Glory & cloudbow

 

Most of the postings I have made have been from the ground level, and those are often of animals. This is more a consequence of opportunity than narrow interest. But, now and then I can glance at our region from above the clouds. This is not just for the wider field of view, but for the things that are only possible to see by looking down, than by looking up. These are the directional things seen opposite the sun when looking down particularly on clouds.

Things seen can be are loosely grouped by whether you are looking down on water clouds, ice clouds, haze, or clear air. Yesterday, I looked down on some water clouds and briefly saw both a cloudbow and a glory. These are at their best when the cloud drops are uniform in size and this was accomplished by flying over a wave cloud. (There was also a faint shadow of the airplane.) 

The cloudbow (left and right side of picture) is easiest to understand. It is about the size of a standard rainbow (about 42° in radius), but unlike the standard rainbow, the colours are faint due to the diffraction in the smallish cloud drops. Just to the inside of the cloud bow there are fainter supernumerary bows.

At the centre of the bow (and centre of the picture) is the much smaller, but brighter, glory. It can be quite colourful with multiple rings if the drops are really uniform. However, in the present view about all that is seen is a small bright circle with a slight horizontal line through it. This line is the shadow of the plane (and so this is the antisolar point).

A fish-eye view out the window of a commercial airplane leaving Castelgar. The cloudbow and supernumerary bow are seen on the left and right side. The glory and (slight) shadow are seen in the centre of the picture.

 

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3 Responses to Glory & cloudbow

  1. Trevor Goward says:

    Fascinating, many thanks; though I’m not sure I understand the significance of this being a “wave cloud”. Is the point that the droplets are uniform owing to the cloud’s recent formation, or is there some other point I’m missing? Sorry to bother you on details, but I really do find this post and your account quite fascinating.

    • Alistair says:

      Trevor, a wave cloud is caused by stable air flowing over one or more mountains. The air is lifted into the cloud and may pass through it in a few minuets. All the cloud drops grow together and are nearly the same size and then they quickly pass out of the down-wind end of the cloud, before they can evolve. So, the position of the wave cloud may be stable, but the cloud drops are constantly replaced by identical ones. For seeing a phenomenon that requires uniform sized drops, a wave cloud is as good as it gets.

  2. Trevor Goward says:

    Thanks for explaining this! With this in mind, I’ll keep my eyes peeled.

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