Axis 2 - Interactions between ocean dynamics and other components of the climate system

The ocean is a geophysical fluid that interacts with other components of the climate system (atmosphere, cryosphere, continents) and is a key player in major natural cycles (carbon cycle, water cycle). Until recently, the ocean-ice numerical models (NEMO-LIM) implemented in the MEOM team were forced at the air-sea interface by bulk formulas in order to simulate an oceanic variability approximately in phase with the variability of the atmosphere. However, this approach distorts the physics of the real ocean-atmosphere system (atmospheric heat capacity assumed to be infinite, SST feedbacks on the wind neglected). The use of coupled models appears to be more physically coherent, but the oceanic evolution may be out of phase with the observations.

More recently, our investigations focus on the study and modelling of ocean-ice-atmosphere interfaces. Very high resolution coupled simulations (NEMO+LIM 1/36° + WRF 1/12°) are carried out over the North Atlantic and compared to idealized models with two main objectives: (i) to study ocean-atmosphere feedbacks, energetics and dynamics of the surface ocean at the scale of eddies and filaments; (ii) to improve the forcing of NEMO by coupling with an atmospheric boundary layer model (Albatros), which is itself guided by a dynamical atmosphere and eventually by reanalysis. At high latitudes, these fine-scale air-sea interactions are mediated by the sea ice, whose rheology is represented in a very realistic way by the NeXtSIM model, also coupled to NEMO. The team relies on the NEMO/NeXtSIM/Albatros suite, on observations to study the fine-scale dynamics of the pack ice (forced and coupled), its impact on local air-ice-sea interactions, and their effect on the climate evolution of the ocean (especially the Arctic Ocean).

We are pursuing work in the framework of internal and external collaborations at the IGE on the ocean-ice sheet interface, in particular to simulate and understand the dynamics of flows under ice shelves and their interactions with the ocean, at the scale of the Southern Ocean. Ensemble approaches will allow us to evaluate uncertainties in these interactions, whether they are related to the chaotic character of oceanic variability or to model uncertainties. Other interesting perspectives are opening up on the likely impact of oceanic chaos on related environments (via the signature on heat content in particular), oceanic biogeochemistry and in the longer term on the coupled ocean-atmosphere system.