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Jonathan Sharples - One of the best experts on this subject based on the ideXlab platform.
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Internal Tide driven tracer transport across the continental slope
Journal of Geophysical Research: Oceans, 2020Co-Authors: Carl P. Spingys, Richard G. Williams, Joanne Hopkins, Rob A. Hall, J. A. Mattias Green, Jonathan SharplesAbstract:The role of the Internal Tide in driving tracer transport across the continental slope is examined using simplified layered theory, channel model experiments and observational diagnostics of near shelf‐edge moorings. The effect of the Internal Tide is interpreted in terms of its Stokes' drift, which is separated into two distinct components: a bolus component, driven by the co‐variance of layer thickness and the velocity; and a shear component, driven by the velocity following the movement of an interface. For a three layer ocean, in the model experiments and observations, the onshore propagation of an Internal Tide drives a Stokes' transport directed onshore in the surface and the bottom layers, and directed offshore in the pycnocline. This reversing structure is due to the bolus component dominating near the boundaries, while the shear component dominates at the pycnocline. In the observational diagnostics, the Stokes' transport is not cancelled by the Eulerian transport, which is mainly directed along bathymetric contours. The Stokes' drift of the Internal Tide then provides a systematic on shelf tracer transport if there is a tracer sink on the shelf, carried in the surface or bottom layers. Conversely, the tracer transport is directed offshore if there is a tracer source on the shelf with plumes of shelf tracer expected to be carried offshore along the pycnocline. This tracer transport as a result of the Internal Tide is diagnosed for heat, salt and nitrate. The depth‐integrated nitrate flux is directed onto the shelf supplying nutrients to the productive shelf seas.
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Internal Tide coherence and decay over a wide shelf sea
Geophysical Research Letters, 2011Co-Authors: Mark Inall, Jonathan Sharples, Dimitry Aleynik, Tim Boyd, Matthew R PalmerAbstract:[1] A quasi-synoptic hydrography and velocity section is used to determine the structure and the decay rate of the Internal Tide (IT) across the broad continental shelf of the Celtic Sea. In these observations the IT is coherent over more than 170 km, about five wavelengths, with an estimated shoreward energy decay scale of 42 km. The inferred IT wavelength-averaged dissipation rate near the shelf edge is estimated as 2.08 × 10−7 Wkg−1, in close agreement with tidally- and vertically-averaged measurements from the region. These results provide the firstin situ evidence of IT coherence over many wavelengths in a shelf sea.
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Internal Tide dissipation mixing and vertical nitrate flux at the shelf edge of ne new zealand
Journal of Geophysical Research, 2001Co-Authors: Jonathan Sharples, Mark C Moore, Edward AbrahamAbstract:An Internal Tide on the NE shelf of New Zealand was observed with a combination of moored temperature loggers and current meters and vertical profiling with a microstructure probe. Internal Tide energy flux across the shelf edge was calculated to be --400 W m -, with considerable variability driven by the passage of a storm through the region. Energy associated with the Internal Tide was significantly greater than the energy of the barotropic Tide or of inertial shear. Dissipation of the Internal Tide calculated from the energy loss between two of the moorings was estimated to be 15 _+ 10 mW m -2. The associated vertical eddy diffusivity was (4 +_ 3) x 10 -4 m 2 s -1. The microstructure observations indicated Internal Tide-driven vertical diffusivities at the nitracline of--7 x 10 -4 m 2 s -1. The observations of vertical eddy diffusivities are combined with measurements of the vertical nitrate gradient to suggest that mixing driven by the Internal Tide is the dominant mechanism for driving diapycnal nutrient supply during summer. The calculated flux of about 12 mmol N m -2 d -1 into the photic zone is suggested to drive significant new subsurface production throughout the summer, amounting to a possible contribution to annual new production on the shelf of 100 g C m -2.
S. M. Kelly - One of the best experts on this subject based on the ideXlab platform.
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Internal Tide Nonstationarity and Wave–Mesoscale Interactions in the Tasman Sea
Journal of Physical Oceanography, 2020Co-Authors: Anna C. Savage, Amy F. Waterhouse, S. M. KellyAbstract: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.
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Internal Tide convergence and mixing in a submarine canyon
Journal of Physical Oceanography, 2017Co-Authors: Amy F. Waterhouse, S. M. Kelly, Jennifer A. Mackinnon, Andy Pickering, Ruth Musgrave, J. D. NashAbstract:AbstractObservations from Eel Canyon, located on the north coast of California, show that elevated turbulence in the full water column arises from the convergence of remotely generated Internal wave energy. The incoming semidiurnal and bottom-trapped diurnal Internal Tides generate complex interference patterns. The semidiurnal Internal Tide sets up a partly standing wave within the canyon due to reflection at the canyon head, dissipating all of its energy within the canyon. Dissipation in the near bottom is associated with the diurnal trapped Tide, while midwater isopycnal shear and strain is associated with the semidiurnal Tide. Dissipation is elevated up to 600 m off the bottom, in contrast to observations over the flat continental shelf where dissipation occurs closer to the topography. Slope canyons are sinks for Internal wave energy and may have important influences on the global distribution of tidally driven mixing.
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a coupled mode shallow water model for tidal analysis Internal Tide reflection and refraction by the gulf stream
Journal of Physical Oceanography, 2016Co-Authors: S. M. Kelly, Pierre F J Lermusiaux, Timothy F Duda, Patrick J HaleyAbstract:AbstractA hydrostatic, coupled-mode, shallow-water model (CSW) is described and used to diagnose and simulate tidal dynamics in the greater Mid-Atlantic Bight region. The reduced-physics model incorporates realistic stratification and topography, Internal Tide forcing from a priori estimates of the surface Tide, and advection terms that describe first-order interactions of Internal Tides with slowly varying mean flow and mean buoyancy fields and their respective shear. The model is validated via comparisons with semianalytic models and nonlinear primitive equation models in several idealized and realistic simulations that include Internal Tide interactions with topography and mean flows. Then, 24 simulations of Internal Tide generation and propagation in the greater Mid-Atlantic Bight region are used to diagnose significant Internal Tide interactions with the Gulf Stream. The simulations indicate that locally generated mode-one Internal Tides refract and/or reflect at the Gulf Stream. The redirected inter...
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Internal Tide interactions with the gulf stream and middle atlantic bight shelfbreak front
Journal of Geophysical Research, 2016Co-Authors: S. M. Kelly, Pierre F J LermusiauxAbstract:Internal Tides in the Middle Atlantic Bight region are found to be noticeably influenced by the presence of the shelfbreak front and the Gulf Stream, using a combination of observations, equations, and data-driven model simulations. To identify the dominant interactions of these waves with subtidal flows, vertical-mode momentum and energy partial differential equations are derived for small-amplitude waves in a horizontally and vertically sheared mean flow and in a horizontally and vertically variable density field. First, the energy balances are examined in idealized simulations with mode-1 Internal Tides propagating across and along the Gulf Stream. Next, the fully nonlinear dynamics of regional Tide-mean-flow interactions are simulated with a primitive-equation model, which incorporates realistic summer-mesoscale features and atmospheric forcing. The shelfbreak front, which has horizontally variable stratification, decreases topographic Internal-Tide generation by about 10% and alters the wavelengths and arrival times of locally generated mode-1 Internal Tides on the shelf and in the abyss. The (sub)mesoscale variability at the front and on the shelf, as well as the summer stratification itself, also alter Internal-Tide propagation. The Gulf Stream produces anomalous regions of O(20 mW m−2) mode-1 Internal-Tide energy-flux divergence, which are explained by Tide-mean-flow terms in the mode-1 energy balance. Advection explains most Tide-mean-flow interaction, suggesting that geometric wave theory explains mode-1 reflection and refraction at the Gulf Stream. Geometric theory predicts that offshore-propagating mode-1 Internal Tides that strike the Gulf Stream at oblique angles (more than thirty degrees from normal) are reflected back to the coastal ocean, preventing their radiation into the central North Atlantic.
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the geography of semidiurnal mode 1 Internal Tide energy loss
Geophysical Research Letters, 2013Co-Authors: S. M. Kelly, J. D. Nash, Nicole L Jones, Amy F. WaterhouseAbstract:[1] The semidiurnal mode-1 Internal Tide receives 0.1–0.3 TW from the surface Tide and is capable of propagating across ocean basins. The ultimate fate of mode-1 energy after long-distance propagation is poorly constrained by existing observations and numerical simulations. Here, global results from a two-dimensional semi-analytical model indicate that topographic scattering is inefficient at most locations deeper than 2500 m. Next, results from a one-dimensional linear model with realistic topography and stratification create a map of mode-1 scattering coefficients along the continental margins. On average, mode-1 Internal Tides lose about 60% of their energy upon impacting the continental margins: 20% transmits onto the continental shelf, 40% scatters to higher modes, and 40% reflects back to the ocean interior. These analyses indicate that the majority of mode-1 energy is likely lost at large topographic features (e.g., continental slopes, seamounts, and mid-ocean ridges), where it may drive elevated turbulent mixing.
J. D. Nash - One of the best experts on this subject based on the ideXlab platform.
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Internal Tide convergence and mixing in a submarine canyon
Journal of Physical Oceanography, 2017Co-Authors: Amy F. Waterhouse, S. M. Kelly, Jennifer A. Mackinnon, Andy Pickering, Ruth Musgrave, J. D. NashAbstract:AbstractObservations from Eel Canyon, located on the north coast of California, show that elevated turbulence in the full water column arises from the convergence of remotely generated Internal wave energy. The incoming semidiurnal and bottom-trapped diurnal Internal Tides generate complex interference patterns. The semidiurnal Internal Tide sets up a partly standing wave within the canyon due to reflection at the canyon head, dissipating all of its energy within the canyon. Dissipation in the near bottom is associated with the diurnal trapped Tide, while midwater isopycnal shear and strain is associated with the semidiurnal Tide. Dissipation is elevated up to 600 m off the bottom, in contrast to observations over the flat continental shelf where dissipation occurs closer to the topography. Slope canyons are sinks for Internal wave energy and may have important influences on the global distribution of tidally driven mixing.
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three dimensional double ridge Internal Tide resonance in luzon strait
Journal of Physical Oceanography, 2014Co-Authors: Maarten C Buijsman, J. D. Nash, Matthew H Alford, Jody M Klymak, Jennifer A. Mackinnon, Sonya Legg, Andy Pickering, David M Farmer, Jaehun Park, Harper L SimmonsAbstract:AbstractThe three-dimensional (3D) double-ridge Internal Tide interference in the Luzon Strait in the South China Sea is examined by comparing 3D and two-dimensional (2D) realistic simulations. Both the 3D simulations and observations indicate the presence of 3D first-mode (semi)diurnal standing waves in the 3.6-km-deep trench in the strait. As in an earlier 2D study, barotropic-to-baroclinic energy conversion, flux divergence, and dissipation are greatly enhanced when semidiurnal Tides dominate relative to periods dominated by diurnal Tides. The resonance in the 3D simulation is several times stronger than in the 2D simulations for the central strait. Idealized experiments indicate that, in addition to ridge height, the resonance is only a function of separation distance and not of the along-ridge length; that is, the enhanced resonance in 3D is not caused by 3D standing waves or basin modes. Instead, the difference in resonance between the 2D and 3D simulations is attributed to the topographic blocking ...
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the geography of semidiurnal mode 1 Internal Tide energy loss
Geophysical Research Letters, 2013Co-Authors: S. M. Kelly, J. D. Nash, Nicole L Jones, Amy F. WaterhouseAbstract:[1] The semidiurnal mode-1 Internal Tide receives 0.1–0.3 TW from the surface Tide and is capable of propagating across ocean basins. The ultimate fate of mode-1 energy after long-distance propagation is poorly constrained by existing observations and numerical simulations. Here, global results from a two-dimensional semi-analytical model indicate that topographic scattering is inefficient at most locations deeper than 2500 m. Next, results from a one-dimensional linear model with realistic topography and stratification create a map of mode-1 scattering coefficients along the continental margins. On average, mode-1 Internal Tides lose about 60% of their energy upon impacting the continental margins: 20% transmits onto the continental shelf, 40% scatters to higher modes, and 40% reflects back to the ocean interior. These analyses indicate that the majority of mode-1 energy is likely lost at large topographic features (e.g., continental slopes, seamounts, and mid-ocean ridges), where it may drive elevated turbulent mixing.
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Reply to comment by T. Gerkema on “Internal‐Tide energy over topography”
Journal of Geophysical Research, 2011Co-Authors: S. M. Kelly, J. D. NashAbstract:[1] Gerkema [2011] objects to Kelly et al.’s [2010] conclusion that Internal‐Tide pressure has zero depth average over a sloping bottom. This objection is based on the unfounded assumption that only Internal‐Tide pressure can exist in a wedge under a rigid lid. Here, we refute this supposition, arguing that Tides in a wedge contain mode 0 pressure because surface and Internal Tides are coupled through wave drag. Moreover, we note that Gerkema’s [2011] definition of Internal‐Tide pressure is incompatible with the accepted baroclinicity condition over a flat bottom, which requires the Internal Tide have zero depth average [Kunze et al., 2002; Gerkema and van Haren, 2007]. Specifically, the pressure field illustrated in Figure 1 of Gerkema [2011] cannot be matched to the known Internal‐Tide solution over a flat abyss without producing unphysical discontinuities. In the following reply, we compare the Internal‐Tide pressures and energy fluxes of Kelly et al. [2010] and Gerkema [2011] for Tides in a wedge connected to a flat abyss [Wunsch, 1968]. We conclude that the Internal‐Tide pressure proposed by Gerkema [2011] is incorrect and his objections to Kelly et al. [2010] are unfounded.
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Internal-Tide generation and destruction by shoaling Internal Tides
Geophysical Research Letters, 2010Co-Authors: S. M. Kelly, J. D. NashAbstract:[1] Internal-Tide generation is usually predicted from local topography, surface Tides, and stratification. However, Internal Tides are often observed to be unrelated to local spring-neap forcing, appearing intermittently in 3–5 day bursts. Here we suggest a source of this intermittency by illustrating how remotely-generated shoaling Internal Tides induce first-order changes in local Internal-Tide generation. Theory, numerical simulations, and observations show that pressure perturbations associated with shoaling Internal Tides can correlate with surface-Tide velocities to generate or destroy Internal Tides. Where shoaling Internal Tides have random phase, such as on the New Jersey slope, time-averaged Internal-Tide generation is unaffected, but instantaneous Internal-Tide generation varies rapidly, altering Internal-Tide energy and possibly affecting nonlinear Internal waves, across-shelf transport, and mixing. Where shoaling Internal Tides are phase-locked to the local surface Tide, such as in double-ridge systems, time-averaged Internal-Tide generation is affected and may result in resonance.
Zhongxiang Zhao - One of the best experts on this subject based on the ideXlab platform.
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Accuracy assessment of global Internal Tide models using satellite altimetry
2020Co-Authors: Loren Carrere, Brian K. Arbic, Brian D. Dushaw, Gary D. Egbert, Svetlana Y. Erofeeva, Florent Lyard, Richard D. Ray, Clement Ubelmann, Edward D. Zaron, Zhongxiang ZhaoAbstract:Abstract. In order to access the targeted ocean signal, altimeter measurements are corrected for several geophysical parameters among which the ocean Tide correction is one of the most critical, but the Internal Tide signature at the surface are not yet corrected globally. Internal Tides can have a signature of several cm at the surface with wavelengths about 50–250 km for the first mode and even smaller scales for higher order modes. The goals of the upcoming Surface Water Ocean Topography (SWOT) mission and other high-resolution ocean measurements make the correction of these small scale signals a challenge, as the separation of all tidal variability from other oceanic signals becomes mandatory. In this context, several scientific teams are working on the development of new Internal Tide models, taking advantage of the very long altimeter time series now available, which represent an unprecedented and valuable global ocean database. The Internal Tide models presented here focus on the coherent Internal Tide signal and they are of three types: empirical models based upon analysis of existing altimeter missions, an assimilative model, and a three-dimensional hydrodynamic model. A detailed comparison and validation of these Internal Tide models is proposed using existing satellite altimeter databases. The analysis focuses on the four main tidal constituents M2, K1, O1 and S2. The validation process is based on a statistical analysis of multi-mission altimetry including Jason-2 and Cryosphere Satellite-2 data, taking advantage of the long-term altimeter databases available. The results show a significant altimeter variance reduction when using Internal Tide corrections on all ocean regions where Internal Tides are generating/propagating. A complementary spectral analysis also gives some estimation of the performance of each model as a function of wavelength, and some insight into the residual non-stationary part of Internal Tides in the different regions of interest.
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decomposition of the multimodal multidirectional m2 Internal Tide field
Journal of Atmospheric and Oceanic Technology, 2019Co-Authors: Zhongxiang Zhao, Jinbo Wang, Dimitris Menemenlis, Shuiming Chen, Bo QiuAbstract:AbstractThe M2 Internal Tide field contains waves of various baroclinic modes and various horizontal propagation directions. This paper presents a technique for decomposing the sea surface height (...
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satellite investigation of the m2 Internal Tide in the tasman sea
Journal of Physical Oceanography, 2018Co-Authors: Zhongxiang Zhao, Matthew H Alford, Harper L Simmons, Dmitry Brazhnikov, Robert PinkelAbstract:AbstractThe M2 Internal Tide in the Tasman Sea is investigated using sea surface height measurements made by multiple altimeter missions from 1992 to 2012. Internal tidal waves are extracted by two...
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The Global Mode‐1 S2 Internal Tide
Journal of Geophysical Research: Oceans, 2017Co-Authors: Zhongxiang ZhaoAbstract:The global mode-1 S2 Internal Tide is observed using sea surface height (SSH) measurements from four satellite altimeters: TOPEX/Poseidon, Jason-1, Jason-2, and Geosat Follow-On. Plane wave analysis is employed to extract three mode-1 S2 Internal tidal waves in any given 250 km by 250 km window, which are temporally coherent over a 20-year period from 1992–2012. Depth-integrated energy and flux of the S2 Internal Tide are calculated from the SSH amplitude and a conversion function built from climatological hydrographic profiles in the World Ocean Atlas 2013. The results show that the S2 and M2 Internal Tides have similar spatial patterns. Both S2 and M2 Internal Tides originate at major topographic features and propagate over long distances. The S2 Internal tidal beams are generally shorter, likely because the relatively weaker S2 Internal Tide is easily overwhelmed by nontidal noise. The northbound S2 and M2 Internal Tides from the Hawaiian Ridge are observed to travel over 3500 km across the Northeast Pacific. The globally integrated energy of the mode-1 S2 Internal Tide is 7.8 PJ (1 PJ = 1015 J), about 20% that of M2 (36.4 PJ). The histogram of S2 to M2 SSH ratios peaks at 0.4, consistent with the square root of their energy ratio. In terms of SSH, S2 is greater than M2 in ≈ 10% of the global ocean and ≥50% of M2 in about half of the global ocean.
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the global mode 1 s2 Internal Tide
Journal of Geophysical Research, 2017Co-Authors: Zhongxiang ZhaoAbstract:The global mode-1 S2 Internal Tide is observed using sea surface height (SSH) measurements from four satellite altimeters: TOPEX/Poseidon, Jason-1, Jason-2, and Geosat Follow-On. Plane wave analysis is employed to extract three mode-1 S2 Internal tidal waves in any given 250 km by 250 km window, which are temporally coherent over a 20-year period from 1992–2012. Depth-integrated energy and flux of the S2 Internal Tide are calculated from the SSH amplitude and a conversion function built from climatological hydrographic profiles in the World Ocean Atlas 2013. The results show that the S2 and M2 Internal Tides have similar spatial patterns. Both S2 and M2 Internal Tides originate at major topographic features and propagate over long distances. The S2 Internal tidal beams are generally shorter, likely because the relatively weaker S2 Internal Tide is easily overwhelmed by nontidal noise. The northbound S2 and M2 Internal Tides from the Hawaiian Ridge are observed to travel over 3500 km across the Northeast Pacific. The globally integrated energy of the mode-1 S2 Internal Tide is 7.8 PJ (1 PJ = 1015 J), about 20% that of M2 (36.4 PJ). The histogram of S2 to M2 SSH ratios peaks at 0.4, consistent with the square root of their energy ratio. In terms of SSH, S2 is greater than M2 in ≈ 10% of the global ocean and ≥50% of M2 in about half of the global ocean.
Glenn S. Carter - One of the best experts on this subject based on the ideXlab platform.
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Coastal‐trapped behavior of the diurnal Internal Tide at O'ahu, Hawai'i
Journal of Geophysical Research: Oceans, 2017Co-Authors: Katharine A. Smith, Mark A. Merrifield, Glenn S. CarterAbstract:The influence of rotation on the structure and propagation of Internal Tides around O'ahu, Hawai'i is investigated using in situ observations and a tidally forced, primitive equation model with realistic bathymetry and stratification. Particular attention is given to the diurnal Internal Tide, which largely has been de-emphasized in previous studies of the region because of the dominance of the semidiurnal Internal Tide but has been determined by recent studies to be a significant contributor to baroclinic variability. Though both diurnal and semidiurnal Internal Tides are generated primarily over Ka'ena Ridge to the northwest of the island, the diurnal Internal Tide propagates clockwise around the island as an imperfectly trapped wave, while the semidiurnal Internal Tide propagates away from the ridge, unaffected by rotation. The diurnal and semidiurnal Internal Tides fall into the superinertial frequency range; however, the diurnal frequency apparently is sufficiently close to inertial (∼ 1.4f) for rotation to affect Internal Tide propagation. The in situ observations support the model finding that diurnal trapping provides the primary source of baroclinic variability along the eastern coast of the island, a stretch of coastline otherwise sheltered from the Internal Tide energy generated over the Hawaiian Ridge. The findings in Hawai'i suggest that coastal trapping of superinertial Internal Tides may be a significant source of variability and mixing in other nearshore systems around the world.
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coastal trapped behavior of the diurnal Internal Tide at o ahu hawai i
Journal of Geophysical Research, 2017Co-Authors: Katharine A. Smith, Mark A. Merrifield, Glenn S. CarterAbstract:The influence of rotation on the structure and propagation of Internal Tides around O'ahu, Hawai'i is investigated using in situ observations and a tidally forced, primitive equation model with realistic bathymetry and stratification. Particular attention is given to the diurnal Internal Tide, which largely has been de-emphasized in previous studies of the region because of the dominance of the semidiurnal Internal Tide but has been determined by recent studies to be a significant contributor to baroclinic variability. Though both diurnal and semidiurnal Internal Tides are generated primarily over Ka'ena Ridge to the northwest of the island, the diurnal Internal Tide propagates clockwise around the island as an imperfectly trapped wave, while the semidiurnal Internal Tide propagates away from the ridge, unaffected by rotation. The diurnal and semidiurnal Internal Tides fall into the superinertial frequency range; however, the diurnal frequency apparently is sufficiently close to inertial (∼ 1.4f) for rotation to affect Internal Tide propagation. The in situ observations support the model finding that diurnal trapping provides the primary source of baroclinic variability along the eastern coast of the island, a stretch of coastline otherwise sheltered from the Internal Tide energy generated over the Hawaiian Ridge. The findings in Hawai'i suggest that coastal trapping of superinertial Internal Tides may be a significant source of variability and mixing in other nearshore systems around the world.
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The Impact of Subtidal Circulation on Internal-Tide-Induced Mixing in the Philippine Sea
Journal of Physical Oceanography, 2014Co-Authors: Colette Kerry, Brian Powell, Glenn S. CarterAbstract:AbstractThis 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-ba...
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the impact of subtidal circulation on Internal Tide generation and propagation in the philippine sea
Journal of Physical Oceanography, 2014Co-Authors: Colette Kerry, Brian Powell, Glenn S. CarterAbstract:AbstractThis study examines the effects of the subtidal circulation on the generation and propagation of the M2 Internal Tide in the Philippine Sea using a primitive equation model. Barotropic to baroclinic conversion at the Luzon Strait is found to vary due to the background circulation changes over the generation site and the changing influence of remotely generated Internal Tides from the Mariana Arc. The varying effect of remotely generated waves results from both changing generation energy levels at the Mariana Arc and variability in the propagation of the Internal Tides across the Philippine Sea. The magnitude and direction of the depth-integrated baroclinic energy fluxes vary temporally, due to a combination of changing generation, propagation, and dissipation. Spatial patterns of Internal Tide propagation near the Luzon Strait are influenced by the locations of mesoscale eddies to the east and west of the strait. The results provide insight into the mechanisms of variability of the baroclinic Tide...
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topographic scattering of the low mode Internal Tide in the deep ocean
Journal of Geophysical Research, 2014Co-Authors: Manikandan Mathur, Glenn S. Carter, Thomas PeacockAbstract:We investigate the role of deep-ocean topography in scattering energy from the large spatial scales of the low-mode Internal Tide to the smaller spatial scales of higher modes. The complete Green function method, which is not subject to the restrictions of the WKB approximation, is used for the first time to study the two-dimensional scattering of a mode-1 Internal Tide incident on subcritical and supercritical topography of any form in arbitrary stratifications. For an isolated Gaussian ridge in a uniform stratification, large amplitude critical topography is the most efficient at mode-1 scattering and small amplitude topography scatters with an efficiency on the order of 5–10%. In a nonuniform stratification with a pycnocline, the results are qualitatively the same as for a constant stratification, albeit with the key features shifted to larger height ratios. Having validated these results by direct comparison with the results of nonlinear numerical simulations, and in the process demonstrated that WKB results are not appropriate for reasonable ocean predictions, we proceed to use the Green function approach to quantify the role of topographic scattering for the region of the Pacific Ocean surrounding the Hawaiian Islands chain. To the south, the Line Islands ridge is found to scatter ∼40% of a mode-1 Internal Tide coming from the Hawaiian Ridge. To the north, realistic, small-amplitude, rough topography scatters ∼5–10% of the energy out of mode 1 for transects of length 1000–3000 km. A significant finding is that compared to large extents of small-amplitude, rough topography a single large topographic feature along the path of a mode-1 Internal Tide plays the dominant role in scattering the Internal Tide.