there is accelerating low-energy particles of air to nearly the speed of light, producing gamma-radiation and, sometimes, a cascade of antimatter. Rowland wants to find out what that strange, unknown "something" is. Firestation is poised to crack the mystery.The full story can be read here: ISS "Firestation" to Explore the Tops of Thunderstorms
Stay tuned for the latest findings!