| 31 | | === S3.2-a — Revisit of surface mass and salt fluxes === |
| 32 | | '''Motivation:''' As a consequence of the embedding of sea-ice into the ocean (see S3.2-b), 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.[[BR]] |
| | 34 | === S1.5-a - Review of new documentation === |
| | 35 | '''Motivation:''' The exchange and proof-reading of new documentation between system team sites before release should ensure consistency of style, readability and accuracy.[[BR]] |
| | 36 | '''Status :''' Carried over from 2009 but expected to start as soon as new documentation is submitted.[[BR]] |
| | 37 | '''Principal Investigator :''' Steven Alderson (sga@noc.soton.ac.uk) [[BR]] |
| | 38 | [[BR]] |
| | 39 | === S3.2-a — Revisit of mass and salt fluxes between ice, ocean and air === |
| | 40 | '''Motivation:''' As a consequence of the embedding of sea-ice into the ocean (see S3.2-b), the total mass of salt of the combined sea-ice/ocean system is |
| | 41 | 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 |
| | 42 | 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. (NOCS team, 3wk)[[BR]] |
| 37 | | '''Motivation:''' To improve the coupling between the sea-ice and ocean models, we embed the sea-ice into the ocean by changing the volume of the ocean and depressing the ocean interface by a depth equal to the mean ice draft. |
| 38 | | The latter is calculated as the water equivalent of the total ice and snow mass in the model grid box using in-situ local densities of seawater. |
| 39 | | The pressure gradient that takes into account the total weight of sea ice and snow in the top model grid box is added to the ocean momentum budget. |
| 40 | | The vertical coordinate is redefined for the whole water column.[[BR]] |
| 41 | | '''Status :''' During 2009 the above scheme was implemented and tested at NOCS in a 100-year long integration of an ORCA2-LIM2 configuration using both |
| 42 | | linear and non-linear free surface options. |
| 43 | | It was also tested for short runs in the ORCA2-LIM3 configurations. |
| 44 | | A longer run in ORCA2-LIM3 will take place early in 2010 and the code committed for the NEMO 3.3 release. |
| | 47 | '''Motivation:''' Replace the unrealistic 'levitating' ice[[BR]] |
| | 48 | '''Main task:''' [[BR]] |
| | 49 | (1) To improve the coupling between the sea-ice and ocean models, we embed the sea-ice into the ocean by changing the volume of |
| | 50 | the ocean and depressing the ocean interface by a depth equal to the mean ice draft. |
| | 51 | The latter is calculated as the water equivalent of the total ice and snow mass in the model grid box using in-situ local densities of seawater. |
| | 52 | The pressure gradient that takes into account the total weight of sea ice and snow in the top model grid box is added to the ocean momentum budget. |
| | 53 | The vertical coordinate is redefined for the whole water column. (v3.3) (NOCS team, 4wk)[[BR]] |
| | 54 | '''Status :''' During 2009 the above scheme was implemented and tested at NOCS in a 100-year long integration of an ORCA2-LIM2 configuration using both |
| | 55 | linear and non-linear free surface options. |
| | 56 | It was also tested for short runs in the ORCA2-LIM3 configurations. |
| | 57 | A longer run in ORCA2-LIM3 will take place early in 2010 and the code committed for the NEMO 3.3 release.[[BR]] |
| | 64 | '''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. [[BR]] |
| | 65 | '''Main task:''' [[BR]] |
| | 66 | (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. [[BR]] |
| | 67 | (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. [[BR]] |
| | 68 | (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. (v3.3) (NOCS team, 4wk)[[BR]] |
| | 69 | '''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. [[BR]] |
| | 70 | '''Principal Investigator :''' George Nurser (agn@noc.soton.ac.uk) [[BR]] |
| 53 | | '''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. Isopycnal diffusion is also being discretized in terms of these triads, obviating the need to smooth isopycnal slopes horizontally with a Shapiro filter (as currently implemented in NEMO), or apply a background horizontal diffusivity that would mix diapycnally. Visbeck et al.'s formulation of spatially varying diffusivities is also being implemented, as an alternative to the current formulation based on the Held and Larichev timescale and the Rossby radius as a lengthscale. Mixed-layer depth is sensitive to the slope limiting that is employed, and a slope limiting algorithm will be added that behaves satisfactorily within and immediately below the mixed layer. [[BR]] |
| | 72 | === S3.2-e — Improved thermodynamics for LIM3 === |
| | 73 | '''Motivation:''' Enhancement of lateral melting paramerisations[[BR]] |
| | 74 | '''Main task:''' [[BR]] |
| | 75 | (1) New parameterisations for lateral melting processes will be incorporated including parameterisations for the effects of waves on fragmentation and melting. (NOCS team, 8wk) [[BR]] |
| | 76 | '''Principal Investigator :''' Yevgeny Aksenov (yka@noc.soton.ac.uk) [[BR]] |
| 55 | | '''Status: ''' A working prototype code for the iso-neutral and skew-flux operator was carefully reviewed in 2009. An final version will be ready for the 3.3 release. 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. [[BR]] |
| 56 | | '''Principal Investigator :''' George Nurser (agn@noc.soton.ac.uk) [[BR]] |
| | 78 | === S3.2-f — Rationalisation of support for ORCA configurations === |
| | 79 | '''Motivation:''' A cleaning and enhancement of code support for global (ORCA) configurations is required to introduce configurations in common use across the community. [[BR]] |
| | 80 | '''Main task:''' [[BR]] |
| | 81 | (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. [[BR]] |
| | 82 | (2) The use of .h90 files will also be suppressed. (NOCS team, 4wk) [[BR]] |
| | 83 | '''Principal Investigator :''' Andrew Coward (acc@noc.soton.ac.uk) [[BR]] |
| | 84 | |
| | 85 | === S3.2-g — Improvement of numerical treatment for vertical diffusion === |
| | 86 | '''Motivation:''' An improvement in the numerical treatment of vertical diffusion can be achieved by replacing the fully implicit scheme with a Crank-Nicholson |
| | 87 | scheme. This approach is widely used in other ocean models (e.g. ROMS) and can be implemented relatively simply. |
| | 88 | '''Main task:''' [[BR]] |
| | 89 | (1) The replacement scheme will be implemented and its performance tested. [[BR]] |
| | 90 | (2) A similar scheme will also be implemented for the bottom friction contribution to the barotropic momentum trend in dynspg_ts. (NOCS team, 1wk)[[BR]] |
| | 91 | '''Principal Investigator :''' Andrew Coward (acc@noc.soton.ac.uk) [[BR]] |
| | 92 | |
| | 93 | === S3.2-h — Implementation of the Neptune effect parameterisation === |
| | 94 | '''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. [[BR]] |
| | 95 | '''Main task:''' [[BR]] |
| | 96 | (1) Add the parameterisation to the reference code [[BR]] |
| | 97 | (2) Test, document and report (v3.3) (NOCS team, 5wk)[[BR]] |
| | 98 | '''Principal Investigator :''' Jeff Blundell (jeff@noc.soton.ac.uk) [[BR]] |
| | 99 | |
| | 100 | === S3.2-h — Implementation of spectral nudging === |
| | 101 | '''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. [[BR]] |
| | 102 | '''Main task'''[[BR]] |
| | 103 | (1) The v2.3 solution will be obtained and implemented in the reference code (v3.3) (NOCS team, 6wk)[[BR]] |
| | 104 | '''Principal Investigator :''' Jeff Blundell (jeff@noc.soton.ac.uk) [[BR]] |
| | 105 | |
