Some things only happen in summer. One of these is an eerie electric blue cloud, made from meteor smoke, which glows in the nighttime skies.
As you watch one of these clouds gleam, cool yourself off by realizing that it is made of ice. The hot moist air of summer meets the cold dust from outer space and produces the rarest and most mysterious of clouds, the noctilucent cloud.
Mysterious glowing noctilucent clouds SOURCE: NASA
They are the newest of all the clouds that we observe. They were first seen in 1885, after the famous explosion of Krakatoa volcano. The volcanic dust filtered out incoming sunlight, forming gorgeous fire-red sunsets. Watching sunsets became an international fad. Then, scientists noticed that after the sun set, mysterious glowing blue clouds began to spread through the skies.
Strangely, even after Krakatoa’s volcanic debris settled, the clouds remained. Indeed they spread. Originally, they could only be seen in the most northern skies of Canada, Europe and Siberia. Now you can see them in the night skies of Colorado and Virginia. No one knows why they are spreading.
Originally, noctilucent clouds only formed in Arctic skies, but now they are spreading south.
They are also the highest clouds in the sky, forming more than 50 miles high in the sky, on the edge of space. They grow only in the air’s mesosphere layer, a high cold layer that is, according to NASA, “one hundred million times dryer than air from the Sahara desert."
How could clouds form in such intensely dry skies?
Clouds are made of water and particles. In the lower atmosphere, water molecules attach to the dust in the air and form droplets. As these droplets float through the sky, too light to fall, they collect into clouds. Scientists were mystified. How could dust get fifty miles high into the air?
This August, data from NASA’s AIM spacecraft has finally found out—most of the dust is from outer space! As meteors plunge into Earth’s atmosphere, they burn up. Only a few reach the surface of the Earth. Their “smoke”, the microscopic dust, floats in the dry upper atmosphere, slowly collecting water molecules and forming ice crystals smaller than the particles in cigarette smoke.
This year’s first observed noctilucent clouds formed on June 13, 2012. SOURCE: NASA
They only form in summer, when hot moist air rises and a few, very few, water molecules rise high enough to cling to the drifting space dust. Then they form glittering sheets of ice, reflecting the lights of the setting sun with an eerie glittering blue light.
So this summer, search the skies about 30 to 60 minutes after the sun sets. You may see the gleaming lights of the clouds from outer space.
Evelyn Browning Garriss, historical climatologist, is a longtime writer for The Old Farmer's Almanac. She is also editor of The Browning World Climate Bulletin and has advised farmers, businesses, and investors worldwide on upcoming climate events and their economic and social impact for the past 21 years.