REPORT OF THE WORKING GROUP MEETING (January 30, 2014)

Participants : Rachid Benshila, Daley Calvert, Julien Calandreau, Jérome Chanut, Laurent Debreu, Christian Ethe, Rachel Furner, Claire Levy, Gurvan Madec, Sébastien Masson

1) Discuss the update of the 3.6 version

History :

• ​AGRIF version (and corresponding NEMO subroutines) has been updated by Julien Calandreau (INRIA) and Laurent Debreu

• Jérome Chanut has made a lot of improvements and bug fixes in his Gilbraltar Strait configuration

• Same for Sébastien Masson in the Pulsation ANR project

• Other developments in LIM, PISCES

Bugs that have been identified and corrected since version 3.4 :

• zwork array (J. Chanut): a global array « zwork » was defined in the libmpp module and (due to a bug in the ​AGRIF converter) this led to several problems and in particular the update step was not performed …

• Diffusion coefficients in the corners of the sponge layern were wrong (J. Chanut)

• Scale factors were not correctly computed in the ghost cells (where it is assumed that we are in full steps) (J. Chanut)

-> same problem for OBC

• TKE (S. Masson): near the boundaries, spatial averaging operations led to wrong Kz in the first cell inside the high resolution domain. Extrapolation is possible but does not fulfill the requirement that with, a mesh refinement factor of 1, the obtained solution of the HR grid is identical to a solution computed without a zoom. S. Masson has implemented exchanges of TKE between coarse and fine grids.

-> Same problem for GLS and for OBC

• Asselin Filter (J. Chanut) : when updating the « after » (n+1) fields, the corresponding corrections of the « now » fields were not done.

• arrays out of bound in procnames in MPI (wrong declarations of ​AGRIF profiles in agrif_declare_variables: jpi, jpj have been replaced by ncli,nlcj)

Bugs / Problems that have been identified

· The bathymetry connection check is not complete (add a check that the coarse grid bathy have been correctly updated)

· Reproducibility is not guaranteed (due to MPI problem) when ln_spc_dyn is set to true in namelist (which means that we take 0 as special value for dynamics in interpolations/updates).

· Recursive updates. When more than 1 zoom level are set, the update should start from the highest resolution grid and go recursively to the root grid. Laurent implemented changes that makes this possible.

• Use of ​AGRIF for degradation online (problème de north pole, coarsening)

• Average operators with update values

• High order operators with coastlines

• BDY problem have been solved

Improvements

• ​AGRIF and time splitting (OK for version 3.6, end of the year, Jérome)
  • only consider forward integration of the forcing mode permits to ensure volume conservation
  • without update of the parent grid right hand side
• Performance of parallel runs
  • allows the distribution of the processors among the fine grids

Rachid Benshila is ready be in charge of the merge

2) What are the known open problems ? (not to be solved for 3.6)

• Number of ghost cells (L. Debreu)
  • Antartic problem (periodicity): require only one ghost cell instead of 2
  • Number of required ghost cells for high order advection schemes may be larger than 2
  • -> Remove hardcoding of the number of ghost cells, do the required modifications to the ​AGRIF “profiles” (Laurent)

• North fold problem

• Timings for each grid

3) What are the main next developments?

• Coupling between grids at the level of the barotropic mode (in time splitting version) (Jérome)
  • requires some modification in the organization of the step routine of NEMO

• Vertical grid refinement (Laurent)
• Online coarsening for tracers using ​AGRIF (L. Debreu, G. Madec)
• ​AGRIF with variable volume

4) Nesting tools:

Two stages:

a) for 3.6 version

• agree on all the points: bathymetry smoothing, update of coarse grids (take the maximum as default)

• Incorporate corrections done by Jean Marc

• The nesting tools are only essential for the creation of bathymetry:
  • forcings can be interpolated on the fly
  • -> Do a list available tools for 3D interpolation (initialization / restart fields)
  • For 3.6 keep the 3D fields interpolation in nesting tools

b) next version

• The definition of vertical coordinates should be done outside NEMO

• Nesting tools for the s coordinates

5) Documentation:

• Update of the nesting tools 3.6 documentation

• Update of the users guide: describes what is possible or not with ​AGRIF.

• Documentation for nesting in NEMO/​AGRIF: starts from the notes of Sebastien, then circulate the powerpoint

• GMD paper

6) Standard configuration and sanity tests

The standard configuration should:

• Include more than one level of embedding (test of the recursive update starting from the finer resolution grid(s))

• Uses time splitting

• Include a zoom in a sea ice area (Labrador Sea, LIM3)

• Include a zoom with PISCES

• Zoom in Perou Chili

Sanitiy tests

• Zoom with a mesh refinement of 1

• Test constancy preservation for tracers

Longer visions of having ​AGRIF zoom in AMM

S coordinates zoom inside a z coordinate parent grid.