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Testing the two‐layer model for correcting near‐cloud reflectance enhancement using LES/SHDOM‐simulated radiances
Author(s) -
Wen Guoyong,
Marshak Alexander,
Várnai Tamás,
Levy Robert
Publication year - 2016
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2016jd025021
Subject(s) - radiance , sky , cloud computing , radiative transfer , remote sensing , cloud fraction , satellite , moderate resolution imaging spectroradiometer , atmospheric radiative transfer codes , environmental science , meteorology , cloud cover , diffuse sky radiation , aerosol , spectroradiometer , physics , scattering , reflectivity , computer science , geography , optics , astronomy , operating system
A transition zone exists between cloudy skies and clear sky; such that, clouds scatter solar radiation into clear‐sky regions. From a satellite perspective, it appears that clouds enhance the radiation nearby. We seek a simple method to estimate this enhancement, since it is so computationally expensive to account for all three‐dimensional (3‐D) scattering processes. In previous studies, we developed a simple two‐layer model (2LM) that estimated the radiation scattered via cloud‐molecular interactions. Here we have developed a new model to account for cloud‐surface interaction (CSI). We test the models by comparing to calculations provided by full 3‐D radiative transfer simulations of realistic cloud scenes. For these scenes, the Moderate Resolution Imaging Spectroradiometer (MODIS)‐like radiance fields were computed from the Spherical Harmonic Discrete Ordinate Method (SHDOM), based on a large number of cumulus fields simulated by the University of California, Los Angeles (UCLA) large eddy simulation (LES) model. We find that the original 2LM model that estimates cloud‐air molecule interactions accounts for 64% of the total reflectance enhancement and the new model (2LM + CSI) that also includes cloud‐surface interactions accounts for nearly 80%. We discuss the possibility of accounting for cloud‐aerosol radiative interactions in 3‐D cloud‐induced reflectance enhancement, which may explain the remaining 20% of enhancements. Because these are simple models, these corrections can be applied to global satellite observations (e.g., MODIS) and help to reduce biases in aerosol and other clear‐sky retrievals.