= Name and subject of the action

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

The PI is responsible to closely follow the progress of the action, 
and especially to contact NEMO project manager if 
the delay on preview (or review) are longer than the 2 weeks expected.

[[PageOutline(2, , inline)]]

== Summary

||=Action       || Develop on multi-grid algorithm for passive tracer transport ( coarsening)                        ||
||=PI(S)        || Clément Bricaud                                                 ||
||=Digest       || Work on the design and starts the development     ||
||=Dependencies || If any                                                ||
||=Branch       || source:/NEMO/branches/{YEAR}/dev_r{REV}_{ACTION_NAME} ||
||=Previewer(s) || Gurvan Madec, Marc Stringer                                                ||
||=Reviewer(s)  || Marc Stringer                                                 ||
||=Ticket       || #XXXX                                                 ||

=== Description

No actions are considered to make the preliminary development on AGRIF to make coarsening with AGRIF

In IMMERSE, a task has started to runs a coupled OCE+ICE+BGC with 2 seperate executable, coupled with OASIS 


The previous implementation ( in NEMO 3.6 ) has been use by Sara Berthet in CNRM (  https://doi.org/10.1029/2019MS001644 ) with PISCES and is in integration in NEMO-MEDUSA at UKMO-NOCS.

A reference paper for the description of the method has been subimitted to GMD (NEMO special issue)

'''2 options are possible:'''

- OPTION 1:  OCE+ICE+BGC  in a single executable ( =no OASIS); this the one already developed in NEMO 3.6
   
   It can be improved by avoiding duplication of routines ( the rewriting of the code for the 2LTS can help), replace the "e3t_max_crs" by the former "facvol" )
 
   It might work also with s-coordinates, different tracer advections schemes and vertical mixing schemes.
  
   They are probably others ways of improvment

- OPTION 2 :  OCE+ICE+BGC with 2 separated executables, coupled with OASIS 
   
   In a first time, the coarsened variables can be computed by the algo developped in OPTION 1 

   and OASIS send the coarsened variables to the BGC component, instead of the HR variables


   In a second time,  the coarsened variables can be computed by OASIS

   
'''Here the work is''':

- to design the implementation, in particular to avoid the duplication of routines and to take care of the compatibility with OPTION 2

- to develop OPTION 1 in a z-coordinate context. 

- In a first time, implementation will be done in TOP component and tested with a synthetic tracer. One advection scheme and one vertical mixing scheme will be treated. This is expected for 2019.

- In a second time, the implementation will be checked for all advection and vertical mixing schemes. It will also developped in s-coordinates. This part need some additional manpower, especially for the s-coordinates. This part is not expected in 2020.

- in a third time, the implementation will be done in PISCES. This part is not expected in 2020.

- OPTION 2 will be treated after, when the separation of executables will be implemented in NEMO 4 reference version.

=== Implementation

{{{#!box width=35em help
Describe flow chart of the changes in the code. \\
List the Fortran modules and subroutines to be created/edited/deleted. \\
Detailed list of new variables to be defined (including namelists), \\
give for each the chosen name and description wrt coding rules.
}}}

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=== Documentation updates

{{{#!box width=55em help
Using previous parts, define the main changes to be done in the NEMO literature 
(manuals, guide, web pages, …).
}}}

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== Preview 

{{{#!box width=50em info
[[Include(wiki:Developers/DevProcess#preview_)]]
}}}

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== Tests

{{{#!box width=50em info
[[Include(wiki:Developers/DevProcess#tests)]]
}}}

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== Review

{{{#!box width=50em info
[[Include(wiki:Developers/DevProcess#review)]]
}}}

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