Impact of microstructure and horizontal heterogeneity of broken cirrus clouds on mean solar radiation fluxes in the visible spectral region: results of numerical simulation
T.B. Zhuravleva, I.M. Nasrtdinov
V.E. Zuev Institute of Atmospheric Optics of Siberian Branch of the Russian Academy of Science, Tomsk, Russia
Keywords: cirrus cloud models, Monte Carlo method, effects of random geometry of clouds, Poisson model, solar radiation fluxes in the visible spectral region
Abstract
The results of statistical simulation of the albedo and diffuse transmission of the atmosphere in the visible region in the presence of overcast and broken cirrus clouds are presented. The main numerical experiments were performed using the third version of the model proposed by a group of authors consisting of B.A. Baum, P. Yang, A.J. Heymsfield et al. (a mixture of particles of different shapes and sizes with a rough surface). To assess the effect of random geometry of clouds on the solar radiation transfer in the atmosphere, G.A. Titov method of closed equations, developed within the framework of a model based on Poisson fluxes of points on straight lines, was used. Analysis of the influence of the microstructure of cirrus clouds on the mean albedo and diffuse transmission at average cloud fraction 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 random geometry effects in optically thin clouds, while in optically dense clouds the range of errors caused by ignoring the horizontal heterogeneity increases and is ~ ± 5% in albedo calculations with an underestimation of the diffuse transmission by ~ 10-20%.
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