Rare clouds (and rainbow)

Fascinated by clouds (and inspired by Vivek's comment) I searched www.nationalgeographic.com for some rare cloud photos. This is what I found.


Rare cloud forms above Antarctica


Rare "rainbow" spotted over Idaho

Source: http://news.nationalgeographic.com/news/2006/08/060804-ice-cloud.html and http://news.nationalgeographic.com/news/2006/06/060619-rainbow-fire.html.