Estimation of global radiation for Sri Lanka

Fre're et al. have given a graphical method to determine a and b of the modified Angstrom formula HH0 = a + b(SZ) Starting from their data the relations a = −0.14 + 1.20(SZ) − 0.82(SZ)2 , b = 1.32 − 2.89(SZ) + 2.24(SZ)2 , are obtained to determine a and b for meteorological stations in Sri Lanka with known values of the annual avergage (SZ) where S is the hours of sunshine and Z the length of the day. Using these values of a and b, the estimates of the annual monthly-mean-daily-global radiation over the island are found to be between 15 and 20 MJ m−2 d−1.