Coloured Cloud? -
Imaged by Radek Grochowski from Babia Góra mountain, 1725m, in Southern Poland. "The temperature was -13 Celsius. Scattered clouds were rising quickly from the valleys and beautiful horizontally parallel colors appeared on them". Imaged near noon, solar altitude 17.5°. ©Radek Grochowski
|The colours are too regular to be iridescence.
They are the colours of a fragment of a 22° circular halo produced by tumbling ice crystals in the clouds rising from the valley.
The irregular cloud shapes mask the halo's curvature but perhaps it is just apparent in the lower image with a wider field of view of 18°.
The low winter sun has dipped the halo slightly below the horizon. The mountain vantage point has dipped horizon ~1° below the true astronomical horizon.