Scalability of Global 0.25° Ocean Simulations Using MOM

Part 8: High Performance Computing and BigDataInternational audienceWe investigate the scalability of global 0.25° resolution ocean-sea ice simulations using the Modular Ocean Model (MOM). We focus on two major platforms, hosted at the National Computational Infrastructure (NCI) National Facility: an x86-based PRIMERGY cluster with InfiniBand interconnects, and a SPARC-based FX10 system using the Tofu interconnect. We show that such models produce efficient, scalable results on both platforms up to 960 CPUs. Speeds are notably faster on Raijin when either hyperthreading or fewer cores per node are used. We also show that the ocean submodel scales up to 1920 CPUs with negligible loss of efficiency, but the sea ice and coupler components quickly become inefficient and represent substantial bottlenecks in future scalability. Our results show that both platforms offer sufficient performance for future scientific research, and highlight to the challenges for future scalability and optimization

Improved determination of sea surface heights close to the Australian coast from ESR-2 satellite radar altimetry

The homogeneous and repeated data coverage over coastal regions from satellite radar altimetry is one important data source for oceanographic and geodetic applications. However, the sea surface heights (SSH) extracted from the altimeter data are often in error close to the coast, due in part to the complex nature of echoes returned from rapidly varying coastal topographic surfaces (both land and sea) and the generally rougher sea state. This paper presents improved SSH results derived from ERS-2 altimeter waveform data (two cycles of 35-day repeat orbit, March to May 1999) near the Australian coast using a coastal retracking system. This system was developed based upon a systematic and comprehensive analysis of return waveforms. Central to the system is the use of two retracking techniques: the iterative least squares fitting and the threshold retracking algorithms. Using the AUSGeoid98 geoid grid as a quasi-independent ground reference and comparing with a broad contaminated distance of ∼10 km obtained from a previous study before retracking, the use of the retracking system is able to reduce this contaminated distance to ∼5 km. However, improved SSH data cannot be recovered by waveform retracking less than ~5 km from the coastline due to predominant land returns in the waveform range window