SMoorthi-emc
commented
4 years ago I don't think the cold2 step described above is true in my case as I changed the run sequence to call write_restart before prep_ocean.
On Wed, May 6, 2020 at 8:43 AM Denise Worthen notifications@github.com wrote:
The current implementation of S2S uses a 1 hour cold start followed by a restart from the cold start. For ease of description, these will be referred to as 'cold1' and 'cold2' below.
Using the NEMS mediator, the cold2 run is initializing the import state for the ocean with all zero fields. This is can be verified by running ufs-s2s-model with field dumping active. For the cold2 run, all fields in the fields_ocnimport(DATE)T00:00:00.nc are zero.
This behaviour is the result of the prep_ocn phase zero-ing the accumulation fields and accumulation counters at the end of the phase. The mediator restart files produced by the cold1 run (mediator_FBaccumAtm_restart.*, mediator_FBaccumAtmOcn_restart.nc, mediator_FBaccumIce_restart.nc) and the accumulation counts (mediator_scalars_restart.txt) all contain zeros as a result.
When the cold2 run starts, the prep_ocn at the top of the run sequence averages these accumulation fields (ie, divides by the accumulation count) to create the import fields for the ocean. Since the fields are zero as well as the counts, the import fields at time 00:00:00 are also zero.
This behaviour is replicated in the current CMEPS implmentation. However, in CMEPS, the presence of a separate accum_avg phase (where the accumulations are zero'd) and restart_write phase allows the run sequence to be adjusted to produce valid (non-zero) mediator restarts for cold1. This involves placing the med_phases_restart_write before of the med_phases_prep_ocn_accum_avg in the cmeps cold1 run sequence.
For the NEMS mediator, this same change cannot be accomplished without separating out the accumulation-related calls from prep_ocn.
A secondary issue w/rt the current cold1/cold2 sequence is that cold1 is at the end of 2 ocean coupling steps. Even if the mediator restarts contain non-zero values (ie, as can be accomplished with CMEPS), this would seemingly result in import fields for the ocean at time 00:00:00 that are in some sense forward by a coupling timestep relative to the ATM and ICE.
An alternative to the cold1/cold2 sequence is to use implement an ocean lag startup. In this case, only the cold2 sequence is implemented but a special setting is used so that the ocean model does not advance on the first coupling timestep. Instead, the ocean model clock is set back to the start time. On the second coupling timestep, the ocean model advances for 2 coupling timesteps. For example, if the coupling timestep is 30 minutes and the internal ocean timesteps are 30 mins (thermo) and 15 mins (dynamic), the model will step forward 2 thermo dynamic timesteps and 4 dynamic timesteps. All subsequent coupling timesteps for the ocean model proceed as normal.
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-- Dr. Shrinivas Moorthi Research Meteorologist Modeling and Data Assimilation Branch Environmental Modeling Center / National Centers for Environmental Prediction 5830 University Research Court - (W/NP23), College Park MD 20740 USA Tel: (301)683-3718
e-mail: Shrinivas.Moorthi@noaa.gov Phone: (301) 683-3718 Fax: (301) 683-3718
DeniseWorthen
junwang-noaa
The current implementation of S2S uses a 1 hour cold start followed by a restart from the cold start. For ease of description, these will be referred to as 'cold1' and 'cold2' below.
Using the NEMS mediator, the cold2 run is initializing the import state for the ocean with all zero fields. This is can be verified by running ufs-s2s-model with field dumping active. For the cold2 run, all fields in the fields_ocnimport(DATE)T00:00:00.nc are zero.
This behaviour is the result of the prep_ocn phase zero-ing the accumulation fields and accumulation counters at the end of the phase. The mediator restart files produced by the cold1 run (mediator_FBaccumAtm_restart.*, mediator_FBaccumAtmOcn_restart.nc, mediator_FBaccumIce_restart.nc) and the accumulation counts (mediator_scalars_restart.txt) all contain zeros as a result.
When the cold2 run starts, the prep_ocn at the top of the run sequence averages these accumulation fields (ie, divides by the accumulation count) to create the import fields for the ocean. Since the fields are zero as well as the counts, the import fields at time 00:00:00 are also zero.
This behaviour is replicated in the current CMEPS implmentation. However, in CMEPS, the presence of a separate accum_avg phase (where the accumulations are zero'd) and restart_write phase allows the run sequence to be adjusted to produce valid (non-zero) mediator restarts for cold1. This involves placing the med_phases_restart_write before of the med_phases_prep_ocn_accum_avg in the cmeps cold1 run sequence.
For the NEMS mediator, this same change cannot be accomplished without separating out the accumulation-related calls from prep_ocn.
A secondary issue w/rt the current cold1/cold2 sequence is that cold1 is at the end of 2 ocean coupling steps. Even if the mediator restarts contain non-zero values (ie, as can be accomplished with CMEPS), this would seemingly result in import fields for the ocean at time 00:00:00 that are in some sense forward by a coupling timestep relative to the ATM and ICE.
An alternative to the cold1/cold2 sequence may be to implement an ocean lag startup. In this case, only the cold2 sequence is implemented but a special setting is used so that the ocean model does not advance on the first coupling timestep. Instead, the ocean model clock is set back to the start time. On the second coupling timestep, the ocean model advances for 2 coupling timesteps. For example, if the coupling timestep is 30 minutes and the internal ocean timesteps are 30 mins (thermo) and 15 mins (dynamic), the model will step forward 2 thermo dynamic timesteps and 4 dynamic timesteps. All subsequent coupling timesteps for the ocean model proceed as normal.