Interesting Contrail Shadow in the Polar Vortex

jamzik

New Member
I was in Milwaukee Wisconsin for the holidays last winter when the Polar Vortex struck the city. Awesome and brutal cold. It got down around minus 22 centigrade when I took these photos. I got up before sunrise, which was about 7:23, (December 29, 2013 - oops, the date might be off a day or two) and went to Big Bay Park, (actually in the suburb of Whitefish Bay) I walked down the bluff to the shore of Lake Michigan, and took a series of many photos as the sun rose. When the air gets that cold, there is something called the Lake Effect. http://en.wikipedia.org/wiki/Lake-effect_snow Moisture is picked up out of the water and the lake surface can be covered in wispy clouds.
_MG_4505-5.jpg
I mostly shot into the sun, as the sun rose through a layer of clouds at the horizon, got some spectacular shots. One in particular though (actually a series of three bracketed shots at different exposures) is what I am posting here. I think they were taken at 7:55, about a half hour after sunrise, but could be a little off here. I am posting two versions here, one a tif from a single raw, run through lightroom, which shows the effect I have questions about, and an hdr version (which gives a little better impression of the whole scene, and looks cooler.)

_MG_4505-6_6-6_7-6_fused.jpg


Lots of cool clouds! From bottom, Lake effect mist, then on the horizon, a bank of clouds that might indicate the far shore of Lake Michigan, and then it gets a little complex. The interesting thing here is the shadow of the contrail (that's what I think it is, but it is dissipated, and the weather is quite strange) on the pillow like cloud. It appears at first glance that the contrail is beneath the pillow cloud and the shadow goes upwards. But I wondered about it, and did a little research. One of best things I found was this quoted from http://earthsky.org/todays-image/jet-contrail-casts-a-shadow and quoting Les Cowley.

"he said: Contrail shadows sometimes appear counter-intuitive. [They may seem to be cast] by a low altitude bright light shining upwards and casting the contrail shadow on a higher cloud.​

The reverse is the case …​

In other words, he said, the jet itself and its contrail are always higher up than the shadow, which is cast on clouds below. By email, Les told me:​

Contrail shadows often don’t look ‘right’ and seem as if the contrail is below the clouds. But the shadow casters – the sun and moon – always shine downwards so the shadow must be below the contrail.

Like all statements there is an exception! At sunset and sunrise rays can travel very slightly upwards to illuminate the underside of clouds. Under those circumstances however a contrail shadow would be a long way from the contrail."
Even though he grants an exception at the end for sunrise and sunset, my working assumption now is that the contrail is above the pillow like cloud, casting a volumetric shadow (sounds good, I read that somewhere) down and through the pillow cloud. I think I have a lovely large sized optical illusion here. (and something about parallax?) Two things to note, the contrail on the upper left hand corner of the image, appearing to pass over a cloud, and the slight dark band, between the bend in the contrail, and the pillow cloud. (and actually, I am calling it a pillow cloud,it looks like my pillow, but it might not fit the definition of a pillow cloud - what is it called?)


I'd appreciate any clarification or comments. Thanks.​





 
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Mick West

Administrator
Staff member
Excellent photos, and quite an interesting three dimensional puzzle to sort out.

I think key to understand it are two fact.

Firstly, the sun is very far away, so if it's a hair above the horizon, then it's above everything else in the sky. The sun is so far away that its rays arrive parallel, and it does not make any sense here to describe the position of the sun in the sky. Instead consider the angle of the sun, which is the same for all the elements in the photo.

Secondly, white plus white. If a cloud is thin, and lit by the sun, then it is not making anything behind it darker. It can only make it more white. So if you have two such clouds, then it does not matter at all to the end visual result whether one is above the other or not. The end result is the same.

So here, the large contrail is above everything. It looks like it is below the streaky cloud because its denser, and hence brighter. But it's actually above it.

So I think the larger contrail matched up with the shadow like this:
20140822-153642-qenri.jpg
 
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captfitch

Senior Member.
In that picture certainly the sun is above the clouds and contrail. However... Is it possible that in the very earliest of sunrise, the curvature of the earth and thus the curvature of clouds could possibly create a situation where the sun could illuminate from below? I don't know how to illustrate that but I imagine someone could. I know I've flown under clouds that were "reverse" lit from below.
 

Trailblazer

Moderator
Staff member
In that picture certainly the sun is above the clouds and contrail. However... Is it possible that in the very earliest of sunrise, the curvature of the earth and thus the curvature of clouds could possibly create a situation where the sun could illuminate from below? I don't know how to illustrate that but I imagine someone could. I know I've flown under clouds that were "reverse" lit from below.
Slightly off topic but isn't that the case with noctilucent clouds, which are much, much higher than ordinary clouds (I've seen 80km mentioned)?

We had a good display of them over the UK a few weeks ago.
 

Gridlock

Senior Member.
So here, the large contrail is above everything. It looks like it is above the streaky cloud because its denser, and hence brighter. But it's actually above it.

Cool photos, thanks for sharing - Mick, I assume ^^ above/below typo?
 

Trailspotter

Senior Member.
A typically terrible illustration.
20140822-163002-s9pcm.jpg
I disagree with the caption and think than normal perspective DOES apply here as well. Like the parallel lines diverging from (or converging into) the same point, the 'parallel' sunlight rays radiate from the Sun. The contrail segment that cast shadow on the cirrus cloud is farther away from the camera/observer that the cloud, therefore its shadow looks bigger because of perspective:
Contrail shadow.png

What confuses our eyes (and brains) is the fact that the cirrus cloud is semitransparent, like a net curtain, so the objects (e.g., contrails) behind it and the shadows they cast on it are seen through it.
 
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Mick West

Administrator
Staff member
I disagree with the caption and think than normal perspective DOES apply here as well.

I was more referring to the position of the sun, so perhaps a bad choice of words on my part. People instinctively think of the sky as being something like a dome, with the clouds and sun painted on the dome. This falls down even just for the clouds (which exist at multiple altitudes.) But is especially bad for celestial objects like the sun
 

Mick West

Administrator
Staff member
I disagree with the caption and think than normal perspective DOES apply here as well. Like the parallel lines diverging from (or converging into) the same point, the 'parallel' sunlight rays radiate from the Sun. The contrail segment that cast shadow on the cirrus cloud is farther away from the camera/observer that the cloud, therefore its shadow looks bigger because of perspective:
Contrail shadow.png

What confuses our eyes (and brains) is the fact that the cirrus cloud is semitransparent, like a net curtain, so the objects (e.g., contrails) behind it and the shadows they cast on it are seen through it.

There's an interesting atoptics page on this:
http://www.atoptics.co.uk/atoptics/rayform.htm

And:
http://blogs.discovermagazine.com/b...2/crepuscular-rays-are-parallel/#.U_j-G7xdX_A

Gives:
 

jamesglory

New Member
I was in Milwaukee Wisconsin for the holidays last winter when the Polar Vortex struck the city. Awesome and brutal cold. It got down around minus 22 centigrade when I took these photos. I got up before sunrise, which was about 7:23, (December 29, 2013 - oops, the date might be off a day or two) and went to Big Bay Park, (actually in the suburb of Whitefish Bay) I walked down the bluff to the shore of Lake Michigan, and took a series of many photos as the sun rose. When the air gets that cold, there is something called the Lake Effect. http://en.wikipedia.org/wiki/Lake-effect_snow Moisture is picked up out of the water and the lake surface can be covered in wispy clouds.
_MG_4505-5.jpg
I mostly shot into the sun, as the sun rose through a layer of clouds at the horizon, got some spectacular shots. One in particular though (actually a series of three bracketed shots at different exposures) is what I am posting here. I think they were taken at 7:55, about a half hour after sunrise, but could be a little off here. I am posting two versions here, one a tif from a single raw, run through lightroom, which shows the effect I have questions about, and an hdr version (which gives a little better impression of the whole scene, and looks cooler.)

_MG_4505-6_6-6_7-6_fused.jpg


Lots of cool clouds! From bottom, Lake effect mist, then on the horizon, a bank of clouds that might indicate the far shore of Lake Michigan, and then it gets a little complex. The interesting thing here is the shadow of the contrail (that's what I think it is, but it is dissipated, and the weather is quite strange) on the pillow like cloud. It appears at first glance that the contrail is beneath the pillow cloud and the shadow goes upwards. But I wondered about it, and did a little research. One of best things I found was this quoted from http://earthsky.org/todays-image/jet-contrail-casts-a-shadow and quoting Les Cowley.

"he said: Contrail shadows sometimes appear counter-intuitive. [They may seem to be cast] by a low altitude bright light shining upwards and casting the contrail shadow on a higher cloud.​

The reverse is the case …​

In other words, he said, the jet itself and its contrail are always higher up than the shadow, which is cast on clouds below. By email, Les told me:​

Contrail shadows often don’t look ‘right’ and seem as if the contrail is below the clouds. But the shadow casters – the sun and moon – always shine downwards so the shadow must be below the contrail.

Like all statements there is an exception! At sunset and sunrise rays can travel very slightly upwards to illuminate the underside of clouds. Under those circumstances however a contrail shadow would be a long way from the contrail."
Even though he grants an exception at the end for sunrise and sunset, my working assumption now is that the contrail is above the pillow like cloud, casting a volumetric shadow (sounds good, I read that somewhere) down and through the pillow cloud. I think I have a lovely large sized optical illusion here. (and something about parallax?) Two things to note, the contrail on the upper left hand corner of the image, appearing to pass over a cloud, and the slight dark band, between the bend in the contrail, and the pillow cloud. (and actually, I am calling it a pillow cloud,it looks like my pillow, but it might not fit the definition of a pillow cloud - what is it called?)


I'd appreciate any clarification or comments. Thanks.​





magnificent photographs!
Blessings,
James:)
 

Lisa P

Active Member
Not West-East but this flight does cross the coast and could be better lined up with the sun

gc.JPG

That is what I started thinking today it may not have been west to east more like the direction above, and the height would have been higher like that. You are really going to a lot of trouble to help I really appreciate it hey.
 
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