Cloud iridescence opposite the sun
I already observed cloud iridescence opposite the sun several times (1 – 2). But until now I always could explain it by the appearance of a deformed glory. But on February 18, 2014, on Mt. Zugspitze, it was different. On the summit of that mountain at 2963 metres above sea level, some altocumulus clouds passed about 500 metres above me. While the shadow of the mountain and a faint glory showed up in a lower cumulus cloud, the colours in the foehn cloud were arranged in bands and seemed to be completely independent from the glory (more pictures here). Also in sunward direction, the altocumulus lenticularis showed similar colourful bands.
Deformed glories are caused by differences in the radii of the cloud droplets, which changes the diameter of the glory. When the droplets become smaller within a short distance, the radius increases, and if the observeer sees only a fragment of the glory, colours may appear distorted. I, however, never before noticed such colour bands in the area where a glory can appear.
Author: Claudia Hinz