Long-term behavior of cloud systems in TOGA COARE and their interactions with radiative and surface processes. Part II: Effects of ice microphysics on cloud-radiation interaction

A two-dimensional cloud-resolving model with a large domain is integrated f or 39 days during the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosp here Response Experiment (TOGA COARE) to study the effects of ice phase pro cesses on cloud properties and cloud radiative properties. The ice microphy sical parameterization scheme is modified based on microphysical measuremen ts from the Central Equatorial Pacific Experiment. A nonlocal boundary laye r diffusion scheme is included to improve the simulation of the surface hea t fluxes. The modified ice scheme produces fewer ice clouds during the 39-d ay simulation. The cloud radiative properties show significant improvement and compare well with various observations. Both the 39-day mean value (202 W m(-2)) and month-long evolution of outgoing longwave radiative flux from the model are comparable with satellite observations. The 39-day mean surf ace shortwave cloud forcing is -110 W m(-2), consistent with other estimate s obtained for TOGA COARE. The 39-day mean values of surface net longwave, shortwave, latent, and sensible fluxes are -46.2, 182.9, -109.9, and -7.8 W m(-2), respectively, in line with the IMET buoy data (-54.6, 178.2, -102.7 , and -10.6 W m(-2)). The offline radiation calculations as well as the cloud-interactive radiati on simulations demonstrate that a doubled effective radius of ice particles and enhanced shortwave cloud absorption strongly affect the radiative flux and cloud radiative forcing but have little impact on the cloud properties . The modeled albedo is sensitive to the effective radius of ice particles and/or the shortwave cloud absorption in the radiation scheme. More complet e satellite observations and theoretical studies are required to fully unde rstand the physical processes involved. The results suggest that the ice microphysical parameterization plays an im portant role in the long-term simulation of cloud properties and cloud radi ative properties. Future field observations should put more weight on the m icrophysical properties, cloud properties, and high-quality radiative prope rties in order to further improve the cloud-resolving modeling of cloud sys tems and the understanding of cloud-radiation interaction.