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Discussion papers | Copyright
https://doi.org/10.5194/acp-2018-676
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 07 Aug 2018

Research article | 07 Aug 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Radiative Effect and Climate Impacts of Brown Carbon with the Community Atmosphere Model (CAM5)

Hunter Brown1, Xiaohong Liu1, Yan Feng2, Yiquan Jiang3, Mingxuan Wu1, Zheng Lu1, Chenglai Wu1,4, Shane Murphy1, and Rudra Pokhrel1 Hunter Brown et al.
  • 1Department of Atmospheric Science, University of Wyoming, Laramie, Wyoming, USA
  • 2Argonne National Laboratory, Lemont, Illinois, USA
  • 3Institute for Climate and Global Change Research, School of Atmospheric Sciences, Nanjing University, Nanjing, China
  • 4International Center for Climate and Environment Sciences, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China

Abstract. A recent development in the representation of aerosols in climate models is the realization that some components of organic aerosol (OA), emitted from biomass and biofuel burning, can have a significant contribution to short-wave radiation absorption in the atmosphere. The absorbing fraction of OA is referred to as brown carbon (BrC). This study introduces one of the first implementations of BrC into the Community Atmosphere Model version 5 (CAM5), using a parameterization for BrC absorptivity described in Saleh et al. (2014). 9-year experiments are run (2003–2011) with prescribed emissions and sea surface temperatures to analyze the effect of BrC in the atmosphere. Model validation is conducted via model comparison to single-scatter albedo and aerosol optical depth from the Aerosol Robotic Network (AERONET). This comparison reveals a model underestimation of SSA in biomass burning regions for both default and BrC model runs, while a comparison between AERONET and model absorption Angstrom exponent shows a marked improvement with BrC implementation. Global annual average radiative effects are calculated due to aerosol-radiation interactions (REari; 0.13±0.01Wm−2) and aerosol-cloud interactions (REaci; 0.01±0.04Wm−2). REari is similar to other studies' estimations of BrC direct radiative effect, while REaci indicates a global reduction in low clouds due to the BrC semi-direct effect. The mechanisms for these physical changes are investigated and found to correspond with changes in global circulation patterns. Comparisons of BrC implementation approaches find that this implementation predicts a lower BrC REari in the Arctic regions than previous studies with CAM5. Implementation of BrC bleaching effect shows a significant reduction in REari (0.06±0.008Wm−2). Also, variations in OA density can lead to differences in REari and REaci, indicating the importance of specifying this property when estimating the BrC radiative effects and when comparing similar studies.

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Short summary
In climate models, organic carbon (OC) in biomass burning smoke has been treated as an atmospheric cooling component by reflecting light back to space. This study incorporates the observationally identified absorbing brown carbon component of OC into the Community Earth System Model, improving the agreement between model and observation and effectively increasing absorption of solar radiation. This change contributes to altered atmospheric dynamics and changes in cloud cover in the model.
In climate models, organic carbon (OC) in biomass burning smoke has been treated as an...
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