Open AccessThe influence of cloud structure and droplet concentration on the reflectance of shortwave radiation
Author(s) -
P. F. Coley,
P. R. Jonas
Publication year - 1996
Publication title -
annales geophysicae
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.522
H-Index - 93
eISSN - 1432-0576
pISSN - 0992-7689
DOI - 10.1007/s00585-996-0845-5
Subject(s) - zenith , liquid water content , cloud fraction , solar zenith angle , cloud computing , channelling , shortwave , cloud albedo , reflection (computer programming) , shortwave radiation , radiation , cloud cover , environmental science , computational physics , cloud top , optics , physics , atmospheric sciences , radiative transfer , ion , quantum mechanics , computer science , programming language , operating system
The effects of cloud shadowing, channelling,cloud side illumination and droplet concentration are investigated with regardto the reflection of shortwave solar radiation. Using simple geometric clouds,coupled with a Monte Carlo model the transmission properties of idealized cloudlayers are found. The clouds are illuminated with direct solar radiation fromabove. The main conclusion reached is that the distribution of the cloud has avery large influence on the reflectivity of a cloud layer. In particular, if thecloud contains vertical gaps through the cloud layer in which the liquid watercontent is zero, then, smaller more numerous gaps are more influential on theradiation than fewer, larger gaps with equal cloud fraction. At very low solarzenith angles channelling of the radiation reduces the reflection expected onthe basis of the percentage cloud cover. At high solar zenith angles theillumination of the cloud edges significantly increases the reflection despitethe shadowing of one cloud by another when the width of the gaps is small. Theimpact of droplet concentration upon the reflection of cloud layers is alsoinvestigated. It is found that at low solar zenith angles where channelling isimportant, the lower concentrations increase the transmission. Conversely, whencloud edge illumination is dominant the cloud distribution is found to be moreimportant for the higher concentrations