Pioneering Ultra-High Resolution Climate Simulation
A team of researchers from universities and national laboratories has published a groundbreaking climate simulation using the Community Climate System Model Version 4 (CCSM4). A global, weather-scale atmospheric model was coupled to a global ocean model that fully resolves tropical and mid-latitude eddies. The models’ horizontal resolutions are 0.25° and 0.1°, five and ten times, respectively, those of standard atmosphere and ocean models used in coupled climate simulations. This is the first effort to simulate the full climate system at such high horizontal resolution for a multi-decade period, and it enables the explicit simulation of climatically important processes. For example, the model realistically developed intense category 4 tropical cyclones causing colder water from below the surface mixed layer to move upward, producing characteristic cold sea surface temperature wakes under and to the right of storm tracks. It also correctly depicted the deepening of and warming below the ocean mixed layer. Additionally, the model realistically reproduced the structure and pathways of explicitly resolved South Atlantic Agulhas ocean eddies, the main constituent of the upper limb of the Atlantic meridional overturning circulation. These are absent in the simulated oceans of standard climate models and are incorrectly represented in high-resolution ocean-only experiments forced with atmospheric fields derived from observations. This new prototype simulation demonstrates that sub-grid scale parameterizations are scale dependent and require improvements and adjustments to remove persistent mean climate biases before high-resolution simulations become routine.
McClean, J. L., D. C. Bader, F. O. Bryan, M. E. Maltrud, J. M. Dennis, A. A. Mirin, P. W. Jones, Y. Y. Kim, D. P. Ivanova, and M. Vertenstein. 2011. “A Prototype Two-Decade Fully-Coupled Fine-Resolution CCSM Simulation,” Ocean Modelling 39(1-2), 10-30, DOI: 10.1016/j.ocemod.2011.02.011.