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Atmospheric Sciences & Global Change
Research Highlights

March 2009

Thin is In

Researchers wait out severe weather to learn about thin clouds—up close and personal.

Results: Ice storms and tornadoes were not enough to stop a team from the Pacific Northwest National Laboratory who traveled to Oklahoma in January to begin an aircraft field study on thin clouds.

No sooner had the group arrived in the state when it was hit with one of the most severe ice storms on record, followed a couple weeks later by deadly tornadoes. The dire conditions forced the team and colleagues from other national laboratories to delay some initial research flights, even moving to a tornado-proof shelter. But when conditions were safe enough to fly, the team quickly got back on track.

The researchers are gathering direct measurements from thin, low-lying clouds as part of a field campaign from January to June 2009 that will ultimately lead to more accurate climate change predictions. The campaign is part of the U.S. Department of Energy's RACORO, is the first long-term aircraft campaign to conduct systematic sampling of cloud properties from the air.

Twin Otter.
The Twin Otter takes off to test the on-board instruments for the RACORO field campaign that began in January 2009. Researchers are gathering data on the properties of certain low-level clouds. The data will be used to make climate model predictions more accurate.

Why it matters:  Clouds contain different amounts of water and ice, which affect their opacity and make them appear either thick or thin. These characteristics directly affect how much sunlight the cloud transmits to Earth or reflects back into space. This energy feedback process is a key component of climate. 

Low-level, thin clouds are often tenuous and scattered, which makes their properties—such as water content and water droplet size—hard to measure accurately with ground-based or satellite instruments. Scientists rely on these measurements as input to climate models, and because these cloud types occur all over the globe, it's important that the models have accurate data.

Methods:  With several flights each week through June 2009, researchers are obtaining data about clouds that reside up to 3.6 kilometers (12,000 feet) up from the Earth's surface. Equipped with a comprehensive set of probes and sensors to measure solar and thermal radiation, cloud microphysics, aerosol properties, and atmospheric state, a Twin Otter aircraft flies over the ARM Climate Research Facility site near Lamont, Oklahoma. This heavily-instrumented research site, established in 1994,  operates continuously to obtain continuous ground-based atmospheric measurements ideally suited to climate studies.

What's next: Researchers will use data from RACORO to validate ground-based measurements and support model simulations and studies of cloud processes.

Acknowledgments: DOE funds the ARM Program and this campaign.  Pacific Northwest National Laboratory manages the structure, processes, and operations of DOE's ARM Aerial Facility. The Pacific Northwest National Laboratory team for the RACORO campaign includes Jason Tomlinson, who leads the campaign for the ARM Aerial Facility; Chuck Long, the principal investigator for several radiometers onboard the Twin Otter; Jennifer Comstock, who serves on the campaign's science steering committee with Long, and Debbie Ronfeld, who is providing ground logistics. This research is part of PNNL's quest to transform the nation's ability to predict climate change and its impacts.

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