The third version of the Community Climate System Model was released in June, 2004. There have been significant changes to the model since then, including changing the atmosphere component to use a finite volume dynamical core. More recently, changes have been made to the deep convection scheme, and to include momentum transport due to convection in the atmosphere component. Recent parameterization changes in the ocean component include reducing the horizontal viscosity, changing how the eddy parameterization scheme transitions into the surface mixed layer, and making its eddy coefficient a function of space and time. In addition, a less diffusive advection scheme has been put into the ocean component. The land component has a new, updated hydrology scheme and changes to the albedo formulation over land. The most important biases in CCSM3 that have been significantly reduced by these changes are: a) the double ITCZ in the tropical Pacific Ocean, b) the period of the NINO3 sea surface temperature variations, c) the precipitation biases over the Amazon and Congo regions, and d) the land surface temperature biases in the high Northern Hemisphere latitudes.
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