Something Like Diamond-dusts Glittering On Plane

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Something like diamond-dusts glittering on plane
Taken by Shiraishi on October 10, 2016 @ Over Japan Sea

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Date Taken: 2016:10:16 13:58:29

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Something like diamond dusts glitter on plane. I saw some glittering particles on a wing of my airplane. They aligns along an arc. I composited the frames from a movie, and I found 2 arcs on the wing. I do not know whether there are actually 2 arcs of ice crystals or one can see 2 arcs due to the relationship among me and the crystals and the Sun. Sony ILCE-7S digital camera; ISO 250, F10, 1/1000s exposure, f=30mm A composite of 132 frame from a 4.4s movie. The movie is here: https://youtu.be/j4JHVEig2Tw

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Im a meteorologist and have been on many plane flights. I have never seen anything like this and I can not explain it.

Posted by roywspencer 2016-10-16 07:48:39

Thank you, roywspencer!
I have never seen anything like this, either.
I am the sort of person who understand or is interested in many kinds of atmospheric optics.
But this phenomenon (something small particles are glittering on a wing for a while) seems not to have characteristics of major/minor atmospheric optics or usual diamond-dusts due to ice crystals.
Somebody knows?

Posted by shiram 2016-10-16 08:05:19

I now think that the plane was flying through ice crystals which are flat plate-shaped. They are reflecting the sunlight when they are at just the right angle as the tumble. At 1/1000 sec shutter speed, and an air speed of 400 knots, there should be 0.2 meter long streaks from the 1/000 sec exposure time, but instead they are not streaked. So I think they are tumbling flat plate-shaped crystals reflecting the sunlight. Air flow over the wing is causing some sort of preferred orientation to the crystals.

Posted by roywspencer 2016-10-16 09:52:01

The wingtip vortex is made visible by the ice crystals. I would not exclude the possibilty that the crystals themselves were formed by the pressure difference on the wings and the vortex just aligned them.
Absolute awsome observation! Thank you for sharing!

Posted by LandyGyebnar 2016-10-16 10:46:06

One thing is not really clear. How could the vortex move against the direction of the planes flight? The vortex is always getting farther back away from the wings and the plane in a widening angle, but here it seems that the vortex foregoes the wing.

Posted by LandyGyebnar 2016-10-16 11:57:11

I think it is rather something happening between the panes of the window.

Posted by Dirk Bauwens 2016-10-16 14:23:33

Thank you, roywspencer.
As you pointed out, the crystals were not streaked even in 1/1000 sec exposure, so I agree that the arcs are not their actual flying path but the crystals are flat plate-shaped and as a result of their tumbling I can see an arc-shape glittering.
However, in order that the crystals tumble to align to reflect the sunlight like an arc, some characteristic flow or vortex may appear around the wing?

Posted by shiram 2016-10-17 08:10:09

Thank you, LandyGyebnar.
There seems to be some flow or vortex, but as you pointed out, it is wonderful that such flow was created near a wing.

Posted by shiram 2016-10-17 08:12:18

Thank you, Dirk Bauwens.
However, I do not think something happened between the panes of window, because the panes are too close to be focused well in this photo.
The distance between the winglet and me was about 25 m (This plane is A340-300). And this photo was taken by F10 and f=20mm in APS-C (30mm-equivalent).
Thus, the depth of field is 1.7 m to infinity. I set AF at the winglet. Even if the best focus was set at the middle of the wing, the depth of field would be 1.5 m to infinity. So, anything between the window panes could not be resolved. Please note that the window edge was blurred by out of focus. If anything between panes could be resolved, the scratches on panes could be also resolved (however, they can not be seen).
Subjectively speaking, I saw the particles in the air outside.

Posted by shiram 2016-10-17 08:23:51

Thank you, for your clarification, shiram. I did some further research on the pressure zones above an airplane wing. I think now that the phenomenon might be caused by flash freezing of water vapour into small crystals in the zone where the ambient air pressure meets the low pressure zone above the airplane wing. Alas, Im no specialist at all.

Posted by Dirk Bauwens 2016-10-19 08:39:45

Thank you, Dirk Bauwens.
I appreciate you did further consideration again.
I am not a specialist of aerodynamics or aeromechanics, either...
I will confirm the solar altitude and direction relative to the airplane at the time this movie was taken.
And I remembered that when this crystals could be seen (several minuites), a fine contrail was intermittently created from the top of the winglet. It suggests there was a supersaturated air? When a plane rushes into such air, a strong pressure change around the wing might cause sudden precipitation and sublimation into plate-shape ice crystals over a wing with a certain inclination, and some of them such that can reflect the sun light toward me could be seen from me and I could see an arc-shape glittering??
I am not a specialist, and I do not know the truth...

Posted by shiram 2016-10-19 09:34:39

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