Performance of Two-Moment Stratiform Microphysics With Prognostic Precipitation in GFDL's CM4.0

We describe the model performance of a new global coupled climate model configuration, CM4-MG2. Beginning with the Geophysical Fluid Dynamics Laboratory's fourth-generation physical climate model (CM4.0), we incorporate a two-moment Morrison-Gettelman bulk stratiform microphysics scheme with prognostic precipitation (MG2), and a mineral dust and temperature-dependent cloud ice nucleation scheme. We then conduct and analyze a set of fully coupled atmosphere-ocean-land-sea ice simulations, following Coupled Model Intercomparison Project Phase 6 protocols. CM4-MG2 generally captures CM4.0's baseline simulation characteristics, but with several improvements, including better marine stratocumulus clouds off the west coasts of Africa and North and South America, a reduced bias toward "double" Intertropical Convergence Zones south of the equator, and a stronger Madden-Julian Oscillation (MJO). Some degraded features are also identified, including excessive Arctic sea ice extent and a stronger-than-observed El Nino-Southern Oscillation. Compared to CM4.0, the climate sensitivity is reduced by about 10% in CM4-MG2. A sophisticated cloud microphysical scheme, along with a mineral dust and temperature-dependent ice nucleation scheme, have been implemented in a new configuration of the Geophysical Fluid Dynamics Laboratory's most recent climate model (CM4.0). This microphysical scheme predicts both mass and number concentrations of cloud drops, ice crystals, rain, and snow, and treats aerosol-cloud interactions more consistently. The ice nucleation on mineral dust aerosol in large-scale clouds is represented more realistically. Centennial-scale global coupled atmosphere-ocean-land-sea ice simulations from this new configuration compare favorably with observations-with improved subtropical stratocumulus clouds and better tropical intraseasonal variability (i.e., the 30- to 90-day Madden-Julian Oscillation). The new configuration also reduces the magnitude of future global warming in response to anthropogenic emissions.