GFDL - Geophysical Fluid Dynamics Laboratory


AM3 (Donner et al., 2011), the atmospheric component of the GFDL coupled
model CM3, was designed with an awareness of key emerging issues in climate
science, including aerosol-cloud interactions in climate and climate change,
chemistry-climate feedbacks, land and ocean carbon cycles and their
interactions with climate change, and decadal prediction. It is GFDL’s
first global atmospheric model to include cloud-aerosol interactions, with
20 interactive aerosol species. AM3 includes interactive tropospheric and
stratospheric chemistry (85 species). AM3 uses emissions to drive its
chemistry and aerosols. Its inclusion of stratospheric chemistry and
dynamics will enable possible interactions between the stratosphere and
troposphere on interannual scales to be included in future studies of
decadal predictability. Its stratosphere has increased vertical resolution
over AM2, with the uppermost level at about 1 Pascal. AM3’s improved
simulation of Amazon precipitation will enhance future coupling into an
earth-system model.

AM3 uses a cubed-sphere implementation of the finite-volume dynamical core.
Earth’s atmosphere is represented as a cube with six rectangular faces.
There is no singularity associated with the north and south poles as with
the spherical representation. Computationally, the core is highly scalable
and efficient at advecting the large number of tracers associated with AM3’s
chemistry and aerosols.

AM3 uses physically based aerosol activation (Ming et al., 2006) to form
cloud droplets. All cloud parameterizations in AM2 were either replaced or
augmented to include sub-grid distributions of vertical velocity required
for these activation calculations. Sub-grid distributions of vertical
velocity are included in AM3’s stratiform clouds (Golaz et al., 2011); deep
convection (Donner et al., 2001, and Wilcox and Donner, 2007) represented by
an ensemble of plumes with mass fluxes and vertical velocities, simple bulk
microphysics, and mesoscale updrafts and downdrafts; and shallow convection
after Bretherton et al. (2004, Mon. Wea. Rev.) with buoyancy sorting,
entraining plumes and vertical velocity.

AM3 Code Released March 2012

The code for this model is publicly available. If you are interested
in downloading the code, please do so here.