FIBOSI · Flow Interaction Between the Ocean Surface and the Interior

he Earth's oceans are carpeted by a highly-energetic turbulent sea of vortices and currents, together with many similar subsurface structures. These structures are particularly numerous at horizontal scales between 1 and 100 km, the `oceanic mesoscale´. They arise from basic fluid dynamical instabilities, together with thermal and wind forcing at the sea surface. They contribute strongly to heat, chemical and biological transport, and hence play a major role in the Earth's climate. Presently, global computational models cannot accurately represent these small-scale structures. To do this, a global model would have to span a vast range of scales, from 1 km to 10,000 km. (The best global model can faithfully represent scale of motion down to 20 km, without excessive numerical dissipation. Closing the gap to 1 km using present computational methods would require computers 10,000 times faster than presently available.) As a result, we have little hope in reliably estimating the impact of mesoscale oceanic turbulence on climate. This project argues for an alternative, complementary approach capable of accurately modelling, and better understanding, the essential features of this turbulent motion. Instead of modelling the entire ocean, we propose to model a representative portion of it, where oceanic turbulence is particularly active. We will focus on characteristic aspects of this turbulence, in particular nonlinear interactions between vortices and between a vortex and a current. We will account for the effects of bottom topography on the sea floor, as well as thermal and wind forcing at the sea surface. Our objective is to comprehensively map out and quantify these interactions, with the practical aim to help better assess their impact on climate.