Seminars

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 the High-Order Method Modeling Environment (HOMME). 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. We are using this capability to perform simulations with 1/8 degree resolution over the central U.S., transitioning to 1 degree over most of the globe. This is a numerically efficient way to study the resolution sensitivity of CAM's many subgrid parameterizations and is now being used in several projects developing "scale aware" parameterizations.  

CAM-­SE uses quadrilateral elements and tensor-­product Gauss-­Lobattoquadrature. 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-viscsoityis used for all numerical dissipation.