AM4.0/LM4.0 was developed from AM3 and HiRAM, and it contains: the hydrostatic version of the FV3 finite-volume cubed-sphere dynamical core, with minor modifications from the version used in AM3; a substantially updated version of the GFDL radiative transfer code, with refitting to line-by-line simulations using the latest spectroscopy and adding 10 um CO2 band among other changes; this increases the TOA radiative forcing due to quadrupling of CO2 by roughly 10%; an alternate topographic gravity wave drag formulation that handles the anisotropy of the subgrid topography naturally and treats the blocked versus wave components of the drag in a distinctive way, among others. [From GDFL NOAA]