Abstract: Based on the measurements of solar radiation and cloud amount in Changbai Mountain in 1982-2001, the diurnal, seasonal, and inter-annual variations of diffuse radiation and diffuse fraction as well as their relationships with cloud amount, cloud type, and solar elevation were analyzed. The diffuse radiation had the characteristics of being the strongest at noon in diurnal course and in July in seasonal course, and showed a decreasing trend from 1982 to 2001. The diffuse fraction was the minimal at noon in diurnal course and the maximal in July in seasonal course, and fluctuated between 0.38 and 0.55 in inter-annual course. Both the diffuse radiation and the diffuse fraction increased with the increase of the high or low cloud amount. The mean daily diffuse radiation and diffuse fraction were linearly positively correlated with the mean daily total or low cloud amount, and the correlation with total cloud amount was closer than that with low cloud amount. Altocumulus had the maximal diffuse radiation and diffuse fraction, followed by Cirrus, Cumulonimbus and Cumulus, and clear sky. The diffuse radiation increased while the diffuse fraction decreased along with solar elevation, fitting quadratic function.

Key words: Taihu Region, Nitrogen wet deposition, Seasonal dynamics, Ecological significance