Climate systems modeling on massively parallel processing computers at Lawrence Livermore National Laboratory

A comprehensive climate system model is under development at Lawrence Livermore National Laboratory. The basis for this model is a consistent coupling of multiple complex subsystem models, each describing a major component of the Earth's climate. Among these are general circulation models of the atmosphere and ocean, a dynamic and thermodynamic sea ice model, and models of the chemical processes occurring in the air, sea water, and near-surface land. The computational resources necessary to carry out simulations at adequate spatial resolutions for durations of climatic time scales exceed those currently available. Distributed memory massively parallel processing (MPP) computers promise to affordably scale to the computational rates required by directing large numbers of relatively inexpensive processors onto a single problem. We have developed a suite of routines designed to exploit current generation MPP architectures via domain and functional decomposition strategies. These message-passing techniques have been implemented in each of the component models and in their coupling interfaces. Production runs of the atmospheric and oceanic components performed on the National Environmental Supercomputing Center (NESC) Gray T3D are described.