Ocean Small Eddies Interaction with Large-scale Circulation and Sea Ice

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Ocean "small eddy motions" at scales of 1-10 km, which are unresolved in all current climate models, may significantly modulate the global ocean circulation and sea ice. Small eddies can produce large vertical velocities (10-100 m/day) and hence efficiently transport heat/buoyancy vertically. Near-surface small-eddy heat flux has been found to be essentially upward and peaks at a large magnitude of ~1000 W/m2 over intervals of days to weeks over the globe, including the ice-covered area. Thus it may cause abrupt and large sea-ice melting events. Small eddies and their buoyancy flux are also found to be actively present at the interior and the abyssal of broad ocean areas. Therefore, such small-eddy buoyancy flux may contribute significantly to ocean overturning circulation according to the transformed Eulerian-mean (TEM) theory. Furthermore, small eddies may exchange large amounts of energy with larger-scale circulation via energy cascade across horizontal and vertical wavenumbers. All of these effects will likely be significant, but have not been well or systematically studied. The long-term goal of my research program is to understand the fundamental physics of the ocean circulation: its dynamics and energetics, the impact from nonlinear scale interactions, and the ocean-ice-atmosphere interaction. My short-term goal is to study the fundamental physics of how small eddies (1-10 km) interact with larger-scale circulation (100 km to global) and sea ice over the timescale of hours to months, often at a process level, using analytical tools and a hierarchy of ocean/ice numerical simulations of global to sub-basin scales. My research group and I will organize this program into four main objectives. The first objective is to investigate how small-eddy driven buoyancy fluxes at the interior and abyssal ocean contribute to the large-scale overturning circulation according to the TEM theory, and how this may modify the classic theories of large-scale overturning circulation by competing with mesoscale eddies and abyssal mixing. The second objective is to investigate how small eddies may nonlinearly supply or draw energy for larger-scale circulation through an inverse or forward cascade across horizontal wavenumbers and baroclinic modes, as well as the sensitivity of such energy interaction with ocean depths and locations. The third objective is to study how the large magnitude of near-surface upward small-eddy heat flux, as already partially identified over ice-covered oceans in simulations and observations, may cause significant ice-melting events and affect the Arctic and Antarctic sea ice budget. The fourth objective is to undertake a theoretical study to understand the generation mechanism of small eddies actively present below the mixed layer in the North Atlantic Ocean and the Southern Ocean. This work will shed light on small-eddy processes observable by SWOT, the future USA-French satellite altimeter to which Canada also contributes.