High resolution and variable resolution capabilities of the Community Atmosphere Model (CAM) with a spectral finite element dynamical core
I will describe our work developing CAM-SE, a highly scalable version of the Community Atmosphere Model (CAM) running with the spectral element dynamical core from NCAR's High-Order Method Modeling Environment. For global 1/4 and 1/8 degree resolutions CAM-SE runs efficiently on hundreds of thousands of processors on modern supercomputers and obtains excellent simulation throughput. CAM-SE also supports fully unstructured conforming quadrilateral grids. I will show results using a variable resolution grid with 1/8 degree resolution over the central U.S., transitioning to 1 degree over most of the globe. We hope that the variable resolution can provide a 10-100 times more efficient way to calibrate and evaluate the CAM 1/8 degree configuration.
CAM-SE uses quadrilateral elements and tensor-product Gauss-Lobatto quadrature. Its fundamental computational kernels look like dense matrix-vector products which map well to upcoming computer architectures. It solves the hydrostatic equations with a spectral element horizontal descritization and the hybrid coordinate Simmons & Burridge (1981) vertical discretization. It uses a mimetic formulation of spectral elements which preserves the adjoint and annihilator properties of the divergence, gradient and curl operations. These mimetic properties result in local conservation (to machine precision) of mass, tracer mass and (2D) potential vorticity, and semi-discrete conservation (exact with exact time-discretization) of total energy. Hyper-viscsoity is used for all numerical dissipation.