B - 2010 NOCS-NEMO team actions

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total weeks : 1+1+3+4+3+4+8+4+1+5+6 = 40 (1 man/year)

B.1 - User Interface

Motivation: Shared daily support to users, web & paper documentation. A reduction in the Paris system team this year will necessitate greater sharing of these responsibilities between the disptributed system team members.
Main task: (1 wk)
Principal Investigator : Andrew Coward (acc@…)

B.2 - Review of new documentation

Motivation: The exchange and proof-reading of new documentation between system team sites before release should ensure consistency of style, readability and accuracy.
Status : Carried over from 2009 but expected to start as soon as new documentation is submitted.
Main task: (1 wk)
Principal Investigator : Steven Alderson (sga@…)

B.3 — Revisit of mass and salt fluxes (end) == (3 wk)

Motivation: As a consequence of the embedding of sea-ice into the ocean (see SB.4), the total mass of salt of the combined sea-ice/ocean system is conserved by removing a volume of water from the ocean when ice forms or adding a volume of water when it melts. When ice forms, salt contained in the water is returned to the ocean, less the salt retained in the ice itself. When ice melts, the salt contained is added back to the ocean.
Status : Carried over from 2009 but work is well advanced. The required modifications in OPA, LIM2 and LIM3 have been performed and validated.
Main task: (3 wk)
(1) Implementation in the trunk+ NVTK + documentation (3 wk) v3.3 release
Principal Investigator : Yevgeny Aksenov (yka@…)

B.4 — Embedded sea-ice (end)

Motivation: Introduce 2 other ways of managing ice-ocean coupling: (1) a levitating sea-ice with mass fluxes and (2) a fully embedded sea-ice (i.e. with sea-ice loading applied to the ocean) (Campin et al. OM 2008)
Status : During 2009 the above schemes were implemented and tested at NOCS in a 100-year long integration of an ORCA2-LIM2 configuration using both linear and non-linear free surface options. they were also tested for short runs in the ORCA2-LIM3 configurations. A longer run in ORCA2-LIM3 will take place early in 2010 and the code committed for the NEMO v3.3 release.
Main task: (4 wk)
(1) Achieve the validation, especially with respect to LIM3 (2 wk)
(2) Implementation in the trunk+ NVTK + documentation (2 wk) v3.3 release

Principal Investigator : Yevgeny Aksenov (yka@…)

B.5 — Embedded CICE

Motivation: Similar changes ro B.3 and B.4 will have to be made in order to fully embed CICE-modelled sea-ice. Subtle differences and problems may arise because of the specificities of CICE. This work is listed separately to ensure that possible delays will not impact on the delivery of an embedded solution for LIM (v3.3) (NOCS team, 3wk)

Main task: (3 wk)

(1) Achieve the validation, especially with respect to LIM3 (2 wk)
(2) Implementation in the trunk+ NVTK + documentation (1 wk) v3.3 or v3.4 release

Principal Investigator : Yevgeny Aksenov (yka@…)

B.6 — Lateral ocean physics (end)

Motivation: Griffies's implementation of the Gent and McWilliams? eddy transport as a skew flux is being implemented. This has the advantage that its numerical discretization can be written in terms of contributions from quarter cells – ‘triads’. This gives a tighter stencil, disallowing 2-gridpoint numerical noise that is permitted by the advective discretization.
Status: A working prototype code for the iso-neutral and skew-flux operator was carefully reviewed in 2009. Considerable care has been taken in the formulation to ensure the tensorial representation is consistent with the variable volume layers (s-coordinate/z* representation). This has been documented and will be provided with the release.

Main task: (4 wk)

(1) Discretise Isopycnal diffusion in terms of these triads. This will obviate the need to smooth isopycnal slopes horizontally with a Shapiro filter (as currently implemented in NEMO), or to apply a background horizontal diffusivity that mixes diapycnally (done).
(2) Implement Visbeck et al.'s formulation of spatially varying diffusivities as an alternative to the current formulation based on the Held and Larichev timescale and the Rossby radius as a lengthscale (done).
(3) Add a slope limiting algorithm (mixed-layer depth is sensitive to the slope limiting that is employed) that behaves satisfactorily within and immediately below the mixed layer. (2wk)
(2) Implementation in the trunk+ NVTK + documentation (2 wk) v3.3 release
Principal Investigator : George Nurser (agn@…)

B.7 — Improved LIM3 thermodynamics

Motivation: Enhancement of lateral melting paramerisations in LIM3
Main task: (8 wk)
(1) New parameterisations for lateral melting processes will be incorporated including parameterisations for the effects of waves on fragmentation and melting. (8wk)
Principal Investigator : Yevgeny Aksenov (yka@…)

B.8 — Support for all ORCA configurations

Motivation: A cleaning and enhancement of code support for global (ORCA) configurations is required to introduce configurations in common use across the community.
Main task: (4 wk)
(1) Support will be improved or added for ORCA1, ORCA05, ORCA025 and ORCA_R12 configurations in such a way that multiple vertical resolutions of each can be maintained.
(2) The use of .h90 files will also be suppressed. (NOCS team, 4wk)
Principal Investigator : Andrew Coward (acc@…)

B.9 — time stepping of vertical diffusion

Motivation: An improvement in the numerical treatment of vertical diffusion can be achieved by replacing the fully implicit scheme with a Crank-Nicholson scheme. This approach is widely used in other ocean models (e.g. ROMS, MARS...) and can be implemented relatively simply.
Main task: (1 wk)
(1) The replacement scheme will be implemented and its performance tested.
(2) A similar scheme will also be implemented for the bottom friction contribution to the barotropic momentum trend in dynspg_ts. (NOCS team, 1wk)
Principal Investigator : Andrew Coward (acc@…)

B.10 — Neptune effect

Motivation: The Neptune effect (Holloway 1992) is a well established parameterisation of the interaction of eddies with topography. The parameterisation is often seen as essential in Arctic ocean simulations even in high resolution models. The improvments it provide to an ORCA1-LIM simulation is shown in Wang and Holloway (OM, 2009).
Main task: (5 wk)
(1) Add the parameterisation to the reference code
(2) Test, document and report (v3.3) (NOCS team, 5wk)
Principal Investigator : Jeff Blundell (jeff@…)

B.11 — Implementation of spectral nudging

Motivation: Work by our Canadian colleagues has demonstrated the potentail benefits of spectral nudging techniques to restore large scale gradients without suppressing meso-scale activity.
Main task (6 wk)
(1) The v2.3 solution will be obtained and implemented in the reference code (v3.3) (NOCS team, 6wk)
Principal Investigator : Jeff Blundell (jeff@…)