Opened 11 months ago

Last modified 4 months ago

#2170 new Task

VALID-02_GeorgeN-evalOSMOSIS

Reported by: acc Owned by: agn
Priority: high Milestone: 2019 WP
Component: TOP Version: trunk
Severity: minor Keywords:
Cc: Review:
MP ready?:
Progress: At 23 May 2019: The OSMOSIS code has been implemented in the v4.0 release of NEMO (presently based on r10833, April 3rd 2019). Work has begun on a range of approaches to reduce the too-deep winter mixed layers. a. Reduction in the effectiveness of the Langmuir mixing in cases where the ratio of the Stokes penetration depth to the boundary layer depth is small. and b. Reduction in effectiveness of shear-turbulent, Langmuir and convective deepening when the respective eddy turnover timescales (hbl/u* etc.) approach the inertial timescale 1/f.

Description (last modified by smasson)

Summary

Action ${ACTION_NAME} Subject
PI(S) George Nurser
Digest The OSMOSIS surface boundary layer scheme introduced in 2017 was tested in fully global configurations in 2018 and some issues uncovered in some circumstances (for example in places where the mixed layer extends to the seabed). Improvements to the parameterisation have been implemented and will be retested in 2019.
Dependencies
Branch NEMO/branches/2019/dev_r11078_OSMOSIS_IMMERSE_Nurser
Previewer(s)
Reviewer(s)
Wiki wiki:2019WP/VALID-02_GeorgeN-evalOSMOSIS

Abstract

The OSMOSIS OBL code work well in summer conditions, but gives too-deep mixed-layers in winter. It is also written assuming a linear equation of state, and has not yet been applied to passive tracers.
Under-ice behaviour has not been checked. All these issues need to be addressed.

Description

he OSMOSIS OBL code has shown promise in giving more realistic, deeper, mixed layers (MLs) in the Southern Ocean in the southern summer. However there are various issues that must be settled before it can be used as an OBL code for global integrations.

  1. ML are too deep in winter, especially over the ACC in southern winter. This problem is being addressed by a) taking account of the effect of the Coriolis force on the turbulence when the eddy-turnover scale approaches the inertial timescale and b) taking account of the lesser effectiveness of Langmuir turbulence in driving mixing when the ML depth becomes very deep relative to the depth to which the Stokes drift penetrates.
  1. Non-local fluxes of passive tracers need to be defined.
  1. The non-linearity of the equation of state needs to be better taken account of.
  1. The behaviour of the model under ice requires detailed examination.
  1. The code has been written for simplicity and ease of understanding rather than performance, and needs to be optimized.
Implementation

Changes will mostly be restricted to the zdfosm.F90 module.

Namelists will need also to be modified.

New variables are not fully known yet.

Reference manual and web pages updates

Chapter will be written for reference manual and text for the user guide

Once the PI has completed this section, he should send a mail to the previewer(s) asking them to preview the work within two weeks.

Commit History (0)

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Change History (5)

comment:1 Changed 9 months ago by nemo

  • Priority changed from low to high

comment:2 Changed 5 months ago by agn

  • Description modified (diff)
  • Progress modified (diff)

23 May. Added description of work on this ticket and progress as of 23 May 2019
Branch will be placed in public NEMo repository in early June
—George Nurser

comment:3 Changed 4 months ago by smasson

  • Description modified (diff)

comment:4 Changed 4 months ago by smasson

  • Description modified (diff)

comment:5 Changed 4 months ago by smasson

  • Description modified (diff)
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