Calculating the Natural Atmospheric Radiation Using the General Circulation Model of the Earth’s Lower and Middle Atmosphere

The paper describes a block for calculating the Earth’s natural atmospheric radiation in the IR range developed for the general circulation model simulating the lower and middle atmosphere. This block uses the new parametrization of molecular absorption in the frequency range from 10 to 2000 cm −1 at the altitude ranging from the Earth’s surface to 76 km. The algorithm for constructing this parametrization takes into account the change in the gas composition of the atmosphere with altitude and has some other significant advantages. In addition, for the numerical solution of the radiation transfer equation, the discrete ordinate method and the computational zenith angle grid with the step of about nine degrees are used. The results of the line-by-line calculations of the Earth’s internal atmospheric radiation field are compared with the results of the calculations performed using parametrization, and it is shown that the presented parametrization is accurate in the lower and middle atmosphere both in the absence of clouds and in the presence of cloud layers with a significant optical thickness.