A NASA satellite has captured these noctilucent or
“night shining” clouds on June 11, 2007. … Very little
is known about how these clouds form over the poles.
Credit: Cloud Imaging Team, U. of Colorado/NASA
Dozens of international scientists are meeting this week in Fairbanks to tackle one of the most mysterious indicators of changing climate in the Arctic — the strange, high clouds that etch the dimming sky above the setting sun.
They’re called noctilucent clouds, and they form at least 50 miles above the surface for reasons scientists have not figured out. Not well documented until a few decades ago, the strange euphemeral bands of crystals are only one of the weird phenomena seen in the mesosphere, the coldest and least studied region of the atmosphere.
As a result, some scientists have called it the “ignorosphere” This untouchable zone ranges from about 30 miles up to about 55 miles out — too high for aircraft and too low for spacecraft and orbiting satellites. But the advent of rocket technology, remote sensing and satellite coverage has peeled back some of its details.
The Eighth International Workshop on Layered Phenomena in the Mesopause Region has brought together dozens of the people in pursuit of these mesopheric mysteries at the University of Alaska Fairbanks. Among other bizarre tidbits from the planet’s air ocean, they will consider airborne soot and wafting meteoric dust, as well as the fantastic rippling of gravity waves and atmospheric tides. Who knew?
Want some late summer reading: Here are 56 study abstracts in a large PDF file.
UAF writer Marmiam Grimes puts it all in perspective in this on-line story:
Noctilucent clouds shine in the dark portion of the sky
over the Poker Flat Research Range in 2005.
Photo courtesy of Richard Collins, UAF Geophysical Institute
As the late summer sun sets in the Arctic, bands of wispy, luminescent clouds shine against the deep blue of the northern sky.
To the casual observer, they may simply be a curiosity, dismissed as the waning light of the midnight sun. But to scientists, these noctilucent ice clouds could be an upper-atmospheric symptom of a changing climate.
“The question which everyone in Alaska is dealing with is what are the symptoms of climate change and, as in medicine, how do these symptoms reflect the underlying processes,” said Richard Collins, a researcher at the Geophysical Institute at the University of Alaska Fairbanks. “It is believed that [these clouds] are an indicator of climate change.”
Between Aug. 20-23, sessions will include information on the latest ground-based and satellite data on the mesopause region, an area of the atmosphere 50 miles above Earth’s surface and the site of the coldest atmospheric temperatures.
Noctilucent clouds form under conditions that counter common logic. They only form in the summer, when solar radiation is most intense, Collins said. That solar heating, rather than warming the mesopause, causes cooling, he said.
“The mesopause region is colder in summer under perpetual daylight than it is in winter under perpetual darkness.”
The reason lies in the movement of air within the atmosphere, Collins said. Solar radiation heats the lower atmosphere, causing a rising cell of air over the summer pole, he said.
One of the first ground sightings of noctilucent clouds in the 2007 season.
Credit: Veres Viktor of Budapest, Hungary taken on June 15, 2007.“As the air rises it cools and that beats out the radiative heating.”
Those cold temperatures allow the ice clouds to form in the mesopause. The clouds could serve as an indicator of climate change because an increase in carbon dioxide, which causes heating in the lower atmosphere, causes cooling in the upper atmosphere.
Collins said the noctilucent clouds are a relatively new phenomenon. History indicates that humans first recorded their presence in the 19th century, he said. Satellite and ground-based data has been limited, he said, but it appears that the clouds have become more prevalent over time.
A new satellite, Aeronomy of Ice in the Mesosphere, or AIM, was launched in April 2007 to observe clouds and their environment in the mesopause, Collins said scientists are looking forward to having more reliable data, which could contribute to a broader understanding of the upper atmosphere, noctilucent clouds and how both fit into the climate system.
