New URL for NEMO forge!

Since March 2022 along with NEMO 4.2 release, the code development moved to a self-hosted GitLab.
This present forge is now archived and remained online for history.
2014WP/2014_SystemSimplification – NEMO

Version 2 (modified by gm, 11 years ago) (diff)


Note on possible system simplification

We need to simplify the code for both maintenance and future evolution. This means fewer options, and a consensus on the default (and thus well validated) set of numerics.

The idea is to change the used choices from :

linear filtered free surface ocean with TVD, "Madec" isoneutral diffusion, and standard equation of state ; levitating sea-ice with virtual salt fluxes

to :

Non linear (vvl) split-explicit (ts) free surface with 3rd order advection (UBS), "Griffies" isoneutral diffusion and TEOS10 ; embedded multi-category sea-ice (exact fluxes).

Free surface & vertical coordinate :

  • remove filtered free surface and all associated solvers
  • default : non-linear free surface
  • linear option set without optimization (i.e. starting from the non-linear case with minimal changes, not optimal changes), or linear case suppressed ??
  • default : variable volume level (vvl), either z*/s*, or z/s-tilde

Needs :

  • split-explicit free surface adapted to AGRIF refinements and TAM
  • tracer solved systematically as thickness weighted tracer: Dt(e3t T)
  • no more substitute (domzgr_substitute.h90): all e3 always defined at before, now and after time steps.
  • sea-ice : embedded sea-ice only, so management of land-fast ice and especially sea-ice approaching the ocean-bottom.

Equation of State (eos) :

  • EOS10 as default + 1 simplified eos. Suppression of the now used EOS.
  • EOS provides systematically alpha and beta (used in ldf_iso, bbl, mld, npc…)
  • no more potential density (mixed layer depth computed from alpha & beta)
  • efficient transfer function from conservative temperature to potential temperature and vice versa.

Coupled interface to the atmosphere :

  • OASIS-MCT only: remove OASIS 3 interface.
  • Multi-category sea-ice interface

Physics :

  • avm defined at t-point ==> suppress avmu, avmv and ~10 lbc_lnk calls
  • LDF: remove 1D and 2D cases, keep only 3D ; laplacian and bilaplacian coefficients defined at the same points (T and F) ; time varying coefficients (Smagorinsky, function of growth rate of baroclinic instabilities): better integration rather than configuration dependent cases
  • TKE remove (use GLS instead?)
  • KPP remove unless if-less KPP is implemented (Lemarié et al 2012). Keeping a validated KPP scheme in the system make sense for comparison purposes.
  • Non-penetrative convection : either correct it (using alpha & beta) or remove it

Configurations :

  • remove all hard coded specific alterations associated with configurations (ORCA,…) while introducing associated input files
  • same for the definition of coordinate system (s, mixed z-s): only a simple case hard coded. For more sophisticated cases, the required information should be read in an input file.

Obsolescent features : to be suppressed

  • remove LIM2 : only LIM3 remains in the system
  • remove OBC : only BDY remains in the system
  • acceleration of convergence (in particular, rdttra function of k ==> unique rdt)
  • remove Neptune effect : ORCA1 run shows its inefficiency.
  • duplicate isoneutral operator: keep only the Griffies' one
  • Smagorinsky (?) : use 3rd order operator (UBS) instead and remove it ?
  • tracer advection schemes: diminish their number. Typically one module for 2 nd /4 th order and one for a 3 rd order scheme, both associated with an optional flux limiter to ensure positivity.

Outputs :

  • remove Dimg format ? (agreement needed from DRAKKAR group)
  • remove IOIPSL: the key issue here is do we believe XIOs is able to work on all existing and foreseen platform?