The Effect of Cloud Geometrical Thickness Variability on Optical Depth

The formulation of the cloud-radiation feedback is compounded by extreme variability of clouds over a wide range of scales. In this study, we address the problem of geometry and spatial inhomogeneity in stratiform cloud layers and its influence on cloud optical depth. The investigation is based on the Cooperative Institute for Mesoscale Meteorological Studies (CIMMS) large eddy simulation model with explicit microphysics (Kogan et al. 1995). The two commonly used parameterizations of the cloud optical depth, which are based on simplified assumptions about cloud geometry and the spatial distributions of cloud parameters, are contrasted with the optical depth calculated using its exact definition as a second moment of the cloud drop distribution function. The goal of the study is to evaluate the bias introduced by different simplifications.