The multi ringed ringed glory, 3-4 rings are visible, is directly opposite the sun and centred on Ed's shadow. The glory is produced by sunlight diffracted almost directly back along its path by very small fog droplets.
There lies an apparent contradiction because the temperature was -18F (-28C). However, in the absence of dust or other nuclei water droplets can exist below 0C in a supercooled state. In exceptionally pure air they can stay supercooled to about -40C. The air over the Greenland Ice Cap is very pure and it will be interesting to find the lowest temperature that Ed can find glories and fogbows. They will soon, however, have to be by moonlight.
The backdrop at right is Mie-Lorentz computation of a glory by IRIS. The result is fully accurate but we have no simple model to visualize how light waves are diffracted by the droplet directly backwards towards the sun.
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