Atmos. Chem. Phys. Discuss., 13, 2415-2456, 2013
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Improved estimate of global dust radiative forcing using a coupled chemical transport-radiative transfer model
L. Zhang1,2,3, Q. B. Li1,2, Y. Gu1,2, K. N. Liou1,2, and B. Meland3
1Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA, USA
2Joint Institute For Regional Earth System Science and Engineering, University of California, Los Angeles, CA 90095, USA
3Department of Mechanical Engineering, University of Colorado, Boulder, CO 80309, USA

Abstract. Atmospheric mineral dust particles exert significant direct radiative forcings and are critical drivers of climate change. Here, we use the GEOS-Chem global three-dimensional chemical transport model (3-D CTM) coupled online with the Fu-Liou-Gu (FLG) radiative transfer model (RTM) to investigate the dust radiative forcing and heating rates based on different dust vertical profiles. The coupled calculations using a realistic dust vertical profile simulated by GEOS-Chem minimize the physical inconsistencies between 3-D CTM aerosol fields and the RTM. The use of GEOS-Chem simulated aerosol optical depth (AOD) vertical profiles as opposed to the FLG prescribed AOD vertical profiles leads to greater and more spatially heterogeneous changes in estimated radiative forcing and heating rate produced by dust. Both changes can be attributed to a different vertical structure between dust and non-dust source regions. Values of the dust AOD are much larger in the middle troposphere, though smaller at the surface when the GEOS-Chem simulated AOD vertical profile is used, which leads to a much stronger heating rate in the middle troposphere. Compared to FLG vertical profile, the use of GEOS-Chem vertical profile reduces the solar radiative forcing effect by about 0.2–0.25 W m−2 and the Infrared (IR) radiative forcing over the African and Asia dust source regions by about 0.1–0.2 W m−2. Differences in the solar radiative forcing at the surface between using the GEOS-Chem vertical profile and the FLG vertical profile are most significant over the Gobi desert with a value of about 1.1 W m−2. The radiative forcing effect of dust particles is more pronounced at the surface over the Sahara and Gobi deserts by using FLG vertical profile, while it is less significant over the downwind area of Eastern Asia.

Citation: Zhang, L., Li, Q. B., Gu, Y., Liou, K. N., and Meland, B.: Improved estimate of global dust radiative forcing using a coupled chemical transport-radiative transfer model, Atmos. Chem. Phys. Discuss., 13, 2415-2456, doi:10.5194/acpd-13-2415-2013, 2013.
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