Atmos. Chem. Phys. Discuss., 9, 22041-22101, 2009
© Author(s) 2009. 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.
Influences of in-cloud aerosol scavenging parameterizations on aerosol concentrations and wet deposition in ECHAM5-HAM
B. Croft1, U. Lohmann2, R. V. Martin1,3, P. Stier4, S. Wurzler5, J. Feichter6, C. Hoose7, U. Heikkilä8, A. van Donkelaar1, and S. Ferrachat2
1Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Canada
2Institute of Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
3Harvard-Smithsonian Center for Astrophysics, Cambridge, USA
4Atmospheric, Oceanic, and Planetary Physics, University of Oxford, Oxford, UK
5Landesamt fur Umwelt, Natur und Verbraucherschutz NRW (LANUV), Recklinghausen, Germany
6Max Planck Institute for Meteorology, Hamburg, Germany
7Department of Geosciences, University of Oslo, Oslo, Norway
8Bjerknes Centre for Climate Research, Bergen, Norway

Abstract. A diagnostic nucleation scavenging scheme, which determines stratiform cloud scavenging ratios for both aerosol mass and number distributions, based on cloud droplet, and ice crystal number concentrations, is introduced into the ECHAM5-HAM global climate model. This is coupled with a size-dependent in-cloud impaction scavenging parameterization for both cloud droplet-aerosol, and ice crystal-aerosol collisions. Sensitivity studies are presented, which compare aerosol concentrations, and deposition between a variety of in-cloud scavenging approaches, including prescribed fractions, several diagnostic schemes, and a prognostic aerosol cloud processing treatment that passes aerosol in-droplet and in-ice crystal concentrations between model time steps. For one sensitivity study, assuming 100% of the in-cloud aerosol is scavenged into the cloud droplets and ice crystals, the annual global mean accumulation mode number burden is decreased by 65%, relative to a simulation with prognostic aerosol cloud processing. Diagnosing separate nucleation scavenging ratios for aerosol number and mass distributions, as opposed to equating the aerosol mass scavenging to the number scavenging ratios, reduces the annual global mean sulfate burden by near to 10%. The annual global mean sea salt burden is 30% lower for the diagnostic approach, which does not carry aerosol in-droplet and in-crystal concentrations between model time-steps as compared to the prognostic scheme. Implementation of in-cloud impaction scavenging reduced the annual, global mean black carbon burden by 30% for the prognostic aerosol cloud processing scheme. Better agreement with observations of black carbon profiles from aircraft (changes near to one order of magnitude for mixed phase clouds), 210Pb surface layer concentrations and wet deposition, and the geographic distribution of aerosol optical depth are found for the new diagnostic scavenging as compared to prescribed ratio scavenging scheme of the standard ECHAM5-HAM.

Citation: Croft, B., Lohmann, U., Martin, R. V., Stier, P., Wurzler, S., Feichter, J., Hoose, C., Heikkilä, U., van Donkelaar, A., and Ferrachat, S.: Influences of in-cloud aerosol scavenging parameterizations on aerosol concentrations and wet deposition in ECHAM5-HAM, Atmos. Chem. Phys. Discuss., 9, 22041-22101, doi:10.5194/acpd-9-22041-2009, 2009.
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