Parallelizing a High Resolution Operational Ocean Model

The Swedish Meterological and Hydrological Institute (SMHI) makes daily forecasts of temperature, salinity, water level, and ice conditions in the Baltic Sea. These forecasts are based on data from a High Resolution Operational Model for the Baltic (HIROMB). This application has been parallelized and ported from a CRAY C90 to a CRAY T3E. Our parallelization strategy is based on a subdivision of the computational grid into a set of smaller rectangular grid blocks which are distributed onto the parallel processors. The model will run with three grid resolutions, where the coarser grids produce boundary values for the ner. The linear equation systems for water level and ice dynamics are solved with a distributed multi-frontal solver. We nd that the production of HIROMB forecasts can successfully be moved from C90 to T3E while increasing resolution from 3 to 1 nautical mile. Though 5 processors of the T3E are 2.2 times faster than a C90 vector processor, speedup and load balance could be further improved.