An Impact Study of Cloud Optical Properties in Weather Modeling

Cloud dynamics, associated with air motions, plays a critical role in general circulation and climate change through cloud radiative heating and latent heating. The focus of this study is to investigate cloud radiative effects on the global radiation balance and the bias change of modeled temperature and winds of Navy Global Environmental Model (NAVGEM). An efficient Rapid Radiative Transfer Model for Global applications (RRTMG) and a bulk-size cloud microphysics of liquid, ice, and precipitable species are being integrated together to study cloud-radiation interactions. Cloud optical properties highly depend on the effective radius of cloud species. Various parameterizations of effective radius are examined and compared to understand the sensitivities of cloud optical depth, albedo scattering, and asymmetry factors in radiative transfer to radiative fluxes and heating rates. The responses of atmospheric dynamics to the variation of cloud optics is investigated with regards to the modeling errors of air temperature and winds in a period of update-cycle short forecasts and in extended long forecasts for the same period. The study reveals that the impact of cloud optical properties can reach a level that affects regional and global height anomaly correlations. Using appropriate cloud effective radius can increase the accuracy of modeled radiative fluxes and effectively reduce the bias of major forecast fields.