Ocean Modeling Community – COMODO

Existing ocean models suffers from a number of well-identified issues that will be addressed during this project. To improve on those issues, the present proposal suggests an innovative evaluation of dissipation mechanisms especially in the context of submesoscale modelling and an improvement of advection-diffusion schemes for the reduction of spurious diapycnal mixing for the accurate representation of active and passive tracers. The second part of the proposal is based on recent advances of our community on vertical coordinate systems, unstructured meshes and non-hydrostatic modelling. The objective is here both to continue fundamental research in these topics and to contribute to the design of future generation models involving their system of equations and numerical methods. The proposed developments will be evaluated thanks to a benchmark suite that covers both idealized test cases design to assess basic important properties of numerical schemes and more complex test cases that will be set-up for a thorough evaluation of progresses made during this project. This benchmark suite, accompanied with the results of the different models, will be made publicly available so as to provide elements for future model developments as well as an opportunity for more theoretical work on numerical schemes to be evaluated in the context of ocean modeling.

First results are related to the reduction of model errors introduced by the numerical discretization. For instance, we proposed a new numerical method for making the intrinsic numerical diffusion more consistent with what happens in reality.
The work also includes the reduction of simplifying assumptions in the equations systems. Thus hydrostatic and incompressibility assumptions have been removed to allow the simulation of increasingly finer scales.
Finally, project members also proposed a mathematical formalism for a rigorous comparison of different classes of approximation methods: finite differences, finite volumes, finite elements.
Improvements induced by all these developments can be assessed using a benchmark suite also designed in this project.

Vertical coordinates, structured and unstructured grids, temporal schemes are among the key issues that are being studied in the research teams involved in the project. Establishing the building blocks of future ocean modeling systems is the driving force of the project.

1. Flavien Gouillon, R. Baraille, M. Boutet, C. Lathuiliere,
Y. Morel, V. Kourafalou, 2013. Potential Vorticity diagnostics
for river plumes modelling. To be submitted to J. Phys. Oceanogr.
2. Michaud H., Marsaleix P., Leredde Y., Estournel C., Bourrin F., Lyard F., Mayet C., Ardhuin F., 2012. Three-dimensional modelling of wave-induced current from the surf zone to the inner shelf. Ocean Science, 8, 657-681, dx.doi.org/10.5194/os-8-657-2012
3. Lemarie F., L. Debreu, A. F. Shchepetkin and J.C. McWilliams,n 2013 : On the stability and accuracy of the harmonic and biharmonic isoneutral mixing operators in ocean models, Ocean Modelling, vol. 52-53, p. 9-35.
4. Anne-Claire Bennis, F. Dumas, F. Ardhuin, B. Blanke, 2013 Mixing parameterization: Rip currents and wave set-up. Submitted to Journal of Geophysical Research – Oceans.
5. Marsaleix P., Auclair F., Duhaut T., Estournel C., Nguyen C., Ulses C., 2012. Alternatives to the Robert-Asselin filter. Ocean Modelling, 41, 53-66, dx.doi.org/10.1016/j.ocemod.2011.11.002

This proposal focuses on the first thematic axis: complex systems modeling, and closely respond to the modeling of environmental sciences thematic of the call for proposal, specifically oceanography. The ocean, coupled with other components (atmosphere, continent, and ice) is a building block of the earth system. Recent events have raised questions on social and economic implications of anthropic alterations of the earth system, i.e. both its long-term evolution and extreme events. A better understanding of the ocean system is a key ingredient for improving our prediction of such implications. Ocean models are essential tools to understand key processes, simulate and forecast events of various space and time scales. The whole French ocean modeling community has been recently assembled under the group name COMODO (COmmunauté de Modélisation Océanique). This community is diverse and offers a variety of applications and numerical approaches for ocean modeling; it also relies at various degrees on the international community. For the first time, this proposal reflects a global effort of the French community to strengthen interactions between its members. This common effort will be directed towars two main objectives: improvement of existing models and numerical methods, guidelines for the development of future generation ocean models.

Existing ocean models suffers from a number of well-identified issues that will be addressed during this project. To improve on those issues, the present proposal suggests an innovative evaluation of dissipation mechanisms especially in the context of submesoscale modelling and an improvement of advection-diffusion schemes for the reduction of spurious diapycnal mixing for the accurate representation of active and passive tracers. The second part of the proposal is based on recent advances of our community on vertical coordinate systems, unstructured meshes and non-hydrostatic modelling. The objective is here both to continue fundamental research in these topics and to contribute to the design of future generation models involving their system of equations and numerical methods. The proposed developments will be evaluated thanks to a benchmark suite that covers both idealized test cases design to assess basic important properties of numerical schemes and more complex test cases that will be set-up for a thorough evaluation of progresses made during this project. This benchmark suite, accompanied with the results of the different models, will be made publicly available so as to provide elements for future model developments as well as an opportunity for more theoretical work on numerical schemes to be evaluated in the context of ocean modeling.