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Warming Creates More Night Shining Clouds

Irene Klotz, Discovery News

The clouds appear more frequently than in the past and form at lower altitudes, which, Russell said, may be due to a buildup of carbon dioxide in the lower atmosphere. The gas traps heat and leaves the upper mesosphere colder than normal.

The scientists believe a difference of just 5 degrees Fahrenheit has profound effects on the clouds' structure and motion.

"A small change in temperature is causing a dramatic change in cloud behavior," Bailey said.

During its first season of operations, AIM confirmed a long-held suspicion that a summertime radar phenomena observed at the polar regions was due to signals bouncing off ionized ice crystals in the upper atmosphere.

Scientists never expected to see so much variation in the clouds.

"It's the changes day-to-day that really surprised us," Bailey said. "Even from orbit to orbit, we can see differences in the behavior of the clouds."

Scientists, for example, tracked a temperature change over five days and found corresponding changes in a cloud's location.

Analysis of the chemical composition of the clouds is under way.

Among the results of AIM's first observational season:

*The clouds appear daily, are widespread and change on an hourly and daily basis.

*The clouds are about 10 times brighter than expected based on previous measurements and vary within horizontal spans of about two miles.

*Ice in the upper atmosphere extends in a continuous layer from about 51 miles to 55 miles above the planet's surface.

*The clouds share characteristics associated with normal tropospheric clouds, suggesting that some of the same dynamics that trigger the planet's weather operate high above Earth as well.

Related Links:

Irene Klotz's blog: Space Diary

Gallery: Noctilucent Clouds

NASA: Astronauts See Noctilucent Clouds