Dr Marcus Thatcher1
1CSIRO Oceans And Atmosphere, Aspendale, Australia
Regional climate models are required to simulate atmospheric processes at spatial resolutions of kilometres and temporal resolutions of less than a minute for time periods of 100+ years. Consequently, such models need to make extensive use of high performance computing facilities. This presentation describes the development of CSIRO’s Conformal Cubic Atmospheric Model (CCAM), which employs a variable resolution, global cubic grid that can be focused over a region using a Schmidt transformation. Since CCAM has no lateral boundaries, we use a scale-selective filter to assimilate global atmospheric circulation into the regional simulation. This approach allows us to scale the simulation size depending on the available computing resources, step-down to finer resolutions much faster than for limited area approaches, as well as maintain the coupling between the regional and global scales. CCAM employs MPI parallelisation, including the use of shared memory within a node, as well as an optional OpenMP parallelisation that improves the performance on Xeon Phi Knights Landing. CCAM also employs a system for reading and writing model data in parallel, based on a clustering of compressed NetCDF4 files for each node. These enhancements allow CCAM simulations to successfully scale beyond 20,000 cores and can achieve 2+ simulation years per day at 2 km resolution. The resultant convective permitting simulations show improvements in the simulated rainfall (particularly for extreme rainfall), as well as for urban areas, coastal regions and complex orography. In turn, the model has applications for urban flooding, air quality and extreme weather research.
Dr Marcus Thatcher has been developing regional climate models at CSIRO for 14 years, and currently leads the Extreme Weather and Climate Team at the CSIRO Oceans and Atmosphere Climate Science Centre.