Scaling climate simulation applications on the IBM Blue Gene/L system

We examine the ability of the IBM Blue Gene/Le (BG/L) architecture to provide ultrahigh-resolution climate simulation capability. Our investigations show that it is possible to scale climate models to more than 32,000 processors on a 20-rack BG/L system using a variety of commonly employed techniques. One novel contribution is our load-balancing strategy that is based on newly developed space-filling curve partitioning algorithms. Here, we examine three models: the Parallel Ocean Program (POP), the Community Ice CodE (CICE), and the High-Order Method Modeling Environment (HOMME). The POP and CICE models are components of the next-generation Community Climate System Model (CCSM), which is based at the National Center for Atmospheric Research and is one of the leading coupled climate system models. HOMME is an experimental dynamical ‘‘core’’ (i.e., the CCSM component that calculates atmosphere dynamics) currently being evaluated within the Community Atmospheric Model, the atmospheric component of CCSM. For our scaling studies, we concentrate on 1/108 resolution simulations for CICE and POP, and 1/38 resolution for HOMME. The ability to simulate high resolutions on the massively parallel systems, which will dominate high-performance computing for the foreseeable future, is essential to the advancement of climate science.