How Do Summer Superstorms Form?
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.
When you’re watching summer weather forecasts on TV, it’s a little unnerving to look at the map and see a massive line of thunderstorms seeming to band together and move in a straight line toward your city or town.
But squall lines, as meteorologists call them, are actually a fairly common phenomenon during the summer season — in the last couple of weeks, we’ve been seeing them everywhere, stretching from Ohio and the South to the the Northeast and Mid-Atlantic states to Indiana to Winnipeg, Canada.
The moist, rising air masses in the atmosphere that cause thunderstorms are enormous, so it’s not really that surprising that multiple storm cells would form at once. Squall lines form along the wedge of colder, higher-pressure air that bumps up against a warm low-pressure area, driving the air upward like a car going up a ramp.
According to the National Weather Service, these squall lines can stretch for hundreds of miles and persist for many hours, with updrafts forming new cells along the edge of the system, and rain and hail following just behind.
Tornadoes sometimes form along the leading edge of a squall line, where they slam into whatever’s in front of them with brutal power, driven by the horizontal spreading effect of the thunderstorm’s downdraft as they descend.
But the worst-case scenario is for a squall line to generate an extremely powerful, fast-moving straight wall of wind called a derecho, which can move at 100 miles per hour over a stretch of several hundred miles. Back in late June 2012, for example, the Ohio Valley/Mid-Atlantic derecho caused protracted, widespread power outages in cities from Cincinnati, Columbus and Dayton to Atlantic City, Baltimore and Washington.
Photo: A shelf cloud forms in front of a squall line of thunderstorms in the Netherlands. Credit: Jumbo0 via Wikimedia Commons