Stratified turbulence and mixing efficiency in a salt wedge estuary
MetadataShow full item record
KeywordCirculation/ Dynamics; Mixing; Shear structure/flows; Turbulence; Observational techniques and algorithms; Ship observations
High-resolution observations of velocity, salinity, and turbulence quantities were collected in a salt wedge estuary to quantify the efficiency of stratified mixing in a high-energy environment. During the ebb tide, a midwater column layer of strong shear and stratification developed, exhibiting near-critical gradient Richardson numbers and turbulent kinetic energy (TKE) dissipation rates greater than 10−4 m2 s−3, based on inertial subrange spectra. Collocated estimates of scalar variance dissipation from microconductivity sensors were used to estimate buoyancy flux and the flux Richardson number Rif. The majority of the samples were outside the boundary layer, based on the ratio of Ozmidov and boundary length scales, and had a mean Rif = 0.23 ± 0.01 (dissipation flux coefficient Γ = 0.30 ± 0.02) and a median gradient Richardson number Rig = 0.25. The boundary-influenced subset of the data had decreased efficiency, with Rif = 0.17 ± 0.02 (Γ = 0.20 ± 0.03) and median Rig = 0.16. The relationship between Rif and Rig was consistent with a turbulent Prandtl number of 1. Acoustic backscatter imagery revealed coherent braids in the mixing layer during the early ebb and a transition to more homogeneous turbulence in the midebb. A temporal trend in efficiency was also visible, with higher efficiency in the early ebb and lower efficiency in the late ebb when the bottom boundary layer had greater influence on the flow. These findings show that mixing efficiency of turbulence in a continuously forced, energetic, free shear layer can be significantly greater than the broadly cited upper bound from Osborn of 0.15–0.17.
Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 1769-1783, doi:10.1175/JPO-D-15-0193.1.
Showing items related by title, author, creator and subject.
Tochko, John Steven (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1978-02)The design and operation of a unique flow measuring instrument for bottom boundary layer studies in the marine environment is documented. The effectiveness of the instrument in acquiring data with which models of near ...
Rainville, Luc; Winsor, Peter (American Geophysical Union, 2008-04-30)Turbulent-scale temperature and conductivity were measured during the pan-arctic Beringia 2005 Expedition. The rates of dissipation of thermal variance and diapycnal diffusivities are calculated along a section from Alaska ...
Observations of turbulence, internal waves and background flows : an inquiry into the relationships between scales of motion Polzin, Kurt L. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1992-09)Oceanic profiles of temperature, salinity, horizontal velocity, rate of dissipation of turbulent kinetic energy (ε) and rate of dissipation of thermal variance (χ) are used to examine the parameterization of turbulent ...