CESM

"The Community Earth System Model (CESM) is a coupled climate model for simulating Earth's climate system. Composed of separate models simultaneously simulating the Earth's atmosphere, ocean, land, land-ice, and sea-ice, plus one central coupler component, CESM allows researchers to conduct fundamental research into the Earth's past, present, and future climate states.

The CESM system can be configured a number of different ways from both a science and technical perspective. CESM supports numerous resolutions, and component configurations. In addition, each model component has input options to configure specific model physics and parameterizations. CESM can be run on a number of different hardware platforms, and has a relatively flexible design with respect to processor layout of components. CESM also supports both an internally developed set of component interfaces and the ESMF compliant component interfaces.

CESM consists of seven geophysical models: atmosphere (atm), sea-ice (ice), land (lnd), river-runoff (rof), ocean (ocn), land-ice (glc), and ocean-wave (wav - stub only), plus a coupler (cpl) that coordinates the geophysics models time evolution and passes information between them.

During the course of a CESM run, the model components integrate forward in time, periodically stopping to exchange information with the coupler. The coupler meanwhile receives fields from the component models, computes, maps, and merges this information, then sends the fields back to the component models. The coupler brokers this sequence of communication interchanges and manages the overall time progression of the coupled system. A CESM component set is comprised of seven components: one component from each model (atm, lnd, rof, ocn, ice, glc, and wav) plus the coupler. Model components are written primarily in Fortran 90/95/2003.

The active (dynamical) components are generally fully prognostic, and they are state-of-the-art climate prediction and analysis tools. Because the active models are relatively expensive to run, data models that cycle input data are included for testing, spin-up, and model parameterization development.

The CESM components can be combined in numerous ways to carry out various scientific or software experiments. A particular mix of components, along with component-specific configuration and/or namelist settings is called a component set or "compset." CESM has a shorthand naming convention for component sets that are supported out-of-the-box.

The compset name usually has a well defined first letter followed by some characters that are indicative of the configuration setup. Each compset name has a corresponding short name. Users are not limited to the predefined component set combinations. A user may define their own component set.

See supported component sets for a complete list of supported compset options.

The grids are specified in CESM by setting an overall model resolution. Once the overall model resolution is set, components will read in appropriate grids files and the coupler will read in appropriate mapping weights files. Coupler mapping weights are always generated externally in CESM. The components will send the grid data to the coupler at initialization, and the coupler will check that the component grids are consistent with each other and with the mapping weights files.

In CESM1.2, the ocean and ice must be on the same grid, but the atmosphere and land and river runoff can each be on different grids. Each component determines its own unique grid decomposition based upon the total number of pes assigned to that component.

CESM supports several types of grids out-of-the-box including single point, finite volume, spectral, cubed sphere, displaced pole, and tripole. This page, Conservative Remapping on Spherical Grids, illustrates a number of these grid types. These grids are used internally by the models. Input datasets are usually on the same grid but in some cases, they can be interpolated from regular lon/lat grids in the data models. The finite volume and spectral grids are generally associated with atmosphere and land models but the data ocean and data ice models are also supported on those grids. The cubed sphere grid is used only by the active atmosphere model, cam. And the displaced pole and tripole grids are used by the ocean and ice models. Not every grid can be run by every component. The ocean and ice models run on either a Greenland dipole or a tripole grid.

Scripts for supported machines and userdefined machines are provided with the CESM release. Supported machines have machine specific files and settings added to the CESM scripts and are machines that should run CESM cases out-of-the-box. Machines are supported in CESM on an individual basis and are usually listed by their common site-specific name. 

The list of available machines are documented in CESM supported machines. Running create_newcase with the "-list" option will also show the list of available machines for the current local version of CESM. Supported machines have undergone the full CESM porting process. The machines available in each of these categories changes as access to machines change over time. "

http://www.cesm.ucar.edu/models/cesm1.2/

http://www.cesm.ucar.edu/