#1713 closed Bug (wontfix)
Bugs in split explicit diffusion
| Reported by: | jchanut | Owned by: | jchanut |
|---|---|---|---|
| Priority: | low | Milestone: | |
| Component: | OCE | Version: | v3.6 |
| Severity: | minor | Keywords: | OPA v3.6 |
| Cc: |
Description (last modified by nicolasmartin)
Description
Few users may be concerned since implicit diffusion is the default in NEMO. Nevertheless, setting ln_zdfexp=.true. (ie split explicit vertical diffusion) will inevitably give wrong results.
Analysis
1) Surface boundary condition (i.e. wind stress) is wrong.
2) (Explicit) bottom friction is not implemented in sub-stepping.
A 1d simulation of wind forced ekman dynamics in shallow water emphasizes the problem (see attached plot).
After bug correction it also shows the equivalence between implicit and split-explicit formulations. Small deviations from theory may come from the approximate no-slip bottom boundary conditions in the model.
Recommendation
Do not use split explicit diffusion for the time being unless you neither have wind nor bottom stresses...
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Change History (7)
Changed 7 years ago by jchanut
comment:1 Changed 5 years ago by nicolasmartin
- Owner changed from nemo to jchanut
- Status changed from new to assigned
comment:2 Changed 5 years ago by nicolasmartin
- Description modified (diff)
comment:3 Changed 5 years ago by nicolasmartin
- Milestone Miscellaneous deleted
- Severity set to minor
comment:4 Changed 5 years ago by jchanut
- Version changed from trunk to v3.6
comment:5 Changed 4 years ago by jchanut
- Resolution set to wontfix
- Status changed from assigned to closed
comment:6 Changed 14 months ago by nemo
- Keywords OPA v3.6 added
1d experiment of shallow water Ekman problem. 10 meter depth, 41 levels, viscosity=13 cm2/s, latitude=45°N, westerly wind stress =0.04 N/m2, linear bottom friction=0.02m/s