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Restart control

As a POP calculation proceeds, restart files are produced at intervals of simulated time specified by the parameter restart_freq in namelist restart_nml. The root of the restart filename is given by the restart_outfile variable. The actual full filename will be restart_outfile.runid.suffix where suffix is a number that depends on restart_freq_opt. If this option is 'nyear', 'nmonth' or 'nday' suffix will be the calendar day in yyyymmdd. If the option is 'nstep', suffix will be the current step number. In the unlikely case that the user chooses 'nhour' or 'nsecond', suffix will be yyyymmdd.[hh,sssss] where hh and sssss denote the current hour or seconds in the current day. A common convention is to give restart files the simple root name 'd' (for dump).

Table: Restart file namelist
&restart_nml LANL
Generation of restart files
restart_freq_opt 'never' 'nyear' 'nyear', 'nmonth', 'nday', 'nhour', 'nsecond', 'nstep','never' units of time for 'restart_freq'
restart_freq 100000 100000 integer > 0 number of units between output of restart files
(CESM1 only)
N/A nstep 'nyear', 'nmonth', 'nday', 'nhour', 'nsecond', 'nstep','never' units of time for 'restart_start'
(CESM1 only)
N/A 1 integer > 0 number of units of restart_start_opt before restart files are started in a run
restart_outfile 'd' '$CASE.pop.r', auto-filled by CESM1 POP2 scripts string ≤ 256 characters root filename (with path prepended, if necessary) for restart files ('runid' and suffixes will be added in the code)
restart_fmt 'bin' 'bin' 'bin','nc' data format (binary or netCDF) for restart output files
leven_odd_on .false. .false. .true.,.false. if .true., creates alternating even/odd restart outputs which overwrite each other
even_odd_freq 100000 100000 integer > 0 frequency (in steps) for even/odd output
pressure_correction .false. .false. .true.,.false. if .true., corrects surface pressure error due to (possible) different timestep. use .false. for exact restart

In addition to these named restart files, additional restart files may be written using the even/odd convention. If leven_odd is set to .true., the model will write restart files every even_odd_freq steps. These files will be named restart_outfile.runid.even,odd where the code alternately writes to an even or odd file. Any previous file of the same name will be overwritten. This capability is particularly useful for backup in case the simulation terminates prematurely; it provides restart capability without needing to keep many named restart files present in the file system. The model writes alternately to each of two such files so that if an error occurs while writing one restart file, the other restart file will still (presumably) be all right.

Restart files contain only the minimum information required to restart the model exactly, so that the results are the same after a restart as would have been the case had no restart been done. This means that two time-levels (n-1 and n) of the prognostic variables (PT, S, U, V and H) must be saved in 64-bit precision. The restart format is governed by the restart_fmt option. Note that using netCDF for restarts on machines that do not use the IEEE binary format standard will result in restart files that are not exact due to internal conversion by the netCDF library. This will prevent exact reproducibility on such machines. Binary format is therefore highly recommended for restart files.

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