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4.8 Output Data

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.

4.8.1 Stdout Output

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.

4.8.2 Restart Files

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 Output Filename Requirements. The form of the restart file names are as follows:


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. Restart Pointer Files

A pointer file is an ascii file named 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.

4.8.3 History Files

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 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: $
Monthly averaged: $
Weekly averaged: $
Daily averaged: $
Instantaneous (histfreq = 'y', 'm', 'w' or 'd'): $
Instantaneous (written every dt, histfreq = 1): $

$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 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 $ and is written to $EXEDIR/init. Information on Averaged Fields

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 $\sigma T_f^4$ 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. Changing Frequency and Averaging

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. Changing Content

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

    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. Changing Directory Location

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 password
To avoid writing files to the MSS, set:
setenv MSSDIR   null:/dev/nul                    # MSS directory path name
setenv MSSRPD   0                                # MSS file retention period

Table 11: Time and Grid Information Written to History File
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$^{2}$
uarea U grid cell area m$^{2}$
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$^{-1}$
f_v meridional ice velocity cm s$^{-1}$
f_Fswdn downwelling solar flux W m$^{-2}$
f_Flwdn downwelling longwave flux W m$^{-2}$
f_snow snow fall rate received from coupler cm day$^{-1}$
f_snow_aice snow fall rate on ice cover cm day$^{-1}$
f_rain rain fall rate received from coupler cm day$^{-1}$
f_rain_aice rain fall rate on ice cover cm day$^{-1}$
f_sst sea surface temperature C
f_sss sea surface salinity g kg$^{-1}$
f_uocn zonal ocean current cm s$^{-1}$
f_vocn meridional ocean current cm s$^{-1}$
f_frzmlt freeze/melt potential W m$^{-2}$
f_Fswabs absorbed solar flux sent to coupler W m$^{-2}$
f_Fswabs_aice absorbed solar flux in snow/ocn/ice W m$^{-2}$
f_albsni snow/ice broad band albedo %
f_Flat latent heat flux sent to coupler W m$^{-2}$
f_Flat_aice ice/atm latent heat flux W m$^{-2}$
f_Fsens sensible heat flux sent to coupler W m$^{-2}$
f_Fsens_aice ice/atm sensible heat flux W m$^{-2}$
f_Flwout outgoing longwave flux sent to coupler W m$^{-2}$
f_Flwout_aice ice/atm outgoing longwave flux W m$^{-2}$
f_evap evaporative water flux sent to coupler cm day$^{-1}$
f_evap_aice ice/atm evaporative water flux cm day$^{-1}$
f_Tref reference temperature C
f_growb basal ice growth cm day$^{-1}$
f_frazil frazil ice growth cm day$^{-1}$
f_snoice snow-ice formation cm day$^{-1}$
f_meltb basal ice melt cm day$^{-1}$
f_meltt surface ice melt cm day$^{-1}$
f_meltl lateral ice melt cm day$^{-1}$
f_Fresh ice/ocn fresh water flux sent to coupler cm day$^{-1}$
f_Fresh_aice ice/ocn fresh water flux cm day$^{-1}$
f_Fhnet ice/ocn net heat flux sent to coupler W m$^{-2}$
f_Fhnet_aice ice/ocn net heat flux W m$^{-2}$
f_strairx zonal atm/ice stress N m$^{-2}$
f_strairy meridional atm/ice stress N m$^{-2}$
f_strtltx zonal sea surface tilt m m$^{-1}$
f_strtlty meridional sea surface tilt m m$^{-1}$
f_strcorx zonal coriolis stress N m$^{-2}$
f_strcory meridional coriolis stress N m$^{-2}$
f_strocnx zonal ocean/ice stress N m$^{-2}$
f_strocny meridional ocean/ice stress N m$^{-2}$
f_strintx zonal internal ice stress N m$^{-2}$
f_strinty meridional internal ice stress N m$^{-2}$
f_strength compressive ice strength N m$^{-1}$
f_divu velocity divergence % day$^{-1}$
f_shear strain rate % day$^{-1}$
f_opening lead opening rate % day$^{-1}$
f_sig1 normalized principal stress component  
f_sig2 normalized principal stress component  
f_daidtt area tendency due to thermodynamics % day$^{-1}$
f_daidtd area tendency due to dynamics % day$^{-1}$
f_dvidtt ice volume tendency due to thermo. cm day$^{-1}$
f_dvidtd ice volume tendency due to dynamics cm day$^{-1}$

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Next: 5 Trouble-shooting Up: 4 Using CSIM4 Previous: 4.7 Information Sent to   Contents