Evolution of Submesoscale Ageostrophic Motions Through the Life Cycle of Oceanic Mesoscale Eddies

Qiu, Bo

doi:10.1029/2018gl080399

Cited by 35 publications

(48 citation statements)

References 42 publications

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“…It should be noted that the ground tracks of currently operating altimeter satellites are unable to resolve relatively small-scale geostrophic signals and potentially introduce errors in the ageostrophic velocity estimation. It has, however, been shown that this does not substantially bias the results when investigating the ageostrophic motions and their relation to geostrophic strain rates 30 .…”

Section: Resultsmentioning

confidence: 98%

“…Nowadays, the number of global positioning system (GPS)-tracked surface drifters is large enough to achieve a global coverage and can provide accurate real-time position time series 24–28 . With a typical sampling interval at about 6 h, the drifters are able to resolve the submesoscale ageostrophic velocity signals at the sea surface globally; this includes both the unbalanced wave motions 29 and submesoscale balanced ageostrophic motions 27,30 .…”

Section: Introductionmentioning

confidence: 99%

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The influence of geostrophic strain on oceanic ageostrophic motion and surface chlorophyll

et al. 2019

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Oceanic submesoscale ageostrophic processes have been progressively recognized as an important upwelling mechanism to close the nutrient budget and sustain the observed primary production of phytoplankton in the euphotic layer. Their relatively small spatio-temporal scales (of 1~10 km and a few days) have hindered a systematic observational quantification of the submesoscale ageostrophic flow variability and its impact on ocean biogeochemistry. By combining surface drifters, satellite altimetry and satellite ocean-color data, we detect that when the strain rate of mesoscale surface geostrophic flow is strong, it favors a higher ageostrophic kinetic energy level and an increase in surface chlorophyll concentration. The strain-induced frontal processes are characterized by a surface chlorophyll increase and secondary ageostrophic upwelling along the light side of the oceanic density front. Further analysis indicates that the balanced ageostrophic motions with longer time scales are more effective in inducing chlorophyll increase than the unbalanced shorter time-scale wave motions.

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Section: Resultsmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

The influence of geostrophic strain on oceanic ageostrophic motion and surface chlorophyll

et al. 2019

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“…The mesoscale eddies contain the majority of the oceanic kinetic energy and the remaining question to answer is how the mesoscale eddies in geostrophic balance transfer energy to smaller scales, where the energy can be dissipated irreversibly. It is believed that ageostrophic motions play a critical role in this process [47]. Thus, it is important to examine the degree of the geostrophy.…”

Section: Geostrophymentioning

confidence: 99%

Anatomy of a Cyclonic Eddy in the Kuroshio Extension Based on High-Resolution Observations

Zhang

Chen

2019

Atmosphere

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Mesoscale eddies are common in the ocean and their surface characteristics have been well revealed based on altimetric observations. Comparatively, the knowledge of the three-dimensional (3D) structure of mesoscale eddies is scarce, especially in the open ocean. In the present study, high-resolution field observations of a cyclonic eddy in the Kuroshio Extension have been carried out and the anatomy of the observed eddy is conducted. The temperature anomaly exhibits a vertical monopole cone structure with a maximum of −7.3 • C located in the main thermocline. The salinity anomaly shows a vertical dipole structure with a fresh anomaly in the main thermocline and a saline anomaly in the North Pacific Intermediate Water (NPIW). The cyclonic flow displays an equivalent barotropic structure. The mixed layer is deep in the center of the eddy and thin in the periphery. The seasonal thermocline is intensified and the permanent thermocline is upward domed by 350 m. The subtropical mode water (STMW) straddled between the seasonal and permanent thermoclines weakens and dissipates in the eddy center. The salinity of NPIW distributed along the isopycnals shows no significant difference inside and outside the eddy. The geostrophic relation is approximately set up in the eddy. The nonlinearity-defined as the ratio between the rotational speed to the translational speed-is 12.5 and decreases with depth. The eddy-wind interaction is examined by high resolution satellite observations. The results show that the cold eddy induces wind stress aloft with positive divergence and negative curl. The wind induced upwelling process is responsible for the formation of the horizontal monopole pattern of salinity, while the horizontal transport results in the horizontal dipole structure of temperature in the mixed layer. species composition (EDDIES) in the Sargasso Sea off Bermuda [5], meso-and submesoscale processes in an intense front (AlborEx) [6] and the northwestern Pacific eddies, internal waves and mixing Experiment (NPEIM) [7], and so forth. Nowadays, main observation methods for field experiment include Argo floats, moored instrumentation, underwater gliders and shipboard survey.Argo profiling floats, which are designed to measure underwater ocean temperature and salinity (T/S) [8], are one of the effective methods to obtain 3D mesoscale eddy structures [9][10][11][12][13]. However, due to the drift features, the detailed structure of a specific eddy is difficult to acquire unless a large number of Argo floats are deployed inside the targeted mesoscale eddy. Reference [14] deployed 17 rapid-sampling Argo floats to study the anticyclonic eddies effects on mode water subduction in the south of the Kuroshio Extension to the east of Japan. In situ mooring observations can usually collect temperature, salinity and current data from the bottom to the surface at a fixed-point where the eddy moves through. Reference [15] designed and conducted a multi-month field campaign to capture the full-depth 3D structure of a pair of anticyclonic and c...

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“…Elipot et al () produced a unique global data set of surface drifter positions and velocities with hourly temporal resolution, which enables studies of near‐surface high‐frequency motion (e.g., inertial and tidal). The surface drifter measurements have been previously used to investigate a wide range of oceanic processes and dynamics, from global velocity climatology (Lumpkin & Johnson, ) and mesoscale coherent vortices (Lumpkin, ) to submesoscale motions (Lumpkin & Elipot, ; Zhang & Qiu, ), near‐inertial waves (Elipot et al, ; Liu et al, ), internal tides (Zaron, ), and relative dispersion (Corrado et al, ). In situ observations by oceanographic moorings or profiling instruments may be suited to obtaining depth‐dependent tidal and higher‐frequency variability for model assessment (e.g., Ansong et al, ; Savage et al, ) and thus complement surface drifter observations.…”

Section: Introductionmentioning

confidence: 99%

Surface Kinetic Energy Distributions in the Global Oceans From a High‐Resolution Numerical Model and Surface Drifter Observations

Ponte

Elipot

et al. 2019

Geophysical Research Letters

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The surface kinetic energy of a 1/48° global ocean simulation and its distribution as a function of frequency and location are compared with the one estimated from 15,329 globally distributed surface drifter observations at hourly resolution. These distributions follow similar patterns with a dominant low‐frequency component and well‐defined tidal and near‐inertial peaks globally. Quantitative differences are identified with deficits of low‐frequency energy near the equator (factor 2) and at near‐inertial frequencies (factor 3) and an excess of energy at semidiurnal frequencies (factor 4) for the model. Owing to its hourly resolution and its near‐global spatial coverage, the array of surface drifters is an invaluable tool to evaluate the realism of tide‐resolving high‐resolution ocean simulations used in observing system simulation experiments. Sources of bias between model and drifter data are discussed, and associated leads for future work highlighted.

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Evolution of Submesoscale Ageostrophic Motions Through the Life Cycle of Oceanic Mesoscale Eddies

Cited by 35 publications

References 42 publications

The influence of geostrophic strain on oceanic ageostrophic motion and surface chlorophyll

The influence of geostrophic strain on oceanic ageostrophic motion and surface chlorophyll

Anatomy of a Cyclonic Eddy in the Kuroshio Extension Based on High-Resolution Observations

Surface Kinetic Energy Distributions in the Global Oceans From a High‐Resolution Numerical Model and Surface Drifter Observations

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