Solar and thermal infrared radiation transfer schemes in the NCEP Global Forecast System (GFS)

This technical memorandum is intended to document the radiative transfer scheme used in the current NCEP’s models. Sections 2-5 review the fundamentals of radiative transfer calculations for atmospheric model applications. Specifically, section 2 gives the basic equation of the radiative transfer in the plane-parallel atmosphere, section 3 and 4 review the approximations for solar and thermal infrared radiation transfer. Section 5 discusses the radiative flux calculation for partially cloudy sky. Sections 2-5 are very important to understand the GFS radiation scheme. Section 6 introduces the RRTM, RRTMG and RRTMGP radiative transfer models. Section 7 discusses the climate data needed for radiative transfer calculation. Section 8 describes the input variables for the GFS radiative transfer modules. Finally, the GFS radiation scheme FORTRAN code structure is explained in section 9.