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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

Turbulent diffusivity profiles on the shelf and slope at the southern edge of the Canada Basin

Yee, R., R. Musgrave, E. Fine, J. Nash, L. St. Laurent, and R. Pickart, "Turbulent diffusivity profiles on the shelf and slope at the southern edge of the Canada Basin," J. Geophys. Res., 129, doi:10.1029/2023JC019932, 2024.

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1 Mar 2024

Vertical profiles of temperature microstructure at 95 stations were obtained over the Beaufort shelf and shelfbreak in the southern Canada Basin during a November 2018 research cruise. Two methods for estimating the dissipation rates of temperature variance and turbulent kinetic energy were compared using this data set. Both methods require fitting a theoretical spectrum to observed temperature gradient spectra, but differ in their assumptions. The two methods agree for calculations of the dissipation rate of temperature variance, but not for that of turbulent kinetic energy. After applying a rigorous data rejection framework, estimates of turbulent diffusivity and heat flux are made across different depth ranges. The turbulent diffusivity of temperature is typically enhanced by about one order of magnitude in profiles on the shelf compared to near the shelfbreak, and similarly near the shelfbreak compared to profiles with bottom depth >1,000 m. Depth bin means are shown to vary depending on the averaging method (geometric means tend to be smaller than arithmetic means and maximum likelihood estimates). The statistical distributions of heat flux within the surface, cold halocline, and Atlantic water layer change with depth. Heat fluxes are typically <1 Wm-2, but are greater than 50 Wm-2 in ~8% of the overall data. These largest fluxes are located almost exclusively within the surface layer, where temperature gradients can be large.

Characterization of mixing at the edge of a Kuroshio intrusion into the South China Sea: Analysis of thermal variance diffusivity measurements

Sanchez-Rios, A., R.K. Shearman, C.M. Lee, H.L. Simmons, L. St. Laurent, A.J. Lucas, T. Ijichi, and S. Jan, "Characterization of mixing at the edge of a Kuroshio intrusion into the South China Sea: Analysis of thermal variance diffusivity measurements," J. Phys. Oceanogr., EOR, doi:10.1175/JPO-D-23-0007.1, 2024.

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15 Jan 2024

The Kuroshio occasionally carries warm and salty North Pacific Water into fresher waters of the South China Sea, forming a front with a complex temperature-salinity (T-S) structure to the west of the Luzon Strait. In this study, we examine the T-S interleavings formed by alternating layers of North Pacific water with South China Sea water in a front formed during the winter monsoon season of 2014. Using observations from a glider array following a free-floating wave-powered vertical profiling float to calculate the fine-scale parameters Turner angle, Tu, and Richardson number, Ri, we identified areas favorable to double diffusion convection and shear instability observed in a T-S interleaving. We evaluated the contribution of double diffusion convection and shear instabilities to the thermal variance diffusivity, X, using microstructure data and compared it with previous parameterization schemes based on fine-scale properties. We discover that turbulent mixing is not accurately parameterized when both Tu and Ri are within critical ranges (Tu > 60, Ri < 1/4). In particular, X associated with salt finger processes was an order of magnitude higher (6.7 x 10-7 K2 s-1) than in regions where only velocity shear was likely to drive mixing (8.7 x 10-8 K2 s-1).

Microstructure Sensing from Autonomous Platforms

Shroyer, E., and L. St. Laurent, eds. "Microstructure Sensing from Autonomous Platforms," Report of the Office of Naval Research Sponsored Workshop, May 2022, Lake Arrowhead, CA, 32 pp.

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26 Dec 2023

Over the last two decades, autonomous sensing of ocean turbulence has progressed from a niche endeavor to one where commercial off-the-shelf hardware is available broadly to the community. This advancement has opened new sampling possibilities, for example, direct observation of turbulence in tropical cyclones, extended observational records much longer than those afforded by ship-based programs, and co-location of multiple platforms for statistical assessment of the natural variation in mixing. The reality of real-time data delivery of turbulence quantities has also introduced challenges for onboard processing, data compression, and quality control of quantities that naturally vary by many magnitudes within short temporal and spatial scales. Developments within autonomous sensing of ocean turbulence continue through advances in software design for efficient and accurate data delivery and hardware design of multiple form factors and sensor combinations. In May 2022, a small group of US scientists convened a two-day workshop focused on Microstructure Sensing from Autonomous Platforms in Lake Arrowhead, California. Workshop attendees were sponsored by ONR for engineering development in this topic area, and, in the spirit of past ONR workshops, the participants shared results and discussed recent innovations. Conversations ranged from a historical perspective of ocean turbulence measurement, to new hardware integration of turbulence sensors with autonomous platforms, to algorithms for onboard processing and real-time data delivery. Participants were tasked with developing short synopses of their presentations – nominally three pages and a few figures – for wider distribution.

More Publications

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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