Strong turbulent mixing induced by internal bores interacting with internal tide-driven vertically sheared flow

2016 ◽  
Vol 43 (5) ◽  
pp. 2094-2101 ◽  
Author(s):  
Eiji Masunaga ◽  
Oliver B. Fringer ◽  
Hidekatsu Yamazaki ◽  
Kazuo Amakasu
Keyword(s):  
Turbulent Mixing ◽  
Internal Tide ◽  
Sheared Flow ◽  
Internal Bores

scholarly journals Energy transformations and dissipation of nonlinear internal waves over New Jersey's continental shelf

2010 ◽  
Vol 17 (4) ◽  
pp. 345-360 ◽  
Author(s):  
E. L. Shroyer ◽  
J. N. Moum ◽  
J. D. Nash
Keyword(s):  
Continental Shelf ◽  
Internal Waves ◽  
Turbulent Mixing ◽  
Internal Tide ◽  
Flux Divergence ◽  
Wave Interactions ◽  
Nonlinear Internal Waves ◽  
Dissipative Loss ◽  
Peak Energy

Abstract. The energetics of large amplitude, high-frequency nonlinear internal waves (NLIWs) observed over the New Jersey continental shelf are summarized from ship and mooring data acquired in August 2006. NLIW energy was typically on the order of 105 Jm−1, and the wave dissipative loss was near 50 W m−1. However, wave energies (dissipations) were ~10 (~2) times greater than these values during a particular week-long period. In general, the leading waves in a packet grew in energy across the outer shelf, reached peak values near 40 km inshore of the shelf break, and then lost energy to turbulent mixing. Wave growth was attributed to the bore-like nature of the internal tide, as wave groups that exhibited larger long-term (lasting for a few hours) displacements of the pycnocline offshore typically had greater energy inshore. For ship-observed NLIWs, the average dissipative loss over the region of decay scaled with the peak energy in waves; extending this scaling to mooring data produces estimates of NLIW dissipative loss consistent with those made using the flux divergence of wave energy. The decay time scale of the NLIWs was approximately 12 h corresponding to a length scale of 35 km (O(100) wavelengths). Imposed on these larger scale energetic trends, were short, rapid exchanges associated with wave interactions and shoaling on a localized topographic rise. Both of these events resulted in the onset of shear instabilities and large energy loss to turbulent mixing.

scholarly journals Climate Process Team on Internal Wave–Driven Ocean Mixing

2017 ◽  
Vol 98 (11) ◽  
pp. 2429-2454 ◽  
Author(s):  
Jennifer A. MacKinnon ◽  
Zhongxiang Zhao ◽  
Caitlin B. Whalen ◽  
Amy F. Waterhouse ◽  
David S. Trossman ◽  
...  
Keyword(s):  
Internal Wave ◽  
Turbulent Mixing ◽  
Low Frequency ◽  
Internal Tide ◽  
Deep Ocean ◽  
Global Ocean ◽  
Primary Role ◽  
Inverse Models ◽  
Lee Waves ◽  
Mixing Rates

Abstract Diapycnal mixing plays a primary role in the thermodynamic balance of the ocean and, consequently, in oceanic heat and carbon uptake and storage. Though observed mixing rates are on average consistent with values required by inverse models, recent attention has focused on the dramatic spatial variability, spanning several orders of magnitude, of mixing rates in both the upper and deep ocean. Away from ocean boundaries, the spatiotemporal patterns of mixing are largely driven by the geography of generation, propagation, and dissipation of internal waves, which supply much of the power for turbulent mixing. Over the last 5 years and under the auspices of U.S. Climate Variability and Predictability Program (CLIVAR), a National Science Foundation (NSF)- and National Oceanic and Atmospheric Administration (NOAA)-supported Climate Process Team has been engaged in developing, implementing, and testing dynamics-based parameterizations for internal wave–driven turbulent mixing in global ocean models. The work has primarily focused on turbulence 1) near sites of internal tide generation, 2) in the upper ocean related to wind-generated near inertial motions, 3) due to internal lee waves generated by low-frequency mesoscale flows over topography, and 4) at ocean margins. Here, we review recent progress, describe the tools developed, and discuss future directions.

scholarly journals Nearshore internal bores and turbulent mixing in southern Monterey Bay

2012 ◽  
Vol 117 (C7) ◽  
pp. n/a-n/a ◽  
Author(s):  
Ryan K. Walter ◽  
C. Brock Woodson ◽  
Robert S. Arthur ◽  
Oliver B. Fringer ◽  
Stephen G. Monismith
Keyword(s):  
Turbulent Mixing ◽  
Monterey Bay ◽  
Internal Bores

The effects of unstable stratification and mean shear on the chemical reaction in grid turbulence

2000 ◽  
Vol 408 ◽  
pp. 39-52 ◽  
Author(s):  
KOUJI NAGATA ◽  
SATORU KOMORI
Keyword(s):  
Chemical Reaction ◽  
Turbulent Mixing ◽  
Mixing Layer ◽  
Stratified Flow ◽  
Laser Doppler Velocimeter ◽  
Grid Turbulence ◽  
Unstable Stratification ◽  
Sheared Flow ◽  
Small Scales ◽  
Neutrally Stratified

The effects of unstable thermal stratification and mean shear on chemical reaction and turbulent mixing were experimentally investigated in reacting and non-reacting liquid mixing-layer flows downstream of a turbulence-generating grid. Experiments were carried out under three conditions: unsheared neutrally stratified, unsheared unstably stratified and sheared neutrally stratified. Instantaneous velocity and concentration were simultaneously measured using the combination of a laser-Doppler velocimeter and a laser-induced fluorescence technique. The results show that the turbulent mixing is enhanced at both large and small scales by buoyancy under unstably stratified conditions and therefore the chemical reaction is strongly promoted. The mean shear acts to enhance the turbulent mixing mainly at large scales. However, the chemical reaction rate in the sheared flow is not as large as in the unstably stratified case with the same turbulence level, since the mixing at small scales in the sheared neutrally stratified flow is weaker than that in the unsheared unstably stratified flow. The unstable stratification is regarded as a better tool to attain unsheared mixing since the shearing stress acting on the fluid is much weaker in the unstably stratified flow than in the sheared flow.

Internal Tide Reflection and Turbulent Mixing on the Continental Slope

2004 ◽  
Vol 34 (5) ◽  
pp. 1117-1134 ◽  
Author(s):  
Jonathan D. Nash ◽  
Eric Kunze ◽  
John M. Toole ◽  
Ray W. Schmitt
Keyword(s):  
Continental Slope ◽  
Turbulent Mixing ◽  
Internal Tide

scholarly journals The Latitudinal Dependence of Shear and Mixing in the Pacific Transiting the Critical Latitude for PSI

2013 ◽  
Vol 43 (1) ◽  
pp. 3-16 ◽  
Author(s):  
J. A. MacKinnon ◽  
M. H. Alford ◽  
Rob Pinkel ◽  
Jody Klymak ◽  
Zhongxiang Zhao
Keyword(s):  
Turbulent Mixing ◽  
Statistical Significance ◽  
Internal Tide ◽  
Latitudinal Dependence ◽  
The Pacific ◽  
Thorpe Scale ◽  
Mixing Rates ◽  
The Pacific Ocean ◽  
Parametric Subharmonic Instability ◽  
Critical Latitude

Abstract Turbulent mixing rates are inferred from measurements spanning 25°–37°N in the Pacific Ocean. The observations were made as part of the Internal Waves Across the Pacific experiment, designed to investigate the long-range fate of the low-mode internal tide propagating north from Hawaii. Previous and companion results argue that, near a critical latitude of 29°N, the internal tide loses energy to high-mode near-inertial motions through parametric subharmonic instability. Here, the authors estimate mixing from several variations of the finescale shear–strain parameterization, as well as Thorpe-scale analysis of overturns. Though all estimated diffusivities are modest in magnitude, average diffusivity in the top kilometer shows a factor of 2–4 elevation near and equatorward of 29°N. However, given intrinsic uncertainty and the strong temporal variability of diffusivity observed in long mooring records, the meridional mixing pattern is found to be near the edge of statistical significance.

scholarly journals Turbulent mixing and wave radiation in non-Boussinesq internal bores

2012 ◽  
Vol 24 (8) ◽  
pp. 082106 ◽  
Author(s):  
Zac Borden ◽  
Tilman Koblitz ◽  
Eckart Meiburg
Keyword(s):  
Turbulent Mixing ◽  
Wave Radiation ◽  
Internal Bores

scholarly journals Climatic Impacts of Parameterized Local and Remote Tidal Mixing

2016 ◽  
Vol 29 (10) ◽  
pp. 3473-3500 ◽  
Author(s):  
Angélique Melet ◽  
Sonya Legg ◽  
Robert Hallberg
Keyword(s):  
Turbulent Mixing ◽  
Water Mass ◽  
Internal Tide ◽  
Meridional Overturning Circulation ◽  
Internal Tides ◽  
Tidal Mixing ◽  
Primary Role ◽  
Ocean Heat Uptake ◽  
Meridional Overturning ◽  
The Impact

Abstract Turbulent mixing driven by breaking internal tides plays a primary role in the meridional overturning and oceanic heat budget. Most current climate models explicitly parameterize only the local dissipation of internal tides at the generation sites, representing the remote dissipation of low-mode internal tides that propagate away through a uniform background diffusivity. In this study, a simple energetically consistent parameterization of the low-mode internal-tide dissipation is derived and implemented in the Geophysical Fluid Dynamics Laboratory Earth System Model with GOLD component (GFDL-ESM2G). The impact of remote and local internal-tide dissipation on the ocean state is examined using a series of simulations with the same total amount of energy input for mixing, but with different scalings of the vertical profile of dissipation with the stratification and with different idealized scenarios for the distribution of the low-mode internal-tide energy dissipation: uniformly over ocean basins, continental slopes, or continental shelves. In these idealized scenarios, the ocean state, including the meridional overturning circulation, ocean ventilation, main thermocline thickness, and ocean heat uptake, is particularly sensitive to the vertical distribution of mixing by breaking low-mode internal tides. Less sensitivity is found to the horizontal distribution of mixing, provided that distribution is in the open ocean. Mixing on coastal shelves only impacts the large-scale circulation and water mass properties where it modifies water masses originating on shelves. More complete descriptions of the distribution of the remote part of internal-tide-driven mixing, particularly in the vertical and relative to water mass formation regions, are therefore required to fully parameterize ocean turbulent mixing.

scholarly journals Three-Dimensional Distribution of Turbulent Mixing in the South China Sea

2016 ◽  
Vol 46 (3) ◽  
pp. 769-788 ◽  
Author(s):  
Qingxuan Yang ◽  
Wei Zhao ◽  
Xinfeng Liang ◽  
Jiwei Tian
Keyword(s):  
South China Sea ◽  
South China ◽  
Turbulent Mixing ◽  
Three Dimensional ◽  
Internal Tide ◽  
The South China Sea ◽  
The South ◽  
China Sea ◽  
Dimensional Distribution ◽  
First Time

AbstractA three-dimensional distribution of turbulent mixing in the South China Sea (SCS) is obtained for the first time, using the Gregg–Henyey–Polzin parameterization and hydrographic observations from 2005 to 2012. Results indicate that turbulent mixing generally increases with depth in the SCS, reaching the order of 10−2 m2 s−1 at depth. In the horizontal direction, turbulence is more active in the northern SCS than in the south and is more active in the east than the west. Two mixing “hotspots” are identified in the bottom water of the Luzon Strait and Zhongsha Island Chain area, where diapycnal diffusivity values are around 3 × 10−2 m2 s−1. Potential mechanisms responsible for these spatial patterns are discussed, which include internal tide, bottom bathymetry, and near-inertial energy.

scholarly journals Turbulent Mixing in a Deep Fracture Zone on the Mid-Atlantic Ridge

2017 ◽  
Vol 47 (8) ◽  
pp. 1873-1896 ◽  
Author(s):  
Louis Clément ◽  
Andreas M. Thurnherr ◽  
Louis C. St. Laurent
Keyword(s):  
Kinetic Energy ◽  
Turbulent Mixing ◽  
Lower Layer ◽  
Tidal Flow ◽  
Internal Tide ◽  
Internal Tides ◽  
Exchange Flow ◽  
Inertial Waves ◽  
Fracture Zones ◽  
Mean Flow

AbstractMidocean ridge fracture zones channel bottom waters in the eastern Brazil Basin in regions of intensified deep mixing. The mechanisms responsible for the deep turbulent mixing inside the numerous midocean fracture zones, whether affected by the local or the nonlocal canyon topography, are still subject to debate. To discriminate those mechanisms and to discern the canyon mean flow, two moorings sampled a deep canyon over and away from a sill/contraction. A 2-layer exchange flow, accelerated at the sill, transports 0.04–0.10-Sv (1 Sv ≡ 106 m3 s−1) up canyon in the deep layer. At the sill, the dissipation rate of turbulent kinetic energy ε increases as measured from microstructure profilers and as inferred from a parameterization of vertical kinetic energy. Cross-sill density and microstructure transects reveal an overflow potentially hydraulically controlled and modulated by fortnightly tides. During spring to neap tides, ε varies from O(10−9) to O(10−10) W kg−1 below 3500 m around the 2-layer interface. The detection of temperature overturns during tidal flow reversal, which almost fully opposes the deep up-canyon mean flow, confirms the canyon middepth enhancement of ε. The internal tide energy flux, particularly enhanced at the sill, compares with the lower-layer energy loss across the sill. Throughout the canyon away from the sill, near-inertial waves with downward-propagating energy dominate the internal wave field. The present study underlines the intricate pattern of the deep turbulent mixing affected by the mean flow, internal tides, and near-inertial waves.

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