Implementation of a Two-Moment Cloud Microphysics Parameterization for Stratiform Clouds of NCAR CESM

Aerosol-cloud-precipitation interactions in modern GCMs remain unresolved and of huge uncertainties due to oversimplified aerosol- and cloud-microphysical parameterizations used in the coarse grid resolutions of global models. Many of the microphysical schemes used in present global models are simplified versions of the original schemes for small to regional scale models. There are relatively few studies trying to use a two-moment cloud microphysical scheme with fully prognostic calculations for all hydrometeors including cloud liquid, ice, rain, snow and graupel to simulate aerosol-cloud-precipitation interactions for stratiform clouds in GCMs to understand and to evaluate the aerosol indirect effects of global scales. A two-moment bulk cloud microphysical scheme (i.e. Chen and Liu, 2004; Cheng et al., 2007, 2010) is implemented into the stratiform clouds of CAM5.2 of NCAR CESM model. Single column model simulations are first carried out and compared to in-situ observational data for validations of implementation of microphysical schemes. Short-term global simulation with prescribed sea surface temperature is also conducted to evaluate the possible impacts from the modification of the physical parameterizations. Global simulation results are further compared to observational results from different satellite data sets especially for cloud fraction and hydrometeors. In particular, a satellite simulator (i.e. Joint Simulator) is applied for comparisons against CloudSat and CALIPSO satellite data. Sensitivity tests regarding to changes in parameters related to macrophysical and microphysical parameterizations of CESM model are also evaluated to understand their possible impacts on the cloud and precipitation simulations.