Experience with the Full CCSM ∗

We present our experiences porting and initial performance of the Community Climate System Model (CCSM3) on the Cray X1. This is the primary model for global climate research in the US and is supported on a variety of computer systems. It will also be used for assessing impacts of climate change for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment. The CCSM is the result of a community modeling effort sponsored by the National Science Foundation, the Department of Energy, and the National Aeronautics and Space Administration. The model development is coordinated by the National Center for Atmospheric Research, and the code has demonstrated performance portability across vector and cache based parallel architectures due to software engineering implementing a tunable internal data structure. The application is composed of five executables run in MPMD mode: a sea ice model (CSIM), a land model (CLM), an ocean model (POP), an atmospheric model (CAM) and a flux coupler (CPL6). Each component model communicates with the coupler using MPI and exploits SPMD distributed memory parallelism with MPI.