Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 16, 5763-5780, 2016
https://doi.org/10.5194/acp-16-5763-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
11 May 2016
Comprehensive tool for calculation of radiative fluxes: illustration of shortwave aerosol radiative effect sensitivities to the details in aerosol and underlying surface characteristics
Yevgeny Derimian1, Oleg Dubovik1, Xin Huang1, Tatyana Lapyonok1, Pavel Litvinov1, Alex B. Kostinski2, Philippe Dubuisson1, and Fabrice Ducos1 1Laboratoire d'Optique Atmosphérique, UMR8518 CNRS, Université de Lille, Villeneuve d'Ascq, 59655, France
2Department of Physics, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931, USA
Abstract. The evaluation of aerosol radiative effect on broadband hemispherical solar flux is often performed using simplified spectral and directional scattering characteristics of atmospheric aerosol and underlying surface reflectance. In this study we present a rigorous yet fast computational tool that accurately accounts for detailed variability of both spectral and angular scattering properties of aerosol and surface reflectance in calculation of direct aerosol radiative effect. The tool is developed as part of the GRASP (Generalized Retrieval of Aerosol and Surface Properties) project. We use the tool to evaluate instantaneous and daily average radiative efficiencies (radiative effect per unit aerosol optical thickness) of several key atmospheric aerosol models over different surface types. We then examine the differences due to neglect of surface reflectance anisotropy, nonsphericity of aerosol particle shape and accounting only for aerosol angular scattering asymmetry instead of using full phase function. For example, it is shown that neglecting aerosol particle nonsphericity causes mainly overestimation of the aerosol cooling effect and that magnitude of this overestimate changes significantly as a function of solar zenith angle (SZA) if the asymmetry parameter is used instead of detailed phase function. It was also found that the nonspherical–spherical differences in the calculated aerosol radiative effect are not modified significantly if detailed BRDF (bidirectional reflectance distribution function) is used instead of Lambertian approximation of surface reflectance. Additionally, calculations show that usage of only angular scattering asymmetry, even for the case of spherical aerosols, modifies the dependence of instantaneous aerosol radiative effect on SZA. This effect can be canceled for daily average values, but only if sun reaches the zenith; otherwise a systematic bias remains. Since the daily average radiative effect is obtained by integration over a range of SZAs, the errors vary with latitude and season. In summary, the present analysis showed that use of simplified assumptions causes systematic biases, rather than random uncertainties, in calculation of both instantaneous and daily average aerosol radiative effect. Finally, we illustrate application of the rigorous aerosol radiative effect calculations performed as part of GRASP aerosol retrieval from real POLDER/PARASOL satellite observations.

Citation: Derimian, Y., Dubovik, O., Huang, X., Lapyonok, T., Litvinov, P., Kostinski, A. B., Dubuisson, P., and Ducos, F.: Comprehensive tool for calculation of radiative fluxes: illustration of shortwave aerosol radiative effect sensitivities to the details in aerosol and underlying surface characteristics, Atmos. Chem. Phys., 16, 5763-5780, https://doi.org/10.5194/acp-16-5763-2016, 2016.
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The study presents a comprehensive tool for accurate calculation of solar flux as part of a novel algorithm GRASP (Generalized Retrieval of Aerosol and Surface Properties). We show that simplification of details in directional properties of atmospheric aerosol scattering and reflectance of underlying surface causes systematic biases in evaluation of aerosol radiative effect. Presented application for satellite data is one more step in the measurement-based estimate of aerosol effect on climate.
The study presents a comprehensive tool for accurate calculation of solar flux as part of a...
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