Two‐Moment Bulk Cloud Microphysics With Prognostic Precipitation in GFDL's Atmosphere Model AM4.0: Configuration and Performance

A two‐moment Morrison‐Gettelman bulk cloud microphysics with prognostic precipitation (MG2), together with a mineral dust and temperature‐dependent ice nucleation scheme, have been implemented into the Geophysical Fluid Dynamics Laboratory's Atmosphere Model version 4.0 (AM4.0). We refer to this configuration as AM4‐MG2. This paper describes the configuration of AM4‐MG2, evaluates its performance, and compares it with AM4.0. It is shown that the global simulations with AM4‐MG2 compare favorably with observations and reanalyses. The model skill scores are close to AM4.0. Compared to AM4.0, improvements in AM4‐MG2 include (a) better coastal marine stratocumulus and seasonal cycles, (b) more realistic ice fraction, and (c) dominant accretion over autoconversion. Sensitivity tests indicate that nucleation and sedimentation schemes have significant impacts on cloud liquid and ice water fields, but higher horizontal resolution (about 50 km instead of 100 km) does not. Plain Language Summary We have implemented a sophisticated cloud microphysical scheme in the Geophysical Fluid Dynamics Laboratory's Atmosphere Model AM4.0. This microphysical scheme predicts both mass and number concentrations of cloud droplets, ice crystals, rain, and snow. Additionally, the nucleation of mineral dust aerosols to ice crystals has been considered as part of an effort to represent aerosol‐cloud‐ice interactions more realistically. We conducted multi‐year global simulations. Simulation results turn out to be in good agreement with observations, and show improvements in coastal stratocumulus, cloud liquid and ice phase partitioning, and the ratio of accretion (collection of cloud drops by raindrops) over autoconversion (collision and coalesce between droplets to form raindrops). Key Points Two‐moment microphysics with prognostic precipitation and ice nucleation schemes have been implemented in Atmosphere Model version 4.0 (AM4.0), referred to as AM4‐MG2 The overall skill scores of AM4‐MG2 are close to AM4.0 Improvements include better coastal stratocumulus, more realistic liquid and ice partitioning, dominant accretion over autoconversion