Abstract
The measured data of global and diffuse solar radiation on a horizontal surface, number of sunshine hours, mean daily ambient temperature, maximum and minimum ambient temperatures, relative humidity and amount of cloud cover, for Jeddah (latitude 21° 42′ 37″ N, longitude 39° 11′ 12″ E), Saudi Arabia for the period (1996-2006) are analysed. The data are employed to develop empirical correlations between the monthly average daily diffuse fraction (H
d
/H) or diffuse transmittance (H
d
/H
0
) and various meteorological parameters such as relative number of sunshine hours (s/s
0
), ambient temperature T, relative humidity R
h
and amount of cloud cover c
w
. The derived correlations are evaluated by making comparisons between measured and calculated values of monthly average daily diffuse radiation H
d
. All the proposed correlations are found to be able to predict the monthly and annual averages daily diffuse radiation with excellent accuracy. It is also inferred that, if the data of the monthly average daily global radiation H and number of bright sunshine hours s are not available, the values of H
d
for the hot-humid zone of Saudi Arabia can be estimated with a reasonable accuracy from the correlations between H
d
/H
0
and the mean daily ambient temperature T.