Atmospheric broadband model for computation of solar radiation at the earth's surface. Application to Mediterranean climate

This paper deals with a new broadband atmospheric model designed for predic ting the total and diffuse solar radiation incident on the earth's surface in medium or large-sized coastal or near-coastal cities, under a clear or c loudy sky. The revised NECKEL and LABS (1981, 1984) solar spectrum is used. The atmospheric transmittance of each atmospheric parameter contributing t o solar radiation depletion, water vapor, ozone, uniformly mixed gases, mol ecules and aerosols, is calculated using parameterized expressions resultin g from integrated spectral transmittance functions. The beam and diffuse ra diation components are obtained as a function of the specific atmospheric t ransmittances. The model requires the following parameters as inputs: total water vapor and ozone amount in a vertical column, sunshine duration and t he surface albedo. The model has been used for validation purposes at two s tations with slightly different characteristics (NOA and Penteli) in the At hens basin, where total and diffuse radiation measurements are available, f or a period of 34 months for NOA and 23 for Penteli. The NOA station is loc ated on a small hill (107 m a.m.s.l.) near the center of Athens, while the Penteli station (500 m a.m.s.l.) is situated in a relatively less polluted area in northern Athens. The clear sky part of the model was tested for 70 individual "clear" days with 2-minute intervals, while the whole model was checked with monthly "mean" days and mean hourly values. A close agreement between the calculated and the measured values of total and diffuse solar r adiation is observed.