Modeling radiative forcing by background aerosol on the basis of measurement data |
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Authors: | I A Gorchakova T A Tarasova M A Sviridenkov P P Anikin E V Romashova |
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Institution: | 1.A.M. Obukhov Institute of Atmospheric Physics,Russian Academy of Sciences,Moscow,Russia;2.Center for Research of the Earth’s Climate System,National Institute for Space Research,Brasilia,Brazil |
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Abstract: | The solar radiation flux incident on the land surface and aerosol radiative forcing are calculated from measurements carried
out under clear skies during the summers of 2004 and 2005 at the Zvenigorod Scientific Station (ZSS) of the A.M. Obukhov Institute
of Atmospheric Physics, Russian Academy of Sciences. In these calculations, the following five models of aerosol optical parameters
are used: a standard model of continental aerosol, a semiempirical model based on measurement data, and three models obtained
from calculations on the basis of the Mie scattering theory for the mean size distribution of aerosol particles (which is
retrieved from aureole measurements). A study of the sensitivity of the flux and forcing to the choice of aerosol model has
shown that the relative error related to the model choice is not large (<5%) for the incident radiation flux and reaches 120%
for aerosol forcing at the atmospheric upper boundary. The aerosol radiative forcing at the atmospheric upper boundary is
also estimated and, according to our calculations, varies from −15 to −2 W/m2. The use (in calculations) of the values of the albedo of single-scattering and the factor of scattering-indicatrix asymmetry
at a wavelength of 550 nm, which were obtained for each of the observation periods, has made it possible to significantly
refine the value of aerosol radiative forcing (compared to that calculated for the means of these parameters over all the
periods). An even more accurate determination of aerosol radiative forcing is possible only when data on the size-distribution
of aerosol particles and their chemical composition for a certain situation under analysis are available. As a result of this
study, two models of the optical parameters of background aerosol have been proposed for use in radiation calculations: a
semiempirical model and a mean model obtained from the calculations based on the theory of scattering. Both models use the
values of the albedo of single scattering and the factor of asymmetry (at a wavelength of 550 nm) retrieved from the measurements
for each of the observation periods. |
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