= ''Name and subject of the action''

Last edition: '''[[Wikinfo(changed_ts)]]''' by '''[[Wikinfo(changed_by)]]'''

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== Summary #summary

||= '''Action'''       =|| AGRIF-05_jchanut_vert_coord_interp             ||
||= '''PI(S)'''        =|| Jérôme Chanut, James Harle                     ||
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'''Digest'''

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{{{#!td

Developments to nesting (IMMERSE T3.2: Lead Mercator-Ocean ,   Participants:   NERC )
The two-way nesting AGRIF capability will be developed in year 1 to allow each inner nest to use a different vertical coordinate from the model in which it is nested. 

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|-
||= '''Dependencies''' =||                                                                            ||
||= '''Target'''       =||                                                                            ||
||= '''Trac Ticket'''  =|| #2222                                                                      ||
||= '''SVN branch'''   =|| [source:/NEMO/branches/2019/dev_r11233_AGRIF-05_jchanut_vert_coord_interp] ||
||= '''Previewer(s)''' =|| Rachid Benshila                                                            ||
||= '''Reviewer(s)'''  =|| TBD                                                                        ||
||= '''Link'''         =|| [[ExtractUrl(.)]] 

== Development plan

 1. Simplify existing AGRIF code (open boundary routines only - update part unchanged): [[BR]]
 source:/NEMO/branches/2019/dev_r10973_AGRIF-01_jchanut_small_jpi_jpj/ [[BR]]
 ticket:2199 [[BR]]
 wiki:2019WP/AGRIF-01_jchanut_small_jpi_jpj 
  - Remove any non purely local update near boundaries, e.g. 3 points velocity filtering near boundaries / upstream advection for tracers for outflows. Target is "specified" open boundaries (this does change the results).
  - Ensure that NEMO-AGRIF handles small (~3x3 points) local mpp sub-domains (the preceding task should enable that more easily - current status is local sub-domains greater than ~10x10 points, e.g. greater than sponge layer width). 
 2. Check current interpolation of vertical nesting (key_vertical).
  - Ensure that with identical vertical grids, results are bit-for-bit identical (VORTEX).
  - Optimization ? Consider existing PPM interpolation at this stage.
 3. Volume connection with different coordinate systems. [[BR]] 
  - Existing code supports only nesting a z-coord model into a z-coord model. Should be more general. 
  - Nesting tools have to be updated to allow this. Grenoble's version of Nesting tools (available on NEMO trac) should be the starting point.
 4. Design test cases (beside VORTEX)
  - One should check how boundary layers react at the domains boundaries (top and bottom): extrapolation methods will matter here.     
  - Overflow test case (3D). Internal Wave packet crossing the boundary. 2D upwelling. Others ?
 5. Implement other remapping methods. 
  - Could be borrowed from D. Engwirda (MOM6) library. 
  - Should be coordinated with Mike Bell who plans to use the package for pressure gradient scheme.
 6. Set up a realistic test case (Denmark strait +Med overflows in ORCA12) in col. with WP6 (TBD). 
  - How far in the validation should we go ? Not sure this is really part of the WP3.


== Preview 

{{{#!box help
[[Include(wiki:Developers/DevProcess#preview_)]]
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== Tests

=== Reproducibility tests (VORTEX, 60 cores, 100 parent steps - diff run.stat 1_run.stat): [[BR]]

==== revision: 11573 [[BR]]
2 way mode (ln_agrif_2way = .true.)
|| jpni x jpnj || jpimax x jpjmax (child) || status ||
||  10  x   6  ||    9   x  13            ||  ref   ||
||   5  x  12  ||   15   x   8            ||   ok   ||
||  12  x   5  ||    8   x  15            ||   ok   ||
||  15  x   4  ||    7   x  18            ||   ok   ||
||   4  x  15  ||   18   x   7            ||  NOK   ||
||  30  x   2  ||    5   x  34            ||  memory corruption  ! ||

1 way mode (ln_agrif_2way = .false.)
|| jpni x jpnj || jpimax x jpjmax (child) || status ||
||  10  x   6  ||    9   x  13            ||  ref   ||
||  30  x   2  ||    5   x  34            ||   ok   ||
||   1  x  60  ||   65   x   4            ||   ok   ||
||  60  x   1  ||    4   x  65            ||   ok   ||

1 way mode is reproducible down to subdomains lower or equal to 4. It means that changes made in #2199 and included in this revision do work as expected. There is still an issue with small mpp subdomains in the update stage that may come from the AGRIF library. 


=== key_vertical tests 

When using the AGRIF_DEMO config with only the Pacific nest results are not comparable between 80 time step runs with and without key_vertical. Differences of O 10^-5^m in the ssh field are observed @11599

== Review