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Snapshot of the global surface speed from the LLC4320 simulation. The square boxes highlight the regions with high-and low-kinetic energy discussed in the section 4.

Snapshot of the global surface speed from the LLC4320 simulation. The square boxes highlight the regions with high-and low-kinetic energy discussed in the section 4.

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Article
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Internal gravity waves (IGWs) and balanced motions (BMs) with scales <100-km capture most of the vertical velocity field in the upper ocean. They have, however, different impacts on the ocean energy budget, which explains the need to partition motions into BMs and IGWs. One way is to exploit the synergy of using different satellite observations, th...

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... direction is motivated by some preliminary results indicating, for example, that IGWs and SBMs exhibit distinct signatures in the sea surface height (SSH) wave number spectrum and not in the KE spectrum. Consequently, to assess the potential of this synergy, our study aims to analyze the respective impacts of BMs and IGWs on different surface fields, using a novel global numerical simulation (with tides included) performed at high resolution (1/48° in the horizontal, with 90 vertical levels) ( Figure 1). The six fields considered include surface ocean currents themselves (or surface KE), and in particular their rotational (relative vorticity or RV) and divergent (DIV) parts, the SSH, and the sea surface temperature (SST) and sea surface salinity (SSS). ...
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... groundbreaking global ocean and sea ice simulation that represents full-depth ocean process with an unprecedented degree of realism is used to characterize BMs and IGWs (Figure 1). The Massachusetts Institute of Technology general circulation model (MITgcm; Marshall et al., 1997;Hill et al., 2007) was the heart of the numerical simulation implemented on a latitude/longitude/polar cap (LLC) configuration (Forget et al., 2015). ...
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... Figure 1 shows a snapshot of surface speed in the global ocean. The coexistence of mesoscale and submesoscale eddies and currents along with internal gravity waves is observable in the snapshot. ...
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... displayed on Figures 8-12 emphasize that some characteristics already pointed out in the KuroshioExtension region (section 3) extend to the World Ocean. First, all the oceans experience a strong seasonality of this partition, with IGWs more dominant in summer and BMs (mostly SBMs) in winter. ...
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... all the oceans experience a strong seasonality of this partition, with IGWs more dominant in summer and BMs (mostly SBMs) in winter. This concerns all fields, except for the SST (Figure 12) and SSS (not shown) fields on which IGWs have almost no impact as for the Kuroshio-Extension region. Second, the differences between SSH and KE already discussed in section 3.1 are ubiquitous in the World Ocean: in regions where IGWs are already dominant (R < 1) in the KE field, SSH is even more affected by IGWs (R ≪ 1). ...
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... the differences between SSH and KE already discussed in section 3.1 are ubiquitous in the World Ocean: in regions where IGWs are already dominant (R < 1) in the KE field, SSH is even more affected by IGWs (R ≪ 1). Third, using the RV and DIV fields (Figures 10 and 11), results further indicate the assumptions used in methodologies based on the Helmholtz decomposition may work only during summer. Fourth, in most of the regions, results do not reveal any particular differences between the two wave bands for the four fields, KE, SST, SSS, and RV. ...
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... analyzing all the oceans in the world, one new result (from Figures 8-12) concerns the significant differences between the two hemispheres. Northern oceans are more affected by IGWs than southern oceans. ...
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... better emphasize this heterogeneity, we have considered four specific regions (two high and two low EKE regions) in each hemisphere. As identified on Figure 1, high EKE regions concern: the Kuroshio-Extension (KEx) and the Gulf Stream regions in the Northern Hemisphere and the Agulhas (AG) and the Antarctic Circumpolar Current (ACC) close to Australia (ACC-AUS) for the Southern Hemisphere. Low EKE regions concern the Northeast Pacific (NEP) and Northeast Atlantic (NEA) regions in the Northern Hemisphere and the South Pacific (SP) and South Atlantic (SA) regions for the Southern Hemisphere. ...
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... explanation for these strong differences between the two summer hemispheres can be expressed in terms of the energy associated with internal tides. Internal tides (including diurnal and semidiurnal tides) as well as their harmonics with smaller scales (supertidal motions) are mostly energetic in the latitude band between 30°S and 30°N as pointed out by Savage, Arbic, Richman, et al. (2017, Figures 12 to 16). However, as emphasized by these authors, internal tides and their harmonics in the Northern Hemisphere are still energetic outside this latitude band, but much less in the Southern Hemisphere. ...
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... motions, the other dominant class of IGWs, are also more energetic in the Northern Hemisphere than in the Southern Hemisphere ( Chaigneau et al., 2008). In Northern Hemisphere, this mostly concerns the whole North Pacific Ocean and the Western part of the North Atlantic Ocean (see Figure 1 in Chaigneau et al., 2008). In Southern Hemisphere, the near-inertial KE is only 65% the one in the Northern Hemisphere (Figure 3 in Chaigneau et al., 2008). ...
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... next analyze the BM and IGW impacts on the RV and DIV fields (Figures 10 and 11) and compare the results with those for the KE field (Figures 8). The purpose is to understand whether the partition of surface motions into rotational and divergent components allows to discriminate the respective contribution of BMs and IGWs on the KE field. ...
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... purpose is to understand whether the partition of surface motions into rotational and divergent components allows to discriminate the respective contribution of BMs and IGWs on the KE field. Results (detailed below) emphasize an even more complex picture than the one described in section 3.2, indicating the assumption based on the DIV contribution explained only by IGWs (Bühler et al., 2014) does not hold everywhere and at any time. ...
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... one hand, the RV field is found to be dominated by BMs in all high EKE regions of the World Ocean, both, in summer and winter (see Figures 10). Low EKE regions are also dominated by BMs in winter in both Hemispheres, but IGWs impacts in summer lead to R ~ 1 in these regions. ...
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... us examine in more details what happens, first, in summer. On one hand, the RV field in high EKE regions of the Northern Hemisphere (Figures 10c and 10d) is almost dominated by BMs over the entire 10-to 100-km band, but in low EKE regions, BMs and IGWs impacts on the RV field are almost equally partitioned. On the other hand, the DIV field is entirely dominated by IGWs in all regions (high and low EKE regions) of this hemisphere. ...
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... low EKE regions of the Northern Hemisphere, during summer, the KE field is strongly dominated by IGWs in both wave bands. This means that (from results for the RV and DIV fields, Figures 10, and 11c and 11d) KE in these regions is mostly captured by the DIV contribution for the two scale bands in summer (since RV is dominated by BMs, Figures 10c and 10d). These results indicate that the Bühler's assumption (that assumes the DIV field dominated by IGWs) should allow to partition motions into IGWs and BMs in the Northern Hemisphere in summer. ...
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... means that the Bühler's assumption should not work in this hemisphere except again for the South Atlantic region. Comparison of Figures 8c and 8d with Figures 11c and 11d indicates, however, that the DIV contribution to KE should be quite weak relatively to the RV contribution. The lack of summer enhancement of DIV due to IGWs south of 40°S is linked to the deep mixed layer. ...
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... expected, SST (Figure 12) and SSS (not shown) in the 10-to 100-km band are totally dominated by BMs in the whole World Ocean during all seasons, even in the NEP region where the IGW impacts on the other fields seem the strongest. This generalizes what was found in section 3 for the Kuroshio-Extension region and the same explanation can be invoked. ...

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... LLC indicates the Latitude-Longitude-polar Cap configuration, and 4,320 represents the number of grid points on each side of the 13 square tiles (J. Dong et al., 2021;Rocha et al., 2016;Torres et al., 2018). The LLC4320 has a horizontal resolution of 1/48° with 90 vertical z-levels over the globe and integration time step is 25 s. ...
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Sea surface currents (SSC) derived from the sea surface height anomalies (SSHA) as measured by multi‐satellite altimeters are widely used for various applications including studies on ocean dynamics, marine ecology, and climate change. However, present SSC products estimated on the assumption of an idealized geostrophic balance is biased. To overcome this idealization, this study considers flow curvature in the estimation of sea surface velocities in the global ocean, with the computation scheme validated using numerical model results. It is demonstrated that the inclusion of curvature into SSC estimations significantly changes SSC dynamic features in terms of kinetic energy, enstrophy (the maximum spatial difference is about 15%), and strain rate (the maximum spatial difference is about 10%). Such correction is of importance to the application studies relying on the SSC products from the satellite measured SSHA.
... The ω-κ spectrum of a given variable φ(x, y, t) is computed in a domain 1000 km in size and over 90 d. We refer the reader to Torres et al. (2018) for the full methodology. Briefly, before computing the ω-k spectrum of a φ(x, y, t), its linear trend is removed and a 3-D Hanning window is subsequently applied to the detrended φ(x, y, t) . ...
... Finally, the 3-D Fourier transform is used to compute a 2-D spectral density, |φ| 2 (κ, ω) where κ is the isotropic wavenumber defined as κ = √ k 2 + l 2 . The transformation from an anisotropic spectrum to an isotropic spectrum is performed following the methodology described by Torres et al. (2018). ...
... The dashed lines in the three panels show the linear dispersion relation curves for internal gravity waves (IGW) associated with the first four baroclinic modes, which helps to identify energetic internal gravity waves. SeeTorres et al. (2018) andQiu et al. (2018) for a detailed explanation of the above partition. ...
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Wind work at the air-sea interface is the transfer of kinetic energy between the ocean and the atmosphere and, as such, is an important part of the atmosphere-ocean coupled system. Since wind work involves winds and ocean currents that span a broad range of spatial and temporal scales, a comprehensive study would require access to observations of a wide range of space and time scales. In the absence of appropriate global observations, our study makes use of a new, global, coupled 5 ocean-atmosphere simulation with horizontal grid spacing of 2-5 km for the ocean and 7 km for the atmosphere. Here we develop a methodology, both in physical and spectral space, to diagnose different components of wind work in terms of forcing distinct classes of oceanic motions, including mean currents, time-dependent large-scale currents and mesoscale eddies, and internal gravity waves such as near-inertial waves. The total simulated wind work has a magnitude of 5.21 TW, a value much larger than reported by previous modeling studies. The total wind work is first decomposed into time-mean and time-dependent 10 components, with the former accounting for 2.23 TW (43%) and the latter 2.98 TW (57%). The time-dependent wind work is then decomposed into two components, a high-frequency component that forces internal gravity waves and a low-frequency component that forces mesoscale eddies and large-scale currents. The high-frequency component is positive at scales between 10 km and 1000 km and represents 75% of the total time-dependent component. The low-frequency component is found to be positive for spatial scales larger than 275 km and ten times larger than the negative part associated with smaller spatial 15 scales. The negative wind work acts as a surface drag that slows down surface currents and damps mesoscale eddies whereas the positive low-frequency part accelerates large-scale currents. The complex and consequential interplay of surface winds and currents in the numerical simulation motivates the need for a winds-and-currents satellite mission to directly observe these wind work components.
... The ω-κ spectrum of a given variable φ(x, y, t) is computed in a domain 1000 km in size and over 90 d. We refer the reader to Torres et al. (2018) for the full methodology. Briefly, before computing the ω-k spectrum of a φ(x, y, t), its linear trend is removed and a 3-D Hanning window is subsequently applied to the detrended φ(x, y, t) . ...
... Finally, the 3-D Fourier transform is used to compute a 2-D spectral density, |φ| 2 (κ, ω) where κ is the isotropic wavenumber defined as κ = √ k 2 + l 2 . The transformation from an anisotropic spectrum to an isotropic spectrum is performed following the methodology described by Torres et al. (2018). ...
... The dashed lines in the three panels show the linear dispersion relation curves for internal gravity waves (IGW) associated with the first four baroclinic modes, which helps to identify energetic internal gravity waves. SeeTorres et al. (2018) andQiu et al. (2018) for a detailed explanation of the above partition. ...
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... Contrary to the dynamics of the balanced flow, inertia-gravity waves exhibit a forward energy flux and dissipate their energy at small viscous scales. Furthermore, recent oceanic observational datasets and realistically forced global-scale ocean model outputs reveal that depending on the geographic location and season, wave energy levels can locally be comparable or stronger than balanced energy (Richman et al. 2012;Bühler et al. 2014;Qiu et al. 2017;Savage et al. 2017;Qiu et al. 2018;Tchilibou et al. 2018;Torres et al. 2018;Lien and Sanford 2019). These datasets have inspired a broad set of investigations aimed at understanding how gravity waves interact with balanced flow and modify quasigeostrophic turbulent dynamics, specifically with an eye on deducing whether waves can form an energy sink for balanced energy. ...
... Contrary to the dynamics of the balanced flow, inertia-gravity waves exhibit a forward energy flux and dissipate their energy at small viscous scales. Furthermore, recent oceanic observational datasets and realistically forced global-scale ocean model outputs reveal that depending on the geographic location and season, wave energy levels can locally be comparable or stronger than balanced energy (Richman et al. 2012;Bühler et al. 2014;Qiu et al. 2017;Savage et al. 2017;Qiu et al. 2018;Tchilibou et al. 2018;Torres et al. 2018;Lien and Sanford 2019). These datasets have inspired a broad set of investigations aimed at understanding how gravity waves interact with balanced flow and modify quasigeostrophic turbulent dynamics, specifically with an eye on deducing whether waves can form an energy sink for balanced energy. ...
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... Our results would indicate that if the Ro > O(1) at any scales in a region, then a forward cascade would likely ensue, which is possible as the dynamics would diverge from the traditional QG phenomenology. This is likely to be the case for most of the surface ocean according to high-resolution simulations (48), which suggest that the submesoscale range of scales are more energetic than what QG dynamics would suggest in most places, and the particular dynamical contributions to these scales, geostrophically balanced motions versus internal gravity waves, are modulated seasonally and spatially. It is worth noting that these high-resolution simulations are far from being converged, and the departure from QG theory is likely to be even more stark as finer scales are resolved and in the real ocean. ...
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The ocean's turbulent energy cycle has a paradox; large-scale eddies under the control of Earth's rotation transfer kinetic energy (KE) to larger scales via an inverse cascade, while a transfer to smaller scales is needed for dissipation. It has been hypothesized, using simulations, that fronts, waves, and other turbulent structures can produce a forward cascade of KE toward dissipation scales. However, this forward cascade and its coexistence with the inverse cascade have never been observed. Here, we present the first evidence of a dual KE cascade in the ocean by analyzing in situ velocity measurements from surface drifters. Our results show that KE is injected at two dominant scales and transferred to both large and small scales, with the downscale flux dominating at scales smaller than ∼1 to 10 km. The cascade rates are modulated seasonally, with stronger KE injection and downscale transfer during winter.
... The spatial variability of the SSH spectral slope within this fixed mesoscale range (Figure 7) is in large part due to the fact that the transition scale varies throughout the basin between the geostrophically balanced flow and unbalanced motions. The transition scale is estimated to be less than 40 km in the western boundary current, on the order of 40-100 km in the interior of subtropical/subpolar regions, and greater than 200 km in the tropics (e.g., Chereskin et al., 2019;Qiu et al., 2017Qiu et al., , 2018Torres et al., 2018). One can therefore derive SSH spectra slope within a mesoscale range that varies geographically (e.g., Vergara et al., 2019). ...
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The wavenumber spectral slope of sea surface height (SSH) computed within the mesoscale range (70–250 km) from satellite altimetry exhibits a large spatial variability which, until now, has not been reproduced in numerical ocean models. This study documents the impacts of including internal tides, high‐resolution bathymetry, and high‐frequency atmospheric variability on the SSH wavenumber spectra in the Atlantic Ocean, using a series of 1/50° North and equatorial Atlantic simulations with a realistic representation of barotropic/baroclinic tides and mesoscale‐to‐submesoscale variability. The results show that the inclusion of internal tides does increase high frequency SSH variability (with clear peaks near 120 and 70 km) and flattens the spectra slope in the mesoscale range in a good agreement with observations. The surface signature of internal tides, mostly in the equatorial Atlantic but also in subtropical regions in the eastern North Atlantic, is the primary reason behind the observed large spatial variability of the spectral slope in the Atlantic. Internal tides are stronger in the tropical regions when compared to higher latitudes because of the stronger barotropic tides and stronger stratification in the upper layer of the water column. High‐resolution bathymetry does play an important role in the internal tide generation on a local scale, but its impact on the modeled large‐scale SSH variability and SSH wavenumber spectra is quite small. High‐frequency wind variability plays only a minor role on the generation of the simulated high‐frequency SSH variability. Impact of altimetry sampling on the computation of the SSH wavenumber spectra is also discussed.
... In these models, internal tides and mesoscale eddies coexist and interact Nelson et al., 2019;Shriver et al., 2014). As shown first in Müller et al. (2015) and later in other studies (e.g., Luecke et al., 2020;Qiu et al., 2018;Savage, Arbic, Richman, et al., 2017;Torres et al., 2018), such models are beginning to partially resolve the internal gravity wave (IGW) continuum (Garrett-Munk spectrum;Garrett & Munk, 1975). Yu et al. (2019) compared KE, over various low-and high-frequency bands, from the hourly drifter data set and output from a high-resolution Massachusetts Institute of Technology general circulation model (MITgcm; Marshall et al., 1997) simulation, forced by both the astronomical tidal potential and atmospheric fields. ...
... Global IGW model simulations, especially MITgcm LLC4320 and from HYCOM, have been widely used by the community to plan for field campaigns (e.g., J. Wang et al., 2018), understand interactions between motions at different length and timescales (e.g., Pan et al., 2020), and provide boundary forcing for higher resolution regional simulations . HYCOM and MITgcm LLC4320 have been used to quantify the relative contributions of low-and high-frequency motions to SSH and KE as a function of geographical location (e.g., Qiu et al., 2018;Richman et al., 2012;Savage, Arbic, Richman, et al., 2017;Torres et al., 2018). The energetics of different classes of oceanic motions are of interest in their own right (Ferrari & Wunsch, 2009). ...
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The geographical variability, frequency content, and vertical structure of near‐surface oceanic kinetic energy (KE) are important for air‐sea interaction, marine ecosystems, operational oceanography, pollutant tracking, and interpreting remotely sensed velocity measurements. Here, KE in high‐resolution global simulations (HYbrid Coordinate Ocean Model; HYCOM, and Massachusetts Institute of Technology general circulation model; MITgcm), at the sea surface (0 m) and at 15 m, are compared with KE from undrogued and drogued surface drifters, respectively. Global maps and zonal averages are computed for low‐frequency (<0.5 cpd), near‐inertial, diurnal, and semidiurnal bands. Both models exhibit low‐frequency equatorial KE that is low relative to drifter values. HYCOM near‐inertial KE is higher than in MITgcm, and closer to drifter values, probably due to more frequently updated atmospheric forcing. HYCOM semidiurnal KE is lower than in MITgcm, and closer to drifter values, likely due to inclusion of a parameterized topographic internal wave drag. A concurrent tidal harmonic analysis in the diurnal band demonstrates that much of the diurnal flow is nontidal. We compute simple proxies of near‐surface vertical structure—the ratio 0 m KE/(0 m KE + 15 m KE) in model outputs, and the ratio undrogued KE/(undrogued KE + drogued KE) in drifter observations. Over most latitudes and frequency bands, model ratios track the drifter ratios to within error bars. Values of this ratio demonstrate significant vertical structure in all frequency bands except the semidiurnal band. Latitudinal dependence in the ratio is greatest in diurnal and low‐frequency bands.
... Unlike previously reported KE wavenumber spectra using Fourier analysis on box regions (e.g., refs. 6,8,9), some of which show a peak at mesoscales O(10 2 ) km, our Fig. 2 reveals that the largest spectral peak occurs at scales approximately 100 times larger, at ≈ 10 4 km, and only in the southern hemisphere. Indeed, a circle of latitude at 50°S has a geodesic diameter of ≈ 8.9 × 10 3 km. ...
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Advent of satellite altimetry brought into focus the pervasiveness of mesoscale eddies $${{{{{{{\bf{{{{{{{{\mathcal{O}}}}}}}}}}}}}}}}({100})$$ O ( 100 ) km in size, which are the ocean’s analogue of weather systems and are often regarded as the spectral peak of kinetic energy (KE). Yet, understanding of the ocean’s spatial scales has been derived mostly from Fourier analysis in small "representative” regions that cannot capture the vast dynamic range at planetary scales. Here, we use a coarse-graining method to analyze scales much larger than what had been possible before. Spectra spanning over three decades of length-scales reveal the Antarctic Circumpolar Current as the spectral peak of the global extra-tropical circulation, at ≈ 10 ⁴ km, and a previously unobserved power-law scaling over scales larger than 10 3 km. A smaller spectral peak exists at ≈ 300 km associated with mesoscales, which, due to their wider spread in wavenumber space, account for more than 50% of resolved surface KE globally. Seasonal cycles of length-scales exhibit a characteristic lag-time of ≈ 40 days per octave of length-scales such that in both hemispheres, KE at 10 ² km peaks in spring while KE at 10 3 km peaks in late summer. These results provide a new window for understanding the multiscale oceanic circulation within Earth’s climate system, including the largest planetary scales.
... The SADCP velocity contains multifrequency signals contributed by different motions, including the geostrophic and cyclogeostrophic balanced flows at low frequencies and the unbalanced part dominated by internal gravity waves at high frequencies (Torres et al. 2018). Conventionally, a temporal or spatial filter is used to separate motions of different scales (Thomson and Emery 2014). ...
... The waves separated from the SADCP velocity are mainly composed of internal waves, like NIWs and internal tides (Torres et al. 2018). Internal tides are weak in the upper 1000 m in this region . ...
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Shipboard observations of upper-ocean current, temperature–salinity, and turbulent dissipation rate were used to study near-inertial waves (NIWs) and turbulent diapycnal mixing in a cold-core eddy (CE) and warm-core eddy (WE) in the Kuroshio Extension (KE) region. The two eddies shed from the KE were energetic, with the maximum velocity exceeding 1 m s ⁻¹ and relative vorticity magnitude as high as 0.6 f . The mode regression method was proposed to extract NIWs from the shipboard ADCP velocities. The NIW amplitudes were 0.15 and 0.3 m s ⁻¹ in the CE and WE, respectively, and their constant phase lines were nearly slanted along the heaving isopycnals. In the WE, the NIWs were trapped in the negative vorticity core and amplified at the eddy base (at 350–650 m), which was consistent with the “inertial chimney” effect documented in existing literature. Outstanding NIWs in the background wavefield were also observed inside the positive vorticity core of the CE, despite their lower strength and shallower residence (above 350 m) compared to the counterparts in the WE. Particularly, the near-inertial kinetic energy efficiently propagated downward and amplified below the surface layer in both eddies, leading to an elevated turbulent dissipation rate of up to 10 ⁻⁷ W kg ⁻¹ . In addition, bidirectional energy exchanges between the NIWs and mesoscale balanced flow occurred during NIWs’ downward propagation. The present study provides observational evidence for the enhanced downward NIW propagation by mesoscale eddies, which has significant implications for parameterizing the wind-driven diapycnal mixing in the eddying ocean. Significance Statement We provide observational evidence for the downward propagation of near-inertial waves enhanced by mesoscale eddies. This is significant because the down-taking of wind energy by the near-inertial waves is an important energy source for turbulent mixing in the interior ocean, which is essential to the shaping of ocean circulation and climate. The anticyclonic eddies are widely regarded as a conduit for the downward near-inertial energy propagation, while the cyclonic eddies activity influencing the near-inertial waves propagation lacks clear cognition. In this study, enhanced near-inertial waves and turbulent dissipation were observed inside both cyclonic and anticyclonic eddies in the Kuroshio Extension region, which has significant implications for improving the parameterization of turbulent mixing in ocean circulation and climate models.
... Since wind runs equatorward alongshore on the EBC, Ekman dynamics transport rich-nutrient water to the mixed layer [2,3], feeding the trophic chain base [4], which explains why a large portion of the world fishery takes place within these regions. On the other hand, internal gravity waves (IGW) account for a higher portion of the total kinetic energy in EBC [5], unlike Western Boundary Currents [5] where balanced motions (BM) do. In addition, low-frequency relaxation of alongshore winds creates an undercurrent that flows poleward, following the continental slope [6]. ...
... Since wind runs equatorward alongshore on the EBC, Ekman dynamics transport rich-nutrient water to the mixed layer [2,3], feeding the trophic chain base [4], which explains why a large portion of the world fishery takes place within these regions. On the other hand, internal gravity waves (IGW) account for a higher portion of the total kinetic energy in EBC [5], unlike Western Boundary Currents [5] where balanced motions (BM) do. In addition, low-frequency relaxation of alongshore winds creates an undercurrent that flows poleward, following the continental slope [6]. ...
... We examined the time-space (x, y, t) and frequency-wavenumber (ω, k, l) domains for the summer and winter months in 2012. Our starting point was the collection of ω-k h (k h stands for the horizontal wavenumber, i.e., k 2 h = k 2 + l 2 ) spectra from Torres et al. [5] to represent surface KE, along with its vortical (ζ) and divergent (δ) parts. As for the spatio-temporal data, we employed the output of a realistic high-resolution ocean simulation (LLC4320) based on the Massachusetts Institute of Technology general circulation model (MITgcm). ...
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Balanced motions (BM) and internal gravity waves (IGW) account for most of the kinetic energy budget and capture most of the vertical velocity in the ocean. However, estimating the contribution of BM to both issues at time scales of less than a day is a challenge because BM are obscured by IGW. To study the BM regime, we outlined the implementation of a dynamical filter that separates both classes of motion. This study used a high-resolution global simulation to analyze the Eastern Boundary Currents during the winter and summer months. Our results confirm the feasibility of recovering BM dynamics at short time scales, emphasizing the diurnal cycle in winter and its dampening in summer due to local stratification that prevents large vertical excursion of the surface boundary layer. Our filter opens up new possibilities for more accurate estimation of the vertical exchanges of any tracers at any vertical level in the water column. Moreover, it could be a valuable tool for studies focused on wave–turbulence interactions in ocean simulations.