Quoted from: G. W , Paltridge, and, et al. Monthly mean solar radiation statistics for Australia[J]. Solar Energy, 1976.
https://www.sci-hub.ren/10.1016/0038-092x(76)90022-0
Tables of monthly mean solar radiation parameters are computed from detailed cloud cover information. The parameters include direct and global daily total energy inputs to horizontal, inclined and "sun-tracking" surfaces. Comparison with measured global radiation at 12 stations reveals virtually no systematic error in the computation scheme, and an error of 2MJm -2day -1~ in the worst case month of any station.
This model takes the solar zenith angle (y), day length S0 and cloud factor (CF) as inputs. Their model assumes that the effect of atmospheric water vapor, regional albedo and aerosol optical air mass on surface radiation is small (less than 5%) . The hourly beam Ib and diffuse Id radiation in(MJ/m2 h) are determined by:
\( 𝐼_𝑏=3.42286[1−exp(−0.075(90−𝜃))] \)
\( 𝐼_𝑑=0.00913+0.0125(90−𝜃)+0.723CF \)
The mean monthly Total daily global radiation on horizontal surface (MJ/m 2day) were computed from correlations below:
\( 𝐻=𝐻_𝑏+𝐻_𝑑 \)
\( 𝐻=(1−𝐶𝐹)∫_"sunrise " ^"sunset " ▒ 𝐼_𝑏 (𝜃)cos𝜃𝑑𝑡+∫_"sunrise " ^"sunset " ▒ 𝐼_d (𝜃)𝑑𝑡 \)
In this work, the integral was simply converted to summationand added up every 15 min to obtain total daily global radiation.
The cloud factor (CF) varies from zero for clear sky to 1 for overcast sky. This parameter could be obtained by use of the numbers of cloudy days in each month and the cloud cover. Cloud cover is observed every three hours in three different ranges: (0–2) octas, (3–6) octas, and (7–8) octas. To convert the cloud cover to cloud factor (CF), the following relationship is used:
\( 𝐶𝐹=((n_1 )+4.5(n_2 )+7.5(n_3 ))/8(n_1+𝑛_2+𝑛_3 ) \)
where n1, n2 and n3 are the total number of days in each month, with zero to 2/8, 3/8 to 6/8, and 7/8 to 8/8 octas, respectively.