Louis St. Laurent
Senior Principal Oceanographer
Model Parameterization, Internal Tides, Abyssal Circulation, Ocean Energetics
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, wavewave 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.
B.S. Physics, University of Rhode Island, 1994
Ph.D. Physical Oceanography, MIT and WHOI, 1999
2000-present and while at APL-UW
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.
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.
Boundary layer energetics of rapid wind and wave forced mixing events
Skyllingstad, E.D., R.M. Samelson, H. Simmons, L. St. Laurent, S. Merrifield, T. Klenz, and L. Centuroni, "Boundary layer energetics of rapid wind and wave forced mixing events," J. Phys. Oceanogr., 53, 1887-1900, doi:10.1175/JPO-D-22-0150.1, 2023.
5 May 2023
The observed development of deep mixed layers and the dependence of intense, deep-mixing events on wind and wave conditions are studied using an ocean LES model with and without an imposed Stokes-drift wave forcing. Model results are compared to glider measurements of the ocean vertical temperature, salinity and turbulence kinetic energy (TKE) dissipation rate structure collected in the Icelandic Basin. Observed wind stress reached 0.8 N m-2 with significant wave height of 46 m, while boundary layer depths reached 180 m. We find that wave forcing, via the commonly used Stokes drift vortex force parameterization, is crucial for accurate prediction of boundary layer depth as characterized by measured and predicted TKE dissipation rate profiles. Analysis of the boundary layer kinetic energy (KE) budget using a modified total Lagrangian-mean energy equation, derived for the wave averaged Boussinesq equations by requiring that the rotational inertial terms vanish identically as in the standard energy budget without Stokes forcing, suggests that wind work should be calculated using both the surface current and surface Stokes drift. A large percentage of total wind energy is transferred to model TKE via regular and Stokes drift shear production and dissipated. However, resonance by clockwise rotation of the winds can greatly enhance the generation of inertial current mean KE (MKE). Without resonance, TKE production is about 5 times greater than MKE generation, whereas with resonance this ratio decreases to roughly 2. The results have implications for the problem of estimating the global kinetic energy budget of the ocean.
Shear turbulence in the high-wind Southern Ocean using direct measurements
Ferris, L., C.A. Clayson, D. Gong, S. Merrifield, E.L. Shroyer, M. Smith, and L. St. Laurent, "Shear turbulence in the high-wind Southern Ocean using direct measurements," J. Phys. Oceanogr., 52, 2325-2341, 10.1175/JPO-D-21-0015.1, 2022.
8 Jun 2022
The ocean surface boundary layer is a gateway of energy transfer into the ocean. Wind-driven shear and meteorologically forced convection inject turbulent kinetic energy into the surface boundary layer, mixing the upper ocean and transforming its density structure. In the absence of direct observations or the capability to resolve sub-grid scale 3D turbulence in operational ocean models, the oceanography community relies on surface boundary layer similarity scalings (BLS) of shear and convective turbulence to represent this mixing. Despite their importance, near-surface mixing processes (and ubiquitous BLS representations of these processes) have been under-sampled in high energy forcing regimes such as the Southern Ocean. With the maturing of autonomous sampling platforms, there is now an opportunity to collect high-resolution spatial and temporal measurements in the full range of forcing conditions. Here, we characterize near-surface turbulence under strong wind forcing using the first long-duration glider microstructure survey of the Southern Ocean. We leverage these data to show that the measured turbulence is significantly higher than standard shear-convective BLS in the shallower parts of the surface boundary layer and lower than standard shear-convective BLS in the deeper parts of the surface boundary layer; the latter of which is not easily explained by present wave-effect literature. Consistent with the CBLAST (Coupled Boundary Layers and Air Sea Transfer) low winds experiment, this bias has the largest magnitude and spread in shallowest 10% of the actively mixing layer under low-wind and breaking wave conditions, when relatively low levels of turbulent kinetic energy (TKE) in surface regime are easily biased by wave events.