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1 Introduction

The Community Climate System Model (CCSM) is a coupled climate model for simulating the earths climate system. Composed of four separate model components simultaneously simulating the earths atmosphere, ocean, land surface and sea-ice, and one central coupler component, the CCSM allows researchers to conduct fundamental research into the earths past, present and future climate states.

Both high- and low-resolution versions of the CCSM have been developed. The high-resolution version is best suited for simulating near-past, present-day and future climate scenarios, while the low-resolution option is commonly used for paleoclimate research and debugging runs. The May 17 2002 CCSM2.0 release specifically supports the high-resolution (T42 atmosphere/land and gx1v2 ocean/sea-ice) for IBM SPII and SGI Origin 2000 platforms.

The CCSM project is a cooperative effort by the US climate researchers. Primarily supported by the National Science Foundation (NSF) and centered at the National Center for Atmospheric Research (NCAR) in Boulder Colorado, the CCSM project enjoys close collaborations with the US Department of Energy and National Air and Space Administration. Scientific development of the CCSM is guided by the CCSM working groups, which meet twice a year. The main CCSM workshop is held each year in June to showcase results from the various working groups and coordinate future CCSM developments among the working groups. More information on the CCSM project, such as the management structure, the scientific working groups, downloadable source code and online archives of data from previous CCSM experiments, can be found on the CCSM website .

1.1 The CCSM component models

The CCSM consists of four dynamical geophysical models linked by a central coupler. The components are:

cpl The Coupler
atm The Atmospheric component
ocn The Ocean component
ice The Sea-ice component
lnd The Land-surface component

During the course of a CCSM integration, each of the four component models integrate forward in time simultaneously, periodically stopping to exchange information with the coupler. The coupler receives fields from the component models, computes, maps and merges this information and sends the fields back to the other component models. By brokering this sequence of communication interchanges, the coupler manages the overall time progression of the coupled model.

1.2 The component models: CAM, POP, CSIM, CLM

Both full dynamical model and data-cycling versions are supplied for each model component. The dynamical models are the complete, fully interactive climate system component models, such as the POP ocean model or the CAM atmosphere general circulation model. The data-cycling models are small, simple codes which simply read static datasets and supply that data to the coupler. The fast and inexpensive data-cycling components can be easily used in place of any of the expensive dynamical models for testing purposes. The CCSM are written in FORTRAN 90 to optimize performance.

The dynamical atmosphere model is the Community Atmosphere Model (CAM), a global atmospheric general circulation model developed from the NCAR CCM3. The primary horizontal resolution is 128 longitude by 64 latitude points (T42) with 26 vertical levels. The hybrid vertical coordinate merges a terrain-following sigma coordinate at the bottom surface with a pressure-level coordinate at the top of the model. More information on the CAM can be found at

The ocean model is an extension of the Parallel Ocean Program (POP) from Los Alamos National Laboratory (LANL). POP grids in CCSM are displaced pole (Greenland Pole) grids at approximately 1-degree (gx1v3) and 3-degree (gx3) horizontal resolutions. The POP web page can be found at

The sea-ice component of CCSM is the Community Sea-Ice Model (CSIM4). The sea-ice component includes the elastic-viscous-plastic (EVP) dynamics scheme, an ice thickness distribution, energy-conserving thermodynamics, a slab ocean mixed layer model, and the ability to run using prescribed ice concentrations. It is supported on high- and low-resolution Greenland Pole grids, which are identical to those used by the POP ocean model. The CSIM web page is

The Community Land Model is the land model for both the CCSM and the un-coupled version of CAM. It is a collaborative project between scientists in the Terrestrial Sciences Section of the Climate and Global Dynamics Division (CGD) at NCAR and the CCSM Land Model Working Group. Other principal working groups that also contribute to the CLM are Biogeochemistry, Paleoclimate, and Climate Change and Assessment. The CLM web page is

The CCSM components are joined by the Coupler. The Coupler controls the rate of model execution and the interchange of all data between the different components. The coupler home page is at

The dynamical models can consume substantial amounts of memory and CPU time while producing large volumes output data. The data-cycling versions of the components simply read existing datasets that were previously written by the dynamical models and pass these data to the coupler. These data-cycling components are very inexpensive to run and produce no output data. For these reasons, the data components are used for both test runs and certain types of model simulation runs. Information on the data models can be found under the CCSM2.0 release page:

1.3 Supported resolutions, configurations and platforms

The current release has been validated on the IBM power3 and SGI O2K class of machines. In addition, the current release runs successfully on Compaq hardware, although it currently does not restart exactly. This will be fixed shortly.

A long control simulation has been carried out with the fully active CCSM configuration at T42 atmosphere and land resolution and gx1v3 ocean and ice resolution. This configuration is scientifically validated and model output will be released.

In addition, a number of additional configurations and resolutions are available with this release. The release version contains three different atmosphere components (atm, datm, latm), two different land models (lnd, dlnd), two different ocean models (ocn, docn), two different sea-ice models (ice, dice), and a single coupler (cpl). These components can be mixed and matched to carry out various climate experiments. NCAR does not guarantee the scientific validity of any configuration except the fully active configuration for which a long control was carried out. For the atmosphere and land components, both T42 and T31 resolutions are available. For the ocean and ice components, both gx1v3 and gx3 resolutions are available. For the latm component, a T62 resolution is supported. In general, there is a shorthand naming convention for configuration setups. These are

In summary, this release contains the following configurations:




and the following table summarizes the tested configurations (only the T42_gx1v3 / B case has been scientifically validated):

             A  B  C  D  F  G  H  I  K  M
T42_gx1v3    *  *  *  *  *     *  *  *
T31_gx3         *                    
T62_gx1v3                   *           *

 * indicates tested configuration

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