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Louis St. Laurent

Senior Principal Oceanographer

Email

lstlaurent@apl.uw.edu

Research Interests

Model Parameterization, Internal Tides, Abyssal Circulation, Ocean Energetics

Biosketch

Louis St. Laurent's research focuses on the influence of small-scale physical phenomena on the large-scale ocean circulation. The thermodynamic properties of the ocean, such as temperature, salinity, and buoyancy, and dynamic properties, such as momentum, energy, and vorticity, are governed by numerous hydrodynamic processes. These include:

- Turbulent processes, such as diffusion and mixing
- Internal waves and internal tides, wave–wave interactions
- Boundary-layer processes, such as friction and topographic drag
- Buoyancy forcing, heating and cooling by the atmosphere
- Convection, double diffusion, and hydrostatic instability

These studies generally focus on energy exchanges between different classes of fluid motion. This includes the transfer of tidal energy that occurs when large-scale tidal flows interact with the topography of the seafloor to produce waves. These investigations are based on the analysis of oceanographic data, including direct measurements of turbulence made during sea-going field programs.

Education

B.S. Physics, University of Rhode Island, 1994

Ph.D. Physical Oceanography, MIT and WHOI, 1999

Publications

2000-present and while at APL-UW

How variable is mixing efficiency in the abyss?

Ijichi, T., L. St. Laurent, K.L. Polzin, and J.M. Toole, "How variable is mixing efficiency in the abyss?" Geophys. Res. Lett., 47, doi:10.1029/2019GL086813, 2020.

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16 Apr 2020

Mixing efficiency is an important turbulent flow property in fluid dynamics, whose variability potentially affects the large‐scale ocean circulation. However, there are several confusing definitions. Here we compare and contrast patch‐wise versus bulk estimates of mixing efficiency in the abyss by revisiting data from previous extensive field surveys in the Brazil Basin. Observed patch‐wise efficiency is highly variable over a wide range of turbulence intensity. Bulk efficiency is dominated by rare extreme turbulence events. In the case where enhanced near‐bottom turbulence is thought to be driven by breaking of small‐scale internal tides, the estimated bulk efficiency is 20%, close to the conventional value of 17%. On the other hand, where enhanced near‐bottom turbulence appears to be convectively driven by hydraulic overflows, bulk efficiency is suggested to be as large as 45%, which has implications for a further significant role of overflow mixing on deep‐water mass transformation.

FLEAT: A multiscale observational and modeling program to understand how topography affects flows in the western North Pacific

Johnston, T.M.S., and 23 others including L. St. Laurent, "FLEAT: A multiscale observational and modeling program to understand how topography affects flows in the western North Pacific," Oceanography, 32, 10-21, doi:10.5670/oceanog.2019.407, 2019.

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1 Dec 2019

Using a combination of models and observations, the US Office of Naval Research Flow Encountering Abrupt Topography (FLEAT) initiative examines how island chains and submerged ridges affect open ocean current systems, from the hundreds of kilometer scale of large current features to the millimeter scale of turbulence. FLEAT focuses on the western Pacific, mainly on equatorial currents that encounter steep topography near the island nation of Palau. Wake eddies and lee waves as small as 1 km were observed to form as these currents flowed around or over the steep topography. The direction and vertical structure of the incident flow varied over tidal, inertial, seasonal, and interannual timescales, with implications for downstream flow. Models incorporated tides and had grids with resolutions of hundreds of meters to enable predictions of flow transformations as waters encountered and passed around Palau’s islands. In addition to making scientific advances, FLEAT had a positive impact on the local Palauan community by bringing new technology to explore local waters, expanding the country’s scientific infrastructure, maintaining collaborations with Palauan partners, and conducting outreach activities aimed at elementary and high school students, US embassy personnel, and Palauan government officials.

Turbulence and vorticity in the wake of Palau

St. Laurent, L., T. Ijichi, S.T. Merrifield, J. Shapiro, and H.L. Simmons, "Turbulence and vorticity in the wake of Palau," Oceanography, 32, 102-109, doi:10.5670/oceanog.2019.416, 2019.

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1 Dec 2019

The interaction of flow with steep island and ridge topography at the Palau island chain leads to rich vorticity fields that generate a cascade of motions. The energy transfer to small scales removes energy from the large-scale mean flow of the equatorial current systems and feeds energy to the fine and microstructure scales where instability mechanisms lead to turbulence and dissipation. Until now, direct assessments of the turbulence associated with island wakes have received only minimal attention. Here, we examine data collected from an ocean glider equipped with microstructure sensors that flew in the island wake of Palau. We use a combination of submesoscale modeling and direct observation to quantify the relationship between vorticity and turbulence levels. We find that direct wind-driven mixing only accounts for about 10% of the observed turbulence levels, suggesting that most of the energy for mixing is extracted from the shear associated with the vorticity field in the island’s wake. Below the surface layer, enhanced turbulence correlates with the phase and magnitude of the relative vorticity and strain levels of the mesoscale flow.

Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center
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