May 2012

Improving the Aerosol Component of Climate Models

Complex aerosol processes accurately captured in climate models with a new, minimal aerosol module.

Click to enlarge photo. Enlarge Photo

Image courtesy of PNNL

Comparison of modeled atmospheric aerosol optical depth or transparency (upper panels) versus measured values from satellites (lower panels). From Liu, X., et al. “Toward a minimal representation of aerosols in climate models: description and evaluation in the Community Atmosphere Model CAM5,” Geosci. Model Dev. 5 709-739 (2012). [doi:10.5194/gmd-5-709-2012].

The Science

The Modal Aerosol Module (MAM) for the Community Atmospheric Model version 5 (CAM5)( the atmospheric component of CESM1) can simulate the aerosol size distribution and mixing states between different aerosol components, and can treat numerous  aerosol physical and chemical processes.

The Impact

MAM’s ability to minimally represent aerosols in Global Climate Models by capture the essentials of aerosol forcing is a substantial achievement that will improve our ability to accurately simulate climate change.

Summary

Accurately simulating climate change requires inclusion of full interactions between tiny aerosol particles, clouds and climate. This in turn requires that aerosol size and mixing conditions be resolved and that multiple species be carried in the climate model. A new aerosol scheme that includes these features is now available for the Community Earth System Model (CESM1). DOE researchers at Pacific Northwest National Laboratory led the development of a Modal Aerosol Module (MAM) for the Community Atmospheric Model version 5 (CAM5), the atmospheric component of CESM1. MAM can simulate the aerosol size distribution and mixing states between different aerosol components, and can treat numerous aerosol physical and chemical processes. Two versions of MAM were developed: a complete version with 7 aerosol modes serving as the benchmark and used for detailed aerosol studies, and a simplified version with 3 aerosol modes used for decade to century climate simulations. MAM does a good job of simulating the temporal and spatial distributions of aerosol mass, number and size distribution, and aerosol optical depth compared to observations, although some biases, such as underestimation of black carbon in the Arctic and underestimation of aerosol loading near source regions, will require further development. MAM is being used in CESM1 for the International Panel on Climate Change 5th Assessment Report. MAM has also been adopted by other major global and regional models (e.g., NASA GEOS-5 and the Weather Research Forecast Model).  The complexities of aerosol properties and processes, and limitations of computer resources have made it a challenge for global climate models (GCMs) to realistically represent aerosols.

Contact

Xiaohong Liu
Pacific Northwest National Laboratory
xiaohong.liu@pnnl.gov

Funding

DOE Office of Science Biological and Environmental Research (BER) program

Publications

Liu, X., et al. “Toward a minimal representation of aerosols in climate models: description and evaluation in the Community Atmosphere Model CAM5,” Geosci. Model Dev. 5 709-739 (2012). http://www.geosci-model-dev.net/5/709/2012/gmd-5-709-2012.htmlExternal link. [DOI: 10.5194/gmd-5-709-2012].

Highlight Categories

Program: BER, CESD

Performer/Facility: University, DOE Laboratory

Last modified: 9/3/2013 12:11:22 PM