Abstract
A new method to calculate hourly direct beam and diffuse irradiation on a horizontal surface using 3-h standard meteorological data is described. Comparisons of computed and observed irradiations are made with hourly data obtained in Carpentras over the 10 yr period 1971–80.
For cloudless days it is found that a good estimate of lower-layer aerosol extinction can be calculated using water-vapor pressure and half-daily sunshine duration. For cloudy days a good estimate of hourly atmospheric transmittance can be estimated from total cloudiness, cloud type and half daily sunshine duration.
