A reduced grid for a parallel global ocean general circulation model |
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| Authors: | M E Wickett P B Duffy G Rodrigue |
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| Institution: | 1. Center for Applied Scientific Computing, Lawrence Livermore National Laboratory, Livermore, CA 94551, USA;2. Climate and Carbon Cycle Modeling Group, Lawrence Livermore National Laboratory, Livermore, CA 94551, USA;3. University of California at Davis, Lawrence Livermore National Laboratory, Livermore, CA 94551, USA;1. The I.Kant Baltic Federal University, A. Nevskogo Street, 14, Kaliningrad, 236041, Russia;2. WD IZMIRAN, Pobeda Avenue, 41, Kaliningrad, 236017, Russia;1. Space Research Institute, Prosp. Akad. Glushkova 40, Build. 4/1, 03187, MSP Kyiv-187, Ukraine;2. Institute of Radio Astronomy NAS of Ukraine, Chervonopraporna St. 4, 61002, Kharkiv, Ukraine;1. Department of Physics and Astronomy, Dartmouth College, Hanover, NH, USA;2. Thayer School of Engineering, Dartmouth College, Hanover, NH, USA;3. Center for Geospace Studies SRI International Menlo Park, CA, USA;4. Plasma Physics Division, Naval Research Laboratory, District of Columbia, Washington, USA;1. Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309-0216, USA;2. Applied Mathematics Department, University of Colorado, Boulder, CO 80309, USA;3. Mathematics Department, University of North Carolina, Chapel Hill, USA |
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| Abstract: | A limitation of many global climate models with explicit finite-difference numerics is the timestep restriction caused by the decrease in cell size associated with the convergence of meridians near the poles. To keep the longitudinal width of model cells as uniform as possible, we apply a “reduced” grid to a three-dimensional primitive equation ocean-climate model. With this grid the number of cells in the longitudinal direction is reduced at high latitudes. The grid consists of subgrids which interact at interfaces along their northern and southern boundaries, where the resolution changes by a factor of three. We extend the finite-difference techniques to these interfaces, focusing on the conservation required to perform long time integrations, while preserving the staggered spatial arrangement of variables and the numerics used on subgrids. The common alternative used to reduce the timestep restriction caused by the spherical grid is the filtering of high-frequency modes from the high-latitude solution. The reduced grid allows an increased timestep while eliminating the need for filtering and reduces execution time per model step by roughly 20%. We implement the reduced grid model for parallel computer architectures with two-dimensional domain decomposition and message passing, with speedup results similar to those of the original model. We present results of model runs showing small effects on the solution and sizable improvements to the execution time. |
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| Keywords: | Ocean modeling Reduced grid Spherical grid |
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