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Master's Defense

Department of Atmospheric Science

Wed., May 30, 3:00 pm, EN6085

Impacts of aerosol dry deposition on black carbon spatial distributions and radiative effects in the Community Atmosphere Model CAM5

Mingxuan Wu

University of Wyoming

Abstract

Dry deposition is an important process affecting the lifetime and spatial distributions of atmospheric aerosols. Black carbon (BC) plays an important role in the Earth’s climate, but is subject to large bias in remote regions in model simulations. In this study, to improve the BC simulations, the scheme of Petroff and Zhang (2010) (PZ10) is implemented into the Community Atmospheric Model version 5 (CAM5), and model simulations using PZ10 are compared with the one using the default scheme of Zhang et al. (2001) (Z01) and observations. The PZ10 scheme predicts much lower dry deposition velocity (Vd) than Z01 for fine particles in Aitken, primary carbon, and accumulation modes, resulting in 73.0% lower of global mean BC dry deposition fluxes and 23.2% higher of global mean BC column burdens. CAM5 with PZ10 increases modeled BC concentrations at all altitudes and latitudes compared to Z01, which improves the agreement with observations of BC profiles in the lower troposphere in the Arctic. It also improves the simulation of surface BC concentrations in high-latitudes remote regions and its seasonality in the Arctic. The global annual mean radiative effects due to aerosol-radiation interactions (REari) and aerosol-cloud interactions (REaci) of BC from the CAM5 experiment using Z01 are 0.61±0.007 and -0.11±0.02 W m-2, respectively, compared to slightly larger REari (0.75±0.01 W m-2) and REaci (-0.14±0.02 W m-2) from CAM5 using PZ10. The results suggest that Brownian diffusion efficiency is a key factor for the predictions of Vd, which requires better representation in the global climate models.


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