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1. Summary
2. Preview
3. Tests
4. Review

Summary

This development is part of IMMERSE project.

a) Extend use of XIOS to read/write restart for SI3 and TOP

b) Use XIOS to read configuration data

Robustness of the functionality:

• Update one of the SETTE tests to use this read/write restart via XIOS to keep this functionality tested

Preview

Error: Failed to load processor box

No macro or processor named 'box' found

Tests

Error: Failed to load processor box

No macro or processor named 'box' found

Review

Some years ago, when we created iom.F90, the idea was to be able to use different IO libraries as transparently as possible...

This was still the case in NEMO 3.6. In that version, you could find 3 different IO libraries: nf90, ioipsl and dimg. the choice between theses libraries was done in iom_def.F90 (lines 30 to 37) https://forge.ipsl.jussieu.fr/nemo/browser/NEMO/releases/release-3.6/NEMOGCM/NEMO/OPA_SRC/IOM/iom_def.F90

The iom routines where therefore organized in a 2 stages modules.

• The first stage is iom.F90 that contains all public subroutines, prepare all the IO work but do the IO work.

All the idea was iom.F90 is the common interface for all IO libraries. https://forge.ipsl.jussieu.fr/nemo/browser/NEMO/releases/release-3.4/NEMOGCM/NEMO/OPA_SRC/IOM/iom.F90

• The second stage is called by iom.F90 subroutines and consist in 3 different IO routines

https://forge.ipsl.jussieu.fr/nemo/browser/NEMO/releases/release-3.6/NEMOGCM/NEMO/OPA_SRC/IOM/iom_nf90.F90 https://forge.ipsl.jussieu.fr/nemo/browser/NEMO/releases/release-3.6/NEMOGCM/NEMO/OPA_SRC/IOM/iom_ioipsl.F90 https://forge.ipsl.jussieu.fr/nemo/browser/NEMO/releases/release-3.6/NEMOGCM/NEMO/OPA_SRC/IOM/iom_rstdimg.F90

The fork toward the different libraries was done in iom.F90, with case statements. See for example iom_rstput interface in this version of iom.F90 (from line 1046)

We think that the use of xios to read/write restarts should try follow this same logic.

-> reintroduce case in iom to be able to switch from native netcdf (nf90) to xios library
-> Ideally, the use of xios for restarts should not be visible somewhere else, no?
-> once the interface is done it is directly usable for all restarts

We know that the reality is more complex that this simple description and developing such interface wont be so easy… We think a good stating point is to follow what is done for nf90 restarts that are performed in 2 steps:

1) 1 time step before restart: define all the restart file using a specific context (so xios_context_initialize and xios_close_context_definition cand be done anytime)
2) fill the file when is it restart time step.

Sebastien and Clement