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20086.0 [No comment] 22.03.2011 12:41 Released

ID: 20086.0, MPI für Meteorologie / Atmosphere in the Earth System
A comparison of model- and satellite-derived aerosol optical depth and reflectivity
Authors:Penner, J. E.; Zhang, S. Y.; Chin, M.; Chuang, C. C.; Feichter, Johann; Feng, Y.; Geogdzhayev, I. V.; Ginoux, P.; Herzog, M.; Higurashi, A.; Koch, D.; Land, Christine; Lohmann, U.; Mishchenko, M.; Nakajima, T.; Pitari, G.; Soden, B.; Tegen, I.; Stowe, L.
Date of Publication (YYYY-MM-DD):2002
Title of Journal:Journal of the Atmospheric Sciences
Journal Abbrev.:J. Atmos. Sci.
Issue / Number:3
Start Page:441
End Page:460
Review Status:Peer-review
Audience:Not Specified
Abstract / Description:The determination of an accurate quantitative understanding of the role of tropospheric aerosols in the earth's radiation budget is extremely important because forcing by anthropogenic aerosols presently represents one of the most uncertain aspects of climate models. Here the authors present a systematic comparison of three different analyses of satellite-retrieved aerosol optical depth based on the Advanced Very High Resolution Radiometer (AVHRR)-measured radiances with optical depths derived from six different models. Also compared are the model-derived clear-sky reflected shortwave radiation with satellite-measured reflectivities derived from the Earth Radiation Budget Experiment (ERBE) satellite. The three different satellite-derived optical depths differ by between - 0.10 and 0.07 optical depth units in comparison to the average of the three analyses depending on latitude and month, but the general features of the retrievals are similar. The models differ by between -0.09 and +0.16 optical depth units from the average of the models. Differences between the average of the models and the average of the satellite analyses range over - 0.11 to +0.05 optical depth units. These differences are significant since the annual average clear-sky radiative forcing associated with the difference between the average of the models and the average of the satellite analyses ranges between -3.9 and 0.7 W m(-2) depending on latitude and is -1.7 W m(-2) on a global average annual basis. Variations in the source strengths of dimethylsulfide-derived aerosols and sea salt aerosols can explain differences between the models, and between the models and satellite retrievals of up to 0.2 optical depth units. The comparison of model-generated reflected shortwave radiation and ERBE-measured shortwave radiation is similar in character as a function of latitude to the analysis of modeled and satellite-retrieved optical depths, but the differences between the modeled clear-sky reflected flux and the ERBE clear-sky reflected flux is generally larger than that inferred from the difference between the models and the AVHRR optical depths, especially at high latitudes. The difference between the mean of the models and the ERBE-analyzed clear-sky flux is 1.6 W m(-2). The overall comparison indicates that the model-generated aerosol optical depth is systematically lower than that inferred from measurements between the latitudes of 10degrees and 30degreesS. It is not likely that the shortfall is due to small values of the sea salt optical depth because increases in this component would create modeled optical depths that are larger than those from satellites in the region north of 30degreesN and near 50degreesS. Instead, the source strengths for DMS and biomass aerosols in the models may be too low. Firm conclusions, however, will require better retrieval procedures for the satellites, including better cloud screening procedures, further improvement of the model's treatment of aerosol transport and removal, and a better determination of aerosol source strengths.
External Publication Status:published
Document Type:Article
Affiliations:MPI für Meteorologie/Biogeochemical System/Atmospheric Aerosol
External Affiliations:Univ Michigan, Dept Atmospher Ocean & Space Sci, Ann Arbor, MI; 48109 USA; Univ Michigan, Dept Atmospher Ocean & Space Sci, Ann Arbor, MI 48109 USA; NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA; Lawrence Livermore Natl Lab, Div Atmospher Sci, Livermore, CA USA; Max Planck Inst Meteorol, Hamburg, Germany; NASA, Goddard Inst Space Studies, New York, NY 10025 USA; Natl Inst Environm Studies, Ibaraki, Japan; Dalhousie Univ, Halifax, NS, Canada; Univ Tokyo, Ctr Climate Syst Res, Tokyo, Japan; Univ Aquila, Dipartimento Fis, I-67100 Laquila, Italy; Princeton Univ, Geophys Fluid Dynam Lab, Princeton, NJ 08544 USA; Max Planck Inst Biogeochem, Jena, Germany; NOAA, Natl Environm Satellite Data & Informat Serv, Off Res & Applicat, Satellite Res Lab, Washington, DC 20233 USA