Bizarre Natural Phenomena Vol. 56 - Red Lights Above Lightning (Red Sprites)

This post is a collaboration with @terrylovejoy who provided me with the photos I used.

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For this phenomenon I want you to become flying superheroes and follow me above a ferocious thunderstorm. We fear no lightning strikes, because hey! We are superheroes and our bodies are not electrically conductive (I get to determine our super powers according to what suits my story best, ok?). 

We are flying up high, wind blows in our hair making us look super hot and we are approaching our big thunderstorm that threatens a city. Bolts strike on the ground, burning trees and houses. Distant screams can be heard alongside the roaring thunder. Panic has gotten all over the city where terrified people run in search of a safe shelter, because they don't want to end up an overcooked barbecue. 

- Right on time, man. Right on time!

- Are you ready?

- Yup!

- Did you get the pop corn?

- Of course! Did you get the beers?

- Here, man!

- I love these shows. You know, we don't get any huge disasters that often nowadays and I can say I miss them.

- Me too.

- Whoa! did you see that?

- You mean the red lights above the clouds?

- Aha!

- What the heck was that?

- I have no freaking idea...

Image credits: @terrylovejoy

I know! I know! I know!

- What is it?

That was a red sprite!

- Did they change the can color in the soft drink?

No! It has nothing to do with sodas. 

- I could use with one right now though, this pop corn made me thirsty.

You can always fly down there and drink some rain water if you like.

- Nah! I'd rather stay here and learn more about this weird light we just saw.

Cool, follow me then...

Red sprites are electrical discharges above thunderclouds. They portray a variety of shapes and are mostly red in color (in some cases they might appear to have blue tips). They are short-lived phenomena that take place in the upper atmosphere (50-90 km above the ground) and they are associated with positive lightning. Although they have been reported since 1886, it was not until 1989 that they were caught on camera. In 2007 sprites were photographed at 10,000 fps. It is a phenomenon not locally restricted and has been observed globally. [2, 3, 4]

Lightning occurs within a cloud, between two clouds or between a cloud and the ground. As charge separation takes place within the cloud, we end up with a positive charge on the top of the cloud and a negative at the bottom. Down on the ground, positive charges build up near the surface of the ground and the road to heavens is soon to be walked. [1]

Within the cloud the "leaders" are formed. Leaders are (according to wikipedia) "electrically conductive channels of ionized gas that propagate through, or are otherwise attracted to, regions with a charge opposite of that of the leader tip". This means that a positively tipped leader will move upwards inside the cloud and the negatively-tipped downwards towards the ground. As the negative leader reaches for the ground, another "ion pathway" begins to form from the positively charged ground. This leader is called a positive or upward "streamer". As the two leaders approach, attachment takes place, we have now a low-resistance path for the imminent discharge (which might not necessarily happen). [1]

Image II from: wikipedia.org - Author: Anynobody - License: CC BY-SA 3.0

Now we have set the road to see the fireworks!

Once we have a "tunnel" that goes through the air and joins the cloud with the ground, the lightning channel experiences some significant resistance drop. From the tip where the attachment took place, electrons start accelerating frantically across the whole length of our streamer "tunnel" and it is then that we see the brightest part of lightning. We now have a plasma channel that will neutralize the opposite charges between the cloud and the ground. [1]

This is what happens most of the times but...

In some cases it is possible for a positive leader to come downwards from the cloud and then we have what is called a positive lightning (with the former example explained above being negative lightning). Positive lightning is a lot rarer as it makes just 5% of total lightning occurrences. It is also a lot more intense than negative lightning and can last up to 10 times longer. [1, 5]

During positive lightning another beautiful phenomenon might also take place and that is red sprites (although it is not impossible for sprites to happen during negative lightning). Lightning ionizes the air above the cloud and the result is these beautiful red flashes, which might stretch as long as 50 km (compared to a usual cloud-to-ground lightning strike that can reach up to 10 km). Red sprites usually appear in groups of two or more, hovering in altitudes of 50-90 km above us (in the mesosphere) with hanging tendrils (that might be colored blue) and branches stretching upwards. [2, 3]

Image credits: @terrylovejoy

According to their shapes, they can be divided into 3 different categories:

• Jellyfish: huge sprites that can extend in areas of 50 to 50 km.
• Column (C-sprites): large scale electrical discharges.
• Carrot: C-sprites with long tendrils. [2]

Sprites have actually been proven to be balls of ionization from the lightning discharge that splits air molecules in the atmosphere into ions. These ionized balls are tossed at heights of 80 km and then start travelling downwards at velocities up to 1/10 the speed of light (30,000 km/sec). This movement is closely followed (some milli-secs later) by a second upward movement of balls of ionization. So technically, sprites are not lightning but air ionization that get their unique color from the elements in the air. The cold plasma that forms way above the thunderclouds excites molecules of hydrogen, nitrogen and oxygen that emit colorful photons before they return to their resting state. [2, 4, 8]

Note also that, sprites do need a thunderstorm to appear, but not all thunderstorms will create sprites. Scientists have come close to explaining sprite generation based on the local plasma irregularities scenario. They noticed the rapid formation of tendrils at the lower parts of the sprites which then expanded more slowly horizontally. After studying video recordings, scientists managed to create a computer model to support their hypothesis, but further studying is required until thei hypothesis is confirmed. Plasma irregularities could be attributed to a sprite that occurred some moments earlier or meteors in the atmosphere, even though neither reason has been proven right yet. [6, 7, 9]

Image credits: @terrylovejoy

I can see your halo

Sprites might come about 1 milli-sec later after sprite halos. These halos have a pancake shape that can reach up to 50 km in diameter and even 10 km in thickness. You can see them form about 70 km above the lightning strike that gives birth to them. Halos are believed to be caused the same way sprites are. [2]

Why don't we know much about them?

Sprites are difficult to observe. Happening above raging storm-clouds, ground observers are not able to see them, unless they are at a specific distance from the storm. Their short lives also make it more difficult to study. For the time being sprites will remain a fascinating puzzle for scientists.

In the meantime, astronauts are lucky to take pictures of them flashing above lightning storm clouds like in this video:

And here is a short sum-up of what we discussed above:

References

[1] wikipedia.org_Lightning
[2] wikipedia.org_Sprite_(lightning)
[3] smithsonianmag.com
[4] smithsonianmag.com
[5] crystalinks.com
[6] iflscience.com
[7] livescience.com
[8] popsci.com
[9] news.psu.edu

This post came after a conversation with @terrylovejoy, our wonderful astrophotographer (you should check out his series on Astrophotography Basics). His photos were generously handed to me to use here and I want to say a big:

THANK YOU @terrylovejoy for that! :)

Thank you so much for your time!

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