Abstract

The DIScrete Ordinate Radiative Transfer (DISORT) and the delta-Eddington models were used to evaluate the relationship between cloud optical depth, t_c and direct, diffuse and global transmitted irradiances in the UV-B region for various solar zenith angles (SZAs), two values of cloud droplet equivalent radius, r_e (7mm and 10mm) and two cases of low (? = 0.05) and high (? = 0.75) albedos under overcast conditions. The study shows that the delta-Eddington model is not suitable for calculating direct and diffuse components separately but it is suitable for calculating diffuse irradiances for overcast conditions for two cases only at northern latitudes where SZAs are large and at southern Canada wheret_c values are always greater than 10. The delta-Eddington model is accurate when calculating the global fluxes anywhere, although it overestimates by an average of 6%. Global transmittance is greater by 7% for smaller droplet sizes (r_e = 7µm) for both cases of low (? = 0.05) and high (? = 0.75) albedos.

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