Noctlucent Clouds Descend the Latitudes

Wired Science reports :

Mysterious, glowing clouds previously seen almost exclusively in Earth’s polar regions have appeared in the skies over the United States and Europe over the past several days.

Formed by ice literally at the boundary where the earth’s atmosphere meets space 50 miles up, they shine because they are so high that they remain lit by the sun even after our star is below the horizon.

The clouds might be beautiful, but they could portend global changes caused by global warming. Noctilucent clouds are a fundamentally new phenomenon in the temperate mid-latitude sky, and it’s not clear why they’ve migrated down from the poles. Or why, over the last 25 years, more of them are appearing in the polar regions, too, and shining more brightly.

“That’s a real concern and question,” said James Russell, an atmospheric scientist at Hampton University and the principal investigator of an ongoing NASA satellite mission to study the clouds. “Why are they getting more numerous? Why are they getting brighter? Why are they appearing at lower latitudes?”

Noctilucent clouds were first observed in 1885 by an amateur astronomer. No observations of anything resembling noctilucent clouds before that time has ever been found. There is no lack of observations of other phenomena in the sky, so atmospheric scientists are fairly sure that the phenomenon is recent, although they are not sure why.

Over the last 125 years, scientists have learned how the clouds form. At temperatures around minus 230 degrees Fahrenheit, dust blowing up from below or falling into the atmosphere from space provides a resting spot for water vapor to condense and freeze. Right now, during the northern hemisphere’s summer, the atmosphere is heating up and expanding. At the outside edge of the atmosphere, that
actually means that it’s getting colder because it’s pushed farther out into space.

The recent observations of noctilucent clouds at all kinds of latitudes provide an extra impetus to understand what is going on up there. Changes are occurring faster than scientists can understand their causes. “I suspect, as many of us feel, that it is global change, but I fear we don’t understand it,” Wickwar said.

“It’s not as simple as a temperature change.”

I had never witnessed NLCs before, and to be honest, I wondered if I would actually notice them if I did get the chance to see them. Wow, was I wrong ... these literally startled me! Thankfully, I was called to go meet a friend this evening, otherwise I wouldn't have been outside to see them. I walked out of my garage, and glanced up expecting to see a mostly dark sky, and this BRIGHT, electric blue bank of NLCs was filling most of the north sky ... gorgeous!

- Mark Poe