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4 Namelist Variables

CSIM uses the same namelists for both the coupled and uncoupled models. This section describes the namelist variables in the namelist ice_nml, which determine time management, output frequency, model physics, filenames, and options for the mixed layer ocean model. The ice namelists for the coupled model are now located in ccsm3/scripts/$CASE/Buildnml_Prestage. Modifications to the uncoupled namelist can be made in ccsm3/models/ice/csim4/src/csim.setup.csh.

A script reads the input namelist at runtime, and writes the namelist information to the file ice_in in the directory where the model executable is located. Therefore, the namelist will be updated even if the ice model is not recompiled. The default values of ice_nml are set in ice_init.F. If they are not set in the namelist in the script, they will assume the default values listed in Tables 3-8, which list all available namelist parameters. The default values shown here are for the coupled model, which is set up for a production run. Several of the varialbes have different values for the uncoupeld, which is set up for a 10 day test run with more frequent output. Only a few of these variables are required to be set in the namelist; these values are noted in the paragraphs below. An example of the default namelist is shown in Section 4.8.1.

Table 3: Namelist Variables for Time Management
Varible Type Default Value Description


Character 'unknown_runid' Text used in netCDF global attributes
runtype Character 'unknown_runtype' Determines if BASEDATE is received from coupler or restart file
istep0 Integer 0 Step counter, number of steps taken in previous integration
npt Integer 99999 Total number of timesteps in a model run, model stops when istep exceeds npt (not used in coupled runs)
dt Double 3600. Timestep in seconds
ndyn_dt Integer 1 Times to loop through ice dynamics
ndte Integer 120 Number of subcycles per timestep in ice dynamics

The time management namelist options are shown in Table 3. runid is a character string that contains descriptive information gathered from the run script. This information is written to the global attributes in the history files. runtype is determined from the value of $RUNTYPE set in the run script. The options for this are discussed in section 6. istep0 is the number of steps taken in a previous integration and is written to the restart file.

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