Eintime Conversion for education and research 04-08-2008 @ 12:48:30|
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The Aeronomy of Ice in the Mesosphere satellite was launched in April to spend two years circling the Earth's poles to investigate the icy clouds seen only during summer nights. The 430-pound satellite is NASA's first dedicated to studying the bright wisps that form 50 miles above ground in the mesosphere, the uppermost reach of the atmosphere.
"These clouds are changing in ways we don't understand," said principal investigator James Russell of Hampton University, the first historically black school to serve as the prime contractor for a NASA satellite mission.
Russell and his colleagues, including Scott Bailey of Virginia Tech, presented their findings Monday at a meeting of the American Geophysical Union in San Francisco. The data comes from the satellite's first summer.
The $140 million NASA satellite is examining environmental factors, such as air pressure, temperature and moisture, that might prompt the cloud changes.
The satellite sighted the pearly clouds daily for three months beginning May 25.
AIM data revealed more ice and more icy clouds in the upper atmosphere than expected, Russell said. The clouds' daily variation could signal global changes in the upper atmosphere, he said.
Bailey said the clouds were so sensitive to environmental changes that even a 5-degree warm-up in the air temperature was enough to dim or dissipate them.
The satellite also revealed the clouds floating over a broad range of the upper atmosphere, from about 49 miles above ground to 56 miles high.
AIM's early data indicates that the processes forming noctilucent clouds might be similar to clouds found in the lower atmosphere, a finding that could affect our understanding of why and how clouds form, Russell said.
With AIM, "we can see the tiniest ice crystals, so we see the actual genesis of the clouds," Bailey said. "For the first time, we're getting the whole picture of the life cycle of the clouds."
The rippling clouds were first reported in 1885. They are called night-shining or noctilucent because their high altitude allows them to continue reflecting sunlight after sunset. The clouds consist of ice crystals formed when water vapor condenses onto dust particles at temperatures between 210 and 235 degrees.
Noctilucent clouds typically form over the cold, dry polar regions but have been migrating to lower latitudes in the past three decades. In recent summers, they have been spotted as far south as 40 degrees latitude, on par with Philadelphia or Denver.
Additionally, the clouds are growing in number and brightening, possibly the result of increasing concentrations of greenhouse gases, particularly carbon dioxide, Russell said.
While carbon dioxide is thought to contribute to global warming on Earth, it cools the upper atmosphere, home to the noctilucent clouds. Their growing population might indicate an unwelcome buildup of carbon dioxide in the Earth's upper atmosphere as well as cooling temperatures.
With three instruments aboard AIM, Russell's team hopes to learn more about the environmental factors that might cause the changes. The instruments are measuring the clouds' abundance and distribution, their particle size distribution, atmospheric temperatures, water vapor concentrations and amount of greenhouse gasses.
Scientists have several possible theories about the glow-in-the-dark cloud formation, Russell said.
One theory suggests that the mesosphere is growing colder because of a buildup in the upper atmosphere of greenhouse gases, particularly carbon dioxide. Concentrations of carbon dioxide that warm the Earth's lower atmosphere instead cool the planet's upper atmosphere, making it more conducive for noctilucent clouds to form, Russell said.
A second possibility is that growing methane emissions are increasing the atmospheric water vapor. In addition, cloud formation requires particles of some kind to provide surfaces for crystals to form. Cosmic dust might be intruding into Earth's atmosphere and changing the ionization in the upper atmosphere that causes particles to form.
Hampton is providing the mission's leadership to run a multi-university science team and has created a virtual project data center so scientists can share data collected by the AIM satellite. Several Hampton University and Virginia Tech students are involved in the project.
Other partners on the AIM project are the University of Colorado, Utah State University, the Naval Research Laboratory, Ball Aerospace and Technology Corp., as well as GATS Inc. of Newport News, which is responsible for software and AIM data management.
Contact A.J. Hostetler at (804) 649-6355 or firstname.lastname@example.org.
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04-08-2008 @ 12:48:30