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PhD Defense

Department of Atmospheric Science

Wed., July 24, 9:00 am, EN6085

Improving Transport and Lifecycle of Black Carbon and Dust in the Community Earth System Model

Mingxuan Wu

University of Wyoming

Abstract

Black carbon (BC) and dust play important roles in the Earth’s climate. In this study, to improve BC transport and lifecycle, the aerosol dry deposition scheme of Petroff and Zhang (2010) (PZ10) is implemented into the Community Earth System Model version 1 (CESM1), 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 than Z01 for fine particles in Aitken, primary carbon, and accumulation modes, resulting in 23.2% higher of global mean BC column burdens. It improves the agreement with observations of BC profiles in the lower troposphere in the Arctic as well as the simulation of BC surface concentrations in high-latitudes remote regions. We evaluate the spatial distributions and temporal variations of dust extinction profiles and dust optical depth (DOD) simulated from CESM1, CESM2, the Energy Exascale Earth System Model version 1 (E3SMv1), and the Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA2) with satellite retrievals from Luo et al. (2015a, 2015b) (L15), Yu et al. (2015) (Y15), Moderate Resolution Imaging Spectroradiometer (MODIS), and Multi-angle Imaging SpectroRadiometer (MISR). We find that CESM1, CESM2, and E3SMv1 underestimate dust transport to remote regions. E3SMv1 improves dust transport and performs better than CESM1 and CESM2 in the Northern Hemisphere (NH) due to higher fraction of fine dust. CESM2 has the worst performance in the NH due to underestimation of dust emission in North Africa but improves dust simulations in the Southern Hemisphere (SH) due to overestimation of dust emission in the SH source regions. We further examine the dust modeling in East Asia. High model biases of dust extinction in the upper troposphere over the Taklamakan Desert, Gobi Desert, and Tibetan Plateau are found. CESM1 with the dust emission scheme of Kok et al. (2014a, 2014b) has the best agreement with observations from over the Taklamakan Desert and Tibetan Plateau. CESM1 underestimates dust surface concentrations at most weather stations due to inability of CESM1 to capture strong surface wind events.

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