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.
#1812 (Surface stresses at wrong time step in zdftke/zdfgls) – NEMO

Opened 7 years ago

Closed 4 years ago

#1812 closed Defect (wontfix)

Surface stresses at wrong time step in zdftke/zdfgls

Reported by: jchanut Owned by: rbourdal
Priority: low Milestone:
Component: OCE Version: trunk
Severity: minor Keywords: GLS TKE mixing
Cc: rbourdal



Gls and tke vertical mixing schemes are discretized in time thanks to backward Euler time stepping (over rdt), but shifted one time step in the past. Hence turbulent quantities are integrated from "kstep-1" to "kstep" leapfrog time steps. This leads to "now" diffusivities/viscosities at kstep. However, surface stresses are obtained from taum which is the surface stress module at kstep+0.5. It should be taken one step in the past at kstep-0.5. I encountered some instabilities due to that.
There is a similar problem with bottom stresses, taub being computed from "now" bottom friction parameter. This is mitigated by now velocities entering the stress which is in agreement with implicit bottom friction.




Would be far better if tke/gls schemes would be integrated from now to after time steps. Then taum would be at the right time step and this would greatly simplify interaction with AGRIF. Sticking with the current implementation, simply recomputing squared surface velocity scales from before stresses could solve the problem.

This said, and in contrary with what is stated in the documentation, I don't think that mixing a backward Euler time stepping over rdt with backward Euler time stepping over 2 rdt does give the correct energetic transfer (through vertical shear) from momentum equations to TKE/GLS schemes.

Commit History (0)

(No commits)

Change History (6)

comment:1 Changed 7 years ago by nemo

  • Keywords GLS added; gls removed

comment:2 Changed 7 years ago by nemo

  • Keywords TKE added; tke removed

comment:3 Changed 7 years ago by clevy

  • Owner changed from jchanut to gm

comment:4 Changed 6 years ago by clevy

  • Cc rbourdal added
  • Owner changed from gm to rbourdal
  • Status changed from new to assigned

comment:5 Changed 6 years ago by nicolasmartin

  • Type changed from Bug to Defect
  • Version changed from v3.6 to trunk

comment:6 Changed 4 years ago by smasson

  • Resolution set to wontfix
  • Severity set to minor
  • Status changed from assigned to closed

Wontfix in the leap-frog environment

Note: See TracTickets for help on using tickets.