3D modeling of atmospheric infrared radiative transfer: coupling a broadband emissivity scheme with the discrete ordinates method

The Atmospheric Radiation field has seen the development of more accurate and faster methods to take into account absorption. Modelling fog formation, where Infrared Radiation is involved, requires accurate methods to compute cooling rates. Radiative fog appears with clear sky condition due to a significant cooling during the night where absorption is the dominant process. Thanks to High Performance Computing, multi-spectral approaches of Radiative Transfer Equation resolution are often used. Nevertheless, the coupling of three-dimensional radiative transfer with fluid dynamics is very computationally expensive. Radiation increases the computation time by around fifty percent over the pure Computational Fluid Dynamics simulation. To reduce the time spent in radiation calculations, a new method using the broadband emissivity has been developed to compute an equivalent absorption coefficient (spectrally integrated). Only one resolution of Radiative Transfer Equation is needed against N_band times N_gauss for an N_band model with N_gauss quadrature points on each band. A comparison with simulation data has been done and the new parameterization of Radiative properties shows the ability to handle variations of gases concentrations and liquid water. A dynamical study through the coupling between the infrared radiation model and Code-Saturne has been done to validate our parametrization. Finally the model was tested on a 3-D domain with idealized buildings to catch 3-D infrared radiative effects due to horizontally inhomogeneities of the liquid water content field and buildings (author)