A Comparison of Model- and Satellite-Derived Aerosol Optical Depth and Reflectivity

• Published in: Journal of the atmospheric sciences 2002-02, Vol.59 (3), p.441-460
• Main Authors: Penner, Joyce E., Zhang, Sophia Y., Chin, Mian, Chuang, Catherine C., Feichter, Johann, Feng, Yan, Geogdzhayev, Igor V., Ginoux, Paul, Herzog, Michael, Higurashi, Akiko, Koch, Dorothy, Land, Christine, Lohmann, Ulrike, Mishchenko, Michael, Nakajima, Teruyuki, Pitari, Giovanni, Soden, Brian, Tegen, Ina, Stowe, Lawrence
• Format: Article
• Language: English
• ISSN: 0022-4928; 1520-0469
• DOI: 10.1175/1520-0469(2002)059<0441:acomas>2.0.co;2

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 super(-2) depending on latitude and is -1.7 W m super(-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 super(-2). The overall comparison indicates that the model-generated aerosol optical depth is systematically lower than that inferred from measurements between the latitudes of 10 degree and 30 degree S. It is not likely