Effect of Microstructure and Horizontal Inhomogeneity of Broken Cirrus Clouds on Mean Solar Radiative Fluxes in the Visible Wavelength Region: Results of Numerical Simulation

We present the results from statistical simulation of the albedo and diffuse transmission of the atmosphere in the visible wavelength region in the presence of overcast and broken cirrus clouds. The main numerical experiments were performed using the third version of the model proposed by B.A. Baum, P. Yang, A.J. Heymsfield et al. (a mixture of particles of different shapes and sizes with a very rough surface). To estimate the effects of the random cloud geometry on the solar radiative transfer in the atmosphere, we used the method of closed equations, proposed by G.A. Titov, and developed within the model based on the Poisson point fluxes on straight lines. Analysis of how the microstructure of cirrus clouds influences the ensemble-averaged albedo and diffuse transmission at moderate cloud fractions showed that the average value of the uncertainty due to the lack of information on the particle shape and size is within ∼ ± 2%. This value is comparable to the effect of the random geometry in optically thin clouds; while in optically dense clouds the range of errors, caused by the neglect of the horizontal inhomogeneity, increases and is ∼ ± 5% in albedo calculations, with underestimation of diffuse transmission by ∼ 10–20%.