Bizarre Natural Phenomena Vol. 57 - A Light Show Above Storm Clouds (Transient Luminous Events)

Hey everyone! Do you remember last week's phenomenon, red sprites? No? Well take a look at that gif, perhaps it will freshen your memory:

Image credits: @terrylovejoy

Red sprites are formed by ionized air thanks to lightning. Cold plasma appears above the storm clouds. It excites the elements in the surrounding air (hydrogen, nitrogen and oxygen) and colorful photons are emitted before these molecules return to their resting state. [Bizarre Natural Phenomena Vol. 56]

What I didn't mention in that last post (and yes, I did it on purpose) was that red sprites are not the only weird lighting phenomenon that puzzles scientists. When it comes to light, nature can be really really imaginative (and so can the people who come up with names for these phenomena). Under the term upper-atmospheric or ionospheric lightning you will meet several weird cases of light phenomena. 

Scroll down, don't be afraid...

Upper-atmospheric or ionospheric lightning describes very short-lived (some fragments of a second) light phenomena formed by plasma that appears thanks to the electrical discharges during lightning. They can be seen way above normal lightning (in the strato- and mesosphere) and are also called Transient Luminous Events (TLE). [1]

Image from the Public Domain through: commons.wikimedia.org

Weird case #1 - Blue jets

Blue jets: These are not necessarily related with cloud-to-ground lightning and appear above severe storm clouds. The blue jets are upward electrical ejections from the positively charged top of a storm cloud. [1, 3, 5]

They were believed to occur because of a negative "screening layer" above the storm cloud. A positive leader crawls upwards to meet the negatively charged region above the cloud (if you don't remember what leaders are, check the previous phenomenon post:Bizarre Natural Phenomena Vol. 56). Upon the meeting of the upwards positive leader and the downward negative one, the very very brief blue jet happens. Blue jets are brighter and rarer than red sprites and they owe their color to molecular atmospheric nitrogen. [1]

Keeping an eye on them

In the beginning of 2017 the National Space Institute of Denmark released the results of a study on blue jets. Thanks to the work of Andreas Mogensen, who took on to becoming an orbiting blue jet paparazzi, we now have material on a phenomenon that still needs further "investigation" [4]

Weird case #2 - Gigantic jets

Unlike blue jets, gigantic jets appear to happen due to the opposite charges within the same cloud (negative bottom - positive top). The leader network of the higher charge cloud part seems to be discharged first and then follows the discharge of the other leader network. One end of this network moves upward to meet with the ionosphere. Gigantic jets are believed to help discharge the ionosphere during a thunderstorm, although they require further observation and studying. [1, 5, 6]

Weird case #3 - Blue starters

Blue starters are shorter and brighter blue jets, but are not blue jets (they are more like a failed attempt to be one). They are mostly seen above hailstorm clouds. [1, 5]

Weird case #4 - Elves

Elves are spreading luminous discs that grow rapidly  at a diameter of about 400 km on the boundary where the stratosphere meets with the ionosphere. Their name stands in for "Emission of Light and Very Low Frequency perturbations due to Electromagnetic Pulse Sources". In simpler words this refers to the electron collisions possibly caused by the electromagnetic pulse from the discharge of lightning. The electrons excite nitrogen molecules and give birth to these beautiful even though short, light shows. [1, 2, 3]

Image through: commons.wikimedia.org - Author: Abestrobi - License: CC BY-SA 3.0

Weird case #5 - Gnomes

Gnomes are believed to be a variation of blue starters, which appear above convective domes. [5]

Weird case #6 - Pixies

No, they are not small human-like creatures that like to hang out with fairies. Pixies are nothing more than peaks of light over convective domes that form gnomes. They live for just 16 millisecs. [5]

Weird case #7 - Trolls

A phenomenon that hasn't been observed for long, trolls are like red "blue jets" and appear as the sprites' tendrils start to expand towards the storm clouds below. [5]

A good sum up of all the above can be found on this image from la.climatologie.free.fr; please click on the link to see it, as I am not sure whether it's copyright protected or not. 

References

[1] wikipedia.org
[2] weather.com
[3] canada.ca
[4] esa.int
[5] albany.edu
[6] livescience.com

Thank you so much for your time!

Until my next post,
Steem on and keep smiling, people!