This image shows how light scattering by small cloud droplets produces multiple effects that are actually all part of the same phenomena. The scene was taken by Leigh Hilbert in Washington State in January ’06. The shadow of the descending aircraft is surrounded by a bright glory (1, 2,) centred just behind the wing where Leigh was seated. Much further from the aircraft shadow is a circular cloud bow (1,2), a form of fogbow (1, 2), produced also by scattering by cloud water droplets. The classical light paths producing it are those of the rainbow (1,2,3) but diffraction by the small droplets produces something much broader and almost lacking in colour. Inside the main cloudbow is a supernumerary arc that, characteristically for cloudbows and fogbows, has more colour saturation than the primary. The more distant clouds at the image top have produced a narrower cloudbow indicating that their droplets were larger.
Good photo and jazzy explanation!
ReplyDeleteTo our halo meeting in the last year we had a discussion about difference between fog bow and cloud bow, because in the mountains comes the fog from overlying clouds. What would you say?
Cordial greetings
Claudia
Hello Claudia! The two names seem to refer more to _where_ the bow is seen. If the droplet sizes are similar then so is the appearance? Are cloud droplets much different?
ReplyDeleteThank for your answer. I mean this case like the picture from Carolin Baumann. This bow orginated in a Stratocumulus Cloud which hanged on the mountain peak. Of course ... on this side of the mount ... was fog ...
ReplyDeleteI've somewhere read, that the fog bow vertical and the cloud bow horizontal. But we've many observations where the bow is (spacially) slanting???
Yes, the geometry of viewing must mean that most fogbows seen on a mountainside will be from a fairly low sun and their centres will therefore be not far below the horizon. Compared with that, most cloudbows from aircraft are seen under a high sun and looking down on a horizontal droplet layer. But of course, fogbows or cloudbows do not really exist in space - they are just a collection of rays entering your eye or camera lens. They look the same regardless of the tilt or otherwise of the droplet layer producing them.
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