Contrail Shadow & Halo

Pictured by Pierre Jobin across the bay of Saint-Brieuc in western France.


Images ©Pierre Jobin, shown with permission
Contrails, their shadows and a 22 halo combine into eerie scenes. The cloud diffused sun surely shines upwards to cast a shadow onto higher cloud. The truth is the reverse. The contrail is above a thin layer of cirrus. The sun casts the shadow downwards onto lower cloud. We see it all through the translucent cloud screen. The reversed view creates the illusion..

 
Ice crystals of the same cirrus layer refract sunlight into a 22 halo. Pierres image nicely shows how the halo forms a dark hole in the sky. Its inner 22 radius red edge marks where sun rays have a minimum deviation through the hexagonal ice prisms. Other angles and skew rays are refracted farther from the sun to brighten the sky outside the halos inner edge. The 22 halo is rather more than a ring!

Smaller crystals or supercooled water droplets have diffracted sunlight to produce the iridescent colours near the sun.

The shadow is seen through the lower cloud layer.

Atmospheric
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