St. Laurent Louis C.

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St. Laurent
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Louis C.
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  • Article
    Vertical kinetic energy and turbulent dissipation in the ocean
    (John Wiley & Sons, 2015-09-21) Thurnherr, Andreas M. ; Kunze, Eric ; Toole, John M. ; St. Laurent, Louis C. ; Richards, Kelvin J. ; Ruiz-Angulo, Angel
    Oceanic internal waves are closely linked to turbulence. Here a relationship between vertical wave number (kz) spectra of fine-scale vertical kinetic energy (VKE) and turbulent dissipation ε is presented using more than 250 joint profiles from five diverse dynamic regimes, spanning latitudes between the equator and 60°. In the majority of the spectra VKE varies as inline image. Scaling VKE with inline image collapses the off-equatorial spectra to within inline image but underestimates the equatorial spectrum. The simple empirical relationship between VKE and ε fits the data better than a common shear-and-strain fine-scale parameterization, which significantly underestimates ε in the two data sets that are least consistent with the Garrett-Munk (GM) model. The new relationship between fine-scale VKE and dissipation rate can be interpreted as an alternative, single-parameter scaling for turbulent dissipation in terms of fine-scale internal wave vertical velocity that requires no reference to the GM model spectrum.
  • Article
    Modification of turbulent dissipation rates by a deep Southern Ocean eddy
    (John Wiley & Sons, 2015-05-07) Sheen, Katy L. ; Brearley, J. Alexander ; Naveira Garabato, Alberto C. ; Smeed, David A. ; St. Laurent, Louis C. ; Meredith, Michael P. ; Thurnherr, Andreas M. ; Waterman, Stephanie N.
    The impact of a mesoscale eddy on the magnitude and spatial distribution of diapycnal ocean mixing is investigated using a set of hydrographic and microstructure measurements collected in the Southern Ocean. These data sampled a baroclinic, middepth eddy formed during the disintegration of a deep boundary current. Turbulent dissipation is suppressed within the eddy but is elevated by up to an order of magnitude along the upper and lower eddy boundaries. A ray tracing approximation is employed as a heuristic device to elucidate how the internal wave field evolves in the ambient velocity and stratification conditions accompanying the eddy. These calculations are consistent with the observations, suggesting reflection of internal wave energy from the eddy center and enhanced breaking through critical layer processes along the eddy boundaries. These results have important implications for understanding where and how internal wave energy is dissipated in the presence of energetic deep geostrophic flows.
  • Article
    Global patterns of diapycnal mixing from measurements of the turbulent dissipation rate
    (American Meteorological Society, 2014-07) Waterhouse, Amy F. ; MacKinnon, Jennifer A. ; Nash, Jonathan D. ; Alford, Matthew H. ; Kunze, Eric ; Simmons, Harper L. ; Polzin, Kurt L. ; St. Laurent, Louis C. ; Sun, Oliver M. T. ; Pinkel, Robert ; Talley, Lynne D. ; Whalen, Caitlin B. ; Huussen, Tycho N. ; Carter, Glenn S. ; Fer, Ilker ; Waterman, Stephanie N. ; Naveira Garabato, Alberto C. ; Sanford, Thomas B. ; Lee, Craig M.
    The authors present inferences of diapycnal diffusivity from a compilation of over 5200 microstructure profiles. As microstructure observations are sparse, these are supplemented with indirect measurements of mixing obtained from (i) Thorpe-scale overturns from moored profilers, a finescale parameterization applied to (ii) shipboard observations of upper-ocean shear, (iii) strain as measured by profiling floats, and (iv) shear and strain from full-depth lowered acoustic Doppler current profilers (LADCP) and CTD profiles. Vertical profiles of the turbulent dissipation rate are bottom enhanced over rough topography and abrupt, isolated ridges. The geography of depth-integrated dissipation rate shows spatial variability related to internal wave generation, suggesting one direct energy pathway to turbulence. The global-averaged diapycnal diffusivity below 1000-m depth is O(10−4) m2 s−1 and above 1000-m depth is O(10−5) m2 s−1. The compiled microstructure observations sample a wide range of internal wave power inputs and topographic roughness, providing a dataset with which to estimate a representative global-averaged dissipation rate and diffusivity. However, there is strong regional variability in the ratio between local internal wave generation and local dissipation. In some regions, the depth-integrated dissipation rate is comparable to the estimated power input into the local internal wave field. In a few cases, more internal wave power is dissipated than locally generated, suggesting remote internal wave sources. However, at most locations the total power lost through turbulent dissipation is less than the input into the local internal wave field. This suggests dissipation elsewhere, such as continental margins.
  • Preprint
    Shoaling of large-amplitude nonlinear internal waves at Dongsha Atoll in the northern South China Sea
    ( 2012-02-10) Fu, Ke-Hsien ; Wang, YuHuai ; St. Laurent, Louis C. ; Simmons, Harper L. ; Wang, Wang
    Shoaling of large-amplitude (~100 m) nonlinear internal waves over a steep slope (~3°) in water depths between 100 m and 285 m near Dongsha Atoll in the northern South China Sea is examined with an intensive array of thermistor moorings and a bottom mounted Acoustic Doppler Current Profiler. During the 44 h study period in May 5–7, 2008, there were four groups of large internal waves with semidiurnal modulation. In each wave group a rapid transition occurred during the shoaling, such that the front face of the leading depression wave elongated and plunged to the bottom and the rear face steepened and transformed into a bottom-trapped elevation wave. The transitions occur in water depths of 200 m and deeper, and represent the largest documented internal wave shoaling events. The observations repeatedly capture the detailed temperature and velocity structures of the incident plunging waves. Strong horizontal convergence and intense upward motion are found at the leading edge of transformed elevation waves, suggesting flow separation near the bottom. The observations are compared with the previous observations and model studies. The implication of the shoaling internal waves on coral reef ecology also is discussed.