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1 Introduction

1.1 CCSM overview

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

The CCSM project is a cooperative effort among 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 the 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

Help is available via email at

Additional CCSM3 documentation, including component user and science guides is available at the CCSM3 website at: .

1.2 CCSM model components

The CCSM consists of four dynamical geophysical models linked by a central coupler. Each model contains ``active'', ``data'', or ``dead'' component versions allowing for a variety of ``plug and play'' combinations. The active dynamical models consume substantial amounts of memory and CPU time and produce large volumes of output data. The data-cycling models (data models), on the other hand, are small, simple models which simply read existing datasets that were previously written by the dynamical models and pass the resulting data to the coupler. These data-cycling components are very inexpensive to run and produce no output data. For these reasons they are used for both test runs and certain types of model simulation runs. Currently, the data models run only in serial mode on a single processor. The dead models are simple codes that facilitate system testing. They generate unrealistic forcing data internally, require no input data and can be run on multiple processors to simulate the software behavior of the fully active system.

The CCSM components can be summarized as follows:

Table 1: CCSM3 Model Components
Model Model Name Component Component Type
    Name Version  
atmosphere atm cam cam3 active
atmosphere atm datm datm6 data
atmosphere atm latm latm6 data
atmosphere atm xatm dead dead
land lnd clm clm3 active
land lnd dlnd dlnd6 data
land lnd xlnd dead dead
ocean ocn pop ccsm_pop_1_4 active
ocean ocn docn docn6 data
ocean ocn xocn dead dead
sea-ice ice csim csim5 active
sea-ice ice dice dice6 data
sea-ice ice xice dead dead
coupler cpl cpl cpl6 active

During the course of a CCSM run, the four non-coupler components simultaneously 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 and sends the fields back to the component models. By brokering this sequence of communication interchanges, the coupler manages the overall time progression of the coupled system. Each model has a full dynamical component, a data-cycling component (atm actually has 2 data cycling components), and a dead-version component. A CCSM component set is comprised of five model components - one component from each model. All model components are written primarily in FORTRAN 90.

1.2.1 Active atmospheric component

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 longitudinal by 64 latitudinal 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.

1.2.2 Active land component

The Community Land Model, CLM, is the result of 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 land model grid is identical to the atmosphere model grid.

1.2.3 Active ocean component

The ocean model is an extension of the Parallel Ocean Program (POP) Version 1.4.3 from Los Alamos National Laboratory (LANL). POP grids in CCSM are displaced-pole grids (centered at Greenland) at approximately 1-degree (gx1v3) and 3.6-degree (gx3v5) horizontal resolutions with 40 and 25 vertical levels, respectively. POP does not support a slab ocean model (i.e. SOM) as is supported by the stand-alone atmosphere model (CAM).

1.2.4 Active sea-ice component

The sea-ice component of CCSM is the Community Sea-Ice Model (CSIM). 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, identical to those used by the POP ocean model.

1.3 Paleo-climate related issues

CCSM3.0 requires modifications to run paleo-climate simulations. Tools were generated to facilitate these types of modifications in CCSM2.0. These tools have not yet been ported to CCSM3.0. In addition, CCSM3.0 has new physical parameterizations (specifically in CAM) that are relevant to only modern day climates. Users who desire to use CCSM3.0 for paleo-climate simulations are encouraged to first contact Zav Kothavala (

1.3.1 Component Sets

The release version contains the following components:

These components can be combined in numerous ways to carry out various science or software experiments. A particular mix of components is referred to as a component set. In general, there is a shorthand naming convention for component sets that are officially supported and which may be used ``out of the box''. Users are not strictly limited to the following component set combinations. A user may define their own component set for a run by manually editing the env_conf file (see section 4.6).

 A = datm,dlnd,docn,dice,cpl
 B =  cam, clm, pop,csim,cpl
 C = datm,dlnd, pop,dice,cpl
 D = datm,dlnd,docn,csim,cpl
 G = latm,dlnd, pop,csim,cpl
 H =  cam,dlnd,docn,dice,cpl
 I = datm, clm,docn,dice,cpl
 K =  cam, clm,docn,dice,cpl
 L = latm,dlnd, pop,dice,cpl
 M = latm,dlnd,docn,csim (mixed layer ocean mode),cpl
 O = latm,dlnd,docn,dice,cpl
 X = xatm,xlnd,xocn,xice,cpl

1.3.2 Component Resolutions

The following component resolutions are supported in CCSM3.0:

The CCSM3 ocean and ice models must share a common horizontal grid. Presently, two different resolutions are officially supported in CCSM: gx1v3 and gx3v5. In both of these grids, the North Pole has been displaced into Greenland. gx1v3 is finer than gx3v5, and has a longitudinal resolution of approximately one degree. Its latitudinal resolution is variable, with finer resolution, approximately 0.3 degrees, near the equator. gx3v5 is the coarser grid, with a longitudinal resolution of 3.6 degrees. Its latitudinal resolution is variable, with finer resolution, approximately 0.9 degrees, near the equator.

In the ocean model, there are 40 vertical levels associated with the gx1v3 resolution, with level thickness monotonically increasing from approximately 10 to 250 meters. It is the combination of the horizontal grid, horizontal land mask, vertical grid, and bottom topography that collectively define the ``gx1v3'' resolution.

There are 25 vertical ocean-model levels associated with the gx3v5 resolution, with level thickness monotonically increasing from approximately 12 to 450 meters. The combination of the horizontal grid, horizontal land mask, vertical grid, and bottom topography is referred to collectively as the ``gx3v5'' resolution.

The CCSM3 atmosphere and land models must also share a common horizontal grid. Currently, four different resolutions are officially supported: T85, T42, T31 and 2x2.5. The first three correspond to gaussian grids, whereas the latter corresponds to a type C grid. All the grids are run in CAM with 26 vertical levels.

The above resolutions are supported ``out of the box'' in the following combinations:

Finally, only certain combinations of components sets and model resolutions are supported by the scripts. The following table summarizes the allowed CCSM3.0 resolution-component set combinations.

Table 2: CCSM3.0 resolution-component set combinations

        Comp-Set     Components              Resolution  Tested	     
           A    datm,dlnd,docn,dice,cpl       T42_gx1v3   Yes	     
           A    datm,dlnd,docn,dice,cpl       T42_gx3v5   No	     
           A    datm,dlnd,docn,dice,cpl       T31_gx3v5   No	     
           B     cam, clm, pop,csim,cpl       T85_gx1v3   Yes
           B     cam, clm, pop,csim,cpl       T42_gx1v3   Yes
           B     cam, clm, pop,csim,cpl       T42_gx3v5   No 
           B     cam, clm, pop,csim,cpl       T31_gx3v5   Yes
           B     cam, clm, pop,csim,cpl     2x2.5_gx1v3   Yes
           C    datm,dlnd, pop,dice,cpl       T42_gx1v3   No
           C    datm,dlnd, pop,dice,cpl       T42_gx3v5   No
           C    datm,dlnd, pop,dice,cpl       T31_gx3v5   No
           D    datm,dlnd,docn,csim,cpl       T42_gx1v3   No
           D    datm,dlnd,docn,csim,cpl       T42_gx3v5   No
           D    datm,dlnd,docn,csim,cpl       T31_gx3v5   No
           G    latm,dlnd, pop,csim,cpl       T62_gx1v3   Yes	     
           G    latm,dlnd, pop,csim,cpl       T62_gx3v5   Yes	     
           H     cam,dlnd,docn,dice,cpl	      T85_gx1v3   No
           H     cam,dlnd,docn,dice,cpl	      T42_gx1v3   No
           H     cam,dlnd,docn,dice,cpl	      T42_gx3v5   No
           H     cam,dlnd,docn,dice,cpl	      T31_gx3v5   No
           H     cam,dlnd,docn,dice,cpl	    2x2.5_gx1v3   No
           I    datm, clm,docn,dice,cpl	      T42_gx1v3   No		     
           I    datm, clm,docn,dice,cpl	      T42_gx3v5   No		     
           I    datm, clm,docn,dice,cpl	      T31_gx3v5   No		     
           K     cam, clm,docn,dice,cpl	      T85_gx1v3   No 	     		     
           K     cam, clm,docn,dice,cpl	      T42_gx1v3   No  	     		     
           K     cam, clm,docn,dice,cpl	      T42_gx3v5   No	     		     
           K     cam, clm,docn,dice,cpl	      T31_gx3v5   No  	     		     
           K     cam, clm,docn,dice,cpl	    2x2.5_gx1v3   No
           K     cam, clm,docn,dice,cpl			     
           L    latm,dlnd, pop,dice,cpl       T62_gx1v3   Yes			     
           L    latm,dlnd, pop,dice,cpl	      T62_gx3v5   Yes		     
           M    latm,dlnd,docn,csim(MLO*),cpl T62_gx1v3   Yes			     
           M    latm,dlnd,docn,csim(MLO*),cpl T62_gx3v5   No
           O    latm,dlnd,docn,dice,cpl       T62_gx1v3   No
           O    latm,dlnd,docn,dice,cpl	      T62_gx3v5   No
           X    xatm,xlnd,xocn,xice,cpl       T85_gx1v3   No	     
           X    xatm,xlnd,xocn,xice,cpl       T42_gx1v3   No	     
           X    xatm,xlnd,xocn,xice,cpl       T42_gx3v5   No	     
           X    xatm,xlnd,xocn,xice,cpl       T31_gx3v5   No	     
           X    xatm,xlnd,xocn,xice,cpl     2x2.5_gx1v3   No	     
           X    xatm,xlnd,xocn,xice,cpl       T62_gx1v3   Yes	     
           X    xatm,xlnd,xocn,xice,cpl       T62_gx3v5   Yes	     

        * MLO indicate Mixed Layer Ocean Mode

1.4 Upgrades from previous releases

The CCSM3.0 release contains significant upgrades from previous releases. The climate simulation capability has been improved and the model runs at new resolutions and on new grids. In addition, new platforms have been added and the CCSM scripts have been completely rewritten to be more easily used by both novice and expert users. They also make it much simpler for the user to add their own platforms to the script by separating out machine-specific settings. This provides the user with the ability to easily tailor the scripts for their particular machine environment.

High-, medium- and low-resolution versions of the CCSM components are supported in CCSM3.0. The higher resolution version (T85_gx1v3) is best suited for simulating near-past, present-day and future climate scenarios, while the lower resolution option (T31_gx3v5) is commonly used for paleoclimate research.

A much larger variety of platforms is now supported. Whereas CCSM2 was only supported on scalar architectures, CCSM3.0 is supported and runs effectively on both scalar and vector platforms. In addition, CCSM3.0 is now supported on several Linux clusters.

CCSM3.0 also includes the introduction of dead models which provide the ability to easily test the CCSM3 software infrastructure.

1.5 Climate validations

Although CCSM3.0 can be run ``out of the box'' for a variety or resolutions and component sets, it must be stressed that not all combinations of component sets, resolution and machines have been tested or have undergone full climate validations.

Long control runs have been carried out on the IBM systems at NCAR with the fully active CCSM components (component set B below) at three different resolutions: T85_gx1v3, T42_gx1v3, T31_gx3v5. As a result, NCAR will only guarantee the scientific validity of runs using the above component set and resolutions on the IBM. No other combination of resolutions, component sets or machines are considered scientifically validated.

Model output from these long control runs will accompany the release. Users should be able to duplicate the climate of the released control runs using the CCSM3.0 source code on the NCAR IBM systems. Bit-for-bit duplication cannot be ensured due to post-release compiler changes that may occur. Users should carry out their own validations on any platform prior to doing scientific runs or scientific analysis and documentation.

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