On the accuracy of the independent column approximation in calculating the downward fluxes in the UVA, UVB, and PAR spectral ranges

摘要: In order to investigate the accuracy of simplification in modeling radiative transfer those solar spectral regions with major impacts on bio-organisms, i.e., UVA (0.32–0.4 μm), UVB (0.28–0.32 and photosynthetically active radiation (PAR, 0.4–0.7 calculations varying treatments cloud geometries (plane-parallel homogeneous (PPHOM), independent column approximation (ICA), three-dimensional (3-D) inhomogeneous) have been performed. The complete sets atmospheric information for 133 realizations are taken from nonhydrostatic mesoscale model (GESIMA). A Monte Carlo (GRIMALDI) has developed that simulates scattering absorption arbitrarily distributions hydrometeors, air molecules, water vapor. Results shown domain-averaged direct total transmission (and so, implicitly, diffuse transmission) at ground surface. PPHOM assumption leads an underestimation (total) downward flux by as much 43 (28) W m−2, which is about 49% (32%) incoming irradiation, whereas results based ICA almost identical 3-D case, except convective clouds where error reaches 5 (2) or 6% (2%) irradiation.