Radiative Effects on the Growth of Cloud Droplets in a 3D LES Model

The effects of longwave cooling and shortwave heating are not commonly considered in the diffusional growth of cloud droplets. However, the growth of individual droplets may be enhanced or reduced depending on the longwave cooling and/or shortwave heating.Therefore, radiative processes may have significant influences on the evolution of droplet size spectrum within the cloud, which may have further impact on the collision-coalescence process and the onset of precipitation. This study uses a WRF-based 3D LES model to investigate the radiative effect on cloud microphysics. It is expected that the radiative effect near cloud boundaries and the spatial variance of radiative heating rates are better represented in the 3D model compared to the 2D simulations in previous studies. Particular focus will be on the radiative effects on droplet size distributions, rain initiation, and turbulence intensity. Radiative effects on macrophysical structures such as cloud thickness will also be explored. Effort will be made to develop a parameterization for the radiative effect on cloud microphysics.