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Understanding of internal solitary wave (ISW) behavior has been limited due to sparse observations. We used high‐resolution Himawari‐8 satellite imagery and mooring observations to reveal the two‐dimensional (x–y) propagation process of ISWs in the South China Sea as they westward propagate onto the Dongsha plateau and encounter Dongsha Atoll. The 2D depiction of wave speed distribution, derived from detected wave crest positions every 10 min, shows the wave speeds range from 3 m s−1 to 1 m s−1 and have a tight correspondence to the local water depth. The correlation coefficient between the wave speeds and the Dubreil–Jacotin–Long (DJL) solutions is around 0.7, with a root mean squared value of 0.26 m s−1, and the representative available potential energy for this region is considered to be 130 MJ m−1. However, diffusions of wave speed in the ISW's lateral direction, particularly around abrupt topography, contribute to occurrences of outliers. Pairs of incident and reflected waves are well recognized east of Dongsha Atoll. The incident wave packet is known to be classified into a‐type and b‐type waves. The reflected waves associated with the b‐wave, identifiable as mode‐1 depression ISWs, are traced back to their generation site at depths of 100–200 m. In contrast, the reflected waves of the a‐wave remain elusive in shallower waters (<300 m), likely due to interference from their longer incident counterparts. The reflected wave, however, is slower and decelerates toward deeper water, deviating from the DJL prediction. These comprehensive observations can help refine models for improved accuracy. Plain Language Summary: Internal solitary waves (ISWs) in the South China Sea that propagate westward onto the Dongsha plateau and encounter Dongsha Atoll are traced. Wave speed varies from 3 m s−1 to 1 m s−1 and corresponds well to the local water depth. The variation of wave speed with depth shows an agreement with the solutions of a standard model (0.7 correlation coefficient), except in regions around abrupt topography. As the wave passes over a seamount, discrepancies in wave speed across the wave's lateral direction can contribute to occurrences of outliers. The incident wave and its reflected counterpart are well recognized semidiurnally to the east of Dongsha Atoll. However, when overlapping with the prior incident wave group, the reflected waves are unclear and difficult to distinguish. The reflected waves can be identified as waves causing isotherms to dip downward and creating a trough‐like depression in the water column. Their propagation speed is generally slower than its incident counterpart. The horizontal 2D depiction of wave speed distribution revisits the process from westward propagating ISWs to their reflected counterpart and improves understanding of reflected waves. Key Points: The spatial evolution of wave speeds with high spatiotemporal resolution mostly agrees with the Dubreil–Jacotin–Long modelAround abrupt topography, the wave's horizontal 2D distribution reveals the lateral diffusion of wave speeds along the wave crestInternal solitary waves propagating westward are observed to reflect off topography around the Dongsha Plateau by both satellite and mooring [ABSTRACT FROM AUTHOR]

Adjoint sensitivity modeling plays an important role in inverse problems, including four‐dimensional variational data assimilation or state estimation, by providing the sensitivity of the objective (or cost) function to the model input data. Although data assimilation has become common in regional ocean modeling, and the model resolution has become high enough to resolve internal tides, it remains unclear whether physically sensible and stable adjoint sensitivity modeling is feasible in the presence of internal waves. As a first step to tackle this problem, this study investigates fundamental properties of the adjoint of a time‐dependent circulation model, and the resulting sensitivity under internal waves. The theoretical and numerical results, based on simple‐internal‐wave theory and MITgcm modeling, show that stable adjoint sensitivity modeling is feasible under fully nonlinear (but stable) hydrostatic internal waves. However, it requires a careful choice of the objective function to obtain sensitivity which has the same propagation properties as (real‐world) internal waves, because the definition primarily controls the directionality and vertical‐mode content of internal‐wave signals in the adjoint model. Also, it should be noted that the internal‐wave signals lack indirect sensitivity through the dependence of the wave‐propagation speed on the model's prognostic variables. An important implication of the results is that the standard form of the objective function, which has been used in data assimilation studies for quasi‐geostrophic flows and barotropic tides, could be problematic for internal tides. Plain Language Summary: A particular method, called adjoint sensitivity calculation, is often used to incorporate observations into numerical simulations, such as weather forecasts. There is a growing need for this sensitivity calculation in regional ocean modeling in the presence of internal waves. Unlike the familiar ocean surface waves, internal waves exist within the ocean interior and have wavelengths of tens of km. This study uses theoretical analysis and numerical modeling to demonstrate that adjoint sensitivity calculation is feasible in the presence of internal waves, and to illustrate fundamental properties of the sensitivity. The results imply that standard assumptions currently used to incorporate observations into numerical simulations may not always work in the presence of internal waves, and suggests how the assumptions could be modified. Key Points: It is feasible to use an adjoint model to obtain sensitivity which has the same propagation properties as fully nonlinear internal wavesInternal‐wave signals in an adjoint model have different natural structure, or modes, from internal waves under real‐world physicsThe objective function definition primarily controls directionality and vertical‐mode content of internal‐wave signals in an adjoint model [ABSTRACT FROM AUTHOR]

The Indonesian throughflow (ITF) in the eastern part of Indonesia passes through the Maluku, Taliabu, Sula, and Buru Islands to the Banda Sea. The average depth of the Buru and Sula Islands is between 1000 m and 5000 m, with a narrow gap (sill) located to the north and south at a depth of 165 m on the sea map. This topography makes for interesting research on the western waters of Buru Island. Therefore, this study aimed to obtain salinity, temperature, and density values as water column stratification associated with the internal wave (IW), thermocline area, and current patterns at specific depths in the waters of Buru Island, Banda Sea. Data were collected from initial observations of Sentinel 1 satellite imagery of Buru Island to obtain an image of the waves in the water area. Furthermore, a single beam echosounder (SBES), conductivity temperature depth (CTD), and Copernicus Marine were analysed at the same position and time. The research found a non-linear IW Mode 2 at depths of 440–540 m with an estimated amplitude length is 40 km and an amplitude height of 100 m. Based on SBES echogram imaging, CTD data analysis, and modelling, there was an increase in IW density, a 35.25 PSU increase in salinity value at depths of 50~200 m, a temperature decrease of 27.5 ◦C to 10 ◦C at depths of 50~300 m, and a density stratification of 23.5 kg/m³ to 27 kg/m³ at depths of 50~300 m. [ABSTRACT FROM AUTHOR]

The internal waves in the South China Sea are highly correlated with the tidal currents in the Luzon Strait, which makes it possible to establish an internal wave prediction model based on internal wave kinematics. However, the kinematic model requires the input of the exact location and time of the initial internal wave for which the generation mechanism of internal waves in the northern South China Sea must be well understood. By analyzing the internal wave field in the northern South China Sea (SCS) simulated using the MIT General Circulation Model (MITgcm) and observations from satellite synthetic aperture radar (SAR) and mooring temperature–salinity–depth (TSD) chains, the source regions and propagation initiation times of internal waves are identified for three typical tidal phases, i.e., the diurnal-tide-dominated phase (DTP), transition tide phase (TTP), and semidiurnal-tide-dominated phase (STP). The generation procedures of Type A and Type B internal waves are discussed in detail with those data. The present study reveals that Type A and Type B waves are generated at the eastern and western ridges, respectively, and both commence their westward propagation at the peak of the eastward tidal flow. The dynamics of lee waves and the resonance effect with double ridges constitute the generation mechanisms of internal waves in the northern SCS. Combined with varying configurations of tidal conditions, topography, and stratification, the generation procedures of Type A and Type B waves in the DTP, TTP, and STP are elucidated with the generation mechanism in a unified and self-consistent way. In short, during DTP, weaker A waves alternate with weaker B waves each day; during TTP, strong A waves and strong B waves appear alternately every day; and there are two weak A waves per day during the STP. The generation mechanism can help in developing future empirical models for generating internal waves using tidal currents, topography, and stratification without requiring complex fluid dynamics calculations. [ABSTRACT FROM AUTHOR]

Symmetric Lamb waves with a phase velocity exceeding the expansion wave velocity in an infinite medium are considered. It has been proven that internal waves (i.e., solutions of the wave equation, which have zero values of the strain and stress components on the surface and nonzero values in the plate bulk) may exist in this region of phase velocities. Parameters of the internal waves (phase velocity, frequency, and wavelength) are calculated; it has been proven that frequencies of the internal waves with the same phase velocity make an arithmetic progression. Several internal waves are considered, and cross sections of the corresponding strained plates are presented (as well as the distributions of the maximum tension and shear values). [ABSTRACT FROM AUTHOR]

Internal Solitary Waves (ISWs) that form on internal density interfaces in the ocean are responsible for the horizontal transport and vertical mixing of heat, nutrients, and other water properties. The waves also induce fluid motion that can induce stresses and motion on floating structures, such as sea ice. This study investigates ISW‐sea ice interactions. Using laboratory experiments, ISWs generated via the lock gate technique are observed interacting with weighted floats of varying sizes. The motion of these floats can be modeled effectively, simply as the average velocity of the fluid under the float, and it is found that when floats are small relative to the wavelength, they behave in the same manner as a fluid particle, but as floats become bigger relative to the wavelength, the maximum velocity decreases, and interaction time increases. This phenomenon is explained simply by the wave‐induced flow as opposed to energy transfer arguments. By using this model with a large sample of theoretical waves, the float motion is parameterized based on the float length and wave parameters. Whilst small floats do not disrupt the flow patterns, the wave‐induced flow under larger floats forms a pair of counter‐rotating vortices at each end of the float. The formation and evolution of these flow features arise as a result of boundary layer separation with the horizontal wave‐induced flow relative to the float velocity. This reveals complex dynamics due to the non‐stationary behavior of both the float and flow. Plain Language Summary: Underwater waves are found in oceans across the world, including in areas with sea ice. They help mix heat, salt and other constituents in the ocean between deep and shallow waters. The Arctic is changing quickly, with summer sea ice extent declining 12.6% per decade, so we are now finding internal waves in newly ice‐free areas. Experiments are used to understand how these waves interact with sea ice. It is found that bigger floats move more slowly and create more flow disturbance, albeit not enough to cause mixing. The way this flow behaves is complicated by the movement of both the model ice, and the wave. Further experimental work is needed to understand the impact of changing the thickness, concentration and shape of the ice on the behavior of these waves. Key Points: Internal Solitary Waves (ISWs) can interact with sea ice in the Arctic Ocean. This process is modeled using laboratory experimentsThe wave‐induced motion of ice is slower when the ice length is large in comparison to the wave, a result explained by the wave form aloneVortices form at the ice edge. They are boundary layer features that depend on the motion of both the ice and ISW [ABSTRACT FROM AUTHOR]

The internal waves in the South China Sea are highly correlated with the tidal currents in the Luzon Strait, which makes it possible to establish an internal wave prediction model based on internal wave kinematics. However, the kinematic model requires the input of the exact location and time of the initial internal wave for which the generation mechanism of internal waves in the northern South China Sea must be well understood. By analyzing the internal wave field in the northern South China Sea (SCS) simulated using the MIT General Circulation Model (MITgcm) and observations from satellite synthetic aperture radar (SAR) and mooring temperature–salinity–depth (TSD) chains, the source regions and propagation initiation times of internal waves are identified for three typical tidal phases, i.e., the diurnal-tide-dominated phase (DTP), transition tide phase (TTP), and semidiurnal-tide-dominated phase (STP). The generation procedures of Type A and Type B internal waves are discussed in detail with those data. The present study reveals that Type A and Type B waves are generated at the eastern and western ridges, respectively, and both commence their westward propagation at the peak of the eastward tidal flow. The dynamics of lee waves and the resonance effect with double ridges constitute the generation mechanisms of internal waves in the northern SCS. Combined with varying configurations of tidal conditions, topography, and stratification, the generation procedures of Type A and Type B waves in the DTP, TTP, and STP are elucidated with the generation mechanism in a unified and self-consistent way. In short, during DTP, weaker A waves alternate with weaker B waves each day; during TTP, strong A waves and strong B waves appear alternately every day; and there are two weak A waves per day during the STP. The generation mechanism can help in developing future empirical models for generating internal waves using tidal currents, topography, and stratification without requiring complex fluid dynamics calculations.

The appearance of internal solitary waves (ISWs) in the Maluku Sea is often captured by satellite imagery. However, no study has revealed details on this phenomenon to date. Here, the characteristics of such ISWs were investigated based on their appearance in synthetic aperture radar (SAR) imagery on 20 February 2015. Two different sources of ISW packets were observed: one packet propagating from the Lifamatola Passage and another from the Sangihe Passage. The vertical structure of the waves was constructed using the Korteweg-de Vries (KdV) model, which suggests an average phase speed of ∼2.8 and 2.7 m s−1 for the first and the second sources, respectively. ISWs originating from the first source had a typical amplitude of O(80 m), while those from the second source were characterized by a lower amplitude of O(40 m). The waves generated horizontal and vertical currents with typical magnitudes of O(1 m s−1) and O(10 cm s−1) for the first source and O(0.6 m s−1) and O(4 cm s−1) for the second source, respectively. The mean energy densities of the first and second sources reached 461 MJ m−1 and 185 MJ m−1, respectively. Single leading solitary wave contained a fraction of approximately 20% and 15% of the baroclinic tidal energy generated in the Lifamatola Passage and Sangihe Passage, respectively.

Large-amplitude internal waves (IWs) with strong lateral shear forces can cause destructive effects on marine engineering structures. In this study, a large eddy simulation (LES) method was employed to simulate the generation and propagation of IWs in a three-dimensional numerical wave tank, and the pressure distribution, flow field characteristics, and force behaviors of two tandem cylinders under the coupling effect of the IWs and slope terrain were studied. The influence mechanism of the normalized value of center-to-center spacing (L) and the diameter of the cylinder (D), i.e., (L/D), on the strength of the vortex disturbance between cylinders was studied by comparing the simulation results of two tandem cylinders with those of a single cylinder (SC) to further explore the mechanical response characteristics of the upstream cylinder (P1) and downstream cylinder (P2). The simulation results showed that the vortex interaction between cylinders is the critical factor that affects the forces acting on the cylinders. The strength of the vortex disturbance could be distinguished by the dimensionless critical center-to-center spacing between cylinders (Lc/D = 3.0). When L/D ≤ Lc/D, the vortex disturbance was severe, causing P1 and P2 to experience significant horizontal positive forces and negative forces, respectively. In the case of L/D > Lc/D, the forces acting on both cylinders gradually returned to those on a single cylinder. [ABSTRACT FROM AUTHOR]

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Submarine melting has been implicated in the accelerated retreat of marine‐terminating glaciers globally. Energetic ocean flows, such as subglacial discharge plumes, are known to enhance submarine melting in their immediate vicinity. Using observations and a large eddy simulation, we demonstrate that discharge plumes emit high‐frequency internal gravity waves that propagate along glacier termini and transfer energy to distant regions of the terminus. Our analysis of wave characteristics and their correlation with subglacial discharge forcing suggest that they derive their energy from turbulent motions within the discharge plume and its surface outflow. Accounting for the near‐terminus velocities associated with these waves increases predicted melt rates by up to 70%. This may help to explain known discrepancies between observed melt rates and theoretical predictions. Because the dynamical ingredients—a buoyant plume rising through a stratified ocean—are common to many tidewater glacier systems, such internal waves are likely to be widespread. Plain Language Summary: Recent acceleration in sea‐level rise has been attributed to the mass loss of glaciers that terminate in the ocean, such as those found in Greenland and Alaska. Warm ocean currents are thought to melt glacier ice, contributing to their loss of mass and retreat. We use moored instruments deployed with autonomous vehicles, as well as a computer simulation, to demonstrate how a previously unconsidered type of current, called an internal wave, is generated at marine‐terminating glaciers. We show that the strength of the waves is related to the amount of subglacial discharge that originates from surface melting occurring at higher elevations on the glacier. Internal waves may contribute to local ice melt, and ultimately glacier mass loss, by mixing warm water in a thin layer immediately adjacent to the glacier. Key Points: First‐ever time series of water velocity in the calving zone of a glacier terminus, enabled by moorings deployed from a robotic vesselEnergetic high‐frequency internal waves were emitted from the subglacial discharge plume and reproduced in a large eddy simulationInternal waves have the potential to significantly increase ambient melt rates by enhancing water velocity across the terminus [ABSTRACT FROM AUTHOR]

In this study, a three-dimensional internal wave (IW)—cylinder—terrain coupled numerical model is established. Based on the large-eddy simulation (LES) method, the IW mechanical characteristics of the cylinder and the flow field evolution around the cylinder over different types of terrains are explored. The similarities and differences in the mechanical characteristics of the cylinders in the environments with and without terrains are compared. The research results show that, when the IWs propagate over terrain, the waveform structures are prone to continuous changes. The intense reverse alternating flow of the upper and the lower water, bounded by the pycnocline, results in huge IWs forces differences between the case without terrains and the cases with terrains. In the case without terrains, the maximum horizontal resultant force on the cylinder is positive, while the resultant forces are negative in the cases with terrain. Compared with the case without terrain, the shallow-water effect caused by the combined action of the terrain and the IWs enhances the flow field strength, making the lower parts of the cylinder suffer larger horizontal forces in the opposite direction to the IW direction. Moreover, the additional vortices produced by the interaction between the IWs and the terrain causes a more complex flow field around the cylinder and the greater forces on the cylinder. [ABSTRACT FROM AUTHOR]

Shear instabilities of stratified fluids are a classical topic with a broad literature. The classic instability takes the form of Kelvin-Helmholtz billows that initially develop in two dimensions, one of which is the vertical. Spanwise instability develops later as part of the transition to a three-dimensionalized state. We simulate mode-2 internal waves on the laboratory scale in a rotating frame of reference that, in the absence of rotation, form spanwise aligned billows on the wave flanks. Rotation breaks the symmetry of the classical shear instability because the wave amplitude decays away from the focussing wall (i.e. the waves generated are internal Kelvin waves). We document the development of the wave and the shear instabilities as the Rossby number is varied, finding that (i) even weak rotation (high Rossby number) leads to a significant modification of the billow three-dimensionalization, (ii) strong rotation (low Rossby number) leads to a strong near wall focussing of turbulence transition that is clearly evident in the second invariant of the velocity gradient, Q, of turbulence theory. For low rotation rates, or intermediate to high Rossby numbers, we identify novel instabilities with billow cores aligned in the along-tank direction, rather than the typical spanwise direction. [ABSTRACT FROM AUTHOR]

Internal wave adalah gelombang laut yang terjadi di lapisan dalam di perairan laut dangkal dan dalam, di mana kemunculannya hanya dapat terjadi jika kolom air terstratifikasi akibat adanya perbedaan densitas massa air. Penelitian ini bertujuan untuk mendeteksi peristiwa internal wave, serta mengukur nilai hambur balik akustik dari internal wave yang terjadi di Selat Lombok. Data yang digunakan adalah hasil pengukuran instrumen broadband echosounder SIMRAD EK80 frekuensi 200 kHz tipe pulsa continuous wave (CW) dengan data pendukung elevasi muka air, suhu, salinitas, dan densitas dari Conductivity Temperature Depth (CTD) “Yoyo” selama 24 jam. Nilai hambur balik didapatkan dengan analisis menggunakan perangkat lunak Sonar5-Pro. Echogram menunjukkan adanya pembentukan nonlinear internal wave disertai dengan adanya turbulensi yang terjadi pada saat gelombang pasang membawa massa air dengan densitas berbeda melewati topografi kasar di Selat Lombok. Nilai backscatter hasil segmentasi berentang dari -75 dB sampai -59 dB.

A moving submarine can generate internal waves, as well as extremely small free surface waves, in a fluid with density stratification. In this study, the internal and free surface wave wakes caused by a moving submarine in two layers of constant density fluid were studied numerically using the commercial software STAR-CCM+. The realizable k−ε turbulence model was used to solve the Reynolds-averaged Navier—Stokes equation, and the volume of the fluid method was used to monitor the fluctuations of the internal interface and free surface. Different cases of a moving submarine with different cruising speeds and relative diving depths were studied. Results showed that the maximum fluctuation amplitude of the free surface increased as the speed of the submarine increased; however, the maximum fluctuation amplitude of the internal interface first decreased and then increased. When the submarine moved at the maximum cruising speed, the maximum fluctuation amplitude of the free surface decreased as the diving depth increased, while the wavelength of the free surface wave was basically the same. If the submarine moved at the minimum cruising speed, then the wave elevation in the free surface was extremely small, but the internal surface had obviously large-amplitude internal waves, and the relative diving depth had a great influence on internal waves. [ABSTRACT FROM AUTHOR]

Significant current velocity near the sea bottom can be induced by internal waves, even for water a few hundred meters in depth. In this study, a nonhydrostatic ocean model was applied to simulate the generation and propagation of internal waves on the continental slope of the northern SCS. Based on the analyses of the vertical profiles of the currents, the propagation of internal waves along the continental slope can be categorized into six modes. The bed shear stress and the bedload transport were calculated to analyze the general characteristics of sediment transport along the continental slope of the northern SCS. Generally, there was no sediment transport on the sea bottom induced by the internal waves when the water depth was deeper than 650 m or shallower than 80 m. The downslope sediment transport dominated the slope at a water depth range of 200~650 m, while the upslope sediment transport dominated the slope at a water depth range of 80~200 m. The predicted directions of the bedload transport are coincident with the field observations of sand wave migration on the continental slope, which further confirms that the main cause of the generation and formation of sand waves on the continental slope of the northern SCS is the strong bottom current induced by the shoaling process of internal waves. [ABSTRACT FROM AUTHOR]

We study an inverse problem for the wave equation, concerned with estimating the wave speed from data gathered by an array of sources and receivers that emit probing signals and measure the resulting waves. The typical approach to solving this problem is a nonlinear least squares minimization of the data misfit, over a search space. There are two main impediments to this approach, which manifest as multiple local minima of the objective function: The nonlinearity of the mapping from the wave speed to the data, which accounts for multiple scattering effects, and poor knowledge of the kinematics (smooth part of the wave speed), which causes cycle skipping. We show that the nonlinearity can be mitigated using a data driven estimate of the wave field at points inside the medium, also known as the "internal wave field."" This leads to improved performance of the inversion for a reasonable initial guess of the kinematics. [ABSTRACT FROM AUTHOR]

Abstract Submarine melting has been implicated in the accelerated retreat of marine‐terminating glaciers globally. Energetic ocean flows, such as subglacial discharge plumes, are known to enhance submarine melting in their immediate vicinity. Using observations and a large eddy simulation, we demonstrate that discharge plumes emit high‐frequency internal gravity waves that propagate along glacier termini and transfer energy to distant regions of the terminus. Our analysis of wave characteristics and their correlation with subglacial discharge forcing suggest that they derive their energy from turbulent motions within the discharge plume and its surface outflow. Accounting for the near‐terminus velocities associated with these waves increases predicted melt rates by up to 70%. This may help to explain known discrepancies between observed melt rates and theoretical predictions. Because the dynamical ingredients—a buoyant plume rising through a stratified ocean—are common to many tidewater glacier systems, such internal waves are likely to be widespread.

The Itsukushima Shrine is located in northern Hiroshima Bay in the Seto Inland Sea (SIS). This structure of great cultural value is preserved as one of the World Heritage Sites in Japan. The shrine was built seaside, 30 cm above the highest tide, to prevent it from submerging. However, from 2011 to 2019, the shrine was submerged four times during September due to internal surges. To study the abnormal tide event on 29 September 2011, a high-resolution numerical ocean circulation model was established using Semi-implicit Cross-scale Hydroscience Integrated System Model (SCHISM). Observed subtidal components of surface elevation in the northern part of the bay decreased due to northerly winds when the typhoon passed east off the bay. After 7–8 days of typhoon passage, the component increased abnormally in the northern part of the bay. Simulation results revealed that a destabilized density stratification by the typhoon winds most likely caused bay-scale internal waves. The internal wave developed after the typhoon passed and was caught from the kinetic energy filtered in the possible internal wave periods. The internal wave propagated southward after the typhoon passage and returned to the northern bay, causing the subtidal component to increase after 7–8 days. Sensitivity tests with various scales of the typhoon were performed, and the test results exhibited a positive relationship between the abnormal tide level and typhoon intensity to some extent. The results can be generally applied to a semi-closed bay or closed water body for internal wave generation and propagation under specific meteorological conditions for coastal protection and disaster prevention.

Seawater temperature plays a key role in underwater acoustics and marine fishery, etc. In oceanographic surveys, it is often desirable to detect the temperature profile and obtain its spatio-temporal variation. The present study shows that the temperatures at the depths which are the three extreme points of the first two empirical orthogonal function (EOF) modes, contain the largest amount of information. Based on the back propagation (BP) neural network, a model for reconstructing the full-depth temperature profile using a few temperatures at fixed depth is established. The experimental result shows that the root mean square error (RMSE) of the temperature profile inversion in the test set is mostly less than 0.2 °C, and the three-dimensional temperature field obtained in this study is relatively reliable. [ABSTRACT FROM AUTHOR]

Internal waves (IW) are crucial contributors to the transport of sediment, heat, and nutrients in coastal areas. While IW have been extensively studied using point measurements, their spatial variability is less well understood. In this paper we present a unique set of high‐resolution infrared imagery collected from a helicopter, hovering over very energetic shoaling and breaking IW. We compute surface velocities by tracking the evolution of thermal structures at the ocean surface and find horizontal velocity gradients with magnitudes that are more than 100 times the Coriolis frequency. Under the assumption of no vertical shear we determine vertical velocities from the obtained horizontal divergence estimates and identify areas of the wave undergoing breaking. The spatial variability of the internal wave occurs on scales from a few to a few hundred meters. These results highlight the need to collect spatio‐temporal observations of the evolution of IW in coastal areas. Plain Language Summary: Oceanic internal waves (IW) form between heavier and lighter ocean water in the ocean interior, covering a wide range of temporal and spatial scales. They are amongst some of the key processes in the ocean—they facilitate transport of heat, sediment, and nutrients which have important implications for plankton and other ocean lifeforms, and serve as a pathway of energy from large to small scale flows. Yet, they are often measured using a point based approach (e.g., a buoy), which is unable to provide a full picture of the spatial variability of these waves and hence might not capture crucial behavior. Here, a unique set of high resolution airborne measurements is presented, covering several kilometers of a shoaling (and breaking) internal wave packet. Velocities at the sea surface are determined from infrared video imagery, using the temperature of the water as a tracer. By applying simple models to the velocity data (no change of horizontal velocity with depth), we show that variations in the vertical transport and in breaking characteristics are significant on many different spatial scales. This work is a step forward in understanding and quantifying the spatial variability of IW and processes associated with their breaking induced flow. Key Points: We present novel high‐resolution airborne observations of the kinematics of shoaling and breaking internal wavesWe find that the active breaking regions of the internal wave drive strong convergence/divergenceThe spatial variability of the internal wave is shown to occur over a broad range of scales, from a few to a few hundred meters [ABSTRACT FROM AUTHOR]

Large-amplitude internal waves (IWs) with strong lateral shear forces can cause destructive effects on marine engineering structures. In this study, a large eddy simulation (LES) method was employed to simulate the generation and propagation of IWs in a three-dimensional numerical wave tank, and the pressure distribution, flow field characteristics, and force behaviors of two tandem cylinders under the coupling effect of the IWs and slope terrain were studied. The influence mechanism of the normalized value of center-to-center spacing (L) and the diameter of the cylinder (D), i.e., (L/D), on the strength of the vortex disturbance between cylinders was studied by comparing the simulation results of two tandem cylinders with those of a single cylinder (SC) to further explore the mechanical response characteristics of the upstream cylinder (P1) and downstream cylinder (P2). The simulation results showed that the vortex interaction between cylinders is the critical factor that affects the forces acting on the cylinders. The strength of the vortex disturbance could be distinguished by the dimensionless critical center-to-center spacing between cylinders (Lc/D = 3.0). When L/D ≤ Lc/D, the vortex disturbance was severe, causing P1 and P2 to experience significant horizontal positive forces and negative forces, respectively. In the case of L/D > Lc/D, the forces acting on both cylinders gradually returned to those on a single cylinder.

This paper describes the results of studying the waves in the southern part of the Sea of Okhotsk on the sea routes between Sakhalin and Iturup islands by means of autonomous wave recorders. The study was performed in order to improve the safety of the maritime transport system and ensure its safe functioning. Analysis of the wave regime and weather conditions in the southern part of the Sea of Okhotsk, has shown that a cyclone of any direction approaching the southern part of the Sea of Okhotsk, causes sea waves with heights of more than 1.7 meters in the considered water area and nearshore of Iturup Island. However, if a cyclone approaches Sakhalin Island from the northwest direction, the height of wind waves and swell in the coastal area of the southeast of the island is small, and here is an opportunity for ships to take shelter from the storm. The analysis of long waves with tidal harmonic periods of 4 hours and more has shown, that they have almost the same oscillation phase for both islands. The internal waves caused by the local features of bathymetry and relief of the coastal zone for each adjacent water area are analyzed. Surface gravitational waves with a period of about 2.8 hours were detected at Kuibyshevsky and Kurilsky bays, and waves with a period of 2.4 hours were detected near the Okhotskoye village at Sakhalin Island. It is shown that the highest Q-factor in the Kurilsk region has the resonant water area for the periods of 4.5 minutes. It is noted that for these waves the phenomenon of a tyagun (harbour oscillations) can be expected during a storm at sea.

The velocity and direction of internal waves (IWs) are important parameters of the ocean, however, traditional observation methods can only obtain the average parameters of IWs for a single location or large area. Herein, a new method based on optical flow is proposed to derive the phase velocity vectors of IWs from X-band marine radar images. First, the X-band marine radar image sequence is averaged, and ramp correction is used to reduce the attenuation of gray values with increasing radial range. Second, the average propagation direction of the IWs is determined using the two-dimensional Fourier transform of the radar images; two radial profiles along this direction are selected from two adjacent radar images; and then, the average phase velocity of the IWs is estimated from these radial profiles. Third, the averaged radar images are processed via histogram equalization and binarization to reduce the influence of noise on the radar images. Fourth, a weighting factor is determined using the average phase velocity of a reference point; the phase velocities on the wave crest of the IWs are subsequently estimated via the optical flow method. Finally, the proposed method is validated using X-band marine radar image sequences observed on an oil platform in the South China Sea, and the error of the phase velocity is calculated to be 0.000 3–0.073 8 m/s. The application conditions of the proposed method are also discussed using two different types of IW packets. [ABSTRACT FROM AUTHOR]

We examined mixing processes within the ice–ocean boundary layer (IOBL) close to the geographic North Pole, with an emphasis on wind‐driven sea ice drift. Observations were conducted from late August to late September 2020, during the final leg of the international Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. Measurements of ice motion, and profiles of currents, hydrography, and microstructure turbulence were conducted. The multifarious direct observations of sea ice and the upper ocean were used to quantify the transport of momentum, heat, and salt in the IOBL. The ice drift was mostly characterized by the inertial oscillation at a semi‐diurnal frequency, which forced an inertial current in the mixed layer. Observation‐derived heat and salinity fluxes at the ice–ocean interface suggest early termination of basal melting and transitioning to refreezing, resulting from a rise in the freezing point temperature by the presence of freshened near‐surface water. Based on the friction velocity, the measured dissipation rate (ε) of turbulent energy can be approximated as 1.4–1.7 times of the "Law of the Wall" criterion. We also observed a spiraling Ekman flow and find its vertical extent in line with the estimate from ε‐based diffusivity. Following passage of a storm, the enhanced oscillatory motions of the ice drift caused trapping of the near‐inertial waves (NIWs) that exclusively propagated through the base of the weakly stratified mixed layer. We accounted Holmboe instabilities and NIWs for the observed distinct peak of the dissipation rate near the bottom of the mixed layer. Plain Language Summary: We examined how sea ice drift in the Arctic Ocean affects the movement of seawater directly under the ice, and how this impacts freezing and melting of the ice itself. During the Multidisciplinary drifting Observatory for the Study of Arctic Climate expedition, we used a number of different instruments to measure air, sea ice and ocean properties on an ice floe between late August and late September 2020. We recorded the drift tracks of the ice, and linked the ice motion to the currents, temperature and salinity within the upper 50 m of the ocean. Strong winds triggered wavy fluctuations and water mixing, in particular close to where the ice and ocean meet. During a storm in mid‐September, the ice stopped melting and started to refreeze even though the water and the air were still relatively warm. We explain this by the presence of surface water that was less salty, and therefore froze faster at higher temperature, and by the ice moving faster than usually observed in the region. In combination, these factors provided favorable conditions for sea ice formation. Our results suggest that the distribution of sea ice meltwater need to be accounted for in order to better predict Arctic sea ice conditions in the future. Key Points: Enhanced ice drift and near‐surface freshened water jointly promoted early termination of basal melting and preconditioning of refreezingTurbulent dissipation rate can be scaled by 1.4–1.7 times of the "Law of the Wall" criterion, with surface buoyancy flux being negligibleNear‐inertial wave was trapped by weakly stratified water in lower mixed layer, which produced turbulence by the Holmboe instability [ABSTRACT FROM AUTHOR]

We present a modeling study of an idealized island with sloping sides in a stratified ocean with internal tides propagating through the domain, which transform into nonlinear internal waves as they encounter shallow depths. In the base condition, representative of a mid‐latitude island with relatively steep super critical slopes, the nonlinear internal waves shoaling on the island wrap around the island, scatter, and create an asymmetric wavefield. Radiation stress gradients from this wavefield and rotation are balanced by pressure gradients and turbulent vertical diffusion in the momentum equations which drive residual mean currents around the island. We explore the effects of different physical parameters including no rotation, higher Froude number, subcritical slope, addition of barotropic tides, larger excursion number, and addition of large‐scale mean currents. All simulations showed formation of residual currents of varying intensity, upwelled deep waters in shallow regions, and cooler waters on the side of the island consistent with the direction of incoming internal tides. While the no rotation and strong mean flow conditions created some upwelling, of all the modeled conditions, the subcritical slope has the greatest potential for creating favorable conditions for benthic organisms through enhanced upwelling. Areas of the world's oceans with stratified waters sufficient to sustain internal tide motions, strong internal tide energy, and local subcritical bottom slopes are likely to have cooler waters and more upwelled deep waters than the surrounding areas, and potentially serve as thermal refugia from future ocean warming. Plain Language Summary: Tides oscillate the world's oceans, and because warmer lighter water sits on cooler dense water, wave energy travels along this interface. This process, called internal tides, creates waves which propagate in the ocean interior and are quite common in the ocean. When these waves encounter a coastline or island they function similarly to waves on a beach: they can turn, change shape, break, or reflect. These changes to the waves can create currents, often quite strong, and pull deeper cooler water into the shallow coastal areas. We performed a modeling study to determine which factors are most important in creating strong currents from these internal tides across a range of possible conditions on islands worldwide. The results show that the internal tides create complex currents and bring cooler dense water into the shallow regions under most conditions. The factor that creates potentially the best conditions for organisms living on the ocean floor is gradual ocean floor slopes (compared to steeper). The results for this condition had strong currents, increased deep ocean waters, and cooler temperatures in the shallow coastal areas which may buffer effects from future ocean warming. Key Points: Internal tides interacting with an island force complex residual currents and upwellingRotation, barotropic tides, large‐scale mean currents and bottom slope all have an influence on the currents and upwellingSubcritical slope has the largest upwelling from internal tides and the greatest potential for creating thermal refugia in a warming ocean [ABSTRACT FROM AUTHOR]

In this study, a three-dimensional internal wave (IW)—cylinder—terrain coupled numerical model is established. Based on the large-eddy simulation (LES) method, the IW mechanical characteristics of the cylinder and the flow field evolution around the cylinder over different types of terrains are explored. The similarities and differences in the mechanical characteristics of the cylinders in the environments with and without terrains are compared. The research results show that, when the IWs propagate over terrain, the waveform structures are prone to continuous changes. The intense reverse alternating flow of the upper and the lower water, bounded by the pycnocline, results in huge IWs forces differences between the case without terrains and the cases with terrains. In the case without terrains, the maximum horizontal resultant force on the cylinder is positive, while the resultant forces are negative in the cases with terrain. Compared with the case without terrain, the shallow-water effect caused by the combined action of the terrain and the IWs enhances the flow field strength, making the lower parts of the cylinder suffer larger horizontal forces in the opposite direction to the IW direction. Moreover, the additional vortices produced by the interaction between the IWs and the terrain causes a more complex flow field around the cylinder and the greater forces on the cylinder.

Mediterranean eddies (meddies) play an essential role in transferring heat, salinity and momentum into the Atlantic Ocean. The rate of heat (and salt) flux from the meddy and its ultimate lifetime are key proxies to understanding how meddies impact the redistribution of heat and salt in the ocean system. A Mediterranean eddy was observed in the Gulf of Caidz in 2007 using seismic and hydrographic data. The spatial distribution of turbulent dissipation rates around the meddy is estimated from the seismically derived internal wave spectra subrange using fine-scale parameterization. Turbulent dissipated rates are lowest ( 10 − 11   W / k g ) within the core of the meddy but rise by nearly two orders of magnitude at the upper and lower boundaries, where signs of double diffusive convection are observed. Along the left flank of the meddy, thermohaline intrusions and interleaving of water masses are found in inverted temperature and salinity profiles, transporting heat laterally from the warm core to the Atlantic water with a flux of around 470   W m − 2 . The meddy presented in this study is shown to decay in 2 years, primarily due to the heat loss associated with thermohaline intrusions. For the first time, heat fluxes around the meddy and its lifetime are quantified using seismic oceanography data, and the methods proposed here can be applied to more seismic datasets in the global oceans. [ABSTRACT FROM AUTHOR]

The quasi-linear or nonlinear interactions among different ocean motions dominate the system internal structure and appearance feature presented in spatial and temporal evolution. However, deficiency of the characteristics set computation model for internal wavenumber spectra proves to be a serious barrier to derive interaction mechanisms of internal waves with large or small scale ocean motions. In this study, a characteristics set computation model for internal wavenumber spectra is proposed for complicated offshore environments. The refraction of current shear instability, bottom topography and the reflection at surface and bottom are attentively considered in the complicated characteristics inlaid scheme. Model results are validated with MODIS retrieved internal wave parameters in the Sulu Sea and Celebes Sea. This original characteristics set computation model for internal wavenumber spectra can be used widely and can further improve the understandings of generation, dissipation, nonlinear wave-wave interaction and mixing process of internal waves. [ABSTRACT FROM AUTHOR]

Significant current velocity near the sea bottom can be induced by internal waves, even for water a few hundred meters in depth. In this study, a nonhydrostatic ocean model was applied to simulate the generation and propagation of internal waves on the continental slope of the northern SCS. Based on the analyses of the vertical profiles of the currents, the propagation of internal waves along the continental slope can be categorized into six modes. The bed shear stress and the bedload transport were calculated to analyze the general characteristics of sediment transport along the continental slope of the northern SCS. Generally, there was no sediment transport on the sea bottom induced by the internal waves when the water depth was deeper than 650 m or shallower than 80 m. The downslope sediment transport dominated the slope at a water depth range of 200~650 m, while the upslope sediment transport dominated the slope at a water depth range of 80~200 m. The predicted directions of the bedload transport are coincident with the field observations of sand wave migration on the continental slope, which further confirms that the main cause of the generation and formation of sand waves on the continental slope of the northern SCS is the strong bottom current induced by the shoaling process of internal waves.

In practical applications, the current ocean internal wave detection technology has large errors, and is significantly affected by the marine environment, and cannot be identified independently. In view of these problems, this study proposes a monitoring method for ocean internal wave early warning based on vector field processing. This method is based on the combined information processing of sound pressure and vibration velocity, and uses the three-dimensional information of the sound field picked up by the ultra-low frequency vector hydrophone. The time-space-frequency three-dimensional tracking and locking of non-cooperative targets can be carried out in the complex ocean background noise field according to the azimuth estimation algorithm. The arrival of internal wave causes the change of the three-dimensional sound velocity profile. The fluctuation of the sound field will lead to the change of the acoustic energy flow intensity of the target signal source. This method realizes the monitoring and prediction of ocean internal waves based on the abnormal jump of the vertical grazing angle caused by the channel distortion of the target signal in the internal wave space. The simulation results show that the vertical grazing angle fluctuates slightly in a normal environment, and the range of change is small. When the internal wave strikes, the grazing angle changes strongly, and the maximum deflection can be abruptly changed to a negative angle, which proves the effectiveness of the method. [ABSTRACT FROM AUTHOR]

The deformation and evolution of internal solitary waves (ISWs) beneath an ice keel can enable potential diapycnal mixing and facilitate upper ocean heat transport, despite a poor understanding of the underlying physics and energetics of ISWs in Polar environments. This study aims to understand the dynamic processes and mixing properties during the evolution of ISWs beneath ice keels in the Arctic Ocean using high‐resolution, non‐hydrostatic simulations. Ice keels can destabilize ISWs through overturning events. Consequently, the initial ISW disintegrates and transfers its energy into secondary smaller‐scale waves. During the ISW‐ice interaction, ISW‐induced turbulent mixing can reach O(10−3) W/kg with a magnitude of resultant heat flux of O(10)W/m. Sensitivity experiments demonstrated that the ISW‐ice interaction weakened as the ice keel depth decreased, and consequently, the resultant turbulent mixing and upward heat transfer also decreased. The ice keel depth was critical to the evolution and disintegration of an ISW beneath the ice keel, while the approximate ice keel shape had little effect. Our results provide an important but previously overlooked energy source for upper ocean heat transport in the Arctic Ocean. Plain Language Summary: Internal wave‐driven mixing plays an important role in both ocean general circulation and climate change. Internal waves (IWs) at mid to low latitudes have attracted much attention; however, our understanding of the evolution and physics of IWs in high‐latitude Polar oceans remains limited. This study aims to explore the evolution and energetics of internal solitary waves (ISWs, a kind of high‐frequency IW) in the ice environment of the Arctic Ocean using non‐hydrostatic 2D simulations. The results reveal the destabilization process of an ISW during its interaction with an ice keel (undersea portion of ice cover). During the ISW‐ice interaction in the Arctic Ocean, ISW‐induced turbulent mixing can reach O(10−3) W/kg with a magnitude of resultant heat flux of O(10) W/m. Thus, the ISW‐ice interaction provides an important, but previously overlooked, energy source for upper ocean heat transport in the Arctic Ocean. Key Points: Destabilization and disintegration of internal solitary waves (ISWs) under ice keels can radiate energy into secondary wavesTurbulent mixing and vertical heat flux are significantly enhanced during ISW‐ice interactionsThe ISW‐ice interaction and resultant heat transfer weaken with the shrinking of ice keels [ABSTRACT FROM AUTHOR]

Internal waves play important roles in modulating the temperature variations and heat transfers in stratified oceans. However, due to the deep ocean measuring approach limitations, it is still challengeable to characterize the temperature fluctuations induced by internal waves in the deep oceans below 2,000 m. In this study, a fleet of rapid‐sampling deep profiling floats with an approximately daily sampling rate was deployed in the northeastern South China Sea (SCS), Philippine Basin (PB), Mariana Arc (MA), and Kuroshio Extension (KE). Results show that the internal waves, internal tides or near‐inertial waves, have considerable imprints on local temperature fluctuations. Geographically, the internal wave induced temperature fluctuations are generally larger in the PB and MA, indicative of a strong deep signature of internal tides generated by local energetic tide‐topography interactions or radiation from remote sources. The temperature fluctuations at 4,000 m can reach up to 7 m°C in most regions, which may cover up real signals of temperature change, posing challenges to assess the deep ocean warming rate through currently insufficient deep profiling floats. Besides, the amplitude of isopycnal displacement in the PB and MA is evidently larger than in KE at 4,000 m, which implies enhanced diapycnal diffusivity and mixing in the deep layers of open oceans with rough topography. Plain Language Summary: Internal waves are ubiquitous in the global ocean, and their propagations are accompanied by the rise and falls of isopycnals which induce fluctuations in local temperature. However, in situ observations of high‐frequency temperature fluctuations in the deep ocean are still insufficient. Here we used a fleet of rapid‐sampling deep profiling floats to assess the temperature fluctuations induced by internal waves. We found that the magnitude of internal wave induced deep ocean temperature fluctuations is evidently stronger than the long‐term trend, especially in the Philippine Basin (PB) and Mariana Arc (MA) with rough topography. Therefore, a more cautious approach should be used to assess the deep ocean warming rate in areas with strong internal waves. Key Points: Internal waves are found to have considerable imprints on temperature fluctuations using rapid‐sampling deep profiling floatsThe temperature fluctuations can reach 7 m °C at 4,000 m, posing challenges to assess the real deep ocean warming rateThe internal waves induced temperature fluctuations in the deep ocean are generally larger in the Philippine Basin and Mariana Arc [ABSTRACT FROM AUTHOR]

Seawater temperature plays a key role in underwater acoustics and marine fishery, etc. In oceanographic surveys, it is often desirable to detect the temperature profile and obtain its spatio-temporal variation. The present study shows that the temperatures at the depths which are the three extreme points of the first two empirical orthogonal function (EOF) modes, contain the largest amount of information. Based on the back propagation (BP) neural network, a model for reconstructing the full-depth temperature profile using a few temperatures at fixed depth is established. The experimental result shows that the root mean square error (RMSE) of the temperature profile inversion in the test set is mostly less than 0.2 °C, and the three-dimensional temperature field obtained in this study is relatively reliable.

The Lombok Strait, as one of the outlet straits, is part of the ITF route, which is directly adjacent to the Indian Ocean. There is a sill in the Lombok Strait, which is a place for internal wave generation. Leg-1 data from the Japan Agency for Marine-Earth Science and Technology in collaboration with the Agency for the Assessment and Application of Technology which is part of the Tropical Ocean Climate Study Expedition including CTD Yoyo and ADCP taken using ship vehicles R/V Kaiyo. CTD Snapshot from PUSHIDROSAL using the KRI Spica 934 vehicle part of the Opssurta Baruna Jaya 2 Expedition. Determination of seawater mass stratification with the criteria for the thermocline layer is = 0.05 °C.m-1. Four types of water masses were identified, Java Sea, mixed seawater mass (Java Sea - ITF) which occurred diapycnal mixing, North Pacific Subtropical Water (NPSW) and North Pacific Intermediate Water (NPIW). The seawater mass stratification in the Lombok Strait based on temperature, salinity and density which are seen to follow the internal tidal pattern. The average values for energy dissipation and vertical diffusivity for each layer and replication were 5.73 x 10-7 W.Kg-1 and 3.67 x 10-2 m2.s-1 for CTD Yoyo and 2.25 x 10-6 W.Kg-1 and 7.38 x 10-2 m2.s-1 for CTD Snapshot. The value obtained is greater than the open ocean and straits in other studies. The high shear value confirms this in the thermocline layer. The Richardson gradient value> 0.25 is relatively constant in the thermocline layer. [ABSTRACT FROM AUTHOR]

The water temperature in the ocean varies according to its depth and generates a thermocline layer. An internal wave can be excited by an object moving near the thermocline layer because the density changes owing to the water temperature. The internal wave propagates and interacts with the surface wave. This study aims to investigate the internal wave propagation in a two-layer stratified flow, generated by 2D hydrofoil (NACA0012) using a RANS based CFD model. Eulerian multiphase methods were used for the modeling of the two-layer stratified flow; Volume of Fluid (VOF) model and mixture model. A two-layer stratified fluid consisting of air(ρair)-water1(ρw1)-water2(ρw2) is considered instead of the thermocline layer to simplify the numerical simulations. The generation and propagation of the internal wave were investigated, with different configurations of the speed and submergence depth of the hydrofoil. The result suggested that the VOF model shows better agreement with the experimental data compared to the mixture model. [ABSTRACT FROM AUTHOR]

The Arctic climate is changing rapidly, with dramatic sea ice declines and increasing upper‐ocean heat content. While oceanic heat has historically been isolated from the sea ice by weak vertical mixing, it has been hypothesized that a reduced ice pack will increase energy transfer from the wind into the internal wave (IW) field, enhancing mixing and accelerating ice melt. We evaluate this positive ice/internal‐wave feedback using a finescale parameterization to estimate dissipation, a proxy for the energy available for IW‐driven mixing, from pan‐Arctic hydrographic profiles over 18 years. We find that dissipation has nearly doubled in summer in some regions. Associated heat fluxes have risen by an order of magnitude, underpinned by increases in the strength and prevalence of IW‐driven mixing. While the impact of the ice/internal‐wave feedback will likely remain negligible in the western Arctic, sea‐ice melt in the eastern Arctic appears vulnerable to the feedback strengthening. Plain Language Summary: The Arctic is changing rapidly, with dramatic declines in sea ice and warming of upper‐ocean waters. Historically, weak ocean mixing has prevented the melting of sea ice by oceanic heat. Scientists have hypothesized that as sea ice melts and open water is exposed to the wind, more energetic internal waves will result. These waves cause mixing in the upper ocean, which can bring heat upwards to the surface and melt more sea ice, thus creating a positive feedback loop. To test the importance of this feedback, we use ocean measurements to estimate "dissipation," a proxy for the internal wave energy that is available to cause mixing. The measurements cover much of the Arctic Ocean for the years 2002–2019. We find that dissipation has increased during summer in recent years. Summer heat transport toward the sea ice has also increased, on average by a factor of 10, as internal wave‐driven mixing became stronger and more prevalent. We estimate that the western Arctic is unlikely to experience significant future sea‐ice melt due to this positive feedback; however, the eastern Arctic may be vulnerable to accelerated sea‐ice melt as increases in dissipation continue. Key Points: Dissipation in the central Arctic has nearly doubled in summer while declining in winter; no interannual trends are found in any regionSummer heat flux in the central Arctic has risen by an order of magnitude due to stronger and more prevalent internal wave‐driven mixingThe eastern Arctic appears particularly vulnerable to accelerated sea‐ice melt due to the strengthening "ice/internal‐wave" feedback [ABSTRACT FROM AUTHOR]

Internal waves occur at the interface between two layers caused by a seawater density difference. The internal waves generated by a body moving in a two-layer fluid are also related to the generation of surface waves because of their interaction. In these complex flow phenomena, the experimental measurements and experimental set-up for the wave patterns of the internal waves and surface waves are very difficult to perform in a laboratory. Therefore, studies have mainly been carried out using numerical analysis. However, model tests are needed to evaluate the accuracy of numerical models. In this study, the various experimental conditions were evaluated using CFD simulations before experiments to measure the wave patterns of the internal waves and surface waves in a stratified two-layer fluid. The numerical simulation conditions included variations in the densities of the fluids, depth of the two-layer fluid, and moving speed of the underwater body.

The sea is stratified with water that has different densities because of pressure, temperature, and salinity. When conducting studies of internal waves in the ocean, the fluid is assumed to have layers that have discrete densities. This assumption is made because it is difficult to achieve layers that exhibit gradual changes in the density of the water. In this study, we used previous studies on ocean waves and their radiation issues in the density layer fluid to investigate the characteristics of internal waves in the ocean and their radiation patterns induced by a moving body in a stratified fluid. We also studied the difference in wave radiation between the density gradient layer and the discrete density layer. We found that the wave radiation patterns depended on the velocity of the moving body and the change in the density of the water. The crest apex shift phenomenon was observed in the density gradient in the layer of fluid.

In this research, density, temperature and salinity fields were investigated in different seasons using observational data of ROPME Marine Cruise in the Persian Gulf (PG). Based on in-situ measurements, areas with density stratification were identified. Having analyzed Landsat and SAR satellite images, internal waves (IW) were detected in different regions of the Persian Gulf and more frequently in the eastern part of the PG related to seawater stratification. Based on analysis of satellite images, it is shown that the length of internal waves crest detected in the north-eastern part of Al-Zhahirah (Qatar) was more than 120 km; while it’s in range of 5 to 20 km in the south and east of Larak Island, 15 to 40 km in the north-east of Abu Musa Island, and 3 to 65 km in the south-east and south of Hondurabi Island. Moreover, IWs with shorter crest’s wide were recognized near Lavan, Siri, Farur, Halul, Khark Islands and Bandar Lengeh, as well. In addition, studying satellite images in the above mentioned areas for a longer time period from 2000 to 2017 showed that IWs mostly occur in the eastern part of the PG in summer and disappear in other seasons.

Mediterranean eddies (meddies) play an essential role in transferring heat, salinity and momentum into the Atlantic Ocean. The rate of heat (and salt) flux from the meddy and its ultimate lifetime are key proxies to understanding how meddies impact the redistribution of heat and salt in the ocean system. A Mediterranean eddy was observed in the Gulf of Caidz in 2007 using seismic and hydrographic data. The spatial distribution of turbulent dissipation rates around the meddy is estimated from the seismically derived internal wave spectra subrange using fine-scale parameterization. Turbulent dissipated rates are lowest (10−11 W/kg) within the core of the meddy but rise by nearly two orders of magnitude at the upper and lower boundaries, where signs of double diffusive convection are observed. Along the left flank of the meddy, thermohaline intrusions and interleaving of water masses are found in inverted temperature and salinity profiles, transporting heat laterally from the warm core to the Atlantic water with a flux of around 470 Wm−2. The meddy presented in this study is shown to decay in 2 years, primarily due to the heat loss associated with thermohaline intrusions. For the first time, heat fluxes around the meddy and its lifetime are quantified using seismic oceanography data, and the methods proposed here can be applied to more seismic datasets in the global oceans.

The quasi-linear or nonlinear interactions among different ocean motions dominate the system internal structure and appearance feature presented in spatial and temporal evolution. However, deficiency of the characteristics set computation model for internal wavenumber spectra proves to be a serious barrier to derive interaction mechanisms of internal waves with large or small scale ocean motions. In this study, a characteristics set computation model for internal wavenumber spectra is proposed for complicated offshore environments. The refraction of current shear instability, bottom topography and the reflection at surface and bottom are attentively considered in the complicated characteristics inlaid scheme. Model results are validated with MODIS retrieved internal wave parameters in the Sulu Sea and Celebes Sea. This original characteristics set computation model for internal wavenumber spectra can be used widely and can further improve the understandings of generation, dissipation, nonlinear wave-wave interaction and mixing process of internal waves.

In this study, a methodology was presented to predict density stratified flows in the near-field of submerged bodies. The energy equation in temperature form was solved coupled with momentum and mass conservation equations. Linear stratification was achieved by the definition of the density as a function of temperature. At first, verifications were performed for the stratified flows passing a submerged horizontal circular cylinder, showing excellent agreement with available experimental data. The ability of the method to cope with variable density was demonstrated. Different turbulence models were used for different Re numbers and flow states. Based on the numerical methods proposed in this paper, the stratified flow was studied for the real scale benchmark DAPRA Suboff submarine. The approach used the VOF method for tracing the free surface. Turbulence was implemented with a k − ω based Detached Eddy Simulation (DES) approach. The effects of submarine speed, depth and density gradient on the free surface wave pattern were quantitatively analyzed. It was shown that, with the increasing of the speed of the submarine, the wavelength and wave height of the free surface wave were gradually increasing. The wave height of the free surface wave was gradually reduced as the submarine’s depth increased. Relative to the speed and submarine depth, the changes of the gradient density gradient have negligible effects on the free surface wave field.

Spatial patchiness of plankton enhances fishery production and carbon export in the ocean. While diel vertical migration (DVM) has been identified as an important factor contributing to vertical patchiness, its effect on horizontal patchiness has never been investigated. We use a simple individual-based zooplankton model to examine the effect of DVM on the horizontal patchiness of four zooplankton groups with differing DVM patterns in a two-dimensional ocean circulation model. We find that zooplankton horizontal patchiness can be induced by two mechanisms: (1) in stratified waters, DVM can synchronize zooplankton vertical positions with the horizontal current velocities that drive them, resulting in horizontal patchiness; and (2) migrating zooplankton tend to aggregate in deep waters when they encounter sea bottom. Due to these mechanisms, zooplankton horizontal patchiness may be ubiquitous in the ocean, enhancing secondary production and fisheries. [ABSTRACT FROM AUTHOR]