Iridescence ~ Order & Disorder  

Two images by Roger Benoit of iridescence at the 3426m Gspaltenhorn in the Swiss Alps.

The top image shows chaotic colours in banner (orographic) cloud formed downwind of the peak. The rapidly formed small droplets in these clouds are ideal for producing iridescence. Turbulence has produced cloud fragments with varying mean droplet sizes from place to place and thus chaotic colours.
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©Roger Benoit
©Roger Benoit
The Gspaltenhorn three days later.

Water droplets are again diffracting sunlight but here they are of uniform size across a widespread haze layer. The diffraction pattern is now ordered - a circular multi-ringed corona.

The exact same processes produce both extremes. Uniform sized drops across a cloud give a corona, widely varying drop sizes from place to place give widely varying colours.