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4.4 Model Physics

The namelist variables for the ice model physics are listed in Table 6. restart is almost always true since most run types begin by reading in a binary restart file. See section 6 for a description of the run types and about using restart files and internally generated model data as initial conditions. kcolumn is a flag that will run the model as a single column if is set to 1. This option has not been thoroughly tested and is not supported.

kitd determines the scheme used to redistribute sea ice within the ice thickness distribution (ITD) as the ice grows and melts. The linear remapping scheme is the default and approximates the thickness distribution in each category as a linear function ((Lipscomb(2001))). The delta function method represents g(h) in each category as a delta function ((Bitz et al.(2001))). This method can leave some categories mostly empty at any given time and cause jumps in the properties of g(h).

kdyn determines the ice dynamics used in the model. The default is the elastic-viscous-plastic (EVP) dynamics (Hunke and Dukowicz(1997)). If kdyn is set to 0, the ice dynamics is inactive. In this case, ice velocities are not computed and ice is not transported. Since the initial ice velocities are read in from the restart file, the maximum and minimum velocities written to the log file will be non-zero in this case, but they are not used in any calculations.

The value of kstrength determines which formulation is used to calculate the strength of the pack ice. The (Hibler(1979)) calculation depends on mean ice thickness and open water fraction. The calculation of (Rothrock(1975)) is based on energetics and should not be used if the ice that participates in ridging is not well resolved.

evp_damping is used to control the damping of elastic waves in the ice dynamics. It is typically set to .true. for high-resolution simulations where the elastic waves are not sufficiently damped out in a small timestep without a significant amount of subcycling. This procedure works by reducing the effective ice strength that's used by the dynamics and is not a supported option.

The value of snow_into_ocean determines what happens to the snow on ice that is ridged. The default value is .true., so the snow cover on ice that undergoes ridging is put into the ocean. If this variable is .false., the snow on ice undergoing ridging remains on the ice.

advection determines the horizontal transport scheme used. The default scheme is the incremental remapping method ((Lipscomb and Hunke(2004))). This method is less diffusive and is computationally efficient for large numbers of categories or tracers. The MPDATA scheme is also available. It is second order accurate, and more computationally expensive than remapping. The upwind scheme is only first order accurate.

For coupled runs, both supported grids (gx3v5 and gx1v3) are 'displaced_pole'. The 'rectangular' option for a regular grid with constant latitude and longitude spacing is not supported.

The values of the snow and ice albedos are now set in the namelist. The ice albedos are those for ice thicker than ahmax, which is currently set at 0.5 m. This thickness is a parameter that can be changed in ice_albedo.F. The snow albedos are for cold snow. no_ice_ic provides an option to initialize the ice model with no ice cover.

Table 7: Namelist Variables for File Names
Varible Type Default Value Description
grid_file Character 'data.domain.grid' Input filename containing grid information.
kmt_file Character 'data.domain.kmt' Input filename containing land mask information.
pointer_file Character 'ice.restart_file' Pointer file that contains the name of the restart file.
incond_dir Character ' ' Directory where netCDF initial condition file is output.
restart_dir Character ' ' Directory where restart files are output.
history_dir Character ' ' Directory where history files are output.
incond_file Character 'incond' Root name of netCDF output initial condition file.
dump_file Character 'iced' Prefix for output file containing restart information.
history_file Character 'iceh' Root name of history files.

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Next: 4.5 File Names Up: 4 Namelist Variables Previous: 4.3 Writing Output   Contents