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1
Savage, Anna C., Amy F. Waterhouse, and Samuel M. Kelly. "Internal Tide Nonstationarity and Wave–Mesoscale Interactions in the Tasman Sea." Journal of Physical Oceanography 50, no. 10 (October 1, 2020): 2931–51. http://dx.doi.org/10.1175/jpo-d-19-0283.1.
Анотація:
AbstractInternal tides, generated by barotropic tides flowing over rough topography, are a primary source of energy into the internal wave field. As internal tides propagate away from generation sites, they can dephase from the equilibrium tide, becoming nonstationary. Here, we examine how low-frequency quasigeostrophic background flows scatter and dephase internal tides in the Tasman Sea. We demonstrate that a semi-idealized internal tide model [the Coupled-Mode Shallow Water model (CSW)] must include two background flow effects to replicate the in situ internal tide energy fluxes observed during the Tasmanian Internal Tide Beam Experiment (TBeam). The first effect is internal tide advection by the background flow, which strongly depends on the spatial scale of the background flow and is largest at the smaller scales resolved in the background flow model (i.e., 50–400 km). Internal tide advection is also shown to scatter internal tides from vertical mode-1 to mode-2 at a rate of about 1 mW m−2. The second effect is internal tide refraction due to background flow perturbations to the mode-1 eigenspeed. This effect primarily dephases the internal tide, attenuating stationary energy at a rate of up to 5 mW m−2. Detailed analysis of the stationary internal tide momentum and energy balances indicate that background flow effects on the stationary internal tide can be accurately parameterized using an eddy diffusivity derived from a 1D random walk model. In summary, the results identify an efficient way to model the stationary internal tide and quantify its loss of stationarity.
2
Lelong, M. P., and E. Kunze. "Can barotropic tide–eddy interactions excite internal waves?" Journal of Fluid Mechanics 721 (March 13, 2013): 1–27. http://dx.doi.org/10.1017/jfm.2013.1.
Анотація:
AbstractThe interaction of barotropic tidal currents and baroclinic geostrophic eddies is considered theoretically and numerically to determine whether energy can be transferred to an internal wave field by this process. The eddy field evolves independently of the tide, suggesting that it acts catalytically in facilitating energy transfer from the barotropic tide to the internal wave field, without exchanging energy with the other flow components. The interaction is identically zero and no waves are generated when the barotropic tidal current is horizontally uniform. Optimal internal wave generation occurs when the scales of tide and eddy fields satisfy resonant conditions. The most efficient generation is found if the tidal current horizontal scale is comparable to that of the eddies, with a weak maximum when the scales differ by a factor of two. Thus, this process is not an effective mechanism for internal wave excitation in the deep ocean, where tidal current scales are much larger than those of eddies, but it may provide an additional source of internal waves in coastal areas where horizontal modulation of the tide by topography can be significant.
3
Kerry, Colette G., Brian S. Powell, and Glenn S. Carter. "The Impact of Subtidal Circulation on Internal-Tide-Induced Mixing in the Philippine Sea." Journal of Physical Oceanography 44, no. 12 (November 26, 2014): 3209–24. http://dx.doi.org/10.1175/jpo-d-13-0249.1.
Анотація:
Abstract This study uses a primitive equation model to estimate the time-varying M2 internal tide dissipation in the Philippine Sea in the presence of the subtidal circulation. The time-mean diapycnal diffusivity due to the M2 internal tide is estimated to be 4.0–4.8 × 10−4 m2 s−1 at the Luzon Strait and 2–9 × 10−5 m2 s−1 in the Philippine Sea basin. The variability in internal tides and their interactions with the subtidal ocean circulation results in significant spatial and temporal variability in the energy available for mixing. The subtidal circulation influences internal-tide-induced mixing in two ways: by introducing variability in internal tide generation and by increased dissipation of baroclinic energy associated with greater velocity shear. Close to the generation site, mixing is dominated by high-mode internal tide dissipation, while in the far field the influence of the mesoscale energy on internal tide dissipation is significant, resulting in increased dissipation. This study presents model-based estimates of the important and relatively unknown effect of mesoscale circulation on internal-tide-induced mixing away from internal tide generation sites in a region of high eddy kinetic energy.
4
Fernández-Castro, Bieito, Dafydd Gwyn Evans, Eleanor Frajka-Williams, Clément Vic, and Alberto C. Naveira-Garabato. "Breaking of Internal Waves and Turbulent Dissipation in an Anticyclonic Mode Water Eddy." Journal of Physical Oceanography 50, no. 7 (July 1, 2020): 1893–914. http://dx.doi.org/10.1175/jpo-d-19-0168.1.
Анотація:
AbstractA 4-month glider mission was analyzed to assess turbulent dissipation in an anticyclonic eddy at the western boundary of the subtropical North Atlantic. The eddy (radius ≈ 60 km) had a core of low potential vorticity between 100 and 450 m, with maximum radial velocities of 0.5 m s−1 and Rossby number ≈ −0.1. Turbulent dissipation was inferred from vertical water velocities derived from the glider flight model. Dissipation was suppressed in the eddy core (ε ≈ 5 × 10−10 W kg−1) and enhanced below it (>10−9 W kg−1). Elevated dissipation was coincident with quasiperiodic structures in the vertical velocity and pressure perturbations, suggesting internal waves as the drivers of dissipation. A heuristic ray-tracing approximation was used to investigate the wave–eddy interactions leading to turbulent dissipation. Ray-tracing simulations were consistent with two types of wave–eddy interactions that may induce dissipation: the trapping of near-inertial wave energy by the eddy’s relative vorticity, or the entry of an internal tide (generated at the nearby continental slope) to a critical layer in the eddy shear. The latter scenario suggests that the intense mesoscale field characterizing the western boundaries of ocean basins might act as a “leaky wall” controlling the propagation of internal tides into the basin’s interior.
5
Fan, Liming, Hui Sun, Qingxuan Yang, and Jianing Li. "Numerical investigation of interaction between anticyclonic eddy and semidiurnal internal tide in the northeastern South China Sea." Ocean Science 20, no. 1 (February 21, 2024): 241–64. http://dx.doi.org/10.5194/os-20-241-2024.
Анотація:
Abstract. We investigate the interaction between an anticyclonic eddy (AE) and semidiurnal internal tide (SIT) on the continental slope of the northeastern South China Sea (SCS), using a high spatiotemporal resolution numerical model. Two key findings are as follows: first, the AE promotes energy conversion from low-mode to higher-mode SIT. Additionally, production terms indicate that energy is also transferred from the SIT field to the eddy field at an average rate of 3.0 mW m−2 (accounting for 7 % of the incoming energy flux of SIT when integrated over the eddy diameter). Second, the AE can modify the spatial distribution of tidal-induced dissipation by refracting, scattering, and reflecting low-mode SIT. The phase and group velocities of the SIT are significantly influenced by the eddy field, resulting in a northward or southward shift in the internal tidal rays. These findings deepen our understanding of the complex interactions between AE and SIT, as well as their impacts on energy conversion, wave propagation, and coastal processes.
6
Qi, Yongfeng, Huabin Mao, Xia Wang, Linhui Yu, Shumin Lian, Xianpeng Li, and Xiaodong Shang. "Suppressed Thermocline Mixing in the Center of Anticyclonic Eddy in the North South China Sea." Journal of Marine Science and Engineering 9, no. 10 (October 19, 2021): 1149. http://dx.doi.org/10.3390/jmse9101149.
Анотація:
Direct microstructure observations and fine-scale measurements of an anticyclonic mesoscale eddy were conducted in the northern South China Sea in July 2020. An important finding was that suppressed turbulent mixing in the thermocline existed at the center of the eddy, with an averaged diapycnal diffusivity at least threefold smaller than the peripheral diffusivity. Despite the strong background shear and significant wave–mean flow interactions, the results indicated that the lack of internal wave energy in the corresponding neap tide period during measurement of the eddy’s center was the main reason for the suppressed turbulent mixing in the thermocline. The applicability of the fine-scale parameterization method in the presence of significant wave–mean flow interactions in a mesoscale eddy was evaluated. Overprediction via fine-scale parameterization occurred in the center of the eddy, where the internal waves were inactive; however, the parameterization results were consistent with microstructure observations along the eddy’s periphery, where active internal waves existed. This indicates that the strong background shear and wave–mean flow interactions affected by the mesoscale eddy were not the main contributing factors that affected the applicability of fine-scale parameterization in the northern South China Sea. Instead, our results showed that the activity of internal waves is the most important consideration.
7
Huang, Xiaodong, Zhaoyun Wang, Zhiwei Zhang, Yunchao Yang, Chun Zhou, Qingxuan Yang, Wei Zhao, and Jiwei Tian. "Role of Mesoscale Eddies in Modulating the Semidiurnal Internal Tide: Observation Results in the Northern South China Sea." Journal of Physical Oceanography 48, no. 8 (August 2018): 1749–70. http://dx.doi.org/10.1175/jpo-d-17-0209.1.
Анотація:
AbstractThe role of mesoscale eddies in modulating the semidiurnal internal tide (SIT) in the northern South China Sea (SCS) is examined using the data from a cross-shaped mooring array. From November 2013 to January 2014, an anticyclonic eddy (AE) and cyclonic eddy (CE) pair crossed the westward SIT beam originating in Luzon Strait. Observations showed that, because of the current and stratification modulations by the eddy pair, the propagation speed of the mode-1 SIT sped up (slowed down) by up to 0.7 m s−1 (0.4 m s−1) within the AE’s (CE’s) southern portion. As a result of the spatially varying phase speed, the mode-1 SIT wave crest was clockwise rotated (counterclockwise rotated) within the AE (CE) core, while it exhibited convex and concave (concave and convex) patterns on the southern and northern peripheries of the AE (CE), respectively. In mid-to-late November, most of the mode-1 SIT energy was refracted by the AE away from Dongsha Island toward the north part of the northern SCS, which resulted in enhanced internal solitary waves (ISWs) there. Corresponding to the energy refraction, responses of the depth-integrated mode-1 SIT energy to the eddies were generally in phase at the along-beam-direction moorings but out of phase in the south and north parts of the northern SCS at the cross-beam-direction moorings. From late December to early January, intensified mode-2 SIT was observed, whose energy was likely transferred from the mode-1 SIT through eddy–wave interactions. The observation results reported here are helpful to improve the capability to predict internal tides and ISWs in the northern SCS.
8
Kunze, Eric, Eric Firing, Julia M. Hummon, Teresa K. Chereskin, and Andreas M. Thurnherr. "Global Abyssal Mixing Inferred from Lowered ADCP Shear and CTD Strain Profiles." Journal of Physical Oceanography 36, no. 8 (August 1, 2006): 1553–76. http://dx.doi.org/10.1175/jpo2926.1.
Анотація:
Abstract Internal wave–wave interaction theories and observations support a parameterization for the turbulent dissipation rate ɛ and eddy diffusivity K that depends on internal wave shear 〈Vz2〉 and strain 〈ξz2〉 variances. Its latest incarnation is applied to about 3500 lowered ADCP/CTD profiles from the Indian, Pacific, North Atlantic, and Southern Oceans. Inferred diffusivities K are functions of latitude and depth, ranging from 0.03 × 10−4 m2 s−1 within 2° of the equator to (0.4–0.5) × 10−4 m2 s−1 at 50°–70°. Diffusivities K also increase with depth in tropical and subtropical waters. Diffusivities below 4500-m depth exhibit a peak of 0.7 × 10−4 m2 s−1 between 20° and 30°, latitudes where semidiurnal parametric subharmonic instability is expected to be active. Turbulence is highly heterogeneous. Though the bulk of the vertically integrated dissipation ∫ɛ is contributed from the main pycnocline, hotspots in ∫ɛ show some correlation with small-scale bottom roughness and near-bottom flow at sites where strong surface tidal dissipation resulting from tide–topography interactions has been implicated. Average vertically integrated dissipation rates are 1.0 mW m−2, lying closer to the 0.8 mW m−2 expected for a canonical (Garrett and Munk) internal wave spectrum than the global-averaged deep-ocean surface tide loss of 3.3 mW m−2.
9
Rapaka, Narsimha R., Bishakhdatta Gayen, and Sutanu Sarkar. "Tidal conversion and turbulence at a model ridge: direct and large eddy simulations." Journal of Fluid Mechanics 715 (January 9, 2013): 181–209. http://dx.doi.org/10.1017/jfm.2012.513.
Анотація:
AbstractDirect and large eddy simulations are performed to study the internal waves generated by the oscillation of a barotropic tide over a model ridge of triangular shape. The objective is to go beyond linear theory and assess the role of nonlinear interactions including turbulence in situations with low tidal excursion number. The criticality parameter, defined as the ratio of the topographic slope to the characteristic slope of the tidal rays, is varied from subcritical to supercritical values. The barotropic tidal forcing is also systematically increased. Numerical results of the energy conversion are compared with linear theory and, in laminar flow at low forcing, they agree well in subcritical and supercritical cases but not at critical slope angle. In critical and supercritical cases with higher forcing, there are convective overturns, turbulence and significant reduction (as much as 25 %) of the radiated wave flux with respect to laminar flow results. Analysis of the baroclinic energy budget and spatial modal analysis are performed to understand the reduction. The near-bottom velocity is intensified at critical angle slope leading to a radiated internal wave beam as well as an upslope bore of cold water with a thermal front. In the critical case, the entire slope has turbulence while, in the supercritical case, turbulence originates near the top of the topography where the slope angle transitions through the critical value. The phase dependence of turbulence within a tidal cycle is examined and found to differ substantially between the ridge slope and the ridge top where the beams from the two sides cross.
10
Dunphy, Michael, Aurélien L. Ponte, Patrice Klein, and Sylvie Le Gentil. "Low-Mode Internal Tide Propagation in a Turbulent Eddy Field." Journal of Physical Oceanography 47, no. 3 (March 2017): 649–65. http://dx.doi.org/10.1175/jpo-d-16-0099.1.
Анотація:
AbstractUnderstanding and predicting how internal tides distort and lose coherence as they propagate through the ocean has been identified as a key issue for interpreting data from the upcoming wide-swath altimeter mission Surface Water and Ocean Topography (SWOT). This study addresses the issue through the analysis of numerical experiments where a low-mode internal tide propagates through a quasigeostrophic turbulent jet. Equations of motion linearized around the slower turbulent field are projected onto vertical modes and assumed to describe the dynamics of the low-mode internal tide propagation. Diagnostics of the terms responsible for the interaction between the wave and the slow circulation are computed from the numerical outputs. The large-scale change of stratification, on top of eddies and jet meanders, contributes significantly to these interaction terms, which is shown to be consistent with an independent scaling analysis. The sensitivity of interaction terms to a degradation of the slow field spatial and temporal resolution indicates that present-day observing systems (Argo network, altimetry) may lack the spatial resolution necessary to correctly predict internal tide evolution. The upcoming SWOT satellite mission may improve upon this situation. The number of vertical modes required to properly estimate interaction terms is discussed. These results advocate development of a simplified model based on solving a modest number of the linearized equations subject to a prescribed mesoscale field and internal tide sources.
11
Lim, Gyuchang, and Jong-Jin Park. "Examining Modulations of Internal Tides within An Anticyclonic Eddy Using a Wavelet-Coherence Network Approach." Applied Sciences 14, no. 3 (January 24, 2024): 1001. http://dx.doi.org/10.3390/app14031001.
Анотація:
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.
12
Dunphy, Michael, and Kevin G. Lamb. "Focusing and vertical mode scattering of the first mode internal tide by mesoscale eddy interaction." Journal of Geophysical Research: Oceans 119, no. 1 (January 2014): 523–36. http://dx.doi.org/10.1002/2013jc009293.
13
Hazewinkel, J., та K. B. Winters. "PSI of the Internal Tide on a β Plane: Flux Divergence and Near-Inertial Wave Propagation". Journal of Physical Oceanography 41, № 9 (1 вересня 2011): 1673–82. http://dx.doi.org/10.1175/2011jpo4605.1.
Анотація:
Abstract The dynamics of a forced, low-mode oceanic internal tide propagating poleward on a β plane are investigated numerically. The focus is on the transfer of energy from the tide to near-inertial oscillations (NIOs) initiated by a weakly nonlinear interaction known as parametric subharmonic instability (PSI). It is shown that PSI is a mechanism for generating NIOs in the upper ocean, which subsequently radiate to depth. The exponentially growing NIOs eventually reach finite amplitude, and further interaction with the tide leads to a quasi-steady state in which dissipation is balanced by a reduction in the poleward tidal flux. The results are sensitive to the prescribed value of the vertical eddy viscosity νe that serves to parameterize the background turbulence. This sensitivity suggests that independent processes leading to turbulence in the upper ocean are able to control the rate of energy transfer from the tide to NIOs. For νe = O(10−5 m2 s−1), the poleward tidal flux decreases approximately 15%. This value is much smaller than was found in previous numerical studies, but it is in reasonable agreement with recent estimates from observations taken near the M2/2 inertial latitude in the Pacific.
14
Hermansyah, Hadi, Agus Saleh Atmadipoera, Tri Prartono, Indra Jaya, and Fadli Syamsudin. "Percampuran Turbulen Di Laut Sulawesi Menggunakan Estimasi Thorpe Analisis." Jurnal Kelautan Tropis 24, no. 2 (April 16, 2021): 211–22. http://dx.doi.org/10.14710/jkt.v24i2.7352.
Анотація:
Dissipation of internal tides will cause mixing, The mixing process at sea plays a key role in controlling large-scale circulation and ocean energy distribution. The purpose of this research was to estimate the turbulent mixing values (vertical eddy diffusivity) of water mass using Thorpe analysis. The results showed that the location where strong mixing occurred in the “near-field” area around Sangihe Island with vertical diffusivity value . Even in areas far-field(far from the generating site) are found vertical diffusivity , the result of internal propagation tides dissipation. Based on the result of the observation, it shows that the level of kinetic energy of eddy turbulen dissipation (ε) in the Sulawesi Sea on all layers has an average value of . The value of ε in the thermocline layer is greatest compared to the mixed surface layer and the almost homogeneous deep layer, the increase in mixing in the area near the ridge due to the closer water column to the base topography. The average turbulent rate of , the strongest fluctuation of value occurs in the thermocline layer, ranging from to with an average of about . The value of this turbulent mixing is higher than the previous measurements in some Indonesian ocean. This is allegedly due to the existence of a strong internal tidal energy and its interaction with topography in the Sulawesi Sea.Disipasi dari pasang surut internal akan menyebabkan terjadinya percampuran, proses percampuran di laut memainkan peran kunci dalam mengendalikan sirkulasi skala besar dan distribusi energi lautan. Tujuan dari penelitian ini adalah untuk mengestimasi nilai percampuran turbulen (difusivitas eddy vertikal) massa air dengan analisis Thorpe. Hasil penelitian ini menunjukkan bahwa percampuran yang kuat terjadi di area sekitar Pulau Sangihe-Talaud dengan nilai difusivitas vertikal . Bahkan pada area yang jauh dari pusat pembangkitan ditemukan difusivitas vertikal , hasil disipasi propagasi pasang surut internal. Berdasarkan hasil pengamatan menunjukan bahwa rata-rata tingkat energi kinetik disipasi turbulen eddy Laut Sulawesi pada semua lapisan adalah . Nilai di lapisan termoklin paling besar dibandingkan dengan lapisan permukaan tercampur dan lapisan dalam yang hampir homogen, peningkatan percampuran di daerah dekat ridge disebabkan makin mendekatnya kolom air dengan topografi dasar. Rata-rata nilai percampuran turbulen sebesar , fluktuasi nilai yang paling kuat terjadi di lapisan termoklin, yang berkisar yaitu antara sampai dengan rerata sekitar . Nilai percampuran turbulen ini lebih tinggi dibandingkan dengan pengukuran sebelumnya di beberapa perairan Indonesia. Hal ini diduga karena adanya energi pasang surut internal yang kuat serta interaksinya dengan topografi yang ada di Laut Sulawesi.
15
Le Boyer, Arnaud, and Matthew H. Alford. "Variability and Sources of the Internal Wave Continuum Examined from Global Moored Velocity Records." Journal of Physical Oceanography 51, no. 9 (September 2021): 2807–23. http://dx.doi.org/10.1175/jpo-d-20-0155.1.
Анотація:
AbstractEnergy for ocean turbulence is thought to be transferred from its presumed sources (viz., the mesoscale eddy field, near-inertial internal waves, and internal tides) to the internal wave continuum, and through the continuum via resonant triad interactions to breaking scales. To test these ideas, the level and variability of the oceanic internal gravity wave continuum spectrum are examined by computing time-dependent rotary spectra from a global database of 2260 current meter records deployed on 1362 separate moorings. Time series of energy in the continuum and the three “source bands” (near-inertial, tidal, and mesoscale) are computed, and their variability and covariability examined. Seasonal modulation of the continuum by factors of up to 5 is seen in the upper ocean, implicating wind-driven near-inertial waves as an important source. The time series of the continuum is found to correlate more strongly with the near-inertial peak than with the semidiurnal or mesoscale. The use of moored internal-wave kinetic energy frequency spectra as an alternate input to the traditional shear or strain wavenumber spectra in the Gregg–Henyey–Polzin finescale parameterization is explored and compared to traditional strain-based estimates.
16
Lamb, K. G., and A. Warn-Varnas. "Two-dimensional numerical simulations of shoaling internal solitary waves at the ASIAEX site in the South China Sea." Nonlinear Processes in Geophysics 22, no. 3 (May 8, 2015): 289–312. http://dx.doi.org/10.5194/npg-22-289-2015.
Анотація:
Abstract. The interaction of barotropic tides with Luzon Strait topography generates some of the world's largest internal solitary waves which eventually shoal and dissipate on the western side of the northern South China Sea. Two-dimensional numerical simulations of the shoaling of a single internal solitary wave at the site of the Asian Seas International Acoustic Experiment (ASIAEX) have been undertaken in order to investigate the sensitivity of the shoaling process to the stratification and the underlying bathymetry and to explore the influence of rotation. The bulk of the simulations are inviscid; however, exploratory simulations using a vertical eddy-viscosity confined to a near bottom layer, along with a no-slip boundary condition, suggest that viscous effects may become important in water shallower than about 200 m. A shoaling solitary wave fissions into several waves. At depths of 200–300 m the front of the leading waves become nearly parallel to the bottom and develop a very steep back as has been observed. The leading waves are followed by waves of elevation (pedestals) that are conjugate to the waves of depression ahead and behind them. Horizontal resolutions of at least 50 m are required to simulate these well. Wave breaking was found to occur behind the second or third of the leading solitary waves, never at the back of the leading wave. Comparisons of the shoaling of waves started at depths of 1000 and 3000 m show significant differences and the shoaling waves can be significantly non-adiabatic even at depths greater than 2000 m. When waves reach a depth of 200 m, their amplitudes can be more than 50% larger than the largest possible solitary wave at that depth. The shoaling behaviour is sensitive to the presence of small-scale features in the bathymetry: a 200 m high bump at 700 m depth can result in the generation of many mode-two waves and of higher mode waves. Sensitivity to the stratification is considered by using three stratifications based on summer observations. They primarily differ in the depth of the thermocline. The generation of mode-two waves and the behaviour of the waves in shallow water is sensitive to this depth. Rotation affects the shoaling waves by reducing the amplitude of the leading waves via the radiation of long trailing inertia-gravity waves. The nonlinear-dispersive evolution of these inertia-gravity waves results in the formation of secondary mode-one wave packets.
17
Shakespeare, Callum J. "Eddy acceleration and decay driven by internal tides." Journal of Physical Oceanography, October 4, 2023. http://dx.doi.org/10.1175/jpo-d-23-0127.1.
Анотація:
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 energisation of the eddies also accelerates the onset of hydrodynamical instabilities and the break down 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% per month increase in the kinetic energy of a typical eddy. Our results provide a basis for parameterising internal tide-eddy interactions in global ocean models where they are currently unrepresented.
18
Fan, Liming, and Xin Wang. "Variability of Internal Wave Strain Over the Western Boundary Region in the North Atlantic." Frontiers in Earth Science 10 (April 12, 2022). http://dx.doi.org/10.3389/feart.2022.855644.
Анотація:
Based on the CTD profiles and mooring measurements of the Line W program in the North Atlantic about 35°N/70°W, we investigated the spatial variability of internal wave-induced strain variance along the Line W section and the associated reasons. The results showed that the internal wave strain variance over the slope could be up to five times larger than that in the interior. We have validated that internal tides and near-inertial waves were not the crucial processes for causing this variability. Meanwhile, we found that the high-frequency internal waves generated by the interaction of anticyclonic eddy and low-frequency internal waves may be a potential cause of strain enhancement. This study implies a potential route of mesoscale eddies to enhance the strain variance induced by internal waves.
19
Lim, Gyuchang, and JongJin Park. "Vertical structural variability of diurnal internal tides inside a mesoscale anticyclonic eddy based on single virtual-moored Slocum glider observations." Frontiers in Marine Science 9 (August 16, 2022). http://dx.doi.org/10.3389/fmars.2022.920049.
Анотація:
The vertical structural variability of the diurnal internal tide (DIT) with a mode-1 wavelength of ~420 km inside a mesoscale baroclinic anticyclonic eddy was examined based on observations by a single virtual-moored (VM) Slocum glider. During the glider observational period from 10 to 19 September 2018, the eddy traveled northward at approximately 50 km, allowing the glider to scan a cross section of 50 km wide and 800 m deep inside the eddy. VM observations showed that DIT experienced a noticeable vertical structural variability near the eddy center. In a range of 30 km horizontally from the eddy center (inner center), DIT’s vertical displacements were significantly intensified in the 400–800-m depth below the eddy. In the range of 30–50 km from the eddy center (outer center), DIT was almost uniformly distributed from the surface to 800-m depth. Owing to the spatiotemporally restricted dataset by the glider, the significance of DIT’s modulation observed inside the eddy can be questionable. As a result of comparing DIT’s vertical structural variability in two domains in terms of available potential energy (APE) and horizontal kinetic energy (HKE) using CTDs inside the eddy and ADCPs outside the eddy, DIT’s vertical structure inside the eddy was significantly distinguished from that outside the eddy. The relative vorticity inside the eddy was estimated based on the satellite dataset; it was negatively great in the inner center (approximately 0.35 – 0.25f) and small in the outer center (approximately 0.2 – 0.1f). These observational behaviors indicate a close relationship between them; the vorticity-dependent modulation of the DIT seems to be observationally confirmed inside the eddy. Further, in order to examine the energy transferring behavior in low vertical modes, a wavenumber spectral analysis was performed on the DIT displacements and the lowest four wavenumbers, Kz (1) through Kz (4), showed a similar behavior to those observed in DIT’s vertical structural variability inside of the eddy; the relative power of the sum of Kz (2) ~ Kz (4) with respect to Kz (1) was strong in the inner center and weakened in the outer center. These results seem to support that the wave–eddy interaction is non-uniform inside the eddy and partially depends on the relative vorticity.
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Cyriac, Ajitha, Helen E. Phillips, Nathaniel L. Bindoff, and Kurt Polzin. "Turbulent mixing variability in an energetic standing meander of the Southern Ocean." Journal of Physical Oceanography, May 2, 2022. http://dx.doi.org/10.1175/jpo-d-21-0180.1.
Анотація:
Abstract This study presents novel observational estimates of turbulent dissipation and mixing in a standing meander between the Southeast Indian Ridge and the Macquarie Ridge in the Southern Ocean. By applying a finescale parameterization on the temperature, salinity and velocity profiles collected from Electromagnetic Autonomous Profiling Explorer (EM-APEX) floats in the upper 1600 m, we estimated the intensity and spatial distribution of dissipation rate and diapycnal mixing along the float tracks and investigated the sources. The indirect estimates indicate strong spatial and temporal variability of turbulent mixing varying from O(10−6) − O(10−3) m2s−1 in the upper 1600 m. Elevated turbulent mixing is mostly associated with the Subantarctic Front (SAF) and mesoscale eddies. In the upper 500 m, enhanced mixing is associated with downward propagating wind-generated near-inertial waves as well as the interaction between cyclonic eddies and upward propagating internal waves. In the study region, the local topography does not play a role in turbulent mixing in the upper part of the water column, which has similar values in profiles over rough and smooth topography. However, both remotely-generated internal tides and lee waves could contribute to the upward propagating energy. Our results point strongly to the generation of turbulent mixing through the interaction of internal waves and the intense mesoscale eddy field.
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Kumar, Nirnimesh, James A. Lerczak, Tongtong Xu, Amy F. Waterhouse, Jim Thomson, Eric J. Terrill, Christy Swann, et al. "The Inner-Shelf Dynamics Experiment." Bulletin of the American Meteorological Society, December 31, 2020, 1–77. http://dx.doi.org/10.1175/bams-d-19-0281.1.
Анотація:
AbstractThe inner shelf, the transition zone between the surf zone and the mid shelf, is a dynamically complex region with the evolution of circulation and stratification driven by multiple physical processes. Cross-shelf exchange through the inner shelf has important implications for coastal water quality, ecological connectivity, and lateral movement of sediment and heat. The Inner-Shelf Dynamics Experiment (ISDE) was an intensive, coordinated, multi-institution field experiment from Sep.-Oct. 2017, conducted from the mid shelf, through the inner shelf and into the surf zone near Point Sal, CA. Satellite, airborne, shore- and ship-based remote sensing, in-water moorings and ship-based sampling, and numerical ocean circulation models forced by winds, waves and tides were used to investigate the dynamics governing the circulation and transport in the inner shelf and the role of coastline variability on regional circulation dynamics. Here, the following physical processes are highlighted: internal wave dynamics from the mid shelf to the inner shelf; flow separation and eddy shedding off Point Sal; offshore ejection of surfzone waters from rip currents; and wind-driven subtidal circulation dynamics. The extensive dataset from ISDE allows for unprecedented investigations into the role of physical processes in creating spatial heterogeneity, and nonlinear interactions between various inner-shelf physical processes. Overall, the highly spatially and temporally resolved oceanographic measurements and numerical simulations of ISDE provide a central framework for studies exploring this complex and fascinating region of the ocean.