Modelling frequency distributions of 5 minute-averaged solar radiation
indexes using Beta probability functions
Theorical and Applied Climatology, (2003)Abstract
Five minute-averaged values of sky clearness, direct and diffuse
indices, were used to model the frequency distributions of these
variables in terms of optical air mass. From more than four years
of solar radiation observations it was found that variations in the
frequency distributions of the three indices of optical air mass
for Botucatu, Brazil, are similar to those in other places, as published
in the literature. The proposed models were obtained by linear combination
of normalized Beta probability functions, using the observed distributions
derived from three years of data. The versatility of these functions
allows modelling of all three irradiance indexes to similar levels
of accuracy. A comparison with the observed distributions obtained
from one year of observations indicate that the models are able to
reproduce the observed frequency distributions of all three indices
at the 95% confidence level.