Internal Tides Research Articles

Observations of Tidally Driven Turbulence over Steep, Small-Scale Topography Embedded in the Tasman Slope

Abstract Enhanced diapycnal mixing induced by the near-bottom breaking of internal waves is an essential component of the lower meridional overturning circulation. Despite its crucial role in the ocean circulation, tidally driven internal wave breaking is challenging to observe due to its inherently short spatial and temporal scales. We present detailed moored and shipboard observations that resolve the spatiotemporal variability of the tidal response over a small-scale bump embedded in the continental slope of Tasmania. Cross-shore tidal currents drive a nonlinear trapped response over the steep bottom around the bump. The observations are roughly consistent with two-dimensional high-mode tidal lee-wave theory. However, the alongshore tidal velocities are large, suggesting that the alongshore bathymetric variability modulates the tidal response driven by the cross-shore tidal flow. The semidiurnal tide and energy dissipation rate are correlated at subtidal time scales, but with complex temporal variability. Energy dissipation from a simple scattering model shows that the elevated near-bottom turbulence can be sustained by the impinging mode-1 internal tide, where the dissipation over the bump is O(1%) of the incident depth-integrated energy flux. Despite this small fraction, tidal dissipation is enhanced over the bump due to steep topography at a horizontal scale of O(1) km and may locally drive significant diapycnal mixing. Significance Statement Near-bottom turbulent mixing is a key element of the global abyssal circulation. We present observations of the spatiotemporal variability of tidally driven turbulent processes over a small-scale topographic bump off Tasmania. The semidiurnal tide generates large-amplitude transient lee waves and hydraulic jumps that are unstable and dissipate the tidal energy. These processes are consistent with the scattering of the incident low-mode internal tide on the continental slope of Tasmania. Despite elevated turbulence over the bump, near-bottom energy dissipation is small relative to the incident wave energy flux.

Ocean Mixing in a Shelf Sea Driven by Energetic Internal Waves

AbstractInternal waves drive ocean mixing and enhance the transport of heat, momentum and other tracers in shelf seas. We collected observations of mixing over a 30‐day period from three cross‐shore moorings placed on the 330, 200 and 150 m isobaths on the offshore side of a pelagic ridge on the Australian North West Shelf. The region is forced by energetic surface and internal tides, exhibits non‐linear internal waves, experiences flow‐topography interactions, and is subject to episodic intense wind events. This complex forcing drove energetic diapycnal mixing at all sites. We identified five dominant internal wave forcing categories: mode‐1 waves at low‐frequency (time scales from double the buoyancy period to 4 hr), mode‐1 waves at high‐frequency (HF) (time scales between the buoyancy period and double the buoyancy period), mode‐2 waves, internal bores, and internal hydraulic jumps. Overall, just 15% of mixing events accounted for 90% of the total observed heat flux over the record. Mixing during internal wave events accounted for as much as 50% of the total heat flux in some locations. Of the internal wave categories, HF mode‐1 waves were the most significant contributors to the total heat flux at all sites (∼20%). On the other hand, internal bores made significant contributions to mixing only at the 200 and 150 m moorings; they made no contribution to mixing at the 330 m mooring. At the shallowest mooring, the different internal wave categories all made similar contributions to the total flux, indicating an increasingly complicated relationship between the evolving internal wavefield and the mixing.

Observations of Tidal Modulation on Diurnal Vertical Displacements of the Oceanic Transition Layer

AbstractFrom continuous high‐frequency and high‐resolution observations of temperature, salinity, current and microstructure in the northern South China Sea during 28–31 May 2021, we found that the transition layer (TL) experienced a regular diurnal vertical fluctuation of ∼20–30 m, likely associated with the displacements of the mixed layer (ML) and tidal shear in the TL. Specifically, surface cooling (heating) caused an erosion (enhancement) of thermal stratification and facilitated (hindered) convection, rapidly deepening (shoaling) the ML and causing corresponding vertical displacements in the TL. The mixture of diurnal and semidiurnal tides, together with internal tides and tidal rectification, resulted in a diurnally varying large shear in the TL. This enhanced shear caused the TL to further descend along with the rapid thickening of the ML, while the relatively weaker shear slowed the uplift of the TL with a rapid shoaling of the ML and resulted in its gradual shoaling.

Examining Modulations of Internal Tides within An Anticyclonic Eddy Using a Wavelet-Coherence Network Approach

Interactions between internal tides and mesoscale eddies are an important topic. However, examining modulations of internal tides inside a mesoscale eddy based on observations is difficult due to limited observation duration and inaccurate positioning within the eddy. In order to overcome these two practical limitations, we use the active navigation capability of underwater gliders to conduct measurements inside the targeted eddy and utilize the wavelet approach to investigate modulations of internal tides with diurnal and semidiurnal periods inside the eddy. Based on the wavelet’s frequency–time locality, we construct scale-specific networks via wavelet coherence (WC) from multivariate timeseries with a small sample size. The modulation of internal tides is then examined in terms of temporal evolutionary characteristics of the WC network’s topological structure. Our findings are as follows: (1) the studied eddy is vertically separated into two layers, the upper (<400 m) and lower (>400 m) layers, indicating that the eddy is surface intensified; (2) the eddy is also horizontally divided into two domains, the inner and outer centers, where the modulation of internal tides seems to actively occur in the inner center; and (3) diurnal internal tides are more strongly modulated compared to semidiurnal ones, indicating the influence of spatial scales on the strength of interactions between internal tides and eddies.

Internal tides off the Amazon shelf – Part 1: The importance of the structuring of ocean temperature during two contrasted seasons

Abstract. The impact of internal and barotropic tides on the vertical and horizontal temperature structure off the Amazon River was investigated during two highly contrasted seasons (AMJ: April–May–June; ASO: August–September–October) over a 3-year period from 2013 to 2015. Twin regional simulations, with and without tides, were used to highlight the general effect of tides. The findings reveal that tides have a cooling effect on the ocean from the surface (∼ 0.3 ∘C) to above the thermocline (∼ 1.2 ∘C), while warming it up below the thermocline (∼ 1.2 ∘C). The heat budget analysis indicates that the vertical mixing is the dominant process driving temperature variations within the mixed layer, while it is associated with both horizontal and vertical advection to explain temperature variations below. The increased mixing in the simulations including tides is attributed to breaking of internal tides (ITs) on their generation sites over the shelf break and offshore along their propagation pathways. Over the shelf, mixing is driven by the dissipation of the barotropic tides. In addition, the vertical terms of the heat budget equation exhibit wavelength patterns typical of mode-1 IT. The study highlights the key role of tides and particularly how IT-related vertical mixing shapes the ocean temperature off the Amazon. Furthermore, we found that tides impact the interactions between the upper ocean interface and the overlying atmosphere. They contribute significantly to increasing the net heat flux between the atmosphere and the ocean, with a notable seasonal variation from 33.2 % in AMJ to 7.4 % in ASO seasons. This emphasizes the critical role of tidal dynamics in understanding regional-scale climate.

Diapycnal mixing induced by salt finger and internal tides on the northwest coast of India

Microstructure measurements of velocity shear from the continental slope of the northwest coast of India (NWCI) in the eastern Arabian Sea are used to quantify the relative importance of double diffusion and internal tides induced diapycnal mixing in the different depth layers. It is found that the hydrographic conditions in the NWCI are conducive to the formation of moderately strong salt fingering (Turner angle between 55° and 72°). However, salt finger-induced vertical mixing dominates only in the upper 180 m of the water column, below which intense shear-driven turbulent mixing due to internal tide reduces its significance. As a result of this, the staircase structures, a measure of salt finger dominance in the water column, are frequent, and the mean temperature change across the interface (DTIH; 0.33 °C) is relatively larger in the upper 180 m compared to sporadic occurrence of steps with a small magnitude of DTIH (0.18 °C) below 180 m. It is also found that in the upper 180 m of the water column in the NWCI, mean diapycnal diffusivity (Kρ) is approximately a factor of eight larger (8.3 ± 1.3 × 10−5 m2s−1) than the estimation in the open ocean region of the eastern Arabian sea (5.4 ± 1.1 × 10−6 m2 s−1). However, due to internal tides, the magnitude of Kρ reaches as large as O (10−2) m2 s−1 below 180 m in the NWCI. The mean downward heat flux estimated in the salt finger-dominated (upper 180 m) layers is ∼ -6.1 Wm-2, and the shear-driven mixing-dominated layers (below 180 m) is ∼ -10.2 Wm-2.

Sensitivity of Internal-Tide Generation to Stratification and Its Implication for Deep Overturning Circulations

Abstract The simple scaling relation for internal-tide generation proposed by Jayne and St. Laurent is widely used for parameterizing turbulent mixing induced by breaking of internal tides. Based on the internal-tide generation derived from a 0.1° ocean general circulation model, we show that depending on which stratification is used, this relation produces different vertical distributions of internal-tide generation. When using the buoyancy frequency at the seafloor, which is a common practice, the scaling relation produces, relative to the model, too-strong internal-tide generation in the upper 2000 m and too-weak internal-tide generation in the lower 2000 m. Moreover, the different vertical distributions in the different ocean basins, characterized by a generally decreasing internal tide generation with increasing depth in the Indo-Pacific but not-decreasing or even increasing internal tide generation with increasing depth in the upper 3000 m of the Atlantic, cannot be captured when using bottom stratification. These unsatisfactory features can be easily removed by replacing the buoyancy frequency at the seafloor by a buoyancy frequency averaged over a large part of the water column. To our knowledge, this sensitivity to stratification has not been explicitly quantified for the global ocean. Because of this sensitivity, the scaling relation of Jayne and St. Laurent should be used with an averaged stratification to ensure a more adequate representation of turbulent diffusivity due to tidal mixing and water mass transformation in the deep oceans.

Analysis of internal tide characteristics in the northwest pacific ocean

The available potential energy of the diurnal internal tide in the Northwest Pacific ocean is studied by using short-term high-frequency mooring observations. The results show that in the upper layer of the ocean, its distribution is relatively chaotic, and it is greater between 1500-1600 m and 2500-3000 m in the middle layer of the ocean. At other depths, it is generally smaller, especially, at the bottom layer of the ocean, it is relatively small. This paper concludes that the marvel of measurement is the best science picks.

Characterization of solitary internal waves in the northern Bali waters

Internal solitary wave (ISW) is an underwater wave, formed due to the evolution of internal tides. The presence of breaking ISWs in coastal areas can potentially influence coastal ecosystems through cross-shelf exchange mechanisms. The southern waters of the Kangean Island and the eastern waters of the Madura Island, known also as part of the northern Bali waters, have been an active habitat for ISW propagation. This study aims to identify and characterize ISW which potentially breaking onshore the Southern Kangean Waters (SKW) and the Eastern Madura Waters (EMW) using Sentinel 1 SAR (Synthetic Aperture Radar) imagery. ISW characterization was carried out using the Korteweg-de Vries (KdV) model. The ISW amplitudes which propagate to EMW varies from 1 - 28 m with a propagation speed of 1.60 - 1.98 m/s, while the ISW which propagate to the SKW has an amplitude of 1 - 60 m with a propagation speed of 0.83 to 2.17 m/s. The results show that the ISW propagating to the SKW has stronger amplitude, phase velocity, and horizontal-vertical velocities than the ISW propagating to the EMW. The maximum speed of the horizontal current triggered by ISW leading to the EMW is 0.03 - 0.17 m/s and the vertical velocity 0.11 - 4.53 cm/s; the maximum speed of horizontal velocity leading to the SKW is 0.02 - 1.29 m/s and the maximum speed of the vertical velocity 0.04 - 19.03 cm/s.

Sedimentary record of bottom currents and internal tides in a modern highstand submarine canyon head

ABSTRACTThe evolution of submarine canyons is primarily controlled by turbidity currents, which erode and fill them over time; however, many other hydrodynamic currents operate within canyons. Bottom currents from these other hydrodynamic processes, including internal tides, can be dominant processes, but their deposits are seldom recognized in sediment cores or the rock record. This study combines autonomous underwater vehicle swath bathymetry imagery and sub‐bottom profiles, high‐resolution sediment core analyses (X‐ray imagery and thin sections), and previously collected seabed video and flow measurements within Logan Canyon head (eastern Canada) to provide a detailed, modern record of facies associated with hydrodynamic processes in a canyon head. These results suggest that bottom currents are responsible for maintaining gullies on canyon sidewalls and an axial channel on the canyon floor. Thin sections of sediment cores reveal that muddy sand in the canyon head consists of mud aggregates and silt and fine‐grained sand, both behaving similarly in terms of flow dynamics. Three facies are present at macro‐scale and micro‐scale: laminated, partially laminated and bioturbated sandy mud. Sedimentary structures include rhythmic sand and mud aggregate couplets, planar to wavy laminations, current ripple cross‐laminations and fining‐upward successions, which are attributed to bottom currents induced by internal tides. Bioturbated facies, characterized by discrete biogenic structures and cross‐cutting relationships, predominate and overprint a mottled background. A mottled bioturbation fabric also alternates with or locally disrupts layering within the partially laminated facies. Internal tide currents, capable of bedload transport and forming ripples, were measured during a monitoring period in the canyon head, followed by rapid re‐establishment of benthos and associated biogenic structures, supporting the core interpretations. Preservation of sedimentary facies associated with these internal tides occurs when the sedimentation rate outpaces the rate of bioturbation, likely during stormier conditions on the shelf. These results represent observations of sedimentary facies associated with modern bottom currents and internal tides, and can be used to interpret similar occurrences within the rock record.

Stability of constrained solitary waves for the Ostrovsky–Vakhnenko model in the coastal zone

In this paper, we consider a nonlinear water wave model describing the evolution of the internal tides in the coastal zone. First, we prove the existence of minimizers for the corresponding energy functional on the L2-norm constrained manifold by the concentrated compactness principle, and thus we obtain a ground state traveling wave solution of the model. Moreover, we show that the solution has exponential decay in the far field. Finally, we show that the traveling wave solution is non-degenerate, and thus the spectral stability of the solution can be obtained by using the instability index theory.

Nutricline adjustment by internal tidal beam generation enhances primary production in idealized numerical models

When the barotropic tide encounters variable bathymetry, fluctuating flow along a topographic slope generates baroclinic tides, or internal tides. There is growing evidence that these internal tides can affect primary production in the euphotic zone, though the dominant mechanisms are unclear. Internal tides move passive phytoplankton through an exponentially varying light field, enhancing primary production near the base of the euphotic zone. In addition internal tides also increase primary production through vertical nutrient advection into the euphotic zone. Topographically generated internal tides can be separated into two regimes: 1) the often highly nonlinear near-field regime where tidal beams are observed and 2) the more linear far-field regime. This study examines the primary production response to these internal tide processes using the Regional Ocean Modeling System (ROMS) coupled to a simple Nutrient, Phytoplankton, Zooplankton, Detritus (NPZD) model configured for an oligotrophic system with the nutricline positioned below 50 m depth. These idealized simulations generate internal tide beams with an oscillating, horizontal body force at the M2 tidal frequency that is applied to domains with a bathymetric step and uniform stratification. Sensitivity of the primary production response to the energy content of the tidal beam is obtained by adjusting the height and slope of the bathymetric step. Simulation results reveal that primary production intensifies along tidal beams due to the local enhancement of parcel vertical displacement (light effect) and nutrient advective flux divergence (nutrient effect). In the near-field regime across the range of step heights and slopes in this study, the nutrient effect is an order of magnitude larger and explains 92% of the variance in primary production versus only 14% for the light effect. The geometry of the generating feature sets the kinematics of the tidal beam. The light effect is limited in the euphotic zone across our domains because realized changes in light experienced over a tidal cycle are small relative to the amount of light available at a particular depth. In contrast, the magnitude of the nutrient effect increases more substantially with tidal beam energy.

Satellite Evidence for Strengthened M2 Internal Tides in the Past 30 Years

AbstractSatellite altimetry sea surface height measurements from 1993 to 2022 are used to show the strengthened mode‐1 M2 internal tides in the past 30 years. Two mode‐1 M2 internal tide models M9509 and M1019 are constructed using the data in 1995–2009 and 2010–2019, respectively. The results show that the global mean M2 internal tides strengthened by 6% in energy. However, the internal tide strengthening is spatially inhomogeneous. Significantly strengthened internal tides are observed in a number of regions including the Aleutian Ridge and the Madagascar‐Mascarene region. Weakened internal tides are observed in the central Pacific. On global average, M1019 leads M9509 by about 10° (20 min in time), suggesting that the propagation speed of M2 internal tides increased. M9509 and M1019 are evaluated using independent altimetry data. The results show that M9509 and M1019 perform better for the data in 1993–1994 and 2020–2022, respectively.

Vertical Mixing in The Onshore Region of The Northwestern Maluku Sea, Indonesia

Spatio-temporal dynamics of vertical mixing in the northwestern Maluku Sea were quantified using the Thorpe Method from archived CTD datasets collected during the expedition of Baruna Jaya VIII RCO-LIPI on November 12–13, 2000. The turbulent kinetic energy (TKE) dissipation rate and vertical eddy diffusivity values inspected the variability of mixing properties. Higher values for both parameters were found at the shallower bathymetry, which is less than 1000 m deep. This suggests that the water column is vertically unstable as a result of being often subjected to internal solitary wave (ISW) breaking events. The strong temporal variability observed from the density profile also indicated a strong impact on internal tide activity. There was temporal fluctuation of the TKE dissipation rate as well as vertical eddy diffusivity values following semidiurnal periodicity, with typical variability up to one order of magnitude for both the dissipation and diffusivity. The range of fluctuation is [6.8×10-8 ? 9.3×10-7] W kg-1 and [1.5×10-5 – 5.4×10-3] m2s-1, respectively in the upper 200 m depth. This water generated a high dissipation rate and vertical diffusivity when regularly exposed to internal solitary waves breaking from the Lifamatola Passage.Keywords: mixing properties, CTD data, turbulent kinetic energy, vertical eddy diffusivity

Propagation Features of Diurnal Internal Tides West of the Luzon Strait Revealed by a Large PIES Array

Abstract Energetic internal tides (ITs) are generated from the Luzon Strait (LS) and propagate westward into the South China Sea (SCS). Owing to the lack of large-scale synchronous measurements, the propagation features and seasonal variations of diurnal ITs remain unclear. From 2018 to 2019, mode-1 diurnal ITs west of the LS were continuously observed using a large-scale moored array of 27 pressure-recording inverted echo sounders (PIESs) and a thermistor chain. Measurements confirmed that diurnal ITs radiate from the LS with a north–south asymmetrical pattern, with the most energetic channel located in the middle and south of the LS. The total energy radiated into the SCS across 120°E is 2.67 GW for the K1 ITs and 1.54 GW for the O1 ITs, approximately 2 times larger than those inferred from satellite observations. K1 dominates among the diurnal ITs, with its maximum isopycnal displacement (amplitude) and energy input to the SCS being the strongest in summer (i.e., 16.3 m and 2.81 GW, respectively). The propagation speed of K1 is higher in summer and autumn along the main channel (i.e., 4.33and 4.36 m s−1, respectively). Seasonal stratification and circulation play important roles in the seasonal variation of amplitude and propagation speed of the K1 ITs. The seasonal variability of diurnal-band ITs, which includes all diurnal constituents, is location-dependent and primarily results from the superposition of the K1 and P1 ITs. In particular, vertical displacement is strong in summer and winter along the main channel of the K1 and P1 ITs. The seasonal amplitude of K1 can modulate this seasonal feature. Significance Statement Internal tides (ITs) are internal waves at tidal frequencies. The Luzon Strait (LS) is one of the most energetic sites to generate large-amplitude ITs. The ITs propagate into the South China Sea (SCS), interact with mesoscale eddies, large-scale circulations, etc., and influence local hydrodynamics as well as ecosystem and sediment transport. This motivated an observation plan to investigate the ITs at the western entrance of the LS. From June 2018 to August 2019, an array of 28 PIESs was deployed in the northeastern SCS, almost covering the western entrance of the LS, to investigate the propagation properties of ITs including their amplitude, phase speed, wavelength, propagation direction, and energy fluxes and their annual and seasonal variations. Here, we primarily focus on the mode-1 diurnal ITs. The new insights enrich our understanding of IT dynamics and seasonal variations and support further improvements in numerical simulations.

Eddy Acceleration and Decay Driven by Internal Tides

Abstract Recent observations and numerical simulations have demonstrated the potential for significant interactions between mesoscale eddies and smaller-scale tidally generated internal waves—also known as internal tides. Here, we develop a simple theoretical model that predicts the one-way upscale transfer of energy from internal tides to mesoscale eddies through a critical level mechanism. We find that—in the presence of a critical level—the internal tide energy flux into an eddy is partitioned according to the wave frequency Ω and local inertial frequency f: a fraction of 1 − f/Ω is transferred to the eddy kinetic energy, while the remainder is viscously dissipated or supports mixing. These predictions are validated by comparison with a suite of numerical simulations. The simulations further show that the wave-driven energization of the eddies also accelerates the onset of hydrodynamical instabilities and the breakdown of the eddies, thereby increasing eddy kinetic energy, but reducing eddy lifetimes. Our estimates suggest that in regions of the ocean with both significant eddy fields and internal tides—such as parts of the Gulf Stream and Antarctic Circumpolar Current—the critical level effect could drive a ∼10% month−1 increase in the kinetic energy of a typical eddy. Our results provide a basis for parameterizing internal tide–eddy interactions in global ocean models where they are currently unrepresented.

Nonlinear Internal Tides in a Realistically Forced Global Ocean Simulation

AbstractThe decay of the low‐mode internal tide due to the superharmonic energy cascade is investigated in a realistically forced global Hybrid Coordinate Ocean Model simulation with 1/25° (4 km) horizontal grid spacing. Time‐mean and depth‐integrated supertidal kinetic energy is found to be largest near low‐latitude internal tide generation sites, such as the Bay of Bengal, Amazon Shelf, and Mascarene Ridge. The supertidal kinetic energy can make up to 50% of the total internal tide kinetic energy several hundred kilometers from the generation sites. As opposed to the tidal flux divergence, the supertidal flux divergence does not correlate with the barotropic to baroclinic energy conversion. Instead, the time‐mean and depth‐integrated supertidal flux divergence correlates with the nonlinear kinetic energy transfers from (sub)tidal to supertidal frequency bands as estimated with a novel coarse‐graining approach. The regular spaced banding patterns of the surface‐intensified nonlinear energy transfers are attributed to semidiurnal mode 1 and mode 2 internal waves that interfere constructively at the surface. This causes patches where both surface tidal kinetic energy and nonlinear energy transfers are elevated. The simulated internal tide off the Amazon Shelf steepens significantly near these patches, generating solitary‐like waves in good agreement with Synthetic Aperture Radar imagery. Globally, we find that regions of high supertidal energy flux also show a high correlation with observed instances of internal solitary waves.

Regional internal tide models need prudent eddy viscosity selections for dependable estimations

Many studies on internal tides (ITs) are conducted through numerical simulations. One major challenge involves the large discrepancies in baroclinic energetics in regional seas, such as the Luzon Strait (LS). These discrepancies may partially be related to the variation in eddy viscosity selections. Evident increase in eddy viscosities can affect the baroclinic energy balances and reduce simulation error in the LS. Finally, horizontal mixing parameterization schemes are found to be significant in improving the performance of regional IT modeling. The finding highlights the significance of eddy viscosity, which may make contributions to improve regional IT estimations.

Characteristics of Internal Solitary Waves near Its Generation Site in the Lombok Strait, Indonesia

Evidence of internal solitary waves (ISWs) formation through the Lee wave mechanism in the Lombok Strait was revealed from the echosounder measurements conducted in November 2017. This study is aimed to characterize the property of ISW packet formed around ~30 km away from the generation site, in the southern part of the strait above the Nusa Penida Sill (NPS), by employing Korteweg-de Vries (KdV) solution. The packet can be categorized as the early stage of ISW formation, consisting of two waves of depression, with typical amplitude of 30 m and 10 m, for the first and second wave, respectively. The waves propagated northward with a typical phase speed of ~1.2 m∙s -1. The waves drive a maximum horizontal velocity anomaly of ~0.8 m∙s - 1 and a vertical velocity anomaly of ~10 cm∙s -1. The amplitude of the ISW packet will be potentially amplified during their propagation away from the strait. This study provides an observational based understanding on the early stage of internal tides evolution in the Lombok Strait, particularly highlights the energy transfer of internal tides through the propagation of internal solitary waves.

Observed near-inertial waves generated by tropical and extratropical cyclones in the East China Sea

Both tropical and extratropical cyclones can affect the East China Sea (ECS) shelf in summer. Based on a current mooring deployed in 2014, near-inertial waves (NIWs) triggered by both extratropical and tropical cyclones were examined. During the observation period, three tropical cyclones (i.e., NEOGURI, MATMO, and NAKRI) passed by the mooring site. MATMO and NAKRI led to obvious near-inertial responses. The weakest tropical cyclone (MATMO) caused the strongest NIWs due to its large translation speed and favorable position relative to the mooring site. Mode 1 dominates the vertical structure of the NIWs caused by tropical cyclones. Due to the modulation of the background vorticity, the NIWs show a significant blueshift. However, the NIWs caused by extratropical cyclones are mainly concentrated near the surface layer with a higher proportion of mode-2 NIWs. The highest value of the near-inertial kinetic energy generated by extratropical cyclones is about half of that generated by tropical cyclones. In addition, both two kinds of cyclones can lead to an enhancement of sub-inertial current in the ECS shelf. The nonlinear interactions between NIWs and semidiurnal internal tides (D2) are also evidenced, with the NIWs being a potential trigger for D2-f waves. This study highlights the important role of NIW on the nonlinear interactions and energy transfer within the internal wave spectral continuum in the continental shelf region.