Abstract
The present study describes the effect of clouds (macro-physical parameters) on global solar radiation (G). Data from four years of hourly measurements of G on a horizontal surface were used. These data were collected at the South Valley University (SVU) meteorological research station (26.2 degrees N, 32.7 degrees E, 96 m above mean see level. In addition, the cloud modification factor for G (CMFG) was estimated in three cases: high-level, mid-level, and low-level clouds. For every level, the variation of hourly CMFG as a function of cloud amount (CA) was illustrated. A third-order polynomial between hourly values of CMFG and CA was established. Furthermore, the effect of CA in the attenuation of G relative to its corresponding value in cloudless conditions is discussed. For cloud cover > 88%, G was reduced by 54%, 34%, and 28% by low-, mid-, and high-level clouds, respectively.