Two-moment bulk cloud microphysics with prognostic precipitation in the
GFDL CM4.0 model: Performance and simulation characteristics
Abstract
We describe the model performance and simulation characteristics 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 cloud 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 (CMIP6) 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 (ENSO). Compared to
CM4.0, the climate sensitivity is reduced by about 10\%
in CM4-MG2.