Enhanced diapycnal mixing with polarity-reversing internal solitary waves revealed by seismic reflection data

Abstract. Shoaling internal solitary waves near the Dongsha Atoll in the South China Sea dissipate their energy and enhance diapycnal mixing, which have an important impact on the oceanic environment and primary productivity. The enhanced diapycnal mixing is patchy and instantaneous. Evaluating its spatiotemporal distribution requires comprehensive observation data. Fortunately, seismic oceanography meets the requirements, thanks to its high spatial resolution and large spatial coverage. In this paper, we studied three internal solitary waves in reversing polarity near the Dongsha Atoll and calculated their spatial distribution of diapycnal diffusivity. Our results show that the average diffusivities along three survey lines are 2 orders of magnitude larger than the open-ocean value. The average diffusivity in internal solitary waves with reversing polarity is 3 times that of the non-polarity reversal region. The diapycnal diffusivity is higher at the front of one internal solitary wave and gradually decreases from shallow to deep water in the vertical direction. Our results also indicate that (1) the enhanced diapycnal diffusivity is related to reflection seismic events, (2) convective instability and shear instability may both contribute to the enhanced diapycnal mixing in the polarity-reversing process, and (3) the difference between our results and Richardson-number-dependent turbulence parameterizations is about 2–3 orders of magnitude, but its vertical distribution is almost the same.

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Enhanced diapycnal mixing by polarity-reversing internal solitary waves in the South China Sea

10.5194/npg-2021-21 ◽

2021 ◽

Author(s):

Yi Gong ◽

Haibin Song ◽

Zhongxiang Zhao ◽

Yongxian Guan ◽

Kun Zhang ◽

...

Keyword(s):

South China Sea ◽

Solitary Wave ◽

Solitary Waves ◽

South China ◽

The South China Sea ◽

Internal Solitary Wave ◽

Internal Solitary Waves ◽

Diapycnal Mixing ◽

Dongsha Atoll ◽

Diapycnal Diffusivity

Abstract. Shoaling internal solitary waves near the Dongsha Atoll in the South China Sea dissipate their energy and thus enhance diapycnal mixing, which have an important impact on the oceanic environment and primary productivity. The enhanced diapycnal mixing is patchy and instantaneous. Evaluating its spatiotemporal distribution requires comprehensive observation data. Fortunately, seismic oceanography meets the requirements, thanks to its high spatial resolution and large spatial range. In this paper, we studied three internal solitary waves in reversing polarity near the Dongsha Atoll, and calculated the spatial distribution of resultant diapycnal diffusivity. Our results show that the average diffusivities along three survey lines are two orders of magnitude larger than the open-ocean value. The average diffusivity in the internal solitary wave with reversing polarity is three times that of the non-polarity-reversal region. The diapycnal diffusivity is higher at the front of one internal solitary wave, and gradually decreases from shallow to deep water in the vertical direction. Our results also indicates that (1) the enhanced diapycnal diffusivity is related to reflection seismic events; (2) convective instability and shear instability may both contribute to the enhanced diapycnal mixing in the polarity-reversing process; and (3) the difference between our and previous diffusivity profiles is about 2–3 orders of magnitude, but their vertical distribution is almost the same.

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A regularized model for strongly nonlinear internal solitary waves

Journal of Fluid Mechanics ◽

10.1017/s0022112009006594 ◽

2009 ◽

Vol 629 ◽

pp. 73-85 ◽

Cited By ~ 21

Author(s):

WOOYOUNG CHOI ◽

RICARDO BARROS ◽

TAE-CHANG JO

Keyword(s):

Stability Analysis ◽

Solitary Wave ◽

Solitary Waves ◽

Wave Solution ◽

Wave Amplitude ◽

Solitary Wave Solution ◽

Shear Instability ◽

Internal Solitary Waves ◽

Strongly Nonlinear ◽

Regularized Model

The strongly nonlinear long-wave model for large amplitude internal waves in a two-layer system is regularized to eliminate shear instability due to the wave-induced velocity jump across the interface. The model is written in terms of the horizontal velocities evaluated at the top and bottom boundaries instead of the depth-averaged velocities, and it is shown through local stability analysis that internal solitary waves are locally stable to perturbations of arbitrary wavelengths if the wave amplitudes are smaller than a critical value. For a wide range of depth and density ratios pertinent to oceanic conditions, the critical wave amplitude is close to the maximum wave amplitude and the regularized model is therefore expected to be applicable to the strongly nonlinear regime. The regularized model is solved numerically using a finite-difference method and its numerical solutions support the results of our linear stability analysis. It is also shown that the solitary wave solution of the regularized model, found numerically using a time-dependent numerical model, is close to the solitary wave solution of the original model, confirming that the two models are asymptotically equivalent.

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Internal solitary waves on the NW African shelf: A heuristic approach to localize diapycnal mixing hotspots

Continental Shelf Research ◽

10.1016/j.csr.2021.104492 ◽

2021 ◽

pp. 104492

Author(s):

Mathieu Gentil ◽

France Floc'h ◽

Thomas Meunier ◽

Angel Ruiz-Angulo ◽

Gildas Roudaut ◽

...

Keyword(s):

Solitary Waves ◽

Heuristic Approach ◽

Internal Solitary Waves ◽

Diapycnal Mixing

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Convectively induced shear instability in large amplitude internal solitary waves

Physics of Fluids ◽

10.1063/1.3030947 ◽

2008 ◽

Vol 20 (12) ◽

pp. 126601 ◽

Cited By ~ 26

Author(s):

M. Carr ◽

D. Fructus ◽

J. Grue ◽

A. Jensen ◽

P. A. Davies

Keyword(s):

Solitary Waves ◽

Large Amplitude ◽

Shear Instability ◽

Internal Solitary Waves

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A model for large-amplitude internal solitary waves with trapped cores

Nonlinear Processes in Geophysics ◽

10.5194/npg-17-303-2010 ◽

2010 ◽

Vol 17 (4) ◽

pp. 303-318 ◽

Cited By ~ 26

Author(s):

K. R. Helfrich ◽

B. L. White

Keyword(s):

Solitary Waves ◽

Large Amplitude ◽

Numerical Solutions ◽

Initial Conditions ◽

Matching Condition ◽

Shear Instability ◽

Internal Solitary Waves ◽

Ambient Flow ◽

The Core ◽

Core Boundary

Abstract. Large-amplitude internal solitary waves in continuously stratified systems can be found by solution of the Dubreil-Jacotin-Long (DJL) equation. For finite ambient density gradients at the surface (bottom) for waves of depression (elevation) these solutions may develop recirculating cores for wave speeds above a critical value. As typically modeled, these recirculating cores contain densities outside the ambient range, may be statically unstable, and thus are physically questionable. To address these issues the problem for trapped-core solitary waves is reformulated. A finite core of homogeneous density and velocity, but unknown shape, is assumed. The core density is arbitrary, but generally set equal to the ambient density on the streamline bounding the core. The flow outside the core satisfies the DJL equation. The flow in the core is given by a vorticity-streamfunction relation that may be arbitrarily specified. For simplicity, the simplest choice of a stagnant, zero vorticity core in the frame of the wave is assumed. A pressure matching condition is imposed along the core boundary. Simultaneous numerical solution of the DJL equation and the core condition gives the exterior flow and the core shape. Numerical solutions of time-dependent non-hydrostatic equations initiated with the new stagnant-core DJL solutions show that for the ambient stratification considered, the waves are stable up to a critical amplitude above which shear instability destroys the initial wave. Steadily propagating trapped-core waves formed by lock-release initial conditions also agree well with the theoretical wave properties despite the presence of a "leaky" core region that contains vorticity of opposite sign from the ambient flow.

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Internal Solitary Waves with shear: beyond DJL theory

10.5194/egusphere-egu2020-4287 ◽

2020 ◽

Author(s):

Marek Stastna ◽

Aaron Coutino ◽

Ryan Walter

Keyword(s):

Solitary Wave ◽

Solitary Waves ◽

Wave Train ◽

Theoretical Description ◽

Internal Solitary Wave ◽

Shear Instability ◽

Internal Solitary Waves ◽

Wave Trains ◽

Set Up ◽

Background Shear

<p>While background shear is ubiquitous in the natural environment, the vast majority of theoretical and numerical studies of internal solitary waves do not include a background shear. &#160;Walter et al 2016, Continental Shelf Research reported on measurements in Monterey Bay in which large amplitude internal solitary wave trains were observed but corresponding waves could not be computed from DJL theory due to the strength of the background shear. &#160;In this talk I will revisit this issue using a classical stratified adjustment set up. &#160;For the case of an exponential, surface trapped background current I will demonstrate that internal solitary wave trains with and without trapped cores coexist with a substantial region dominated by stratified shear instability and/or Rayleigh Taylor instability. &#160;I will then demonstrate the type of internal wave train that results in cases when the the variational formulation of the DJL equation fails to converge. I will speculate on implications for theoretical description of such waves and for more realistic simulations in the coastal ocean.</p>

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