What's a model restart?
A restart allows the model to continue a forecast with a succession of individual runs, each one starting where the other one left off. e.g. running an extended forecast of 100 days with 5 separate runs of 20 days each. A restart will always be exact, that is, the results of the restarted forecast should always match a single run of the model for the same total length (assuming all settings remain the same).
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n.b. the restarted run must always have the same parallel decomposition (TASKS x THREADS)
How to configure restarts
The namelist NAMRES controls model restarts (see ifs/namelist/namres.h). The most useful variables in this namelist are: NFRRES and NRESTS.
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The first value for NRESTS must indicate the number of valid restarts required and be of the same sign as the rest of the entries. See examples below.
Examples
| Code Block | ||||
|---|---|---|---|---|
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&NAMRES
NFRRES=-24,
/ |
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The value of NFRRES is normally set to 1 if using NRESTS. If NFRRES is set > 1 it is multiplied to the restart time. In the above example, if NFRRES was changed to 2, the model would still give 3 restart files but this time at 96hrs, 240hrs and 384hrs.
Files created
Restart files
The output files all begin with the name 'srf'. One file will be created per MPI task. The files are written as unformatted binary (not GRIB) in order to preserve precision.
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By default, old restart files are not deleted which might be a concern at high resolutions. One restart file at T1279 is approx 500Mb when using 128 MPI tasks, giving a total restart file requirement of approx 64Gb per output instance. Changing this behaviour is not possible via NAMRES. Instead, edit the file ifs/setup/sures.F90 and change the default value of LDELRES to TRUE. This will be changed for a future release of OpenIFS.
Restart namelist
A file, 'rcf' will be created by the model at each timestep when the restart files are written. This file contains the NAMELIST NAMRCF that informs the model what it needs to know to restart the model.
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Conversely, if you don't want to run a restart but want to repeat the run, do delete the rcf file (and the srf files). If you don't the model will attempt to continue the run according to the namelist in the rcf file.
Model code
The key subroutines for restarts are:
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