OBEY YOUR THIRST: A sprite emerges from the top of a thunderstorm in Myanmar, caught on film by astronauts aboard the International Space Station's Expedition 31. (Photo: NASA Earth Observatory)
As their name suggests, "red sprites" are strange, ghostly phenomena that few humans have ever seen. They're so elusive for two main reasons: They appear in the upper atmosphere above thunderstorms, and they last for just a few milliseconds.
Despite these hurdles, however, astronauts aboard the International Space Station managed to capture the above photo of a red sprite pulsing upward from a thunderstorm over Myanmar. The image was taken April 30 by members of ISS Expedition 31, and posted online this week by NASA's Earth Observatory.
This image is the latest step in a relatively recent quest to document and demystify red sprites. While airplane pilots had periodically reported seeing these enigmatic outbursts for decades, the first photographic evidence didn't come until 1989, followed by more photos from NASA space shuttles over the next decade. Scientists dubbed them "sprites" in 1993, and now regularly record them as part of ongoing research into the secrets of thunderstorms. Still, a chance sighting like this is rare.
Red sprites are just one of several "transient luminous events" (TLEs) that emerge from the tops of thunderstorms, along with other atmospheric oddities like elves and blue jets. This illustration from the U.S. National Severe Storms Laboratory offers a visual breakdown of where lightning and TLEs occur (click image to enlarge):
Here's a more in-depth explanation of sprites, courtesy of the University of Alaska:
"Sprites are massive but weak luminous flashes that appear directly above an active thunderstorm system and are coincident with cloud-to-ground or intracloud lightning strokes. Their spatial structures range from small single or multiple vertically elongated spots, to spots with faint extrusions above and below, to bright groupings which extend from the cloud tops to altitudes up to about 95 km. Sprites are predominantly red. The brightest region lies in the altitude range 65-75 km, above which there is often a faint red glow or wispy structure that extends to about 90 km. Below the bright red region, blue tendril-like filamentary structures often extend downward to as low as 40 km. Sprites rarely appear singly, usually occurring in clusters of two, three or more."
Sprites' origins remain mysterious, but scientists have found some clues in recent years. Weak lightning doesn't seem to cause them, for example, and they're associated more with positively charged strikes than negative ones. And while they're still inherently hard to see from Earth's surface, NASA does note that "viewers on the ground can occasionally photograph sprites by looking out on a thunderstorm in the distance (often looking out from high mountainsides over storms in lower plains)."
For an easier look at red sprites in action, check out the following video, which shows footage of sprites over Wyoming slowed down to 1/100 of real time:
Also on MNN:
- Interactive: What causes lightning?
- Seven lightning safety tips for summer
- High-speed video shows lightning enigmas
- Photos: The world's weirdest weather
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