The ice model produces three types of output data. A file containing ASCII text, also known as a log file, is created for each run that contains information about how the run was set up and how it progressed. A series of binary restart files necessary to continue the run are created. A series of netCDF history files containing gridded instantaneous or time-averaged output are generated during a run. These are described below.
Diagnostics from the ice model are written to an ASCII file that consists of a copy of the ice setup script file, information from the compilation, a record of the input parameters, and how hemispherically averaged, maximum and minimum values are evolving with the integration. Certain error conditions detected within the ice setup script or the ice model will also appear in this file. Upon the completion of the simulation, some timing information will appear at the bottom of the file. The file name is of the form ice.log.$LID, where $LID is a timestamp for the file ID. It resides in the $EXEROOT directory. The frequency of the diagnostics is determined by the namelist parameter diagfreq.
Restart files contain all of the initial condition information
necessary to restart a previous simulation. These files are in a
standard IEEE 64 bit binary format. A restart file is not necessary for
an initial run, but is highly recommended. The initial conditions
that are internal to the ice model produce an unrealistic ice cover
that an uncoupled ice model will correct in several years. The initial
conditions from a restart file are created from an equilibrium solution,
and provide more realistic information that is necessary if coupling
to an ocean model. The frequency at which restart files are created
is controlled by the namelist parameter dumpfreq. These restart
files contain the ice state variables and the land mask information.
The names of these files are proceeded by the namelist parameter
dump_file and, by default are written out yearly to the directory
$EXEROOT/rest.
The names of the restart files follow the CCSM2.0 Output Filename Requirements.
The form of the restart file names are as follows:
$CASE.csim.r.yyyy-mm-dd-sssss
For example, the file $CASE.csim.r.0002-01-01-00000 would be written out at the end of year 1, month 12. A file containing the name of a restart file is called a restart pointer file. This filename information allows the model simulation to continue from the correct point in time, and hence the correct restart file. These pointer files are described in the next section.
A pointer file is an ascii file named rpointer.ice that contains the path and filename of the latest restart file. The model uses this information to find a restart file from which initialization data is read. The pointer files are written to and then read from the /scripts/$CASE directory. For 'startup' runs, a pointer is created by the ice setup script using $BASEDATE to create the file name. Pointer files are also created by the ice model during execution at the frequency determined by namelist variables set in the ice model dumpfreq and the coupler rest_freq. Whenever a restart file is written, the existing restart pointer file is overwritten. The namelist variable pointer_file contains the name of the pointer file. Pointer files seldom need editing. The contents are usually maintained by the setup script and the the component model.
History files contain gridded data values written at specified times
during a model run. The netCDF file names are prepended by the character
string given by history_file in the ice_nml namelist.
This character string has been set according to CCSM2.0 Output Filename Requirements.
If history_file is not set in the namelist, the default character string
'iceh' is used. The user can specify the frequency at which the data
are written. Options are also available to record averaged or instantaneous data.
The form of the history file names are as follows:
Yearly averaged: $CASE.csim.h.yyyy.nc
Monthly averaged: $CASE.csim.h.yyyy-mm.nc
Weekly averaged: $CASE.csim.hw.yyyy-mm-dd-sssss.nc
Daily averaged: $CASE.csim.h.yyyy-mm-dd.nc
Instantaneous (histfreq = 'y', 'm', 'w' or 'd'): $CASE.csim.h.yyyy-mm-dd-sssss.nc
Instantaneous (written every dt, histfreq = 1): $CASE.csim.h.yyyy-mm-dd-sssss.nc
$CASE is set in the main setup script. All history files are written to the directory $EXEDIR/hist. Changes to the frequency and averaging will affect all output fields. The best description of the history data comes from the file itself using the netCDF command ncdump -h filename.nc. Variables containing grid information are written to every file and are listed in Table 11. In addition to the history files, a netCDF file containing a snapshot of the initial ice state is created at the start of each run. The file name is $CASE.csim.i.yyyy-mm-dd-sssss.nc and is written to $EXEDIR/init.
In computing the monthly averages for output to the history files, most arrays are zeroed out before being filled with data. These zeros are included in the monthly averages where there is no ice. For some fileds, this is not a problem, for example, ice thickness and ice area. For other fields, this will result in values that are not representative of the field when ice is present. Some of the fields affected are:
In some cases, a non-zero value is set where there is no ice.
For example, Tsfc has the freezing point averaged in, and Flwout
has 
averaged in. At lower latitudes, these values
can be erroneous.
To aid in the interpretation of the fields, a field called ice_present is written to the history file. It contains information on the fraction of the time-averaging interval when any ice was present in the grid cell during the time-averaging interval in the history file. This will give an idea of how many zeros were included in the average.
The frequency at which data are written to a history file as well as the interval over which the time average is to be performed is controlled by the namelist variable histfreq. Data averaging is invoked by the namelist variable hist_avg. The averages are constructed by accumulating the running sums of all variables in memory at each timestep. The options for both of these variables are described in Table 5. If hist_avg is true, and histfreq is set to monthly, for example, monthly averaged data is written out on the last day of the month.
To remove a field from this list, add the name of the logical variable associated with that field to the &icefields_nml namelist in the ice.setup.csh file and assign it a value of .false.. For example, to remove ice thickness and snow cover from the history file, add
&icefields_nml
f_hi = .false.
, f_hs = .false.
/
to the namelist. When all fields listed in Tables 5 and
11 are written to the history file, the file size is
39.3 MB. When the twelve fields received from the coupler are removed (see section
4.7.1), the file size is 33 MB.
By default, the history files will be written to the directory $EXEDIR/hist. Modifications to $EXEDIR can be made in the main setup script. The directory hist is appended to $EXEDIR in the ice setup script so that the ice model history files are written into a separate directory.
There is an option to write the restart and history files to NCAR's Mass Storage System (MSS). In the main setup script, set
setenv MSSDIR mss:/$MSSNAME/csm/$CASE # MSS directory path name setenv MSSRPD 365 # MSS file retention period
$MSSNAME is set to your login name in capital letters. This will write history and restart files to the MSS with a one year retention period. The password is set to your login name:
setenv MSSPWD $LOGNAME # MSS file write passwordTo avoid writing files to the MSS, set:
setenv MSSDIR null:/dev/nul # MSS directory path name setenv MSSRPD 0 # MSS file retention period
| Field | Description | Units |
| time | model time | days |
|---|---|---|
| time_bounds | boundaries for time-averaging interval | days |
| TLON | T grid center longitude | degrees |
| TLAT | T grid center latitude | degrees |
| ULON | U grid center longitude | degrees |
| ULAT | U grid center latitude | degrees |
| tmask | ocean grid mask (0=land, 1=ocean) | |
| tarea | T grid cell area | m |
| uarea | U grid cell area | m |
| dxt | T cell width through middle | m |
| dyt | T cell height through middle | m |
| dxu | U cell width through middle | m |
| dyu | U cell height through middle | m |
| HTN | T cell width North side | m |
| HTE | T cell width East side | m |
| ANGLET | angle grid makes with latitude line on T grid | radians |
| ANGLE | angle grid makes with latitude line on U grid | radians |
| ice_present | fraction of time-averaging interval that any ice is present |
| Logical Variable | Description | Units |
|---|---|---|
| f_hi | grid box mean ice thickness | m |
| f_hs | grid box mean snow thickness | m |
| f_Tsfc | snow/ice surface temperature | C |
| f_aice | ice concentration (aggregate) | % |
| f_aice1 | ice concentration (category 1) | % |
| f_aice2 | ice concentration (category 2) | % |
| f_aice3 | ice concentration (category 3) | % |
| f_aice4 | ice concentration (category 4) | % |
| f_aice5 | ice concentration (category 5) | % |
| f_u | zonal ice velocity | cm s |
| f_v | meridional ice velocity | cm s |
| f_Fswdn | downwelling solar flux | W m |
| f_Flwdn | downwelling longwave flux | W m |
| f_snow | snow fall rate received from coupler | cm day |
| f_snow_aice | snow fall rate on ice cover | cm day |
| f_rain | rain fall rate received from coupler | cm day |
| f_rain_aice | rain fall rate on ice cover | cm day |
| f_sst | sea surface temperature | C |
| f_sss | sea surface salinity | g kg |
| f_uocn | zonal ocean current | cm s |
| f_vocn | meridional ocean current | cm s |
| f_frzmlt | freeze/melt potential | W m |
| f_Fswabs | absorbed solar flux sent to coupler | W m |
| f_Fswabs_aice | absorbed solar flux in snow/ocn/ice | W m |
| f_albsni | snow/ice broad band albedo | % |
| f_Flat | latent heat flux sent to coupler | W m |
| f_Flat_aice | ice/atm latent heat flux | W m |
| f_Fsens | sensible heat flux sent to coupler | W m |
| f_Fsens_aice | ice/atm sensible heat flux | W m |
| f_Flwout | outgoing longwave flux sent to coupler | W m |
| f_Flwout_aice | ice/atm outgoing longwave flux | W m |
| f_evap | evaporative water flux sent to coupler | cm day |
| f_evap_aice | ice/atm evaporative water flux | cm day |
| f_Tref | reference temperature | C |
| f_growb | basal ice growth | cm day |
| f_frazil | frazil ice growth | cm day |
| f_snoice | snow-ice formation | cm day |
| f_meltb | basal ice melt | cm day |
| f_meltt | surface ice melt | cm day |
| f_meltl | lateral ice melt | cm day |
| f_Fresh | ice/ocn fresh water flux sent to coupler | cm day |
| f_Fresh_aice | ice/ocn fresh water flux | cm day |
| f_Fhnet | ice/ocn net heat flux sent to coupler | W m |
| f_Fhnet_aice | ice/ocn net heat flux | W m |
| f_strairx | zonal atm/ice stress | N m |
| f_strairy | meridional atm/ice stress | N m |
| f_strtltx | zonal sea surface tilt | m m |
| f_strtlty | meridional sea surface tilt | m m |
| f_strcorx | zonal coriolis stress | N m |
| f_strcory | meridional coriolis stress | N m |
| f_strocnx | zonal ocean/ice stress | N m |
| f_strocny | meridional ocean/ice stress | N m |
| f_strintx | zonal internal ice stress | N m |
| f_strinty | meridional internal ice stress | N m |
| f_strength | compressive ice strength | N m |
| f_divu | velocity divergence | % day |
| f_shear | strain rate | % day |
| f_opening | lead opening rate | % day |
| f_sig1 | normalized principal stress component | |
| f_sig2 | normalized principal stress component | |
| f_daidtt | area tendency due to thermodynamics | % day |
| f_daidtd | area tendency due to dynamics | % day |
| f_dvidtt | ice volume tendency due to thermo. | cm day |
| f_dvidtd | ice volume tendency due to dynamics | cm day |