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Master's Defense

Department of Atmospheric Science

Wed., Jul. 26, 11:00 am, EN6085

Implementation of a brown carbon parameterization in the Community Earth System Model (CESM): model validation, estimation of brown carbon radiative effect, and climate impact

Hunter Brown

University of Wyoming


A recent development in the representation of aerosols in climate models is the realization that some components of organic carbon (OC), emitted from biomass and biofuel burning, can have a significant contribution to short-wave radiation absorption in the atmosphere. The absorbing fraction of OC is referred to as brown carbon (BrC). This study introduces one of the first implementations of BrC into the Community Earth System Model (CESM), using a parameterization for BrC absorption 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 (SSA) and aerosol optical depth from the Aerosol Robotic Network (AERONET), as well as comparison with a laboratory derived parameterization for SSA dependent on the (black carbon (BC))/(BC+OC) ratio in biomass burning emissions. These comparisons reveal a model underestimation of SSA in biomass burning regions for both default and BrC model runs. Global annual average radiative effects are calculated due to aerosol-radiation interactions (REari; 0.129±0.021 W m-2), aerosol-cloud interactions (REaci; 0.073±0.056 W m-2), and surface albedo change (REsac; -0.060±0.035 W m-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. REsac suggests increased surface albedo with BrC implementation. Lastly, comparisons of BrC implementation approaches find that this implementation may do a better job of estimating BrC radiative effect in the Arctic regions than previous studies with CESM.

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