Atmos. Chem. Phys. Discuss., 10, 24499-24561, 2010
www.atmos-chem-phys-discuss.net/10/24499/2010/
doi:10.5194/acpd-10-24499-2010
© Author(s) 2010. This work is distributed
under the Creative Commons Attribution 3.0 License.
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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.
Modeling sea-salt aerosol in a coupled climate and sectional microphysical model: mass, optical depth and number concentration
T. Fan and O. B. Toon
Laboratory for Atmospheric and Space Physics, Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, USA

Abstract. Sea-salt aerosol mass, optical depth, and number concentration over the global oceans have significant implications for aerosol direct and indirect climate effects. We modeled sea-salt aerosol in a coupled climate and sectional microphysical model, CAM/CARMA, with aerosol dynamics including sea salt emission, gravitational sedimentation, dry deposition, wet scavenging, and particle swelling. We aimed at finding an integrated sea salt source function parameterization in the global climate model to simultaneously represent mass, optical depth, and number concentration. Each of these quantities is sensitive to a different part of the aerosol size distribution, which requires a size resolved microphysical model to treat properly. The CMS source function introduced in the research, based upon several earlier source functions, reproduced measurements of mass, optical depth and number concentration as well as the size distribution better than other source function choices we tried. However, as we note, it is also important to properly set the removal rate of the particles. The source function and removal rate are coupled in producing observed abundances. We find that sea-salt mass and optical depth peak in the winter, when winds are highest. However, surprisingly, particle numbers and CCN concentrations peak in summer when rainfall is lowest. The quadratic dependence of sea salt optical depth on wind speed, observed by some, is well represented in the model. We also found good agreement with the wind speed dependency of the number concentration at the measurement location and the regional scale. The work is the basis for further investigation of the effects of sea-salt aerosol on climate and atmospheric chemistry.

Citation: Fan, T. and Toon, O. B.: Modeling sea-salt aerosol in a coupled climate and sectional microphysical model: mass, optical depth and number concentration, Atmos. Chem. Phys. Discuss., 10, 24499-24561, doi:10.5194/acpd-10-24499-2010, 2010.
 
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