= Trough grid refinement (AGRIF nesting & coarsening)
Last edition: '''[[Wikinfo(changed_ts)]]''' by '''[[Wikinfo(changed_by)]]'''
= Coarsening of physics for biogeochemistery model =
== Presentation ==
A capacity of coarsening physics to force a BGC model coupled to NEMO has been developped in NEMO_3.6. This capacity allow to run 'online' a BGC model coupled to OPA-LIM with a lower resolution, to reduce the CPU coast of the BGC model, while preserving the effective resolution of the dynamics.
This capacity is not included in the [https://forge.ipsl.jussieu.fr/nemo/browser/branches/2015/nemo_v3_6_STABLE/NEMOGCM NEMO_3.6] , but is available in a specific [https://forge.ipsl.jussieu.fr/nemo/browser/branches/2015/dev_r5003_MERCATOR6_CRS branch] of the 3.6 stable. This branch is regularly phazed with the NEMO_3.6.
An associated ticket to follow evolution is [https://forge.ipsl.jussieu.fr/nemo/ticket/1426 here].
A presentation is available [xxx here], where the methodology is presented.
== How to ? ==
To activate the coarsening, key_crs should be added to list of cpp keys. This key will only activate the coarsening of dynamics.
Some parameters are available in the namelist_cfg:
{{{
! passive tracer coarsened online simulations
!-----------------------------------------------------------------------
nn_factx = 3 ! Reduction factor of x-direction
nn_facty = 3 ! Reduction factor of y-direction
nn_msh_crs = 0 ! create (=1) a mesh file or not (=0)
nn_crs_kz = 3 ! 0, volume-weighted MEAN of KZ
! 1, MAX of KZ
! 2, MIN of KZ
! 3, 10^(MEAN(LOG(KZ))
! 4, MEDIANE of KZ
ln_crs_wn = .false. ! wn coarsened (T) or computed using horizontal divergence ( F )
! !
ln_crs_top = .true. !coarsening online for the bio
/
}}}
- '''Only nn_factx = nn_facty = 3''' is available and the coarsening only works for grids with a T-pivot point for the north-fold lateral boundary condition( ORCA025, ORCA12,ORCA36,...).
- '''nn_msh_crs = 1''' : will activate the generation of the coarsened grid meshmask.
- '''nn_crs_kz''' : is the operator to coarsene the vertical mixing coefficient.
- '''ln_crs_wn''' : when key_vvl is activated, this logical has no effect; the coarsened vertical velocities are computed using horizontal divergence.
when key_vvl is not activated, coarsened vertical velocities are computed using horizontal divergence ( ln_crs_wn = .false )
or coarsened vertical velocities are computed with an average operator ( ln_crs_wn = .true. )
- '''ln_crs_top = .true''': should be activated to run BCG model in coarsened space; so only works when key_top is in the cpp list and eventually key_pisces or key_my_trc.
== Choice of operator to coarsene KZ ==
A sensiblity test has been done with an Age tracer to compare the different operators. The 3 and 4 options seems to provide the best results.
Some results can be found [xxx here]