Global Radiation Calculation as applied in WOFOST/CGMS1
When the sunshine duration is known, the global radiation is calculated using the Ångström-Prescott formula. Constants depend on the geographic location.
where Rg : Incoming daily global solar radiation [J m-2 d-1]
Ra : Daily extra-terrestrial radiation  [J m-2 d-1]
Aa : Empirical constant  [-]
Ba : Empirical constant  [-]
n : Bright sunshine hours per day [hr]
Ld : Astronomical day length  [hr]
Constants:
Spatial variation:

When sunshine duration is not available but minimum and maximum temperature and cloud cover are known, the Extended Hargreaves (a.k.a. Supit ) formula is applied. Constants depend on geographic location:

where Rg Incoming daily global solar radiation [J m-2 d-1]
Ra Daily extra-terrestrial radiation  [J m-2 d-1]
CC Mean total cloud cover during daytime [octa]
Tmax Maximum temperature [°C]
Tmin : Minimum temperature [°C]
As : Empirical constants [°C-0.5]
Bs : Empirical constants [-]
Cs : Empirical constants [J m-2 d-1]
Constants:
Spatial variation:

When only minimum and maximum temperatures are known, the Hargreaves equation is applied. Again, the constants depend on geographic location:

where Rg Incoming daily global solar radiation [J m-2 d-1]
Ra Daily extra-terrestrial radiation [J m-2 d-1]
Tmax Maximum temperature [°C]
Tmin : Minimum temperature [°C]
Ah : Empirical constants [°C-0.5]
Bh : Empirical constants [J m-2 d-1]
Constants:
Spatial variation:

For information on available data contact Privateers N.V.





1CGMS is the Crop Growth Monitoring System as applied by the European Commission