On SPRITES in Earth Science

Illustration of a SPRITE. Released under a CC license. Find more information here: http://commons.wikimedia.org/wiki/File:Upperatmoslight1.jpg
Illustration of a SPRITE. Released under a CC license. Find more information here: http://commons.wikimedia.org/wiki/File:Upperatmoslight1.jpg

I will start by mentioning that this particular physical phenomenon’s name is made for lovers of weird acronyms.

SPRITE: Stratospheric/mesospheric PeRturbations by Intense Thunderstrom Electrificaton.

Good one, ey?

The picture to the left is an illustration, I like very much, but there are oodles of good pictures and videos everywhere on the internet. Search for “Sprite” and “Transient Luminous Event” here.

So, what are SPRITES? I think the best way to approach their nature is by beginning at the ground, or close to it. When there is a thunderstorm, the cloud itself is electrified with electric charge separating within the cloud, ions at the top, and electrons at the bottom.

Charge separation means there is an electric field inside the cloud. This is not necessarily a stable configuration, and when the electric field in the cloud becomes too strong, the atmosphere around the cloud may be electrified, as well, and electric discharges can happen.

The electrical discharges we see most often, we call lightning, or, more accurately, cloud-to-ground lightning. When these happen, there is another electric field, a strong one, too, between the cloud and the ground.

One should not use a word like this about a physical system, but I will do it anyway: During a lightning event, the atmosphere is plainly weird. It behaves weird, it looks weird, and weird stuff happens.

If the lightning fulfills certain (not yet quite known conditions), the electric fields in the cloud and between the cloud and the ground somehow reconfigure themselves to result in another intense electric field somewhere above. This new electric field may, in fact, reach far above the cloud.

If these “flipped-upwards” electric fields are strong enough, electric discharges will happen there, too. These high-altitude discharges are called Transient Luminous Events, because, in some ways, they are lightning, and in some ways are not – as I mentioned, it is all just a wee bit weird.

There are a great many types of Transient Luminous Events, such as ELVES, GNOMES, TROLLS and others, but the most prominent ones are the SPRITES:

Vertical extension: up to 60 km (!)
Duration: a few milliseconds

I hope I will see one before I die.


2015-03-14 18.46.20Alexander is a physicist, teacher and science communicator who is currently working at the Norwegian Centre for Space-related Education at Andøya Space Center in Norway. Even though, in his case, work and play do overlap, the content on this webpage is entirely private. You can follow Alexander on Twitter, Facebook and Google +.

 

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