This is a copy and paste from the Nasa website spaceweather.com:
'A-BOMB' SPRITE OVER THE CARIBBEAN: On Sept. 18th, Frankie Lucena of Cabo Rojo, Puerto Rico, photographed an enormous sprite over the Caribbean Sea. For a split-second, the sky was illuminated by a mushroom-shaped flash:Oscar van der Velde, a member of the Lightning Research Group at the Universitat Politècnica de Catalunya, explains what Lucena photographed:
"This type of sprite is often called 'jellyfish' or 'A-bomb,' and ranks as the largest type of sprite in both horizontal and vertical dimensions," he says. "It consists of a bright halo approximately 85 km above Earth's surface surrounding sprite elements with long tendrils reaching down as low as ~30 km above ground level."
"This kind of sprite tends to be triggered by a very impulsive positive cloud-to-ground flash," van der Velde adds.
The curious thing is, Lucena did not observe an instigating lightning bolt. Instead, just before the sprite appeared, he recorded a bright point-like flash of light. "Was it a cosmic ray hitting the camera?" wonders Lucena. Play the entire video to see the flash. Another possibility: The point-like flash could have been a cloud-to-ground strike mostly eclipsed by intervening clouds.
If Lucena did photograph something new triggering a sprite, perhaps it shouldn't come as a big surprise. The field is relatively new. Although sprites have been seen for at least a century, most scientists did not believe they existed until after 1989 when sprites were photographed by cameras onboard the space shuttle. There is still much to learn.
