Community Climate Model

This paper is a brief overview of a parallel version of the NCAR Community Climate Model, CCM2, implemented for MIMD massively parallel computers using a message-passing programming paradigm. The parallel implementation was developed on an Intel iPSC/860 with 128 processors and on the Intel Delta with 512 processors, and the initial target platform for the production version of the code is the Intel Paragon with 2048 pro-cessors. Because the implementation uses a standard, portable message-passing library, the code can be easily ported to other multiprocessors supporting a message-passing program-ming paradigm, or run on machines distributed across a network. The parallelization strategy used is to decompose the problem domain into geographical patches and assign each processor to do the computation associated with a distinct subset of the patches. With this decomposition, the physics calculations involve only grid points and data local to a processor and are performed in parallel. Using parallel algorithms developed for the semi-Lagrangian transport, the fast Fourier transform and the Legendre transform, both physics and dynamics are computed in parallel with minimal data movement and modest change to the original CCM2 source code.