Greenland Ice Cap Optics
|Coronae are a diffraction phenomena.
Light incident on an individual droplet is scattered from its surface. The scattered light propagates outwards as spherical waves.
The waves overlap and interfere. In directions where overlapping wave crests coincide there is light. Where crests coincide with troughs of the other wave there is destructive interference - darkness.
The result in the far field is a circular diffraction pattern of a bright central aureole surrounded by ever fainter rings.