Analysis of CCCma Radiative Transfer Calculations for Single‐Layer Overcast Ice Clouds

Abstract Understanding interactions between incoming shortwave (SW) solar radiation and clouds is essential for quantifying and modeling Earth's Radiation Budget (ERB). Ice clouds are particularly problematic due to their wide variability in crystal habits, sizes, and shapes. In this study, data from NASA's Cloud and Earth Radiative Energy System (CERES) are used to identify single‐layer overcast ice clouds and calculate surface and top‐of‐atmosphere (TOA) SW fluxes using the Canadian Centre for Climate Modeling and Analysis (CCCma) Radiative Transfer Model (RTM). A total of 361 SW flux observations from 11 surface sites spanning different climatic regions, together with CERES SYN1deg satellite observations at the TOA, are used to evaluate the CCCma RTM's performance. The CCCma RTM exhibits mean bias errors (MBEs) of +3.7 W m −2 at the surface and +4.1 W m −2 at the TOA, with root mean square errors (RMSEs) of 72.7 and 33.2 W m −2 , respectively. Correspondingly, the CERES SYN1deg Fu‐Liou RTM shows MBEs of −12.1 and +18.5 W m −2 and RMSEs of 75.0 and 34.5 W m −2 for surface and TOA, respectively. MBE differences between the two RTMs are due to differing treatments of model physics, while their larger RMSEs at the surface result from both imprecise inputs and spatial variabilities of both inputs and surface observed flux.