The prescribed ice mode is a functionality feature that is needed for certain standalone CAM runs such as AMIP (Atmospheric Model Intercomparison Project) style runs. In this mode, the sea ice concentration is read from a file and replaces the prognostic concentrations computed in the model. The sea ice dynamics is turned off in this mode and the sea ice thickness is reset to 2 m in the northern hemisphere and 1 m in the southern at every timestep. The main purpose of this mode is to compute the surface fluxes, snow depth, albedos, and surface temperature over the ice by using the 1D thermodynamics in the sea ice model. This mode is not energy conserving and is mainly intended as a testbed for atmospheric sensitivity experiments.
The input netCDF file name required for this prescribed mode is set in the CCSM scripts or via the CICE build-namelist as follows:
$CODEROOT/ice/cice/bld/build-namelist -config config_cache.xml \
$presaero_type -csmdata \$DIN_LOC_ROOT -infile ccsm_namelist \
-inputdata $CASEBUILD/cice.input_data_list \
-namelist "&cice $CICE_NAMELIST_OPTS \
stream_fldfilename='$CCSMSSTFN' \
stream_domfilename='$CCSMSSTFN' \
stream_year_first=$DOCN_SSTDATA_YEAR_START \
stream_year_last=$DOCN_SSTDATA_YEAR_END \
model_year_align=$DOCN_SSTDATA_YEAR_START \
stream_fldvarname='ice_cov' /" || exit -1
The variables in upper case letters are set during the CCSM configure step and passed through to the CICE namelist. The ice concentration variable is assumed to be "ice_cov". There also needs to be a reconizable time axis like "days since 0001-01-01" in the netCDF file so that the time interpolation can be handled within the ice model.