On the Hunt for High-Speed Sprites

by Jason Major on August 23, 2012

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A bright red sprite appears above a lightning flash in a photo captured from the ISS

Back on April 30, Expedition 31 astronauts aboard the ISS captured this photo of a red sprite hovering above a bright flash of lightning over Myanmar. Elusive atmospheric phenomena, sprites are extremely brief bursts of electromagnetic activity that are associated with powerful lightning discharges, but exactly how and why they form isn’t yet known — although recent research (along with some incredible high-speed video) is shedding new light on sprites.

Although the appearance of bright high-altitude flashes above thunderstorms have been reported by pilots for nearly a century, it wasn’t until 1989 that a sprite was captured on camera — and the first color image of one wasn’t taken until 1994.

So-named because of their elusive nature, sprites appear as several clusters of red tendrils above a lighting flash followed by a breakup into smaller streaks, often extending as high as 55 miles (90 km) into the atmosphere. The brightest region of a sprite is typically seen at altitudes of 40-45 miles (65-75 km).

Because they occur above storms, only last for a thousandth of a second and emit light in the red portion of the visible spectrum (to which our eyes are the least sensitive) studying sprites has been notoriously difficult for atmospheric scientists. Space Station residents may get great views but they have lots of other things to do in the course of their day besides sprite hunting! Luckily, a team of scientists were able to capture some unprecedented videos of sprites from airplanes in the summer of 2011, using high-speed cameras and help from Japan’s NHK television.

Chasing storms over Denver via plane for two weeks, researchers were able to locate “hot zones” of sprites and capture them on camera from two planes flying 12 miles apart. Combining their videos with ground-based measurements they were able to create 3-dimensional maps of the formation and evolution of individual sprites.

Based on the latest research, it’s suggested that sprites form as a result of a positive electrical charge within a lightning strike that reaches the ground, which leaves the top of the cloud negatively charged — a one-in-ten chance that then makes conditions above the cloud “just right” for a sprite to form higher in the atmosphere.

“Seeing these are spectacular,” said Hans C. Stenbaek-Nielsen, a geophysicist at the University of Alaska in Fairbanks, Alaska, where much sprite research has been conducted. “But we need the movies, because not only are they so fast that you could blink and miss them, but they emit most of their light in red, where the human eye is relatively blind.”

An example of how energy can be exchanged between lower and higher regions of Earth’s atmosphere, it’s been suggested that sprites could also be found on other planets as well, and may provide insight into the exotic chemistries of alien atmospheres.

Read more on NASA Heliophysics here.

Main image: Image Science & Analysis Laboratory, NASA Johnson Space Center. Inset image: the first color image of a sprite  (NASA/UAF.) Video: NHK.

About 

A graphic designer in Rhode Island, Jason writes about space exploration on his blog Lights In The Dark, Discovery News, and, of course, here on Universe Today. Ad astra!

Torbjörn Larsson August 23, 2012 at 3:58 PM

Inverted lightning.

Another (or maybe the same, I can’t tell from the description) form of positive strikes, which generates ~ 100 times the power of normal strikes, is when thunderclouds tops gets blown away from the base. A cloud gets a naturally negative base due to the way its convection of drops works. The thus positively charged top can generate a direct strike to ground from a more concentrated charge from a higher position, and it also has to loop around the mirror charge the base generates at the ground, all resulting in a more energetic strike.

This type of positive strikes are often associated with certain areas as the conditions should be right for them. (Which is why I know of them, for some reason it happens more frequently in parts of Sweden.) It would be interesting to know if they generate “sprites” or “super sprites”.

Peristroika August 24, 2012 at 3:05 AM

That shot of the close up of the sprites forming and exploding is amazing! This is one more fascinating field of research! With real world implications!

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