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Delta 4-Heavy launch
The Boeing Delta 4-Heavy rocket is launched from Cape Canaveral on its demonstration flight. (4min 35sec file)
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Onboard the Heavy
An onboard camera records the launch of Boeing's Delta 4-Heavy rocket from liftoff through separation of the outer boosters. (4min 40sec file)
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Launch of Atlas 5
The Lockheed Martin Atlas 5 rocket launches at 7:07 a.m. EST from Cape Canaveral carrying the AMERICOM 16 communications spacecraft. (6min 22sec file)
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Press site view
The sunrise launch of Atlas 5 is shown in this view from the Kennedy Space Center press site at Complex 39. (QuickTime file)
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Rocket rollout
Riding on its mobile launching platform, the Atlas 5 rocket is rolled from its assembly building to the launch pad at Complex 41 just hours before the scheduled liftoff time carrying AMC 16. (4min 41sec file)
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Atlas 5 news briefing
Mission officials hold the pre-launch news conference in Cape Canaveral on Thursday, Dec. 16 to preview the flight of Atlas 5 with AMC 16. (40min 41sec file)
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AMC 16 launch preview
Preview the launch of Lockheed Martin's Atlas 5 rocket carrying the AMERICOM 16 communications spacecraft with this narrated animation package. (2min 52sec file)
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The AMC 16 spacecraft
This narrated movie provides an overview of the Lockheed Martin-built AMC 16 spacecraft for operator SES AMERICOM. (3min 30sec file)
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Deep Impact overview
Rick Grammier, NASA's Deep Impact project manager from the Jet Propulsion Laboratory, provides a detailed overview of the spacecraft and its mission. (4min 54sec file)
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Science preview
Deep Impact principal investigator Michael A'Hearn explains how the comet collision will occur and what scientists hope to learn. (7min 11sec file)
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Pre-flight news briefing
The pre-flight news conference is held at NASA Headquarters on December 14 to preview the Deep Impact mission to intercept a comet and blast a projectile into it. (54min 19sec file)
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Polluted clouds hold less moisture, less Earth cooling
NASA NEWS RELEASE
Posted: December 29, 2004

A NASA study found some clouds that form on tiny haze particles are not cooling the Earth as much as previously thought. These findings have implications for the ability to predict changes in climate.

Andrew Ackerman, a scientist at NASA Ames Research Center, located in California's Silicon Valley, and his colleagues found, when the air over clouds is dry, polluted clouds hold less water and reflect less solar energy. Ackerman is the study's principal author.

Contrary to expectations, scientists observed polluted, low-lying clouds do not generally hold more water than cleaner clouds. Low clouds cool the planet by reflecting sunlight away from the Earth's surface, and more water makes a cloud more reflective.

Previously, scientific consensus was, that since polluted clouds precipitate less, they should contain more water and reflect more sunlight back into space. Most predictions of global climate change assume less precipitation will result in clouds holding more water, reflecting more sunlight and counteracting greenhouse warming.

"The natural laboratory we used to look at the contrasts between clean and polluted clouds is a phenomenon called ship tracks, which are long lines of clouds with smaller cloud droplets that form on the exhaust particles from ships," Ackerman said.

"The results of this work should provide for more realistic treatment of polluted clouds in climate models, improving predictions of future climate," Ackerman said. "In the meantime, it's critical that we thoroughly test these new theoretical results. NASA's latest generation of Earth-observing satellites provides a powerful tool for doing just that, by observing how ship tracks are affected by the humidity of the air above them," he said.

Ship track measurements were taken off the west coast of the United States from polar-orbiting satellites and aircraft flying through the clouds. The Moderate Resolution Imaging Spectroradiometer (MODIS) Airborne Simulator instrument (comparable to the MODIS instruments on NASA's Terra and Aqua satellites), aboard a NASA ER-2 aircraft flying above the clouds, was also used to gather data. The measurements show cloud water decreases more often than it increases in polluted clouds.

To understand how cloud water changes in polluted clouds, the team of scientists created a 3-D computer model to simulate atmospheric motions and the formation of precipitation by clouds. The researchers tested their model by comparing its predictions with measurements from field projects devoted to characterizing marine stratocumulus clouds.

After verifying that the model reproduced the behavior of real clouds, the scientists asked their computer model how pollution affects clouds. In agreement with previous work, the computer simulations showed, when air over a cloud is humid, cloud water increases in polluted clouds. However, when air over a stratocumulus cloud deck is dry, surprisingly, simulations indicated that water decreased in polluted clouds, consistent with the behavior observed in ship tracks.

Ackerman's co-investigators included Michael Kirkpatrick, University of Tasmania, Hobart, Australia; David Stevens, Lawrence Livermore National Laboratory, Livermore, Calif.; and O. Brian Toon, University of Colorado, Boulder. The researchers' findings appear in the journal Nature.