ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-6-1815-2006 An AeroCom initial assessment – optical properties in aerosol component modules of global models Kinne S. 1 Schulz M. 2 Textor C. 2 Guibert S. 2 Balkanski Y. 2 Bauer S. E. 3 Berntsen T. 4 Berglen T. F. 4 Boucher O. 5 6 Chin M. 7 Collins W. 8 Dentener F. 9 Diehl T. 10 Easter R. 11 Feichter J. 1 Fillmore D. 8 Ghan S. 11 Ginoux P. 12 Gong S. 13 Grini A. 4 Hendricks J. 14 Herzog M. 12 Horowitz L. 12 Isaksen I. 4 Iversen T. 4 Kirkevåg A. 4 Kloster S. 1 Koch D. 3 Kristjansson J. E. 4 Krol M. 16 Lauer A. 14 Lamarque J. F. 8 Lesins G. 17 Liu X. 15 Lohmann U. 18 Montanaro V. 19 Myhre G. 4 Penner J. 15 Pitari G. 19 Reddy S. 12 Seland O. 4 Stier P. 1 Takemura T. 20 Tie X. 8 Max-Planck-Institut für Meteorologie, Hamburg, Germany Laboratoire des Sciences du Climat et de l’environnement, Gif-sur-Yvette, France The Earth Institute at Columbia University, New York, NY, USA University of Oslo, Department of Geosciences, Oslo, Norway Laboratoire d’Optique Atmosph’erique, USTL/CNRS, Villeneuve d’Ascq, France Hadley Centre, Met Office, Exeter, UK NASA Goddard Space Flight Center, Greenbelt, MD, USA NCAR, Boulder, Colorado, USA EC, Joint Research Centre, IES, Climate Change Unit, Ispra, Italy Goddard Earth Sciences and Technology Center, UMBC, Baltimore, MD, USA Batelle, Pacific Northwest National Laboratory, Richland, USA NOAA, Geophysical Fluid Dynamics Laboratory, Princeton, NJ, USA ARQM Meteorological Service Canada, Toronto, Canada DLR, Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany University of Michigan, Ann Arbor, MI, USA Institute for Marine and Atmospheric Research Utrecht (IMAU) Utrecht, The Netherlands Dalhousie University, Halifax, Canada ETH Zürich, Switzerland Universita degli Studi L’Aquila, L’Aquila, Italy Kyushu University, Fukuoka, Japan 29 05 2006 6 7 1815 1834 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/6/1815/2006/acp-6-1815-2006.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/6/1815/2006/acp-6-1815-2006.pdf

The AeroCom exercise diagnoses multi-component aerosol modules in global modeling. In an initial assessment simulated global distributions for mass and mid-visible aerosol optical thickness (aot) were compared among 20 different modules. Model diversity was also explored in the context of previous comparisons. For the component combined aot general agreement has improved for the annual global mean. At 0.11 to 0.14, simulated aot values are at the lower end of global averages suggested by remote sensing from ground (AERONET ca. 0.135) and space (satellite composite ca. 0.15). More detailed comparisons, however, reveal that larger differences in regional distribution and significant differences in compositional mixture remain. Of particular concern are large model diversities for contributions by dust and carbonaceous aerosol, because they lead to significant uncertainty in aerosol absorption (aab). Since aot and aab, both, influence the aerosol impact on the radiative energy-balance, the aerosol (direct) forcing uncertainty in modeling is larger than differences in aot might suggest. New diagnostic approaches are proposed to trace model differences in terms of aerosol processing and transport: These include the prescription of common input (e.g. amount, size and injection of aerosol component emissions) and the use of observational capabilities from ground (e.g. measurements networks) or space (e.g. correlations between aerosol and clouds).