paNTICA: A Fast 3D Radiative Transfer Scheme to Calculate Surface Solar Irradiance for NWP and LES Models

Abstract

The resolution of numerical weather prediction models is constantly increasing, making it necessary to consider three-dimensional radiative transfer effects such as cloud shadows cast into neighboring grid cells and thus affecting radiative heating. For that purpose, fast approximations are needed since threedimensional radiative transfer solvers are computationally far too expensive. For the solar spectral range, different approaches of how to consider three-dimensional effects were presented in the past—in particular, the tilted independent column approximation (TICA), which aims at improving the calculation of the direct radiation, and the nonlocal tilted independent column approximation (NTICA), which is used to additionally correct the diffuse radiation.