Thursday, September 20, 2007

Contrail Colours

These two photos were taken by "Controll" and Mónika Landy-Gyebnár (Noli) in Hungary. The pictures show wonderful colour stripes in the contrails. The most fascinating thing is that the stripes have the airplane as their centre instead of the Sun, and as the plane was flying, the colours did not change depending on the angle to or the distance from the Sun.

The explanation of this phenomenon may lie in the varying consistency of the exhaust. The water vapour condenses, freezes, and the ice crystals become larger and larger. During this process, the refractive characteristics of the particles constantly change, and if the circumstances are ideal and the trail is not too thick, we might see such beautiful colour patterns. For the explanation, we owe thanks to “Uncinus”.

There are more photos available in this topic. See Controll's collection of colourful contrails and another picture taken by Mónika Gyebnár-Landy.

8 comments:

Michiel de Boer said...

I believe the colors are not created by the airplane's exhaust, but 'air pressure' causing condensation. Because of the freezing cold and high humidity the condensation is not temporary but freezes, and a mini- mother-of-pearl cloud exists. See the web-link for a picture showing a clear example (without colors). In this picture the trail clearly does not only come from the exhaust but also from the wings.

Noli said...

Les, yes, in some of Controll's pics the phenomena can be iridescence, there we can see the direction of sunlight, and the colour range is OK with the direction.
But what can we think when the Sun is not in the right direction and the colour range (with being regular) has its center on the plane? The sunlight comes from the side of the contrail, not from ahead or behind.
On my second observation of coloured contrail (25-08-2007) I could make more pics:
http://users.atw.hu/ediacara3/cc1_0825.jpg
http://users.atw.hu/ediacara3/cc2_0825.jpg
http://users.atw.hu/ediacara3/cc3_0825.jpg
They were shot 4 seconds from each other. On the first one the bright 22° and circumscribed halo can be seen, so you can see the Sun's direction is at the side of the contrail. As the plane went towards the Horizon sunlight still came form its side. (It's the same situation on my first pic linked in the post here - where we can see contrail's shadow showing the Sun's direction)
At my first observation the pics were:
http://users.atw.hu/ediacara3/cc1_0818.jpg
http://users.atw.hu/ediacara3/cc2_0818.jpg
http://users.atw.hu/ediacara3/cc3_0818.jpg
I've marked where the Sun was.

So I couldn't understand how can simple iridescence give explanation to it with the colours being in regular order, centered at the plane? Your explanation _with_ the explanation of Uncinus (editor of http://contrailscience.com) might give a wider look at problem. Without your explanation I could not get into the second question: what features of some contrails allow them to become coloured?
And some more: Why mostly the inner part of the contrail is colured? This miht be answered with turbulence behind the plane, assorting the droplets/ice crystals by size?
So with one question answered there are always others opened...
Thanks a lot for correcting the post! (yes, the text seems to be too short...)

Ágnes Kiricsi said...

Many thanks Les, for the comment, and Noli, for the further explanation on the problem you have found about the Sun's direction and the colour range.
Michiel, I think you might be interested in this photo:
http://gallery.site.hu/u/
Controll/kondenz/32432194.jpg.html
(Sorry, I had to cut the link into 2 parts). If I can see it well, it probably shows what you mentioned about the wings!

Michiel de Boer said...

@Ágnes: Yes that's what I mean. The rainbow colors do not come from exhaust but from the air pressure created by the wings. Click my name again to see an excellent example of the on Airliners.net by Josef P. Willems. Use the search on that website to see a lot more very nice examples: http://tinyurl.com/yqgq2n

Michiel de Boer said...

And @ Noli: The principle of the colors is because all particles in that area have the same size, and so reflect the same color. Because more water is condensating on these ice chrystals, the crystals grow and the color changes. On a certain point they differ in size to much, or have become too large to reflect a single color, and the trail is 'white'.

Noli said...

michiel: your las comment is what I tried to tell in so-so many words...
I do not know enough about the physics of aerodynamic things, that's why I'm trying to take more photoes of coloured contrails.

uncinus said...

This is the result of an Aerodynamic Contrail. The colors are due to particle sizes. See

This poster

Noli said...

uncinus, thanks a lot for the link!!!