Internal Waves in the General Oceanic Circulation

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Internal waves propagate in the volume of the ocean, and are influenced by density variations, as well as the Earth's rotation. When they break, they mix and move water up from the cold abyss, and heat down from the sun-bathed surface. When forced by wind, internal waves are very active in the upper ocean, participate in direct atmosphere-ocean exchanges, and might extract energy out of the large-scale vortices that contain the majority of the ocean's kinetic energy. These vortices are called geostrophic and are characterized by a balance between pressure gradients and the Coriolis force. ***I propose to study how internal waves influence the oceanic circulation over large spatial scales (100 km to global) and long time scales (months to centuries). My group and I will mostly use analytical and numerical tools and organise this program into three main directions. The first direction is about internal tides, namely waves, that oscillate at tidal frequencies. We will investigate how they create or destroy potential vorticity, which is the quantity that best describes geostrophic vortices. We will also study the opposite situation: how internal tides are refracted by geostrophic vortices, and how this unsteady refraction of the tide could affect measurement made by SWOT, the future USA-French satellite altimeter to which Canada also contributes. The second direction will investigate how geostrophic flows lose energy to internal waves when they flow against the corrugated bottom, and how these internal waves eventually dissipate this energy. Our hypothesis is that internal waves interact with deep hydraulic jumps (which could be described as underwater waterfalls) to enhance deep breaking, dissipation and mixing. We will study this phenomenon in two- and three-dimensional numerical simulations. The third direction of research will be to study the interactions between internal waves and small-scale geostrophic flows, such as small vortices or oceanic fronts near the surface of the ocean. We will study how waves propagating in fronts break and how they extract energy out of fronts. We will also undertake a theoretical study to understand the conservation laws that regulate interactions between internal waves and small-scale geostrophic flows. This work might shed light on processes, observable by SWOT.