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ABSTRACT
The authors evaluate the climate produced by the Community Climate SystemModel, version 4, runningwith the new spectral element atmospheric dynamical core option. The spectral element method is configured to use a cubed-sphere grid, providing quasi-uniform resolution over the sphere and increased parallel scalability and removing the need for polar filters. It uses a fourth-order accurate spatial discretization that locally conserves mass and total energy. Using the Atmosphere Model Intercomparison Project protocol, the results from the spectral element dynamical core are compared with those produced by the default finite-volume dynamical core and with observations. Even though the two dynamical cores are quite different, their simulated climates are remarkably similar. When compared with observations, both models have strengths and weaknesses but have nearly identical root-mean-square errors and the largest biases show little sensitivity to the dynamical core. The spectral element core does an excellent job reproducing the atmospheric kinetic energy spectra, including fully capturing the observed Nastrom-Gage transition when running at 0.1258 resolution.
1. Introduction
Here we report on the climate produced by a spectral element atmospheric dynamical core option within the Community Climate System Model (CCSM), version 4. The CCSM is a state-of-the-art climate model with atmosphere, ocean, land, and ice component models that exchange information through a flux coupler (Gent et al. 2011). The spectral element dynamical core comes from the High-Order Method Modeling Environment (HOMME; Dennis et al. 2005, 2012), which has been integrated into the CCSM Community Atmosphere Model (CAM). The standalone HOMME model is also used for research into other numerical methods, such as discontinuous-Galerkin (Nair 2009), adaptive mesh refinement (St-Cyr et al. 2008), and implicit time integration (Evans et al. 2010). We refer to CAM with the spectral element dynamical core as CAM-SE, CAMwith the default finite volume dynamical core (Neale et al. 2011, manuscript submitted to J. Climate) as CAM-FV, and CAM with the Eulerian global spectral method (Collins et al. 2006) option as CAM-EUL.
CAM-SE is capable of using fully unstructured grids. Support for unstructured grids and the integration of the spectral element method inCAMwas made possible by the decoupling of dynamics and physics used in CAM's process split approach (Williamson 2002), the extensive infrastructure work to support unstructured grids (Worley and Drake 2005), and the CCSM...