THE TRANSMISSION OF SUNLIGHT THROUGH CLOUDY SKIES - AN ANALYSIS BASEDON STANDARD METEOROLOGICAL INFORMATION

This work examines the use of standard meteorological information to d escribe the attenuation of sunlight associated with cloudy skies. Data sets consisting of broadband ultraviolet and total spectrally integrat ed solar irradiance are available for Chicago over the period April-Oc tober 1993. A series of regression models seeks to explain variability in the measured irradiances using fractional cloudiness, cloud-ceilin g altitude, and visibility as independent variables. Fractional cloud cover alone can explain 39%-51% of the variance in the radiation data. Regression models that combine all three independent variables can in crease the explained variance to 61%-77%, depending on local time and spectral region. Comparison of broadband ultraviolet irradiances with simultaneous total solar irradiances indicates that cloudy skies provi de less attenuation in the former dataset.