INFLUENCE OF CUMULUS CLOUDS ON DIFFUSE AND TOTAL ULTRAVIOLET, PHOTOSYNTHETICALLY ACTIVE, AND INTEGRAL SOLAR RADIATION

G. M. Abakumova, E. I. Nezval, and O. A. Shilovtseva

Data of long-term (1965–1995) hourly visual cloud observations and surface actinometric measurements for the warm period (May–September), performed at the Meteorological Observatory of Moscow State University, are used to estimate the occurrence of cumulus clouds and their influence on diffuse and ultraviolet (λ ≤ 380 nm), photosyntetically active (380 nm ≤ λ ≤ 710 nm), and integral (λ ≤ 4000 nm) solar radiation. Ratios of diffuse and total radiation in cloudy conditions to corresponding values for clear sky (Cd and Cq) were used to estimate the influence of cumulus clouds on solar radiation. The influence of different methods of taking account of atmospheric transparency on these ratios is investigated. Statistical characteristics of Cd and Cq for each cloud amount are presented. It is shown that the ratio (S/D) of integral direct solar radiation incident on a perpendicular surface to diffuse radiation can be used as an average estimate of the amount of cumulus clouds.