Skywatchers See 'Bumper Crop' of Colorful Sprites
Jason Ahrns, a graduate student at the University of Alaska-Fairbanks, goes sprite-chasing at night during electrical storms. Here he captures column-shaped red sprites over Red Willow County, Nebraska, on Aug. 12, 2013.
A “jellyfish” sprite photographed over Republic County, Kansas, on August 3, 2013. "I have very good low light eyesight, and I've watched tons of sprites in real time on the context cameras so I know exactly what and where to look. I was watching intently out the window while I snapped these shots, and the camera caught a sprite that I didn't see," writes Ahrns in his blog: http://musubk.blogspot.fr/2013/08/sprites-2013-update-4.html
Like flames from a butane lighter, three blue jets (slightly blurred due to the motion of the aircraft) appear above the lightning-lit clouds in this photo taken over Republic County, Kansas, on August 3, 2013. Ahrns describes this picture as the "the cream of the crop," due to the difficult nature of capturing blue jets. "Since jets tend to hug the top of the clouds it's understandable that they're more difficult for a ground observer to see/photograph, so it makes sense that being up in a sprite-chasing aircraft would give me a serious advantage," he writes.
"Unlike sprites, blue jets aren’t directly triggered by lightning, but seem to be somehow related to the presence of hail storms," reports the Smithsonian: http://blogs.smithsonianmag.com/artscience/2013/08/scientists-capture-rare-photographs-of-red-lightning/.
Red sprite over Canadian County, Oklahoma, on August 6, 2013. "I was also able to see quite a few jets with my naked eyes! That's a first for me, and I'm always excited to see a new sky phenomenon for myself. I still haven't been able to see a sprite naked-eye, and it impresses me just how difficult that actually is," Ahrns writes.
Ahrns' Nikon D7000 on a flexible tripod points out the window of the sprite-chasing aircraft, a Gulfstream V with the National Center for Atmospheric Research. "I butted the camera up against the window glass and put my weight on it to get rid of most of the wobbles and light leaks, but the motion of the aircraft itself still showed up, especially when we hit a patch of turbulence (we are, you know, flying right next to a thunderstorm)," he writes.
For some ambitious photographers, the summer thunderstorm season means one thing: capturing spites.
These electrical discharges, which occur high over thunderstorm clouds, can be as elusive to catch as their name implies. But not this summer.
“Lately there has been a bumper crop of sprites,” amateur astronomer and long-time sprite hunter Thomas Ashcraft said in an interview with SpaceWeather.com.
Ashcraft this week photographed a particularly massive sprite over western Oklahoma, nearly 300 miles away from his observatory in New Mexico.
“According to my measurements, it was 40 miles tall and 46 miles wide. This sprite would dwarf Mt. Everest,” Ashcraft told SpaceWeather.com
Sprites have been observed for at least 100 years, but hard evidence of their existence didn’t come until 1989 when they were imaged by cameras flying aboard a NASA space shuttle, according to astronomer Tony Phillips, who runs the SpaceWeather.com website.
“My method for photographing sprites is fairly simple,” Ashcraft told Phillips. “First I check for strong thunderstorms within 500 miles using regional radar maps accessible on the Internet. There must be a locally clear sky to image above the distant storm clouds.
“Then I aim my cameras out over the direction of the thunderstorms — which will be hot red or purple on the radar maps — and shoot continuous DSLR exposures. I usually shoot continuous 2-second exposures but if there is no moon then I will shoot up to 4-second exposures. Then I run through all the photographs and if I am lucky some sprites will be there. It might take hundreds to usually thousands of exposures, so be prepared for many shutter clicks.”
Ashcraft does his sprite hunting with a modified near-infrared DLSR but any DLSR will work, he added. “It does require persistence and a little bit of luck.”
Photo: Near-infrared image of triple sprites over Oklahoma on June 23. Credit: Thomas Ashcraft for Discovery News