Photo credit - Bill Valentine

Photo credit – Bill Valentine

Cloud of the Day – Noctilucent

Photo credit - Jan Koeman

Photo credit – Jan Koeman

You thought nacreous clouds were high? Well, at as much as 80,000 feet they are, but compared to noctilucent clouds, nacreous are practically scraping the ground. Like nacreous, noctilucent clouds are best seen when the Sun is just below the horizon for the observer. They are so high that they are still illuminated by the Sun when it’s getting dark on the ground. That’s why they’re called noctilucent, or “night shining.” These clouds, also called polar mesospheric clouds, have been observed at well over eighty kilometers above the ground.

Photo credit - Ralph Croning

Photo credit – Ralph Croning

Noctilucent clouds are made of ice crystals. That requires water vapor and nucleation particles for the vapor to condense on. The water vapor is pumped up there by the strong convective energy found in the summer months. Even at that extreme height, some of the water can make it. Getting the particles that high is much more difficult. The best candidates are from the most powerful volcanoes, and dust actually sifting down from space.

The color of noctilucent clouds ranges from white to electric blue, glowing as if with their own light. There is no precipitation from noctilucent clouds.


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