Abstract
Abstract. We use a single aerosol model to explore the effects of the differing meteorological fields from the NCAR CAM5 and GFDL AM3 models. We simulate the global distributions of sulfate, black carbon, organic matter, dust and sea salt using the University of Michigan IMPACT model and use these fields to calculate aerosol direct and indirect forcing, thereby isolating the impacts of the differing meteorological fields. Over all, the IMPACT-AM3 model predicts larger burdens and longer aerosol lifetimes than the IMPACT-CAM5 model. However, the IMPACT-CAM5 simulations transport more black carbon to the polar regions and more dust from Asia towards North America. These differences can mainly be attributed to differences in: (1) the vertical cloud mass flux and large-scale precipitation fields which determine the wet deposition of aerosols; (2) the in-cloud liquid water content and the cloud coverage which determine the wet aqueous phase production of sulfate. The burden, lifetime and global distribution, especially black carbon in polar regions, are strongly affected by choice of the parameters used for wet deposition. The total annual mean aerosol optical depth (AOD) at 550 nm ranges from 0.087 to 0.122 for the IMPACT-AM3 model and from 0.138 to 0.186 for the IMPACT-CAM5 model (range is due to different parameters used for wet deposition). Even though IMPACT-CAM5 has smaller aerosol burdens, its AOD is larger due to the much higher relative humidity in CAM5 which leads to more hygroscopic growth. The corresponding global annual average anthropogenic and all-sky aerosol direct forcing at the top of the atmosphere ranges from −0.25 W m−2 to −0.30 W m−2 for IMPACT-AM3 and from −0.48 W m−2 to −0.64 W m−2 for IMPACT-CAM5. The global annual average anthropogenic 1st aerosol indirect effect at the top of the atmosphere ranges from −1.26 W m−2 to −1.44 W m−2 for IMPACT-AM3 and from −1.74 W m−2 to −1.77 W m−2 for IMPACT-CAM5.
Highlights
The effects of different meteorological fields from different climate models has been explored within the atmospheric aerosol and climate modeling community through both model intercomparisons that use a single aerosol model with different meteorological driving fields (e.g. Liu et al, 2007; Zhang et al, 2010) and through coupled aerosol/climate model intercomparisons where a range of different models are compared (e.g. Penner et al, 2002, 2006; Kinne et al, 2006; Schulz et al, 2006; Textor et al, 2006; 2007; Shindell et al, 2008)
C1 has stronger net warming effect than A1 in central Africa and the ocean area downwind to its west coast. This is partially due to the higher low cloud coverage in CAM5 than AM3 which increases the absorption by black carbon/organic matter from biomass burning in C1
We predicted the global distributions of sulfate, black carbon, organic matter, dust and sea salt, aerosol optical depth, and anthropogenic aerosol direct and 1st indirect effects
Summary
The effects of different meteorological fields from different climate models has been explored within the atmospheric aerosol and climate modeling community through both model intercomparisons that use a single aerosol model with different meteorological driving fields (e.g. Liu et al, 2007; Zhang et al, 2010) and through coupled aerosol/climate model intercomparisons where a range of different models are compared (e.g. Penner et al, 2002, 2006; Kinne et al, 2006; Schulz et al, 2006; Textor et al, 2006; 2007; Shindell et al, 2008). We follow the approach first studied in Liu et al (2007) where a single aerosol model, the University of Michigan IMPACT aerosol model, is driven by two sets of meteorological fields: one from the NCAR Community Atmosphere Model (version 5) and one from the GFDL AM3 model. Both models are participating the Coupled Model Intercomparison Project Phase 5 (CMIP5).We analyze the differences and uncertainties of aerosol simulations (for sulfate, organic matter, black carbon, dust and sea salt) solely caused by differing meteorology.
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