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30 December 2011

Mother of Pearl - First polar stratospheric clouds of northern winter form around the Arctic Circle

As December draws to a close, the first polar stratospheric clouds of northern winter are forming around the Arctic Circle. P-M Hedén photographed the phenomenon last night over Tänndalen, Sweden:


"Wow, what a lovely sight!" says Hedén. "They appeared in the sunset sky next to Venus and the crescent Moon."

Also known as "nacreous" or "mother of pearl" clouds, these icy clouds form in the lower stratosphere when temperatures drop to around minus 85ºC. Sunlight shining through tiny ice particles ~10µm across produce the characteristic bright iridescent colors by diffraction and interference.

"Nacreous clouds far outshine and have much more vivid colours than ordinary iridescent clouds, which are very much poor relations and seen frequently all over the world," writes atmospheric optics expert Les Cowley. "Once seen they are never forgotten."

more images: from Krystian Rosa of Brandbu, Norway; from Patricia Cowern of Porjus,Sweden

- Spaceweather.com