scholarly journals Shore-Based Video Observations of Nonlinear Internal Waves across the Inner Shelf *,+

2014 ◽  
Vol 31 (3) ◽  
pp. 714-728 ◽  
Author(s):  
Sutara H. Suanda ◽  
John A. Barth ◽  
Rob A. Holman ◽  
John Stanley
Keyword(s):  
Internal Wave ◽  
Internal Waves ◽  
Propagation Speed ◽  
Surface Expression ◽  
Inner Shelf ◽  
Average Width ◽  
Pixel Intensity ◽  
Nonlinear Internal Waves ◽  
Video Observations

Abstract Shore-based video remote sensing is used to observe and continually monitor nonlinear internal waves propagating across the inner shelf. Month-long measurements of velocity from bottom-mounted acoustic Doppler current profilers and temperature from thermistor chains at the 10- and 20-m isobaths are combined with sea surface imagery from a suite of cameras (Argus) to provide a kinematic description of 11 borelike internal waves as they propagate across the central Oregon inner shelf. The surface expression of these waves, commonly seen by eye as alternating rough and smooth bands, are identified by increased pixel intensity in Argus imagery (average width 39 ± 6 m), caused by the convergence of internal wave-driven surface currents. These features are tracked through time and space using 2-min time exposure images and then compared to wave propagation speed and direction from in situ measurements. Internal waves are refracted by bathymetry, and the measured wave speed (~0.15 m s−1) is higher than predicted by linear theory (<0.1 m s−1). Propagating internal waves are also visible in subsampled Argus pixel time series (hourly collections of 17 min worth of 2-Hz pixel intensity from a subset of locations), thus extending the observational record to times without an in situ presence. Results from this 5-month record show that the preferred sea state for successful video observations occurs for wind speeds of 2–5 m s−1. Continued video measurements and analysis of extensive existing Argus data will allow a statistical estimate of internal wave occurrence at a variety of inner-shelf locations.

scholarly journals Estimation of Propagation Speed and Direction of Nonlinear Internal Waves from Underway and Moored Measurements

2021 ◽  
Vol 9 (10) ◽  
pp. 1089
Author(s):  
Seung-Woo Lee ◽  
Sung-Hyun Nam
Keyword(s):  
Internal Waves ◽  
Ocean Circulation ◽  
Doppler Shift ◽  
Time Lag ◽  
Propagation Speed ◽  
Propagation Direction ◽  
Practical Significance ◽  
Nonlinear Internal Waves ◽  
In Situ Data

Propagation speed and direction of nonlinear internal waves (NLIWs) are important parameters for understanding the generation and propagation of waves, and ultimately clarifying regional ocean circulation. However, these parameters cannot be directly measured from in-situ instruments, but can only be estimated from post-processing in situ data. Herein, we present two methods and an optimal approach to estimate the propagation speed and direction of waves using underway and moored observations. The Doppler shift method estimates these parameters from apparent observations concerning a moving ship using the Doppler shift induced by the changing relative distance of the NLIWs from the moving ship. The time lag method estimates the parameters using the distance between two locations of the NLIW observed at different times and the time lag. To optimize the speed and direction of NLIWs, the difference in the propagation direction independently estimated by the two methods needs to be minimized concerning the optimal propagation speed to yield the optimal propagation direction. The methods were applied to two cases observed in the northern East China Sea in May 2015 and August 2018. This study has practical significance for better estimating the propagation speed and direction of NILWs particularly over a broad continental shelf.

Study of Nonlinear Internal Waves and Impact on Offshore Drilling Units

2011 ◽  
Author(s):  
Nishu V. Kurup ◽  
Shan Shi ◽  
Zhongmin Shi ◽  
Wenju Miao ◽  
Lei Jiang
Keyword(s):  
Numerical Model ◽  
South China Sea ◽  
Internal Wave ◽  
Internal Waves ◽  
South China ◽  
Andaman Sea ◽  
Offshore Drilling ◽  
Nonlinear Internal Waves ◽  
Drilling Operations ◽  
Drilling System

Internal waves near the ocean surface have been observed in many parts of the world including the Andaman Sea, Sulu Sea and South China Sea among others. The factors that cause and propagate these large amplitude waves include bathymetry, density stratification and ocean currents. Although their effects on floating drilling platforms and its riser systems have not been extensively studied, these waves have in the past seriously disrupted offshore exploration and drilling operations. In particular a drill pipe was ripped from the BOP and lost during drilling operations in the Andaman sea. Drilling riser damages were also reported from the south China Sea among other places. The purpose of this paper is to present a valid numerical model conforming to the physics of weakly nonlinear internal waves and to study the effects on offshore drilling semisubmersibles and riser systems. The pertinent differential equation that captures the physics is the Korteweg-de Vries (KdV) equation which has a general solution involving Jacobian elliptical functions. The solution of the Taylor Goldstein equation captures the effects of the pycnocline. Internal wave packets with decayed oscillations as observed from satellite pictures are specifically modeled. The nonlinear internal waves are characterized by wave amplitudes that can exceed 50 ms and the present of shearing currents near the layer of pycnocline. The offshore drilling system is exposed to these current shears and the associated movements of large volumes of water. The effect of internal waves on drilling systems is studied through nonlinear fully coupled time domain analysis. The numerical model is implemented in a coupled analysis program where the hull, moorings and riser are considered as an integrated system. The program is then utilized to study the effects of the internal wave on the platform global motions and drilling system integrity. The study could be useful for future guidance on offshore exploration and drilling operations in areas where the internal wave phenomenon is prominent.

scholarly journals The Lifecycle of Nonlinear Internal Waves in the Northwestern South China Sea

2019 ◽  
Vol 49 (8) ◽  
pp. 2133-2145 ◽  
Author(s):  
Jianjun Liang ◽  
Xiao-Ming Li ◽  
Jin Sha ◽  
Tong Jia ◽  
Yongzheng Ren
Keyword(s):  
South China Sea ◽  
Internal Waves ◽  
South China ◽  
Internal Tide ◽  
In Situ Measurements ◽  
Shelf Break ◽  
Undular Bore ◽  
Nonlinear Internal Waves ◽  
Seasonal Thermocline

AbstractThe life cycle of nonlinear internal waves (NIWs) to the southeast of Hainan Island in the northwestern South China Sea is investigated using synergistic satellite observations, in situ measurements, and numerical simulations. A three-dimensional, fully nonlinear and nonhydrostatic model with ultrafine resolution shows that a diurnal internal tide emanates from a sill in the Xisha Islands at approximately 215 km away from the local shelf break. The internal tide transits the deep basin toward the shelf break and reflects at the sea bottom and seasonal thermocline in the form of a wave beam. Arriving at the shelf break, the internal tide undergoes nonlinear transformation and produces an undular bore. Analyses of in situ measurements reveal that the undular bore appears as sharp depressions of the strong near-surface seasonal thermocline. The undular bore gradually evolves into an internal solitary wave train on the midshelf, which was detected by the spaceborne synthetic aperture radar. This finding has great implications for investigating NIWs in other coastal oceans where waves are controlled by remotely generated internal tides.

Propagation and transformation of nonlinear internal waves of tidal origin observed in the northeastern East China Sea

2020 ◽  
Author(s):  
Seung-Woo Lee ◽  
SungHyun Nam
Keyword(s):  
East China Sea ◽  
Internal Waves ◽  
Bottom Topography ◽  
Wave Interaction ◽  
Propagation Speed ◽  
East China ◽  
Modal Interactions ◽  
Nonlinear Internal Waves ◽  
China Sea ◽  
Mode 2

<p>Oceanic nonlinear internal waves (NLIWs) play an important role in regional circulation, biogeochemistry, energetics, vertical mixing, and underwater acoustics, causing hazards to marine engineering and submarine navigation. Mainly generated by the interaction of the barotropic tides with the bottom topography, they propagate and transform due to wave-wave interaction process. Here, we present characteristics of first two modes of NLIWs observed using high-resolution spatiotemporal data collected in a relatively flat area in the northeastern East China Sea in May 2015. Six groups of NLIWs were identified from the observations: four groups of mode-1 and two groups of mode-2. The amplitude, propagation speed, and characteristic width of mode-1 NLIWs had ranges of 4–16 m, 0.53–0.56 m s<sup>-1</sup>, and 310–610 m, respectively. The mode-2 NLIWs propagate eastward slowly with a speed less than 0.37 m s<sup>-1</sup> with a comparable amplitude of 4–14 m and longer characteristic width of 540–1920 m. Intermodal interactions may take a role in the evolution of mode-1 NLIWs west of the observational area. Our results characterizing the two modes of NLIWs highlight the significance of propagation and transformation of NLIWs and their modal interactions on a broad and shallow shelf.</p>

Nonlinear internal wave generation over the Yermak Plateau 

2021 ◽  
Author(s):  
Gabin Urbancic ◽  
Kevin Lamb ◽  
Ilker Fer ◽  
Laurie Padman
Keyword(s):  
Internal Wave ◽  
Arctic Ocean ◽  
Internal Waves ◽  
Wave Generation ◽  
The Arctic ◽  
Nonlinear Internal Wave ◽  
Nonlinear Internal Waves ◽  
The Arctic Ocean ◽  
Yermak Plateau ◽  
Internal Wave Generation

<p>North of the critical latitude (78.4), internal waves of the M<sub>2</sub> tidal frequency can no longer freely propagate, and the energy conversion from the barotropic to the internal tides vanishes. Near the continental slopes around the Arctic Ocean, internal wave energy is enhanced and comparable to values at mid-latitudes (Rippeth et al. 2015, Levine et al. 1985). Observations on the northern flank of the Yermak Plateau (YP) has characterized the region as one of enhanced internal wave activity and nonlinear internal waves have been observed (Czipott et al. 1991, Padman and Dillon 1991).</p><p>The YP is a bathymetry feature stretching out into the Fram Strait north-west of Svalbard. The YP plays a prominent role in the Arctic’s heat balance due to its interaction with the West-Spitsbergen current which is a main contributor to the heat transport into the Arctic Ocean. Nonlinear waves generated over the YP are a significant energy source for mixing and can therefore modulate and force exchange processes.</p><p>To study the nonlinear internal wave generation mechanisms over the YP, we used a high resolution, nonlinear, non-hydrostatic model. We found that nonlinear internal waves are forced not by the M<sub>2</sub> but the K<sub>1</sub> tide which has been observed to have significant variability over the YP (Padman et al. 1992). Barotropic, diurnal shelf waves generated on the eastern side of the YP propagates counter-clockwise, amplifying the cross-slope currents. This amplification is the necessary condition for nonlinear internal wave generation over the YP.</p>

scholarly journals Turbulence Asymmetries in Bottom Boundary Layer Velocity Pulses Associated with Onshore-Propagating Nonlinear Internal Waves

2020 ◽  
Vol 50 (8) ◽  
pp. 2373-2391 ◽  
Author(s):  
Johannes Becherer ◽  
James N. Moum ◽  
John A. Colosi ◽  
James A. Lerczak ◽  
Jacqueline M. McSweeney
Keyword(s):  
Internal Waves ◽  
Residence Time ◽  
Surf Zone ◽  
Internal Tide ◽  
Inner Shelf ◽  
Bottom Boundary ◽  
Nonlinear Internal Waves ◽  
Leading Role ◽  
Bottom Boundary Layers ◽  
Shelf Region

AbstractThe inner shelf is a region inshore of that part of the shelf that roughly obeys Ekman dynamics and offshore of the surf zone. Importantly, this is where surface and bottom boundary layers are in close proximity, overlap, and interact. The internal tide carries a substantial amount of energy into the inner shelf region were it eventually dissipates and contributes to mixing. A part of this energy transformation is due to a complex interaction with the bottom, where distinctions between nonlinear internal waves of depression and elevation are blurred, indeed, where polarity reversals of incoming waves take place. From an intensive set of measurements over the inner shelf off central California, we identify salient differences between onshore pulses from waves with properties of elevation waves and offshore pulses from shallowing depression waves. While the velocity structures and amplitudes of on/offshore pulses 1 m above the seafloor are not detectably different, onshore pulses are both more energetically turbulent and carry more sediments than offshore pulses. Their turbulence is also oppositely skewed: onshore pulses slightly to the leading edges, offshore pulses to the trailing edges of the pulses. We consider in turn three independent mechanisms that may contribute to the observed asymmetry: propagation in adverse pressure gradients and the resultant inflection point instability, residence time of a fluid parcel in the pulse, and turbulence suppression by stratification. The first mechanism may largely explain higher turbulence in the trailing edge of offshore pulses. The extended residence time may be responsible for the high and more uniform turbulence distribution across onshore compared to offshore pulses. Stratification does not play a leading role in turbulence modification inside of the pulses 1 m above the bed.

The fate and impact of internal waves induced by strong shear current over a marginal ridge

2020 ◽  
Author(s):  
Peiwen Zhang ◽  
Wenjia Min
Keyword(s):  
Internal Wave ◽  
Internal Waves ◽  
Vertical Mixing ◽  
Internal Tide ◽  
Stratified Flow ◽  
Internal Tides ◽  
Energy Field ◽  
Nonlinear Internal Waves ◽  
Highly Nonlinear ◽  
Shear Current

<p>Internal waves with strong vertical mixing could be induced by stratified flow over seafloor obstacles. Noted that the stratified flow not only trigger internal tides, but also highly nonlinear internal waves like internal lee waves and internal solitary waves over steep topography features, and the highly nonlinear internal waves are suggested to play an important role in turbulence and mixing. As a typical seafloor obstacle, ridge could significantly modified the propagation of internal tide, internal lee wave and internal solitary wave. We focused on I-Lan ridge with asymmetrical topography feature in Kuroshio region. To the north of the I-Lan ridge, the depth of Philippine basin reached 4000m compared with the depth of 1500m in the south of the ridge, leading to different characteristics of internal wave energy field and ecological characteristics between two sides. Based on numerical simulations, we revealed the generation and propagation of internal waves over marginal ridge, causing by the shear current induced by Kuroshio. We also discussed the turbulence kinetic energy contributed by linear internal waves and nonlinear internal waves, providing the strength of vertical turbulent mixing around the I-Lan ridge. Then we demonstrated the characteristics of complex internal wave field in the strong background shear current over I-Lan ridge.</p>

scholarly journals Statistics of Nonlinear Internal Waves during the Shallow Water 2006 Experiment

2016 ◽  
Vol 33 (4) ◽  
pp. 839-846 ◽  
Author(s):  
Mohsen Badiey ◽  
Lin Wan ◽  
James F. Lynch
Keyword(s):  
Continental Shelf ◽  
Shallow Water ◽  
Internal Waves ◽  
Three Dimensional ◽  
Propagation Speed ◽  
Mapping Technique ◽  
Nonlinear Internal Waves ◽  
Ocean Environment ◽  
Reference Track ◽  
Time Varying Environment

AbstractDuring the Shallow Water Acoustic Experiment 2006 (SW06) conducted on the New Jersey continental shelf in the summer of 2006, detailed measurements of the ocean environment were made along a fixed reference track that was parallel to the continental shelf. The time-varying environment induced by nonlinear internal waves (NLIWs) was recorded by an array of moored thermistor chains and by X-band radars from the attending research vessels. Using a mapping technique, the three-dimensional (3D) temperature field for over a month of NLIW events is reconstructed and analyzed to provide a statistical summary of important NLIW parameters, such as the NLIW propagation speed, direction, and amplitude. The results in this paper can be used as a database for studying the NLIW generation, propagation, and fidelity of nonlinear internal wave models.

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