Frequency-Based Correction of Finescale Parameterization of Turbulent Dissipation in the Deep Ocean

Ijichi, Takashi; Hibiya, Taketoshi

doi:10.1175/jtech-d-15-0031.1

Cited by 19 publications

(46 citation statements)

References 25 publications

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“…Turbulent energy dissipation rates were measured using a free‐fall vertical microstructure profiler VMP‐5500 manufactured by Rockland Scientific International Inc. With reference to Ijichi and Hibiya () and Nagasawa et al (), vertical profiles of microscale velocity shear are divided into consecutive ∼10‐m‐depth bins and vertical wave number shear spectra ϕ ( m ) are calculated using ∼1‐m‐wide Hanning windows. In order to eliminate the influence of the instrumental motion, components that are coherent with three‐axis accelerometer signals are subtracted from the raw spectra.…”

Section: Observations and Data Analysismentioning

confidence: 99%

“…GEMCs measure the horizontal electric field generated by the ocean current crossing the Earth's magnetic field. The obtained data are processed following Ijichi and Hibiya () and then horizontal velocity with 5‐m resolution relative to a depth‐independent constant is calculated. LADCP data are processed using the Lamont‐Doherty Earth Observatory processing software (Thurnherr, ), where 4‐m‐resolution vertical shear is calculated using “shear method” (Fischer & Visbeck, ) and 20‐m‐resolution absolute velocity is calculated using “velocity inversion method” (Visbeck, ) with bottom‐track data and GPS time series as constraints.…”

Section: Observations and Data Analysismentioning

confidence: 99%

“…Since direct measurements of microscale (<1 m in vertical) turbulence are time consuming and require expensive instruments, finescale parameterizations of deep ocean mixing (for more details, see section ), which estimate the turbulent dissipation rates using finescale ( O (10 − 100m) in vertical) velocity and/or density profiles that can be relatively easily obtained, have been developed (e.g., Gregg, ; Gregg et al, ; Ijichi & Hibiya, ; Polzin et al, ; Wijesekera et al, ). Hibiya et al () examined the validity of the finescale parameterizations near prominent topographic features in the North Pacific by comparing the turbulent dissipation rates estimated from each parameterization and those obtained from microstructure measurements.…”

Section: Introductionmentioning

confidence: 99%

“…They found that the internal wave spectra deviated from the Garrett‐Munk (GM) spectra (Cairns & Williams, ; Garrett & Munk, , ) in these region, so that the shear‐based G89 (Gregg, ) and the strain‐based W93 (Wijesekera et al, ) parameterizations became erroneous but the Gregg‐Henyey‐Polzin (GHP; Gregg et al, ; Henyey et al ; Polzin et al, ) parameterization, which took into account the distortion of the spectrum, could estimate the turbulent dissipation rates more accurately. Recently, Ijichi and Hibiya () pointed out the defect of the frequency correction by the GHP parameterization and presented a new parameterization. This Ijichi‐Hibiya (IH) parameterization could predict the turbulent dissipation rates more accurately than GHP in the Izu‐Ogasawara Ridge where the internal wave spectra are significantly biased to lower frequencies (Ijichi & Hibiya, ).…”

Section: Introductionmentioning

confidence: 99%

“…Recently, Ijichi and Hibiya () pointed out the defect of the frequency correction by the GHP parameterization and presented a new parameterization. This Ijichi‐Hibiya (IH) parameterization could predict the turbulent dissipation rates more accurately than GHP in the Izu‐Ogasawara Ridge where the internal wave spectra are significantly biased to lower frequencies (Ijichi & Hibiya, ).…”

Section: Introductionmentioning

confidence: 99%

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Assessment of Finescale Parameterizations of Deep Ocean Mixing in the Presence of Geostrophic Current Shear: Results of Microstructure Measurements in the Antarctic Circumpolar Current Region

Takahashi

Hibiya

2019

JGR Oceans

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The Southern Ocean is thought to be one of globally significant mixing hotspots. In this study, we carried out simultaneous measurements of microscale turbulence and finescale shear/strain in the south of Australia to assess the validity of the existing finescale parameterizations of deep ocean mixing in the Antarctic Circumpolar Current (ACC) region where geostrophic shear flows coexist with the background internal wavefield. It is found that turbulent dissipation rates are overall small but the internal wavefield is more energetic than the Garrett-Munk (GM) wavefield. Finescale shear/strain ratio (R ) well exceeds the GM value in the deep layer south of the Southern ACC Front, suggesting that the local internal wave spectra are significantly biased to lower frequencies. Through the comparison of the directly measured turbulent dissipation rates with those inferred from finescale parameterizations, we find that the Gregg-Henyey-Polzin and Ijichi-Hibiya parameterizations, both of which take into account the distortion of the GM frequency spectrum in terms of R , can predict well the turbulent dissipation rates at most of the stations, whereas the shear-based parameterization (the strain-based parameterization) tends to overestimate (underestimate) the directly measured turbulent dissipation rates. However, at the observation stations located on the ACC jets, both the Gregg-Henyey-Polzin and Ijichi-Hibiya parameterizations tend to overestimate the turbulent dissipation rates by a factor of ∼3. The most likely cause of the overestimates is spatial anisotropy of the internal wavefield associated with large-amplitude monochromatic near-inertial internal waves and/or internal lee waves. Plain Language SummaryThe Southern Ocean is a special place where the Antarctic Circumpolar Current (ACC) coexists with the energetic internal waves generated by strong westerly wind as well as the ACC impinging on rough topographic features and strong turbulent mixing occurs. Because of the difficulty of direct measurements of turbulent mixing, it is common to employ parameterizations to estimate the intensity of turbulent mixing ( ). However, these parameterizations are formulated on the basis of the internal wave theory and do not take into account the existence of strong flows like the ACC. Therefore, in this study, we carry out direct measurements of turbulent mixing to assess the validity of existing parameterizations of deep ocean mixing in the ACC region. Through the comparison of the directly measured and those inferred from parameterizations, we find that the Gregg-Henyey-Polzin and Ijichi-Hibiya parameterizations can predict well at the most of the observation stations but tend to overestimate by a factor of ∼3 at the stations located on the ACC jets. These overestimates are most likely explained by the spatially anisotropic internal wavefield associated with large-amplitude monochromatic internal waves, which are generated and/or amplified by the ACC.

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Section: Observations and Data Analysismentioning

confidence: 99%

Section: Observations and Data Analysismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Assessment of Finescale Parameterizations of Deep Ocean Mixing in the Presence of Geostrophic Current Shear: Results of Microstructure Measurements in the Antarctic Circumpolar Current Region

Takahashi

Hibiya

2019

JGR Oceans

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Internal tides recorded at ocean bottom off the coast of Southeast Taiwan

et al. 2016

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An ocean‐bottom experiment consisting of an array of four ocean‐bottom seismometers (OBS) was conducted off the coast of southeast Taiwan during May–July 2011. We develop comprehensive analyses of the space‐time kinematics of the tidal signals recorded in the compact high‐sensitivity temperature loggers (CHTL) and the OBS geophones at the ocean bottom with depths ranging from 1254 to 1610 m. The evidence suggests that internal tides are responsible for the recorded signals: baroclinic internal waves (mainly the M2 tide) are generated by barotropic tidal currents in the Luzon Strait. The internal tides exhibit gradual phase changing and irregularly fluctuating strength, leaving signatures in the CHTL as ambient temperature variations, signifying low‐mode wave motions within the stratified water layers; and in OBS geophones as intermittent “tremor” agitations, signifying high‐mode turbulent flows on the seafloor. The M2 internal tides across our array are found to propagate in the northeast direction at speeds ranging from 1 to 2+ m s−1. Furthermore, the internal tides are identified at the ocean‐bottom based on an operational hydrodynamic hindcast/forecast model. The simulations show good agreement with the observed temperature variation on the seafloor and substantiate the vertical velocity and displacement of the water parcel driven by the internal tides. The joint detection of the temperature and tremor signals provides further information about the interactions of internal tides with the seafloor topography and the associated energy dissipation. Our results elucidate the space‐time ubiquity of the internal tides at the ocean bottom, which is an important interface of dynamic oceanography.

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Direct Estimates of Turbulent Mixing in the Indonesian Archipelago and Its Role in the Transformation of the Indonesian Throughflow Waters

Nagai

Hibiya

Syamsudin

2021

Geophysical Research Letters

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The Indonesian Archipelago (IA) is a key region of the climate system, since the atmospheric deep convection attributed to the high sea surface temperatures (SSTs) in this region drives the Walker circulation and influences climate on the global scale (Clement et al., 2013; Neale & Slingo, 2003). Tidal mixing enhanced in the IA is thought to be one of the major factors contributing to the SST change around this region (Koch-Larrouy et al., 2010; Nagai & Hibiya, 2020; Sprintall et al., 2014). Actually, Ffield and Gordon (1996) and Ray and Susanto (2016) found a clear spring-neap tidal cycle in satellite SST data in the IA, suggesting the effects of tidal mixing on the SST change in this region. Tidal mixing in the IA is also thought to influence the large-scale ocean circulation through the Indonesian Throughflow (ITF), which is responsible for transporting a large amount of water (10-18 Sv) and heat (∼0.7 PW) from the western Pacific warm pool to the Indian Ocean (Gordon & McClean, 1999; Susanto & Song, 2015). The ITF waters significantly change their properties while passing through the tidal mixing zone of the IA and consequently influence the Agulhas and Leeuwin Currents (Gordon, 2005). The first estimate of mixing intensity in the IA was made by Ffield and Gordon (1992), who used a one-dimensional advection-diffusion model to show that an area-averaged vertical diffusivity of K V ∼ 10 −4 m 2 s −1 is necessary to explain the evolution of water-mass properties (temperature, salinity,

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Frequency-Based Correction of Finescale Parameterization of Turbulent Dissipation in the Deep Ocean

Cited by 19 publications

References 25 publications

Assessment of Finescale Parameterizations of Deep Ocean Mixing in the Presence of Geostrophic Current Shear: Results of Microstructure Measurements in the Antarctic Circumpolar Current Region

Assessment of Finescale Parameterizations of Deep Ocean Mixing in the Presence of Geostrophic Current Shear: Results of Microstructure Measurements in the Antarctic Circumpolar Current Region

Internal tides recorded at ocean bottom off the coast of Southeast Taiwan

Direct Estimates of Turbulent Mixing in the Indonesian Archipelago and Its Role in the Transformation of the Indonesian Throughflow Waters

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