The Geophysical Fluid Dynamics Laboratory's (GFDL) next-generation atmospheric general circulation model (AM3) is being developed as part of a coupled earth-system model aimed at addressing a new class of scientific questions related to cloud-aerosol interactions and the land and ocean carbon cycles. Model parameterizations related to clouds and convection have been changed significantly from those in GFDL's IPCC AR4 coupled models in order to enable physically based treatments of cloud-aerosol interactions. In particular, deep convection, shallow convection, and stratiform clouds are characterized by probability distribution functions for sub-grid vertical velocity to enable calculation of supersaturation at appropriate scales for droplet activation by aerosols. AM3 will also adopt a new finite-volume dynamical core without polar singularities.

Early results of simulations with AM3 will be presented and key challenges remaining in its development summarized.