Cloud Watching 102: The Rarest Clouds

June 9, 2013

Credit: NASA
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They’re back! Noctilucent clouds, the rarest, newest and most mysterious of clouds have begun.

These are clouds from outer space, formed by meteor dust. These electric blue clouds are only seen in summer and they have returned to our skies. Indeed, they arrived on May 13, the earliest onset on record!

Notice how bright noctilucent clouds are compared to the lower-lying clouds at the bottom left of the picture. Source -- NASA

Normally noctilucent clouds are restricted to the most northern skies, but this year, they reach all the way to Middle America.

What you are watching is ice and meteor dust. When meteors burn up in the upper atmosphere, they leave dust, like smoke. When the hot moist air of summer meets the cold dust from outer space, it forms clouds roughly 50 miles (83 km) high in the atmosphere. When the light from the rising or setting sun hits these sheets of icy smoke, it glows an eerie blue and seems to ripple like waves across the skies.

The glowing clouds are formed when the light from the setting or rising sun strikes the icy clouds floating high in the atmosphere. Source: NASA and the Naval Research Laboratory, Washington, D.C.

The first time scientists ever record seeing noctilucent clouds was 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 have spread south. Originally, they were seen only 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.

No one knows why this year’s clouds are arriving so early. This is the peak of the solar cycle and normally strong solar winds dramatically reduce the amount of dust floating in the upper atmosphere. However, this year, the clouds are ignoring the rules.

Normally, the clouds appear 30 to 60 minutes after sunset. So look to the skies, Middle America. You get to share the show that Canadians have been enjoying for a century. If you are lucky, you will see the rarest clouds on Earth.

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Evelyn Browning Garriss, historical climatologist, blogger, writer for The Old Farmer's Almanac, and editor of The Browning Newsletter, has advised farmers, businesses, and investors worldwide on upcoming climate events and their economic and social impact for the past 21 years.

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