Submesoscale transition from geostrophic flows to internal waves in the northwestern Pacific upper ocean

Qiu, Bo; Nakano, Toshiya; Chen, Shuiming; Klein, Patrice

doi:10.1038/ncomms14055

Cited by 108 publications

(154 citation statements)

References 49 publications

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“…We do not observe a distinct seasonal cycle in EKE wavenumber spectra, in contrast to recent studies that show higher energy within the submesoscale range during winter (Callies et al, 2015;Qiu et al, 2017). Submesoscale motions have a variety of generation mechanisms including mixed layer instability, direct wind forcing, or Charney instability, all of which are sensitive to surface mixing and hence show a seasonal dependence (McWilliams, 2016).…”

Section: Discussioncontrasting

confidence: 92%

“…This is at least partly due to contrasting coastlines: at 25°N, the FC is constrained within a channel and unable to sustain large meanders, and mesoscale eddies that form upstream are sheared apart as they are advected through the narrowing and shoaling channel (Fratantoni et al, 1998). The observed slopes are similar to those reported by Callies and Ferrari (2013) in the Gulf Stream extension but steeper than in the Kuroshio (k À2.3 ; Qiu et al, 2017) and in the subtropical North Pacific (k À2 ; Callies & Ferrari, 2013). Indeed, the EAC system is unique among WBCs for its large EKE-to-KE ratio (Boland & Hamon, 1970;Godfrey et al, 1980).…”

Section: Discussionmentioning

confidence: 55%

“…At the regional level, WBCs play a critical role in shelf circulation and coastal ecology, mixing water masses and upwelling nutrients into the sunlit surface layers where they are utilized by ecological communities (Lee et al, 1981;Shulzitski et al, 2015) and commercial fisheries (Richardson et al, 2009). Recent observations reveal seasonality in the submesoscale flow field over the open ocean and WBC extensions (Callies et al, 2015;Qiu et al, 2017), with a more energetic submesoscale eddy kinetic energy (EKE) field during wintertime. Recent observations reveal seasonality in the submesoscale flow field over the open ocean and WBC extensions (Callies et al, 2015;Qiu et al, 2017), with a more energetic submesoscale eddy kinetic energy (EKE) field during wintertime.…”

Section: Introductionmentioning

confidence: 99%

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The Kinematic Similarity of Two Western Boundary Currents Revealed by Sustained High‐Resolution Observations

Archer

Keating

Roughan

et al. 2018

Geophysical Research Letters

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Western boundary currents (WBCs) modulate the global climate and dominate regional ocean dynamics. Despite their importance, few direct comparisons of the kinematic structure of WBCs exist, due to a lack of equivalent sustained observational data sets. Here we compare multiyear, high‐resolution observations (1 km, hourly) of surface currents in two WBCs (Florida Current and East Australian Current) upstream of their separation point. Current variability is dominated by meandering, and the WBCs exhibit contrasting time‐mean velocities in a Eulerian coordinate frame. By transforming to a jet‐following coordinate frame, we show that the time‐mean surface velocity structure of the WBC jets is remarkably similar, considering their distinct local wind, bathymetry, and meandering signals. Both WBCs show steep submesoscale kinetic energy wavenumber spectra with weak seasonal variability, in contrast to recent findings in other ocean regions. Our results suggest that it is the mesoscale flow field that controls mixing and ocean dynamics in these regions.

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Section: Discussioncontrasting

confidence: 92%

Section: Discussionmentioning

confidence: 55%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The Kinematic Similarity of Two Western Boundary Currents Revealed by Sustained High‐Resolution Observations

Archer

Keating

Roughan

et al. 2018

Geophysical Research Letters

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“…Indeed, a flattening of the KE spectrum at scales smaller than 20 km due to an increased contribution of ageostrophic internal waves in the Gulf Stream region has been reported by Callies and Ferrari (). Further, recent decompositions of regional high‐resolution models (Capet et al, ), and one‐dimensional ship‐track data have confirmed steep (shallow) scaling of rotational (divergent) modes (Bühler et al, ; Qiu et al, ; Rocha et al, ), with hints at the aforementioned transition in the slope of the KE spectrum (Bühler et al, ).…”

Section: Interpretation and Conclusionmentioning

confidence: 93%

Surface Ocean Enstrophy, Kinetic Energy Fluxes, and Spectra From Satellite Altimetry

et al. 2018

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Spectra and fluxes of enstrophy and kinetic energy (KE) are estimated in different parts of the midlatitudinal oceans using geostrophic currents derived from altimetry data. The presence of a strong inverse flux of surface KE is confirmed at scales larger than approximately 200 km, whereas a robust enstrophy cascading regime, accompanied by an approximate k−3 KE spectrum, is observed from about 200 to 100 km. The character of fluxes and spectra is shown to compare favorably with those from a comprehensive Earth system model. In addition, as gridded altimeter data are affected by smoothening and interpolation, the qualitative robustness of the results is verified by sensitivity experiments using space and time‐filtered output from the Earth system model. Given the rotational character of the flow, this large‐scale inverse KE and smaller‐scale forward enstrophy transfer scenario is consistent with expectations from three‐dimensional rapidly rotating and strongly stratified turbulence studies as well as detailed analyses of spectra and fluxes in the upper‐level midlatitude troposphere. In further accord with results from the atmosphere, decomposing the currents into stationary and eddy components (demarcated here by variability greater and less than 100 days, respectively), it is seen that, in addition to the eddy‐eddy contribution, the stationary‐eddy and stationary‐stationary fluxes play a significant role in the inverse (forward) flux of KE (enstrophy). Thus, it is quite possible that, from about 200 to 100 km, the altimeter is capturing the rotationally dominated portion of a surface oceanic counterpart of the upper tropospheric Nastrom‐Gage spectrum.

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“…This emphasizes the different impacts of SBMs and IGWs in terms of KE budget. Further results from Callies et al (), Rocha, Chereskin, et al (), Rocha, Gille, et al (), and Qiu et al () indicate IGWs and SBMs are both characterized by a strong seasonality. On one hand, SBMs are much more energetic than IGWs in winter, when surface frontal instabilities at small‐scale (such as mixed‐layer instabilities) are more efficient because of the large mixed‐layer depths (Callies et al, ; Mensa et al, ; Qiu et al, ; Rocha, Gille, et al, ; Sasaki et al, ; Su et al, ).…”

Section: Introductionmentioning

confidence: 89%

Partitioning Ocean Motions Into Balanced Motions and Internal Gravity Waves: A Modeling Study in Anticipation of Future Space Missions

et al. 2018

Self Cite

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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, the only observations with global coverage, and a reasonable spatial and temporal resolution. But we need first to characterize and understand their signatures on the different surface oceanic fields. This study addresses this issue by using an ocean global numerical simulation with high‐resolution (1/48°). Our methodology is based on the analysis of the 12,000 frequency‐wave number spectra to discriminate these two classes of motions in the surface kinetic energy, sea surface height, sea surface temperature, sea surface salinity, relative vorticity, and divergence fields and for two seasons. Results reveal a complex picture worldwide of the partition of motions between IGWs and BMs in the different surface fields, depending on the season, the hemisphere, and low and high eddy kinetic energy regions. But they also highlight some generic properties on the impact of these two classes of motions on the different fields. This points to the synergy of using present and future satellite observations to assess the ocean kinetic energy on a global scale. The 12,000 frequency‐wave number spectra represent a World Ocean Atlas of the surface ocean dynamics not fully exploited in the present study. We hope the use of this World Ocean Atlas by other studies will lead to extend much these results.

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Submesoscale transition from geostrophic flows to internal waves in the northwestern Pacific upper ocean

Cited by 108 publications

References 49 publications

The Kinematic Similarity of Two Western Boundary Currents Revealed by Sustained High‐Resolution Observations

The Kinematic Similarity of Two Western Boundary Currents Revealed by Sustained High‐Resolution Observations

Surface Ocean Enstrophy, Kinetic Energy Fluxes, and Spectra From Satellite Altimetry

Partitioning Ocean Motions Into Balanced Motions and Internal Gravity Waves: A Modeling Study in Anticipation of Future Space Missions

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