A New High-Resolution Global Climate Simulation Using Community Atmosphere Model Version 5 and an Eddy-Resolving Ocean Model

Tuesday, May 13, 2014 - 07:00
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As part of the early use of the new NCAR-Wyoming supercomputer Yellowstone, a state-of-the-art high-resolution Community Earth System Model (CESM) simulation was performed. The atmospheric component was CAM5-Spectral Element at 1/4deg., and ocean component the Parallel Ocean Program (POP2) at 1/10deg. This present-day run employed 23,404 cores, costing 250K pe-hours per simulated year and made about 2 simulated years per day. One hundred years of simulation were made to give robust statistics of interannual variability and also allow for some analysis of decadal variability. Initial top-of-atmosphere radiation imbalances of just over 1Wm-2 were reduced to less than 0.5Wm-2 by the end of the run. Major results were that annual mean SST in the Equatorial Pacific and ENSO variability were well simulated compared to standard resolution models, as were Tropical and Southern Atlantic SST. In addition, the high resolution of the model enabled small-scale features of the climate system to be represented, such as air-sea interaction over ocean frontal zones, mesoscale systems generated by the Rockies, and the ocean response to strong wind jets and tropical cyclones. The Arctic and Antarctic sea ice extent and annual cycle compared well with observations in the early decades of the run but reduced significantly by the end of the run. A feature of this run, and all high resolution CAM runs, is that the precipitation in the Inter-tropical Convergence Zone is excessive. In addition the simulation exhibited substantial sub-surface warming, in common with some previous high-resolution studies. Associated single component and lower-resolution runs are used to help attribute the strengths and weaknesses of the fully coupled high resolution run.