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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.