John Metcalfe was CityLab’s Bay Area bureau chief, covering climate change and the science of cities.
Jason Ahrns searches at night for huge, mysterious eruptions of sparks that appear high over thunderstorms.
As recently as 25 years ago, the world had no clue that huge showers of crimson sparks were erupting in the atmosphere high above thunderstorms. Called red sprites, this fleeting form of lightning appears only for a few milliseconds and is still the subject of much mystery and speculation.
Given their relative rarity and fleeting nature, a researcher hunting sprites (and their cousins, blue jets) can be like Ahab scouring the briny deep for that damnedable whale. When somebody does manage to get a photo of one, they're typically quick to nail it to the Internet's wall for all to admire. The latest image of a red sprite is a doozy: It was taken Tuesday night by Jason Ahrns, a 31-year-old grad student who is conducting night flights above Oklahoma City to study the elusive phenomenon. (Universe Today was the first outlet to the photo.) Ahrns also took this fantastic high-speed video, showing a cluster of sprites shooting off in frigid, high-altitude air. It's slowed down by about 666 times:
Ahrns typically researches the aurora borealis at the University of Alaska Fairbanks; the great sprite chase is a side project he's working on with scientists from the National Science Foundation, the U.S. Air Force and elsewhere. Ahrns is a busy guy, probably hopping aboard a Gulfstream jet at this moment, but he recently took the time to email a few details about what might be the coolest job on earth:
What are you and your team doing up there in the air? Hunting sprites, only?
We are hunting sprites for the purpose of studying their formation and propagation. We're doing this using high speed cameras, required due the the very short lifespan of a sprite (the whole thing is over in the few milliseconds). A typical camera running at TV speeds would only get the sprite in a single frame, and you can tell nothing about how it forms and evolves. So we use the high speed cameras which actually let us watch it evolve, as you saw in the video I posted.
Why is it important to understand sprites?
The first reason, and one I totally agree with, is because they are there. And even more so, because they're really cool. But more practically, they represent an energy input into the middle atmosphere, and it's not clear how much of an impact they have on the weather or the longer-term climate. They should also affect the ozone layer, but to what degree? Theses are things we can't know until we know more about the sprites.
On another front, the long strands/tentacles/whatever you want to call them (we call them streamers) open a path for electric sparks to jump, and the same streamers occur with more mundane sparks, such as static electricity or lightning bolts. Streamers are also used in industrial applications for the production of ozone and gas and water-pollution cleaning, for example.
The size and speed of the streamers are related to the air density, so that they get larger and slower when the air is less dense. When we observe sprites in the high atmosphere, the air is very low density, so we see these same type of streamers, but much larger and slower (as fast as they still are!) than streamers on the ground. So our sprite research may provide insight into the basic physics of streamer discharges, which is important basically anywhere it's important to understand electric discharge, such as the ones mentioned above.
What is the ideal conditions for a sprite to appear? Thunderstorms, obviously, but I believe you mentioned on your blog something about positive charges?
We want "positive" lightning strokes, which is just a type of stroke where the cloud has a buildup of positive charge and releases a bolt. Most lightning strokes are "'negative," where the cloud has a buildup of negative charge. The ratio of negative to positive is roughly 10 to 1, so it's not the most common type of lightning, but it's not that uncommon either. But more than a simple "positive" lightning stroke, we also want the stroke to have moved a lot of charge. So we look for a large, positive-charge moment change, which is basically the positive strokes weighted by how much charge was moved.
Any large thunderstorm will probably produce the conditions we're looking for, to a greater or lesser degree – and I don't think it's really well understood why some are to a greater or lesser degree. I don't understand it, anyway; maybe someone else does.
Is the sprite you captured on Tuesday something people in OKC could've possibly also seen?
It is possible to see sprites from the ground, but since they occur above the storm, you need to be out to the side with a clear view above, preferably on top of something tall. People with meteor cameras running at their homes do capture sprites sometimes, but they are generally low resolution because they're so far away and usually using a very wide angle lens. But yes, if you're in the right place and time, you can see them from the ground with your eyes; it's difficult but not at all impossible. I've never seen one personally, only in the cameras.