Introducing, the Green Ghost

May 31, 2020: Want to discover something new? Keep an eye on the tops of thunderstorms. Sprites, trolls, elves and pixies: These are just a handful of the exotic phenomena that have surprised researchers monitoring cloudtops since the 1980s. In fact, a new one has just been discovered. Introducing, the Green Ghost.

Thomas Ashcraft captured one over New Mexico on May 25th. Play his movie, and look for the green afterglow following the flash of this magnificent jellyfish sprite:

vimeosplash

“In the past week I’ve captured two Green Ghosts over west Texas that were generated by strong peak current lightning strokes,” says Ashcraft. “The one on May 25th registered¬† 118 kAmperes on the National Lightning Detection Network and saturated VLF lightning sensors as far away as great Britain and Germany.”

“As far as I know there are no scientific journal articles regarding this new phenomenon and a handful of citizen scientists are leading the way,” says Ashcraft.

Green Ghosts were discovered only 1 year ago by Hank Schyma, a Houston Texas-based storm chaser better known to his fans as Pecos Hank. “It was May 25, 2019,” recalls Schyma. “I video recorded some sprites over a storm in Oklahoma. Later, when I reviewed the footage, I noticed a mysterious green afterglow above some of the larger sprites.”

greenghost

Above: From the archives of Thomas Ashcraft, a Green Ghost photographed in 2014. “At the time I did not realize what I had captured,” he says.

Schyma worked closely with another storm chaser, Paul M. Smith. “We shared the footage with scientists and others on social media. Nobody had heard of it before. Many argued it might be a camera sensor artifact. Over the following weeks and months, Paul captured multiple other ghosts at high resolution, silencing the skepticism.”

At the moment, no one knows for sure what causes Green Ghosts. Their color may be a clue. Green is commonly seen in auroras and airglow, two upper atmospheric phenomena that get their verdant hue from excited atoms of oxygen. The same could hold true for Green Ghosts. When the tops of strong sprites hit the airglow layer ~90 km above Earth’s surface, oxygen atoms might briefly glow green.

Right or wrong, this hypothesis inspired the name Ghost. “It is an acronym for Green emissions from excited Oxygen in Sprite Tops,” explains Schyma. “More importantly, we named them ghosts to maintain the theme of other transient luminous events such as sprites, trolls, elves and pixies.”

In the USA, sprite season is just getting underway as summer approaches, bringing severe electrical storms. Stay tuned for more ghost stories.

 

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