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Atmospheric Sciences & Global Change
Research Highlights

January 2012

The Proof is in the Clouds

Accuracy of new WRF-Chem version validated by studying cloud behavior

stratocumulus cloud
A stratocumulus cloud deck over the South Pacific Ocean, as seen by NASA's Moderate Resolution Imaging Spectroradiometer (MODIS). Image courtesy of the National Aeronautics and Space Administration Earth Observatory and obtained from the NASA Terra satellite. Enlarge Image

Results: For most people, clouds are just an indication of whether it's a "good" or "bad" day. A team of scientists from Pacific Northwest National Laboratory found that certain clouds hold the key to climate behavior prediction. The researchers improved the modeling system to simulate the way clouds interact with particles in the air. The team assessed the state-of-the-art model's ability to simulate clouds and their interaction with fine particles in the air and pollution.

Why It Matters: Accurate prediction of how heavy pollution will influence climate is one of the best ways to protect the future of the planet.  Scientists can help by creating models of how the climate responds to many different variables. Projecting how clouds over oceans may be influenced by pollution, tiny bits of smoke, or chemicals is important because these clouds are part of a cycle that influences temperatures and precipitation in many areas of the world. Researchers showed the value of a model to predict complex interactions between atmospheric pollution and clouds.

Methods: It is important to study the accuracy of different climate modeling systems so scientists can determine the minimum level of complexity necessary to produce meaningful climate prediction.

A research team assessed simulations produced by WRF-Chem coupled with a new module, using observations from the VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS). They analyzed VOCALS data, as well as satellite images and data.

The team performed comprehensive evaluations of the models in simulating aerosols, clouds, and their interactions. Aerosols and aerosol-cloud interactions not only influence cloudiness and precipitation, but also lowers and modifies the cloud-top height, and a mean subsidence above the cloud top. They showed that WRF-Chem was accurate down to a very a small time scale in predicting aerosol interactions with cloud properties.

WRF-Chem is a regional meteorological model, with major improvements in aerosol and chemistry modules supplied by PNNL.

What's Next? Validating the WRF-Chem model predictions of the regional climate and energy budget was the first step. Scientists can now use WRF-Chem to quantify and evaluate many other issues, such as quantifying the impacts of human-caused and natural emissions on the regional climate.

Acknowledgments: The research was funded by the U.S. National Oceanic and Atmospheric Administration (NOAA) Atmospheric Composition and Climate Program and performed by Drs. Qing Yang, William Gustafson Jr., Jerome D. Fast, Hailong Wang, Mr. Richard C. Easter, and Ms. Elaine G. Chapman of PNNL; Dr. Hugh Morrison of the National Center for Atmospheric Research; Dr. Yin-Nan Lee of Brookhaven National Laboratory; Dr. Scott N. Spak of the Public Policy Center, University of Iowa; and Dr. Marcelo A. Mena-Carrasco of the Center for Sustainability Research, Universidad Andrés Bello.

Reference: Yang Q, WI Gustafson Jr, JD Fast, H Wang, RC Easter, H Morrison, Y-N Lee, EG Chapman, SN Spak, and MA Mena-Carrasco. 2011. "Assessing Regional Scale Predictions of Aerosols, Marine Stratocumulus, and Their Interactions During VOCALS-Rex Using WRF-Chem." Atmospheric Chemistry and Physics 11:22663-22718. DOI:10.5194/acpd-11-22663-2011.

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The stratocumulus cloud

Stratocumulus clouds are large, dark, and rounded masses organized into sheets. The Southeast Pacific region contains the world's most extensive and persistent sheets of low-sitting stratocumulus clouds, shading large swaths of the ocean. Scientists are looking at ways that pollution and atmospheric chemistry influence the formation of these shading clouds. Ocean temperature has a significant impact on local and regional weather conditions and long-term climate change, so it's important to understand these ocean-hugging stratocumulus clouds.