The GFDL Global Atmospheric Chemistry-Climate Model AM4.1: Model
Description and Simulation Characteristics
Abstract
We describe the baseline model configuration and simulation
characteristics of GFDL’s Atmosphere Model version 4.1 (AM4.1), which
builds on developments at GFDL over 2013–2018 for coupled
carbon-chemistry-climate simulation as part of the sixth phase of the
Coupled Model Intercomparison Project. In contrast with GFDL’s AM4.0
development effort, which focused on physical and aerosol interactions
and which is used as the atmospheric component of CM4.0, AM4.1 focuses
on comprehensiveness of Earth system interactions. Key features of this
model include doubled horizontal resolution of the atmosphere
(~200 km to ~100 km) with revised
dynamics and physics from GFDL’s previous-generation AM3 atmospheric
chemistry-climate model. AM4.1 features improved representation of
atmospheric chemical composition, including aerosol and aerosol
precursor emissions, key land-atmosphere interactions, comprehensive
land-atmosphere-ocean cycling of dust and iron, and interactive
ocean-atmosphere cycling of reactive nitrogen. AM4.1 provides vast
improvements in fidelity over AM3, captures most of AM4.0’s baseline
simulations characteristics and notably improves on AM4.0 in the
representation of aerosols over the Southern Ocean, India, and
China—even with its interactive chemistry representation—and in its
manifestation of sudden stratospheric warmings in the coldest months.
Distributions of reactive nitrogen and sulfur species, carbon monoxide,
and ozone are all substantially improved over AM3. Fidelity concerns
include degradation of upper atmosphere equatorial winds and of aerosols
in some regions.