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Published October 16, 2002 | public
Journal Article

Predicting global aerosol size distributions in general circulation models


To better represent the indirect effect of aerosols on climate, a size-resolved simulation of aerosol microphysics, size distributions, number and mass concentrations has been incorporated into the GISS general circulation model (GCM). The TwO-Moment Aerosol Sectional (TOMAS) microphysics model used here conserves aerosol number as well as mass. It has high size resolution, 30 bins between 0.01 and 10 mum diameter. As a first application, a size-resolved simulation of sulfate has been performed. The model reproduces important features of the atmospheric aerosol such as number concentrations that increase with altitude and land-sea contrasts in aerosol number concentrations and size distributions. Comparisons with observations show that simulated size distributions are realistic and condensation nuclei (CN) concentrations agree with observations within about 25%. Predicted cloud condensation nuclei (CCN) concentrations are also in reasonable agreement with observations, although there are locations for which agreement would be improved by including other aerosol components such as sea salt and carbonaceous aerosols. Sensitivity scenarios show that uncertainties in nucleation and primary emissions from fossil fuels can have significant effects on predictions of CN and CCN concentrations.

Additional Information

The authors would like to thank Graham Feingold for answering questions regarding the microphysics algorithm and providing sample code. Bernd Kärcher provided observational data in advance of publication. We thank Tim Bates and others at PMEL for making data sets from cruises available. Credit should go to two anonymous reviewers who took time to make thorough, specific, and constructive comments on a lengthy manuscript. This study has been supported by a graduate fellowship from the Fannie and John Hertz Foundation as well as by the National Aeronautics and Space Administration Earth Observing System Interdisciplinary Science program (NASA EOS-IDS).

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