Comparison of the RWDM6 and MG Microphysics Schemes in Precipitation Simulation With the GRIST Model

Realistic representation of cloud and precipitation processes is crucial for climate simulations. A revised double-moment 6-class (RWDM6) cloud microphysics scheme with prognostic precipitation, instead of the Morrison-Gettelman scheme, is implemented into the Global-to-Regional Integrated forecast System (GRIST) model to improve its numerical hydrological cycles, and the impact of the treatment of grid-scale precipitation is assessed with climate simulations. With more realistic vertical hydrometeor distribution, the double-moment scheme with prognostic precipitation not only improves the vertical distribution of water vapor and temperature but also reduces biases in medium and high clouds and cloud forcing radiation compared to the diagnostic scheme. Hydrological cycles and corresponding atmospheric thermodynamics are improved with the revised scheme. Additionally, a clear reduction in precipitation over the Intertropical Convergence Zone and mid-latitude storm track regions is observed with the RWDM6 scheme, aligning closer consistency with the observations compared to the original model results. With respect to the model precipitation sensitivity to time step, the RWDM6 scheme simulates consistent precipitation intensity throughout, while the diagnostic scheme exhibits significant biases at different time steps. The RWDM6 scheme with the prognostic treatment of precipitation shows a remarkable contribution to cloud microphysics in the GRIST climate model.