Changing the Number of Ice Thickness Categories

The number of ice thickness categories affects ice model input files in three places:

• $NCAT in the run script
• The source code module ice_model_size.F90
• The initial condition (restart) file in the input file directory

The number of ice thickness categories is set in ccsm3/scripts/$CASE/Buildexe/cice.buildexe.csh using the variable called $NCAT. The default value is 5 categories. $NCAT is used to determine the CPP variable setting (NCAT) in ice_model_size.F90. $RES is the resolution of the grid, 100x116 (gx3v7) and 320x384 (gx1v6) for low and medium resolution grids, respectively.

NOTE

To use one ice thickness category, the following changes will need to be made in the namelist:

  , kitd          = 0
  , kstrength     = 0

With these settings, the model will use the delta scheme instead of linear remapping and a strength parameterization based on open water area and mean ice thickness.

The information in the initial restart file is dependent on the number of ice thickness categories and the total number of layers in the ice distribution. An initial condition file exists only for the default case of 5 ice thickness categories, with four layers in each category. To create an initial condition file for a different number of categories or layers, these steps should be followed:

• Set $NCAT to the desired number of categories in
  ccsm3/scripts/$CASE/Buildexe/cice.buildexe.csh.
• Set the namelist variable dumpfreq = 'm' in
  ccsm3/scripts/$CASE/Buildnml_Prestage/cice.buildnml.csh
  to print out restart files monthly.
• Set the namelist variable restart = .false. in ccsm3/scripts/$CASE/Buildnml_Prestage/cice.buildnml.csh
  to use the initial conditions within the ice model.
• Run the model to equilibrium.
• The last restart file can be used as an initial condition file.
• Change the name of the last restart file to iced.0001-01-01.$GRID.
• Copy the file into the input data directory or directly into the the executable directory.

Note that the date printed inside the binary restart file will not be the same as 0001-01-01. For coupled runs, $BASEDATE will be the starting o date and the date inside the file will not be used.