Experiments on the interaction of Large-Scale Oceanic Oirculation with Eddies, Jets and Internal Waves using Optical Altimetry

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ABSTRACTOCE-0648575This is an experimental investigation of the oceanic circulation and its small-scale, yet energetic, components. Using a newly discovered laboratory remote-sensing technique which we call optical altimetry, the interaction of the circulation with eddies, internal waves and jet-like concentrations of flow will be studied. The circulation of the subpolar North Atlantic Ocean is the particular focus. There, several external sources of circulation have been identified (wind, deep convection, and incursion of currents from north and south). An internal source of general circulation, the eddy stirring of the potential vorticity (PV) field, will be evaluated in detailed dynamics experiments using idealized ocean basins with significant bottom topographic features. Parallel numerical experiments will be carried out using a layered, hydrostatic ocean model. The specific experiments planned are (i), the concentration of general circulation into jets and fronts with steady flow interacting bottom topography, (ii), large-scale circulation driven by quasi-geostrophic, time-variable flow over a field of complex seafloor ridges and seamounts, (iii), eddy-topography interaction with density stratification including the life-cycle of a baroclinically unstable coastal current and, (iv), internal waves and convection interacting with stratified, gesotrophic flows. Optical altimetry exploits the parabolic shape of the surface of a rotating fluid as a Newtonian telescope, allowing the entire surface elevation field to be imaged with better than 1 micron resolution, and high lateral resolution. By projecting a rainbow image on the surface, we recover accurate elevation, velocity and vorticity fields. Stratified experiments will use interior layer thickness sensing, also optically. The fourth set of experiments requires special comment. Numerical modeling of these high latitude oceans rarely incorporates non-hydrostatic, non-geostrophic dynamics, and in this area 3-dimensional lab experiments can have impressive spatial resolution. With our new experimental capability the back-and-forth interaction among basin-scale circulation and internal waves, fronts, convection and 3-dimensional turbulence can be explored. All are known to be strong in the subpolar oceans. Hydraulic 'down-slope jets' form as flow crosses significant bottom topography, and their interaction with mesoscale cyclonic eddy generation will be investigated; internal wave radiation and trapping by isolated vortices and vortex assemblages will be explored, as will the back-and-forth conversion of energy between boundary-layer turbulence and geostrophic flow.Intellectual Merit: Potential vorticity dynamics is the key, underlying field theory of thecirculation of oceans and atmosphere. It expresses powerful relationships between eddy activity and general circulation. Developing and exploiting this 'PV thinking' is important both as basic science, and as support for important simulations of global climate models, which cannot resolve all the detailed high-latitude processes which control the PV field.Broader impacts: Understanding the ocean climate system is of key importance to the largerproblem of global warming and its predicted effect in slowing the global ocean circulation. Most climate models run with increasing greenhouse gases find a slowing of the Atlantic meridional overturning, by as much as 40%, during this century. If one looks closely, the dynamics of the subpolar Atlantic is a crucial component of this effect. There is interaction of lateral gyre circulations interact with the global meridional overturning circulation. Beyond climate research, this work on basic PV dynamics impacts our understanding of circulations of the atmosphere, and the atmospheres of other planets. It has strong relationships with the fate of Earth's ecosystems under global warming.