Internal waves, submesoscale currents and their interactions in the ocean

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The first few tens of meters under the ocean surface contain more heat than the entire atmosphere. It is therefore crucial to understand the influence of the oceans on the world's climate. Density variations and the rotation of the Earth determine the shape and fate of ocean currents. When turbulence arises, mixing moves water and nutrients up from the cold abyss, and heat down from the sun-bathed surface. The friction happening between water molecules in the process of turbulence also removes excess energy in the ocean, closing its energy budget. In the past few years, physical oceanographers have grown increasingly confident that flows that are a few tens of kilometres wide or less are crucial to our understanding of these exchanges. These scales are at least one order of magnitude smaller than the current resolution of numerical climate models, leading to many unresolved processes. In order to properly include them, our community needs to come up with algorithms that are based on a rigorous understanding of the underlying physics to make up for this lack of resolution. This proposal focuses on improving our fundamental understanding of said ocean physics happening at these scales. We aim to investigate the possible routes to turbulence around the ocean boundaries, be they the wind-driven ocean surface or its rough bottom. When it comes to the ocean surface, this proposal also aims to accompany the preparation and first stages of the future Surface Water and Ocean Topography satellite mission, expected to launch in 2022. My group and I will use mathematical theories, numerical simulations of fluid motion, and machine learning algorithms to answer four (categories of) questions: 1. How do internal tides interact with slower, submesoscale currents? Internal tides are internal waves, waves that propagate in the volume of the oceans, and they oscillate at the same frequencies as the tide. Submesoscale currents are usually a few kilometres wide, and induce spinning that is as fast as that induced by Earth's rotation. These two processes are in the crosshairs of SWOT, and crucial for creating turbulence. 2. How does turbulence get created within submesoscale currents? That is, what destabilizes the currents, and can internal waves precipitate their demise? 3. What kind of turbulence do currents create when they encounter underwater topography? Do internal tides or underwater mountain waves play a role? 4. How do internal waves and currents create turbulence in the Arctic Ocean when the sea ice is receding? With this proposal, we plan to hire four graduate students and their replacements once they graduate, and to support a handful of undergraduate research experiences each year.