As lightning zigzagged across the night sky in southeast Nebraska earlier this month, researchers in a jet some 200 miles away raced back and forth, filming an otherworldly show above the thunderheads.
Massive fields of reddish-purple lightning, rarely visible to people, convulsed across the sky. From the August flight has emerged images of the “sprites,” as the lightning is called, and those pictures have ignited the imagination as they circulate across the blogosphere.
The lightning is rarely seen because of its faintness, color and brevity. Cloud cover is another reason that sprites are hard to see.
Sprites last a few thousandths of a second and are at the end of the color spectrum that is hardest for the human eye to detect. If sprites were more distinct, they'd easily be visible above nighttime storms on the horizon or to more pilots flying above clouds. After all, sprites can be huge — sometimes 45 miles tall and 30 miles wide.
Instead, sprites have been mostly the stuff of lore — bright lights seen out the corner of a person's eye or observed by the occasional pilot who had no way of backing up the claim.
Even from a research plane high in the sky, sprites can be difficult to see. Such was the case when doctoral student Jason Ahrns captured his photos above Nebraska at 2:30 a.m. Aug. 12.
What Ahrns saw with his human eye was different from what the camera captured.
“They look gray, very tall, and they flash in and out unbelievably quickly,” he said. “Even knowing what a sprite is, and that we were flying next to a sprite storm, I still wasn't sure if I was just seeing things until I checked the camera.”
Ahrns saw gray because the sprite was too faint to activate the color receptors in his eyes, he said. His camera, a Nikon D7000, captured the truer color — red.
When he posted his pictures online, they began circulating on blogs, including on news sites for NPR and the Washington Post.
That pictures of this elusive lightning would be captured above Nebraska is not surprising — the Great Plains are a storm-rich part of the planet that lends itself to research. Researchers come to hunt tornadoes and other elements of powerful storms in Nebraska and surrounding states. The skies above the Cornhusker State have yielded images of sprites since research began in the early 1990s.
Several dozen universities are studying sprites, including the University of Florida and Stanford and Duke Universities. In general, researchers believe that sprites are a link in the Earth's electrical circuit, itself a little-understood process.
Duke scientist Steven Cummer said understanding the effect of sprites on the atmosphere is important, as is knowing whether there is a connection between sprites and climate. For example, what if sprites contribute to the depletion of the ozone layer? And as climate change intensifies severe weather, will sprites become more common?
This month's expedition was funded by the National Science Foundation and brought together scientists from the University of Alaska-Fairbanks, U.S. Air Force Academy and Fort Lewis College, Ahrns said. The mission was flown on a Gulfstream V jet operated by the National Center for Atmospheric Research Earth Observing Laboratory.
James Moore, of the Earth Observing Laboratory, oversaw the forecasting to find storms that would produce sprites. He said the mission captured sprites about a half-dozen times over three weeks.
Sprites occur with only the most intense lightning storms, about 10 percent of the time.
Don MacGorman, a physicist with the National Severe Storms Laboratory, said that as technology advances, more is being learned about sprites. When sprites were first discovered in 1989, scientists didn't even know that sprites were lightning.
“This shows how little we know about the atmosphere,” MacGorman said. “How many things are out there that are unsuspected, that are hiding somewhere that we haven't seen before or can't bring our instruments to measure?”