Nacreous Clouds

The display of December 22, '14 over Oslo imaged 38 minutes after sunset by Lars Brubaek .

"I first photographed the clouds at 13:30 above a low sun. A few reddish wisps were still visible 51 minutes after sunset. Treatment: graduated filters to even out the large differences in luminosity and render the cloudlit ground fog visible."

Image ©Lars Brubaek, shown with permission

The image nicely captures the visual impact of nacreous clouds. A darkling sky, intense bright electric colours, films slowly stretching and curling high above.

The 15-25 km high stratospheric clouds remain in sunshine after sunset on the ground. Their colours are from diffraction by the tiny ice crystals that compose them. These Type II polar stratospheric clouds are often embedded in less luminous and more noxious Type I PSCs of nitric and sulfuric acids. Type II cloud particles destroy stratospheric ozone by catalytic reactions on their surfaces.

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