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This study investigates effects of drizzle and cloud horizontal inhomogeneity on cloud effective radius (r_e) retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS). In order to identify the relative importance of various factors, we developed a MODIS cloud property retrieval simulator based on the combination of large‐eddy simulations (LES) and radiative transfer computations. The case studies based on synthetic LES cloud fields indicate that at high spatial resolution (∼100 m) 3‐D radiative transfer effects, such as illumination and shadowing, can induce significant differences between retrievals ofr_e based on reflectance at 2.1 μm (r_e,2.1) and 3.7 μm (r_e,3.7). It is also found that 3‐D effects tend to have stronger impact onr_e,2.1 than r_e,3.7, leading to positive difference between the two (Δr_e,3.7−2.1) from illumination and negative Δr_e,3.7−2.1from shadowing. The cancellation of opposing 3‐D …