http://signs-of-the-times.org/signs/chains/signs20060801_Dry.php#14443d350467b2ab8096643fd52
Rare clouds 'could indicate global warming'
Rare clouds 'could indicate global warming'
I've seen clouds like this over the mountains and foothill areas while traveling in Colorado in recent years in areas over 5000 feet. The sun wasn't rising or setting either. Then again, maybe what I saw then wasn't the same cloud type, but they sure looked like it -- sort of flat, soft on the edges, very colorful mother of pearl type shades to them.
[...]
Also known as mother of pearl clouds, these formations only occur high in the atmosphere, in some of the coldest temperatures on Earth.
But their ethereal beauty may conceal a dark secret - it is thought that chemical reactions on the surface of the clouds help deplete the ozone layer.
This spectacular picture was taken at sunset in East Antarctica. The clouds' formation is dependent on a combination of extreme weather conditions, including temperatures below minus 80c, and they are visible only at sunrise and sunset.
This nacreous cloud was captured on film by scientists at the Mawson research station, who estimate it had formed 12 miles above Earth, in winds of 140mph and in temperatures as low as minus 83c.
Researcher Dr Andrew Klekociuk said clouds as spectacular as this are very rare. "You have to be in the right part of the world in winter and have the sun just below your horizon to see them," he added.
"Our expeditioners at Mawson are in one of those special parts of the world."
[...]