• COMODO (2011-2016, PI)

Project abstract: COMODO is a research project supported by the french national research agency (ANR). The 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 suffer 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.

• HEAT (2014-2018, PI for the Inria Partner, (PI: Thomas Dubos, LMD/Ecole Polytechnique))

Project abstract: The latest-generation atmospheric models like the hydrostatic icosahedral dynamical core DYNAMICO carry the promise of addressing scientific issues that remain out of reach with current operational models. Putting these latest-generation models to work to answer scientific questions nevertheless requires significant effort and collaboration between experts of the numerics, computing, and scientific use of such models. HEAT sets up such a collaboration in order to address extreme atmospheric modelling applications and remaining numerical and computational challenges.

We will pioneer numerical modelling of the general atmospheric circulation of gaseous giant planets and achieve significant milestones towards millennial-scale Earth system simulations relevant for paleoclimatology. In terms of numerical and computational challenges, our objectives are to address the higher-order extension of highly scalable numerical methods for transport and dynamics, and bottlenecks for non-hydrostatic modelling, especially elliptic problems.

Jupiter and Saturn have fast-rotating atmospheres, prone to powerful global winds and intense convective and wave activity. The ambition of HEAT is to put together a team of experts able to design and implement unprecedented high-resolution global circulation experiments for Saturn and Jupiter developing significant wave activity and elucidate how this wave activity forces the global circulation, a dynamical process that is also key to the terrestrial climate. In a longer perspective, our effort will equip France and Europe with a state-of-the-art operating model to interpret the results from the NASA mission JUNO and the ESA mission JUICE towards the Jovian system.

In order to understand large climate reorganizations that occurred during the last deglaciation we will gradually develop a new ESM based on DYNAMICO together with the land surface model ORCHIDEE, the aerosols model INCA and the ocean/sea-ice model NEMO, with a careful analysis of key conservation constraints. In addition to long equilibrium simulations, short global 30 km resolution simulations of key periods in the past will offer new possibilities to refine the comparison of model results with regional paleoclimate observations.

On the numerical side we shall explore WENO approaches to non-oscillatory, accurate finite volume transport as well as the discontinuous Galerkin method in order to offer a range of accuracy/efficiency trade-offs for DYNAMICO's transport scheme that may be important in the presence of sharp fronts and strong nonlinear interactions. For the dynamics formal accuracy is crucial for reducing the imprinting caused by mesh irregularities. We shall pursue the mixed finite element approach, which yields excellent discrete conservation properties.

Finally, as we approach exascale capability, global modelling will become possible at fine spatial scales where the hydrostatic approximation becomes problematic. On the one hand, we aim at extending DYNAMICO to non-hydrostatic dynamics while maintaining scalability, ability to relax certain terrestrial approximations and exact conservation of mass, energy, vorticity, for long-term simulations. On the other hand we will explore innovative solutions aimed at improving the scalability of key components of long- time-step approaches, especially the associated elliptic solvers.

Beyond HEAT, the work produced by all tasks, and the expertise gained, will contribute to strengthen the world-class capability of the French climate and weather modelling community to address an extended range of future scientific challenges related to past, present and future atmospheric dynamics at global and regional scales. By bringing together geoscientists and applied mathematicians, and by contributing to events such as the CEMRACS summer school and the PDEs on the Sphere workshop, HEAT will strengthen the French applied maths community committed to atmospheric modelling and contribute to its insertion in the corresponding international community.

• CHRONOS (PI: Florian Lemarié)

Time integration schemes

Other ongoing projects are linked with the development and/or the use of the AGRIF software.