Three-dimensional radiative interactions in a polluted broken cloud system

[1] This paper is a theoretical study of short-wave radiative interactions in a polluted broken cloud scene encountered during the Indian Ocean Experiment (INDOEX). Towards this goal, the nadir reflectance has been obtained by integrating INDOEX in-situ observations and a 3D Monte-Carlo Aerosol-Cloud radiation model. The comparison of 2D radiative transfer and independent pixel approximation ( IPA) results demonstrates that IPA substantially underestimates nadir reflectances between the clouds. The effect can be explained by the radiative smoothing resulting from the horizontal photon transport. For the polluted cloud scene considered, the radiative smoothing is responsible for a 50% bias in aerosol optical depth retrieved between the clouds based on the plane-parallel theory.