07 March 2016

Quantifying the Impact of Cloud Uncertainties on Aerosol Effects

Summary

Heavy air pollution in East Asia, especially China, is changing the East Asian monsoon, weakening both precipitation and circulation. More robust modeling of aerosol particle effects on climate is required to reach definite conclusions about this anomalous trend.

Traditionally, the climate modeling community studies the aerosol effect by looking at the differences between two numerical simulations: one with current or higher aerosol emissions and another with no or lower emissions. The framework for this study, developed by Department of Energy scientists at Pacific Northwest National Laboratory, integrates a smart sampling approach and a surrogate model to understand the aerosol effects on the East Asian monsoon climate, as simulated in the Community Atmosphere Model (CAM5). They conducted 256 simulations to quantify how the model responds to uncertain parameters of cloud microphysical properties and aerosol particle (e.g., sulfate, black carbon, and dust) emission factors. The results show that these prevailing aerosol particles have very different impacts on the East Asian monsoon climate through aerosol-cloud-radiation interactions (a complex set of interactions between particles, clouds, and the sun’s radiation). The aerosol particle effects do not always have an expected, one-to-one response to a change in emissions. This study was limited to the fast response of aerosol effects (e.g., atmospheric heating, changes to clouds and cooling the surface) and the microphysical effects of stratiform clouds (low-level, fog-like clouds). The results suggest that further research is required to quantify the full response and determine how aerosol particles may also affect convective (stormy) clouds.

Researchers developed a new framework of parameters to understand aerosol particle effects on the East Asian monsoon climate and improve the modeling accuracy of a popular atmosphere model. When they quantified the model responses to uncertain parameters for cloud microphysics and aerosol emissions, they were able to show that sulfate, black carbon, and dust aerosol particles have very different impacts on the climate.

Contact
Yun Qian
Pacific Northwest National Laboratory (PNNL)
Publications
Yan, H, Y Qian, H Wang, C Zhao, M Wang, B Yang, X Liu, and Q Fu.  2015.  "A New Approach to Modeling Aerosol Effects on East Asian Climate: Parametric Uncertainties Associated with Emissions, Cloud Microphysics, and their Interactions."  Journal of Geophysical Research: Atmospheres 120: 8905-8924.
Acknowledgments

This study is based on work supported by the U.S. Department of Energy (DOE), Office of Science, Biological and Environmental Research as part of the Regional and Global Climate Modeling Program. The Pacific Northwest National Laboratory (PNNL) is operated for DOE by Battelle Memorial Institute under contract DE-AC05-76RL01830. The National Energy Research Scientific Computing Center (NERSC) provided computational resources. All model results are stored at a PNNL cluster and available upon request. Please contact Yun Qian (yun.qian@pnnl.gov).