© Stephen HummelOur changed atmosphere: A huge line of thunderstorms 100 miles away generated a fantastic display of red sprites, as seen from McDonald Observatory. They were easily visible with the naked eye, although not in color. Bands of airglow colored the sky red and green, although those features were not apparent to the naked eye. The large storm system generated gravity waves, which caused a ripple effect in the airglow.
Stephen Hummel was walking across the famous University of Texas observatory grounds a couple hours after sunset on May 13th when he noticed the flash of lightning from a distant thunderstorm. "I saw a large column of sprites leaping into the sky and rushed to set up my camera," he says. Aiming southeast towards the city of Alpine, he recorded this movie:
The video shows alternating bands of red and green airglow gliding overhead like ripples in a giant pool of water. At the same time, red bolts of upward directed lightning (sprites) flashed so brightly "I could see them with my unaided eye," he says. "It was a fantastic display."
Filming the sky in rural southwest Texas can be a little risky. Hummel explains: "I had just hiked to the top of a ridge for a better view, and was a little out of breath as I set up my camera. Just then I heard the eerie sound of a mountain lion's call. I left the camera running while I returned to the safety indoors! Later, I gathered the footage, hoping for the best. I was amazed by the results and surprised the airglow was so evident."
Both the sprites and the ripples originated in a towering thunderstorm about 180 miles away. This weather radar map shows Hummel's location (starred) and the instigating storm system:
The thunderstorm was strongly convective with powerful updrafts. Essentially, it pounded the upper atmosphere from below, creating a bulls-eye pattern of pressure waves in the mesosphere more than 80 km above the ground. This pattern impressed itself upon the airglow layer near the edge of space, amplifying aurora-like colors which are usually too faint to see.
Comment: Not likely. More likely, it's the other way around; the 'cosmic weather' caused the thunderstorm.
It's no coincidence that Hummel saw sprites at the same time. Mesoscale convective storm systems produce a lot of upward directed lightning. Indeed, sprite hunters often train their cameras above the cloudtops of such systems to get the best shots. Strong updrafts are key ingredients of both phenomena.
More sprites and atmospheric bullseyes are in the offing. Northern spring is thunderstorm season and a great time to catch these events. Are you ready?
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